Study On Preparation,Photocatalytic Properties And Mechanism Of Niobium/Titanate Composite Photocatalysts

With the energy crisis and organic pollutants in water becoming more and more serious,how to effectively solve those pollutants with low energy consumption is an overwhelming problem in the filed of environmental governance.Recently,semiconductor photocatalytic technology are regarded as a very promising method and attracted widespread attention.Because they can convert solar energy into chemical energy.Among those semiconductor materials,perovskite-type composite oxides are becoming increasingly popular due to their stable structure,abundant sources and high photoactivity property.Nevertheless,many perovskite materials have also some disadvantages such as wide bandgap energy and not respond to the visible light region,which limits the improvement of their photocatalytic activity.Therefore,in this work,we have systematically studied above questions by using sodium niobate（NaNbO₃）and lanthanum titanate（La₂Ti₂O₇）.These two perovskite photocatalytic materials were hybridized with other semiconductor nanoparticles by adopting an in-situ composite technology.The photocatalytic properties of the samples were controlled by adjusting microstructures.The separation mechanism of photogenerated electron-hole pairs of the samples was discussed under visible light illumination.The synergistic photocatalytic mechanism of the as-developed composites was also analyzed.The main contents are presented as follows:（1）NaNbO₃ cubic block was prepared by one-step hydrothermal method with using niobium pentoxide（Nb₂O₅）and sodium hydroxide（NaOH）as raw materials.The Ag₂SO₃/NaNbO₃ hybrids photocatalyst have been fabricated via a facile in-situ method at room temperature.Moreover,the samples structure,morphology and optical properties were characterized by X-ray diffraction（XRD）,scanning electron microscopy（FE-SEM）,ultraviolet-visible diffuse reflectance spectroscopy（UV-Vis DRS）,and X-ray photoelectron spectroscopy（XPS）,respectively.Furthermore,the photocatalytic activity of the samples was evaluated by degradation of rhodamine B（RhB）and methyl orange（MO）solutions under visible light illuminate.In addition,the main active species in the process of degradation and the mechanism of photocatalytic degradation were also discussed.Experimental results show that the photocatalytic degradation efficiency of the as-fabricated hybrids appears the trend of first increasing and then decreasing with increasing the dosage of NaNbO₃.When the molar ratio of Ag₂SO₃ to NaNbO₃ was 1:0.7,the as-fabricated composites have the best photodegradation efficiency of 96.4%in 30 min for rhodamine B and 97.1%in 60 min for methyl orange,respectively.They are obviously higher than that of pure samples.Moreover,the band gap energy of the as-fabricated samples is decreased from 3.15 eV to 3.04 eV,which is beneficial to increasing the absorption of visible light.In addition,holes(h^（10）)play a major role as well as superoxide free radicals（?₂O^-）and hydroxyl radicals（?OH）play an assistant role during the photocatalytic degradation process.（2）Two-dimensional precursor La₂Ti₂O₇（2D-LTO）was prepared by one-step hydrothermal method with adjusting the technological parameters and the raw material ratios of titanium sulfate（Ti（SO₄）₂）and lanthanum nitrate（La（NO₃）₃）.Moroever,the AgI/2D-LTO photocatalytic composites were fabricated by through a facile in-situ method.The structure,morphology and optical properties of the pure AgI,pure 2D-LTO and AgI/2D-LTO composites were characterized by XRD,FE-SEM,UV-Vis DRS,EIS and XPS,respectively.RhB dilute solution as the target degradation solution was used to evaluate the photocatalytic activity of the samples.The main active species and degradation mechanism of RhB were also discussed in detail.Experimental results show that this method can improve the absorption of visible light and the efficiency of photogenerated hole-electron separation and transformation of pure samples.Moreover,the photocatalytic degradation efficiency of the as-synthesized hybrids shows the tendency of first increasing and then decreasing with increasing the usage of 2D-LTO.When the usage of 2D-LTO was 10%,the as-developed hybrids possesse the maximum of 93.1%,which is 44.3 times higher than that of pure 2D-LTO.Furthermore,the band gap energy of 2D-LTO is reduced from 3.36 eV to 2.53 eV after it is hybridized with AgI nanoparticles.In addition,?₂O^-is the main active substance during the process of photocatalytic degradation.