Recent advances on composite hydrogels designed for the remediation of dye-contaminated water and wastewater: A review

Dye-contamination in water supplies, industrial effluents, and rivers is one of the major water pollution issues. It has put at risk the drinking-water supplies around the globe. Various remediation approaches have been extensively developed and tested to minimize this worrying scenery. In particular, adsorption techniques are often ranked as one of the most prominent strategies to treat dye-contaminated water likely due to their attractive practical and economic advantages. Overall, the efficiency of adsorptive removal of dyes from water is closely related to the adsorbent material features, which has a critical role in this process. Currently, thousands of materials (raw or processed) have been tested as adsorbents. Otherwise, none of them have achieved the prominent status assigned to the hydrogels. Frequently labeled as an ideal adsorbent, the leading role of these soft materials towards the adsorptive removal of dyes from the water was consolidated almost two decades ago, when the introduction of different materials into the hydrogel matrices resulted in composite materials with unique properties. In this paper, an entirely conceptual and critical review of literature is presented, focusing on the tremendous potential of composite hydrogels to remediate dye-contaminated water. Specifically, the main advances related to the use of composite hydrogels containing clay minerals, carbonaceous materials, organic fibrils and whiskers, magnetic and metallic particles, and other inorganic fillers are reviewed in this paper. Additionally, general methods to prepare composite hydrogels, the main effects ascribed to the composite formation are addressed in this paper. Finally, the main drawbacks and challenges associated with the application of these types of hydrogels are reviewed to understand the research gap and limitations regarding their practical use. We believe that the information provided in this review paper may contribute to enhance the scientific basis for the practical and efficient use of these fascinating adsorbent materials. (C) 2020 Elsevier Ltd. All rights reserved.