Synthesis Of Ag₃PO₄Modified Semiconductor Photocatalysts And Their Application In Organic Pollutants Degradation

The prospect of utilizing semiconductor photocatalysis as a platform for removal of environmental pollutants have recently attracted much attention due to its potential advantages such as low selectivity, mild reaction conditions and high reaction rate. Complex photocatalysts are made up by semiconductors with different positions of valence band and conduction band, which can promote effective separation of photo-generated carriers and improve light response, photocatalytic activity and stability. Ag3PO4, as a narrow band gap semiconductor (2.4eV), can give a strong response to visible light in wide range, but exhibits a poor optical, thermal and chemical stability. However, it can be used to modify the wide band-gap semiconductor in order to widen the range of the light response, improve the separation and transport of photogenerated carriers, and promote the generation of active radicals and catalytic efficiency. Therefore, in this thesis, Ag3PO4was employed to modify BiPO4and g-C3N4. The morphology, structure and optical properties of the composite photocatalysts were characterized and the photocatalytic activity of the composites was also investigated. The main contents are as follows:(1) g-C3N4catalysts were synthesized by temperature-programmed calcination with melamine or urea as precursors, respectively. The g-C3N4derived from urea precursor (g-C3N4-U), showed flocculent structure and better dispersion. In addition, g-C3N4-U showed high photocatalytic activity against RhB under the irradiation of visible light.(2) BiPO4@Ag3PO4photocatalyst with core/shell nanorod structure was synthesized by combining hydrothermal and ion exchange methods. BiPO4@Ag3PO4core/shell nanorods had uniform size. The edge of light absorption for BiPO4nanorods redshifted obviously after modified by Ag3PO4. BiPO4@Ag3PO4core/shell nanorods showed a high visible-light response and their core-shell heterostructure improved the separation of photogenerated electrons and holes so that the efficiency of photocatalytic degradation of RhB was increased. RhB was totally discolored in60min and40min under the visible light and simulated solar illumination, respectively. In addition, the photogenerated holes of BiPO4@Ag3PO4core/shell nanorods played a key role in the photocatalytic oxidation degradation process.(3) Two-dimensional porous g-C3N4/Ag3PO4nanocomposites were prepared by an in situ deposition method. The light absorption of g-C3N4modified by Ag3PO4was significantly enhanced with the edge redshifted. The recombination of the photo-generated electron-hole was significantly reduced, and the transport of the photo-generated carriers accelerated. Under the irradiation of visible light, compared with g-C3N4or Ag3PO4, the efficiency of photodegradation against4-chlorophenol for porous g-C34/Ag3P4nanocomposites was significantly enhanced, which is up to5.6times higher than that of Ag3PO4. By electron paramagnetic resonance and fluorescence characterizations, one of the main active species during photocatalytic reaction of porous g-C3N4/Ag3PO4nanocomposites was proved to be OH.