High silica zeolites used to clean-up water polluted with sulfonamide antibiotics: from multidisciplinary model studies to real applications and regeneration techniques.

Sulfonamide antibiotics are persistent pollutants present in surface and subsurface waters in both agricultural and urban environments. Their anionic nature makes them highly mobile along soil profile and is responsible for their accumulation into water bodies. Owing to their environmental diffusion and persistence, sulfonamides are responsible to induce high level of resistance in bacteria through by-pass mechanism. Sulfamethoxazole (SMX), a broad spectrum biostatic sulfanilamide, has become a pointof interest because of its prevalence in contaminated wastewaters at concentrations correlated to bacterial resistance and genetic mutations in organisms. To limit the diffusion of resistance determinants, it is of utmost importance to identify sustainable strategies against this antibiotic class to be adopted for water clean up purpose. In this work, high silica zeolites (Y, mordenite, and ZSM-5) with pore opening sizes comparable to SMX dimensions has been positively evaluated to clean-up water polluted with sulfonamides. SMX incorporation and localization into the pore of each zeolite was defined along with medium-weak and cooperative host-guest interactions in which water molecules play a certain role only in zeolite Y and mordenite. Rietveld structure refinement revealed that the incorporation of SMX molecules caused changes in the dimension of the zeolite channel systems, when compared to the parent zeolite, and a close vicinity of the heterocycle ring nitrogen to the framework. To define possible strategies for the exhausted zeolite regeneration, the efficacy of some chemico-physical treatments on the zeolite loaded with different sulfonamides was evaluated. The evolution of photolysis, Fenton, photo-Fenton, thermal treatments, and solvent extraction and the occurrence in the zeolite pores of organic residues eventually entrapped was elucidated by a combined thermogravimetric (TGA-DTA), diffractometric (XRPD), and spectroscopic (FTIR) approach. The recyclability of regenerated zeolite was evaluated over several adsorption/regeneration cycles, due to the treatment efficacy and its stability and ability to regain the structural features of the unloaded material. Finally, among several regeneration techniques applied to exhausted zeolite samples, thermal treatment and solvent extraction showed the best performance