Green synthesis and characterization of amorphous silica nanoparticles from fly ash

Abstract

Abstract The present study reveals an efficient and cost-effective method for the synthesis of silica nanoparticles from the silico-aluminous class F fly ash. The fly ash is rich in silica and as a renewable source attracts wide attention towards it. The present method has several advantages over previous methods like excellent yields with high purity and less expensive. The fly ash based synthesis of silica nanoparticles involves two steps: extraction of silica in the form of sodium silicate by NaOH treatment followed by formation of silica gel by neutralizing the alkaline sodium silicate with diluted HC by sol-gel method. The synthesized silica nanoparticles characterized by characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-Ray diffraction (XRD), Field Emission Scanning Electron Microscope and Electron diffraction spectroscopy (FESEM-EDS), transmission electron Microscope (TEM) and Atomic Force Microscope (AFM). The amorphous nature of silica nanoparticles was confirmed by XRD due to a broad hump from 15-300 two-theta region with a peak centred at 21.70, which was also supported by the SAED pattern. FTIR reveals the three characteristic bands of the silica nanoparticles in the region of 400-1200 cm-1. The microscopic techniques confirmed the morphology of the silica nanoparticles. The sizes of the silica nanoparticles vary from 20-70 nm, which have spherical shaped, aggregated which have a tendency to form a cluster. EDS helped in the elemental detection and purity of the silica nanoparticles at every step. The calcination and purification have a positive role in the purity of the samples. The purity of the final silica nanoparticles varies 90-96%.