Synthesis of polyaniline/ <scp> TiO ₂ </scp> nanocomposites: effects of acid and aniline concentrations on material properties and photocatalytic performance for sulfamethoxazole degradation

Abstract BACKGROUND This work investigated the synthesis of TiO 2 ‐P25/polyaniline (PANI) nanocomposites, denoted as PANI– TiO 2 , via chemical oxidative polymerization under different aniline:H + molar ratios, and evaluated their performance in heterogeneous photocatalysis (HP). Although this parameter is directly related to PANI properties, it has been insufficiently explored in the literature. Therefore, the aniline concentration was fixed while two conventional HCl concentrations (0.1 and 1.0 mol L −1 ) were employed. RESULTS Significant differences were observed in both PANI and PANI–TiO 2 synthesized under distinct aniline:H + ratios. Spectroscopic characterization revealed that PANI synthesized in 0.1 mol L −1 HCl exhibited more oligomeric structures, lower oxidation degree, and reduced electrical conductivity. The incorporation of TiO 2 ‐P25 promoted stabilization of quinoid segments in PANI, induced a core–shell morphology, and shortened the synthesis time. The composites synthesized in 1.0 mol L −1 HCl exhibited improved dispersion in water, an important characteristic for HP applications. Photocatalytic experiments demonstrated that TiO 2 ‐P25, a benchmark and challenging catalyst for visible‐light sensitization, exhibited photosensitization by PANI under both visible and UV irradiation. Under visible‐light irradiation, the TP20HA sample, synthesized in 1.0 mol L −1 HCl, achieved approximately 35% sulfamethoxazole (antibiotic) removal after 120 min. Under UV irradiation, the same sample exhibited an apparent rate constant approximately 18% higher than that of TiO 2 ‐P25. CONCLUSION The photosensitization of TiO 2 ‐P25 depended on nanocomposite characteristics and HP experimental parameters, including the spectral range of incident radiation, color, and pH of the contaminant solution. The results demonstrated that the aniline:H + ratio strongly influenced the physicochemical properties and photocatalytic performance of the obtained materials. © 2026 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).