Enhancing Cr(VI) reduction and immobilization by magnetic core-shell structured NZVI@MOF derivative hybrids
2020
Fang, Ying | Wen, Jia | Zhang, Haibo | Wang, Qian | Hu, Xiaohong
Hexavalent chromium (Cr(VI)) has significantly threatened the environmental health because of its distinct toxicity. A novel magnetic core-shell structured NZVI@ZD composite was designed for simultaneous adsorption and reduction of Cr(VI). NZVI@ZD was synthesized by carbonization of the as-prepared core-shell structure NZVI@zeolitic imidazole framework-67 (ZIF-67). After carbonization, the original ZIF-67 shell shape was preserved well with marginal parts developing to graphitized carbon. Both cobalt (Co) and NZVI nanoparticles were finely dispersed in the porous ZIF-67 derivative (ZD). NZVI@ZD exhibited excellent removal performance for Cr(VI), owing to its high specific surface area and large pore size favorable for Cr(VI) adsorption and diffusion. The maximum adsorption capacity of NZVI@ZD for Cr(VI) was surprisingly as high as 226.5 mg g⁻¹, surpassing the pristine ZIF-67 (29.35 mg g⁻¹) and NZVI@ZIF-67 (36.53 mg g⁻¹). Zeta potential and X-ray photoelectron spectroscopy (XPS) spectra revealed that electrostatic attraction, reduction and precipitation might be involved in the Cr(VI) removal process by NZVI@ZD, resulting in the conversion of the adsorbed Cr(VI) to Cr(III) of lower toxicity and an eventual immobilization on the NZVI@ZD. The magnetic core-shell structured NZVI@ZD possessed superior adsorptive reactivity for Cr(VI) to most other traditional or newly reported materials, thus should be deemed highly efficient for Cr(VI)-contaminated wastewater treatment.
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