Removal of methylene blue from aqueous solution with silica nano-sheets derived from vermiculite

Abstract

The adsorption kinetics of a cationic dye, methylene blue (MB), onto the silica nano-sheets derived from vermiculite via acid leaching was investigated in aqueous solution in a batch system with respect to contact time, initial dye concentration, pH, and temperature. Experimental results have shown that increasing initial dye concentration favors the adsorption while the acidic pH and temperature go against the adsorption. Experimental data related to the adsorption of MB on the silica nano-sheets under different conditions were applied to the pseudo-first-order equation, the pseudo-second-order equation and the intraparticle diffusion equation, and the rate constants of first-order adsorption ( k 1), the rate constants of second-order adsorption ( k 2) and intraparticle diffusion rate constants ( k int) were calculated, respectively. The experimental data fitted very well the pseudo-second-order kinetic model. The activation energy of system ( E a) was calculated as 3.42 kJ/mol. The thermodynamics parameters of activation such as Gibbs free energy, enthalpy, entropy were also evaluated and found that Δ G*, Δ H*, and Δ S* are 65.95 (71.63, 77.45) kJ/mol, 0.984 (0.776, 0.568) kJ/mol, and −0.222 (−0.223, −0.224) kJ/(K mol) at 20 (45, 70) °C, respectively. The desorption of the dye on the silica nano-sheets using ethanol was also investigated primarily.