Green synthesized nanoscale zero-valent iron impregnated tea residue biochar efficiently captures metal(loid)s for sustainable water remediation.

Pristine or modified nanoscale zero-valent iron (nZVI) synthesized though conventional chemical reduction have been widely recommended for remediating metal(loid)-contaminated water. However, their eco-friendliness is often challenged with the concomitant bio-toxicity and secondary environmental risks. Alternatively, this study utilized waste tea leaves extract and remaining residue as the reducing agent and pyrolytic matrix to innovatively fabricate a green synthesized nZVI impregnated tea residue biochar (G-nZVI/TB). Since the performances, mechanisms, and potential applications of G-nZVI/TB for simultaneous removal of metal cation and metalloid anion remain unclear, typical synthetic aqueous solutions and real wastewaters were systematically tested. The adsorption isotherms showed that the calculated maximum adsorption capacities of G-nZVI/TB for various meta(loid)s were 1.4-10.7 fold higher than those of TB. Although Cd(II) competed with Pb(II) for adsorption on G-nZVI/TB, they synergistically promoted As(III) sequestration. The SEM and FTIR spectra demonstrated that G-nZVI nanoparticles were uniformly dispersed onto TB framework, whereas newly grafted groups like Fe-O, C=O, and C-N accelerated metal(loid)s bonding. The results of batch experiments, XRD, and XPS comprehensively elucidated that metal(loid)s were predominantly separated from polynary systems via electrostatic adsorption, ion exchange, co-precipitation, cation-π interaction, oxidation-complexation, and B-type ternary complexation. In synthetic industrial wastewater and real paddy field drainage with divergent environmental conditions, 0.5 g L optimized G-nZVI/TB efficiently captured over 92.4% metal(loid)s at their concentrations ranging from 0.04 to 3 mg L, indicating its excellent selective adsorption effectiveness and extensive compatibility for practical application in reusing multi-metal(loid)s contaminated wastewater. Overall, these findings provide new insights into developing green nano-functional materials for sustainable water purification.