Biodegradable genipin cross-linked chitosan/pea protein isolate sponges for effective adsorption of methyl blue: Batch experiments and quantum chemical analysis

[Display omitted] •Double cross-linked chitosan/pea isolate protein sponge adsorbents were prepared.•Pea isolate protein improves the adsorption capacity of the sponge for dye.•The Qm of composite sponges for MEB dye were 1003.28 mg/g.•The electrostatic and hydrogen bond interactions were the adsorption mechanisms.•Composite sponges are capable of degrading more than 70 % in soil in 21 days. This study successfully prepared double crosslinked chitosan (CS) and pea protein isolate (PPI) composite sponges using genipin as a crosslinking agent and investigated their effectiveness as an adsorbent for methyl blue (MEB) in aqueous solutions. The composite sponges were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller measurement, swelling tests, gel fraction measurement, zeta potential, and X-ray diffraction. Additionally, the effects of genipin content, pea protein isolate content, sponge dosage, initial pH of the solution, adsorption time, dye concentration, and adsorption temperature on dye removal ability were studied. The results showed that at pH 3.0 and a dye concentration of 100 mg/L, the adsorption capacity of the sponge for methyl blue was found to be 351.6 mg/g. At 298 K and after 720 min, with a dye concentration of 700 mg/L, the maximum adsorption capacity of the sponge for methyl blue reached 959.3 mg/g. The adsorption process follows a pseudo-second-order kinetic model and a Langmuir isotherm. Theoretical analysis using density functional theory suggests that the adsorption of methyl blue by the composite sponge is attributed to the anionic sulfonic acid group of the dye. The composite sponge degraded 76.1 % after being buried in soil for 21 days. This study reveals the enormous potential of biodegradable chitosan-protein-based sponges in effectively removing methyl blue dye pollutants from wastewater.