Optimization of Methylene Blue Removal from Aqueous Media by Photocatalysis and Adsorption Processes Using Coconut Biomass-Based Composite Photocatalysts

Biomass-based composites (BCPs) containing TiO₂ were successfully synthesized by one-step sol–gel method and applied to methylene blue (MB) removal from water. The calcination temperature and the appropriate TiO₂/biomass ratio played an important role on adsorption and photocatalytic capacity of the composites. The effects of variables, such as composites concentration (50–200 mg L⁻¹), initial pH (5–9), and irradiation intensity (10–40 W m⁻²), were investigated applying response surface methodology for process optimization. The BCP400-50:50 (meaning composite formed by 50%:50% Ti: coconut biomass) exhibited the best removal performance (94%), surpassing the commercial TiO₂-P25 (53%). Differently from other studies that focused specifically on photocatalysis performance, the present study investigated the adsorption mechanisms for MB removal by BCP. The adsorption data were well described by the Langmuir isotherm (maximum capacity of 294.12 mg g⁻¹) and pseudo-second-order kinetic models indicating chemisorption as the rate-limiting mechanism of the process. Coconut shell biomass showed great potential for the application in BCP composites. Since BCPs had high MB adsorption capacity, it provides an attractive complementary water treatment option due to the low cost and abundant availability of such agro-industrial waste.