Recent advances in nanoadsorbents for the efficient removal of nickel ions from aqueous solutions

Nickel is a toxic and carcinogenic metal, and its existence in water bodies is a major hazard to human and environmental health. Sludge production, high operating costs, and low efficiency at low metal concentrations are some of the shortcomings of conventional nickel elimination treatment strategies like chemical precipitation, ion exchange, and membrane filtration. Nanotechnology effectively removed nickel ions from water. The use of nanotechnology offers an effective route toward the removal of nickel ions (Ni²⁺) from water, and this paper reviews recent advances in nanoadsorbents that are designed for this purpose. Through experimental adsorption studies, surface-functionalization strategies, and isotherm/kinetic modelling, the review highlights that the best carbon-based nanomaterials, metal oxides, biopolymer nanocomposites, and hybrid structures all show better adsorption capacities and faster kinetics compared to bulk materials. Ni²⁺ selectivity is significantly enhanced by functional groups such as amidoxime, carboxyl, thiol, and amine; magnetic nanoadsorbents allow easy separation with stable multi-cycle reuse. Adsorption efficiency is strongly modulated by pH, temperature, contact time, initial metal concentration, and competitive ions, dominated by mechanisms including electrostatic attraction, surface complexation, ion exchange, and chelation. Major challenges lie in limitations in scale-up, production cost, and uncertainties on environmental impacts. Greener synthesis, improvement of regeneration efficiency, and comprehensive toxicity testing are encouraged by the review to promote practical and sustainable applications.