Facile Modification of a Polythiophene/TiO₂ Composite Using Surfactants in an Aqueous Medium for an Enhanced Pb(II) Adsorption and Mechanism Investigation

Surfactants are considered to have a strong affinity to metal ions. Thus, it is a novel design by employing sodium dodecyl­benzene­sulfonate (NaDBS) and hexadecyl­trimethyl­ammonium bromide (CTAB) surfactants to functionalize polythiophene/TiO₂ composite via a facile and green method to improve the Pb²⁺ removal efficiency from the aqueous solution. Techniques such as Fourier transform infrared spectroscopy, zeta potential analysis, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and N₂ isotherm analysis revealed changes in surface properties after modification, and adsorption active sites were also extensively detected. Batch adsorption investigations were carried out to study their adsorption behaviors for lead­(II), and the diffusion process was carefully investigated and described via kinetic models including the Weber–Morris and pseudo-second-order model. The results indicated that modification with NaDBS or CTAB significantly changed the adsorption behavior and increased the monolayer adsorption capacity of polythiophene/TiO₂ composite for Pb²⁺, from 151.52 mg/g to 198.41 or 213.22 mg/g. The entire adsorption process results comprehensively confirmed that the diffusion rate of Pb²⁺ ions was controlled by the film and intraparticle diffusion, and the combination rate of Pb²⁺ with active sites was limited by chemisorption. Pb²⁺ ions were also detected to interact with adsorption active sites including sulfur atoms, hydroxyl groups, and surfactants.