Synergistic adsorption–photocatalysis in TiO₂/activated carbon composites: optimization of p-nitrophenol degradation and application to real textile wastewater treatment

The photocatalytic degradation of persistent nitro-aromatic pollutants is often limited by poor light utilization and fast electron-hole recombination in conventional TiO 2 systems. In this work, TiO 2 /carbon composites were prepared using activated carbon (AC) and biomass-derived biochars as supports and evaluated for the degradation of p -Nitrophenol ( p -NP). Among the different compositions studied, 20 wt% TiO 2 supported on AC showed the best performance, achieving ~ 65% degradation of 20 ppm p -NP within 60 min under UV irradiation, with a pseudo-first-order rate constant of 0.0195 min⁻¹. Characterization results indicate that the improved activity is mainly due to band-gap narrowing (Eg ≈ 2.27 eV), suitable surface charge (-20.7 mV), and effective charge transfer at the TiO 2 -carbon interface, which together reduce charge recombination. In comparison, TiO 2 supported on biochars exhibited lower activity, attributed to higher ash content, lower conductivity, and weaker interfacial interaction. The optimized TiO 2 /AC composite was further tested with real textile wastewater and achieved ~ 42% degradation, confirming its applicability under complex conditions. These results show that proper selection of carbon support and TiO 2 loading is crucial for improving photocatalytic performance in wastewater treatment.