Design and characterization of three pillar[5]arene-functionalized microcrystalline celluloses as a green adsorbent for efficient removal of methylene blue from aqueous solutions: a comparative study

Methylene blue (MB) is a cationic dye widely used in textile and other industries and its removal is vital as it is a serious environmental pollutant due to its persistence in wastewater. For this purpose, the surface of microcrystalline cellulose was firstly derivatized with a pillar[5]arene derivative and multi amine chains. The Uv-vis, TGA, FT-IR, SEM and XRD methods were used for the photochemical, thermal, morphological and structural characterizations of the functionalized surfaces ( MCC-APTMS-P[5] , MCC-TPED-P[5] and MCC-TMPTA-P[5] ). The prepared hybrid materials were used for the removal of MB in optimum conditions. Adsorption isotherm studies were conducted to elucidate the interaction mechanisms between MB and pillar[5]arene-functionalized microcrystalline celluloses. Batch adsorption experiments were conducted to evaluate the effects of various parameters including adsorbent dosage (0.001–0.01 g), pH (1−10), initial MB concentration (5–20 mg/L), temperature (25–55 °C), and contact time (5–180 min). Equilibrium data at different temperatures were evaluated using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models, with corresponding equations and parameters provided to describe the adsorption behavior. The thermodynamic parameters of adsorption—Gibbs free energy change (ΔG, kJ/mol), entropy change (ΔS, J/mol K−1), and enthalpy change (ΔH, kJ/mol) were calculated using the following equations. The maximum monolayer adsorption capacities for MB were determined to be 99.01 mg g−1 for MCC-APTMS-[5] , 103.09 mg g−1 for MCC-TPED-P[5] , and 108.70 mg g−1 for MCC-TMPTA-[5] under the optimized operating conditions of pH 10.0, a temperature of 25 °C (298 K), an adsorbent dosage of 0.0025 g, and a contact time of 30–45 min. The data clearly indicate that the materials developed in this work exhibited significantly higher performance in eliminating MB from aqueous environments.