Surface Modification of Silica Coated ZnO Nanoparticles with 3-Aminopropyltriethoxysilane by Microwave-Assisted Method and Its Effect on the Properties of Coated Samples

The present study investigates silica coated ZnO prepared by microwave-assisted sol-gel method from tetraethoxysilane (TEOS) and commercial ZnO nanoparticles, and further treated with 3-aminopropyltriethoxysilane (APTES) to change the surface characteristics. For the silica coating of ZnO nanoparticles in a batch type microwave apparatus, two kinds of TEOS/ZnO starting ratios (=0.3, 0.5) were used. The transmission electron microscope (TEM) images of coated samples with different TEOS/ZnO starting ratios suggested that uniform silica coating on the ZnO surface was observed for the coated sample with a TEOS/ZnO ratio of 0.5; whereas, the ZnO surface was partly exposed on the sample with a TEOS/ ZnO ratio of 0.3. When these silica coated ZnO nanoparticles were used as starting materials for APTES treatment, it was revealed that 5 wt% (=APTES/silica coated ZnO) of APTES loading was enough to change the dispersion property of the sample with a TEOS/ZnO ratio of 0.5 in the organic solvent/water system. On the contrary, a higher APTES loading amount (10 wt%) was needed for the sample with a TEOS/ZnO ratio of 0.3 to observe the same phenomenon. The results of TEM observation, Fourier Transform Infrared (FT-IR) analysis, and Zeta potentials for the coated samples supported the results of dispersion tests in the organic solvent/water system. Photo-catalytic activities of the samples with a TEOS/ZnO ratio of 0.5 kept at low level (less than 5% compared to bare ZnO) with increasing APTES loading amounts. In contrast, those of the samples with a TEOS/ZnO ratio of 0.3 were reduced with increasing APTES loading amounts.