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Research On The Preparation And Photocatalytic Properties Of Niobium Oxide Nanomaterials

Posted on:2017-05-03Degree:MasterType:Thesis
Country:ChinaCandidate:Q C WangFull Text:PDF
GTID:2271330488484958Subject:Chemical engineering
Abstract/Summary:PDF Full Text Request
With the increasing of environmental pollution and energy shortage, the sustainable development of human society has attracted much attention. The photocatalysis is recognized as one type of the promising ways to solve this problem. Owning to its low energy consumption, no two pollution, and high efficiency, photocatalytic technology has been widely used in the areas of organic synthesis, degradation of organic pollutants, and splitting H2O, etc. The photocatalyst is the most important factor for the high efficiency utilization of photocatalytic technology. Among those photocatalysts, Recent investigations of the the niobium oxide-based semiconductor materials have demonstrated exceptional physical properties such as unique catalytic properties. In this dissertation, based on the phase composition and crystal structure of niobium oxide, a series of the Nb2O5-based semiconducting nanomaterials have been synthesized by a facile and general hydrothermal method. Importantly, the Nb2O5-based hybrids could not only exhibit enhanced photocatalytic activity for the decomposition of RhB solution, but also catalyze the evolution of aldehydes from photocatalytic reaction of alcohols and O2 under visible-light irradiation. The details are summarized as follows:(1) Nb2Os·nH2O/Nb2O5 composites, an efficient heterogenous photacatlyst, were facilely prepared in high yield by a simple one-pot hydrothermal method. In order to understand the formation process of nanocomposites, effects of the glacial acetic acid usages and the hydrothermal treatment time were investigated. It is found that the unique acid environment provided by glacial acetic acid is essential for the formation of the hybrid Nb2O5 structures. However, the hydrothermal reaction temperature is a vital factor in effectively adjusting Nb2O5·nH2O/Nb2O5 composite phases.When the reaction temperature is 100℃, the sample was amorphous Nb2O5 nH2O with a small amount of Nb2O5.The BET specific surface area of the smple is up to 293 m2/g. and the average particle size is 20-40 nm. In addition, the as-obtaiend nanocomposite exhibits enhanced photocatalytic ctivity for the decomposition of RhB solution. The experimental results further indicated that t ·O2- may be an important oxidizing active species in photosensitized reaction under visible light. At the same time, the as-obtaiend Nb2O5-based nanocomposite also exhibits enhanced photocatalytic ctivity for the photocatalytic oxidation of aromatic alcohols to corresponding aldehydes in presence of O2, and the selectivity is almost 100%.(2) Nb3O7(OH)/Nb2O5 composites were synthesized by a facile one-step hydrothermal method using niobium hydroxide oxide as niobium source, and citric acid as chelating agent. To understand the formation process of the Nb2Os-based nanocomposites, effects of the citric acid usages and the hydrothermal treatment time were studied. The results show that the hydrothermal reaction temperature has a great influence on the composition and structure of Nb2O5 and Nb3O7(OH), and the specific surface area and the average particle size of the as-prepared Nb3O7(OH)/Nb2Os nanocomposites is 241 m2/g and 20-150 nm, respectively. This as-obtained sample could not only exhibit enhanced photocatalytic activity for the decomposition of RhB solution, but also catalyze the evolution of aldehydes from photocatalytic reaction of alcohols and O2 under visible-light irradiation. For the Nb3O7(OH)/Nb2Os composites prepared at 210℃, the Nb3O7(OH)/Nb2O5 composites afforded a conversion of 21%, and need of special note is high benaldehyde selectivity (>99%).Herein, to explore the nature of the composite-performance relationship of niobium oxide-based semiconducting materials, the development of alternative methodologies for the facile and well-controlled synthesis of novel niobium oxide-containing hybrids as well as understanding of the composite-/structure-dependent properties remains an important issue.
Keywords/Search Tags:hydrothermal method, niobium oxide, photocatalysis, RhB degradation, alcohols oxidation
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