Muhammad Ali Bhatti

Aneela Tahira

Ahmed Ali Hullio

Umair Aftab

Ayman Nafady

Brigitte Vigolo

Zafar Hussain

Oxygenated terminals of milky sap of Calotropis procera transformed 1D ZnO structure to 0D nanoparticles for enhanced

Keywords: Milky sap of CP, biosynthesis, ZnO nanostructures, photodegradation

come

Introduction

Synthetic dyes have been used extensively in various industries including textile, paper, plastic leather, food, and others. Many of them these dyes belong to azo compounds like methylene blue (MB), methyl orange (MO), Congo red (CR), direct black 38 (DB38), and malachite green (MG) containing chromophore (-N=N-) in their chemical structures [START_REF] Zhu | Effective photocatalytic decolorization of methyl orange utilizing TiO2/ZnO/ chitosan nanocomposite films under simulated solar irradiation[END_REF]. It has been remained a practice for the discard of these azo dyes directly or indirectly into environment and ecosystem of our water without or less likely treatment. Owing to their stable nature, they have been found hazardous and threat to life due to mutagenic and carcinogenic properties [START_REF] Mathur | Review of the mutagenicity of textile dye products[END_REF]. The stable nature of these dyes do not allow them for spontaneously degradation in the water, hence they have been causing pollution not for ecosystem of water but at the same time for our atmosphere, therefore the toxic effects on the aquatic life unavoidable. For these reasons, different wastewater treatment methods have been utilized and proposed [START_REF] Kumar | ZnO nano-mushrooms for photocatalytic degradation of methyl orange[END_REF][START_REF] Chamjangali | Synthesis and application of multiple rods gold-zinc oxide nanostructures in the photocatalytic degradation of methyl orange[END_REF][START_REF] Razali | Degradation of methyl orange mediated by CuOdoped ZnO photocatalysts[END_REF][START_REF] Tripathy | Photocatalytic degradation of methyl orange dye by ZnO nanoneedle under UV irradiation[END_REF][START_REF] Tian | Microwaveinduced crystallization of AC/TiO2 for improving the performance of rhodamine B dye degradation[END_REF]. The challenges faced by these established methods include the complicated working principle, high cost and some of them produces secondary class of pollutants during the degradation process. Therefore, it is very essential to realize new approaches with complementary technologies with low cost, environment friendly, ecofriendly, and highly efficient to transform these stable dyes into harmless minerals without producing the secondary pollutants. Among these methods, the photocatalysis has been found thee potential approach for the complete mineralization of these organic dyes into harmless products like H 2 O, and CO 2 . Today, the photocatalysis is strongly supported by the advancement in the field of material science due to extensive manipulation of wide range of materials at nanoscale dimension, hence vigorous efforts have been devoted to synthesizing and characterize for the wastewater treatment applications. It is the reason, wide range of nanostructured materials have been applied particularly the semiconducting materials including TiO 2 [START_REF] Liu | Synthesis of N and La codoped TiO2/AC photocatalyst by microwave irradiation for the photocatalytic degradation of naphthalene[END_REF], ZnO [START_REF] Chidambaram | ZnO/Ag heterostructures embedded in Fe3O4 nanoparticles for magnetically recoverable photocatalysis[END_REF], Fe 2 O 3 [START_REF] Liu | A magnetically separable photocatalyst based on nest-like γ-Fe2O3/ZnO double-shelled hollow structures with enhanced photocatalytic activity[END_REF], CdS [START_REF] Vázquez | Electrophoretic deposition of CdS coatings and their photocatalytic activities in the degradation of tetracycline antibiotic[END_REF], and ZnS [START_REF] Pathania | Photocatalytic degradation of highly toxic dyes using chitosan-g-poly (acrylamide)/ZnS in presence of solar irradiation[END_REF] for the photocatalytic applications. Beside other semiconducting metal oxides photocatalysts, zinc oxide (ZnO) is intensively investigated for the photodegradation of diverse organic dyes due its significant catalytic activity, tunable optical band gap, low cost, easy to fabricate and ecofriendly. However, the potential emergence of ZnO as photocatalyst for the practical applications is restricted by the wide band gap, low density of catalytic sites and fast charge recombination rate of electron sand holes [START_REF] Pathania | Photocatalytic degradation of highly toxic dyes using chitosan-g-poly (acrylamide)/ZnS in presence of solar irradiation[END_REF]. Overcoming these main issues of ZnO for the photocatalytic applications, various efforts have been effectively taken into consideration such as adaption of new morphologies [START_REF] Chidambaram | ZnO/Ag heterostructures embedded in Fe3O4 nanoparticles for magnetically recoverable photocatalysis[END_REF], use of new synthetic routes [START_REF] Chidambaram | ZnO/Ag heterostructures embedded in Fe3O4 nanoparticles for magnetically recoverable photocatalysis[END_REF], engineering of optical band gap via efficient dopant, making composites systems, and using natural compounds from the plant extracts and biomass wastes as green methodology of preparation of ZnO nanostructures [START_REF] Govindaraju | Silver, gold and bimetallic nanoparticles production using single-cell protein (Spirulina platensis) Geitler[END_REF]. Recently, the green preparation strategy is being used with overwhelming, depicting its low cost, environment friendly, scale up, and avoiding the high consumption of toxic chemicals for the synthesis of ZnO nanostructures [START_REF] Scarano | Properties of phytochelatin-coated CdS nanocrystallites formed in a marine phytoplanktonic alga (Phaeodactylum tricornutum, Bohlin) in response to Cd[END_REF]. The plant extract is associated with the presence of large amounts of surface modifying agents, reducing agents, oxidizing agents, capping, and stabilizing agents which together play a vital role in controlling the size of nanostructured material, evolving the unique architecture of nanostructured morphologies [START_REF] Govindaraju | Silver, gold and bimetallic nanoparticles production using single-cell protein (Spirulina platensis) Geitler[END_REF][START_REF] Scarano | Properties of phytochelatin-coated CdS nanocrystallites formed in a marine phytoplanktonic alga (Phaeodactylum tricornutum, Bohlin) in response to Cd[END_REF][START_REF] Lengke | Biosynthesis of silver nanoparticles by filamentous cyanobacteria from a silver (I) nitrate complex[END_REF][START_REF] Muthuvel | Synthesis of CeO2-NPs by chemical and biological methods and their photocatalytic, antibacterial and in vitro antioxidant activity[END_REF]. For this purpose, the recent literature shows the intense use of wide range of plant extracts for the preparation of ZnO nanoparticles like Azadirachta Indica (L) [START_REF] Elumalai | Green synthesis, characterization and antimicrobial activities of zinc oxide nanoparticles from the leaf extract of Azadirachta indica (L.)[END_REF], Eucalyptus globulus (E. globulus) [START_REF] Siripireddy | Facile green synthesis of zinc oxide nanoparticles by Eucalyptus globulus and their photocatalytic and antioxidant activity[END_REF] , Moringa Oliefera leaf extract [START_REF] Elumalai | Green synthesis of zinc oxide nanoparticles using Moringa oleifera leaf extract and evaluation of its antimicrobial activity Spectrochim[END_REF], Cassia fistula plant extract [START_REF] Suresh | Green synthesis of multifunctional zinc oxide (ZnO) nanoparticles using Cassia fistula plant extract and their photodegradative, antioxidant and antibacterial activities[END_REF], Citrus aurantifolia (lemon) peel extract [START_REF] Çolak | Green synthesis and characterization of nanostructured ZnO thin films using Citrus aurantifolia (lemon) peel extract by spin-coating method[END_REF], leaf extract of Calotropis Gigantea [START_REF] Chaudhuri | Biosynthesis of zinc oxide nanoparticles using leaf extract of Calotropis gigantea: characterization and its evaluation on tree seedling growth in nursery stage[END_REF], Vitex negundo leaf extract [START_REF] Ambika | Green biosynthesis of ZnO nanoparticles using Vitex negundo L. extract: Spectroscopic investigation of interaction between ZnO nanoparticles and human serum albumin[END_REF], Caralluma Fimbriata extract [START_REF] Mishra | Caralluma fimbriata extract induced green synthesis, structural, optical and photocatalytic properties of ZnO nanostructure modified with Gd[END_REF], and Solanum nigrum leaf extract [START_REF] Ramesh | Green synthesis of ZnO nanoparticles using Solanum nigrum leaf extract and their antibacterial activity Spectrochim[END_REF].

Furthermore, Sharma et al (2016) and Dobrucka et al (2016) have synthesized ZnO nanoparticles using Jacaranda mimosifolia and Trifolium pratense flowers extracts [START_REF] Sharma | Biosynthesis of ZnO nanoparticles using Jacaranda mimosifolia flowers extract: synergistic antibacterial activity and molecular simulated facet specific adsorption studies[END_REF][START_REF] Dobrucka | Biosynthesis and antibacterial activity of ZnO nanoparticles using Trifolium pratense flower extract[END_REF].The synthesis of ZnO nanoparticles using Lime juice has been reported by Pandit 2017 [START_REF] Hinge | Solar-assisted synthesis of ZnO nanoparticles using lime juice: a green approach[END_REF]. And the Suresh et al, utilized the Artocarpus Gomezianus (AG) as fuel and followed by the combustion process for the preparation of ZnO nanoparticles [START_REF] Suresh | Artocarpus gomezianus aided green synthesis of ZnO nanoparticles: luminescence, photocatalytic and antioxidant properties Spectrochim[END_REF], whereas Yuvakkumar et al [START_REF] Yuvakkumar | Novel green synthetic strategy to prepare ZnO nanocrystals using rambutan (Nephelium lappaceum L.) peel extract and its antibacterial applications[END_REF] has taken Nephelium lappaceum L. (rambutan) peel extract for the biosynthesis of ZnO nanostructured material.

Calotropis procera is a desert plant known in Greeco-Arab medicine as Ushar or Madar.

Tropical and subtropical regions like Asia and Africa, have a large population of this plant [START_REF] Millar | Plants of Dhofar; The Southern Region of Oman, Traditional, Economic and Medicinal Uses. The office of the Advisor for Conservation of the Environment[END_REF].

The ancient Egyptians were aware of the plant's medical properties; excavations at Helwan in Egypt revealed that the herb was used during the Neolithic period [START_REF] Greiss | Elhamy, Anatomical Identification of plant remains and other materials from (1) El-Omari excavation at Helwan from the first dynasty[END_REF] In 'Berliner' papyrus, the plant is indicated for the treatment of nodular leprosy [START_REF] Ebbell | contribution to the earliest history of leprosy[END_REF]. Since one decade, numerous scientific investigations have been conducted on different parts of this plant. According to Prakash et al. [START_REF] Prakash | Effect of oral administration of forty two indigenous lants extracts on early and late pregnancy in albino rats[END_REF], C. procera negatively impacts both early and late pregnancy in rats. The extract of this plant extract is used an anticancer [START_REF] Ayoub | Screening of plants used in Sudan folk medicine for anticancer activity[END_REF] and nematocidal [START_REF] Nandal | Preliminary screening of some weeds and shrubs for their neomatocidal activity against Meloidogyne javanica[END_REF] properties. The flowers of C. procera have a highly substantial antibacterial and anti-inflammatory activity [37]. Calotropis procera (C. Procera, CP) is among the class of Apocynaceae and it is widely used for medicinal applications such as fever, diarrhea, asthma, painful muscle spasms and an aspiration and cleansing [START_REF] Muthuvel | Green synthesis of cerium oxide nanoparticles using Calotropis procera flower extract and their photocatalytic degradation and antibacterial activity[END_REF]. The CP is also applied for detoxify of the blood, making healthy hair, enhancing the liver function and to maintain the blood sugar levels. The CP plant is carrier of wide range of phytochemicals including triterpenoids, flavonoids, glycosides, anthocyanins, α-amyrin, βamyrin, lupeol, β-sitosterol, flavonols, mudarine and resins l [START_REF] Mali | A review on pharmacological activities of calotropis procera[END_REF]. The king draw was used to generate the molecular structure of various natural compounds of CP as shown in Scheme 1. and applied for the photodegradation of methyl orange. However, CP being the abundant desert and agriculture land plant around the world and carrying the favorable phytochemicals of milky sap is not investigated and there is no report about the use of CP to improve to photocatalytic properties of ZnO material towards the photodegradation of malachite green (MG) and methylene blue (MB). Moreover, the role of different of volumes of CP on the structural disorder of ZnO and their role on the pH dependent photocatalytic functionality of MG and MB degradation in aqueous solution have never been studied and reported to date. Importantly, the role of terminated oxygen groups present in the biomass for the alteration of morphology from one dimensional (1D) to zero dimensional (0D) nanoparticles has not been highlighted and studied previously.

In this study, an ecofriendly, cost effective and rapid method for the synthesis of 0D ZnO nanoparticles using milky sap of CP was carried out. We have utilized milky sap of stem, flowers and leaves of CP for the preparation of ZnO nanostructures and studied their photocatalytic effectiveness during photodegradation of MB and MG under alkaline and acidic conditions. These observed findings propose a new functional aspect for the synthesis of ZnO nanostructures with outperform functionality under alkaline conditions and their suitability as an alternative photocatalyst for the practical applications.

Material and methods

2.1.Material

Zinc acetate dihydate (ZnC₄H₆O₄ Mm: 183.48 g/mol), ammonia aqueous solution (33%), ethanol (C 2 H 5 OH, 99%), sodium hydroxide (NaOH), hydrochloric acid (HCl, 37%), methylene blue (MB) and malachite green (MG) were bought from Merck and used as received with no additional sophistication. The deionized water was used to make a desired solution.

2.2.Milky sap collection from Calotropis procera and biosynthesis of ZnO nanostructures

Calotropis procera (CP) is commonly known by sodom apple and belonging to apocynaceae family. The milky sap was collected from the various parts of CP including flower, stem and leaves. The CP plant was located at the mountain locality of University of Sindh jamshoro and prior to collection of milky sap, it was washed and cleaned several times with the deionized water. The volume of 50 mL of milky sap was obtained and used for the growth of ZnO nanostructures. The synthesis of ZnO nanostructures in the presence of milky sap of CP was performed by the solvothermal method. A solvothermal process is low cost, facile, ecofriendly and environment friendly, and can be used for the large scale synthesis of nanostructured materials. In typical preparation process, we have used 2.22 g of zinc acetate dihydrate and 5 mL of 33% aqueous ammonia solution in 100 mL of the deionized water. At the same time, 15 mL of milky sap of CP was mixed with 20 mL of ethanol and homogenized mechanically. Then, milky sap dissolved into ethanol was added in the four beakers containing zinc precursor of 2.22 g of zinc acetate dihydrate and 5 mL of 33% aqueous ammonia with different volumes like 2 mL, 4 mL, 6 mL, and 8 mL respectively. The milky sap is carrying different types of stabilizing agents, capping agents and chelating agent like oxygen terminals which could bind effectively with zinc ions and played a dynamic role in the structure transformation and enhancement of photocatalytic properties of ZnO. For understanding the role of milky sap of CP, we have prepared the pure sample of ZnO under the same conditions without the use of milky sap. The solvothermal process was initiated by covering the growth solutions with aluminum sheet and left for chemical reaction at 95 o C for 5 hours. Afterwards, the white product of ZnO precipitates was settled at the bottom of each beaker and collected onto the ordinary filter paper and washed several times with the ethanol followed by deionized water. Then, the white product of ZnO was left to dry at 65 o C for 12 hours. Later, the white product of ZnO of each sample was kept in China clay made crucible and thermally treated at 250 o C for 3 hours in air. After the thermal combustion, ZnO samples were used for the structural, morphological, and photocatalytic applications.

2.3.Morphology, crystal phase and optical characterization of as biosynthesized ZnO nanostructures

The crystalline phase and purity of as prepared ZnO nanostructures with milky sap of CP were explored by powder X-ray diffraction (XRD) technique with scanning two theta angle from 10° to 90° and X rays with a wavelength of 1.5406 ˚ were generated from Cu anode by applying potential of 45 kV with a current of 45 mA [START_REF] Khatami | Plant-mediated green syn-thesis of silver nanoparticles using Trifolium resupinatum seed exudate and their antifungal efficacy on Neofusicoccum parvum and Rhizoctonia solani[END_REF]. The crystalline size was estimated by using Scherrer equation (D = K λ/ βcos θ), here D is d-spacing of particular crystal planes, K is constant (0.9), λ as wavelength of used X-rays (1.5406 ˚A), β is the angular full width at half maximum in radians and θ is the Bragg's angle. The morphology of milky sap assisted ZnO nanostructures was investigated by using low resolution scanning electron microscopy (SEM model JEOL JSM-5910). The SEM imaging was done with the accelerated voltage of 20 kV and prior to analysis the samples were coated with 5 nm gold coating in order to measure the well resolved images. The SEM imaging was collected with polaroid P/N 665 film [START_REF] Shiri | Synthesis and character-ization of bromine source immobilized on diethylenetriamine-functionalized magnetic nanoparticles: a novel, versatile and highly efficient reusable catalyst for organic synthesis[END_REF][START_REF] Ullah | Using palynomorphological characteristics for the identification of species of Alsinoideae (Caryophyllaceae): a systematic approach[END_REF]. The optical features about the biosynthesized were studied by employing UV-visible spectrophotometer (PE Lamda 365) with wavelength 200-800 nm range [START_REF] Hemmati | Biosynthesis of silver nanopar-ticles using oak leaf extract and their application for electrochemical sensing of hydrogen peroxide[END_REF].

2.4.Photocatalytic activity of biosynthesized ZnO nanostructures

The photodegradation was carried out with the use of 5 mg of different ZnO nanostructures obtained with milky sap of CP were mixed with dye solution , homogenized with in ultrasonic bath for 20 min in the dark. The placement of dye solution with ZnO nanostructures in ultrasonic bath was done in order to achieve the equilibrium of adsorption and desorption process. The photodegradation of both MB and MG dyes with milky sap assisted ZnO nanostructures was done under the illumination of ultraviolet of light. For comparison, the photodegradation of MB and MG with pure ZnO sample was also carried out. For the photocatalytic activity, various ZnO nanostructures were treated with MG dye concentration of 10.96×10 -5 M and MB of 3.12×10 -5 M. Then, 50 mL of each dye solution was taken and 5 mg of each sample of ZnO was added and stirred for 30 min to reach an adsorption-desorption equilibrium in the dark and we noticed that there was about 4-6 % adsorption and further no visible changes were noticed with naked eyes. The dyes solution with photocatalyst were placed in homemade UV light box consisting of six UV lamps of wavelength of (365 nm and power of 60 W). Afterwards, 2 mL of aliquots of dye solution was used in the cuvette and evaluated its absorption value by the UV-visible spectrophotometer (PE Lamda 365) for wavelength range from 250 to 750 nm. The process of each measurement was repeated for different intervals of time to monitor the degradation rate with the decrease in the absorbance for both MG and MB dyes under the illumination of UV light. The percent degradation was quantified by the following relationship: Photodegradation efficiency (%) =A 0 -A t / A 0 × 100 Herein, the A 0 and A t were initial and after certain interval time dye absorption and same equation was used to evaluate the photocatalytic properties of pure ZnO and milky sap assisted and pure ZnO as shown in Figure 1. The observed reflections were well matched with the hexagonal phase of ZnO with typical wurtzite structure as reported previously [START_REF] Gibb | Synthesis of hydroxyl-footed cavitands[END_REF]. Various XRD reflections were identified at wide range of two theta angle as shown herein at 2(θ 0 ) 201), ( 004) and ( 202)respectively. All the noticed XRD reflections were further supported by the standard JCPDS card (01-079-0208). There have been no additional reflections which could not be labelled, confirming the high purity of as prepared ZnO samples. The relative intensity of (101) crystal plane was decreased with increasing amount of milky sap of CP, suggesting that the alteration of one dimensional nanostructures into heterogeneous structure due to driving role of oxygenated and hydroxyl groups of milky sap of CP. These oxygenated groups result the diverse and multidirectional approach of nucleation during the growth process, consequently the transformation of morphology was expected as proven by SEM analysis.

Interestingly, the shift in the two theta along the (100) crystal plane was noticed as shown in These oxygenated groups could be responsible for the new ways of crystal orientation during the growth process, hence we have noticed the complete transformation of nanorod like morphology into spherical particles [START_REF] Yun | SINTERING BEHAVIOUR AND ELECTRICAL CHARACTERISTICS OF ZnO VARISTORS PREPARED BY PECHINI PROCESS[END_REF][START_REF] Ryu | Synthesis of ZnWO 4 Nanopowders by Polymerized complex Method[END_REF]. These observations could be supported from the XRD results in terms of change in the intensity of reflections which enabled the crystal orientation in the multiple directions in the presence of milky sap of CP as shown in Figure 2b-e. Previously, it has been reported that the morphology of nanostructured material is highly dependent on the nature biomolecules present in the biomass of plants [START_REF] Radhakrishnan | Green synthesis of copper oxide nanoparticles mediated by aqueous leaf extracts of Leucas aspera and Morinda tinctoria[END_REF]. Additionally, it has been described in the literature that the spherical morphology is more likely useful for the antibacterial activity as it can easily go inside the bacterial strains and thereby show an effectiveness to kill biological cell [START_REF] Pugazhendhi | Photocatalytic properties and antimicrobial efficacy of Fe doped CuO nanoparticles against the pathogenic bacteria and fungi[END_REF]. On the basis of morphological characterization about the biosynthesized material, a hypothesis for the formation mechanism of nanoparticles is depicted in scheme 2. Given that C.

procera extract is the abundant source of phytochemicals and many of the rich with terminated atoms with lone pair which could effectively bound with the Zn 2+ ions during hydrothermal process. Then, the kinetics of zinc ions binding with hydroxyl groups could be well controlled, hence shaping the structure from nanorods to nanoparticles. The availability of capping agents and chelating agents from milky sap of CP ultimately supported for the formation of nanoparticles [START_REF] Luque-Morales | ZnO semiconductor nanoparticles and their application in photocatalytic degradation of various organic dyes[END_REF].

The elemental information was verified by measuring the energy dispersive spectroscopy spectra (EDS) for each sample of ZnO prepared with, 2, 4, 6 and d 8 mL of milky sap of CP as shown in eV in this study could be verified from published works [START_REF] Gibb | Synthesis of hydroxyl-footed cavitands[END_REF]. Furthermore, it should be noted in the literature that narrowing band gap may be caused by the loading of the dopant into ZnO, creation of O and Zn vacancies, improved crystal quality at higher annealing and other factors [START_REF] Saad Algarni | Photocatalytic degradation of some dyes under solar light irradiation using ZnO nanoparticles synthesized from Rosmarinus officinalis extract[END_REF]. We have already observed from EDS analysis that there is presence of Cl, S, C and Mg possibly they have been added into the crystal of ZnO, consequently the optical band gap was reduced.

3.2.Photocatalytic applications of as prepared ZnO nanostructures with milky sap of CP a. MG degradation

The photocatalytic applications of as biosynthesized ZnO nanostructures were chosen on two aspects one as the wastewater treatment and its environmental impacts and other is the water pollution causing many issues for the aquatic life especially the aquaculture systems. Hence, we have applied the newly modified ZnO nanostructures on the MB and MG for the evaluation of their photocatalytic effectiveness. First, we have examined the photodegradation of MG using 10.96×10 -5 M in aqueous solution against the pure ZnO and biosynthesized ZnO samples with 2, 4, 6 and 8 mL of milky sap of CP under the illumination of UV light. The absorbance spectra of MG using pure ZnO as photocatalyst were recorded with different intervals of time like 25, 50, 75, 100, 125 and 150 min as enclosed in Figure 5a. The absorbance spectra were measured with the gap of 25 min as shown in Figure 5a. It is obvious that the relative decrease in the absorbance is limited, suggesting the poor performance of pure ZnO, owing to its wide band gap and the fast charge recombination of electron and holes during the photocatalysis process as previously described by several studies [START_REF] Chen | Prepartion, characterization and activity evaluation of p-n junction photocatalyst p-NiO/n-ZnO[END_REF][START_REF] Bhatti | Efficient photo catalysts based on silver doped ZnO nanorods for the photo degradation of methyl orange[END_REF][START_REF] Bhatti | Enzymes and phytochemicals from neem extract robustly tuned the photocatalytic activity of ZnO for the degradation of malachite green (MG) in aqueous media[END_REF]. The degradation kinetics was also described by pseudo first order kinetics as illustrated in Figure 5b and the ratio of dye concentration after certain time of degradation process and the initial dye concentration was also measured as shown in Figure 5c, indicating the pseudo first order kinetics which is mainly governed by the concentration of MG. The degradation efficiency of pure ZnO was also investigated against the degradation of MG and identified by a very low of 31.3% as shown in Figure 5d and describing the solid reasons for the manipulation of pure ZnO properties by adapting new methodologies for improvement in the photocatalytic properties of ZnO. Similarly, pure ZnO was used for the photodegradation of MB and the obtained UV-visible absorbance spectra, reaction kinetics and degree efficiency studies are enclosed in Figure 6a-d. Again, the performance of pure ZnO was found limiting and could not be useful for the practical applications.

Because the pure ZnO has limited photocatalytic activity and it has very less like potential to be used for practical applications of wastewater treatment in its pure form [START_REF] Chen | Prepartion, characterization and activity evaluation of p-n junction photocatalyst p-NiO/n-ZnO[END_REF], therefore new roadmaps are highly needed based on ZnO by enhancing its photocatalytic properties for the development of real time photocatalysts in the near future. This is the reason, we have used the natural source of desert plant CP and it is widely distributed around the world, but its utilization

towards

b. Degardation of MB

Furthermroe, the photodegradation of MB was performed with the use of biosynthesized ZnO nanostructures in the presence of 2, 4, 6 and 8 mL of milky sap of CP. Before, the degradation of MB, the absorance spectrum of bare dye was taken as shwon in Figure 9 and it is shown by the absorbance bands in the region of 664 and 612 nm, idicating the typcial sulfur-nitrogen conjugate bonding features and they have been labeled as the chromophoric groups within the MB molecular structure [56]. It has been observed that the intensity of both peaks should decrease once the degradation proces is started, would confirmt the cleavage of sulfur0nitragen congugate bonding sites and further demethylation could result into other intermediates [START_REF] Sharma | Thermodynamic and kinetic studies of methylene blue degradation using reactive adsorption and its comparison with adsorption[END_REF][START_REF] Han | imultaneous enhancement of methylene blue degradation and power generation in a microbial fuel cell by gold nanoparticles[END_REF]. the MB as well as shown in Figure 10d. The kinetics was also examined about the degradation of MB under the influence of biosynthesized ZnO nanostructures as given in Table 1 and from the kinetics parameters it is confirmed that photodegradation was followed by pseudo first order kinetics and it is only governed by the decrease in the absorbance of MB. The kinetics study of MB degradation is illustrated by Figure 11a,b. The relative degradation of efficiency of various samples of ZnO synthesized with 2, 4, 6 and 8m mL of milky sap of CP is enclosed in Figure 11c and it was noticed in the order 36.9%, 51.0%, 62.4% and 86.32% r4spectievly. These findings again, confirm that the morphology, optical band gap reduction, small crystallite size and surface modified features dependence performance of biosynthesized towards the degradation of MB in aqueous solution.

3.3.Effect of pH of MG and MB dye solution on the photocatalytic properties of ZnO nanostructures

The effect of pH of dye solution on the performance evaluation of biosynthesized ZnO nanostructures was evaluated for the samples prepared with 8 mL of milky sap of CP using a degradation. This is because the higher alkaline conditions offer high amount of hydroxyl groups which played a dominant role in degrading the MG as a main radical component as shown in Figure 12c. Similarly, the reaction kinetics was studied and described by the pseudoorder kinetics and mainly governed by the concentration of MG as shown in Figure 12e. The degradation of efficiency was found as 93.4 % for various samples of ZnO using 8 mL of milky sap of CP for the time period of 20 min as enclosed in Figure 12f. The high performance at pH 10 is attributed to the point zero charge as previously observed by several studies [START_REF] Rao | Kinetic study on the photocatalytic degradation of salicylic acid using ZnO catalyst[END_REF][START_REF] Sobana | The effect of operational parameters on the photocatalytic degradation of acid red 18 by ZnO[END_REF]. This is because at alkaline pH, the surface of ZnO is decorated with negatively charged hydroxyl which favored the degradation kinetics [START_REF] Konstantinou | TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations: a review[END_REF]. However, under the acidic conditions the surface of ZnO is rich with positively charge of hydronium ions which repelled the cationic dyes like MG, hence poor performance was observed at pH 4 of MG dye solution [START_REF] Rao | Kinetic study on the photocatalytic degradation of salicylic acid using ZnO catalyst[END_REF]. The pH 10 of MG dye solution was also slightly varied from 10 to 10.4 during the degradation process. Additionally, it has been shown that the slow degradation kinetics under acidic situations is attributed to the corrosive nature dye solution for the etching of ZnO [START_REF] Behnajady | Kinetic study on photocatalytic degradation of CI Acid Yellow 23 by ZnO photocatalyst[END_REF][START_REF] Comparelli | UVinduced photocatalytic degradation of azo dyes by organic-capped ZnO nanocrystals immobilized onto substrates[END_REF]. At the same time, the influence of pH of MB dye solution was also studied with the ZnO sample prepared with 8 mL of milky sap of CP and its degradation kinetics and efficiency were studied as shown in Figure 13a-f. Both the rate constant, and degradation efficiency were highly enhanced by the change in the pH of dye solution. The degradation kinetics was following pseudo-order kinetics and suggesting that the MB concentration is the effecting the rate of degradation. The summary of obtained results in terms of rate constant with the use of different volumes of milky sap of CP and the effect of pH of dye solution are given in Table 1. Both the volume of milky sap of CP and pH of dye solution were found the key indicators for enhanced performance of as prepared ZnO sample with 8m mL. After the degradation process, the pH 4, 8 and 10 was slightly increased 4.3, 8.2 and 10.3 respectively.

3.4.Generalized photodegradation mechanisim

The photodegradation is accompanied by photoexcitation, migration of charges, charge separation and redox process on the surface of photocatalyst as already described [START_REF] Li | Efficient persistent photocatalytic decomposition of nitrogen monoxide over a fluorescence-assisted CaAl2O4: (Eu, Nd)/(Ta, N)-codoped TiO2/Fe2O3[END_REF]. The Later, these highly actiev radcials particpate in the dergadtaion of organic polutatnts like MB and MG [START_REF] Palanisamy | Sol-gel synthesis of mesoporous mixed Fe2O3/TiO2 photocatalyst: application for degradation of 4chlorophenol[END_REF]. The photodegradation of organic dyes using nanostructured materials is mainly giverned by the dimension, shape orientation and surface properties of as prepared nanostructured materials [START_REF] Muthuvel | Green synthesis of cerium oxide nanoparticles using Calotropis procera flower extract and their photocatalytic degradation and antibacterial activity[END_REF]. The performance evaluation of presented work was compared with the previous studies in terms of degradation efficiency, degradation time and synthesis method as given in Table 2. It is obvious that the presented method of material synthesis is low cost, green, ecofriendly, environment friendly, scale up production of material and the degradation performance is either superior or equal to many of the recently reported works. The improved performance of biosynthesized ZnO could be related to presence of the impurities like Mg, Cl, C and S in the samples suing milky sap of CP, and it has shown that the relative amount of them is increasing with increasing amount of milky sap of CP. These impurities may play role in making the crystal defects, narrowing the optical band gap and variation in the surface chemical composition of ZnO, consequently they have shown favorable role towards the dye degradation as confirmed by the use of higher volume of milky sap of CP.

Conclusions

In summary, we have prepared ZnO nanostructured materials using milky sap of CP through

Scheme 1 :

 1 Scheme 1: Molecular structure of different chemical compounds carried by CP

  ZnO nanostructures.The dye degradation kinetics was studied through under given mathematical equation: ln Whereas C o and C t are the dye initial concentration and after a specific time intervals for the illustration of rate constant (K) values in (min -1 ). The concentration of both dyes was expressed as mg/L. Furthermore, the effect of pH of dye solution on the degradation rate was studied using different ZnO samples. The pH of dye solution was adjusted by the use of aqueous solutions of 0.2M NaOH and HCl.3. Result and discussion3.1. Crystal phase, morphology and optical studies of milky sap of CP assisted ZnO nanostructuresCrystal phase information was verified by the distinctive reflection patterns of biosynthesized ZnO nanostructures using powder XRD technique as shown in Figure1. The XRD reflections were measured for the four samples of ZnO obtained with 2, 4, 6 and 8 mL of milky sap of CP

Figure 1b .Figure 2 .

 1b2 Figure 1b. This is connected to the wide range of polymeric biomolecules from milky sap of CP which created stress on the crystal orientation, hence shift towards right angel was observed as shown in Figure1b. The induction of shift in two theta could cause the defects in the crystal arrays and introduced the imperfection in the crystal arrays of ZnO[START_REF] Gibb | Synthesis of hydroxyl-footed cavitands[END_REF]. Moreover, the XRD results were used to describe the average crystallite size of biosynthesized ZnO nanostructures using Scherrer equation. The calculations of average crystallite size of different samples of ZnO prepared with 2, 4, 6 and 8 mL of milky sap of CP and pure ZnO were found in the order as 30.7 nm, 28.9 nm, 27.5 nm , 26.1 nm and 32.6 nm respectively a shown in Figure1c. It is obvious that the 8 mL of milky sap of CP resulted the lowest average crystallite size of ZnO owing to the high density of oxygenated terminal groups which reduced the size of crystal. According to M.G Demissie, et al. the average crystal size of biosynthesized ZnO NPs has decreased with increasing volume of plant extract. This is because of the variation in the amount of effective capping and stabilizing agents which controlled on the size of nanoparticles, and avoided the possibility of aggregation, hence size of ZnO nanoparticles was decreased[START_REF] Demissie | Synthesis of zinc oxide nanoparticles using leaf extract of lippia adoensis (koseret) and evaluation of its antibacterial activity[END_REF]. Furthermore, the morphology of as prepared ZnO nanostructures with various volumes of milky sap of CP was also examined using low resolution scanning electron microscopy (SEM) as depicted in the Figure2. The pure ZnO was identified with typical one dimensional (1D) nanorod like morphology with obvious hexagonal faces, however they were found randomly oriented with high degree of size heterogeneity as shown in Figure2a. The milky sap of CP has shown the dynamic contribution towards the transformation of 1D nanorod into zero dimensional (0D) rounded particle like structure with dimension of 400-600 nm. The increasing volume of milky sap has shown the significant indicators about the formation of special particles like morphology, and it could be attributed to the wide range of oxygenated terminal groups from the different natural compounds of milky sap. They have allowed the easy access to the zinc ions for binding and the hydrophobic part of each molecule have evolved the morphology into spherical shape.

Figure 3 . 4 .

 34 Figure 3. Except pure sample of ZnO which only consists Zn and O as main elements. However, the milky sap assisted ZnO nanostructures do not only contain Zn, and Om but at the same time Cl, S, C and Mg were also detected as shown in Figure3and such elemental chemical composition of milky sap of CP is reported elsewhere. The optical characterization in terms of optical band gap determination was also carried out to know the influence of milky sap of CP on the tuning the band gap, hence UV-visible absorbance spectra were measured as shown in Figure4. The band gap calculations were done by extra plotting of (αhʋ) 2 plot versus (hʋ) photon energy. Herein, e α is known as absorption coefficient and it can be determined from the absorbance spectra by employing the Kubelkamunk theory, and h is the plank's constant, ʋ is frequency of used photons[START_REF] Debeila | The influence of gold on the optical properties of sol-gel derived titania[END_REF]. The linear part after extrapolation of (αhʋ) 2 versus photon of energy (hʋ) gives out the value of optical band gap as shown in Figure4. The obtained optical band gap for pure ZnO sample was observed around 3.34 eV, and the ZnO material prepared with 2, 4, 6 and 8 mL of milky sap of CP was estimated as 2.90 eV, 2.86 eV, 2.83 eV and 2.77 eV respectively. The band gap of milky sap assisted ZnO nanostructures was significantly reduced, revealing an outstanding role of variety of biomolecules from the CP affecting the optical features of as prepared material. The validation of band calculations of pure ZnO of 3.34

  photocatalytic applications is limited despite it carries wide range natural compounds including reducing agents, stabilization agents, capping agents and oxygen terminated groups for the evolution of surface morphology of ZnO nanostructures and modification of its optical properties. The milky sap of CP with different volumes like 2, 4, 6 and 8 mL were used to study the structural disorder, optical characteristics variations and the degradation effectiveness of ZnO nanostructures as shown in Figure7. It can be visualized that the absorbance of MG decreased very sharply with the use ZnO samples prepared with different amounts of milky sap of CP. This confirms that the presence of natural products in the milky sap of CP have shown an excellent role to drive degradation rate swiftly as shown in Figure7. Obvious role of 8 mL of milky sap of CP on the enhancement of photocatalytic of properties could be seen from Figure7d. The estimated values of kinetic parameters of MG degradation are enclosed in Table1and they were obtained from the plot's ln (C 0 /C t ) versus time as shown in Figure8a. The degradation kinetics of MG was described by the pseudo first order kinetics as indicated by the (C t /C o ) of MG as illustrated in Figure8b. The degradation percentage of various of samples of ZnO prepared with 2, 4, 6 and 8m mL of milky sap of CP was found as 47.8%, 66.4%, 78.5% and 85.3% as shown in Figure8crespectively. From the degradation efficiency analysis, it is worth to note that the 8mL of milky sap of CP has demonstrated the highest value among the 2, 4 and 6 mL of milky sap of CP, revealing that it contains higher amount of natural compounds which together drive the degradation process very efficiently. These observations suggest that the 8 mL of milky sap of CP has offered high reduction in the optical band gap, high enhancement in the catalytic sites of ZnO, and high provision of electron and hole pairs during the photocatalysis with minimum charge recombination rate. The high generation of electrons and holes offers the large number of production of radicals like o OH and o O 2 -to degrade MG very effectievly and effcienctly.

  Figure 10a-d. It is clear, that the 8 mL like in case of MG, has shown dominant role in degrading

8 .

 8 22×10 -5 M MG as shown in Figure 12. The pH of bare 8.22×10 -5 M MG solution was 6.3. The pH of 8.22×10 -5 M MG was adjusted with the use of 0.2M NaOH and HCl solutions and 5 mg of sample of biosynthesized ZnO nanostructures was mixed with the MG dye solution and the pH of dye solution was used like 4, 8, and 10 as shown in Figure 12a-c. The well adsorption and desorption equilibrium were achieved by mechanical stirring in dark. Afterwards, the pHmaintained dye solutions with 5 mg of each sample ZnO were irradiated with UV light and analyzed for the decrease in the absorbance of UV light. The pH 4 of MG dye solution related decreases in the absorbance is enclosed in the Figure 12a. It is highly observed that the acidic pH of MG dye solution has shown the limiting decrease in the absorbance, indicating the unfavorable dye degradation due to the low density of radicals like hydroxyl or peroxide in the acidic solution, hence poor performance of degradation was noticed. The pH 4 of MG was changed to 4.3 during the degradation process. We have also studied the kinetics dye degradation in the pH 4 and observed performance is defined by the low values of rate constant and the reaction kinetics was predominated by pseudo-order kinetics as shown in Figure 12d. The most noticed observation is about the ZnO sample prepared with 8 mL of milky sap of CP that has shown the enhanced degradation rate. The degradation of MG under acidic environment of MG dye solution was found as 55.1% for the time period of 90 min for different samples of ZnO with the use of 8 mL of milky sap assisted nanostructures as shown in Figure 12f. Furthermore, the pH 8 of MG dye solution was used to illustrate the effect of pH on the photocatalytic performance of ZnO nanostructures obtained with 8 mL of milky sap of CP as shown in Figure 12b. It can be seen the activity of material is enhanced with increase in the pH of dye solution from slightly alkaline conditions. We also studied the kinetics of degradation of MG under slightly alkaline conditions and analysis is enclosed in the Figure 12e. The kinetic study has revealed better reaction rate and 8 mL of milky sap assisted ZnO nanostructured has demonstrated the significant rate constant value as shown in Figure 12e. The relative degradation efficiency of ZnO sample prepared with 8 mL of milky sap of CP was observed as 92.6as enclosed in Figure 12f. It was noticed that the pH 8 of MG dye solution was changed to 8.3 after the degradation process. At the same time, have investigated the higher alkaline pH of 10 of MG dye solution against the ZnO nanostructures synthesized with 8 mL of milky sap of CP as shown in Figure 12 c with contributed decrease in the absorbance of light. These results of pH 10 strongly suggest the outperform functionality of ZnO as photocatalyst against MG dye

2 -) 2 -

 22 reactive species like (h + , OH -and o O have been observed when photons of particualr light are striking on the surface of photocatalyst. For the possible illustration of possible photodegradation mechansism by consideirng the reported research works[START_REF] Muthuvel | Green synthesis of cerium oxide nanoparticles using Calotropis procera flower extract and their photocatalytic degradation and antibacterial activity[END_REF][START_REF] Sin | Punica granatum mediated green synthesis of cauliflower-like ZnO and decorated with bovine bone-derived hydroxyapatite for expeditious visible light photocatalytic antibacterial, antibiofilm and antioxidant activities[END_REF][START_REF] Lam | Green synthesis of Fe-ZnO nanoparticles with improved sunlight photocatalytic performance for polyethylene film deterioration and bacterial inactivation[END_REF][START_REF] Chin | 3-D/3-D Z-Scheme Heterojunction Composite Formed by Marimo-like Bi2WO6 and Mammillaria-like ZnO for Expeditious Sunlight Photodegradation of Dimethyl Phthalate[END_REF][START_REF] Chin | 0-D/3-D heterojunction composite constructed by decorating transition metal oxide nanoparticle on peony-like ZnO hierarchical microstructure for improved photodegradation of palm oil mill effluent[END_REF][START_REF] Lam | Ameliorated photodegradation performance of polyethylene and polystyrene films incorporated with ZnO-PVP catalyst[END_REF]. At the time of irradation of light, the electrons are moving from valence band to condctuon of band of , thereby creating a hole in the valence band as shown in Scheme 3. This scenerio offers the simultaneous prodcution of electron and hole pairs and they have heven interacting with the water and generate wide range of oxidizing radicals like hydroxyl ( o OH) and superoxide ( o O

Scheme 1 :

 1 Scheme 1: Preparation of ZnO nanostructures using milky sap of CP from leaves, stem and flowers using solvothermal process followed calcination in the air

Figure 1 :Figure 2 :

 12 Figure 1: (a) XRD patterns of pure ZnO and biosynthesized ZnO samples with milky sap of CP (b), (b) shift at higher angle localized at (002) (c) calculated average crystallite size

Figure 4 :

 4 Figure 4: Kubelka-Munk plots of (a) pure ZnO and biosynthesized ZnO samples grown with different volume of milky sap of CP like 2, 4, 6 and 8 mL

Figure 5 :

 5 Figure 5: (a) UV-vis absorbance for the decomposition of MG under ultra violate light exposure using pure ZnO, (b, c) Kinetics study of MG degradation (d) removal percentage of MG using pure ZnO.

Figure 6 :

 6 Figure 6: (a) UV-vis absorbance for decomposition of MB under ultra violate light exposure using pure ZnO, (b, c) Kinetics study of photodegradation of MB, (d) percent degradation efficiency of MB

Figure 8 :Figure 9 :

 89 Figure 8: (a, b) Kinetics study of MG using ZnO nanostructures prepared with different volumes of milky sap of CP like 2, 4, 6 and 8 mL, (c) degradation efficiency of MG

Figure 10 : 8 mLFigure 11 :Figure 12 :

 1081112 Figure 10: (a-d) UV-vis absorbance for decomposition of MB dye under ultra violate light using ZnO nanostructures prepared with different volumes of milky sap of CP like 2, 4, 6 and 8 mL

Figure 13 :

 13 Figure 13: (a-c) UV-vis absorbance for decomposition of MB under ultra-violate light exposure using ZnO sample prepared with 8 mL of milky sap of CP in different pH values like 4, 8 and 10, (d-e) Kinetics study of MB under various pH values, (f) degradation efficiency of MB at 4, 8 and 10 pH values

  36.619 o , 34,335 o , 36.100 o , 47.367 o , 56.313 o , 62.645 o , 66.033 o , 67.641 o , 68.737 o , 72.362

o and 76.588 o corresponded to crystal plane including (100), (002), (101), (102), (110), (103), (200), (112), (

Acknowledgement

The authors extend their sincere appreciations to Researchers Supporting Project number (RSP2023R79), King Saud University, Riyadh, Saudi Arabia, for partial funding of this work.

Data Availability Statement

Data will be made available on reasonable request

Author contributions

Muhammad Ali Bhatti, did synthesis of ZnO nanostructures and evaluate the partial photocatalytic properties Aneela Tahira, did XRD analysis Ahmed Ali Hullio, did analysis of obtained photodegradation results Umair Aftab, did optical bandgap analysis Ayman Nafady, partially supervised the work and edit the draft of manuscript Brigitte Vigolo, did the SEM analysis and edit the draft of paper Zafar Hussain Ibupoto, supervised the work and wrote the first draft of manuscript

Conflict of Interest

Authors declare no conflict of interest in the presented research work


Thibaud Boncourt
email: thibaud.boncourt@univ-paris1.fr

Jean-Vincent Holeindre
email: jean-vincent.holeindre@u-paris2.fr

Jean Joana
email: joana.jean@numericable.fr

Nonna Mayer
email: nonna.mayer@sciencespo.fr

Political Science Communities Challenged by Internationalisation. The Case of France

Keywords: France, History of political science, Internationalisation, Multiple correspondence analysis, Sociology of the social sciences

The internationalisation of political science is an uneven process. Existing studies have shown that it is characterised by centre-periphery relationships, with dominant Western countries setting the international standards of the discipline and scholars from the East and the Global South struggling to adapt to these standards. Fewer studies, however, have been devoted to the tensions that internationalisation creates within the Western world of political science. Through a study of the case of France, this article argues that some of the countries that enjoy a rather dominant position globally may still be internally divided by the changes brought about by internationalisation. The article portrays French political science as divided between institutions and scholars that are strongly connected to international venues, and others that are not. It concludes that the internationalisation of political science is best portrayed as a conflicted process and a point of contention, rather than a smooth process of gradual convergence.

Introduction

The fact that the internationalisation of the social sciences, and of political science in particular, is an uneven process has been well documented. The dominant argument is that this process is characterised by centre-periphery relationships, with dominant Western countries setting the international standards of the discipline and scholars from the East and the Global South struggling to adapt to these standards, often at the price of tensions with national intellectual traditions (Keim et al., 2014, Heilbron et al., 2018).

Fewer studies, however, have been devoted to the tensions that internationalisation creates within the Western world of political science. This article studies the fact that some of the countries that enjoy a rather dominant position globally -sustained by a critical mass of scholars, a historically dominant language, and distinctive intellectual traditions that circulate beyond national boundaries -may still be internally divided by the changes brought about by internationalisation. What shapes do these divisions take? How does internationalisation change national configurations?

This article answers these questions by studying the case of France. As a rather large Western country that is traditionally seen as relatively closed off to the rest of the world and reluctant to internationalise itself [START_REF] Daguerre | Murder by numbers: the slow death of French political science[END_REF][START_REF] Billordo | Publishing in French political science journals: an inventory of methods and sub-fields[END_REF], France is analysed as an extreme case which renders visible processes that are at work in other national political science communities.

The article starts from the observation that the very term of "internationalisation" is controversial within the discipline. Defined by some as the fact of publishing and speaking in Anglophone journals and congresses, it is understood by others in a much broader sense, notably at the linguistic level. Like other studies in this symposium (see Tronconi and Engeli), this article does not intend to solve this issue by proposing a theoretical definition of internationalisation. Rather, it focuses on the way in which internationalisation is understood and practiced. The article starts by studying the different ways in which the term is understood in institutional discourses. It then studies the way in which internationalisation is indeed practised by French political scientists through an analysis of three non-exclusive dimensions: citations, publications, and recruitments.

Methodologically, the article relies on qualitative and quantitative data collected in the framework of a collective report produced at the request of the French Political Science Association (AFSP), and concerning chiefly the 2013-2017 period [START_REF] Boncourt | Quelle internationalisation pour la science politique française ?[END_REF].

Discourses were studied via an analysis of official guidelines and reports produced by some of the institutions responsible for evaluating political scientists (CNU and CNRS -see below), and via expert interviews with relevant members of the discipline (conducted with members of CNU and CNRS, with scholars with a strong international experience, and with scholars involved in representing French political science internally, for example in the framework of the International Political Science Association). Practices were studied through an analysis of the citations in the dominant national journal of political science (Revue française de science politique); the profile of recently hired political scientists (via a thorough analysis of their online CVs); and the productions of research centres in political science (via an online survey, in which a couple of subjective questions were also included -the survey was sent to twenty-one centres, eight of which replied). While the data does not cover all potential aspects of internationalisation, it is sufficient to bring to light the existence of divisions within French political science with respect to this process. Thus, the article portrays French political science as broadly internationalised but internally divided between institutions and scholars that are strongly connected to international venues, and others that are not. It concludes that the internationalisation of political science is best portrayed as a conflictual process and a point of contention, rather than a smooth process of gradual convergence.

Professional discourses: the flexible character of the term "internationalisation"

French political scientists have contrasting representations of internationalisation. The assessment they make of the internationalisation of their discipline, and of the means likely to make it evolve, are strongly determined by the way in which they define the notion.

Internationalisation is generally perceived as a positive phenomenon and a resource, which must be sought both at individual and institutional levels [START_REF] Mesr | Guide Mobilité Internationale des Enseignants-Chercheurs[END_REF]). This appears quite clearly in institutional discourses. In a 2017 document presenting the criteria for evaluating researchers in political science, the National Centre for Scientific Research's (CNRS) Section 40 (which is responsible for recruiting and overseeing the careers of researchers whose work deal with the topics of "Politics, Power and organisation")1 considers internationalisation as one of the "general principles" that should guide their evaluation, alongside research activities, publications and professional environment. Internationalisation is described as a "needed dimension of researchers' activity", even if its evaluation should be "modulated" according to seniority (CoNRS Section 40, 2017). For the recruitment of junior Research Fellows, the applicants' ability to take part in international debates is appreciated, through their integration into international research networks or cooperations. For the recruitment as Research Director, Section 40 places an even greater emphasis on the international recognition of works carried out by the candidates. This partially overlaps with criteria mentioned by annual reports of the National Universities Council (CNU) -a representative body in charge of organising the careers of university teachers-researchers and of granting candidates the right to apply ("qualification") to assistant professor and professor positions. Internationalisation can be an asset, but it is not a major criterion for being "qualified" for assistant professor positions. However, it is a much clearer criteria for being qualified for full professorships, and for the allowance of various types of gratifications and career advancements. The directors of French research centres also put forward a positive vision of internationalisation. In the survey we conducted among research centres, all eight respondents except one presented internationalisation as desirable. The majority of interviewees also responded positively to the question of whether their researchers were sufficiently internationalised, and there was a consensus on encouraging internationalisation and supporting it, especially for young researchers.

Despite this generally positive view of internationalisation, doubts and reservations also arose from time to time. In the same survey of research centres, some answers evoked the risk of "imposing standards". In its 2014 annual report, the CNRS Section 40 also displayed a very nuanced approach of internationalisation. Internationalisation was presented as being "encouraged", but the report also highlighted the risk of "hasty pressures" that could "lead to the standardisation and impoverishment of academic knowledge and devices" (CoCNRS Section 40, 2014: 16). One of the perceived risks was that of reducing internationalisation to one of its dimensions -most notably publishing in English.

As pointed out elsewhere in this symposium (see Kostova et al.), these reservations are linked to the uncertainty that weighs on this notion, and to the diversity of criteria that are put forward to evaluate internationalisation. Both in the responses to the survey of research centres and in the institutional speeches, there is no generic definition of internationalisation, and the "indicators" used to specify the notion are defined in various ways. The CNRS section 40 mentions "research stays abroad, cooperation with research teams, animation of scientific networks, organisation of panels or symposia, participation in conferences, expertise for international institutions, publications, etc…". Likewise, CNU annual activity reports do not explicitly define internationalisation, which only appears as one of the criteria being used for evaluating applicants' CVs. At the assistant professor qualification level, internationalisation is defined between the lines as the "participation in international networks and international congresses such as APSA, ISA, IPSA…". These elements are more detailed for full professor qualification since "internationalisation" is considered of greater importance at this level. In addition to the participation in international networks, partnerships and congresses, additional criteria are mentioned: publications "in English", expertise for international research organisations, peer reviewing in international journals and invited lectures in foreign universities.

Beyond this diversity, internationalisation seems to be implicitly defined by all these institutional bodies as the ability to engage with international scientific controversies. But this general definition encompasses three concrete dimensions: the international dissemination of works produced in French research institutions; the reception and appropriation of foreign works; and the co-production of political science on a transnational stage. Depending on the institutional discourse under study, these three dimensions are alternatively applied to the individual and institutional level (research centres and universities in particular). The most frequently used criteria are: publishing in a foreign language (most often English), involvement in transnational networks, and the hosting of foreign researchers. These different definitions of internationalisation also influence the professional discourses about the factors that impede internationalisation, and the way in which it may be improved.

The issue of language proficiency (beyond English) has come up repeatedly in our study of such discourses. In the questionnaires and interviews, the progress achieved by teachers and researchers was mentioned, particularly with regard to oral proficiency in the English language, notably among the younger generations. Relatedly, participation in international symposia was described as quite common. However, publishing in English (or another foreign language) was described as often posing much greater challenges than oral communication as it implied, in addition to mastering the language, knowing the journals and publication spaces, opening up to other scientific issues and debates, adopting other methods of presenting evidence, and writing.

French political scientists based abroad or foreign Assistant Professors recruited at Sciences Po with whom we spoke mentioned the discrepancy that may exist between scientific debates as they are reflected by international journals (mainly in English) and debates taking place in

France or in the French-speaking world: for example, while political theory is strongly represented internationally, it is hardly represented in panels and activities of French Association of Political Science congresses, Universities or the CNRS. Likewise, objects of study trivialised at the world level, such as political psychology, subaltern studies or studies on peace, remain relatively marginal in the French scientific space where other themes are prominent (the social history of ideas, multilateralism, international organisations, etc.). In addition, the relatively rare use of quantitative methods compared to what is practiced elsewhere was mentioned. But contrary to what one might expect, this gap is not perceived as a major obstacle for all researchers. Interviewees readily pointed out that this insertion into "international" issues already existed for certain researchers and certain sub-disciplines:

comparative politics, international relations, political theory and European studies which were perceived as vectors of internationalisation. In addition, even if certain sub-fields were identified as less open internationally, exchanges were seen as still possible. It was emphasised that the fact that international political science is not monolithic allowed French political scientists to defend their own specific differences. As a result, several interviewees insisted on the need to have a flexible approach to internationalisation, which takes into account the peculiarities of the social sciences as they are practiced in France. Some also insisted that it is possible to debate with other related disciplines internationally, such as sociology, anthropology, history, etc.

The way in which internationalisation is taken into account in the framework of recruitment or career advancement is one of the points on which there was no broad consensus.

In our survey, a majority of research centre directors considered that the way in which recruitments were carried out in universities or at CNRS constituted an obstacle to internationalisation. As noted by French-speaking researchers based abroad or by members of institutions such as CNU, the French university market appears to be relatively closed off: at assistant professor level, the CNU qualification rate of doctors who defended their thesis in a foreign language tends to be lower than that of other applicants, even if it has increased over time (see below). Even though CNRS is perceived as more open to internationalisation than universities, the dominant idea remains that investment in internationalisation is insufficiently taken into account at the institutional and recruitment level. By contrast, some of the members of CNU and CNRS that we interviewed emphasised their reluctance to give more weight to internationalisation in recruitment or promotion, given that the possibilities of internationalisation are unequally distributed according to research objects, teaching load, access to resources, and gender.

Professional practices: internationalisation on its way

Discourses reveal tensions about the meaning and legitimate uses of "internationalisation" in French political science. The remainder of this article studies the way in which internationalisation is actually practiced and valued. As studying all the different dimensions highlighted in Table 1 is beyond the scope of this article, we only focus on publication practices (section 2) and the way in which they are appreciated in professional recruitments (section 3).

Our study of publication practices relies on two types of data: data about the main national professional review, the Revue française de science politique; and about the publications of French political science laboratories.

Revue Française de Science Politique

One of the ways to evaluate the internationalisation of a discipline is to look at its journals and the articles they publish. We focus here on the main political science journal in France, the Revue française de science politique (RFSP), launched in 1951 in the wake of the creation of the French Political Science Association (1949). After contextualising the international visibility of the journal in relation to the main citation indexes, we turn to a study of the authors who publish in RFSP, on the basis of a content analysis of all articles published between 2014 and 2017 with the exception of book reviews and review essays.

Visibility

English is the main language for scientific exchanges, affecting the share of non-English journals and articles in the main citation indexes databases. To answer this challenge CNRS has been funding the translation of several social sciences journal, including RFSP, available in English on Cairn International since 2010 2 . RFSP is now also accessible on J-Store.

However, boosting an English-tongue audience is not only a question of language, but of culture. If one restricts oneself to the French Google Scholars Metrics, the RFSP comes in thirty-sixth position out of the hundred top publications, with an h5-index 3 of 10. It puts it at the same level as another French political science journal, Politix, and a little behind the sociological journals, three of which rank higher. Revue française de sociologie is second, Sociologie du travail twentieth and Actes de la recherche en sciences sociales twenty-fourth (respective h5-indexes of 14, 13, and 11) 4 .

2 https://www.cairn-int.info/journal-revue-francaise-de-sciencepolitique.htm?contenu=english-full-text-articles. 3 The h-index is defined as the highest number of publications of a scholar that received h or more citations each. The h5-index is the h-index for articles published in the last 5 complete years. 4 https://scholar.google.fr/citations?view_op=top_venues&hl=en&vq=fr.

However, the ranking of RFSP is clearly lower in a broader international perspective.

In the 2018 Scopus / Elsevier Index5 , RFSP ranked 220th out of 545 with a Cite Score of 0.61. A serious handicap though is the fact that the RFSP is not yet included 7 in the reputed Reuters-Thomson Social Sciences Citation Index (SCCI), while Politix is, as well as many national political science reviews (Brazilian, Canadian, Chilean, Italian, Spanish etc.) and the Revue française de sociologie. It is not included either in the new index 'ERIH Plus' (European Reference Index for the Humanities). Started by the European Science Foundation (ESF) and https://www.scimagojr.com/journalrank.php?area=3300&type=j&category=3320

.The Scimago Journal Rank indicator (SJR) is the average number of weighted citations received in the year considered by the documents published in the journal for the 3 previous years. 7 The procedure is on its way, involving the verification of criteria such as regularity of publication, peer-reviewing etc. its Standing Committee for the Humanities in the European Research Area (HERA), now transferred to the Norwegian Social Science Data Services (NSD), this index takes into account social science journals since 2014 and its aim is precisely to make more visible high quality European scientific publications 8 .

Publications

To evaluate the degree of internationalisation of what RFSP publishes, we look both at book reviews (are these books French or foreign?) 9 and regular research articles. We take into account the countries where article authors are based and the location of their fieldwork (France, other European countries, rest of the world, supranational). We also classify the bibliographic references, whether they are only French or include some in English or another foreign language. This is put in the context of the disciplinary subfield of the article (political sociology, international relations, public policies, methodology, political theory) and the methods it uses (qualitative or quantitative). Mapping subfields and methods allows us to compare French publications with dominant international trends.

Since 2010, when RFSP reconsidered its book-review policy, 230 books are reviewed every year on average, thirty-five per cent of which are published by foreign editors, mostly in English. As for the hundred articles published over the four years we processed (table 2), they were written by 120 authors, three quarters of whom were French, and mostly in the subfield of political sociology, a specific tropism of French political science. The fieldworks reflect a large opening on the rest of the world, only thirty-one per cent of the articles dealing exclusively 8 http://corist-shs.cnrs.fr/ErihPlus_2014 . 9 Data provided by the RFSP's publication director Yves Déloye.

with France and nineteen being comparative in scope. Their methodology is essentially, and increasingly, qualitative, putting the journal at odds with some of the mainstream international political science journals that mostly focus on quantitative research. Only eleven per cent of the RFSP articles processed rely on quantitative methods. Libia [START_REF] Billordo | Publishing in French political science journals: an inventory of methods and sub-fields[END_REF] study of RFSP over the period 1970-2004, found that thirty-four per cent of the total of articles published were based on a quantitative methodology and a quarter if she excluded non-empirical articles (i.e political theory) 10 . She noted that, during the same period, their share of the articles published by the American Political Science Review oscillated between sixty and eighty per cent.

As for the bibliographic references of the articles (5631, 2940 of which in 2014-15 and 2691 in 2016-17), they show a marked international scope. Forty-eight per cent on average are in English, six per cent in another language, less than half in French (forty-six per cent). In special issues devoted to the cases of Italy ("Florence (1200-1530): Reinventing the Political", 2014) and America ("The American State", 2014), the proportion of references to foreign literature was even higher, up to fifty-one per cent of references in English and sixty per cent in another language than French or English.

10 However, her criteria raise some problems of comparability with our own study and other analyses come to a smaller proportion of articles based on quantitative data during the same period [START_REF] Boncourt | Is European political science different from European political sciences? A comparative study of the EJPR, Political Studies and the RFSP 1973-2002[END_REF]. In French 40% 52% 46%

In English 51% 46% 48%

In another language 9% 2% 6%

What research centres produce

Another way to look at publication practices is to adopt a "bottom up" approach, by gathering data from scholars themselves. We therefore surveyed the productions of political science research laboratories (Table 3). Among the twenty-one political science research centres identified as such by the French Political Science Association, eight responded to the survey.

While they cannot be taken as purely representative of the discipline, they are diverse in terms of their geographical location (three in Paris, five in the rest of France) and institutional settings (five in Institutes of political studies, three in faculties of law and political science) 11 .

With regard to the publication of articles in peer-reviewed journals in English or other non-French languages, there is a relatively homogeneous situation between the laboratories.

The average proportion of publications in a foreign language varies between twenty-five and thirty per cent for the majority of the laboratories studied. Two laboratories stand out. One with results much higher than these figures, and one for which this proportion is much lower.

Roughly, similar proportions are found with regard to oral communications in a foreign language, whether or not accompanied by written text.

These figures confirm that the national arena remains the privileged place of communication -written or oral -for French political scientists, but also that participation in symposia or foreign journals, essentially English-speaking ones, is a fairly common and uniformly distributed practice. This internationalisation decreases for publications of works requiring more structured exchange or dissemination practices. For each laboratory except one (L1), the proportion of contributions to edited books in a foreign language or of edited books or journal special issues is lower, or even much lower that it is for articles in peer reviewed journals or communications in conferences. This can be explained by a strategy of French political scientists who tend to downplay the importance of this type of support to develop their internationalisation. But it shows also, more surely, a lack of integration in the international research networks which underlie the realisation of this type of product.

Internationalisation appears even less developed for the publication of monographs in foreign languages, particularly in English. French scholars mostly tend to publish monographs in French. This can be explained by the difficulty of getting manuscripts accepted by foreign publishers -whatever the reasons -or by the cost of writing in a language other than one's own a manuscript whose fate would be particularly uncertain.

Furthermore, these data reveal differences depending on the geographic or institutional location of the laboratories. The two laboratories located in Sciences Po Paris have internationalisation rates significantly higher than the others: articles in peer reviewed journals in English represent more than three quarters of its productions for one (seventy-six per cent), close than half (forty-seven per cent) for the other. For non-Paris IEPs, the difference with Law and Political Science Faculties is less clear, although the limited size of our sample prevents conclusions from being drawn. We can also note a correlation between the level of internationalisation of publications and the "productivity" of laboratories: the laboratory which is distinguished by a particularly strong degree of internationalisation ( L2) is also the one with the lowest publication index per researcher (2,07) while one of those with the lowest internationalisation rate (L6) is also the one whose productivity is one of the highest (5,27).

The different value of internationalisation in professional practices

Such differences between institutions in terms of their internationalisation practices are also tangible at the level of recruitment. This section looks at the extent to which newly hired teacher-researchers invest in international or national endeavours, and assesses whether different institutions have different recruitment strategies when it comes to the international profile of their new staff.

We collected data on the 123 early career scholars who were hired in permanent positions of maître de conférence (MCF, i.e. assistant/associate professor) and chargé de recherche (CR, i.e. full time researcher) in France, over a five year time period (2013)(2014)(2015)(2016)(2017). By analysing their online CVs, we collected data on their individual properties (gender, age, nationality), career to date (past doctoral and postdoctoral institutions), their publications (the number of languages of publications at the time of hiring), and their research areas.

At first glance, the job market appears to be relatively closed off: the vast majority of our respondents are French and defended their PhD dissertation in France and in French, with only seven dissertations carried out in the framework of a joint international supervision, and seven fully carried out abroad. However, there are signs of internationalisation in that the majority of the theses under study have an international outlook (while forty-five focus on

France, seventy-two compare France with another country, study another country altogether, or focus on transnational or international objects), a third of our sample has held a postdoctoral position abroad, and the mean number of publications in foreign languages is three -with substantial differences however, as a third of our sample has only published in French.

In order to better compare the profiles of the individuals under study, we used a multiple correspondence analysis (MCA) based on the following variables. Active variables (Figure 1) included having worked as a postdoc in France (dichotomous), elsewhere in Europe (dichotomous), in North America (dichotomous), or elsewhere in the world (dichotomous); the number of publications (between two and four, between five and ten, between eleven and twenty, more than twenty); the proportion of publications in foreign languages (0 %, 4-9 %, 10-25 %, 26-50 %, 51-75 %, 76-100 %); the fact of having published in English (dichotomous) or in another non-French language (dichotomous). Supplementary variables (Figure 2) included gender, place of thesis defence, year of recruitment, time lapse between defence and recruitment, discipline and sub-discipline, and cases studied in the course of Ph.D. theses.

The MCA's first dimension (horizontal axis) accounts for 13.7 per cent of the total inertia. It is strongly associated with the share of publications in foreign languages -this share is highest for individuals located on the right side of the graph. This dimension is also associated with postdocs abroad -those with such a postdoc are located on the right side of the graph.

Thus, this first axis locates individuals according to the degree of internationalisation of their professional practices (publications in foreign languages and professional mobility). The second dimension (vertical axis), which accounts for 10.9 per cent of the total inertia, is linked to the number of publications. It locates those who have published the most at the top of the graph, and those who have published the least at the bottom. The MCA locates at the top / top left at the graph scholars hired as CNRS chargés de recherche. This region of the graph also features long gaps between the Ph.D. and the time of hiring, theses carried out in neighbouring disciplines (history, sociology, etc.), and case studies centred on France. Thus, these scholars appear to be relatively experienced and productive, though less internationalised than those hired by Sciences Po Paris -similar, in that respect, to those hired by the other Sciences Po.

The MCA locates at the bottom left of the graph scholars hired as maîtres de conférence in universities. These scholars are more junior, less internationalised, and have often done their Ph.D. in French universities.

These observations indicate that different institutions follow different criteria when hiring new staff, notably with respect to internationalisation. While the latter is key to Sciences Po Paris hirings and, to a lesser extent, in other Sciences Po and CNRS, it is less valued in the rest of the universities. This conclusion fuels the idea that internationalisation is not practiced in the same way and to the same degree in different institutions. Internationalisation appears to be not universally accepted as an evaluation criterion, and may even be a point of contention between institutions of different status and prestige. While this means French political science is relatively inclusive -different (non-)internationalisation strategies may pave the way to obtaining a permanent academic position -it also makes for relatively blurry evaluation criteria -meaning it makes it harder to know which boxes one should tick in order to stand a chance on the academic job market.

The data also allows us to draw several observations about the shape internationalisation tends to take in the French context. Firstly, the internationalisation of newly hired scholars is mostly directed towards Europe, notably in terms of postdoctoral fellowships abroad. Sciences Po Paris assistant professors are the only ones to lean more towards North America. Secondly, foreign country case studies and international comparisons tend to be associated with a stronger professional internationalisation. In terms of subdisciplines, comparative politics and, to a lesser extent, public policy analysis are associated with a higher degree of internationalisation than, in this order, international relations, political theory, and political sociology.

Thirdly, scholars recruited right after their Ph.D. tend to be less internationalised than the others -which is logical in the sense that being relatively junior means that they are less likely to have had the time to hold a postdoctoral position abroad.

Fourthly, women tend to be less internationalised than men at the time of hiring. While they publish in foreign languages as much as men, they are less likely to have held a postdoctoral position abroad. Though this is again related to seniority at the time of hiring, as the time between thesis completion and hiring is slightly lower for women than men (3.6 and 4 years respectively), other dynamics likely are at play, as previous studies have shown that men are more represented than women in international academic mobility [START_REF] Walters | Gender equality in academic tourism, hospitality, leisure and events conferences[END_REF].

Lastly, scholars hired in the most recent years are located on the right of the graph: the more recent cohorts tend to be more internationalised than the elder ones. Thus, even though the period of time studied here is limited, the MCA hints at potential changes over time, characterised by an increasing value of internationalisation for recruitments.

These observations show that the degree of internationalisation varies not only according to the hiring academic institutions, but also according to the social properties of scholars. In other words, researchers are unequal when it comes to internationalisation opportunities.

Conclusion

This study portrays French political science as internally divided by internationalisation. The term appears to be loosely defined by both researchers and evaluation agencies, and practicing internationalisation appears to be unequally important in different parts of the French academic field. Efforts to become more internationalised are unlikely to register equally on the scale of judgement in different institutions.

More broadly, this study suggests that the international landscape of political science is not only divided between a "centre" mostly made up of Global North countries and a "periphery" mostly consisting of Global South countries. Rather, the Global North is itself internally divided, not only between countries but within them as well. Depending on their socialisation, their professional positions, and the way in which they relate to more or less clear evaluation schemes, researchers value internationalisation to very varying extents. When they do "internationalise" themselves, they do it in diverse ways, as "internationalisation" is itself made up of practices that are considered valuable to varying degrees. This study therefore suggests that the study of internationalisation should be made more subtle by taking into account the complex way in which this plural process relates to individual career trajectories.

By focusing on France, a case ever considered as atypical, this study runs the risk of overemphasising the contested character of internationalisation. We believe, however, that the French case simply sheds more visible light on processes occurring elsewhere -those by which what is considered "valuable", "prestigious", and "high quality" in the scientific field is the object of constant struggles.

  schemes with foreign institutions

  It displayed a higher score than other French journals of the discipline such as Critique internationale or Raisons politiques (0.20 and 0.32), but lower than several other national political science journals in Europe, such as the Swiss Political Science Review (2.1) and the Rivista Italiana di Scienza Politica (0.96), and lower than the central journal in sociology (Revue française de sociologie, 0.76). Among the 525 political science journals of the 2019 Scimago index base 6 , the RFSP ranked 179 th , with an SJR of 0.381 (versus 0.31 the year before) and an h-index of 24 (versus 23). A ranking way behind the star American journals (the American Journal of Political Science had a SJR of 7.131 and a h-index 161, the American Political Science Review of respectively 5.872 and 167), as well as the British Journal of Political Science (3.820 and 91), and the Italian and Swiss political science reviews (0.959/26 and 0.597/10).

Figure

  Figure 1. MCA -Active variables.

  of supplementary variables onto the graph (Figure2), four groups of newly hired political scientists are identified.Those hired as assistant professors at Sciences Po Paris are located at the upper right of the graph. The MCA also locates in this same region of the graph as foreign researchers, those with a Ph.D. thesis carried out abroad, and those with the longest gaps between their Ph.D. and the time of hiring. Descriptive statistics also indicate that Sciences Po's newly hired assistant professors publish mostly and, in some cases, only in English, and that they have almost all held a postdoctoral position abroad.The MCA locates at the bottom / bottom right of the graph scholars hired as maîtres de conférence in the non-Parisian Sciences Po. These scholars are slightly more junior and less internationalised (in terms of postdocs and publications) than their Paris colleagues, but they often have studied foreign countries in the course of their work.

Table 1

 1

	summarises these

Table 2 .

 2 Articles published in RFSP 2014[START_REF] Boncourt | Quelle internationalisation pour la science politique française ?[END_REF]

	2014-15	2016-17	Total

Table 3 .

 3 Proportion of scientific productions in foreign languages, calculated on the basis of the productions declared in the latest evaluation report of HCERES (per laboratory, noted L).

	Source: authors' survey.
		L. 1	L. 2	L. 3	L. 4	L. 5	L. 6	L. 7	L. 8
	Articles in Peer
	reviewed Journal
	published in non-
	French language	29	77,7	23,9	11,4	51,7	21,5	30,5
	In English (%)	29	75,9	21,3	7	47	18,6	26,9
	In other foreign	(0)	(1,8)	(2,6)	(4,4)	(4,7)	(2,9)	(3,6)
	language (%)

The French system has a dual structure: CNRS is responsible for hiring full-time researchers, while universities hire "teachers-researchers".

https://www.scopus.com/sources.uri . CiteScore is the number of citations received by a journal in one year to documents published in the three previous years, divided by the number of documents indexed in Scopus published in those same three years.

Political science is represented in the Institute of Political Studies (IEP, also called Sciences Po), which are part of the "Grandes écoles" system and focus on the multidisciplinary training of future public and private sector elites, and in faculties of law and political science in the regular university system.

This index is based on the number of articles published in peer-reviewed journals per researcher.

Acknowledgements

We would like to thank all the colleagues who accepted to take part in this study in various ways, as well as the AFSP team for its support throughout this study.