Synthesis, characterization and use of amphoteric hydrogels in cationic and anionic dye adsorption

Abstract

This study looked into the synthesis of amphoteric hydrogels and the use of hydrogels in the adsorption process to remove dyes from aqueous solutions. Sodium 4-vinylbenzenesulfonate (4VBS), [2-(Methacryloyloxyloxy)ethyl]trimethylammonium chloride (MOEAMCl) monomers, N,N'-methylenebisacrylamide (MBAAm) crosslinker, and ammonium persulfate (APS) radical initiator were used to produce hydrogels in adsorbent synthesis investigations. Techniques like TGA, SEM, and FTIR were used to characterize the hydrogels. The synthesized hydrogels were subjected to swelling tests in a variety of conditions (buffer solutions at pH levels of 3, 5, 8, and 10, as well as in urea and sodium chloride solutions). According to the swelling results, the hydrogels exhibited the highest swelling behavior at pH 3, with a decrease in swelling as the pH increased. A significant reduction in swelling ratios was observed with increasing 4VBS monomer concentration at pH 3. For the adsorption studies, tartrazine (TART) was selected as an acidic dye, and methylene blue (MB) as a basic dye, with the hydrogel [4VBS-MOEAMCl (50:50)] (SYB-5) used as the adsorbent. The neutral charge point of SYB-5 was determined to be 4.5. The effects of pH, adsorbent dosage, contact time, initial dye concentration, matrix ion effects, and temperature on the adsorption of TART and MB onto SYB-5 hydrogel were investigated. Under optimal conditions (m = 0.15 g, pH=10, and V = 50 mL), the adsorption capacity of SYB-5 hydrogel for MB was 137 mg/g, and for TART (m = 0.5 g, pH=1.5, and V = 50 mL), it was 11 mg/g.