Garlic (Allium sativum) extract mediated synthesis of self-redox SnO₂ nanomaterials for reduction of Cr(VI) under dark condition

Hexavalent chromium [Cr(VI)] is a highly toxic heavy metal mainly released from various industrial processes. Its high-water solubility allows to readily enter the human body and posing serious health risks. Therefore, its remediation through catalytic reduction is an essential and effective treatment strategy. In this study, a green technology approach was employed to synthesize SnO₂ catalyst nanomaterials, with varied properties, for the reduction of Cr(VI) under dark condition. Various ratios of the two tin precursors, SnCl₂·2H₂O and SnCl₄·5H₂O, were used to modulate the catalyst characteristics. An extract from fresh garlic (Allium sativum) served as an efficient nucleating and precipitating agent for the formation of SnO₂ nanoparticles. The electronic properties, morphologies, crystal phases, and chemical states of the resulting SnO₂ nanomaterials were characterized. The SnO₂ nanocatalyst synthesized from SnCl₂·2H₂O (Sn-2) demonstrated 100 % Cr(VI) reduction efficiency within 14 min with a rate constant 68 times higher than SnO₂ derived from SnCl₄·5H₂O (Sn-4), which itself showed only 5.6 % reduction activity. Remarkably, combining equal weight ratios of both precursors to produce SnO₂ catalyst enhanced the Cr(VI) reduction to 100 % within 10 min. The presence of point defects and self-redox interactions between Sn²⁺ and Sn⁴⁺ in SnO₂ played pivotal roles for the reduction of Cr(VI) under dark conditions. Taken together, the green synthesized SnO₂ nanomaterials could offer significant potential for environmental remediations and public health protection.