Tailored multifunctional composite hydrogel based on chitosan and quaternary ammonium ionic liquids@montmorillonite with different chain lengths for effective removal of dyes and 4-nitrophenol

Herein, quaternary ammonium ionic liquids (DM) with different chain lengths was successfully synthesised for the removal of sodium montmorillonite (MMT) and a composite hydrogel (DMCHA) was prepared. The hydrogel was used for the synergistic removal of organic pollutants such as cationic dyes (methylene blue: MB, rhodamine B: RhB), anionic dyes (methyl orange: MO, indigo red: IC) and nitrobenzene compounds (4-nitrophenol: 4-NP) from wastewater. Notably, the maximum adsorption amounts of MB, MO, IC and RhB were 349.68, 325.42, 306.08 and 332.85 mg/g, respectively, at 298.15 K. The reduction of 4-NP by composite hydrogels loaded with Ni-NPs showed excellent catalytic performance (Kapp = 0.17). The adsorption process of DM16CHA on dyes conforms to the Langmuir model, obeys the proposed first-order model of intraparticle diffusion, and is spontaneous and heat-absorbing. Selectivity experiments with mixed dyes solutions indicate promising applications for DM16CHA. The adsorption mechanism of DM16CHA on the four dyes was mainly based on electrostatic and hydrogen bonding interaction. The cyclic adsorption experiments showed that DM16CHA has excellent recyclability. Furthermore, DM16CHA has excellent antimicrobial and mechanical properties that endow the gel-based adsorbent with contamination resistance and durability. The DM16CHA provides an economical, efficient, green and promising strategy for industrial wastewater treatment and environmental protection.