Construction of Thiol-Functionalized Chitin and Its Adsorption Performance and Mechanism for Pd(II)
Recovery of palladium from Pd-bearing wastewater is economically and environmentally significant. Adsorption is a promising method due to its simplicity, low cost, and high efficiency. In this study, a novel thiol-modified adsorbent (CHT-SH) was synthesized via one-step functionalization of inexpensive chitin (CHT) with thioglycolic acid. At room temperature and pH=2, CHT-SH exhibited an experimental adsorption capacity of 223.67 mg·g−1 for Pd(II), which was approximately 7 times higher than that of pristine CHT (30.6 mg·g−1). Kinetic and isotherm studies indicated that the adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm model, with a maximum theoretical adsorption capacity of 248.89 mg·g−1, suggesting monolayer chemisorption. Characterization (FTIR, SEM, XPS, XRD) and density functional theory (DFT) calculations revealed that the adsorption mechanism primarily involved synergistic coordination of nitrogen and sulfur atoms, along with electrostatic interactions. Furthermore, CHT-SH demonstrated good reusability, retaining stable adsorption capacity after five adsorption-desorption cycles. Compared to other adsorbents that rely on redox mechanisms and are costly, CHT-SH offers comprehensive advantages. This work provides a cost-effective and efficient adsorbent for Pd(II) recovery from wastewater, offering technical support and theoretical reference for practical applications.