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Dyes are one of the most hazardous chemicals causing significant environmental pollution and affecting water quality. Majority of the existing methods for dye removal and degradation involve synthetic membranes and use of hazardous chemicals, further resulting in secondary pollution. The present study reports polysaccharide based novel composite hydrogel as biodegradable matrix for pH-responsive selective adsorption of cationic/anionic dyes. This membrane showed pH-responsive adsorption of methyl green (MG) and methyl orange (MO) with similar adsorption equilibrium, i.e., 315 and 276 mg g−1, respectively. Interestingly, selective adsorption at different pH has allowed separation of dye mixtures that holds incredible industrial importance for dyes recovery. The hydrogel matrix was able to completely separate MG, a model cationic dye at neutral pH from the dye mixture whereas, it was possible to remove 60% MO, a model anionic dye at acidic pH. Furthermore, comprehensive isothermal and kinetic studies of adsorption revealed that Freundlich isotherm describing the multilayer coverage and pseudo-second-order kinetics were followed. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. In fact, the membrane was reusable for at least ten cycles and exhibited desorption efficiency of 80 and 60% for MO and MG, respectively, which may be further recycled to make the process environmentally sustainable. Overall, this study proposes an inexpensive, simple, biologically safe, and efficient adsorbent material for dye effluent treatment.

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Hydrogels are a soft material that undergoes cross-linking between polymers to form a hydrophilic three-dimensional network. In fact, similarity to body tissue, soft consistency, biocompatibility, and elasticity, impart a protagonic role of hydrogel to be applied as a biomaterial. In response to external cues, stimuli-responsive hydrogels are particularly impactful, enabling remarkable levels of control over material properties. They can endure changes in swelling behavior, permeability, network structure, and mechanical strength. Nevertheless, such changes induce single-cycle or reversible transitions, so hydrogels can regain their initial state once the trigger is removed. Recently, polysaccharide-based hydrogels with stimuli-responsive properties resulted in developing biomimetic structures for a widespread biotechnological application owing to their excellent biodegradability, biocompatibility, nonimmunogenicity, functional properties, ease of gelation, and derivatization. This review will initially highlight recent advances in cross-linking methods and chemistry for preparing stimuli-responsive hydrogels. Subsequently, state-of-the-art techniques to understand the structural, chemical, and rheological behavior of polysaccharide-based stimuli-responsive hydrogel will be discussed. Additionally, the responsiveness of polysaccharide hydrogel toward diverse stimuli such as redox, temperature, light, pH, magnetism, electricity, etc., with a broad spectrum of applications will be described in detail. This review also attempts to address the lacunae of existing stimuli-responsive hydrogel and their future perspectives.