Review on nickel-based adsorption materials for Congo red.

Excessive synthetic dyestuffs in the aquatic environment pose various ecological and health issues that are detrimental to sustainable development. Adsorption is considered a feasible technique of eliminating dye pollutants from the water environment because of its advantages of high efficiency, low cost, easy operation, and absence of secondary pollution. Among the many dyes, Congo red (CR) is a widely used azo dye. Nickel-based materials, including nickel hydroxide, nickel oxide, nickel-containing layered double hydroxides, nickel-based spinel and metal-organic frameworks, metallic nickel, nickel-based sulfide, and nickel composites, have been extensively studied for CR adsorption due to their morphological diversity, large specific surface area, and strong affinity toward CR. However, fabricating nickel-based adsorbents with high efficiency and stability and excellent recyclability for practical application remains a challenge. This review outlines the research progress of nickel-based materials in CR adsorption. The interaction between CR molecules and nickel-based adsorbents is systematically presented, and the possible adsorption mechanisms are summarized. Finally, the challenges and future development directions of the practical application of nickel-based adsorbent materials are proposed.