Coffee Silver Skin: A Useful Adsorbent Substrate for Norfloxacin Removal and Photodegradation

Abstract

This work proposes the use of Coffee Silver Skin, a by-product of coffee production, as an adsorbent substrate for the removal of the antibiotic Norfloxacin from water and assesses the possibility of regenerating it through advanced oxidation processes. In detail, the study was developed by showing the best conditions for the pollutant removal, in which the adsorption process occurred with the main involvement of electrostatic interactions. A preliminary desorption approach in the presence of salt-based solutions, i.e., NaCl and 0.1 M MgCl₂, was followed with the aim of desorbing the non-photodegraded Norfloxacin from the regenerated adsorbent. Therefore, indirectly, the quantitative evaluation of photodestroyed Norfloxacin was assessed according to selected working conditions: UV light, UV light/H₂O₂, UV light/TiO₂, and UV light/TiO₂/H₂O₂. Moreover, a comparison with the literature devoted to Norfloxacin photodegradation directly in water was accomplished. The use of UV light/TiO₂ occurred as the best approach for the purpose of obtaining the complete degradation of Norfloxacin in 6 h. On the other hand, the use of H₂O₂ did not improve the process. Thus, to reduce the irradiation time, Norfloxacin degradation was evaluated simultaneously during its release from the adsorbent, in a 0.1 M MgCl₂ solution, retrieving a similar and well-known behavior observed when the pollutant was degraded in water. In 3 h, the desorbed Norfloxacin was destroyed, enabling the recycling of Coffee Silver Skin for up to 3 cycles.