Adsorption of Methylene blue (MB) dye Using NiO-SiO2NPs Synthesized from Aqueous Solutions: Optimization, kinetic and equilibrium studies

The applicability of the synthesized NiO-SiO2NPs as a novel adsorbent for eliminating Methylene Blue (MB) dye from aqueous media was investigated. Various techniques including BET, FT-IR, XRD, SEM and EDS were used to characterize this novel adsorbent. The investigation showed the applicability of NiO-SiO2NPs as an available, suitable and low-cost adsorbent for proper removing of MB dye from aqueous media. The effect of pH, adsorbent dosage (dose), initial MB dye concentration (C0) contact time (tc) and temperature (T) on the removal percentage (Ad%) of MB dye onto NiO-SiO2NPs was studied and the optimum value of each factor was determined (pH=7, dose=0.1g, C0=30 mg/L, tc=15 min and T=298.0 K). The experimental equilibrium data was fitted to the conventional isotherm models and accordingly Langmuir isotherm has good applicability for the explanation of experimental data with maximum adsorption capacity of the MB dye for SiO2 and NiO-SiO2NPs were roughly 117.0 and 140.0 mg/g respectively. Kinetics experiments were performed to investigate the adsorption kinetics, the pseudo-second-order kinetics coincided quite with the kinetic results. The thermodynamic behavior of the adsorption process was studied by considering the effect of temperature on the adsorption capacity, where the results showed that the process is spontaneous (∆G, Ad 0<0) at used temperature range and exothermic (∆H, Ad 0<0) with ∆S, Ad 0<0. Based on the magnitude of ∆H, Ad 0<0, it was concluded that the studied adsorption process is a physisorption one.