Diclofenac is one of the most frequently detected pharmaceuticals in water bodies since its removal by most conventional wastewater treatment plants is low. Efficient sorbents for diclofenac removal based on the adsorption of a specially synthesized polycation, poly N-methyl 4-vinyl pyridine iodide co styrene (QPVPcS), to montmorillonite, were developed. These composites, at low (0.1 g/g) and high (0.2 g/g) polymer loadings, were characterized by zeta-potential, X-ray diffraction (XRD), FTIR and thermal gravimetric (TGA) measurements. Zeta potential reached charge reversal at both polymer loadings. FTIR measurements suggest that at a low polymer loading the main configuration is as trains while at a high loading it is also as loops and tails. Polymer intercalation was observed by XRD measurements at low and high polymer loading; however, complete exclusion of the intercalated water occurred only at high polymer loadings. Water exclusion at high loadings was supported by TGA measurements which also indicated that the polymer adsorbs in more than one mode. The positively charged composites promoted electrostatic interactions with anionic diclofenac (pKa=4.15). However; studying the effect of ionic strengths on the removal of diclofenac by QPVPcS composites (in comparison to polycation composites without aromatic groups) indicated that in the case of QPVPcS π–π interactions contributed significantly to diclofenac binding. Adsorption isotherms of diclofenac to the composite and to granular active carbon (GAC) were adequately described by the Langmuir equation and did not differ significantly. However, the adsorption kinetics of diclofenac to the composite was significantly more rapid than to GAC. Finally, the fast kinetics of diclofenac binding to the composite was advantageous in filtration and diclofenac removal by composite filters was more efficient than by GAC filters.
hagay.kohayl@mail.huji.ac.il
