Régis Guégan
email: regis.guegan@univ-orleans.fr

Tiago De Oliveira

Julien Le Gleuher

Yoshiyuki Sugahara

Tuning down the environmental interests of organoclays for emerging pollutants: Pharmaceuticals in presence of electrolytes

The impact of electrolytes on the adsorption of emerging pollutants: pharmaceuticals onto layered materials: a raw clay mineral and its nonionic and cationic organoclay derivatives was studied. The selected pharmaceuticals: amoxicillin, norfloxacin, sulfamethoxazole, metoprolol, carbamazepine, and trimethoprim show different electric charges: zwitterionic, anionic, cationic and neutral and hydrophobic character (different LogP). Without any salts, the set of complementary data obtained by UV and infrared spectroscopies, X-ray diffraction points out the importance of the electric charge which represents a key parameter in both the spontaneity and feasibility of the adsorption. In contrast, the hydrophobicity of the analytes plays a minor role but determines the magnitude of the adsorbed amount of pharmaceuticals onto organoclays. With a dual hydrophilic and hydrophobic behavior, nonionic organoclay appears to be the most polyvalent material for the removal of the pharmaceuticals. In the presence of electrolytes (NaCl at a concentration of 1 x 10 -2 mol L -1 ), both nonionic and cationic organoclays show a decrease of their efficiencies, whereas the adsorption is particularly enhanced for Na-Mt except for the cationic species (trimethoprim and metoprolol). Thus, in realistic experimental conditions close to those of natural effluents, raw clay mineral appears as the most appropriate sorbent for the studied pharmaceuticals while it raises the question of the usefulness of organoclays in water remediation strategy.

Introduction

The chemical modification of swelling-type clay minerals, by using surfactants of different nature: cationic, nonionic, zwitterionic to get organoclays, enhances the adsorption efficiency but also extents the range of adsorbed organic molecules [START_REF] Stockmeyer | Adsorption of organic compounds on organophilic bentonites[END_REF][START_REF] Stapleton | Sorption of Pentachlorophenol to HDTMA-Clay as a Function of Ionic Strength and pH[END_REF][START_REF] Liu | Adsorption/Desorption in a System Consisting of Humic Acid, Heavy Metals, and Clay Minerals[END_REF][START_REF] El-Nahhal | Adsorption of phenanthrene on organoclays from distilled and saline water[END_REF][START_REF] Groisman | Sorption of organic compounds of varying hydrophobicities from water and industrial wastewater by long-and short-chain organoclays[END_REF][START_REF] Shen | Phenol sorption by organoclays having different charge characteristics[END_REF][START_REF] Gao | Adsorption of Sulfonamide Antimicrobial Agents to Clay Minerals[END_REF][START_REF] Polubesova | Water Purification from Organic Pollutants by Optimized Micelle-Clay Systems[END_REF][START_REF] Bekçi | Equilibrium studies for trimethoprim adsorption on montmorillonite KSF[END_REF][START_REF] Deng | Bonding mechanisms and conformation of poly(ethylene oxide)-based surfactants in interlayer of smectite[END_REF][START_REF] Polubesova | Water remediation by micelle-clay system: Case study for tetracycline and sulfonamide antibiotics[END_REF][START_REF] Guégan | ADSORPTION OF A C10E3 NON-IONIC SURFACTANT ON A Ca-SMECTITE[END_REF][START_REF] Guégan | Intercalation of a Nonionic Surfactant (C10E3) Bilayer into a Na-Montmorillonite Clay[END_REF][START_REF] Sarkar | Remediation of hexavalent chromium through adsorption by bentonite based Arquad® 2HT-75 organoclays[END_REF][START_REF] Zhang | Sorption and desorption of carbamazepine from water by smectite clays[END_REF][START_REF] Guégan | Confinement effects on water structure in membrane lyotropic phases[END_REF][START_REF] Lee | Removal of anionic metals by amino-organoclay for water treatment[END_REF], Park et al. 2011[START_REF] Guegan | Self-assembly of a non-ionic surfactant onto a clay mineral for the preparation of hybrid layered materials[END_REF][START_REF] Zha | The removal of amoxicillin from wastewater using organobentonite[END_REF], Guégan et al. 2015[START_REF] Thiebault | Adsorption mechanisms of emerging micropollutants with a clay mineral: Case of tramadol and doxepine pharmaceutical products[END_REF][START_REF] De Oliveira | Coupled Organoclay/Micelle Action for the Adsorption of Diclofenac[END_REF][START_REF] De Oliveira | Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions[END_REF], Guégan et al. 2017[START_REF] De Oliveira | Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment[END_REF]. Thus, numerous studies pointed out the interests of organoclays as adsorbents, going as far as to suggest these materials as perennial and realistic solutions for the remediation of wastewater or as tertiary treatment for drinking water [START_REF] Stockmeyer | Adsorption of organic compounds on organophilic bentonites[END_REF][START_REF] Polubesova | Water Purification from Organic Pollutants by Optimized Micelle-Clay Systems[END_REF][START_REF] Polubesova | Water remediation by micelle-clay system: Case study for tetracycline and sulfonamide antibiotics[END_REF][START_REF] Undabeytia | A clayvesicle system for water purification from organic pollutants[END_REF]). In the latter case, the adsorption displays the main interest to avoid any degradation of the molecules but requires a recycling of the hybrid materials after being in contact with pollutants. The efficient adsorption of diverse organic pollutants: pharmaceuticals, and other phytosanitary products in batch experimental conditions illustrates the interests of cationic organoclays [START_REF] Alther | Using organoclays to enhance carbon filtration[END_REF], Park et al. 2011). Due to their dual hydrophilic-hydrophobic behaviors and possible cation exchange capacity, nonionic organoclays represent polyvalent adsorbents towards many organic products [START_REF] Deng | Intercalation and surface modification of smectite by two non-ionic surfactants[END_REF], Guégan et al. 2015[START_REF] De Oliveira | Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment[END_REF]. The previous batch adsorption experiments were conducted under unrealistic conditions (i.e. use of synthetic water without any organic matter or with only monomolecular matrix), quite distant from those in natural effluents. Indeed, in effluents, several antagonistic effects may occur: competition between molecules and organic matter, electrolytes which may tune down the interests of organoclays as adsorbents.

In a natural context, the presence of electrolytes and their fluctuations of concentration may affect the adsorption/desorption equilibrium lead to a release of adsorbed pollutants onto layered materials playing the role of carrier phases for pollutants. Besides the complexity of the whole interaction that may be involved, the impact of ionic strength on the adsorption of both organic and inorganic species can be considered now as being well established for clay minerals [START_REF] Liu | Adsorption/Desorption in a System Consisting of Humic Acid, Heavy Metals, and Clay Minerals[END_REF][START_REF] Gao | Adsorption of Sulfonamide Antimicrobial Agents to Clay Minerals[END_REF][START_REF] Wang | Influence of pH, soil humic/fulvic acid, ionic strength, foreign ions and addition sequences on adsorption of Pb(II) onto GMZ bentonite[END_REF]): Electrolytes can act as a screening effect which limits the transfer of the analytes, or enhances the adsorption through ionic bridges. If the effects of the ionic strength for clay minerals are relatively well understood, interestingly, research works focusing on organoclays and organic pollutants including pharmaceuticals appear scarce [START_REF] Stapleton | Sorption of Pentachlorophenol to HDTMA-Clay as a Function of Ionic Strength and pH[END_REF][START_REF] El-Nahhal | Adsorption of phenanthrene on organoclays from distilled and saline water[END_REF][START_REF] Anirudhan | Adsorptive removal of tannin from aqueous solutions by cationic surfactant-modified bentonite clay[END_REF].

Pharmaceutical products are frequently found in large quantities in numerous effluents, with compounds identified as persistent in the natural environment due to their molecular complexity but also possible associations with mineral phases that may preserve them. These molecules of relatively moderate molecular masses show various degrees of freedom and complex molecular behaviors as diverse as their therapeutic actions with hydrophobic features and acid-base properties that modulate their electrical charge with pH.

Their presence in the natural environment at concentrations reaching several nanograms is recognized to cause adverse effects on many ecosystems and represents a public health matter involving the interests of numerous scientists focusing on the development of novel adsorbents [START_REF] Adriano | Adsorption of amoxicillin on chitosan beads: Kinetics, equilibrium and validation of finite bath models[END_REF][START_REF] Bekçi | Equilibrium studies for trimethoprim adsorption on montmorillonite KSF[END_REF][START_REF] Kim | Adsorption characteristics of antibiotics trimethoprim on powdered and granular activated carbon[END_REF][START_REF] Liu | Sorption of norfloxacin by lotus stalk-based activated carbon and iron-doped activated alumina: Mechanisms, isotherms and kinetics[END_REF][START_REF] Moussavi | Preparation, characterization and adsorption potential of the NH4Cl-induced activated carbon for the removal of amoxicillin antibiotic from water[END_REF][START_REF] Kodešová | Pharmaceuticals' sorptions relative to properties of thirteen different soils[END_REF][START_REF] De Oliveira | Coupled Organoclay/Micelle Action for the Adsorption of Diclofenac[END_REF][START_REF] Nielsen | Analysis of the competitive adsorption of pharmaceuticals on waste derived materials[END_REF][START_REF] De Oliveira | Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions[END_REF][START_REF] Limousy | Amoxicillin removal from aqueous solution using activated carbon prepared by chemical activation of olive stone[END_REF].

The objective of this study concerns the understanding about the adsorption and possible desorption of diverse pharmaceuticals onto cationic and nonionic organoclays in the presence of electrolytes that mimic the experimental conditions of the natural context. Thus, this research work represents a rupture to the previous studies aiming at characterizing the adsorption of pharmaceuticals onto organoclays in batch situation with synthetic waters where only thermal or kinetic parameters were investigated. To understand the impact of the ionic strength, six pharmaceutical products (PPs) with different features: electric charges (cationic, zwitterionic, nonionic, anionic or neutral products), hydrophobic character with LogP ranging from -1.03 to 2.45, were adsorbed onto both nonionic and cationic organoclays. The effectiveness of adsorption of PPs onto organoclays was compared to: a sodium exchanged montmorillonite (from Wyoming) via a multi-technique approach including X-ray diffraction, infrared and UV-Visible spectroscopies, providing important insights in the different interactional mechanisms and their evolutions in the presence of electrolytes.

Materials and techniques

Materials

The montmorillonite (Mt) used in that study was obtained from the Source Clay Minerals Repository, University of Missouri (Columbia, MO). This clay mineral (from Wyoming) was used as a starting material for organoclay preparation but also as a referenced adsorbent. The structural formula can be expressed as: (Ca 0.12 Na 0.32 K 0.05 )[Al 3.01 Fe(III) 0.41 Mn 0.01 Mg 0.54 Ti 0.02 ]-[Si 7,98 Al 0.02 ]O 20 (OH) 4 . Mt was fractioned below 2 µm by gravity sedimentation. Then, the resulting clay mineral was purified and sodium (Na + ) exchanged. This montmorillonite (Na-Mt) exhibits a cation exchange capacity (CEC) of 93 meq per 100 g clay.

Polyoxyethylene (20) oleyl ether (Brij ® -O20) and Benzyldimethyltetradecylammonium (BDTA) chemicals were supplied from Sigma Aldrich Chemical company. These two chemicals: Brij and BDTA are nonionic and cationic surfactants respectively. Aqueous solutions of surfactants with Millipore deionized water were prepared at a concentration of 1 time the CEC of Mt clay for BDTA, and at about 1.13 x 10 -3 mol.L -1 for Brij-O-20. Then, these surfactant solutions were mixed to Mt aqueous dispersions before being stirred at 300 rpm for 24 h. At the end of this procedure, the solutions were centrifuged at 3000 rpm for 20 min and the supernatants were removed and the solid fractions (organoclays) were recovered.

The resulting organoclays were dried at 100°C for 24 h before using them as adsorbents or prior any analyses.

Experimental techniques

The concentration of the six pharmaceutical compounds before and after being in contact with the layered adsorbents: raw clay mineral and organoclays was obtained by UV-Visible analysis using an Evolution 220 spectrophotometer (Thermo Scientific). Fourier transform infrared (FTIR) measurements in the range 650-4000 cm -1 , were recorded using a Thermo Nicolet 6700 FT spectrometer equipped with a Deuterated Triglycine Sulfate (DTGS) detector and a Nicolet Continuum microscope. The powder samples were spread over a NaCl window of the microscope. The analyzed sample area was a square of side 100 µm chosen under the microscope 15X Infinity Reflechromat objective. The analyses were performed in transmission mode and each spectrum corresponded to the average of 256 scans collected at 2 cm -1 resolution. The d 001 spacing's of the layered materials before and after being in contact with the antibiotics were determined by the first 00l reflection from the X-rays patterns which were recorded in a conventional θ-θ Bragg-Brentano configuration by using a Thermo Electron ARL'XTRA diffractometer equipped with a Cu anode (CuK α = 1.5418 Å) coupled with a Si(Li) solid detector. The diffractograms on dry samples (100°C for 24 h) were performed between 1 and 24° (2θ) with an angular and time steps of 0.04° and 10 s, respectively. mineral and its nonionic and cationic organoclays derivatives using at least 10 initial aqueous solutions ranging from 10 mg L -1 up to 4 g L -1 (for AMX, or below the possible maximum concentration according to the solubility of each pharmaceutical compound).

Adsorption of PPs

AMX displays a LogP of about 0.87 and 2 pK a couples of 3.23 and 7.43 while NFX show a LogP of -1.03 and owns 2 pK a of 5.77 and 8.68 (for strongest acidic and basic form), leading to cationic-zwitterionic-anionic behavior respectively along the pH range 0-14 (Table 1). In contrast, SMX with a LogP of 0.89 (solubility in water about 610 mg L -1 at 37°C) shows a pK a couple of 6.16 and 1.97 for strongest acidic and basic form respectively, driving to a cationic-neutral-anionic sequence following the pH. TRI shows a LogP of 1.28 and has a water solubility of 400 mg L -1 (at 25°C) and exhibits a cationic to neutral behavior (pK a =7.16). With a similar water solubility of about 400 mg L -1 , MTP displays the same acid base behavior with a cationic to neutral sequence (pK a =9.67) and shows a LogP of 1.88.

Finally, CBZ has the largest LogP value at about 2.45 among the selected PPs in this study and is neutral (or nonionic hydrophobic compound) on the whole pH range with a poor solubility in water of about 18 mg L -1 . At a pH value close to that of effluents (pH=6.5 of a study), AMX and NFX are mainly zwitterionic, with a predominance of about 90 and 80%

and anionic (10%) and cationic (20%) respectively (checked by chromatography analyses and consolidated by some literature data). SMX shows a neutral-anionic behavior with a ratio of 30/70%. TRI is essentially in its cationic form with a frequency of 80% (20% other species are in neutral forms) while only MTP cations are present (Table 1).

The solid to liquid ratio was identical with 100 mg of sorbents used for 50 mL of PPs aqueous solutions in centrifuge tubes. Samples were shaken on a rotary shaker at 50 rpm during 24 h in order to reach the equilibrium and then centrifuged at 5000 rpm for 25 min. Both supernatants and sorbents after contact with the PPs were removed and analyzed through UV-Visible spectroscopy. The effect of the ionic strength was achieved by the addition of NaCl salts at a concentration of 1.0 x 10 -2 mol L -1 . The amount of adsorbed PPs was calculated by the difference between the initial and equilibrium final concentrations that allowed us to determine the equilibrium adsorption isotherms. Prior XRD and FTIR characterizations, the entire resulting organoclays and Mt after adsorption of PPs were dried at 100°C for 48 h. No release of organic compounds was observed based on prior thermal gravimetry analyses (i.e. organic compounds have large molecular masses with poor volatility and are usually degraded in the temperature range 250-350°C).

Results and discussion

Organoclay Characteristics

The whole layered materials: BDTA-Mt, Brij 0. Since the adsorption properties of the organoclays mainly depend on the kind of surfactants used, two different surfactants of different nature (nonionic and cationic) and saturated and unsaturated were used. Thus, the prepared materials display complementary properties: from cation exchange capacity, and hydrophilicity for untreated Na-Mt, dual hydrophilicity/phobicity for Brij 0.4 -Mt; to hydrophobicity or organophilicity and even possible anion adsorption ability for BDTA-Mt [START_REF] Guégan | Nonionic organoclay: A 'Swiss Army knife' for the adsorption of organic micro-pollutants?[END_REF][START_REF] De Oliveira | Coupled Organoclay/Micelle Action for the Adsorption of Diclofenac[END_REF][START_REF] De Oliveira | Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions[END_REF][START_REF] De Oliveira | Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment[END_REF]). In addition, the difference

Interaction mechanisms of the PPs onto layered materials without electrolytes

Case of cationic species: Metoprolol and Trimethoprim

The Figure 2 shows the equilibrium adsorption isotherms of the whole pharmaceuticals onto the three sorbents in this study. These isotherms represent the adsorbed amounts of the pharmaceuticals onto the layered materials after being in contact for 24 hours under stirring (batch experiments), as a function of the equilibrium concentration of pharmaceuticals. As expected for cationic compounds that can be ion-exchanged with the inorganic cations located within the interlayer space of untreated or raw swelling clay minerals, the adsorption isotherms onto Na-Mt reveal a Langmuir or L-type line shape, which is well known for adsorption cases (Figure 2) [START_REF] Bekçi | Equilibrium studies for trimethoprim adsorption on montmorillonite KSF[END_REF], Guégan et al. 2015[START_REF] Thiebault | Adsorption mechanisms of emerging micropollutants with a clay mineral: Case of tramadol and doxepine pharmaceutical products[END_REF][START_REF] De Oliveira | Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment[END_REF]. Interestingly similar behavior can be observed onto both nonionic and cationic organoclays, which thus confirms the proper adsorption of the two cationic pharmaceuticals (metoprolol and trimethoprim) on the three adsorbents. Interestingly, with a similar water solubility value as TRI, the adsorption of metoprolol (MTP) displays a different behavior without any notable saturation for both Na-Mt and Brij 0.4 -Mt, whereas it appears rather limited onto BDTA-Mt as it could be expected for cationic species [START_REF] Guégan | Nonionic organoclay: A 'Swiss Army knife' for the adsorption of organic micro-pollutants?[END_REF][START_REF] De Oliveira | Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment[END_REF]). In the latter case, the adsorbed amount reaches a maximum value of about 1.26 x 10 -4 mol g -1 , in contrast to those of 5.08 x 10 -4 and 5.62 x 10 -4 mol g -1 for Brij 0.4 -Mt rand Na-Mt respectively. Similar trends about the small affinity of the PPs with BDTA-Mt are reflected with the fitting parameters derived from both the Langmuir and Freundlich models which are minimum. The Freundlich constant K F represents the volume of water that can be treated per gram of material. By using this parameter to list a material adsorption capacity, it is possible to find a similar degree of affinity of both MTP and TRI with the adsorbents: Brij 0.4 -Mt (K F = 8.35 x 10 -3 Lg -1 ) > Na-Mt (K F = 4.72 x 10 -2 Lg -1 ) > BDTA-Mt (Table 2).

As expected with organic cations proportion of both TRI and MTP, a limited adsorption onto BDTA-Mt is observed. For cationic species, the adsorption is mainly driven by electrostatic interaction through cation exchange with the inorganic cations (Na + ) in the case of Na-Mt and Brij 0.4 -Mt [START_REF] Bekçi | Equilibrium studies for trimethoprim adsorption on montmorillonite KSF[END_REF], Guégan et al. 2015[START_REF] Thiebault | Adsorption mechanisms of emerging micropollutants with a clay mineral: Case of tramadol and doxepine pharmaceutical products[END_REF][START_REF] De Oliveira | Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment[END_REF]. In BDTA-Mt, such cation exchange is no more possible due to the presence of cationic surfactant within the interlayer space. Despite the lack of any electrostatic interaction, the organophilic character of both adsorbent (BDTA-Mt) and the analytes (here MTP and TRI), contributes to a favorable adsorption, as the parameter 1/n comprised between 0.1 and 1 underlines [START_REF] Kodešová | Pharmaceuticals' sorptions relative to properties of thirteen different soils[END_REF]. With 20% of neutral species for TRI, the repulsion forces are reduced by enhancing the transfer of mass of organic species. For both Na-Mt and Brij 0.4 -Mt materials (for which the whole inorganic cations are presumed to be accessible), the main driving force for adsorption involves electrostatic interaction with cation exchanges between Na + and amine moieties of TRI and MTP [START_REF] Bekçi | Equilibrium studies for trimethoprim adsorption on montmorillonite KSF[END_REF]. Additionally, due to the presence of a hydrophobic environment and the versatility of the material with a dual hydrophobic/hydrophilic behavior, Brij 0.4 -Mt offers supplementary adsorption sites leading to an increase of the adsorption of TRI in contrast to Na-Mt, and their intercalation within the interlayer space of the whole layered materials. This intercalation cannot be observed for organoclays where the intercalated surfactants already increased an interlayer space. In contrast, the intercalation with similar amount of adsorbed PPs could be highlighted in Na-Mt, with an extension of the phyllosilicate galleries reaching about 15.5 and 14.7 Å for TRI and MTP respectively, comparatively to that of Na-Mt: 9.6 Å (Figure 3).

Adsorption of zwitterionic species: case of the Amoxicillin and Nofloxacin

Amoxicillin (AMX) shows a great affinity to the whole adsorbents with an adsorption at large amount (5.68 x 10 -3 mol g -1 ) onto the whole layered materials, with a bold affinity of AMX for BDTA-Mt. By using K F (Table 2 and Figure 2n and q max ), the affinity of AMX is as follows: BDTA-Mt > Brij 0.4 -Mt > Na-Mt. The slight excess of BDTA + combined with their hydrophobic character favor the adsorption of AMX with its CO 2 -moieties through electrostatic and hydrophobic interactions [START_REF] Adriano | Adsorption of amoxicillin on chitosan beads: Kinetics, equilibrium and validation of finite bath models[END_REF][START_REF] Putra | Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: Mechanisms, isotherms and kinetics[END_REF][START_REF] Belhachemi | Removal of Amoxicillin Antibiotic from Aqueous Solutions by Date Pits Activated Carbons[END_REF]. In contrast, AMX can be cation exchanged in Na-Mt, leading to its intercalation with an increase of the interlayer spacing to nearly 15 Å in agreement with a molecular size of AMX, driving to an adsorbed amount larger than the value of the CEC (9.29

x 10 -4 mol g -1 ) (Figure 3). This suggests that additional forces such as ion-dipole and even hydrophobic interaction contribute also in the adsorption in a second step but in a lesser extent. Similar mechanisms can be found in Brij 0.4 -Mt with a larger adsorption of PP due to the hydrophobic nature of the organo-layered material.

Norfloxacin (NFX) displays a great affinity to Na-Mt with an adsorbed amount close to the CEC: 8.48 x 10 -4 molg -1 and a K F of 7.80 x 10 -2 L g -1 . Indeed, at a pH=6.5, NFX shows 17% cationic and 83% zwitterionic species, driving to possible substitution of Na + cations in both Na-Mt and Brij 0.4 -Mt. However, in the latter case, the presence of a nonionic surfactant may restrict the proper diffusion and ion-exchange to occur, diminishing in that way the number of accessible Na + to be exchanged. The adsorbed amount of NFX onto Brij 0.4 -Mt at about 4.24 x 10 -4 mol g -1 represents half the value of the CEC, suggesting that 50% of the exchangeable inorganic cations can be mobilized in the adsorption of NFX, and thus leads to a lower K F (in comparison to that of Na-Mt) of 5.66 x 10 -2 L g -1 . With an adsorbed amount of only 2.39 x 10 - 4 molg -1 , the adsorption onto BDTA-Mt appears rather low. This trend is also confirmed with the parameter derived from Freundlich equation. Such low affinity of NFX to a cationic organoclay is nevertheless normal due to (i) the repulsive forces between analyte and BDTA-Mt, (ii) the limitation to perform any ion-exchange and (iii) the hydrophilic nature of NFX (LogP =-1.03). However, as a zwitterionic compound, NFX displays also some negative charges that may be responsible of its adsorption onto BDTA-Mt. Indeed, for organoclays prepared at concentration above 1 CEC with additional , surfactant can be organized in paraffin structure with a wide expansion making it easier the intercalation of organic compounds and even anionic species.

With the observation of additional bands related to those of the pharmaceuticals, FTIR technique confirms proper the adsorption of NFX onto layered materials onto layered materials (Figure 4). Additionally, this technique can give new insights in the moieties of the molecules in interaction with the layered materials as it could be discussed in previous research works [START_REF] Guégan | Nonionic organoclay: A 'Swiss Army knife' for the adsorption of organic micro-pollutants?[END_REF][START_REF] De Oliveira | Coupled Organoclay/Micelle Action for the Adsorption of Diclofenac[END_REF][START_REF] De Oliveira | Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions[END_REF]).

The integrated intensity of the absorption bands characteristics of the NFX in the reduced spectral range between 1270 and 1570 cm -1 related to the modes of elongation of CO of the ester and acid functions allows one to follow the evolution of the adsorption with an analysis onto a solid as it could be possible with adsorption isotherms determined through UV spectroscopy with difference of concentrations in liquid samples. The resulting evolution of the integrated intensities of the vibration bands of NFX shows similar trends as the adsorption isotherms highlighted with a better affinity of NFX to Na-Mt > Brij 0.4 -Mt > BDTA-Mt (Figure 5).

Adsorption of a neutral or nonionic hydrophobic compound: case of the

Carbamazepine CBZ shows a limited solubility in water (18 mg L -1 ) due to its hydrophobic character and may be one of the main reasons about its persistence in numerous effluents. Thus, the adsorbed amount of this pharmaceutical onto the whole layered materials appears quite low, one order of magnitude lower than the other studied PPs in this study. Nevertheless, the resulting adsorption isotherms at the equilibrium point out the affinity of CBZ for the whole adsorbents which is enhanced for BDTA-Mt > Brij 0.4 -Mt and Na-Mt with a maximum adsorbed amount reaching about 2.53 x 10 -5 , 1.18 x 10 -5 and 4.14 x 10 -6 mol g -1 respectively. As expected, the hydrophobic character of CBZ limits the transfer of mass onto Na-Mt while the hydrophobic environment in the organoclays allows its proper adsorption.

Besides being nonionic and hydrophobic compound, CBZ can be weakly ionizable and holds punctual partial electric charge allowing possible physisorption processes that could be responsible for an adsorption [START_REF] Zhang | Sorption and desorption of carbamazepine from water by smectite clays[END_REF][START_REF] Kodešová | Pharmaceuticals' sorptions relative to properties of thirteen different soils[END_REF]. Thus, CBZ may be sorbed onto Na-Mt through possible hydrogen bonds with the surface silanol groups (located in the edges of the phyllosilicate sheets in very small amounts) and for both organoclays with weak molecular hydrophobic interaction in addition with possible π-π interactions in the case of BDTA-Mt explaining the large adsorbed amount in the latter case.

Adsorption of an anionic compound: the sulfamethoxazole

The adsorption of sulfamethoxazole (SMX) is effective for the three materials as the adsorption isotherms revealed with a gradual growth of the adsorbed amount as the concentration is increased without reaching any plateau (Figure 2). The affinity of SMX is particularly enhanced for BDTA-Mt > Brij 0.4 -Mt > Na-Mt as both q m and K F stressed out (Table 2). At a pH of 6.5, SMX is mainly anionic (67%) and neutral (33%). Thus, as expected, the adsorption of this pharmaceutical onto Na-Mt is considerably limited. However, neutral SMX can be totally adsorbed through probable ion-dipole interaction, leading to its intercalation besides its hydrophobic character, as it could be observed by X-ray diffraction data (Figure 3). Indeed, q m reaches 2.56 x 10 -4 mol g -1 onto Na-Mt which matches with a deviation of only 4% of the amount of SMX in its neutral form. However, the existence of negative charge at the surface of Na-Mt associated to weak polarizability of SMX considerably prevents further adsorption due to repulsive effects [START_REF] Gao | Adsorption of Sulfonamide Antimicrobial Agents to Clay Minerals[END_REF].

Indeed, the deprotonated form of sulfamethoxazole significantly decreases the ability of the sulfonamide group of sulfamethoxazole to be able to perform π-π interactions with the πdonor functions of the materials [START_REF] Chen | Functionalization, pH, and ionic strength influenced sorption of sulfamethoxazole on graphene[END_REF]. In Brij 0.4 -Mt, the introduction of surfactant shields these repulsive forces while introducing a hydrophobic environment, leading to an adsorption in a larger proportion than Na-Mt. Thus, neutral SMX can be adsorbed onto the nonionic organoclay through accessible inorganic Na + cations, while the hydrophobic environment due to the presence of surfactant, allows a lager adsorption of the other species. With similar hydrophobic environment combined with a slight excess of BDTA + , SMX is adsorbed in large amount with deprotonated moieties (π-π electron donoracceptor interaction), and also hydrophobic-type molecular interactions [START_REF] Rostamian | A comparative adsorption study of sulfamethoxazole onto graphene and graphene oxide nanosheets through equilibrium, kinetic and thermodynamic modeling[END_REF].

Impact of the ionic strengths on the adsorption of organoclays to PPs

Besides not being the most efficient sorbent, the adsorption efficiency of the layered materials in this study reasonably appears quite suitable for pharmaceuticals. However, depending on the nature of the organic pollutants, their adsorption capacities that can be similar to activated carbons. The experiments were essentially performed in synthetic water without any change of electrolytes. In a natural context, effluents show diverse electrolytes at different concentrations that may significantly perturb the magnitude of the adsorption or lead to a possible desorption. Thus, as described previously, the main driving force for the adsorption of pharmaceuticals results from electrostatic interactions, which are known to be sensitive to any change of the ionic strengths with usually the observation of an increase of the adsorbed amount (Gao andPedersen 2005, Bekçi et al. 2006).

As it was expected, the ionic strength plays on the magnitude of the adsorption of the whole pharmaceuticals. Both line shapes and evolution of the isotherms follow the same trend as before but, except metoprolol the values of the maximum adsorbed amount of pharmaceuticals as well as the parameters derived from the fitting procedure and more particularly K F which appears affected with a change of the experimental conditions (Figure 2 and Table 2). However, both nonionic and cationic organoclays show a decrease of their efficiencies, in contrast to Na-Mt for which the adsorption is particularly enhanced except for the cationic species (TRI and MTP) and thus appears as the most appropriate sorbent for the studied pharmaceuticals in the presence of NaCl at a concentration of 1 x 10 -2 mol L -1 .

For the cationic species (TMP and TRI), the addition of electrolytes reduces the total adsorption capacity of the three materials. For TRI, a decrease in the adsorbed quantities of about 8.4%, 34.2% and 25.1% can be observed whereas for MTP, it reaches a variation of 8.0%, 1.6% and 15.7% for Na-Mt, BDTA-Mt and Brij 0.4 -Mt respectively. By focusing on K F , the same trend is confirmed. As expected for BDTA-Mt, organic cations are poorly adsorbed and can be mainly adsorbed through hydrophobic interaction and it is verified in the case of MTP where the NaCl salts do not affect the adsorbed amount, nor K F . It is interesting to observe how the speciation of the organic compounds plays again on the adsorption. With the presence of an electrolyte, the transfer of nonionic TRI is considerably reduced and explains why the decrease of the adsorbed amount onto BDTA-Mt. Indeed, the presence of Na + cations may shield the sites of adsorption and induces a competition effect which does not favor the sorption of neutral species to cationic organoclay. Moreover, Na + ions are known to perturb electron-acceptor π-π-electron interactions and may explain also the decrease of TRI onto BDTA-Mt. For sorbents where exchange of cations process is possible (i.e. Na-Mt and Brij 0.4 -Mt) Na + ions in solution compete to other organic cations, here the pharmaceuticals and thus limits the adsorption. An intercalation of Na + was confirmed by atomic absorption spectroscopy (not shown) and also observed through X-ray diffraction patterns (Figure 3), with a shift to large 2θ angle values of the 00l reflection where the interlayer space decreases from 15.01 to 14.48 Å and from 14.66 to 14.23 Å for both TRI and MTP respectively after the addition of salts.

With q max amount and K F as main parameters to appreciate the affinity between analytes to sorbents, the presence of NaCl does induce any large change in the sequence of affinity of both AMX and NFX with the layered materials (Figure 2 and Table 2). However, the presence of the electrolytes reduces the transfer of the pharmaceuticals onto organoclays with a decrease of the adsorbed amounts for AMX of about 25% and 27% and for NFX by 49% and 70% for both BDTA-Mt and Brij 0.4 -Mt respectively. In contrast, Na-Mt shows a clear improvement of the adsorption capacities in the presence of NaCl. Indeed, the maximum adsorbed amounts are 2.69 x 10 -3 and 9.91 x 10 -4 molg -1 for AMX and NFX respectively representing an increase of 190% and 17%. The study of the solid phase by FTIR of Na-Mt also brings a confirmation of the improvement of the adsorption in the presence of electrolyte and confirms the general trends observed with the isotherms (Figures 45).

The addition of salts may change the solubility and hydrophobicity of substances in solution that can reduce the adsorption capacity of adsorbents [START_REF] Anirudhan | Adsorptive removal of tannin from aqueous solutions by cationic surfactant-modified bentonite clay[END_REF]Ramachandran 2006, Bui and[START_REF] Bui | Influence of ionic strength, anions, cations, and natural organic matter on the adsorption of pharmaceuticals to silica[END_REF]. A loss of hydrophobicity could indeed penalize the interactions of the similar range of energy involved in the adsorption of pharmaceuticals to organoclays.

Electrolytes in solution may also combine with pharmaceuticals and reduce considerably their diffusion at a surface of the layered materials. The grafting of surfactant onto the surface of the layered materials acting as a brush may prevent a possible diffusion within the interlayer space of the pharmaceuticals or probably the presence of salts aside the organoclays shield the possibility of adsorption of zwitterionic compounds (Figure 6) [START_REF] Vinu | Adsorption of l-histidine over mesoporous carbon molecular sieves[END_REF].

The presence of NaCl that amplifies the polarizability of the molecules via ionic bridges and thus causes a drop-in of the hydrophobicity [START_REF] Anirudhan | Adsorptive removal of tannin from aqueous solutions by cationic surfactant-modified bentonite clay[END_REF] is likely to explain the change of affinity between CBZ and Na-Mt. The addition of salts does affect the main driving force (hydrophobic interaction) for the adsorption of CBZ to organoclays allowing one to obtain similar adsorbed amounts. However, the possibility to interact through ionic bridges to Na-Mt enhances considerably the adsorption capacity showing an ability to adsorb CBZ at even larger extent than organoclays (Figure 2). Similarly, Na-Mt represents the best suitable material for anionic compounds in presence of electrolytes, where the adsorbed amounts show an increase by reaching 170% to reach 7.01 x 10 -4 mol g -1 .The addition of salts must change the state of charge of SMX with the possible formation of ion complexes of which nature is different from the surface properties of organoclays and therefore limit its mass transfer. This combination of sodium ions with the deprotonated groups of the molecules leads to the establishment of repulsive forces in regards to the cationic organoclay and decreases its adsorption capacity. Such ion-molecule complexations may explain an improvement in the adsorption in the opposite case of initially repulsive interactions which can be extended to the results obtained for Na-Mt.

Conclusions

With a study of six pharmaceuticals showing diverse chemical nature (zwitterionic, anionic, cationic and neutrals as well as displaying different hydrophobicity) onto layered materials based on clay minerals with diverse properties (cation exchange, organophilicity, anion adsorption ability) without any electrolytes, electrostatic interactions appear to be the main adsorption mechanisms while hydrophobic parameter plays a second role. However, this latter feature is important since the intercalation of surfactant drives to an organic environment with novel adsorption sites, thus improving the adsorption of pharmaceuticals.

As expected with adsorption mechanisms that bear on electrostatic interactions, the ionic strength strongly affects the adsorption processes of pharmaceuticals with a drastic reduction of the efficiency of both cationic and nonionic organoclays. Such decrease results from (i) a competition effect between salts and the organophilic surface of organoclays to the pharmaceuticals, and (ii) a noticeable change in the properties of the aqueous solution that may decrease the hydrophobic character of organic compounds. In contrast, the improvement of the adsorption properties of Na-Mt in the presence of electrolytes can be explained by electric double layers or Debye model and the screening of the electrostatic repulsions with the introduction counter-ions at a surface of the phyllosilicate sheets. Indeed, with monovalent salts, the Debye screening length is quite reduced and decreases the magnitude of the repulsion relative to the van der Waals attraction. This phenomenon obviously favors the adsorption of organic compounds onto Na-Mt, where ion-dipole interaction through the presence of counter-ions located at the surface of the phyllosilicate sheets. In organoclays, the presence of surfactant already reduces the repulsion forces between the inorganic sheets but generates a hydrophobic environment with the grafting of an organic layer or brush. This combination contributes to the improvement of the adsorption efficiency of organoclays without any electrolytes. However, with salts, their adsorption abilities for pharmaceuticals remain identical or appear considerably reduced. In Na-Mt, salts are located to a surface which lessen the Debye screening length. In contrast, for organoclays the introduced ions remain in solution and may interact with organic compounds, leading to a backward shift of the desorption/adsorption equilibrium. This can go farer since the adsorption of organic compounds to a clay mineral generates step by step a hybrid material, equivalent to organoclays obtained with surfactants, of which efficiency is decreased. Worse, it can drive to the desorption of the adsorbed organic compounds as we could observed (not shown here) and thus raises the question of the usefulness of organoclays in water remediation strategy.

Table 1: Characteristics of the pharmaceutical products used in this study: solubility, pKa, LogP and speciation. LogP corresponds to the value of the hydrophobic character of the compounds (a LogP equals to zero corresponds to a compound with an equilibrated balance between its hydrophobic and hydrophilic moieties, while a Log P negative and positive represents a hydrophilic and hydrophobic compound). The red, green, blue and association of blue and red circles symbolizes the electric charge of the pharmaceuticals at a pH=6.5: positive, neutral, negative and zwitterion respectively.

  ]propan-2-ol, and carbamazepine (CBZ) or 5-Carbamoyl-5Hdibenz(b,f)azepine were purchased from Sigma-Aldrich Chemical, and assumed to have a purity > 98%. These products were used in batch adsorption experiments onto raw clay

  4 -Mt organoclays, and Na-Mt were characterized by both XRD and FTIR (supporting data) analyses. As expected, the proper intercalation of the surfactants within the interlayer space of the starting Na-Mt was confirmed by a shift at low angle values (2θ) of the 00l reflections. With the introduced concentrations (1 time the value of the CEC for the cationic surfactant and a similar amount for the Brij), the expansion of the interlayer space reaches 18.3 Å for both BDTA-Mt and Brij 0.4 -Mt organoclays, corresponding to lateral bilayers organization (Figure1). FTIR spectra confirm such surfactant organization and show typical features characteristics of the organic compounds, such as the absorption bands at 2840-2920 cm -1 relative to the symmetric and antisymmetric CH 2 stretching vibrations of the surfactant alkyl chains, of which frequencies stress out gauche conformation of the molecules[START_REF] Guégan | ADSORPTION OF A C10E3 NON-IONIC SURFACTANT ON A Ca-SMECTITE[END_REF][START_REF] Guégan | Intercalation of a Nonionic Surfactant (C10E3) Bilayer into a Na-Montmorillonite Clay[END_REF][START_REF] Guegan | Self-assembly of a non-ionic surfactant onto a clay mineral for the preparation of hybrid layered materials[END_REF][START_REF] Guegan | Sandwich organization of non-ionic surfactant liquid crystalline phases as induced by large inorganic K4Nb6O17 nanosheets[END_REF]) (supporting data).

Figure 1 :

 1 Figure1: Schematic representation of the whole geo-sorbents used in this study: Na-Mt clay mineral, BDTA-Mt (100% of the compensations cations are substituted toBDTA through cation exchange) and Brij0.4-Mt, a nonionic organoclay (where the inorganic cations are kept within the interlayer space and Brij is intercalated involving ion-dipole interaction) showing lateral bilayers organization. The sorbents used in this study display singular adsorption properties: hydrophobicity/philicity, cation/anion retention which will be highlighted with six pharmaceuticals ofdifferent chemical nature.

Figure 2 :Figure 2a :Figure 2b :Figure 2c :Figure 2d :Figure 2e :Figure 2f :

 22a2b2c2d2e2f Figure 2: Effect of the ionic strength with the addition of NaCl electrolytes (10 -2 M) on the equilibrium adsorption isotherms of a) Amoxicillin (AMX), b) Sulfamethoxazole (SMX), c) Trimethoprim (TRI), d) Metoprolol (MTP), e) Norfloxacin (NFX) and f) Carbamazepine (CBZ) onto untreated Na exchanged montmorillonite: Na-Mt (circle), BDTA-Mt (triangle top) and Brij0. Q e represents the adsorbed amount of pharmaceutical while C e is the equilibrium pharmaceutical concentration. The solid lines represent the fits by using the Langmuir equation model.

Figure 3 :Figure 5 :

 35 Figure 3: 3D evolution of the X-ray diffraction patterns (selected data) of Na-Mt after the adsorption of Trimethoprim (TRI), Sulfamethoxazole (SMX), Amoxicililin (AMX) and Metropolol (MTP) with and without any electrolytes (NaCl at a concentration of 10 -2 M). With an interlayer distance (d 001 spacing) of about 18 Å, and an average molecular size of 5 Å for the pharmaceuticals, no structural changes in the evolution of the organoclays are observed.

Figure 6 :

 6 Figure 6: Schematic representation of the impact of the salts on the adsorption/desorption of the pharmaceuticals onto Na-Mt, Brij 0.4 -Mt, and BDTA-Mt. The presence of electrolytes favors the adsorption with the creation of ionic bridges to Na-Mt while it backwards the adsorption/desorption equilibrium of pharmaceuticals onto both nonionic and cationic organoclays showing a poor efficiency in experimental conditions close to that of effluents.

Table 2 :

 2 Adsorption isotherm constants determined with Langmuir, Freundlich model fits for the adsorption of the whole pharmaceuticals: Amoxicillin (AMX), Sulfamethoxazole (SMX),

	570
	571	Trimethoprim (TRI), Metoprolol (MTP), Norfloxacin (NFX) and Carbamazepine (CBZ) onto
	572 573	untreated Na exchanged montmorillonite: Na-Mt, BDTA-Mt and Brij 0.4 -Mt with and without salts (NaCl at a concentration of 1 mol L -1 ).
	574
	575
		Adsorbant	Analytes		Langmuir			Freundlich
				q max	K L	∆G°	r²	K F	1/n	r²
				(mol.g -1 )	(L.mol -1 )	(kJ.mol -1 )		(L.g -1 )
		Na-Mt	AMX	9.29 x 10 -4	9.73 x 10 1	-11.72	0.988	4.71 x -2	0.94	0.984
			AMX + NaCl	2.69 x 10 -3	9.98 x 10 1	-11.79	0.984	1.60 x -1	0.95	0.966
		BDTA-Mt	AMX	5.68 x 10 -3	1.46 x 10 2	-12.76	0.972	2.07 x -1	0.81	0.983
			AMX + NaCl	4.28 x 10 -3	1.15 x 10 2	-12.15	0.994	1.87 x -1	0.87	0.992
		Brij 0.4 -Mt	AMX	4.44 x 10 -3	1.31 x 10 2	-12.48	0.996	2.04 x -1	0.88	0.997
			AMX + NaCl	3.23 x 10 -3	1.02 x 10 2	-11.85	0.993	1.79 x -1	0.94	0.991
		Na-Mt	SMX	2.56 x 10 -4	4.87 x 10 2	-15.85	0.967	1.24 x -2	0.73	0.964
			SMX + NaCl	7.01 x 10 -4	3.30 x 10 3	-20.75	0.988	3.18 x -2	0.57	0.957
		BDTA-Mt	SMX	9.73 x 10 -4	4.78 x 10 3	-21.69	0.976	4.55 x -2	0.59	0.961
			SMX + NaCl	6.98 x 10 -4	1.63 x 10 3	-18.95	0.958	2.88 x -2	0.58	0.991
		Brij 0.4 -Mt	SMX	6.97 x 10 -4	5.06 x 10 2	-15.95	0.976	2.43 x -2	0.66	0.930
			SMX + NaCl	3.21 x 10 -4	4.90 x 10 2	-15.87	0.989	2.06 x -2	0.77	0.986
		Na-Mt	TRI	3.80 x 10 -4	5.98 x 10 3	-22.27	0.982	3.44 x -3	0.33	0.901
			TRI + NaCl	3.48 x 10 -4	5.15 x 10 3	-21.89	0.998	2.92 x -3	0.33	0.899
		BDTA-Mt	TRI	2.78 x 10 -4	4.46 x 10 3	-21.52	0.922	2.79 x -3	0.36	0.907
			TRI + NaCl	1.83 x 10 -4	6.76 x 10 2	-16.69	0.995	2.47 x -3	0.51	0.999
		Brij 0.4 -Mt	TRI	4.13 x 10 -4	7.59 x 10 4	-28.78	0.928	8.35 x -3	0.40	0.996
			TRI + NaCl	3.61 x 10 -4	5.20 x 10 3	-21.92	0.992	3.15 x -3	0.34	0.997
		Na-Mt	NFX	8.48 x 10 -4	4.54 x 10 3	-21.57	0.984	7.80 x -2	0.62	0.997
			NFX + NaCl	9.91 x 10 -4	4.96 x 10 3	-21.79	0.983	8.96 x -2	0.61	0.988
		BDTA-Mt	NFX	2.39 x 10 -4	9.53 x 10 2	-17.57	0.980	9.74 x -3	0.64	0.975
			NFX + NaCl	1.23 x 10 -4	5.33 x 10 2	-16.08	0.998	2.64 x -3	0.61	0.994
		Brij 0.4 -Mt	NFX	4.24 x 10 -4	4.42 x 10 3	-21.50	0.958	5.66 x -2	0.66	0.977
			NFX + NaCl	1.26 x 10 -4	6.47 x 10 2	-16.58	0.840	6.27 x -3	0.73	0.864
		Na-Mt	CBZ	4.14 x 10 -6	5.63 x 10 4	-28.02	0.873	2.26 x -3	0.65	0.972
			CBZ + NaCl	2.54 x 10 -5	1.80 x 10 5	-30.99	0.976	3.22 x -2	0.66	0.975
		BDTA-Mt	CBZ	2.53 x 10 -5	1.41 x 10 5	-30.38	0.977	2.75 x -3	0.67	0.943
			CBZ + NaCl	2.33 x 10 -5	1.34 x 10 5	-30.24	0.984	2.26 x -2	0.66	0.985

Acknowledgements

The authors would like to thank the Région Centre Val de Loire (Project MONITOPOL2017 -00117247) for their financial support.

(selected data).

Research Highlights

The electric charge of pharmaceuticals (PPs) governs their adsorption Organoclays improve the adsorption of PPs due to their hydrophobic nature Without any salts, organoclays show a certain efficiency in the adsorption of PPs

The adsorption is enhanced onto Na-Mt in presence of an electrolyte

Organoclays appear as poor sorbent materials in presence of salts


Laurent Ottaviani

Stéphane Biondo

Mihai Lazar

Wilfried Vervisch

Julian Duchaine

Frédéric Milesi

Olivier Palais

Dominique Planson

Frank Torregrosa

Influence of P+ layer parameters on 4H-SiC UV PiN photodetector characteristics

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.


A Maudet

G Touya

C Duchêne

S Picault

Improving multi-level interactions modelling in a multi-agent generalisation model: first experiments

Introduction

This paper introduces a beginning PhD study seeking to improve the modelling of multi-level interactions between cartographic objects within a generalisation process. What we call "interaction" between two objects is the fact that the transformation of one object is computed while considering the other one (e.g. a building is displaced away from another one, the new position of a point is computed to solve equations in which other points are involved). Interactions translate the contextual nature of generalisation. Our aim is to overcome remaining issues linked to multi-level interaction not addressed by current approaches in automated generalisation.

The remainder of the paper is structured as follows. Section 2 describes the motivations for this work. Section 3 introduces a recent interactions-oriented multilevel model from the multi-agent literature and its adaptation to generalisation. Section 4 describes first experimentations on a case study. Finally, section 5 concludes and draws some perspectives of further work.

Motivation -identifying unsolved problems

Before exposing the unsolved problems the PhD study focuses on, we analyse some existing approaches using a typology based on the levels of interactions between objects. By level, we mean space into which it is coherent for objects to interact in order to contribute to the generalisation process (e.g. the building of a same block, the roads of a same network). Among existing approaches of automated generalisation, some are based on transversal interactions, i.e. interactions between objects of the same level. For instance, [START_REF] Aslan | An Incremental Displacement Approach Applied to Building Objects in Topographic Mapping[END_REF], or [START_REF] Duchêne | The CartACom model: transforming cartographic features into communicating agents for cartographic generalisation[END_REF] in the CartACom model, solve conflicts between single objects by moving them away from each others. Continuous optimisation approaches express intra-or inter-objects constraints as equations on their points and then base their resolution on interactions between points [START_REF] Højholt | Solving Local and Global Space Conflicts in Map Generalisation Using a Finite Element Method Adapted from Structural Mechanics[END_REF][START_REF] Sarjakoski | Simultaneous Graphic Generalisation of Vector Data Sets[END_REF][START_REF] Sester | Optimization approaches for generalization and data abstraction[END_REF]. Other approaches explicitly model several levels of objects and enable hierarchical interactions. The AGENT model [START_REF] Ruas | Modèle de généralisation de données géographiques à base de contraintes et d'autonomie[END_REF] represents composition relationships between entities called components (e.g. buildings), and groups called meso objects (e.g. urban blocks). A component may be a single entity called micro, or another meso. Such relations are called composition relationships since the meso object is composed of its components. The micro and meso objects are modelled as autonomous agents that apply generalisation algorithms to themselves. Meso agents trigger their components and can impose some transformations to them to solve shared conflicts. The GAEL model [START_REF] Gaffuri | Object-field relationships modelling in an agent-based generalisation model[END_REF] adds the notion of field agents, representing single objects or background objects like the relief, which can dynamically decompose themselves into a set of points (their vertices) and then orchestrate their iterative displacement under constraints. The interactions are hierarchical (field/points) and transversal (e.g. the points trigger each other). With these existing approaches, a generalisation process can use:

-Transversal interactions between points (GAEL, continuous optimisation) or between single objects (CartACom). -Hierarchical interactions between objects linked by a composition relationship (AGENT, GAEL where the composition is from an object to its vertices).

A few attempts have been made to sequentially use both kinds of interactions. In GAEL, the fields activate their points (hierarchical interactions) in response to a transversal interaction, but the issue of "when to switch from the transversal to the field-points interactions?" is not solved. The CollaGen model [START_REF] Touya | CollaGen: Collaboration between automatic cartographic generalisation processes[END_REF] enables to sequentially use several models (and thus several kinds of interactions), but while considering each process as a black box, so that one object is only involved in one interaction scheme at a time.

We consider it is not enough. First, because on top of "composition", which is well represented in the AGENT and GAEL model, "inclusion" is a second kind of hierarchical relationships that drives contextual generalisation, as identified by Mustière and Moulin (2002). Inclusion relationships notably occur when one object acts as "spatial support" for objects of equal or lower dimension that have to stay within it, as defined by [START_REF] Jaara | A model for preserving the consistency between topographic and thematic layers throughout data migration[END_REF], e.g. bus stops or accidents on a road. The issues implied by this kind of relationship cannot be solved in an easy way, like adding the bus-stop, or the accident, to a vertex of the road. Indeed, the position of objects is more dependant on the "semantic" description of the road (e.g. "in a bend", "near a junction") than the geometric one. Second, because in either cases (composition or inclusion), it can be necessary to use more than only hierarchical or only transversal interactions (Figure 1):

-"Diagonal" interactions (between objects at different levels) can be needed, e.g. when a group of two adjacent buildings needs to interact as a whole with a neighbouring road or building (Figure 1a). The word "diagonal" is used, since we consider links between the two buildings and the whole as "vertical" (between objects of different levels with a hierarchical relation), and links between buildings (both aggregated buildings and the others) as "horizontal" (within one level). -An object involved in a hierarchy may need to hierarchically interact with its "parent" but also transversally interact with its pairs, e.g. a bus station should stay on the road when the road's shape is modified, but also remain consistent with other bus stations (Figure 1b). -An object can be involved in more than one hierarchical relationship, e.g. a building can belong to two rows of buildings (Figure 1c) or a bridge is included in both a road and a river (Figure 1d).

Currently, these issues are not solved in a satisfying way. The existing models are used on the portions where they are effective and adjustments are manually done for the resulting conflicts. A satisfying result would be to have a completely automated process that orchestrates the interactions between agents from all levels.

Our hypothesis is that a generic modelling of multi-level interactions should help in addressing these issues in a more comprehensive way. Multi-level modelling has recently been intensively studied in the multi-agents domain. It resulted in several models, among which one, called PADAWAN, seems to have very interesting properties in our context. Therefore, we will try to improve the current AGENT, GAEL and CartACom agent approaches of generalisation with this model. Figure 1. Some cases where the alternative hierarchical OR transversal interactions is not sufficient.

Reusing a multi-agent framework designed for multi-level simulation 3.1 PADAWAN: general presentation

In this section, we present the PADAWAN model [START_REF] Picault | An Interaction-Oriented Model for Multi-Scale Simulation[END_REF]. First, it allows agents to encapsulate environments, (either physical or social) which can themselves host lower-level agents (e.g. a lift is an agent moving between floors, and an environment hosting other agents). This can be used to represent geographical objects acting as a spatial support for others (such as a road which "includes" bus stations), or composition relations between objects (such as groups of buildings which can be reified by specific meso agents). Then, any agent can be situated in several environments at the same time. Thus the structure of the multi-level hierarchy can be more complex than a mere tree and allows for instance the modelling of a bridge belonging to both a road and a river. Figure 2a shows the organisation of a shopping arcade instance, with the PADAWAN model: stores are both environments in which clients, alarms and other stores may be situated, and agents situated themselves in environments (e 0 represents the top level environment in which all agents are embedded).

Finally, the behaviour representation in PADAWAN relies upon an interaction-based model called IODA [START_REF] Kubera | IODA: An Interaction-Oriented Approach for Multi-Agent Based Simulations[END_REF], where interactions are condition/action rules involving several agents. The contextual variations in agents behaviours, depending on the environment they are situated in, is expressed by an interaction matrix (what interactions can occur between pairs of agent families) attached to each environment as shown in Figures 2b and2c. This could help represent that e.g. buildings would not apply the same generalisation rules in city center blocks and suburban blocks.

d c b a

Yet, the PADAWAN model was designed for multi-agent simulation: it has to be adapted to the context of generalisation which is not simulation but spatial problem solving.

Integration for AGENT: adaptation and implementation

As a first step of our work, we focus on the adaptation of the AGENT model into the PADAWAN paradigm seeking to obtain the same results. We express the algorithms used by AGENT into PADAWAN interactions. In AGENT, constraints propose actions to be solved (e.g. a "change into smallest surrounding rectangle" to solve a "squareness" constraint). In PADAWAN, the interactions are allowed by so called preconditions (conditions necessary for an interaction to be possible) and motivated by so called triggers (conditions that motivate the interaction), e.g. for a client agent, the "Take" interaction with an item agent is allowed by the "have enough money" precondition and the "need this item" trigger. The influence of constraints on the triggering of possible actions has to be expressed in PADAWAN. In this purpose, we introduce the notion of constraint advice. A constraint may express a favourable, unfavourable, indifferent or opposite advice on the application of an action on the object. According to the advices of all constraints and the unsatisfaction of some of these constraints, the model decides if an action will be triggered, launched with reluctance, or not launched at all (because it is likely that the execution of the action will have negative and hardly reversible effects on the result).

Once the actions to execute are chosen, they are ordered according to several factors: the importance for the constraint to be solved and the degree of unsatisfaction of the constraint. Each action is tested on the object, and if it effectively enhances the satisfaction degree, is validated.

a b c

Using this model, we express the interactions of encapsulated by an urban block in Figure 3).

Figure 3. An interaction matrix for a block environment. The block as a host may interact on himself in one way (when transforming into town center, i.e. being filled in a single colour), or on its buildings (when suppressing or displacing some of them, or when activating them). When activated, a building may do some operation on itself.

As it appears in the matrix, there are only hierarchical (host/building cell) and reflexive (Ø column) interactions. The purpose of PADAWAN is to take into account relations including all kinds of agents, for instance building/ building interactions. This other kinds of relation will be used when adapting CartACom and GAEL models to PADAWAN. CartAGen is a platform implementing some generalisation algorithms, including the AGENT model [START_REF] Renard | Capitalisation problem in researchexample of a new platform for generalisation: CartAGen[END_REF]. Our proposition is implemented in this platform and the results are compared with those of the original AGENT model (Figure 4). The global satisfaction value (S) is computed from the satisfaction of each constraint. Each action are proposed and tested in a given order. S is used to validate the effectiveness of an action after trying it. If S decreases, the action is cancelled. the AGENT model, we obtain the same result as with the native version of the AGENT model.

Implementation and results

We remind that the purpose of this first step was to adapt an existing model to another one. The expected improvements were not on the efficiency, nor the effectiveness, but on the flexibility to manage multi-level interactions. The results prove that the modified PADAWAN model is as good as the former AGENT model. The next section shows with a case study that it is additionally a good way to model diagonal interactions.

Case study: the dead-end streets and their neighbourhood

The section focuses on the generalisation of dead-end streets and their neighbourhood inside an urban generalisation by AGENT. After the problem being presented, new generalisation operations are defined, and then integrated into the adapted PADAWAN model.

Presentation of the case study

During the generalisation process, road symbols are enlarged to fit the perception threshold. This enlargement may reduce the space between two road sections, and prevent other objects like buildings to find room to display. This problem especially occurs with dead-end streets (Figure 5). Whit the current AGENT model, to solve this sort of problem, the more common solution when there is not even enough space for one row of building is to suppress the dead-ends first and, if necessary, the buildings. But a better way may be to displace dead-ends to give enough space to the buildings. This displacement will impact the structure of the dead-ends' neighbourhood. To maintain consistency with reality, we need to move objects in the neighbourhood of the dead ends. Also, when a dead-end is moved, its junction node with the network is moved too. This displacement may cause inconsistencies with other elements located on the road, like bus stations. Of course, these objects continue to be hosted in other environments, and they have to manage the previously existing constraints besides the new ones (e.g. the buildings are always in a block, so they need to respect a constraint of density carried by the block; the bus station needs to preserve its relative position to other stations within the road).

The next section presents how to model this constraint based dead-end displacement problem.

a b c

Modelling of the problem

The problem may be modelled in different ways. First, we describe a modelling with only vertical and horizontal relations based on the principle of AGENT and CartACom, and second we propose a modelling with a more complex multi-level architecture using our modified PADAWAN model. A simple way is to model the dead-end road as an agent in a block, as shown in Figure 6a. This agent interacts with neighbouring buildings. This may be either horizontally and directly in a CartACom way, or vertically and through a meso agent in an AGENT way. However, we add complexity to existing models with the addition of a new type of objects in the urban block. This raises a problem to calibrate the constraints and interactions, which is already difficult in the original approaches. Instead, a model for the organisation of the objects involved in the problem, as PADAWAN environments and agents is proposed (Figure 6b). A first step is to define the dead-end as an object type in our model. We do not only consider the dead-end as a road, but we define a "dead-end estate" agent that encapsulates a PADAWAN environment including all the building reachable by the dead-end road, and the deadend road itself. This environment is created using a buffer delimiting a surface around the dead-end road. All buildings overlapping the buffer are considered as included in the dead-end estate. The purpose of this dead-end estate agent is to consider it as a whole for some operations, but the objects situated inside need to be considered as individuals for some other operations. It is an instance of multi-level situation with "diagonal" interactions, since the dead-end estate is considered as an element of the block level, as the buildings inside it. Figure 7 shows an instance of encapsulation relations in a block with dead-ends. Then, two constraints are defined (one for each side of the dead-end) to detect if there is enough room on the left resp. on the right for at least one row of buildings. If the value is too small (compared to a minimal value calculated on the mean size required by a typical building and on the width of the road), the constraint is unsatisfied. A raytracing strategy is used to detect objects on the left resp. right of a section: for some points of the section, a ray orthogonal to the section is traced. This indication gives us a way to evaluate the satisfaction of each of the two "is there enough room on this side of the dead-end" constraint. Those constraints are carried by the previously define dead-end estate agent.

Having the left (resp. right) constraint unsatisfied is a trigger (in the PADAWAN sense) for a "slide to right" (resp. "slide to left") action, which a b

-Slides the dead-end road toward the direction opposite here there is not enough room -Moves the buildings hosted by the dead-end estate by translating them with the same displacement vector. The priority for this constraint to be solved is high because room needs to be freed to allow buildings to be generalised correctly. But this approach does not model the need to respect information consistency on the roads. Therefore, to avoid inconsistencies, for now, a displacement is not allowed when a junction with another road is detected close to the dead-end junction, so that the order of junctions with dead-ends along a road cannot be accidentally modified. All that information is expressed as interactions and integrated in the matrix associated to the environment encapsulated by the block (Figure 8).

To complete the process, an interaction to order and activate the dead-end estate agent in a block environment, is needed. This interaction is carried by the block agent. The dead-end estate agents to activate are sorted depending on the distance of the dead-end to a non-dead-end road.

Figure 8. Modified interaction matrix from Figure 3 including a new agent family and associated interactions.

The complexity of this modelling is higher than the one from original AGENT solutions, but remains in the same proportions. In future works, new constraints will be implemented, including more computing and complex situations. One of the aim of the PhD study is to manage this complexity using mechanisms of the new model.

Results

The proposed solutions have been implemented in the CartAGen platform. The new agent type "dead-end estate" has been defined. New algorithms, new interactions and associated interactions matrix has been implemented. Figure 9 shows results obtained in an urban area, with displaced dead-end on the left of the figure. These results are more interesting than the previous way consisting in deleting all small dead-ends.

Conclusion and perspectives

Some unsolved generalisation problems were identified as multi-level issues that require to go further than the existing multi-agent models. To propose a solution, we assume that a more formalised way to express interactions between agents in multilevel context may be a first step to solve them. To do that, we choose the PADAWAN model from the MAS literature. As a first step of our demonstration of the usability of PADAWAN as a model for cartographic generalisation, the AGENT model has been adapted to the PADAWAN model. This adaptation needed adjustments and enhancements to PADAWAN. The dead-end streets case study is our first concrete new problem. To solve it, a model for dead-ends street agents and algorithms was proposed and integrated in PADAWAN model. The first results show better generalisation of blocks with deadend streets. A next step is to consider the problem integrating the order of elements on roads and propose an understandable way to describe the orchestration of the agents with multilevel interactions. After that, the objectives are to solve other problems, including those detailed in part 2 and to fusion the three COGIT MAS for generalisation: AGENT, CartACom and GAEL relying on the enhanced PADAWAN paradigm.

Figure 2 .

 2 Figure 2. A hierarchical architecture in the PADAWAN model and instances of interaction matrix. (a) rectangular shapes indicate environments and oval shapes agents. An arrow indicates a location relation. For instance, Client 1 is located in Store 1. (b) the interaction matrix for environment encapsulated by Store 1 , Store 3 and Store 4 . The one indicated by (c) is for Store 2 and Store 5 and include a different interaction.

Figure 4 .

 4 Figure 4. Comparisons of the AGENT model, without and with PADAWAN. The same results are obtained.

Figure 5 .

 5 Figure 5. (a) a map portion including dead-ends street at 1:25k symbolisation scale. (b) the same portion at 1:50k symbolisation scale with road symbols enlarged and related buildings (surrounded in red) magnified to reach minimum size at 1:50k. (c) same as (b) displayed smaller.

Figure 6 .

 6 Figure 6. Two way of modelling the problem.

Figure 7 .

 7 Figure 7. Definition of the organisation of PADAWAN environments and agents.

Figure 9 .

 9 Figure 9. Instance of displacement of dead-end streets for a 1:50k map. (a) the original data (1:25k). (b) the generalized data for a 1:50k map. (c) same as (b) displayed smaller.