Study On The Preparation And Photocatalytic Performance Of Niobium-based Functional Composites

Recently,a series of environmental problems caused by energy shortages and industrial contamination have aroused the keen concern of researchers all over the world.As one of the most promising approach to solve the above problems,semiconductor photocatalysis has been paid an increasing attention.It is regarded as a "green" technology,since it can produce hydrogen and oxygen by water splitting,inactivate viruses,eliminate various contaminants and catalytic activation of organic reaction under the irradiation of sunlight.Due to its controllable band structure,non-toxicity and high stability,niobium-based semiconductor photocatalysts have attracted much attention.However,the photo-induced electrons and holes in niobium-based semiconductors are easily to recombine,releasing the input energy as worthless photons and heat,resulting in low photocatalytic efficiency.Besides,a wide band gap of the materials leads to a low utilization efficiency of the solar light.In this paper,my main research objects are potassium niobite(KNbO3)and niobium pentoxide(Nb2O5).To overcome the above problems exist in niobium-based materials,my paper was focused on the following three parts to improve their photocatalytic efficiency,which lay a foundation for the rapid development of niobium-based semiconductor catalysts.The first part was to load some KNbO3 needles that are easily to agglomerate on the surface of vermiculite(VMT),which is a natural mineral material possesses a large surface area and outstanding absorption property.Through synergy between adsorption and photocatalysis,the pollutant removal efficiency was improved.The second one was the synthesis of black mesoporous Nb2O5-x nanorods(BMNb)with abundant oxygen vacancies.The mesoporous structure was beneficial to increase the reaction sites and improve the photocatlytic efficiency.The introduction of oxygen vacancy could regulate the band gap of the catalyst,widen its spectral respond range,and realize the effective utilization of visible light.The last one was to fabricate a direct Z-scheme heterostructured photocatalyst by growing Nb2O5 nanospheres on the petals of the ZnIn2S4 microspheres,thus preventing the recombination of the photoinduced electrons and holes,improving its photocatlytic efficiency.The main research contents are as follows:1.Three-dimensional(3D)KNbO3/VMT was synthesized by a hydrothermal method to grow KNbO3 rods in array on the inner and outer surfaces of VMT using niobium chloride as the niobium resource,and the composite displayed good removal performance of methylene blue(MB).VMT is a natural phyllosilicate material that not only possesses a large surface area,but also shows an outstanding absorbability.On the one hand,using VMT as a substrate for KNbO3 can prevent the agglomeration of KNbO3 powder,increase the active sites of the reaction,and reduce the recovery cost of the reaction.On the other hand,combined with the strong adsorption capacity of VMT,photocatalysis and adsorption can work together to improve the pollutant removal efficiency.After illumination for 105 min,the removal rate of MB in aqueous solution could be higher than 81%.Moreover,the environmentally friendly KNbO3/VMT material is easy to synthesize and is expected to be a promising structured photocatalyst for the removal of dyes.2.An effective and simple strategy was utilized to synthesize black mesoporous Nb2O5-x nanorods(BMNb)with abundant oxygen vacancies.The formation of oxygen vacancy reduces the bandgap of Nb2O5 which extend the photoresponse from the ultraviolet to the visible and infrared light regions.In addition,the mesoporous structure of BMNb lead to a higher surface area than the as-prepared Nb2O5 precursor(36.24 m2 g-1 cf 8.69 m2 g-1).Benefitting from coordinated regulation of structure and composition,the BMNb exhibits better photocatalytic performance than Nb2O5 in aerobic oxidative coupling of amines to imines under visible light irradiation at room temperature(280.61?mol of N-benzylidene benzylamine obtained,10 h).The yield of BMNb for benzylamine oxidation increases by 63%over the Nb2O5.This work could open new perspectives to design efficient photocatalytic organic oxidation catalysts.3.A bifunctional ZnIn2S4/Nb2O5(ZIS/NbO)photocatalyst was fabricated by growing Nb2O5 nanospheres on the petals of ZnIn2S4 microspheres via a facile hydrothermal approach.The composite possessed a direct Z-scheme heterostructure that was confirmed by the in situ irradiated X-ray photoelectron spectroscopy(ISI-XPS)and electron spin resonance(ESR)measurements.Thus,the rate of hydrogen evolution for optimized ZIS/NbO(6026 ?mol g-1 h-1)was higher than that of Nb2O5(2157 ?mol g-1 h-1)and ZnIn2S4(3328 ?mol g-1 h-1).Furthermore,the ZIS/NbO also showed excellent performance for oxidation of biomass-derived intermediate 5-hydroxymethylfurfural(HMF)to value-added products(85.5%of HMF conversion).More importantly,the coupled photocatalytic H2 reduction and HMF oxidation were achieved on ZIS/NbO Z-scheme heterostructure at the same time.Due to the presence of direct Z-scheme heterojunction that prevents the recombination of photogenerated electron and hole in the composite,the ZIS/NbO displayed better photocatalytic performance than that of sole Nb2O5 and ZnIn2S4.Our findings are expected to offer a broad optical window for fabricating bifunctional heterostructured composites for coupled photocatalytic reduction and oxidation.In this paper,three different strategies were used to modify KNbO3 and Nb2O5 to obtain a promoted photocatalytic performance.The modified niobium-based materials showed improved performance on the removal of organic dye pollutants,catalytic activation of organic reaction and water splitting.Our findings expanded the application of the niobium-based materials in the field of photocatalysis,and are also expected to offer a broad optical window for fabricating functionalized semiconductor photocatalyst with improved performance,which laid a foundation for the rapid development of niobium-based materials.