Recyclable green hydrogel adsorbents with excellent adsorption capacity for removal of methylene blue

The recyclable green carboxymethyl chitosan-oxidized sodium alginate-gelatin/polyacrylamide double network hydrogel was simply and rapidly synthesized by one-pot method. This hydrogel with satisfactory mechanical properties was used to adsorb methylene blue, showing a high adsorption capacity, recyclability and environmental friendliness. The results showed that the adsorption of methylene blue solution (50 mL of 50 mg·L–1) with 15 mg of adsorbent resulted in a removal rate of over 93%, and the adsorption rate was still over 86% after 7 adsorption–desorption cycles. The adsorption of methylene blue by hydrogel adsorbents was consistent with the Langmuir adsorption isotherm model and pseudo-second-order kinetic adsorption process, mainly through electrostatic and hydrogen bonding interactions. In this work, the prepared hydrogels have a high adsorption capacity and stable cycle adsorption–desorption, which are beneficial to the application in the purification of dye wastewater.