| Summary: | 博士 === 國立臺灣科技大學 === 材料科學與工程系 === 104 === Photocatalysis is one of the prospective techniques to overcome the energy shortage problem and global warming. It has been used widely in many applications such as elimination of gaseous and water pollutants, self-cleaning, antibacterial materials, and water splitting. However, work on enhancing the capability of photocatalysis is ongoing because photocatalysts with high activity and reactive selectivity are required for applications. Some limitations of photocatalyst to obtain high efficiency have been found due to the fast recombination rate of photo carriers. To overcome the limitation, some strategies such as coupling two semiconductors or depositing metal on surface of semiconductors with suitable band edge position can reduce the recombination phenomena. To draw new prospects in this field, metal/p-n nanoheterojunction photocatalyst (Ag-deposited p-type CuBiS2/n-type TiO2 nano composite) and p-n heterojunction between n-type solid solution and p-type semiconductors ((AgIn)xZn2(1-x)S2/Ag2S nanorods) have been successfully synthesized by solution based processes. Their morphologies, structures, and textures were carefully characterized by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffractometry (XRD). On the other hand, the suitable combination of Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectra (DRS), UV-vis spectrophotometry, X-ray photoelectron spectroscopy (XPS), thermogravimetry analysis (TGA) and Hall measurement were used to characterize and analyze performances of as-designed photocatalyst systems.
There are three parts in this work. The first part deals about the growing of CuBiS2 nanoparticles and thin TiO2 layer on SiO2 sphere to form nano p-n heterojunction and the depositing Ag on its surfaces as electron trapping to reduce the recombination rate between photo carriers. This work is the first report of CuBiS2 semiconductor nanoparticles used as a material for photodegradation. The data showed that the SiO2/TiO2/CuBiS2/Ag composite particles completely degraded 50 mL of 10 ppm AB 1 dye solution in only 5 min under UV light irradiation and 100 mL of 5 ppm AB 1 dye solution in 30 min under visible light irradiation. The good photocatalysis of the composite spheres is attributed to the establishment of a good p−n heterojunction interface between the p-type CuBiS2 and n-type TiO2 semiconductors with the assistance of Ag nanoparticles.
In the second part, the as-prepared photocatalyst of SiO2/TiO2/CuBiS2/Ag composite particles was embedded into thin nylon film to improve its recyclability and to solve the post treatment problems which need high cost and time in the processes. The post treatment is the process of refreshing photocatalyst after being used for removing pollutants. The embedded photocatalyst in thin nylon film (hybrid composite film) was stable and reusable without any post treatment process between the photocatalytic degradation sessions.
The third part of this work was dealing with the heavy metal pollutant such as hexavalent chromium (Cr(VI)) by photocatalytic reduction to precipitate Cr(VI) as Cr(OH)3 with lower toxicity. In the third part, the concepts of p-n heterojunction and solid solution were simultaneously used to utilize high bandgap material such as ZnS and suppress the recombination rate of photo carriers. The photocatalyst was designed by doping Ag and In into ZnS lattice and followed by coupling with p-type Ag2S semiconductor to form Ag2S nanoparticle-decorated (AgIn)xZn2(1-x)S2 nanorod photocatalyst. The results showed only 20 mg of the as-prepared nanocomposites could reduce 100 mL of 10 ppm potassium dichromate by almost 100% in less than 90 min without adding any hole scavenger agents and pH adjustment (pH = 7). The good photocatalytic reduction was related to the narrower bandgap of (AgIn)xZn2(1−x)S2 solid solution because of the hybridized orbitals of Ag, In, Zn, and S and low recombination rate of photogenerated electron and hole pairs due to the effectiveness of p-type Ag2S and n-type (AgIn)xZn2(1−x)S2 nanoheterojunctions. This work not only gives a contribution to the creation of visible light photocatalysis for wide-bandgap semiconductors, but also extends our technological viewpoints in designing highly efficient metal sulfide photocatalyst.
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