Green-synthesized TiO₂ nanoparticle–activated carbon composite from Chrysophyllum albidum seed shells for sustainable remediation of textile dye-polluted water

The tie-and-dye industry is a thriving industry in Nigeria that generates large volumes of wastewater laden with dyes and auxiliary chemicals, indiscriminately disposed of into the environment. This study develops a green and sustainable remediation approach for textile dye-contaminated water using titanium dioxide nanoparticles (TiO₂ NPs) supported on steam-activated carbon derived from Chrysophyllum albidum seed shells (CSAC). The TiO₂ NPs were synthesized via a green route using green tea (Camellia sinensis) leaf extract. The synthesized TiO₂ NPs, raw CSAC, and TiO₂NPs–CSAC composite were applied to the adsorption of Procion Red MX dye (PRMXD), following characterization. Process optimization using a Definitive Screening Design (DSD) under Response Surface Methodology (RSM) yielded a desirability value of 0.994. The model predicted maximum removal efficiencies of 98.97% (TiO₂NPs–CSAC) and 97.91% (CSAC) under the following optimal conditions: adsorbent dosage of 0.5 g/L, pH 11, temperature of 33.28 °C, initial dye concentration of 99.99 mg/L, and a contact time of 59.76 min. Adsorption followed a pseudo-second-order kinetic model and fitted the Freundlich isotherm, indicating multilayer adsorption. When applied to real Adire textile effluent (ATE), removal efficiencies were 70.32% and 66.48% for TiO₂NPs–CSAC and CSAC, respectively. Both adsorbents demonstrated excellent stability over five regeneration cycles, although efficiency decreased to 55.35% and 40.89%, respectively, by the fifth cycle. Post-treatment analyses confirmed significant reductions in color, BOD₅, alkalinity, and heavy metal levels (Ni, Zn, Cd, Cu). The findings highlight TiO₂NPs-CSAC as an efficient, green adsorbent for industrial wastewater management.