Environmentally Benign Synthesis Methods of Zero-Valent Iron Nanoparticles

Zero-valent iron nanoparticles (nZVI) have already proven their efficacy in the reductive disposal of a wide array of environmental contaminants in numerous laboratory and field trials. However, their large-scale application in remediation applications is hindered by the high costs and the legislative issues associated with the conventional nZVI synthesis method that relies on NaBH4 as a reducing agent. The two common strategies to replace sodium borohydride are (i) totally "green" nZVI syntheses based on plant extracts, and (ii) "semigreen" nZVI synthesis based on less toxic and more cost-effective industrial chemical reducing agents. In this paper we present a comparative evaluation of green and semigreen synthesis methods. The former utilized coffee, green tea, and Virginia creeper (Parthenocissus tricuspidata) leave extracts, the latters were based on sodium dithionite and sodium borohydride. nZVI synthesis was done in untreated tap water at room temperature to reduce the environmental footprint of the process. nZVI performance was assessed on the basis of time-dependent oxidation/reduction potential measurements and also by the reductive dehalogenation of volatile chlorinated organics in groundwater samples from an actual field test.