Preparation Of Nanostructured(Ga_1-xZn_x)(N_1-xO_x) Photocatalysts And Their Visible Light Driven Photocatalytic Hydrogen Production Properties

Because of the urgent need for clean energy to tackle the issues of fossil energy depletion and environmental pollution,application of clear and renewable energy resourceshas become first priority.Solar energy has been regarded as one of the perfect substitution energy resources because of its pollution free and abundant radiation regions.And the conversion of solar energy to hydrogen by photocatalysts from water splitting has attracted massive research interest.(Ga_1-x Zn_x)(N_1-xO_x)is a photochemical stable,high photocatalytic efficiency and visible-light driven photocatalyst for water splitting into H₂ and O₂.At present,(Ga_1-xZn_x)(N_1-xO_x)were usually obtained by heating a mixture of metal oxide submicrometer powders under flow of ammonia at really high temperature.The obtained(Ga_1-xZn_x)(N_1-xO_x)were aggressive powders with very low specific surface areas.Due to the nature of photocatalytic reaction is transformation of photogenerated carriers from interior to surface and participating in oxidation-reduction reaction on surface of photocatalyst.More carriers would participate in reaction in littler nanocrystals,which contributes higher photocatalytic efficiency.Therefore,(Ga_1-xZn_x)(N_1-xO_x)with ultrafine grain size must have greatly improved photocatalytic efficiency.Consequently,it is highly desirable to tailor the structure of(Ga_1-xZn_x)(N_1-xO_x)on nanoscale for higher photocatalytic efficiency.This thesis focused on the fabrication and study of(Ga_1-xZn_x)(N_1-xO_x)nanomaterials.The effects of the particle size,morphology and nanostructures on the catalytic performance were examined in detail.The application of the nanostructured photocatalytic was also systematically investigated.?1?Zn-Ga-LDHs nanosheets with specific surface area of 22.3 m²/g were prepared by coprecipitation method.It is possible to use LDHs containing Zn²⁺and Ga³⁺ions as precursors for(Ga_1-xZn_x)(N_1-xO_x)solid solutions because these ions are already homogeneously mixed at an atomic scale,and the Zn/Ga ratio can be tailored according to need.(Ga_1-xZn_x)(N_1-xO_x)nanoparticle was readily obtained by the nitridation of Zn-Ga-LDHs with greatly reduced reaction temperature and time.The nanoparticle with specific surface area of 51.0 m²/g was hexagonal plates,narrow size distribution and good dispersion.H₂ production rate of(Ga_1-xZn_x)(N_1-xO_x)nanoparticle was 2.9 times than(Ga_1-xZn_x)(N_1-xO_x)powders.?2?Zn?OAc?₂-Ga?NO₃?₃/PVP composite nanofibers prepared by electrospinning were calcined in air to decompose the PVP and crystallize into zinc-gallium oxide.The obtained zinc-gallium oxide fibers consisted of nanocrystals smaller than 5 nm were hundreds micrometers length with porous surface.The zinc-gallium oxide nanofibers were completely nitride at 500⁷00°C under NH₃ flow.The obtained(Ga_1-xZn_x)(N_1-xO_x)nanofibers were uniform and mesoporous with a super thin diameter of 100 nm and very high specific surface area of 85.5 m²/g.Compared to(Ga_1-xZn_x)(N_1-xO_x)powders,the porous(Ga_1-x Zn_x)(N_1-xO_x)nanofibers exhibit 3.1times improved photocatalytic activity for water splitting.?3?A series of(Ga_1-x Zn_x)(N_1-xO_x)-rGO nanocomposite photocatalyst with different rGO content have been prepared via hydrothermal and nitridation.The graphene sheets were fully exfoliated and decorated with(Ga_1-xZn_x)(N_1-xO_x)nanocrystals.Compared with bare(Ga_1-x Zn_x)(N_1-xO_x),the(Ga_1-xZn_x)(N_1-xO_x)-rGO demonstrated higher specific surface area,smaller particle size,enhanced visible light absorption and increased photocatalytic activity for visible-light driven water splitting.And photocatalyst with 30 wt.%graphene had the best activity,that the rate of H₂production is almost 5 times higher than that of bare(Ga_1-x Zn_x)(N_1-xO_x)particles.?4?The(Ga_1-xZn_x)(N_1-xO_x)nanoparticle was deposited on the AZO glass via electrophoretic deposition,which was a physical deposition process,and formed a film electrode.Tickness and transmittance of film was influenced by the deposition time.In the electrode,(Ga_1-xZn_x)(N_1-xO_x)nanoparticles was function part which generated electron-hole pairs under light irradiation.After deposited 4 min,the photocurrent intensity of(Ga_1-xZn_x)(N_1-xO_x)electrode was strongest.After heat treatment,the photocurrent intensity of the electrode was 0.43 mA/cm²,which was twice of that of untreated sample.?5?(Ga_1-x Zn_x)(N_1-xO_x)photoanode with 3D hierarchical structures was prepared by electrophoretic deposition on Ti mesh substrate and nitridation.Its morphology was influenced by deposition time in Zn?NO₃?₂ solution.The(Ga_1-xZn_x)(N_1-xO_x)photoanode was mesoporous structures duo to nitridation process.After nitridation,sample that electrodeposited in Zn?NO₃?₂ solution 30 min,then in Zn?NO₃?₂ and Ga?NO₃?₃ mix solution 20 min,showed the highest photocurrent intensity of 3.05mA/cm².The photocurrent intensity of the sample was improved in Na₂SO₄ solution with pH=13.