Nina Gnougon

Coulibaly

Sami Rtimi

Aymen Amin Assadi

Khalil Hanna
email: khalil.hanna@ensc-rennes.fr

Nano-sized iron oxides supported on polyester textile to remove fluoroquinolones in hospital wastewater

Keywords: iron oxide, supported catalyst, peroxymonosulfate, fluoroquinolones, hospital wastewater

In this study, we examined the removal kinetics of two fluoroquinolones (FQs), flumequine (FLU) and ciprofloxacin (CIP), in synthetic (SWW) and real hospital wastewaters (RHW) using FeOx thin films, peroxymonosulfate (PMS) and visible light. Nano-sized iron oxides (FeOx) supported on polyester textile (PES) were synthesized by a novel high-power impulse magnetron sputtering method (HiPIMS). The O2/Ar ratio is an important factor to tune the Fe A c c e p t e d m a n u s c r i p t oxidation, which controls the composition of thin film and thus capability of the resulting FeOx for PMS activation. Based on scavenging experiments, sulfate radicals were shown to be predominantly involved in the heterogeneous oxidation reaction. Competitive effects with reactive species could explain the lower degradation rate constants in mixture relative to those in single systems. In contrast to chloride, organic matter, sulfate and phosphates commonly found in RHW, dramatically decreased the removal performance of both target compounds, FLU and CIP. However, increasing PMS concentration to 3 mM improved considerably the degradation and mineralization, even in real wastewaters. The good stability and reusability of FeOx/PES material has been confirmed in hospital wastewater over five successive oxidation cycles.

• Introduction

Fluoroquinolones (FQs) are one of the largest group of antibiotics with an increased use in hospitals, households and veterinary medicine. 1,2 . They were recently classified as a priority risk group because they can cause bacterial resistant. 3,4 Among FQs, flumequine (FLU) and ciprofloxacin (CIP) represent almost the entire consumption of quinolone antibiotics in the European Union. 5 FLU and CIP were detected at 6.9 μg g -1 in soil 6 and from 2.5 to 50 ng L -1 in aquatic environments. 7 To remove these compounds from contaminated effluents or wastewaters, different strategies have been developed. One of these technologies is advanced oxidation processes (AOPs) which are able to generate reactive oxygen species (ROS) and then achieve degradation of organic compounds. 8,9 Among AOPs, the photocatalysis process appears as an economic and sustainable technology, particularly when solar light is used as an energy.

When a photon with energy higher than the band gap energy (Eg) of the semiconductor is applied, a photogenerated electron (e -) in the valence band is excited into the conduction band, leaving a positive hole (h + ) in the valence band. 10 The photogenerated charge carriers allow the oxidation of organic compounds through the formation of hydroxyl radicals (OH). [10][11][12] Metal oxides (e.g. Fe-(oxy)hydroxides) can be used as environmentally benign semiconductors, and appear to meet the criteria to promote photo-assisted Fenton reactions. 10,[13][START_REF] Xu | Magnetic Nanoscaled Fe3O4/CeO2 Composite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of 4-Chlorophenol[END_REF][START_REF] Xu | Use of iron oxide nanomaterials in wastewater treatment: A review[END_REF][START_REF] El Mehdi Benacherine | Heterogeneous photoinduced degradation of amoxicillin by Goethite under artificial and natural irradiation[END_REF] It was reported that photogenerated electrons on the surface of semiconductors could activate peroxymonosulfate (PMS), and generate sulfate radicals (2.5-3.1 V). [START_REF] Zhu | Visible-light-induced photocatalysis and peroxymonosulfate activation over ZnFe 2 O 4 fine nanoparticles for degradation of Orange II[END_REF] However, little is known about the ability of PMS-activation process to effectively remove contaminants in real wastewaters where target contaminants are found with many A c c e p t e d m a n u s c r i p t other substances. In addition, most of published studies used semi-conductor materials in suspension where recovery and/or potential reuse imply costly steps, especially in industrial settings. [START_REF] Kanakaraju | Titanium dioxide/zeolite integrated photocatalytic adsorbents for the degradation of amoxicillin[END_REF][START_REF] Dong | Immobilization of Polymeric g-C 3 N 4 on Structured Ceramic Foam for Efficient Visible Light Photocatalytic Air Purification with Real Indoor Illumination[END_REF][START_REF] Shan | Immobilisation of titanium dioxide onto supporting materials in heterogeneous photocatalysis: A review[END_REF] For this reason, supporting semi-conductors on glass, stainless steel, membrane filters, ceramic or textile has gained great attention, especially in wastewater treatment technologies. [START_REF] Kanakaraju | Titanium dioxide/zeolite integrated photocatalytic adsorbents for the degradation of amoxicillin[END_REF][START_REF] Dong | Immobilization of Polymeric g-C 3 N 4 on Structured Ceramic Foam for Efficient Visible Light Photocatalytic Air Purification with Real Indoor Illumination[END_REF][START_REF] Shan | Immobilisation of titanium dioxide onto supporting materials in heterogeneous photocatalysis: A review[END_REF] Furthermore, the use of visible light-responsive materials may offer cost benefits due to the unlimited sunlight energy. The present work will examine, for the first time, the visible light-responsive photocatalytic activity of supported materials for FQs removal in real hospital wastewaters. In the visible light photocatalysis, the charge transfer rates as well as the hole-electron recombination rate are two critical factors, which could also be affected by the structures, surface properties and morphologies of solids. These key properties can be controlled by the synthesis methods and operational conditions.

In order to develop cost-effective wastewater treatment solutions, we have investigated how the white-light LED could enhance FQs removal in synthetic wastewater (SWW) and in real hospital wastewater (RHW). For this reason, we have deposited nanoscale FeOx on polyester textile (PES) using high-power impulse magnetron sputtering (HiPIMS) under different Ar/O2 ratios in the sputtering chamber. The spectral absorption and the band gap energies of the resulting oxides have been determined by mean of diffuse reflectance spectroscopy (DRS).

The FeOx loading on PES was determined by X-ray fluorescence (XRF) and surface atomic percentages of Fe and O were determined using X-ray photoelectron spectroscopy (XPS). The nanoparticles distribution and thickness on PES was obtained by Transmission Electron Microscopy (TEM). Finally, the reusability of FeOx/PES system was investigated in hospital wastewater over five oxidation cycles and the influence of wastewater components on the overall performance was discussed. and tert-butyl alcohol (t-BuOH, C4H10O), sodium nitrate (NaNO3), sodium sulphate (Na2SO4) disodium phosphate (Na2HPO4), citric acid (C6H8O7), ascorbic acid (C6H8O6) and sucrose (C12H22O11) were purchased from the Sigma-Aldrich. Hydrogen peroxide (H2O2; 35%, v/v),

NaOH and HCl (37% extra pure) were provided from Acros Organics. The Fe-target in metal form of 5 cm in diameter (99.99% pure) was purchased from K. Lesker Ltd. UK. The standard Leonardite Humic acid (LHA) was provided by International Humic Substances Society (IHSS). Standard solutions were prepared with high-purity water obtained from a Millipore Milli-Q system with 18.2 MΩ cm resistivity. A hospital wastewater sample was provided by the University Hospital Center of Rennes (Rennes city, France) (compositions listed in Table S1, †).

HiPIMS sputtering of FeOx-PES

The FeOx coatings were prepared using a High Power Impulse Magnetron Sputtering (HiPIMS). The HiPIMS deposition of metals was carried out in an AJA-vacuum system. The sputtering chamber was evacuated to 10 -5 Pa by a turbo-molecular pump. The HiPIMS short pulses avoid a glow-to-arc transition during plasma particle deposition. The sample holder A c c e p t e d m a n u s c r i p t was rotating at a speed of 18 rpm. The HiPIMS was operated at a frequency of 100 Hz with a duty cycle of 1%. The magnetic field caused by the magnets behind the Fe-target in the magnetron sputtering (HiPIMS) setting cannot go out due to its para-magnetization. [START_REF] Rtimi | Bactericide effects of transparent polyethylene photocatalytic films coated by oxides under visible light[END_REF] This hinders the formation of the plasma and thus inhibit the Fe-deposition. In order to fix this problem, the target was machined to let the magnetic field pass through the target. This allows forcing the electrons to follow the normal hopping trajectory along the target as previously reported. [START_REF] Rtimi | Bactericide effects of transparent polyethylene photocatalytic films coated by oxides under visible light[END_REF] Different FeOx/PES catalysts were synthesized corresponding to the % O2 in the sputtering chamber as 0, 3, 5 and 10 % and are called FeOx0, FeOx3, FeOx5 and FeOx10 respectively.

The polyester (PES) used corresponds to the EMPA test cloth sample No 407. It is a polyester Dacron, type 54 spun, plain weave ISO 105-F04 used for color fastness determinations. The thickness of the FeOx sputtered layers was determined a profilometer (Alphastep500-TENCOR, error: ± 10%). FeOx was sputtered on silica wafers up to 5 minutes in the same conditions as the sputtering on PES fabrics. They were sputtered on 2 × 2 cm size of PES.

Characterizations of FeOx-PES catalysts

The FeOx loading was determined by XRF (PANalytical PW2400 spectrometer). The surface atomic percentages of Fe and O were then determined with XPS analysis using an AXIS NOVA photoelectron spectrometer (Kratos Analytical, Manchester, UK) equipped with monochromatic AlKα (hν = 1486.6 eV) anode. The proportions of each elements of FeOx-PES were determined from peak-areas using known sensitivity factors. [START_REF] Shirley | High-Resolution X-Ray Photoemission Spectrum of the Valence Bands of Gold[END_REF] The spectral absorption of the deposited FeOx on PES has been carried out using a diffuse reflectance spectroscopy (DRS) in a Perkin Elmer Lambda 900 UV-VIS-NIR spectrometer using bare PES as a standard for baseline. The device is provided for with a PELA-1000 in the A c c e p t e d m a n u s c r i p t wavelength range of 200-800 nm. The scan resolution was fixed to 2 nm steps. The oxides supported on PES with 2 × 2 cm size, folded in a few layers, were placed in the working window of the attachment with diffuse reflection. Owing to the large scattering contribution to the reflectance spectra, the rough UV-vis reflectance data cannot be used directly to assess the absorption coefficient of the sputtered samples. [START_REF] Rtimi | Supported TiO2 films deposited at different energies: Implications of the surface compactness on the catalytic kinetics[END_REF] The absorption of the samples was plotted in Kubelka-Munk (KM) arbitrary units versus wavelength.

The sputtered FeOx thin films were imaged using FEI Osiris transmission electron microscope (TEM), operated at 200 kV, with spot size of 5, dwell time 50 µs and real time 600 s. Before imaging, the fibers were embedded in epoxy polymer then cut with ultramicrotome into thin layers with thickness of ~ 80 nm. These layers were placed on carbon grids then images were acquired.

Removal experiments and analytical methods

A recirculation glass reactor system, described in Fig. S1 (See Electronic supplementary information, †), was used to investigate the removal performance of supported FeOx under visible light irradiation. A peristaltic pump (Easy-Load Masterflex Head XX80 ELO 05) was used to circulate the solution into the photoreactor. A light source was a flexible visible light LED strip containing white 10 cold-LEDs. The distance between the LED lamps was fixed at 8 cm from the solution. The LED lamps emit white light at 455 nm and further broadband Stokes-shift light emitted at roughly 500-600 nm. The emission spectrum of this white LED lamp was previously reported in Gao et al. (2016). [START_REF] Gao | Insights into the mechanism of heterogeneous activation of persulfate with a clay/iron-based catalyst under visible LED light irradiation[END_REF] A digital lux meter was used to measure the average light intensity of LED lamps (0.5 mW/cm 2 ). The photo-reactor was covered by aluminum foil to prevent the penetration of natural light. All photocatalytic experiments were A c c e p t e d m a n u s c r i p t performed at ambient temperature (20 ± 2°C) and the pH was adjusted to 7.0 ± 0.2 using 0.1 M HCl or 0.1 M NaOH solutions. 200 mL of 5 µM of FQs (FLU and CIP) solutions are injected at a constant flow rate (325 mL min -1 ). At each time interval, 1.5 mL of solution was collected to determine the concentration of each pollutant by high performance liquid chromatography (HPLC). An Alliance UV controller high performance liquid chromatography (HPLC) system equipped with an a uto-sampler (Waters 717 plus), a C18 column (250 mm×4.6 mm i.d., 5 μm) and a UV detector (246 nm for FLU, Alliance UV 2489) was used. The mobile phase was a mixture of water/acetonitrile (55:45 v/v for FLU and 85:15 v/v for CIP) containing 0.1% of formic acid. The flow rate of the mobile phase was set at 1 and 0.5 mL min -1 in an isocratic mode for FLU and CIP, respectively.

Mineralization in hospital wastewater (or removal of total organic carbon) was examined with a TOC-meter (Shimadzu TOC-VCSH). The iron leaching concentration during reaction was measured using 1,10-phenanthroline method. All experiments were conducted in triplicates and showed a good reproducibility within 5% of average standard deviation.

• Results and discussion

• Visible light-assisted oxidation using supported FeOx samples

The catalytic activity of FeOx/PES prepared with different O2 content in the sputtering chamber was investigated at neutral pH under visible light (Figure 1). Assuming that the visible light promoted oxidation generates reactive species leading to the degradation of the target compound, and the concentration of these species are constant over the reaction time, removal kinetics can be described according to the pseudo-first-order equation (Eq (1)):

(1)

A c c e p t e d m a n u s c r i p t

Where kapp, the pseudo-first-order apparent rate constant (h -1 ), is obtained by linear regression of ln (Ct/Co) versus time t.

It is worth noting that the oxidation kinetics on the FeOx3 cannot be accurately described by simple equations that include classical exponential functions (e.g., pseudo-first order model).

Instead, we calculated an initial rate constant over the first stage of reaction ( i.e., 10 h) by plotting a linear regression of -ln(Ct/C0) versus time. This behavior particularly observed for the most reactive system (i.e. FeOx3) can be ascribed to the complexity of involved reactions including accumulation and competition of reaction products and/or a gradual change of the reactivity of surface sites. For this reason, only a solid line used as a visual guide is shown in Figure 1.

Control tests showed that removal of FLU by adsorption onto FeOx/PES material is negligible. No significant FLU removal was observed with FeOx0 (no oxygen added during the sputtering of Fe on PES). However, the preparation of FeOx with a low oxygen content (i.e. 3% O2, FeOx3) during the sputtering led to higher kapp, 0.21 h -1 and 97% of FLU removal.

When the oxygen content exceeded 3%, the FLU kinetic removal dropped down to 0.008 h -1 and 0.004 h -1 for FeOx5 and FeOx10 samples, respectively. This discrepancy in catalytic activity is probably due to difference in type and amount of iron oxides generated on PES surface during the deposition phase. A qualitative analysis of DRS UV-Vis spectral suggested that the lower oxygen content allowed more visible light absorption in FeOx samples (Figure 2). The band-gaps determination of the sputtered layers in FeOx3 was found to be between 1.9 and 2.2 eV with an absorption edge maximum at around 450 nm (See Figure 2 for FeOx3), thereby suggesting a potential photo-activity in the visible range of light. [START_REF] Strens | Diffuse reflectance spectra and optical properties of some iron and titanium oxides and oxyhydroxides[END_REF] Due to the low FeOx loading (0.1 ± 0.007 wt.% PES determined by XRF) and presence of different secondary iron corrosion products of elemental Fe, a quantitative Even at 0% O2 (i.e. O2/Ar ratio of zero), surface oxidation occurs which can be attributed to the existence of water vapor in the sputtering chamber at the operating conditions, as previously reported. [START_REF] Rtimi | Design, testing and characterization of innovative TiN-TiO 2 surfaces inactivating bacteria under low intensity visible light[END_REF] The great activity of the FeOx3 could also be attributed to the homogeneous distribution of Fe/FeOx-nanoparticles on the polyester with no apparent cracks (Figure 3a-c). A layer of ~35 nm thick can be estimated, which is in accordance with the thickness determined by profilometry of 32-42 nm (Figure 3d).

Radical species in the FeOx 3 /PMS/Visible light system

To test whether other oxidation systems and/or combined processes exhibit high performance of FLU removal as observed for the FeOx3/PMS/visible light, removal kinetics were performed with each system separately using the most active FeOx sample (i.e. FeOx3) (Figure 4). As previously reported in literature, [START_REF] Li | Peroxymonosulfate activation for efficient sulfamethoxazole degradation by Fe3O4/β-FeOOH nanocomposites: Coexistence of radical and non-radical reactions[END_REF] visible light cannot activate PMS, while Feoxides can activate PMS for contaminant degradation (kapp = 0.018 h -1 and 55 % removal).

FeOx3 showed 28% of FLU removal under visible light irradiation, indicating a photocatalytic activity of the supported/sputtered material. Only the combination of PMS, visible light and FeOx3 led to complete FLU removal. The addition of other type of oxidants has been also tested using two common oxidants (i.e., PS and H2O2) (Fig. S2,†). While H2O2 is completely inefficient, PS exhibits lower efficiency for FLU removal than PMS.

To determine the involved species in the FeOx3/PMS/visible light system, formation of radical species such as SO4 •-and • OH was investigated by assessing the effects of 2-propanol A c c e p t e d m a n u s c r i p t and tert-butyl alcohol, because of their different selectivity (i.e., second-order rate constants) with hydroxyl and sulfate radicals [START_REF] Wu | Sulfate Radical Photogeneration Using Fe-EDDS: Influence of Critical Parameters and Naturally Occurring Scavengers[END_REF][START_REF] Rodríguez | Determination of main species involved in the first steps of TiO2 photocatalytic degradation of organics with the use of scavengers: The case of ofloxacin[END_REF][START_REF] Kamagate | Activation of persulfate by irradiated laterite for removal of fluoroquinolones in multi-component systems[END_REF] . Iso-propanol reacts with both OH and SO4 ( = 1.9×10 9 M 1 s 1 31 and = 4-7.4×10 7 M 1 s 1 32 ), while t-butanol can be considered to be more selective toward OH ( = 6.0×10 8 M -1 s -1 31 ) than SO4 •-( = 4-8.4×10 5 M -1 s -1 33 ). The percentage of the hydroxyl radical ( • OH) and sulfate radical (SO4 •-) reacted with FLU and scavenger can be estimated using the bimolecular rate constants and concentration of each species.

According to our calculations (Table S2, †), t-Butanol (5 mM) is selective for OH since it will react with more than 98 % of hydroxyl radical. Isopropanol has been used at two high concentrations (i.e. 10 and 20 mM) to ensure effective and total scavenging of both radical species. Addition of 5 mM of t-BuOH resulted in a slight decrease in FLU degradation (Fig. S3, †), suggesting that hydroxyl radical is not the main reactive species generated here. The slight inhibition observed here is likely due to the reactivity of t-BuOH with SO4 •-under our experimental conditions (Table S2, †). Addition of a higher dose of i-PrOH resulted in almost complete inhibition of FLU degradation, confirming the predominance of sulfate radical (Fig.

S3, †).

Taken together, these results suggest that the FLU removal in the FeOx3/PMS/visible light system proceeds via a radical-pathway. Bound FLU reacts with holes (h + ) and PMS with electron, both generated upon irradiation of FeOx3 (band gap = 2.2 eV and with an absorption edge maximum at around 450 nm). In addition, PMS can also be activated by Fe species on the surface of FeOx3 and then produce sulfate radicals. These different reactions are given in the ESI (Text S1).

Effects of mixture and wastewater components on the removal performance

A c c e p t e d m a n u s c r i p t

To examine the removal ability of the FeOx3/PMS/visible light system when target contaminant co-exists with other contaminants, oxidation kinetics were investigated in mixture of FLU and CIP. Higher reactivity of CIP was observed as compared to FLU in single and mixture systems (kapp,CIP = 4.1 h -1 vs kapp, CIP = 3.1 h -1 in single and mixture system, respectively) (Figure 5). While removal kinetics of FLU showed an initial fast-reaction phase following by a slow stage before an almost total removal at 48h of reaction time, the CIP removal kinetic exhibited classical shape, i.e. single-stage leading to faster and total removal of CIP (Figure 5). This is probably due to the strong reactivity of CIP containing cyclopropane and piperazine rings with sulfate radicals, though the second-order rate constants of FLU and CIP with sulfate radicals are quite close (= 1.8×10 9 M -1 s -1 34 ~ = 1.2×10 9 M -1 s -1 , [START_REF] Mahdi-Ahmed | Ciprofloxacin oxidation by UV-C activated peroxymonosulfate in wastewater[END_REF] ). It is reported that the SO4 •-induces the cleavage of the cyclopropane moiety via loss of one or two CH2 units, whereas the presence of piperazine ring containing two amine-N is highly reactive with SO4 •-. [START_REF] Guo | Enhanced degradation of aqueous norfloxacin and enrofloxacin by UV-activated persulfate: Kinetics, pathways and deactivation[END_REF][START_REF] Jiang | Sulfate radical-based oxidation of fluoroquinolone antibiotics: Kinetics, mechanisms and effects of natural water matrices[END_REF] This discrepancy in reactivity and/or degradation mechanism may also explain the observed kinetic behavior of CIP versus FLU, and multistage removal kinetics may arise from the competition of mother compound with accumulated byproducts. As expected, CIP and FLU kinetic rate constants decreased 1.3-and 4.2-times, respectively, in the mixture system (Figure 5b), probably due to the competition effects of compounds towards reactive species. It is worth noting that the removal kinetics of CIP or FLU in mixture system exhibited single-stage shape, with a greater reactivity of CIP close to that observed in single system (Figure 5b). S1, †), they exhibited similar inhibitive effects whatever the target compound, FLU or CIP (Figure 6).

FLU and CIP removal in SWW and RHW systems (compositions listed in

In order to understand inhibitive effects of wastewater components, FLU removal was investigated in presence of various components as those detected in real wastewaters.

Chloride, phosphate, nitrate and sulfate anions are the most inorganic ligands detected in hospital wastewaters, while organic matter and organic ligands (e.g. sucrose and citric acid)

were chosen to emulate the organic loading in wastewater. Natural organic matter and organic compounds exhibited significant to complete inhibitive effect on FLU degradation (Figure 7).

Despite the ability of citric acid to complex iron and promote Fenton reaction, [START_REF] Silva | Degradation of the herbicide tebuthiuron using solar photo-Fenton process and ferric citrate complex at circumneutral pH[END_REF] significant inhibition was observed. This is probably because of the high ligand loading used in these experiments with respect to the FLU concentration (e.g. molar ratio [Citric acid]/[FLU] = 52;

[Sucrose]/[FLU] = 58). Indeed, high concentrations of ligands lead to strong radical scavenging effects, [START_REF] Buxton | Critical Review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅Oin Aqueous Solution[END_REF] thereby offsetting potential enhancing effect from the citrate-iron coordination.

In photo-assisted removal studies, NOM can alter the degradation mechanism through scavenging effects of NOM components and/or light attenuation depending of the total loading. [START_REF] Lado Ribeiro | Impact of water matrix on the removal of micropollutants by advanced oxidation technologies[END_REF] In the present study, LHA is used as a representative organic matter, which possesses a high oxidation state and high aromaticity, and contains oxygenated polycyclic aromatics and carboxylic compounds which have greater affinity to metal oxides. [START_REF] Kerndorff | Sorption of metals on humic acid[END_REF][START_REF] Yang | Interactions of Humic Acid with Nanosized Inorganic Oxides[END_REF][START_REF] Jayalath | Surface Adsorption of Suwannee River Humic Acid on TiO2 Nanoparticles: A Study of pH and Particle Size[END_REF] If the generation of reactive species took place on the FeOx3 surface, binding of LHA may poison surface reactivity and scavenge radical species. However, XPS measurements failed to A c c e p t e d m a n u s c r i p t accurately assess whether and to which extent organic compounds bind to the oxide layer, probably because of strong contribution of the polyester substrate in carbon percentage. On the other hand, since organic anions can react strongly with radical species, as for instance the reaction of sucrose with hydroxyl radicals, = 2.3 × 10 9 M -1 s -1 , 31 the strong inhibition observed here is likely due to radical scavenging effects.

The inorganic compounds (i.e., phosphate, nitrate, chloride and sulfate) can react with the sulfate radical, and thus generate novel reactive species with lower or higher reactivity than the sulfate radicals towards target compounds. However, chloride ions exhibited lesser inhibitive effect than phosphate or nitrate, despite its higher reaction constant rate with sulfate radicals ( = 1.2 × 10 6 M -1 s -1 ; 32 =2.1 × 10 6 M -1 s -1 ; 43 =3.0 × 10 8 M -1 s -1 [START_REF] Buxton | Critical Review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅Oin Aqueous Solution[END_REF][START_REF] Yang | Comparison of Halide Impacts on the Efficiency of Contaminant Degradation by Sulfate and Hydroxyl Radical-Based Advanced Oxidation Processes (AOPs)[END_REF] ). This could be explained if the reaction of chloride ions with sulfate radicals generates other reactive species, which can react effectively with target compound, and thus counterweight the scavenging effect. Previous work showed that increasing in chloride concentration up to 10 mM enhanced CIP degradation in UV-activated PMS system, due to the formation of chlorine active species. [START_REF] Ao | Medium pressure UVactivated peroxymonosulfate for ciprofloxacin degradation: Kinetics, mechanism, and genotoxicity[END_REF] Indeed, PMS can react with Cl -to form HOCl and Cl2, which exhibit great selectivity towards compounds containing electron-rich organic moieties. [START_REF] Sichel | Feasibility studies: UV/chlorine advanced oxidation treatment for the removal of emerging contaminants[END_REF]47 In addition, Cl - may convert SO4 •-into HO • radicals, as previously reported. 48 Indeed, fast reaction of SO4 •- with Cl -yields chlorine atoms (Cl • ) as primary products, which in turn initiates a cascade of subsequent reactions depending on pH. At neutral pH as in the present study, Cl • mainly reacts with water yielding HO • radicals. 48 It is worth noting that the molar ratio of inorganic ligands to the target compound is so high (e.g. around 300 for phosphate and sulfate) that scavenging or inhibitive effects are likely expected in these experiments.

As an attempt to check whether the oxidant dose can be considered as a limiting factor in the degradation of FLU in RHW, the concentration of PMS was increased from 0.5 mM to 2, 3

A c c e p t e d m a n u s c r i p t and 5 mM (Figure 8). The kinetic constant increased from 0 to 0.010 h -1 , 0.058 h -1 and 0.632 h -1 with increasing PMS dose from 0 to 5 mM. Complete removal of FLU was observed with 3 and 5 mM, suggesting that increase in PMS concentration would generate sufficient sulfate radicals to achieve FLU removal, even in real wastewater. Furthermore, increasing in PMS concentration form 3 to 5 mM enhanced the mineralization extent from 25% to 56 %, respectively.

The reusability of FeOx3/PES was then investigated in RHW over five successive runs, with 3 mM of PMS concentration and at pH 7.0 ± 0.2 (Figure 9). The kinetic rate constants were then determined for each run, as displayed in Fig. S4, †. While degradation performance is not significantly affected (83% of FLU removal is still observed after 5 cycles), a slight decrease in kinetic rate constant was observed. This could be probably due to the oxidation of FeOx surfaces over oxidation cycles and/or presence of organic and inorganic compounds on the surface (e.g. organic matter, phosphate, etc.). The Fe/O atomic ratio of FeOx3 determined by XPS decreased to 0.72, thereby suggesting oxidation of the nano-oxide layer coating PES.

However, the very low iron leaching during oxidation cycles (< 0.02 µM) suggests a great chemical stability of the FeOx3-PES system.

• Conclusion

The PMS/FeOx3 can be effectively used for flumequine and ciprofloxacin removal in real wastewaters under low intensity visible light. Using the HiPIMS method, the O2/Ar ratio is a key to synthesize a good promoter for PMS activation. The higher degradation rate constant of CIP relative to those of FLU could be explained by the high reactivity of SO 4 •- radical with cyclopropane ring. Kinetic rate constants were found lower in binary systems

  ; > 98% chemical reagent) and CIP (C17H18FN3O3; > 98%), PS (Na2S2O8), PMS [available as Oxone (KHSO5 • 0.5KHSO4 • 0.5K2SO4)], isopropanol (i-PrOH, C3H8O)

A

  c c e p t e d m a n u s c r i p t determination of the composition of each thin film cannot be obtained. Nevertheless, the Fe/O atomic ratio of FeOx3 determined by XPS, after subtracting possible contribution of the polyester substrate in O atomic percentage, is close to 1 which is in line with a Fe-oxide such as wüstite (FeO).

A c c e p t e d m a n u s c r i p t with respect to

  those of individual compounds. Moreover, natural organic matter, phosphates and sulfate can considerably inhibit the fluoroquinolone removal in wastewaters, while nitrates and chloride ions exhibited lesser inhibitive effect. In addition, binding of ligands such as phosphates and organic ligands to the oxide surface may alter surface reactivity and thus reduce interactions with contaminants and/or PMS. The sulfate radicals (SO 4 •-) can be trapped by organic and inorganic ligands found at relatively high loading in wastewater compared to the target contaminant. However, increase in PMS concentration up to 3 mM can generate more radical species and then enhance the removal of target compound, even in real hospital wastewaters. The five successive oxidation runs and the low iron leaching indicated a good stability of catalytic activity of the FeOx3-PES system. The results have important implications for cost-effective removal of FQs under visible light irradiation and thus wastewater treatment technologies. 47 E. A. Serna-Galvis, S. D. Jojoa-Sierra, K. E. Berrio-Perlaza, F. Ferraro and R. A. Torres-Palma, Structure-reactivity relationship in the degradation of three representative fluoroquinolone antibiotics in water by electrogenerated active chlorine, Chemical Engineering Journal, 2017, 315, 552-561. 48 H. V. Lutze, N. Kerlin and T. C. Schmidt, Sulfate radical-based water treatment in presence of chloride: Formation of chlorate, inter-conversion of sulfate radicals into hydroxyl radicals and influence of bicarbonate, Water Research, 2015, 72, 349-360.

Figure 1 .

 1 Figure 1. Removal of FLU with different FeOx, synthetized under different O2 level

A c c e p t e d m a n u s c r i p tFigure 2 .

 2 Figure 2. Diffuse reflectance spectroscopy (DRS) of FeOx sputtered samples under different

A c c e p t e d m a n u s c r i p t

  Figure 3a-c. Transmission Electron Microscopy (TEM) analysis of the HiPIMS sputtered

A c c e p t e d m a n u s c r i p t

Figure 4 .

 4 Figure 4. Comparison of different processes for FLU removal. Experimental conditions:

A c c e p t e d m a n u s c r i p tFigure 5 .

 5 Figure 5. Removal kinetics of FLU and CIP in (a) single and (b) mixture system.

A c c e p t e d m a n u s c r i p tFigure 6 .

 6 Figure 6. Effect of water matrix on (a) FLU and (b) CIP removal in single systems.

A c c e p t e d m a n u s c r i p tFigure 7 .

 7 Figure 7. Effect of organic compounds (a) and inorganic anions (b) on FLU removal in UPW

A c c e p t e d m a n u s c r i p tFigure 8 .

 8 Figure 8. Effect of PMS concentration on FLU removal in RHW using FeOx3-PES. Experimental conditions: [FLU] 0 = 5µM, [FeOx3] = 0.26 g m -2 , pH0 = 7.0 ± 0.2, visible reaction time = 48 h, V = 200 mL, recirculation flow rate = 325 mL min -1 . Abbreviations: FLU = flumequine, PMS = peroxymonosulfate, RHW = Real Hospital Wastewater, FeOx3 corresponding to 3% O2 in the sputtering chamber.

A c c e p t e d m a n u s c r i p tFigure 9 .

 9 Figure 9. Removal kinetics of FLU in RHW over five successive runs. Experimental conditions: [FLU] 0 = 5 µM, [PMS] 0 = 0.5 mM, [FeOx3] = 0.26 g m -2 on PES, reaction time =

A c c e p t e d m a n u s c r i p t

Table S1 ,

 S1 †) were complete inhibition of FLU degradation in both systems, and a dramatic decrease of CIP oxidation in SWW and RHW (kapp, CIP = 0.042 h -1 vs kapp, CIP = 0.048 h -1 in SWW and RHW, respectively). Though the synthetic and real wastewaters have contrasting chemical composition and significant difference in pH value (Table

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Conflicts of interest

There are no conflicts to declare.