Synergistic photocatalytic degradation of methylene blue using TiO2 composites with activated carbon and reduced graphene oxide: a kinetic and mechanistic study

Abstract

This comprehensive study explored the removal of methylene blue (MB) from aqueous solutions as a model pollutant, utilizing solar-driven photocatalysis with nano-sized titanium dioxide (TiO₂) and composites with activated carbon (AC) and reduced graphene oxide (RGO). This research introduces continuous solar reactor instead of conventional batch experiments investigating its design configuration. Utilizing response surface methodology (RSM), the study determined the optimal process conditions (MB concentration at 30 mg/L, pH 8.82, irradiation time 138 min), under which TiO₂ achieved a 93.13% MB removal efficiency. The study further revealed that the integration of TiO₂ with AC and RGO (5% wt.) significantly enhanced the MB photocatalytic degradation. The TiO₂/AC composite achieved 98.3% MB degradation in 138 min of solar exposure, related to its large specific surface area of 146 m²/g and a pore volume of 0.439 cm³/g. Likewise, the TiO₂/RGO composite demonstrated 97% removal with a surface area of 102 m²/g and a pore volume of 0.476 cm³/g, significantly better than nano-TiO₂. Additionally, the research investigated the role of the solar reactor configuration on MB removal. Using 26 mm Pyrex tube diameter with 15 cm long on parabolic aluminum concentrator inclined at 30° optimally achieved the peak MB degradation efficiency. Recyclability tests shown a noticeable decrease in nano-TiO₂ efficiency to 56.03% without regeneration; however, after regeneration following the third cycle, the efficiency significantly recovered to 70.07%. Thereby, this paper introduces an innovative, continuous, and well-designed solar reactor system for dye removal, employing nano-TiO₂ and its composites with AC and RGO for improved photocatalytic efficiency under statistically optimized process conditions.