Preparation And Properties Of The Micro-nano Photoelectricatalyst Based On The Keg Gin-type Fe-substituted Heteropolyacid Salt

Heteropolyacid salts (also known as polyoxometalates) belong to metal oxide clusters heteropoly compounds which possess unique structures and electro-catalytic properties. According to the ratio of the central atom and heteroatom, structures of heteropolyacid salts can be categorized into Keggin-type, Dawson-type, Anderson-type, Silverton-type, Waugh-type, and Lindquist-type. The formula of Keggin-type heteropolyanion is [XM12O40]x-8(X=Si, Ge, x=4; X=P, As, x=3; M=W, Mo). The ratio of central atom to the heteroatom is estimated to be1:12. It adopts the Td symmetry model and shows relatively stable. In addition, the basic framework of Keggin-type contains forty oxygen atoms with four kinds of bond. The activity of each bonding state oxygen atoms is different, which indicates strong coordination with transition metal ions and protons, and then Keggin-type transition metal substituted heterophony salt was formed. With intense study of polyoxometalates, more and more researchers become interested in Keggin-type transition metal-substituted heteropolyanion in the field of photo catalytic.Through changing the heteroatoms or the transition metals, Keggin-type transition metal-substituted heteropolyanion can adjust its photo-inspiration and oxidoreduction properties. Thus this material has wide application prospects in photo catalysis, electric catalysis, composite materials, environment management and the field of energy. The Keggin-type transition metal-substituted heteropolyanion and their derivatives, especially Na4PWn1139Fe(Ⅲ)(H2O), showed high catalytic activity in some catalytic process. Because of its wider pH (2～8) range and high catalytic activity, Na4PW11O39Fe(Ⅲ)(H2O) has achieved excellent result in the electrochemical catalysis and photochemical catalysis. However, since high solubility of Na4PW11O39Fe(III)(H2O) in water, there has been separation and recycling troubles. A way to solve the problem is that Na4PWn1139Fe(III)(H2O) fabricated by heterogeneous or insoluble catalysis.In this paper, Sodium ion (Na+) of Keggin-type transition metal-substituted heteropolyanion was replaced firstly by Cesium ion (Cs+) with ion exchange reaction. The product Cs4PW11Fe(Ⅲ)O39(H2O) can solve the problem of catalyst separation successfully. Then,0.006mol/L Cs4PW11Fe(Ⅲ)O39(H2O) was used as a precursor to fabricate Cs4PW11Fe(Ⅲ)O39(H2O)/Si film, through direct growth on the surface of the mono-crystalline silicon under hydro-thermal conditions with180℃for ten hours. On the basis of the X-ray diffraction (XRD) characterization and scanning electron microscope (SEM) surface characterization of the Cs4PW11Fe(Ⅲ)O39(H2O)/Si, surface photo-voltage of Cs4PW11Fe(Ⅲ)O39(H2O)/Si and degradation Rhodamine B experiment of Cs4PW11Fe(Ⅲ)O39(H2O)/Si were performed. The experimental results showed that Cs4PW11Fe(Ⅲ)O39(H2O) crystals grow in a form of cubic close packing on the surface of silicon up to a magnitude of micron, forming a micro-nano crystal film with few layers. The Cs4PW11Fe(Ⅲ)O39(H2O)/Si film exhibits good photoelectric efficiency, and degradation Rhodamine B experiment of Cs4PW11Fe(Ⅲ)O39(H2O)/Si showed that Cs4PW11Fe(Ⅲ)O39(H2O)/Si has good catalytic activity to Rhodamine B, therefore it expected to be applied in the field of photoelectric conversion and water pollution management.