Adsorptive sequestration of cationic dyes from aqueous medium using a novel carom seed-activated carbon/Mg-doped SnO2 nanocomposite

In the recent past, metal oxide-based biomass-activated carbon nanocomposites have garnered significant attraction for adsorptive removal of many aquatic contaminants. In this study, a novel nanocomposite adsorbent prepared of Mg-doped SnO 2 NPs and carom seed-activated carbon (CS-AC) was evaluated for adsorptive performance and efficacy towards two cationic dyes, methyl violet (MV) and malachite green (MG) from aqueous solutions. The CS-AC was prepared using 10% polyphosphoric acid (CS:H 6 P 4 O 13 = 3:1) as an activator, while Mg@SnO 2 NPs were obtained through a green route. The physicochemical characteristics of the carom seed-activated carbon/Mg-doped SnO 2 nanocomposite, CS-AC/Mg@SnO 2 NC were described by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy-energy dispersed X-ray spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller (BET) analysis. The specific surface area of CS-AC/Mg@SnO 2 NC, quantified by BET analysis, was 70.97 m 2 /g. The batch adsorption method was employed to determine the optimal operational conditions for dyes removal, which were found to be dosage (MV; MG: 0.35 g/L), contact time (MV; MG: 15 min), initial solution pH (MV: 6; MG: 5), operating temperature (MV; MG: 298 K) and initial concentration (MV; MG: 40 mg/L). The modelling of equilibrium results using different isotherm models corresponded well to the Temkin and Langmuir models for MV and MG, respectively with a Langmuir saturation capacity of CS-AC (185 mg MV/g and 219 mg MG/g) and CS-AC/Mg@SnO 2 NC (195.0 mg MV/g and 276.0 mg MG/g) at 298 K. The kinetics of the reaction was appropriated by the pseudo-second order model with both intraparticle and liquid film models governing the diffusion. The thermodynamic parameters demonstrated spontaneity/feasibility (negative Δ G °) and exothermic (negative Δ H °) nature of the dye’s elimination process. The adsorption process was principally driven by pore filling, electrostatic interaction, π–π, n –π interaction, van der Waals and hydrogen bonding. The exhausted adsorbent was regenerated using ethanol as a desorbing solvent. The CS-AC/Mg@SnO 2 NC exhibited high reusability with an adsorption efficiency of 71% (MV) and 68% (MG) up to the fifth cycle. The aforementioned results demonstrated a considerable potency of the CS-AC/Mg@SnO 2 NC for the economical and effective depollution of cationic dyes particularly MV and MG from the liquid phase.