Formation of SiC nanocrystals prepared by sol-gel processing of green carbon sources and DFT calculations

SiC nanocrystals are synthesized by sol-gel processing with tetraethoxysilane and green carbon sources (sugar, molasses, and stevia extract) as starting materials. The reactions of carbon precursors and silicon were investigated using density functional theory. To obtain the discrepancy between the energy levels of the interacting orbitals of precursors, molecules were optimized using B3LYP/6-31+G(d,p) method. XRD, FE-SEM, TG-DTA and FTIR analysis were implemented in order to compare the efficiency of different carbon sources. According to XRD experiments, SiC nanocrystals prepared by sugar and molasses had no contamination, while the sample prepared by stevia has impurity in the form of carbon and silica. TG-DTA results revealed that this difference is due to the fact that the carbon source in stevia did not react efficiently with silicon. Moreover, based on the DFT study and HOMO and LUMO analysis on the reactive energy of silicon and carbon precursors, it is revealed that sugar has the best reactivity among carbon sources for SiC formation.