Eco-Engineered Alginate Zr/Mn Hydrogel for Ultra-Efficient Cr(VI) Removal: Insights into Mechanism and Performance

A novel hydrogel composite, Na-ALG@Zr/Mn, was synthesized and tested for its ability to remove toxic hexavalent chromium from water. Advanced characterization techniques, including FTIR, XRD, BET, SEM–EDX, TEM, and XPS, confirmed the formation of a mesoporous structure, effective surface interactions, and successful incorporation of metal oxides. The composite showed outstanding efficiency at low pH (3–4), mainly due to strong electrostatic attraction and redox reactions that reduce Cr(VI) to Cr(III). Kinetic studies align closely with the fractal pseudo-second order model, suggesting that chemisorption primarily drives the process. Isotherm analysis shows the Liu model as the best fit, with a maximum adsorption capacity of 688.8 mg/g at 298 K. Thermodynamic evaluation indicates the adsorption is spontaneous and endothermic, evidenced by negative Gibbs free energy and positive enthalpy change. XPS spectra confirm the reduction of Cr(VI) and its strong interaction with functional groups on the composite surface. To gain a clearer understanding of the electronic properties and how Cr(VI) adsorbs onto the synthesized Na-ALG@Zr/Mn nanocomposite, we performed DFT (Density Functional Theory) calculations with the B3LYP/6-311G(d,p) basis set. These outcomes emphasize Na-ALG@Zr/Mn's potential as a cost-effective, environmentally friendly, and efficient adsorbent for removing Cr(VI) from contaminated water.