Immobilization of Green Synthesized Silver Nanoparticles onto Amino-Functionalized Silica and Their Application for Indigo Carmine Dye Removal

In the present work, we have applied a green method for the synthesis of silver nanoparticles (AgNPs) onto amino-functionalized silica using Nigella sativa (black seed) aqueous extract as an eco-friendly and efficient reducing agent. The factors influencing the functionalization of silica and AgNPs loading have been considered. The samples were characterized by elemental analysis, FTIR, XRD, TGA, SEM, and EDX and used for the removal of indigo carmine (IC) dye from aqueous solution. The mean particle size of immobilized AgNPs was calculated from the XRD pattern using the Scherrer equation and is equal to about 26 nm. Adsorption experiments were carried out as batch studies at different contact times, temperature, adsorbent dosage, and initial dye concentrations. The IC adsorption equilibrium was attained after about 20 min of contact time. The equilibrium data shows that the Langmuir model was more reasonable to depict the IC adsorption, and the maximum adsorption capacity of IC is 73.05 mg/g. Based on the kinetic analysis, the adsorption process follows a pseudo-second-order equation. The estimation of the thermodynamic parameters such as the Gibbs free energy, entropy, and enthalpy changes of the adsorption process indicated the feasibility and endothermic nature of IC adsorption. The modified surface was found to be extremely stable in the aqueous medium, and no significant leaching of AgNPs was observed. Thus, immobilization of AgNPs may advance reuse, reduce environmental risks associated with leaching of AgNPs, and enhance cost-effectiveness.