Low-Temperature Solution Synthesis And Photocatalytic Performances Of Aurivillius Bi₂MO₅F ?M=Nb, Ta? And Their Composites

In the recent decades, photocatalytic degradation of harmful pollutants by semiconductors has received considerable attention. Due to its outstanding stability and oxidability, TiO2 is one of the best photocatalysts for environmental remediation. Even so, low photocatalytic efficiency and poor solar efficiency(maximum 5%) have hindered the commercialization of this technology. Therefore, many researchers have diverted their attention to exploit new photocatalysts. In the process of searching for efficient light driven oxide photocatalysts, Aurivillius bismuth based compounds were recognized as potential candidates. The special layered structure of Aurivillius compounds is effective to reduce the recombination of photo-generated carriers. It was suggested that the lone-pair distortion of Bi 6s orbital in these bismuth based semiconductors may cause the pronounced overlap of O 2p and Bi 6s orbitals in the valence band, which is benefit to the mobility of photo-generated carriers for improving the photocatalytic activity. In this thesis, Aurivillius Bi2MO5F(M = Nb, Ta) and Bi2(Nbx,Ta1-x)O5F(x = 0.3, 0.5, 0.7) composites were synthesized by the solvothermal method at a low temperature. In addition, their photocatalytic performances were investigated systematically. The content of this thesis mainly includes the following aspects:(1) Hierarchical Bi2NbO5 F porous hollow microspheres were prepared by the simple solvothermal method. The phase, morphology, structure and the elemental composition of as-synthesized sample were characterized by XRD, SEM, TEM, HRTEM and EDS data. The reaction mechanism was discussed by the phase evolution of the samples prepared with different reaction times. The BET surface area and porosity of as-prepared Bi2NbO5 F were studied by its nitrogen absorption-desorption property. UV-vis result shows that the band gap of Bi2NbO5 F photocatalyst is 2.85 eV. The photocatalytic activities of the as-prepared sample were investigated by the rhodamine-B, methyl orange, methylene blue and methyl blue photodegradation under ultraviolet light irradiation. The results show that: the as-synthesized sample has excellent photocatalytic activities for different dyes. This is mainly attributed to the direct photocatalysis of Bi2NbO5 F semiconductor. Among the results, the time of rhodamine-B photodegradation is the shortest and the photocatalytic reaction rate constant is the largest. The catalyst shows different photodegradation performances for different dyes. Rhodamine-B photodegradation shows the best photocatalytic activity. Different dye has different structure and color group. Therefore, the amount of energy that different dye degradation required is different.(2) Hierarchical Bi2TaO5 F porous hollow microspheres were synthesized by the simple solvothermal method with a low temperature in liquid. The phase, morphology, structure and the elemental composition of as-synthesized sample were characterized by XRD, SEM, TEM, HRTEM and EDS data. The growth mechanism of Bi2MO5F(M = Nb, Ta) was discussed by the phase and morphological evolution of the samples prepared with different reaction times. The BET surface area and porosity of as-prepared Bi2TaO5 F were studied by its nitrogen absorption-desorption property. UV-vis result shows that the band gap of Bi2TaO5 F photocatalyst is 2.94 eV. The photocatalytic activities of the as-synthesized sample were investigated by the rhodamine-B, methyl orange, methylene blue and methyl blue photodegradation under ultraviolet light. The results show that: the as-synthesized sample has excellent photocatalytic activities for different dyes. This is mainly attributed to the direct photocatalysis of Bi2TaO5 F semiconductor. Since the band gap of Bi2TaO5 F is slightly wider than Bi2NbO5 F, Bi2TaO5 F photocatalyst exhibit lower activities for those four dyes photodegradation.(3) Hierarchical porous solid microspheres Bi2(Nb0.5,Ta0.5)O5F composite photocatalyst was synthesized by the similar solvothermal method with a low temperature in liquid. The phase, morphology, structure and the elemental composition of as-synthesized sample were characterized by XRD, SEM, TEM, HRTEM and EDS data. The result of UV-vis shows that band gap of Bi2(Nb0.5,Ta0.5)O5F composite material is 2.74 eV. The possibility of its photocatalytic mechanism were discussed through Bi2(Nbx,Ta1-x)O5F(x = 0.3, 0.5, 0.7) composites photocatalytic performance for the rhodamine-B photodegradation.