Fabrication Of Ordered Core-Shell Photocatalysts With Heterojunction And Their Performance In Degradation Of Organic Pollutants In Aqueous Solution

Photocatalysis, one of the most attractive techniques for environmental pollution control, has been widely investigated. However, the photocatalytic oxidation technology always suffers from the difficulties of separating suspended photocatalyst particles from aqueous solution. Meanwhile, TiO2 can not absorb visible light effectively as well as the low quantum yield. These disadvantages limit the development of photocatalysis. Inner electric field of heterojunction can provide a driving force for the separation of photogenerated electron-hole pairs. Structure heterojunction in the shape of photocrystals can take advantage of slow photons to facilitate absorption of the interesting light. Window effect of heterojunction can widen absorption range by utilizing photoresponse ability of both semiconductors. Higher photocatalytic efficiency might be obtained with improved electrode. In this dissertation, the following work has been done:(1) TiO2/Pt coaxial nanotube Schottky arrays on Ti substrate (TiO2/Pt-Ti) were fabricated by electrodeposition and subsequent chemical vapor deposition method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction patterns (XRD) indicated that the as-prepared samples were vertically well-aligned TiO2-Pt coaxial nanotube arrays, and the outer TiO2 nanotube was anatase with the preferential orientation of (101) plane. The asymmetry of the current-voltage (I-V) curve revealed that a schottky barrier had been formed between TiO2 and Pt. They displayed enhanced photocurrent (about 6 times of that of TiO2 nanotube) under zero bias potential. For the degradation of phenol under UV light irradiation, the TiO2-Pt coaxial nanotube array exhibited a much higher photocatalytic efficiency (up to 87%) than did the TiO2 nanotube array, and the kinetic constant of it was 2.3 times as great as that of the TiO2 nanotube array.(2) Inverse TiO2/Pt opals Schottky structures on the Ti substrate were fabricated by electrodeposition and liquid phase deposition. These samples were of ordered network, which was built by the Pt skeleton frame and the outer TiO2 layer. The TiO2 layer was identified as anatase with the preferential orientation of (101) plane. The experiments of short-circuit photocurrent (SCPC) and photocatalytic degradation of phenol were also conducted under the UV irradiation in order to evaluate the photoactivity of the samples. By tuning the red edge of photonic stop-band overlapping the absorption maximum of anatase (at 360 nm), both the UV absorption and the carrier separation of the samples were improved. For the degradation of phenol under UV light irradiation,98% phenol was degradated by TiO2/Pt opals.The kinetic constant using the optimal inverse TiO2/Pt opals (0.992 h-1) was 3.3 times as great as that of pristine TiO2 nanocrystalline film (TiO2-nc) on Ti substrate. The overall additional enhancement of TiO2/Pt-320 including two contributions:130% was arising from "Schottky barrier" and the other was aring from "photonic effect".(3) SiC/Si nanowire arrays on Si wafer (SiC/Si NWs) were fabricated by chemical etch and magnetron sputtering. Diffuse reflectance UV-vis spectra (DRS),â… -â…¤curve indicated that SiC/Si possesses both the UV absorption of SiC and visible light absorption of Si nanowire. The optical sample was obtained by a 2 h magnetron sputtering. After HF treatment, SiC/Si shows a stronger photoelectric response.The visible light (>400 nm) photoconversion efficiency for SiC/Si NW was 2.82%. For the photoelectrocatalytic degradation of phenol under visible light irradiation, the kinetic constant using SiC/Si NW cathode (0.393 h-1) is 6.3 times as large as that (0.062 h-1)of SiC film on Si wafer (SiC/Si wafer). Furthermore, there was a synergetic effect between photocatalysis and electrochemical processes. This result demonstrates that SiC/Si NW cathode could utilize visible light to decompose phenol with a considerable efficiency.The above results illuminated that reasonable designed heterojunction photocatalysts possessed not only enhanced quantum effiency but also visible light activity; Moreover, heterojunction photocatalysts with photonic crystals structure have the ability of light enrichment. Both of them can improve the photocatalytic ability of photocatalysts.These studies provide feasible method to optimize the photocatalytic ability and was hoped to develop heterojunction theory and photonic crystal theory in pollution controlling.