Enhanced adsorption of molybdenum(VI) from aquatic solutions by chitosan-coated zirconium–iron sulfide composite

[Display omitted] •CS@Zr-FeS showed higher Mo(VI) removal efficiency compared to FeS.•The removal of Mo(VI) follows the pseudo-second-order adsorption kinetics.•Hydrogen bonding and surface complexation were the main Mo(VI) removal mechanisms.•CS@Zr-FeS showed good applicability to pH and aerobic environment.•CS@Zr-FeS maintained high Mo(VI) removal efficiency after 60 days’ aging. Nano-sized iron sulfide (FeS) plays a vital role in heavy metal removal; However, FeS nanoparticles are easily agglomerated, oxidized, and deactivated due to their poor stability. In order to solve these problems, this work synthesized chitosan-coated zirconium–iron sulfide composite (CS@Zr-FeS) by the coprecipitation method using FeS, zirconia sol (ZrO2), and chitosan (CS) as the raw materials and tested it for enhancing the performance of molybdenum(VI) removal. The obtained CS@Zr-FeS exhibited a higher specific surface area (85.43 m2/g) than FeS (47.92 m2/g), with the maximum molybdenum(VI) adsorption capacity of 120.80 mg/g. The adsorption of molybdenum(VI) onto CS@Zr-FeS followed the pseudo-second-order kinetics and Langmuir isotherm. The adsorption process was partially inhibited by the competing anions (e.g., PO43− and HCO3−) and humic acids but was not influenced by dissolved oxygen. Moreover, the obtained CS@Zr-FeS had high stability. Spectroscopy analysis and density functional theory (DFT) calculations demonstrated that hydrogen bonding and surface complexation were the primary mechanisms for molybdenum(VI) removal. These results imply that the CS@Zr-FeS composite exhibits a higher potential for molybdenum(VI) removal from the aquatic solutions than the pristine FeS nanoparticles.