Design,Synthesis And Photocatalytic Properties Of Cu-TiO₂ Based Photocatalysts

In order to solve the bottleneck problems of narrow light response range,low photocatalytic efficiency,and easy agglomeration and loading difficulties in the synthesis and application process of nano TiO2 photocatalytic materials,the synthesis of Cu doped TiO2(Cu-TiO2)nanocrystal colloid based photocatalysts was carried out in this paper.Cu-TiO2 nanocrystal colloid was synthesized and the band structure of TiO2 nanocrystal was regulated by Cu doping.The mechanism of enhanced photocatalytic performance of TiO2 by Cu doping was studied.Then the photocatalytic performance of Cu-TiO2 nanocrystal colloid was further improved by size control of the nanocrystal or the synthesis of Cu-TiO2/g-C3N4 and Cu-TiO2/CuS heterojunction photocatalysts.The photocatalytic properties of the prepared Cu-TiO2 based photocatalysts were studied using benzene and NO as model gaseous pollutants and Escherichia coli and Staphylococcus aureus as model microorganisms..The main research contents are as follows:(1)A Cu-TiO2 nanocrystal colloid was successfully synthesized by solhydrothermal approach at a low temperature.The synthesis strategy of Cu-TiO2 nanocrystal colloid and the effect of Cu doping on the band structure of TiO2 were studied with emphasis.The results indicated that Cu doping introduced impurity levels above the valence band of TiO2,making the valence band move up.Meanwhile,Cu doping also introduced oxygen vacancies(OVs)in TiO2 lattice,forming defect levels in the energy band of TiO2.Therefore,under the synergistic effect of Cu doping and OVs,the bandgap of TiO2 was narrowed,resulting in enhanced visible light absorption capacity and improved charge carrier separation efficiency.When the doping concentration of Cu was 3.0 mol%,the degradation rate of benzene by Cu-TiO2 under visible light for 4 h reached 87.1%,and the antibacterial rate against Escherichia coli and Staphylococcus aureus was beyond 99.99%.The photocatalytic performance of Cu-TiO2 was far better than that of pristine TiO2.(2)The grain size of Cu-TiO2 nanocrystals in colloid was controlled by nonsurfactant hydrazine hydrate and the controlling mechanism was studied.Hydrazine hydrate promoted the decomposition of peroxy complex polymer and the formation of TiO6 octahedral by reacting with HO2-ions and peroxy bonds in Cu-Ti peroxy complex polymer(Cu-PTA)sol,thus promoting the nucleation of anatase TiO2 and reducing the grain size.Therefore,the grain size of Cu-TiO2 was controlled without introducing impurity ions into the colloid.Cu-TiO2 with optimized grain size showed enhanced photocatalytic properties,the benzene degradation rate of which reached 99.7%under visible light for 4 h,and the conversion rate of NO reached 68.3%under continuous flow.(3)A S-scheme heterojunction of Cu-TiO2/g-C3N4 was designed and synthesized by grinding-hydrothermal method.g-C3N4 nanosheets were mechanical exfoliated and dispersed in Cu-PTA sol after high-energy ball milling,and then Cu-TiO2 nanocrystals were crystallized on the surface of g-C3N4 nanosheets,thus the systhesis of Cu-TiO2/g-C3N4 heterogeneous dispersion was realized.The S-scheme charge transfer mechanism of Cu-TiO2/g-C3N4 heterojunction was revealed by in situ XPS characterization and the promotion effect of S-scheme charge transfer on carrier separation was studied.The visible light absorption and photocatalytic performance of Cu-TiO2/g-C3N4 heterojunction was enhanced with the increase of g-C3N4 content in the heterojunction.When the g-C3N4 content was 5.0 mol%,the NO conversion rate of the heterojunction reached 75%with a good cyclic stability.(4)A p-n scheme heterojunction of Cu-TiO2/CuS was designed and synthesized by an in-situ sulfidation method.The band structures of P-type semiconductor CuS and N-type semiconductor Cu-TiO2 were mathed well,and the p-n heterojunction structure was constructed successfully by in situ sulfurization growth of CuS on the surface of Cu-TiO2.The recombination of CuTiO2 with narrow-gap CuS further expanded the visible light absorption range to realize full spectral absorption of visible light,and thus improved photoenergy utilization and photocatalytic activity.The Cu-TiO2/CuS heterojunctions obtained by in-situ sulfidation of Cu-TiO2 nanocrystal colloid with Cu doping concentration of 1.0 mol%exhibited the highest NO conversion rate of 85%,which was about 1.3 times that of Cu-TiO2.