Green synthesis of tannic acid functionalized graphene hydrogel to efficiently adsorb methylene blue

Abstract Tannic acid (TA) functionalized graphene (TA-rGO) was synthesized by a simple and green method using TA as both reducing agent and capping agent, avoiding the use of additional chemical stabilizers. pH-responsive TA functionalized graphene hydrogel (TRGAA) was then synthesized by random copolymerization of 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPSA) and acrylic acid (AA) in the presence of TA-rGO. The chemical composition and molecular structure of the resulting hydrogel were characterized by means of FTIR, XPS, Raman spectra, TGA, and SEM. The effects of adsorbent category, pH value, initial dye concentration, adsorption time, and adsorption temperature on the adsorption process were systematically studied. The results indicated that the introduction of AMPSA and AA had significantly improved the adsorption capacity of the hydrogel. The adsorption behaviors of the hydrogel conformed to Langmuir isothermal model and pseudo-second-order model. The adsorption capacity of TRGAA hydrogel to methylene blue was significant, with the maximum adsorption capacity of 1000 mg/g. In addition, ethanol was used as the desorbent to investigate the reuse efficiency, and TRGAA hydrogel could still maintain a good adsorption effect even after 6 adsorption-desorption cycles. TRGAA hydrogel was an ideal adsorbent for cationic dyes, which was owing to the synergistic effect of distinctive chemical composition and porous layered structure. This work based on the green synthesis and high adsorption capacity of TRGAA hydrogel might has important theoretical significance and practical value for developing the application of graphene-matrix composite materials in the field of environmental protection.