Optical Properties of the Carbon-Modified TiO₂ Prepared by Microwave Carbonization Process

Abstract

The carbon-modified TiO 2 were synthesized through microwave carbonization of ethanol by using a domestic microwave oven. This process enabled to form the carbonaceous compounds on the surface of TiO 2 and created several new mid-gap bands into the original bandgap within few minutes operation. The sample showed a remarkable visible-light absorption even at the wavelength of around 800nm. The promotion of photocatalytic activity under visible and ultraviolet (UV) light irradiation were also confirmed by the I 3 formation in KI aqueous solution. The I 3 formation rate of carbon-modified TiO 2 per unit mass under visible light is almost 25 times higher than that of pure TiO 2. The mid-gap optical absorption mechanisms were investigated through analysis of absorption edges. It is revealed that surface state change against microwave-treatment time results in different mid-gap optical absorption processes.

Effect of microwave irradiation on the electronic structure of ZnO

“…13 Figure 2 shows the absorption coefficient spectra. These spectra were converted from 14 the diffuse reflection spectra using Kubelka-Munk formula [9,17 ], which is 15 expressed by Eq. (1) as 16…”

“…Here, α is the absorption coefficient, S is the scattering coefficient, and R is the diffuse 17 reflectance. S is assumed to be constant, which is usually reasonable around the 18 absorption edge [9]. 19…”

“…Moreover, there is not an energy difference in the band-edge 7 emissions between the two specimens at low temperature, suggesting that the bandgap 8 energy at room temperature is 3.26 eV for both specimens. 9 On the other hand, for ZnO with MW irradiation, an additional energy state is created 10 near the conduction band due to the defect level generation by MW irradiation, which 11 may be attributed to the plasma emission such as a zinc plasma and an oxygen plasma 12 by MW irradiation or to the thermal effect induced by MW heating. Because, in the 13 previous reports [13,14], the plasma emission of zinc atom and oxygen atom was 14 observed by microwave irradiation, and it shows that atoms of zinc and oxygen in ZnO 15 are emitted from the sample.…”

“…Additionally, MW sintering has been reported to improve the electronic 7 property of ZnO as a varistor for semiconductor application [6][7][8]. 8 Sonobe et al reported that the surface modification of TiO 2 for enhancement of 9 catalytic activity and the direct reduction without a reducing agent of TiO 2 were 10 available by MW treatment [9,10]. Similarly, the enhancement of the photocatalytic 11 activity of PbMoO 4 by MW irradiation has been reported [11].…”

Microwave material processing for green technology

“…To date, several approaches have been studied for microwave material processing such as the sintering of ceramics [1-3], metal powders [4][5][6][7], and the upgrading of the photocatalytic activity of Ti02 [8].…”