Modification And Photocatalytic Performance Of Nanostructure Nb₂O₅

The energy crisis and environmental pollution are important issue in morden society.In recent years,using semiconductor nanomaterials for photocatalytic degradation of various organic contaminants in the environment has increased.Semiconductor oxides have shown great potential for application in solving energy and environmental problems.Niobium pentoxide（Nb₂O₅）is one of the more typical semiconducting materials because of its similar bandgap（3.4 e V）to titanium dioxide（Ti O2）and its low toxicity,a more negative conduction band edge position,good chemical stability,thermodynamic stability,comparable electron injection efficiency,high recycling rate,relatively high photocatalytic activity and high recycle rate is considered as a good photocatalyst candiate.However,the relatively wide band gap of Nb₂O₅（3.4 e V）restricts its applications only under UV light,while UV light only accounts for 3%-5% of sunlight,in order to make full use of sunlight,we need to modify the semiconductor oxide Nb₂O₅.The modification with the non-metal,metal,semiconductor/carbon clusters and the supported noble metal indicate that it can exhibit excellent optical properties.Although Nb₂O₅ semiconductor oxides are widely used,especially photodegradation of organic dye molecules.It is noteworthy that relatively few reports have been made on modified Nb₂O₅ materials,especially the modification with double-non-metallic elements and the introduction of noble metals,which inspired us to do the corresponding work.In this work,C,N co-modified Nb₂O₅ nanoneedles,Zn2+ doped C/Nb₂O₅ nanoparticles and novel Au@Void@Nb₂O₅ core–shell nanocomposites were synthesized and these modified measures extend the absorption spectrum of catalysts to the visible light region,which is beneficial for improving its photocatalytic performance towards photodegradation of rhodamine B（Rh B）and rhodamine 6G（Rh 6G）under visible light irradiation.Their enhanced properties were performed by a series of characterization.Based on the above content,our work as follows:1.C,N co-modified niobium pentoxide（Nb₂O₅）nanoneedles have been successfully synthesized via a facile hydrothermal method with niobium chloride（Nb Cl5）as a precursor and triethylamine as both the carbon and nitrogen source.The formation process of Nb₂O₅ nanoneedles has been presented in detail by investigating the effect of the crystallization temperature,the amount of triethylamine and the calcinations temperature.The as-prepared Nb₂O₅ nanoneedles exhibit more efficient photocatalytic activity thancommercial Degussa P25 and commercial Nb₂O₅ towards photodegradation of rhodamine B（Rh B）under visible light.Special chemical species,such as carbonate species and NOx species,that exist on the surface of the as-prepared catalyst could extend the absorption into the visible region and thus enhance the photocatalytic activity of the Nb₂O₅ nanoneedles.At the same time,the obtained C,N co-modified Nb₂O₅ nanoneedles exhibit excellent stability even after three successive cycles.A possible photodegradation mechanism was proposed and the corresponding photodecomposition process of Rh B over the Nb₂O₅ nanoneedles was elucidated by the reactive species trapping experiment,suggestingthat h+ and O2·-play major role in the photodegradation of Rh B in aqueous solution.2.Novel Zn doped C/Nb₂O₅ nanoparticles have been prepared successfully via a simple hydrothermal technology.The as prepared nanoparticles presented enhanced crystallinity with ultrafine morphology and Zn2+ was confirmed to exist as the form of Zn O randomly on the surface of C/Nb₂O₅ nanoparticles by XRD,TEM and XPS characterization.The amount of surface oxygen vacancies（SOVs）on the surface of catalyst reaches an optimal value when the molar ratio of Zn/Nb is 10 % proved by XPS and SPS results.The photocatalytic activity over the catalysts with an optimal doping amount of Zn2+ exhibited much more efficient photocatalytic activity than P25,commercial Nb₂O₅ by degradation of rhodamine（Rh B）and rhodamine（Rh 6G）under visible light irradiation.3.In this chapter,novel Au@Void@Nb₂O₅ core–shell nanocomposites have been fabricated through a facile sol–gel method.The construction process of this core–shell nanostructure has been presented in detail.The as-prepared core–shell nanostructure exhibits nanosphere morphology with Nb₂O₅ acting as the shell and Au nanoparticles acting as the core,which was proved by SEM and TEM.The noble metal Au core protected by the Nb₂O₅ shell from aggregation and deterioration.The core–shell nanocomposites demonstrate excellent visible light absorptioas shown by the UV-Vis diffuse reflectance spectra.The surface plasmon resonance（SPR）effects of Au core is benefit for the electron transitions between Au core and Nb₂O₅ shell.The as-prepared photocatalyst Au@Void@Nb₂O₅-2 calcined at 300 °C exhibits higher photocatalytic efficiency than Au@Si O2@Nb₂O₅-2-300 °C,Nb₂O₅ and P25 by degradation of rhodamine B（Rh B）under visible light.Fluorescence spectrometry（PL）demonstrated that the Au@Void@Nb₂O₅-2-300 °C catalyst exhibited a lower electron-hole recombination rate after removal of Si O2.Under the irradiation of visible light,the asprepared Au@Void@Nb₂O₅-2-300 °C nanocomposites showed better photacatalytic performance than the commercial P25,commercial Nb₂O₅ and Au@Si O2@Nb₂O₅-2-300 °C towards photodegradation of Rh B aqueous solution.We also investigated the effects of the amount of Au wt % on the photocatalytic performance.In the photodegradation process of the Rh B solution,holes（h+）play a more important role than hydroxyl radicals（·OH）over the as-prepared photocatalyst,which was analyzed using active species trapping experiments and photoluminescence（PL）spectroscopy.Moreover,the photocatalyst Au@Void@Nb₂O₅-2-300 °C exhibits excellent durabilityof photocatalytic activity even after five successive cycles.This contribution gives a new perspectivefor designing and preparing novel metal-Nb₂O₅ nanostructure catalysts for energy and environmental application.