Green Synthesis of Iron Nanoparticles Using Green Tea and Its Removal of Hexavalent Chromium

Abstract

Chromium (VI) is a ubiquitous groundwater contaminant and it is dangerous to both ecological and human health. Iron nanoparticles (nFe) have a large specific surface area and they are highly efficient in removing chromium (VI) from aqueous solution. However, since the traditional reductive synthesis of nFe is relatively expensive and often causes secondary pollution, it is necessary to develop a low-cost green synthetic method using plant extracts. Synthetic conditions are important for obtaining highly active chromium-removing nanomaterials. In this paper, a green tea extract was used to prepare nFe and the effects of synthetic conditions on subsequent remediation performance were investigated. The optimal conditions included a green tea extract/Fe2+ ratio of 1:2 (91.6%), a green tea extract temperature of 353 K (88.3%) and a synthetic temperature of 298 K (88.1%). Advanced material characterization techniques, including XPS, SEM-EDS, TEM, and Brunauer–Emmett–Teller (BET) confirmed that the average particle size was between 50–80 nm, with a specific surface area of 42.25 m2·g−1. Furthermore nFe had a core-shell structure, where Fe (0) constituted the core and a shell was composed of iron oxide. Finally, a mechanism for synthesizing nFe by green tea extract was proposed, providing a theoretical basis for optimized synthetic conditions for preparing nFe when using green tea extract.