Templated synthesis of NiO/SiO₂ nanocomposite for dye removal applications: Adsorption kinetics and thermodynamic properties

There is an ongoing effort to develop economical routes to synthesize NiO/SiO₂ nanocomposites due to their importance as catalysts, adsorbents, magnetic materials etc. This study reports the synthesis of NiO/SiO₂ nanocomposite via a soft templating approach using low-cost precursors. Cetyltrimethylammonium bromide (CTAB) was utilized as a soft template, where nickel chloride was premixed with CTAB to get a modified template. Sodium silicate was used as an economically feasible source of SiO₂. The surface morphology, crystalline phase, and colloidal stability of the synthesized NiO/SiO₂ nanocomposite were explored by field-emission scanning electron microscope (FE-SEM), powder x-rays diffraction (p-XRD), and dynamic light scattering (DLS) techniques, respectively. The synthesized composite was applied for the removal of Rhodamine B (RhB) dye. The adsorption process of RhB on the surface of NiO/SiO₂ nanocomposite was investigated in detail. The % removal of RhB was observed as a function of (i) time, (ii) temperature, (iii) pH, (iv) dye concentration, and (v) adsorbent dosage to find the optimum conditions for the adsorption process. The kinetics and equilibrium studies showed that the adsorption process obeys pseudo-second-order kinetics and Langmuir isotherm model (R² = 0.99). Thermodynamic parameters (ΔG, ΔH) suggested that the adsorption process is spontaneous and endothermic. The comparison indicates that the adsorption capacity (68.02 mg g⁻¹) of synthesized NiO/SiO₂ nanocomposite is significantly higher as compared to various SiO₂ based adsorbents reported in the literature for treating RhB in wastewater.