One-pot synthesis of dual-sites adsorbent based on recycling spent Lithium-ion batteries: Matter cycle, orderly grafting, and copper adsorption

Waste carbon residue (WCR), a hazardous solid waste discharged from spent lithium-ion batteries recovery industry, have caused serious environmental pollution. In this work, WCR with ferric impurity was recycled as dual-sites adsorbents for efficient removal of Cu2+ in wastewater. The adsorbent, sulfhydryl grafting Fe(OH)3/graphite (SFG), was synthesized by one-pot method. In this process, the ferric impurity was transformed into amorphous Fe(OH)3 in-situ, and sulfhydryl (-SH) was orderly grafted on adsorbent surface by regulation of 3-(Trimethoxysilyl) propyl methacrylate (TPM). In the regulation, TPM combined adsorbent surface and cysteine molecule by its inorganic and organic ends. Furthermore, the filtrate and adsorbent could be reused many times. The adsorption kinetics followed the pseudo-second-order model, the isotherm fitted better with the Freundlich isotherm model, which indicated that the adsorption of Cu2+ on SFG was a multilayer and heterogeneous chemisorption process. Langmuir maximum adsorption capacity of Cu2+ was 185.2 mg/g which was higher than many similar adsorbents. Adsorption mechanisms were explored by material characterizations and DFT calculations. The –OH groups of Fe(OH)3 reacted with Cu2+ via ion-exchange, the sulfur atom in –SH groups chelated with Cu2+ by transferring electrons to Cu atom. Synergistic effect of Fe(OH)3, sulfhydryl, and TPM provided SFG with outstanding adsorptive performance to Cu2+ contamination.