Solar Chlorine Activation for Efficient Rhodamine B Removal in Strong Basic pH: Processing Conditions, Radicals Probing, and TiO2 Nanocatalyst Effect

Abstract

In recent years, there has been growing interest in the application of UV/chlorine advanced oxidation processes for wastewater treatment. However, few studies have investigated this process in a strongly basic medium (pH > 10), which is a common characteristic of many industrial effluents. In addition, the use of artificial UV lamps in these processes can be costly. To address these challenges, we investigated the use of solar light (referred to as Solar-L) in the Solar-L/chlorine process for the degradation of Rhodamine B (RhB) in a strongly basic medium (pH 11). We found that separate solar light or chlorination showed no degradation after half an hour, but the Solar-L/chlorine process effectively degraded RhB, with complete removal achieved in only 30 min, using 1000 µM ClO−. The process also resulted in a significant reduction of TOC, i.e., 60% after 120 min and 80% after 240 min. Our results indicate that both •OH/O•− and reactive chlorine species (RCS) were involved in the degradation process, while O3 played no role. The process performance improved with the decreasing initial contaminant concentration and increasing temperature (up to 55 °C). The addition of a TiO2 nanocatalyst to the Solar-L/chlorine system significantly improved the RhB degradation efficiency by more than 30%. It was found that neither adsorption (on TiO2) nor Solar-L/TiO2 photolysis contributed to the dye removal by the Solar-L/chlorine/TiO2 system. Instead, the improvement associated with the Solar-L/chlorine/TiO2 system was related to the involvement of hypochlorite in the photocatalytic reaction at the catalyst surface. A detailed discussion of the effect of TiO2 was carried out based on the physicochemical properties of RhB and TiO2 catalyst with respect to the solution’s pH. In conclusion, this study highlights the potential of solar light as a sustainable and efficient technology for the treatment of polluted water in strong basic media in the presence of chlorine and chlorine/TiO2 as additives. These valuable findings provide a basis for the future research and development of this promising technology for water treatment applications.