Preparation of pH/temperature-sensitive semi-interpenetrating network hydrogel adsorbents from sodium alginate via photopolymerization for removing methylene blue

Sodium alginate-based hydrogels are particularly attractive because of their special properties such as biocompatibility, biodegradability, renewability, and ion exchange properties, and their mechanical performance can be greatly improved through forming semi-interpenetrating networks. Herein, a pH/temperature-sensitive semi-interpenetrating network hydrogel was fabricated by photopolymerization of N, N-dimethylacrylamide, N-isopropylacrylamide, and N, N'-methylenebisacrylamide in the presence of sodium alginate. The swelling ratio of the hydrogels reached 3263% in distilled water when the molar ratio of monomer to crosslinker was 150:1 and mass concentration of sodium alginate was 2%. The hydrogels were pH/temperature sensitive, and their swelling behavior had good cycling performance. Selective adsorption experiments showed that the hydrogel had good adsorption selectivity for the cationic methylene blue in binary dye systems. The maximum adsorption capacity was 151.79 mg/g with 250 mg/L methylene blue solution, 35 °C and pH = 10. The adsorption behavior could be well described by Langmuir isothermal model and pseudo-second-order kinetic model, suggesting that methylene blue adsorption was monolayer chemisorption. The adsorption capacity was still 75.91% of the initial adsorption capacity after five consecutive adsorption–desorption cycles, revealing that the adsorbent possessed good regeneration capacity. The efficient adsorbent described here was prepared by a facile strategy, so it holds great potential in wastewater treatment.