# Adsorption of Metolachlor and Its Transformation Products, ESA and OXA, on Activated Carbons
## 4 Conclusions  
Four activated carbons have been tested for the adsorption of metolachlor and its metabolites OXA and ESA, one commercially available and three synthesized from lignocellulosic residues. The synthesis of these three adsorbents was carried out by chemical activation employing K\({}_{2}\)CO\({}_{3}\) and H\({}_{3}\)PO\({}_{4}\) as activating agents, revealing an important effect on its adsorption capacities as a function of the activation process as well as the starting material nature. The samples activated with potassium carbonate (R-KC and S-KC) demonstrated the higher adsorption capacities for the metolachlor and its metabolites ESA and OXA, this being the first time that an efficiency higher than 80% was reported for these compounds. As a general trend, higher adsorption was observed for the activated carbons with greater porous development. Microporosity seems to be the main factor governing the adsorption capacity containing reactive sorption sites and the presence of mesopores facilitates the transport of the adsorbates to reach the microporosity. Additionally, the surface chemistry resulted in an important factor to consider for the TPs adsorption favoring the electrostatic interactions between the carbon surface and these anionic molecules. OXA was easily adsorbed compared to ESA, on samples R-KC and S-KC, due to its lowest molecular weight, fitting better in the pores of these two adsorbents. Finally, the study of the initial concentration revealed a lower adsorption capacity for both metabolites on R-KC sample when the concentration employed is close to that found in groundwater, this being an important factor to be considered.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11167342/s1](https://www.mdpi.com/article/10.3390/app11167342/s1)]([https://www.mdpi.com/article/10.3390/app11167342/s1](https://www.mdpi.com/article/10.3390/app11167342/s1)), Table S1: Physicochemical properties of MET, ESA and OXA, Figure S1: Nitrogen adsorption/desorption isotherms at \(-\)196 \({}^{\circ}\)C for R-KC samples obtained by physical and wet impregnation, Table S2: Textural parameters obtained from the N\({}_{2}\) adsorption/desorption isotherms at \(-\)196 \({}^{\circ}\)C for R-KC samples obtained by physical and wet impregnation, Figure S2: Thermogravimetric profiles of R-KC and S-KC with (a,b) MET and (c,d) OXA adsorbed. The pristine materials are included for comparison. Experimental conditions: Ar flow 50 mL/min up to 900 \({}^{\circ}\)C (ramp 10 \({}^{\circ}\)C/min). Figure S3: Evolution of adsorption as a function of contact time obtained at 25 \({}^{\circ}\)C on the four studied adsorbents for a) ESA and b) OXA metabolites (0.2 g compound/g adsorbent). The error bars represent the standard deviation.  
Conceptualization, A.G.-B. and B.C.; methodology, A.G.-B. and B.C.; formal analysis, A.G.-B.; writing--original draft preparation, A.G.-B.; writing--review and editing, A.G.-B., B.C. and P.S.; funding acquisition, B.C. All authors have read and agreed to the published version of the manuscript.  
This work was co-financed by the European Union and the Conseil Regional du Centre-Val de Loire region through the European Regional Development Fund. We gratefully acknowledge the financial support provided by the PIVOTS project and the Conseil Regional du Centre-Val de Loire (ARD 2020 program and CPER 2015-2020), the French Ministry of Higher Education and Research (CPER 2015-2020) and subsidy funds from CNRS and University of Orleans and the Centre Val de Loire Region. This work has been carried out as part of the regional project DEPRICAME.  
The authors declare no conflict of interest.