Site Energy Distribution Coupled with Statistical Physics Modeling for Cr(VI) Adsorption onto Coordination Polymer Gel.

In this work, a novel pristine coordination polymer gel composed of zirconium and 2-amino-5-mercapto-1,3,4-thiadiazole is unveiled and explored to remove Cr(VI) from aqueous systems. A Box-Behnken design, coupled with a genetic algorithm and desirability function, was used for optimizing the controllable factors for maximum removal efficiency. Under optimized conditions (A = 50 mg L, B = 40 mg, C = 90 min, and D = 4), 99% of Cr(VI) was removed, and the saturation adsorption capacity recorded was 132.37 mg g. The adsorption data were investigated through statistical physics modeling. The most suited statistical physics model (monolayer with three energies; = 0.994-0.997, χ = 0.008-0.024), combined with site energy distribution analysis, XPS, and FTIR, unraveled the uptake mechanism. At the first and third active sites, Cr(VI) uptake was multimolecular ( > 1), while at the second active site, it was a mixed multimolecular (298 K, > 1) and multidocking (308 and 318 K, < 1). The adsorption energy values indicated the involvement of coordination exchange ( = 53.40-58.47 kJ mol), electrostatic interaction ( = 29.56-32.29 kJ mol), and hydrogen bonding ( = 24.68-28.35 kJ mol) in Cr(VI) adsorption. The BSf(1.5, α) model fitted best ( = 0.976-0.994, χ = 0.023-0.377) to the kinetic data under all conditions. Common coexisting ions had no significant impact on removal efficiency (% > 97% at 1:3), and the sorbent could be reutilized up to 5 uptake-elution cycles (>96% efficiency). The practical utility of ZrAMTD was investigated by remediating Cr(VI) contaminated real water samples (% ≥ 92.91%).