| Semiconductor photo catalysts can effectively solve the problem of environmental pollution,but their application still has some limitations such as easy recombination of photogenerated electron-hole pairs and poor redox ability.In order to solve these problems,the surface electronegativity of graphite-like phase carbon nitriding was changed by modification.The specific morphology of exposed active crystal surface BiVO4 was taken as the matrix,and the principle of surface heterojunction and the electric field built in the interface as well as polarization charge induced the change of interface energy band structure was used.The g-C3N4/(110)facet BiVO4 heterojunction,the g-C3N4-BiVO4-Ag heterojunction and the Z-scheme BiV04(010)-Ag-g-C3N4 heterojunction photocatalysts were constructed by the methods consist of semiconductor-composite and noble metal loading,which can realize the spatial separation of photogenerated carriers and the preparation from type-II to Z-scheme heterojunction.enhancing the redox ability of the photo catalyst,and improving its carrier migration separation efficiency.The main results are divided into the following four points:(1)The g-C3N4 powders with different morphologies and surface electronegativity are obtain after acidification-calcination-oxidation-exfoliation.The-NH2 groups in melamine are acidified to-NH3NO3 groups by acid treatment,and further oxidation reduce the existence of C-N-H bonds,thereby promoting the formation of C-N-C and N-(C)3 bonds in g-C3N4 and enhancing the redox ability of g-C3N4;Both acid treatment and exfoliation are beneficial to increase the pore volume of g-C3N4,and promote formation of lamellar g-C3N4 structure.(2)The g-CN4/(110)BiVO4 heterojunction photocatalyst with negatively charged g-C3N4 deposited on the BiVO4(110)facet was prepared by the light deposition method.Under the synergistic effect of the BiVO4 surface heterojunction and the built-in electric field at the interface,the conduction band electrons of g-C3N4 finally migrate to the BiVO4(010)facet,and the valence band holes of the BiVO4(010)facet finally migrate to the valence band of g-C3N4,which enhances the transfer of interface charges and effective separation of photo-generated carriers.The transient and steady-state photocurrent of the heterojunction photocatalyst is 3.1 times that of BiVO4.After 120 min of visible light irradiation,the degradation rate of heterojunction photocatalyst for RhB reached 4.85 times than that of BiVO4.(3)NaIO3 was added as an electron trapping agent,the g-C3N4-BiVO4-Ag heterojunction photocatalyst with the negatively charged g-C3N4 deposited onto the BiVO4(110)facet and the metal Ag particles deposited onto the BiVO4(010)facet was prepared by two-time light deposition method.Under the synergy of the electrostatic attraction between g-C3N4 and BiVO4 and the surface heterojunction,the separation of carriers can be accelerated.While the heterojunction photocatalyst enhances light absorption,the high-energy hot electrons generated by the plasma can reduce O2 molecules produce reactive ·O2-groups to degrade dye molecules.After the heterojunction photocatalyst was visible light irradiated for 150 min,the degradation of RhB reached 76.3%,and the degradation rate reached 0.0088 min-1,which was 5.38 times that of BiVO4.(4)The Ag was selectively reduced on the BiVO4(010)facet by light irradiation,and then the positively charged g-C3N4 was deposited onto the BiVO4(010)facet.Under the synergistic effect of the interface energy band bending caused by the polarization charge and the internal existence in the composite system,BiVO4(010)-Ag-g-C3N4 Z-scheme heterojunction is prepared on BiVO4(010)facet.It promotes the separation and migration of photo-generated carriers and improves the oxidation-reduction ability of the photocatalyst.The Z-scheme heterojunction is exposed to visible light irradiation for 150 minutes,the degradation rate of RhB is 80%,which degradation rate is 6.12 times than that of BiVO4. |
PDF Full Text Request