Reduction of carcinogenic chromium by green synthesized nickel nanoparticles: A sustainable approach for environmental remediation

Hexavalent chromium (Cr (VI)) contamination in water sources poses severe environmental and health risks due to its carcinogenic nature. Recent advances in nanotechnology have reported promising solutions for remediating Cr (VI)-contaminated environments. Compared to bulk zero-valent iron, nano-nickel exhibits superior electrical conductivity and facilitates faster electron transfer during redox reactions, thereby enhancing Cr (VI) reduction efficiency. Unlike zero-valent iron, which oxidizes readily, nano-nickel is more resistant to corrosion, offering greater stability in aqueous environments and extending its functional lifespan. This study investigates the efficacy of green-synthesized nickel nanoparticles (Ni NPs) for reducing Cr (VI) to the less toxic trivalent chromium (Cr (III)). Ni NPs were synthesized using an eco-friendly approach with Ocimum sanctum (Tulsi) seed extracts serving as both reducing and stabilizing agents. The synthesized Ni NPs were characterized using FE-SEM, TEM, EDS with elemental mapping, XRD, XPS, and FTIR techniques. Batch experiments were conducted to assess Cr (VI) reduction under varying conditions, including Ni NP dosage, initial Cr (VI) concentration, pH, and contact time. Results showed efficient Cr (VI) reduction, with a significant decrease in Cr (VI) concentration within 20 minutes. The effect of pH was also studied, revealing an optimal reduction at pH 2. Kinetic analyses further elucidated the reduction mechanism, showing that the reaction follows first-order kinetics with a high linear regression coefficient (R 2 = 0.9764–0.9923) across tested concentrations. These findings demonstrate that green-synthesized Ni NPs provide an efficient, eco-friendly, and cost-effective strategy for Cr(VI) remediation, supporting sustainable approaches for environmental protection and public health. • Green Ni nanoparticles synthesized using Ocimum sanctum (Tulsi) seeds. • Ni NPs efficiently reduce carcinogenic Cr (VI) to less toxic Cr (III). • Nearly 100% Cr (VI) reduction achieved within 20 minutes at pH 2. • Reduction follows first-order kinetics with high correlation (R² > 0.97). • Ni NPs show excellent recyclability with >99% efficiency over 5 cycles.