Efficient elimination of Cr(vi) in groundwater using nano zero-valent iron synthesized with Ginkgo biloba extracts: enhanced mechanism and reduced toxicity

Abstract

Various industrial activities have led to increasingly serious hexavalent chromium (Cr(VI)) contamination in the aquatic environment. Thus, the search for a clean and effective remediation agent is essential. Novel nZVI particles were synthesized from Ginkgo biloba extracts and characterized by SEM with EDS, TEM, FTIR, XRD, and XPS. GB-nZVI had better Cr(VI) removal performance compared to nZVI synthesized from mulberry and hawthorn leaves. A total of 5 mg L⁻¹ Cr(VI) can be completely eliminated at a pH of 3, temperature of 313 K, and dosage of 1.0 g L⁻¹ nZVI. Simultaneously, the pseudo-first-order and -second-order models, internal diffusion model, and Elovich model were employed to fit the removal process of Cr(VI). The fitting results indicated that the elimination of Cr(VI) was achieved via the combined effect of adsorption and reduction. Coexisting ions evidently suppressed the removal of Cr(VI) with the inhibition of NO₃⁻ < Cl⁻ < SO₄²⁻ < HCO₃⁻. Salicylic acid, oxalic acid, and citric acid contributed to the elimination of Cr(VI). Additionally, the tomato seed toxicity test demonstrated that the germination rate of the Cr(VI) solution treated with GB-nZVI was up to 95.55%, while that of the untreated Cr(VI) solution seeds was only 48.89%. An aging experiment that proceeded for 15 days showed that GB-nZVI could still remove 94.36% of Cr(VI), which is much higher than that achieved by nZVI (49.17%). The effective reduction of Cr(VI) proves the development potential of the green synthesis of nZVI from Ginkgo biloba extracts.