Enhanced adsorption of the cationic dyes in the spherical CuO/meso-silica nano composite and impact of solution chemistry.

In this study, the spherical mesoporous silica (meso-silica MCM-41) and that inorganically modified with CuO (CuO/MCM-41 nano composite) were synthesized and characterized. It was demonstrated that CuO were successfully loaded in the synthesized nano composite CuO/MCM-41. Importantly, the loaded CuO had a significant enhancement effect on the adsorption of Crystal violet and Methylene blue. Adsorption kinetic of the tested cationic dyes in the synthesized materials fitted the pseudo-second-order kinetic model and Weber's intra-particle diffusion model well. According to the Langmuir isotherm model, the maximum adsorption capacities (Qmax) of the CuO/MCM-41 towards Crystal violet and Methylene blue increased to 52.9 and 87.8mg/g, while those of the pure MCM-41 were 46.2 and 65.7mg/g, respectively. Due to the surface charge of CuO and the protonation of the dye molecules, the electrostatic forces between the loaded CuO and the organic cationic dyes contributed to the enhancement effect. Additionally, the presented results indicated that the adsorption of the cationic dyes in the CuO/MCM-41 depended on pH and ion strength of the solution but insignificantly on the coexisted humic acid due to the mesoporous character of CuO/MCM-41 nano composite.