Remarkable recycling processes of conjugated polymers with titanium dioxide quantum dots as photocatalysts for photodegradation of hazardous industrial wastewater

• A novel polyaniline-titanium dioxide quantum dot (PA-TQD) composite was developed, showing enhanced photocatalytic degradation of methyl orange in wastewater under solar light. • The PA-TQD composite exhibited a 60% degradation efficiency, significantly higher than polyaniline alone (35%) but lower than TiO₂ quantum dots (93%). • The composite demonstrated high thermal stability and maintained 73.8% photocatalytic activity after four reuse cycles. • The study highlights potential applications in sustainable wastewater treatment. This study presents the synthesis and characterization of a novel polyaniline-titanium dioxide quantum dot (PA-TQD) composite for enhanced photocatalytic degradation of hazardous industrial wastewater. The composite was synthesized via in-situ polymerization and characterized using FTIR, XRD, TEM, BET, and TGA, confirming the integration of TiO₂ quantum dots (2.8–5.3 nm) into the polyaniline matrix (particle size 35–40 nm). BET analysis revealed a surface area of 50.30 m²/g for PA-TQD, significantly higher than 28.18 m²/g for pure polyaniline, contributing to its improved photocatalytic activity. Photocatalytic degradation experiments on methyl orange dye demonstrated a 60.1% degradation efficiency under xenon irradiation, compared to 35% for polyaniline alone. The photocatalytic rate constant of PA-TQD was 0.032 min⁻¹, indicating enhanced performance. In recycling tests, PA-TQD retained 73.8% of its photocatalytic efficiency after four cycles, showcasing strong reusability. TGA analysis confirmed the composite's enhanced thermal stability, with minimal weight loss up to 250 °C. COD analysis of real industrial wastewater samples showed effective pollutant reduction, with COD values for PA-TQD ranging from 756 to 1212 ppm. However, further optimization is needed to meet regulatory limits set by Saudi environmental laws (<1000 ppm COD). The synergy between polyaniline and TiO₂ quantum dots enhances charge separation, increases active sites, and makes PA-TQD a promising recyclable photocatalyst for sustainable wastewater treatment applications.