Synthesis And Property Study Of Perovskite-type Tantalite And Niobate Nanosized Photocatalysts

Under the dual pressures of the energy crisis and environmental pollution, photocatalytic technology has attracted more attention in the fields of hydrogen production and photodegradation of organic pollutants. Researchers are constantly exploring photocatalysts with simple synthetic method, wide photo-harvesting range, and more effective photocatalytic absorption of sunlight. Tantalate and niobium show high photocatalytic activities for water splitting and photodegradation due to their unique electronic structure and energy band structure, and now they has become a hot research field. However, these photocatalysts are mostly synthesized via a tedious reaction process with high temperature. In addition, tantalate(niobate)-based photocatalysts can only be excited by UV light due to their large band gaps. To solve this issue, most of the works depend on the doping of heterogeneous elements. However, the simpler self-doping method, which is developed in recent years, has not been reported in the studies of tantalum(niobium) photocatalysts.In the present dissertation, some novel methods are explored to synthesize self-doped tantalum(niobium) photocatalysts. Since our synthetic methods have low alkalinity, low reaction temperature and short reaction time, the producted photocatalysts exhibit excellent water splitting and photodegradation activities. The present work is mainly divided into the following five aspects:1. Self-doped NaTaO3 nanoclusters were synthesized using a facile and one-pot lowtemperature solvothermal method. Ta4+ in NaTaO3 bulk greatly narrows its band gap to 1.70 eV and thus extends its photoresponse from UV to visible light region. Self-doped NaTaO3 nanoclusters obtained at the low solvothermal temperature of 110 oC are composed of nearly spheracal particles with size of ~50 nm, which leads to enhanced visible-light photocatalytic activity for water splitting(H2 release rate is 61μmol/h/g) and dye degradation without loading any co-catalysts such as Pt or NiO commonly used in other literatures.2. Rhombohedral Nb4+ self-doped KNbO3(S-KN) nanorods with visible-light photocatalytic activity were fabricated via a one pot, solvothermal method. Compare with the pristine KNbO3 prepared by conventional synthetic method as other reports, the presence of Nb4+ greatly narrows its band gap and thus extends its photoresponse from the UV to the visible light region, and exhibits visible-light photocatalytic activity for water splitting. Moreover, S-KN/Nb4N5 heterostructures were obtained by nitridizing S-KN sample for different times, which exhibited significantly enhanced photocatalytic activity for hydrogen production under visible light irradiation.3. Perovskite-type SrNb O2 N nanoparticles have been synthesized via a solvothermal method followed by post-thermal nitridation. The resultant SrNbO2 N nanoparticles with an average diameter of ~40 nm can harvest visible light due to their lower band gap of 1.94 e V. The photocatalytic studies revealed that the uniform SrNbO2 N nanoparticles exhibited high photocatalytic activity for H2 evolution(H2 release rate is 148.3 μmol h-1g-1, using Pt as co-catalysts) and high degradation efficiency for methylene blue under visible light irradiation. The SrNbO2 N nanoparticles also showed high photocatalytic stability under a long-term water splitting reaction.4. Nb4+ self-doped NaNbO3 microcubes with visible-light photocatalytic activity were fabricated via one pot, solvothermal method. Compared with pristine NaNbO3 prepared by conventional synthetic method, the presence of Nb4+ greatly narrows its band gap and thus extends its photoresponse from the UV to the visible light region. They exhibit visible-light photocatalytic activity for water splitting. Furthermore, after nitridizing self-doped NaNbO3 microcubes for 1 hour, the NaNbO3/Nb4N5 heterostructures were obtained, which also exhibit significantly enhanced visible light photocatalytic activity.5. Peanut shape perovskite-type LiTaO3 nanoparticles were synthesized via a hydrothermal method followed by low temperature calcination at 500 oC. The resultant LiTa O3 nanoparticles with diameters less than 100 nm exhibit excellent ultraviolet absorption ability. The studies on different calcination temperatures found that the LiTa O3 sample obtained at 500 oC has the highest water splitting performance, and the H2 release rate is 153.5 μmol h-1 g-1, which is about 25 times than those of other reports. The LiTaO3 nanoparticles also showed high photocatalytic stability under a long-term water splitting reaction.