Facile synthesis of a polythiophene/TiO₂ particle composite in aqueous medium and its adsorption performance for Pb(II)

A polythiophene/TiO₂ (PTh/TiO₂) particle composite was synthesized by a facile and green method via (NH₄)₂S₂O₈-catalyzed oxidative polymerization of thiophene in acidic aqueous medium to adsorb Pb²⁺ ions from aqueous solution, and the synthesis mechanism was proposed. The particle composite was carefully characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric (TG) analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and zeta potential analysis, and it showed that the composite prepared had a high specific surface area of 229.66 m² g^-1. Various factors such as adsorbent dosage and solution pH influencing the adsorption were investigated. The isotherm results indicated that the adsorption performance of Pb²⁺ on the composite fitted the Langmuir model, and the maximum adsorption capacity reached 151.52 mg g^-1 at 25°C, 170.36 mg g^-1 at 35°C and 173.61 mg g^-1 at 45°C. The present adsorption system can be described most favorably by a pseudo-second-order model, confirming that chemisorption such as chelation may be the adsorption rate-limiting step. Meanwhile, adsorption was a spontaneous and endothermic process with increased entropy. In addition, regeneration by HCl-elution and NaOH-activation was possible, and the composite could be used repeatedly without any significant reduction in its adsorption capacity after 6 adsorption-desorption cycles. Furthermore, the adsorption mechanisms were investigated.