The Estimation of the Surface Properties of Metal Oxides by the Use of TCNQ Adsorption

Abstract

The electron-donor properties of metal oxides (magnesia, alumina, silica, titania, zinc oxide, and nickel oxide) were investigated by means of TCNQ adsorption. When TCNQ was adsorbed on the surfaces of the metal oxides from its acetonitrile solution, the surfaces of the metal oxides acquired the colorations characteristic of each oxide. The coloration was caused by the formation of TCNQ anion radicals on the metal oxide surfaces. The presence of the TCNQ anion radicals on the colored metal oxide surfaces was confirmed by studying the ESR absorption and electronic spectra. The radicals were formed as a result of electron transfer to TCNQ from the metal oxide surfaces. The order of the radical-forming activity, determined by ESR, was as follows: magnesia>zinc oxide>alumina>titania>silica>nickel oxide. The electron-donor property of the metal oxide surfaces might be dependent on the natures of the semiconductor and the surface hydroxyl ion.