Bio-dye-sensitized TiO₂ nanophotocatalysts for visible-light-driven sustainable wastewater treatment

The limited visible-light activity of titanium dioxide (TiO₂) restricts its application in solar-driven photocatalysis for wastewater treatment. In this study, TiO₂ nanoparticles were sensitized with natural plant-derived dyes-chlorophyll from Eichhornia crassipes (water hyacinth) and anthocyanin from Nymphaea rubra (red water lily)-to extend their optical response into the visible spectrum. Dye extraction was followed by TiO₂ sensitization, and the resulting nanocomposites were comprehensively characterized using FTIR, UV-Vis, XRD, SEM-EDX, and TGA analyses. Results confirmed successful dye adsorption without altering TiO₂'s anatase-dominant crystalline phase. UV-Vis spectra revealed broadened visible-light absorption, particularly in anthocyanin-sensitized TiO₂, due to strong π→π* transitions and hydroxyl-functional group interactions. Photocatalytic activity was evaluated via methylene blue (MB) degradation under visible light, optimizing parameters such as dye concentration, pH, catalyst dosage, and initial pollutant load. Anthocyanin-sensitized TiO₂ exhibited superior performance, achieving 75% degradation under optimal conditions, compared to 66% for chlorophyll-sensitized TiO₂. Neutral pH and moderate catalyst dosage (0.2 g L^-1) favored maximum efficiency. Reusability tests over five consecutive cycles demonstrated both catalysts retained over 80% of their initial activity, with anthocyanin-sensitized TiO₂ showing higher stability. This eco-friendly approach leverages abundant, renewable plant pigments to enhance TiO₂'s photocatalytic efficiency without costly or hazardous modifications. The findings highlight the potential of natural dye-sensitized TiO₂ as a sustainable and cost-effective photocatalyst for visible-light-driven wastewater treatment, offering a promising pathway toward scalable, green water purification technologies.