Morphology and visible photoluminescence modulation in dye-free mesoporous silica nanoparticles using a simple calcination step

Synthesis of dye-free mesoporous silica nanoparticles and the effect of calcination on their photoluminescence properties are reported here. Mesoporous silica nanoparticles were synthesized using a modified Stöber method and calcined at different temperatures. Samples were characterized by transmission electron microscopy (TEM), BET surface area analyzer, thermogravimetry analyzer, Fourier Transform Infrared spectroscopy (FTIR), photoluminescence spectroscopy, and X-ray photoelectron spectroscopy (XPS). Silica nanoparticles calcined at 400 °C exhibited maximum porosity with highest specific surface area of 828 m2.g–1. Uncalcined porous nanoparticles exhibit broad visible light photoluminescence (from 400 nm to 600 nm), and its intensity varies significantly after calcination, mainly due to the creation of carbon impurities and oxygen defects within the silica lattice. Carbon impurities during calcination are formed from the remaining organic residue at the nanoparticle's surface and can be removed by calcining the particles above 400 °C and thereby, improving the visible light photoluminescence intensity of these nanoparticles.