A critical review on the removal of anionic dyes by cross-linked resin: Recent progress, challenges and future perspective

Anionic dyes find widespread applications in an array of industrial processes, which leads to generation of toxic dye wastewater that is of great environmental concern. Adsorption is a widely used method for dye removal because of its effectiveness and simplicity. In particular, cross-linked resins are pivotal due to the advantages of fine-tuning their porosity, surface functionalities, and ease of regeneration under milder conditions. Herein, we wish to provide recent advances on the challenges and opportunities of adsorptive removal of anionic dyes from contaminated water by hyper-crosslinked resins. We present a brief critical comparative analysis of the existing approaches for the removal of anionic dyes, followed by extensive elaboration on the adsorptive removal of anionic dyes by polymeric resins. Discussion on the role of porosity, surface area, and presence of active functionalities in the adsorption efficiency is covered. In addition, critical factors such as optimization of maximum adsorption capacity, adsorption mechanisms that influence dye separation, and regeneration/recyclability of adsorbents are also reviewed. Moreover, we have delineated in detail the influence of pH on the structure and properties of anionic dyes. Furthermore, a detailed discussion on the toxicity and hazardous effects of anionic dyes on human health, aquatic life and the environment, have been reviewed. Finally, a discussion on the research gaps and possible viable solutions on the topic is also covered. We believe that this review will provide a basis to discover efficient and cost-effective adsorbents for the removal of anionic dyes from wastewater.