Toluidine blue is an acidophilic metachromatic dye that selectively stains acidic tissue components [1]. In this study, SiO2 nanoparticles were used to remove Toluidine blue dye in a batch system. In order to reach a maximum removal efficiency (R%), optimum conditions were explored by means of experimental design approach. The experimental factors were considered such as: pH, contact time, sorbent dosage (m) and dye concentration (Cd) in the solution. Response surface methodology (RSM) including faced central composite design (FCCD) was employed to optimize the removal conditions and to propose an appropriate regression model along with related surface plots. The optimum conditions obtained for 99% removal of dye : pH=6, m= 0.06 g and Cd= 850 mg/L. Langmuir Isotherm fitted well than other Isotherms with equilibrium experimental data and yield the maximum monolayer adsorption of 55.25 mg/g. Second-order kinetic model described well the dynamic behavior of the current adsorption process. The desorption efficiencies with HCl, HNO3, CH3COOH and NaOH were low. Also it was found that presence of Na+, K+,Ca2+ and Mg2+ ion have no significant interference on adsorption efficiency. FT-IR analysis identified that the functional groups of sorbent were involved in the adsorption process.
