Microwave-assisted sol-gel template-free synthesis and characterization of silica nanoparticles obtained from South African coal fly ash

In this study, we prepared a silica nanoparticle from South African fly ash (SAFA), using a facile microwave (MW)-assisted sol-gel template free syntheses method. Prepared silica nanoparticles (SNPMW) were characterized using X-ray fluorescence (XRF) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transition electron microscope (TEM), Brunauer-Emmett-Teller (S BET) surface area analysis, and ultraviolet visible diffuse reflection spectroscopy. XRF analysis suggests SAFA as fly ash class F. The XRD pattern reveals the structural composition of SAFA and the amorphous nature of extracted SNP, while the FTIR assay shows the presence of silanol and siloxane groups. SEM and TEM analyses revealed primary silica nanoparticles were roughly spherical with sizes of about <200 nm. EDX spectra confirm the presence of SiO2. The optical bandgap of SNPMW was established to be 4.67 eV. The application of SNPMW demonstrated that it can be used to remove Pb2+ from an aqueous solution. Test results show the optimum treatment time as 60 minutes, while removal efficiency increases from 66.76 to 96.64% as the pH rises from 3 to 5, but as the pH rises above 5, the efficiency decreases. The use of an MW-assisted sol-gel preparation method gave rise to an elevated reaction rate with minimal contamination and thinner particle size SNPMW, which was utilized for the removal of Pb2+ in an aqueous solution.