Abstract
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In this paper, we reported an environmental friendly and cost-effective method to prepare magnetic nanoparticles decorated tea waste (Fe3O4-tea) composites by chemical co-precipitation of Fe3+/Fe2+ on waste tea leaves. Various physical and chemical characterizations indicated that the synthetic Fe3O4 nanoparticles were combined to the tea powder surface by chemical bonds. When tested as an adsorbent for Cu(II) and Zn(II) removal, the Fe3O4-tea composites showed an unexpected high sorption capacity and satisfactory regeneration performance, better than those of naked Fe3O4 and other reported materials. The results showed that the maximum sorption capacities of Fe3O4-tea calculated from Langmuir isotherm model were 95.44mgg−1 for Cu(II) and 68.78mgg−1 for Zn(II) at pH 6.0. Interestingly, it was found that much higher adsorption capacity was achieved for Cu(II) on Fe3O4-tea rather than that for Zn(II) adsorption, which was attributed to the higher ionic potential of Cu(II), preferably penetrating into smaller pores. Furthermore, in the binary-solute system, Cu(II) exhibited greater inhibition for Zn(II) sorption, suggesting stronger affinity of Fe3O4-tea for Cu(II). Relatively, pseudo-second-order equation was the optimal model to describe the kinetics of Cu(II) and Zn(II) sorption, suggesting a chemisorption with the adsorption mechanism via M-O or M-N bonding. X-ray photoelectron spectroscopy (XPS) analysis showed that the enrichment of Cu(II) and Zn(II) was attributed to the abundant binding sites (e.g., –OH, –COOH and –NH groups) of Fe3O4-tea, which made stable complex compound with Cu2+ or Zn2+. This work provides a facile and general approach to synthesize promising magnetic biochar materials for wastewater treatment.