Surface modification of silicon carbide nanoparticles by azo radical initiators

The surface of silicon carbide (SiC) nanoparticles was modified with three types of azo radical initiators: 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylpropionamidine)dihydrochloride (AMPA), and 2,2'azobis[N-(2-carboxyethyl)-2-methylpropionamidine)n-hydrate (ACMPA). The radical species generated from the azo initiators successfully reacted with the unsaturated hydrocarbons on the surface of SiC nanoparticles. Consequently, the hydrophobic SiC surface became hydrophilic, and the dispersion stability of SiC nanoparticles in aqueous solution improved significantly. Further, it was found that the stability of SiC nanoparticles in aqueous solution under various pH values could be controlled by the structure of the azo radical initiators. When SiC nanoparticles reacted with AIBN and were further hydrolyzed by NaOH aqueous solution, since carboxyl groups were introduced on their surface, their stability improved at pH >= 5. Contrarily, when SiC nanoparticles were modified with AMPA, amine groups were formed on the SiC surface so that SiC nanoparticles were stabilized at pH <= 3. When SiC nanoparticles were modified by ACMPA, which consists of both amine groups and carboxyl groups, the modified SiC nanoparticles possessed amphoteric properties; the SiC nanoparticles were stabilized at pH 3 and 11. It was deduced that modifying SiC nanoparticles with azo radical initiators is a significant method for tuning the surface properties of SiC nanoparticles.