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 N-2 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.