Mechanistic and modeling insights into caffeine adsorption on triazole and terephthalic acid functionalized Mg-Zn-Fe...

The pervasive presence of caffeine in water bodies demands efficient remediation strategies. This study developed novel triazole (TZ)- and terephthalic acid (PDC)-functionalized Mg-Zn-Fe layered double hydroxides (LDHs) for caffeine (CFN) adsorption. Composites were characterized (FTIR, XRD, BET, TGA, FESEM) and process variables optimized via Box-Behnken design/RSM. Adsorption followed pseudo-second-order kinetics and the Langmuir isotherm, indicating chemisorption-driven monolayer uptake. Advanced statistical physics modeling provided deeper mechanistic insight, revealing a multi-dentate adsorption geometry (n = 0.64-0.81), governed by π-π interactions, hydrogen bonding, and complexation (ΔE = 12.37-16.53 kJ mol^-1). The process was spontaneous, endothermic, and exhibited excellent reusability (>61% capacity after 5 cycles) with strong resilience to humic acid and competing ions. A scaling cost-analysis projected operational expenses as low as $0.124-$1.421 per 100 L of treated water. The novelty resides in the first simultaneous use of nitrogen-heterocyclic (TZ) and aromatic dicarboxylate (PDC) ligands within a ternary Mg-Zn-Fe LDH framework, integrated with the Advanced Monolayer statistical physics model, RSM optimization, and techno-economic analysis in a unified caffeine remediation study. In conclusion, TZ- and PDC-functionalized Mg-Zn-Fe LDHs are highly effective, economical, and scalable adsorbents for caffeine removal, offering a promising solution grounded in tunable chemistry and multi-scale mechanistic understanding.