Fabrication And Photocatalytic Performance Of Semiconductor Composite Materials Derived From Layered Double Hydroxide Precursors

Increasing attention has recently been paid to semiconducting photocatalysts due to their potential industrial applications in areas such as environmental cleaning and solar energy conversion. Because the traditional CdS photocatalst has low quantum efficiency and undergoes photocorrosion when exposed to visible light, modification of CdS or development of solid solution photocatalytic materials has attracted a wide spread attention. In recent years, device of photocatalyst to achieve continuous operation and easy recovery has been a research hotspot. Therefore, our research mainly focuses on the controllable preparation, device and the enhancement of photocatalytic performance of the visible-light response sulfide semiconductor materials. A series of sulfide semiconductor photocatalysts have been fabricated through in-situ sulfuration process using layered double hydroxides (LDHs) as precursors. By changing the chemical composition of LDHs precursors and controlling the sulfuration reaction process, we have synthesized a series of sulfide solid solution materials with controllable composition, morphology and structure. Meanwhile, combining the solvent evaporation and in-situ sulfuration process, the CdS/LDHs transparent films has been fabricated and the photocatalytic performance of the solid solution and the CdS/LDHs films have been investigated in detail. Our research work may be regarded as some experimental basis for the further study on compositon control, structural design, and enhancement of photocatalytic performance of sulfide semiconductor materials.The innovation of this work and results are as follows:1. In order to beat "low quantum efficiency and photocorrosion" of traditional CdS nanoparticles in photocatalysis field, according to the characteristics that the metal cations within the LDHs layers arrange orderly on an atomic level, a series of ZnxCd1-xS solid solution nanoparticles have been fabricated via sulfuration of a single precursor—a ZnCdAl-containing LDH and gaseous H2S. The highly dispersed ZnxCd1-xS nanoparticles with a mean average diameter of 3.0-4.0 nm, which are were arranged regularly inside a matrix of amorphous alumina. The band gap of the ZnxCd1-xS nanoparticles can be controlled by adjusting the Zn/Cd molar ratio. Under visible light irradiation, methylene blue (MB) can be photodegraded, and the photocatalytic performance of the ZnxCd1-xS solid solution increased with decreasing Zn mole fraction, and reached a maximum for a Zn mole fraction of 0.20.2. A series of mesoporous ZnxCd1-xS solid solution with controllable band gap and hydrophobic properties have also been prepared by selective extracting of amorphous alumina using strong alkali. After selective leaching of alumina, the surface area and pore size of the mesoporous ZnxCd1-xS solid solution has increased observably, and the original element composition, morphology and crystal structure has been well retained. The band gap of the mesoporous ZnxCd1-xS was monotonically red shifted whin visible light region as the amount of alumina reduced, and their photocatalytic activities for MB photodegradation were extremely enhanced.3. According to the characteristics of LDHs with alterable metal element type and the controllable preparation of LDHs films, (00l)-oriented Zn1-xFexS nanocomposite film have been fabricated through solvent evaporation and gas-solid sulfuration process derived from ZnFe-LDH, achieving the topotactic transformation from the LDHs precursor film to sulfide semiconductor film. The morphology and interface microsturcture of Zn1-xFexS nanocomposite film have been investigated systematically, and the relationship between element composition and the photoabsorption properties has been discussed. Our method provides a novel way to fabricate new types of chalcogenide semiconductor nanocomposite film.4. According to the characteristics of LDHs with exchangeable interlayer anions, transparent (00l)-oriented CdS/LDH composite thin films with tuneable CdS particle size have been successfully synthesized using a template synthesis method based on ion-exchange and the two-dimensional confinement effect of LDHs. The well-defined supramolecular LDH template affords good control over the formation of CdS nanoparticles, and the size of the CdS particles in the LDH host can be controlled by adjusting the length of time of sulfuration reaction. Because of the promising combination of LDH properties (stability, transparency, and anisotropy) with those of semiconductor nanoparticles, we expectthese composite films to have some interesting applications as photocatalysts, or in chemical sensors and nonlinear optical devices.