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

Chromium (VI) is a ubiquitous groundwater contaminant and it is dangerous to both ecological and human health. Iron nanoparticles (<i>n</i>Fe) 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 <i>n</i>Fe 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 <i>n</i>Fe 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 <i>n</i>Fe had a core-shell structure, where Fe (0) constituted the core and a shell was composed of iron oxide. Finally, a mechanism for synthesizing <i>n</i>Fe by green tea extract was proposed, providing a theoretical basis for optimized synthetic conditions for preparing <i>n</i>Fe when using green tea extract.