Facile preparation of NiFeO decorated chitosan-graphene oxide for efficient remediation of Co(II) and adsorption mechanism.

In the background of severe water pollution, adsorption is a charming technique for heavy metal remediation. In this work, NiFeO decorated chitosan-graphene oxide (NFCG) was prepared by simple hydrothermal method for Co(II) remediation application. Adsorption mechanism was elaborately elucidated based on multiple evidences extracted from adsorption fitting (isotherms, thermodynamics and kinetics), spectroscopic test (XPS, UV-Vis absorption, fluorescent emission and Raman spectra) and the hard-soft acid-base (HSAB) theory inspection. Result shows, for Co(II) with initial concentration 200 mg·L, NFCG with dosage 500 mg·L reaches adsorption equilibrium in 24 min, rendering removal percentage and adsorption amount 96.87 % and 387.48 mg·g, respectively. Owing to the efficient recovery enabled by paramagnetism, NFCG keeps adsorption amount 311.01 mg·g for Co(II) after six consecutive cycles. Moreover, NFCG exhibits selectivity towards Co(II) under the coexistence of common interfering substances. Adsorption fitting suggests chemical adsorption based on heterogeneous affinity. Spectroscopic analysis discloses, CO, CO, -C(=O)NH-, OH and aromatic part contribute to Co(II) adsorption via electron donation, forming CoO bond. This atomic scale adsorption mechanism was substantiated by HSAB theory calculation. In brief, this work provides basic knowledge and technical support for fabricating high efficiency magnetic bio adsorbent.