Hexametaphosphate cross-linked chitosan beads for the eco-efficient removal of organic dyes: Tackling water quality

There is an increasing trend of developing various low-cost grafted natural amino polysaccharides for the biosorptive removal of noxious dye effluents like Malachite green (MG) and anionic Reactive Red-195 (RR-195) dyes from aqueous solution. Chemically cross-linked chitosan microsphere (CTS-HMP), a promising non-toxic biosorbent possessing high charge density and thermal stability was prepared by using hexametaphosphate as ionic cross-linker. Batch biosorption experiments were carried out under different temperatures (298, 308 and 318 K), pH (2.0-10.0), initial concentrations (25-250 mg L-1), adsorbent dosage (0.01-0.1 g) and contact times (0-180 min) to understand the optimum experimental conditions and simultaneously evaluate the adsorption isotherms and kinetics of CTS-HMP. Biosorption equilibrium was established in 120 and 60 min for MG and RR195 removal process. The pseudo-equilibrium process was best described by the pseudo-second-order kinetic (R-2 >= 0.98), Freundlich and Temkin isotherm model (R-2 >= 0.90). The removal rate of MG and RR-195 gradually increased (69.40 and 148 mg g(-1)) at 250 mg L-1 of initial concentration till 100 and 50 min of contact period in a single contaminant system, though the removal efficiency of acid dye was-2 times higher compared to basic dye under optimum conditions (p < 0.05; t-test). Thermodynamic parameters indicated exothermic (MG) and endothermic (RR-195) nature of spontaneous dye removal. The activation energy of sorption (E-a) was <50 kJ mol(-1) which highlighted the importance of physical adsorption process. Therefore, the obtained results clearly validate the sustainable utilization of CTS-HMP as a promising functionalized chitosan microparticles/agent for removing dye effluents from the contaminated aqueous phase.

Automated summary

The study shows that chemically cross-linked chitosan microsphere can effectively remove dyes from wastewater, with the best removal efficiency at 69.40 and 148 mg g(-1) under certain experimental conditions. The removal rates of different dyes vary under optimal conditions, as shown by adsorption isotherm and kinetics analysis. Parameters like temperature, pH, initial concentration, adsorbent dosage, and contact time have significant impacts on the removal efficiency.