Adsorption of methylene blue onto [Emim][Cl] – ionic liquid functionalized spent cigarette filters: Kinetic and thermodynamic analysis

The study explores a sustainable approach to synthesizing ionic liquid (IL) functionalized dried spent cigarette filters (SCF) for the removal of methylene blue (MB) dye from aqueous solutions. The study deals with the porous cellulose structure of SCF functionalizing with 1-ethyl-3-methylimidazolium chloride [Emim][Cl], synthesizing an efficient adsorbent SCFIL. Further XRF, FT-IR studies confirmed the effective functionalization of [Emim][Cl] onto SCF reported an increase in chlorine of SCF from 0.348% to 2.9771%. Whereas BET analysis shows an increase in specific area, pore volume from 0.87 m2/g, 0.002 cm3/g (SCF) to 19.92 m2/g, 0.033 cm3/g (SCFIL) respectively. Furthermore, the SCFIL is tested as an adsorbent for MB dye removal under various parameters; pH (2–10), dosage (1:1–1:3 g), agitation speed (100–400 rpm), equilibrium concentration (0–100 mg L−1), time (0–1400 min). The adsorption behavior followed Langmuir isotherm with qmax = 84.16 mg g−1, while kinetic studies align with pseudo-second order kinetics, indicating the chemisorption as dominating phenomenon. Thermal analysis confirmed the stability of SCFIL, reporting ΔG° values (−0.4438, −0.8030, −1.2448 kJ/mol), ΔS° = 0.04117 J/mol K, and ΔH° of 12.7112 kJ/mol, representing the adsorption process is spontaneous and endothermic. Lastly, reusability studies reported the decreasing efficiency of adsorbent from 80% to 37% after three successive cycles.