| Currently, the human activity’s main source of energy is still fossil fuel, which hascaused the global warming and environmental degradation, thus inconveniencing andthreatening human life. Facing this problem, people are striving to alleviate this situation andimprove the environment, such as developing new energy resources to replace non-renewableresources, and reduce pollute discharge and protect the environment. The application ofphotocatalytic technology to enhance the environment and to develop hydrogen energy is aconsiderably promising project.Photocatalysis is a technology in which the catalysis’s electron transits from valenceband to conduction band under light irradiation, producing electron-hole pairs (e--h+), thengenerate active groups such as hydroxyl radicals (OH) and superoxide radicals (O2-). Theseactive groups have the functions of anti-microbial, deodorization, oil decomposition, mouldand algae proofing, and air purification. There are various kinds of photocatalyst, amongwhich the most well-known and most thoroughly studied is nano TiO2, which is featured inhigh in photochemical stability, environmental friendly, non-toxic to human health, strong incatalytic ability and long duration. However, TiO2is a wide band-gap semiconductor(Anatase~3.2eV, Rutile phase~3.0eV, Brookite phase~3.03eV), which can only beactivated by UV-light while the visible light that accounts for43%of sunlight cannot beabsorbed, resulting in a low efficiency in sunlight utilization. In addition, the latticeimperfection in TiO2can act as the combination center of e--h+thus affect the efficiency ofphotocatalytic. Therefore, the key factors in manufacturing highly active photocatalyst are tonarrow the energy gap and restrain the recombination of electrons and holes.Based on the relationship between structure and properties of nanomaterials，theperformances of photocatalysts are relate to the morphology, crystalline, crystal face exposed,and so on. Now, the new nanostructured materials continue to emerge, new synthesistechnology continues to improve, and new analytical technology continues to mature. Toimprove the catalytic properties and promote the progress of photocatalytic technology,studying the construction and performances of photocatalysts has important significance andpractical value.In this thesis, TiO2was choosed as the main material; we prepared different Ti3+ self-doped TiO2and conbined with other semiconductros. The micro-structural, morphologiesand photoelectric conversion performance were studied. The main research contents are asfollows:1. Ti3+self-doped TiO2(A)/TiO2(R) heterojunctions comprising anatase TiO2(TiO2(A))nanoparticles and rutile TiO2(TiO2(R)) nanorods were synthesized by a simple hydrothermalmethod using Zn as the reductant. The structure, crystallinity, morphology, and chemical stateof the as-prepared samples were characterized by X-ray diffraction (XRD), transmissionelectron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM),X-ray photoelectron spectroscopy (XPS), and UV–Vis diffuse reflectance spectroscopy(UV-Vis DRS). Zn acts as a reducing agent and Zn2+stabilizes the oxygen vacancies.Meanwhile, the generated ZnO clusters promote phase transformation from TiO2(A) toTiO2(R). The visible-light photocatalytic degradation of dyes was analyzed. The Ti3+self-doped TiO2(A)/TiO2(R) heterojunctions exhibited an extended visible light absorptionand higher visible-light photocatalytic activity than that of commercial P25TiO2in thephotodegradation of Methylene blue and Rhodamine B under visible-light irradiation. Ti3+self-doping expanded the light-response range, and the formed heterojunctions at theinterface of TiO2(A) nanoparticles and TiO2(R) nanorods efficiently reduced therecombination of photoinduced electron–hole pairs.2. Ti3+self-doped titanium–zinc hybrid oxides with different phase compositions andmorphologies were successfully synthesized using Zn powder as the reductant and Zn sourceby a chemical-reduction precipitation method with subsequent thermal treatment. Thefabricated Ti3+self-doped TiO2(A)/TiO2(R), TiO2(A)/TiO2(R)/ZnTiO3, and TiO2(A)/ZnOheterojunctions were characterized by XRD, TEM and HRTEM, XPS and UV–Vis DRS. Theeffects of various Ti/Zn molar ratios and preparation processes on the structural,morphological, optical, photocurrent and photocatalytic properties of the resultant sampleswere investigated systematically. Results reveal that Ti3+self-doping enhances thephotoabsorption capability of titanium–zinc hybrid oxides in the visible-light region.Moreover, different processes and Ti/Zn molar ratios play great influences on the structure,morphology, optical, photocurrent and photocatalytic properties of the final products. Ti3+self-doped titanium–zinc hybrid oxides exhibit excellent photocurrent and photocatalyticactivity than pure TiO2and ZnTiO3under visible-light irradiation. The most active Ti3+ self-doped titanium–zinc hybrid oxides photoanode presents significantly improved watersplitting performance. The synergistic effect between the Ti3+self-doped and heterojunctionsis responsible for the enhanced performance of these materials.3. Ti3+self-doped TiO2-x/SnO2/SnS2heterojunctions were prepared and the photoelectricconversion performances were studied. Tin powder was used as reductant. The different Sn/Timolar ratio influence the composition and properties of the purducts. The obtained samplesexhibits excellent photoelectric conversion properties and photocatalytic properties.4. Ga-doped and containing oxygen vacancies (Ov) TiO2-xwith different phasecompositions and morphologies were successfully synthesized by a chemical precipitationwith subsequent hydrothermal treatment method. The fabricated TiO2(A)/TiO2(R),TiO2(A)/TiO2(B) heterogeneous junctions were characterized by XRD, HRTEM, XPS, andUV–Vis DRS. The effects of Ga/Ti molar ratios on the structural, morphological, optical,photoelectrochemical and photocatalytic properties of the resultant samples were investigatedsystematically. Results reveal that different Ti/Ga molar ratios play great influences on thestructure, morphology, optical, photoelectrochemical and photocatalytic properties of thefinal products. The heterogeneous junctions exhibit excellent photocurrent and photocatalyticactivity than pure TiO2under visible-light irradiation. The most active heterogeneous junctionphotoanode presents significantly improved water splitting performance, with high hydrogenproductivity up to4.4mL h-1(196.4umol h-1) at0.25V vs. saturated calomel electrode withan almost constant rate during9h.5. Reduced TiO2-x/BiOCl heterojunctions were synthesized by a simple one-pothydrothermal method using hydrazine hydrate as the reductant, complexing agent, andprecipitant. The structure, crystallinity, morphology, chemical state, and photoelectrochemicalproperties of the samples were characterized. The TiO2-xnanoparticles contained largeamounts of Ti3+, Ti2+, and Ov, while the BiOCl nanosheets had an exposed {001} facet withhigh catalytic activity. The Ti3+, Ti2+, and Ov expanded the light-response range and increasedthe electron transfer rate. The heterojunctions formed at the interface of the reduced TiO2-xnanoparticles/BiOCl nanosheets exhibited a wider visible-light absorption band and higherphotocatalytic activity than those formed at the pure TiO2/BiOCl interface. Theseheterojunctions also efficiently reduced the recombination of photoinduced electron–hole pairs. |
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