Evaluation of the mesoporous silica material MCM-41 for competitive adsorption of Basic Violet 5BN and Basic Green from industrial dye wastewater

Abstract

MCM-41 is demonstrated to be an efficient adsorbent for the removal of two representative cationic dyes, namely Basic Violet 5BN (BV) and Basic Green (BG). Characterization of the adsorbent was studied by FTIR, X-ray diffraction, and Brunauer-Emmett-Teller. And various parameters including the solution pH, adsorbent dosage, contact time, initial cationic dye concentration, and temperature were systematically analyzed. It was found that the adsorption was pH independent and the maximum removal percentage of 86.81% BV occurred at pH 5.0 and 25°C using 0.3-g MCM-41, whereas 94.79% BG under the same experimental conditions. Besides, both the adsorptive removal of BV and BG by MCM-41 increased with the adsorbent dosage and contact time, but decreased with the initial dye concentration and temperature. In single component systems, equilibrium data were well presented by the Langmuir isotherm, suggesting the adsorption to be monolayer. And the E values (<8 kJ/mol) resulted from the D–R isotherm fitting showed the adsorption was physical in nature. The adsorption kinetics fitted better with the Lagergren pseudo-second-order model, and rate-controlling steps were both the external diffusion and intraparticle diffusion. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°< 0) indicated that the adsorption process was feasible, spontaneous, and exothermic. Furthermore, competitive adsorption existed between the mixed dyes, and the removal efficiency and adsorption capacity of the dyes in binary component systems were lower than those in single systems. The adsorption isotherm and kinetic data of the binary component systems could also be well described by the Langmuir and Lagergren pseudo-second-order models. High recovery percentage of BV and BG by 0.1-M NaOH solution allowed excellent desorption and regeneration of the cationic dyes in practical applications.