Preparation of citric acid/porous starch composite adsorbents and their adsorption studies

Recently, studies on the removal of methylene blue (MB) in an efficient and environmentally friendly manner and the effective treatment of wastewater polluted by dyes have attracted significant interest from researchers in fields ranging from fundamental environmental research to applied chemical engineering. Herein, a citric acid (CA)-based polymeric adsorbent, porous starch-citric acid (PST-CA), was initially prepared via a dry and wet reaction by introducing polyhydroxy compounds as the starting material, which was further successfully used for the adsorption treatment of MB. The effects of adsorbent dose, solution pH, contact time, the initial concentration of solution and temperature on the adsorption were thoroughly investigated. In particular, a series of tests revealed that the adsorption mechanism between the adsorbent and MB is chemisorption, mainly relying on electrostatic and hydrogen bonding interactions. The maximum theoretical adsorption capacities of PST-CA-G and PST-CA-S for MB were 381.67 mg g(-1) and 882.96 mg g(-1), respectively. The results of the regeneration tests and the generalization tests showed that this adsorbent is more suitable for the adsorption of cationic dyes and it has favorable reusability. Also, CA-based polymeric adsorbents have great potential for use in dye wastewater applications.