Montmorillonite-supported Ag/Sn@CeO₂ via phyto-mechanochemical engineering: enhanced crystal violet adsorption and...

Crystal Violet (CV) dye and CO₂ emissions represent two major environmental threats that demand cost-effective and multifunctional remediation materials. In this study, a silver/tin co-doped cerium oxide nanocomposite supported on montmorillonite (Mt-Ag/Sn@CeO₂) was synthesized via continuous phyto-mechanochemical twin screw extrusion using Melothria scabra leaf extract as a green reducing agent. The composite was characterized by using FTIR, XRD, SEM, EDS, zeta potential, N₂ adsorption-desorption isotherm, BJH pore size analysis, and ICP-OES. The adsorption performance of Mt-Ag/Sn@CeO₂ and Ag/Sn@CeO₂ toward CV dye was systematically evaluated by optimizing pH, contact time, adsorbent dose, initial dye concentration, and temperature. For CV dye removal, Mt-Ag/Sn@CeO₂ achieved 96.08% removal compared with 89.22% for Ag/Sn@CeO₂ (10 mg L^-1 dye, 20 mg dose, pH 9, 298 K, 180 min). The maximum adsorption capacities, estimated from the Langmuir model, were 36.50 mg g^-1 and 28.77 mg g^-1, respectively. Adsorption data were best described by the Freundlich isotherm alongside the pseudo-second-order kinetic model, consistent with chemisorption on a heterogeneous surface with multilayer dye uptake. Thermodynamic analysis confirmed that the adsorption process is exothermic and spontaneous (ΔG° < 0 at all studied temperatures). Furthermore, Mt-Ag/Sn@CeO₂ demonstrated CO₂ adsorption capacity of 3.92 mmol g^-1 at 298 K and 900 mmHg, surpassing several reported clay-based adsorbents. These results confirmed that the mechanochemically engineered Mt-Ag/Sn@CeO₂ composite is an effective dual-function adsorbent with potential for simultaneous water and air remediation.