Nanoscale Zero-Valent Iron / Silver@Activated Carbon-Reduced Graphene Oxide: Efficient Removal of Trihalomethanes from Drinking Water

Abstract

AC-supported nanoscale zero-valent iron composites (nZVI/AC) exhibit significant environmental implications for trihalomethanes (THMs)-contaminated water remediation. To improve the adsorption and degradation capability of AC, herein, a composite (AC-RGO@nZVI/Ag) consisting of AC, reduced graphene oxide (RGO), nanoscale zero-valent iron (nZVI), and silver (Ag) was synthesized and characterized using several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, N 2 adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The analysis of textural and morphological structures showed that a tightly-attached RGO film, amorphous iron, and weak crystal silver nanoparticles with a size of 20 ‒ 30 nm were evenly immobilized on the support. Specific surface area increased by 19.12% after supporting RGO, and it decreased after supporting nZVI and Ag due to partial blockage of micropores. The experimental results showed that 0.75% Fe and 0.44% Ag were immobilized on the AC-RGO composite. The surface of Fe was concurrently coated by iron oxides (Fe 2 O 3 , FeOOH) and Ag. The adsorption capacity of THMs in descending order was AC-RGO@nZVI/Ag > AC-RGO@nZVI > AC-RGO > AC. THMs molecules were eliminated through multilayer reaction processes. In these processes, CHBrCl 2 and CHBr 2 Cl are mainly decomposed into CH 3 Cl and CH 2 Cl 2 , and CHBr 3 and CHCl 3 are primarily degraded into CH 2 Br 2 and CH 2 Cl 2 , respectively. The existence of more Br atoms in THMs molecules was beneficial to the removal efficiency and adsorption capacity of THMs, along with a higher oxidation degree of the Fe surface. Conclusively, THMs-contaminated water could be remediated by coupling the AC pre-enrichment and the reactivity of nZVI/Ag.

Keywords: Activated carbon, Reduced graphene oxide, Nanoscale zero-valent iron, Silver, Trihalomethanes