Removal of refractory organic compounds from water by adsorption using carbon xerogel cylinders coupled with in situ regeneration using H2O2 electro-generation and UV radiation

Abstract

The process developed in this study is based on the adsorption of refractory organic compounds (ROCs) onto carbon xerogels, coupled with in situ regeneration of the adsorbent by H2O2 electro-generation and enhanced ROC decomposition via OH radicals due to UV illumination. The in situ regeneration of the carbon materials aims to replace the usual thermal regeneration, which is costly and gradually degrades the adsorption properties. In this work, carbon xerogels are synthesized via a sol-gel process and molded as cylinders that are used as adsorbents for ROCs. The specific surface area of these cylinders varies between 30 and 680 m2/g when the resorcinol/sodium carbonate (R/C) ratio is modified between 100 and 1500 during the synthesis. Their excellent adsorption properties are highlighted for three model pollutants (i.e., p-nitrophenol, methylene blue, and ibuprofen), and it is determined that the optimal cylinders have an R/C ratio of 750. In parallel, the electro-generation of H2O2 within these cylinders is demonstrated, reaching an H2O2 concentration of 5 mg/L when using the most porous carbon cylinder (i.e., the optimal one). The use of UV light combined with the electro-generation of H2O2 enables the efficient production of hydroxyl radicals. Finally, in situ regeneration of the optimal saturated carbon cylinders for the model pollutants is successfully performed. Indeed, the results of carbon cylinder regeneration for the three pollutants show that the H2O2 electro-generation combined with the UV illumination completely mineralized the three pollutants previously absorbed on the carbon cylinders. These promising results open the way for a new method that regenerates adsorbent materials in situ without the use of thermal treatments.