Comprehensive understanding of adsorption and reduction on 2,4-DCP and Cr(VI) removal process by NZVI-rGO: Performance and mechanism

Abstract

In this study, nano zero-valent iron-reduced graphene oxide (NZVI-rGO) was successfully synthesized and applied for 2,4-DCP and Cr (VI) removal. Characterization results show that NZVI particles were successfully loaded on rGO nanosheets increasing the dispersibility of particles. Removal experiments indicate that the existence of rGO significantly enhanced the removal efficiency of 2,4-DCP and Cr (VI) compared with bare nano zero-valent iron. The removal rate of 2,4-DCP and Cr(VI) increased from 33.24 % and 63.14 % to 100 % and 98.40 %, respectively. Pseudo-second-order model and Langmuir isotherm model could better explain the 2,4-DCP removal process. The removal mechanism of 2,4-DCP in the process of simultaneous removal is adsorption, including π-π interaction, hydrogen bonding and n-π EDA interaction between Cr(VI) and 2,4-DCP. Cr(VI) is firstly fixed on the surface of NZVI-rGO by electrostatic interaction. The electrostatic interaction between γ-FeOOH and Cr(VI) and the strong connection formed by n-π EDA interaction between Cr(VI) and 2,4-DCP promote the adsorption of Cr(VI) in coexisting system. Subsequently, Cr(VI) is reduced to Cr(III) by accepting the electrons donated by NZVI, and Cr(III) interacts with OH− in the solution to generate Cr(OH)3 precipitate. The existence of rGO accelerates the rate of electron transfer to Cr(VI) in NZVI. This study provides theoretical support for remediation of combined pollution of chlorinated organics and heavy metals.