Synergistic Enhancement of Cr (VI) Adsorption via Al/Mg Co-Doping of UiO-66-NH₂: Synthesis, Characterization, and Mechanistic Insights

Heavy metal contamination in industrial wastewater remains a critical global environmental concern. In this study, an Al/Mg/Zr-MOF (AMZ-MOF) was synthesized via a solvothermal method and systematically evaluated for Cr (VI) removal from aqueous solutions. Comparative analysis demonstrated that AMZ-MOF exhibited superior Cr (VI) removal efficiency relative to pristine Zr-MOF, Mg/Zr-MOF, and Al/Zr-MOF. The synthesized AMZ-MOF composite was subjected to comprehensive characterization using FESEM, TEM, XRD, BET, FTIR, and XPS analyses. The study systematically investigated the influence of key operational parameters, including contact time, temperature, pH, and initial Cr (VI) concentration, on the composite’s sorption behavior. AMZ-MOF demonstrated exceptional performance, achieving a maximum Cr (VI) sorption capacity of 185.2 mg/g. Remarkably, the sorbent exhibited rapid initial uptake kinetics, reaching adsorption equilibrium within 120 min. Mechanistic insight was gained through adsorption isotherm and kinetic modeling, revealing that the process is best described by the Langmuir isotherm and the Pseudo-Second-Order kinetic model, suggesting monolayer adsorption onto a heterogeneous surface and chemisorption as the rate-limiting step, respectively. Further FTIR and XPS analyses corroborated the proposed sorption mechanism, clarifying the key functional groups and surface interactions involved in Cr (VI) removal. The proposed adsorbent demonstrated excellent reusability over five adsorption–desorption cycles, underscoring its stability and practical potential for Cr (VI) remediation.