Green Synthesis of pH-Responsive, Self-Assembled, Novel Polysaccharide Composite Hydrogel and Its Application in Selective Capture of Cationic/Anionic Dyes

Abstract

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.

Stimuli-Responsive Polysaccharide-Based Smart Hydrogels and Their Emerging Applications

“…The presence of oppositely charged polyelectrolytes undergoes strong electrostatic interactions to yield a self-assembled polyelectrolyte complex (PEC). , Hence, the participating polymers must be ionized and possess opposite charges. In the case of natural polysaccharides, chitosan most commonly forms PEC via electrostatic interaction between its positive amino group and opposite negative groups of numerous polyelectrolytes such as alginate, gellan, and κ-carrageenan . Srivastava et al reported PEC formation among a cationic amino group of chitosan along with an anionic carboxylate group of gellan and a sulfate group of κ-carrageenan to fabricate green self-assembled pH-responsive hydrogel .…”

“…47 Moreover, osmotic pressure generated by the electrostatic interaction through ion and counterion movement triggers the swelling capacity of ionic polysaccharides. 29 Due to the natural diffusion of swelling medium into polymers, their porous structure forms capillary channels that account for pH change responses. In contrast, a hydrogel with cationic charges containing a positive pendant group, such as amines, exhibits swelling when the pH falls below the pK b due to protonation responsible for increased electrostatic repulsion.…”

“…As a result, this spectrum can be used to determine how the components of a composite hydrogel are cross-linked. Simultaneously, a change in the fingerprint region’s FT-IR spectrum, such as adding, omitting, or shifting the peaks, is critical to the confirmation of a hydrogel formation . Also, polysaccharides are known to have abundant hydroxyl and carbonyl groups.…”

“…In addition, the interconnected porous structure facilitates the penetration of water into the gel network, allowing the adsorption of heavy metal ions and dyes onto the active adsorption sites. In this regard, Srivastava et al fabricated gellan/ κ-carrageenan/chitosan (GG/CR/CH) pH-responsive hydrogel via electrostatic interaction devoid of any chemical cross-linker . Based on its pH-responsive swelling capacity due to the presence of ionic polysaccharides, this hydrogel was capable of successfully adsorbing and separating both cationic and anionic toxic dyes.…”

Mussel-Inspired Magnetic Dissolving Pulp Fibers Toward the Adsorption and Degradation of Organic Dyes

“…Adsorption is one of the most effective methods to treat organic dyes, and it is widely used because of its relatively low cost and easy operation. Various adsorbents have been designed to remove dyes in water and have considerable adsorption capacities, such as activated carbon ( Tang et al, 2017 ; Zhang et al, 2019 ; Soares et al, 2021 ), functional carbon materials ( Magno et al, 2020 ; Xing et al, 2020 ; Zhang et al, 2020 ), composite hydrogel ( Srivastava and Roy Choudhury, 2021 ), and metal oxide ( Rastogi et al, 2017 ; Xu et al, 2020 ; Şerban and Enesca, 2020 ). Among these methods, chemistry reduction has gained popularity because of its ease of use, high efficiency, clean processing, and low cost.…”