Surface Treatment of Silicon Carbide Using TiO₂(IV) Photocatalyst

Abstract

Silicon carbide (SiC) and diamond were decomposed to CO(2)(g) by the photocatalysis with TiO(2) at room temperature, although the decomposition rate of diamond was very slow. According to the XPS spectra of Si2p on the SiC surface, SiO(2) was simultaneously formed on the surface by the TiO(2) photocatalysis. The thickness of the SiO(2) formed on the SiC surface during the photocatalytic oxidation for 1 h was estimated to be about 40 A from the depth profile of the XPS spectra using Ar etching. The SiC surface was oxidized by the TiO(2) photocatalysis even under the condition without a direct contact with the TiO(2). This indicates that the photocatalytic oxidation of the SiC occurs due to active oxygen species photogenerated on the TiO(2) surface, but not by hole produced in the valence band of the TiO(2). Moreover, a remote surface treatment system using the quartz beads coated with TiO(2) was developed for the SiC surface oxidation. Consequently, the TiO(2) photocatalysis will be very useful for the surface treatment of SiC such as photopatterning without defects and damage to the substrate because the photocatalytic reaction is carried out under mild conditions.

Probing Defect Sites on TiO2 with [Re3(CO)12H3]: Spectroscopic Characterization of the Surface Species

“…Since the discovery of photocatalytic water splitting by titania electrodes, [1] the surface chemistry of titania has been investigated extensively, often with the goals of improved properties for photocatalytic reactions, [2,3] sensor applications, and applications as a support for catalytic groups. [4][5][6] Numerous investigations of titania surfaces have been carried out with single crystals under ultrahigh vacuum conditions, typically with samples lacking hydroxyl groups; some investigations have focused on the defect sites.…”

“…The probe molecules O 2 , CO and CO 2 that have been used to characterize rutile (1 1 0) are weakly bound to the defect sites, being desorbed at temperatures well below ambient. Although anatase is known to be more reactive and have higher surface areas than rutile for several photocatalytic applications, [2,3,[9][10][11] there are still no reports of investigations of anatase surface defects with probe molecules. Our goal was to characterize the surface sites of anatase (prepared in a high-area porous form with surface hydroxyl groups) by a probe molecule of another class, one that would be rather strongly bound and offer spectroscopic signatures to help elucidate its interactions with the surface.…”

Toxicological Issues of Nanoparticles Employed in Photocatalysis

“…Similarly, the conduction band electron can react with adsorbed molecular oxygen forming superoxide radicals and subsequently hydrogen peroxide (H 2 O 2 / However, the oxidizing potential of photocatalytic materials is not limited to their surface, as oxidizing species can diffuse away from the photocatalytic surface, inducing redox reactions in the bulk. This effect is usually called remote photocatalysis and is most likely mediated through hydrogen peroxide and singlet oxygen [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45] [46], [27]. However, in the case of remote photocatalysis, the reaction rate and thus the product yield is usually one or two orders of magnitude lower than that of the process occurring at the photocatalyst surface.…”

Zn:In(OH)ySz Solid Solution Nanoplates: Synthesis, Characterization, and Photocatalytic Mechanism

“…When the outer system contains only water, 83.5% of the RhB is kept within the membrane packaged-container and 16.5% of the RhB diffuses into the outer water after 1 h. However, when the outer system is a Fenton reagent, only 5% of the RhB remains in the container and no RhB is detected outside after 1 h, because · OH generated by the Fenton reagent can pass through the membrane and degrade RhB both inside and outside the container. It also can be seen that only H 2 O 2 is unable to degrade the RhB within 1 h. When employing water, TiO 2 , and UV light as the outer system, the percentage of RhB in the container declines to 56% after 1 h, which mainly results from the diffusion of reactive oxygen species such as · OH generated in the TiO 2 -mediated photocatalytic process (18,19). However, with water, Zn:In(OH) y S z -SSN, and VL as the outer system, the percentage of RhB in container shows no appreciable difference with that employing pure water as outer system, indicating that there is little entry of bulky · OH or · O 2 -through the membrane.…”