Removal of AV 90 dye using ordered mesoporous carbon materials prepared via nanocasting of KIT-6: Adsorption isotherms, kinetics and thermodynamic analysis

Abstract

CMK-8 type ordered mesoporous carbon (OMC) materials were prepared by hard-templating method using KIT-6 as a mesoporous silica template. The influence of synthesis parameters on the structural properties of KIT-6 and OMC samples was investigated. In the studied temperature range (60–150 °C), suitable hydrothermal treatment temperature to obtain well-ordered mesoporous KIT-6 sample was determined as 120 °C. Mesoporous carbons were prepared by using KIT-120 sample as a hard-template. NaOH solution was used to remove silica from the silica–carbon matrix and at the end of two leaching cycles, the pore volume and the surface area decreased by 1/3 with the change in NaOH concentration from 1 M to 4 M. Finally, 2 M NaOH concentration and one leaching number were determined as the best conditions to obtain mesoporous carbon (C2M1) with a high uniformity, high surface area (1020 m2/g), high pore volume (0.98 cm3/g), and relatively high wall thickness (6.25 nm). In the adsorption studies, the optimum pH value was determined as 2 for anionic Acid Violet 90 (AV 90) dye adsorption on C2M1 sorbent. The highest dye removal was achieved as 1311.5 mg/g at 298 K, pH 2 and 360 mg/L dye concentration. Langmuir, Freundlich, Temkin, and Henry adsorption isotherm models were used to examine the adsorption mechanism, and Freundlich isotherm model with a relatively higher correlation factor (R2 > 0.94) was found to be the best-fitted model to the experimental data. Pseudo second order kinetic model was determined as suitable to explain kinetic behavior of the adsorption process. Thermodynamic analysis of the experimental data revealed that the adsorption process of AV 90 dye on C2M1 sorbent was exothermic with an enthalpy change of –22.82 kJ/mol and the activation energy was found to be 45.8 kJ/mol. The N2 adsorption–desorption and FTIR analysis of the used sorbent revealed that the mesopore structure was preserved and there was no significant change in structural bonds after AV 90 adsorption. Results show that CMK-8 type mesoporous carbon material is a promising sorbent for the removal of AV 90 dye from aqueous solution.