Layer-by-Layer Adsorption And Reaction Method For The Preparation Of Metal Phosphate Films And Their Functionalization

Layer-by-layer (LbL) assembly has been widely used as a versatile method for fabricating multilayer thin films with well-tailored structure and composition. Although many methods on fabricating functionalized multilayer films have been established, and numerous substances have been assembled successfully, it still remains challenge for the preparation of inorganic thin films, such as metal phosphate film with many superior properties. In this dissertation,we mainly focus on the development of an facile method for the preparation of inorganic metal phosphate films, which named layer-by-layer adsorption and reaction method. And, the properties of as-prepared metal phosphate films for their potential applications were studied.In chapter 2, as an extension of SILAR method and surface sol-gel process, we developed a layer-by-layer adsorption and reaction method for the preparation of titanium phosphate ultrathin films. We demonstrate that amorphous titanium phosphate films with composition of mainly Ti(HPO4)2 can be prepared by repetitive adsorption of a substrate from aqueous Ti(SO4)2 solution and subsequent reaction in aqueous phosphate salt (PS) solution. The as-prepared titanium phosphate films are uniform, highly stable, and their thickness can be well controlled by adjusting the number of adsorption-reaction cycles and pH value of Ti(SO4)2 and phosphate salt solutions. The layer-by-layer adsorption and reaction method provides a facile way to prepare ultrathin films of titanium phosphate and other kinds of metal phosphates.Inchapter 3, we fabricated composite films of titanium phosphate (TiPS)/Prussian blue (PB) by the alternate deposition of TiPS layer and PB nanocrystals. The layer of TiPS was fabricated by the layer-by-layer adsorption and reaction method. The layer of PB nanocrystals was fabricated by sequential adsorption of FeCl3 solution and K4[Fe(CN)6] solution. Instead of producing films of TiPS layer alternated with a PB nanocrystal layer, the TiPS/PB composite films have a structure in which the interstices of the PB nanocrystal films are filled with TiPS component. The presence of the TiPS component makes the interpenetration of counter ions during the electrochemical reaction of PB become easier and enhanced electrochemical properties in TiPS/PB composite films than in pure PB nanocrystal films is obtained. TiPS/PB composite films can catalyze the electrochemical reduction of H2O2 and are potentially useful as H2O2 biosensors.In chapter 4, we show that silver ions can be incorporated into titanium phosphate ultrathin films by a simple ion exchange process conducted at 50°C and room temperature. Silver ions were dispersed homogeneously in the normal direction of titanium phosphate film. In situ reduction by NaBH4 produced silver nanoparticles embedded in titanium phosphate film. The ion-exchanged titanium phosphate films are effective in prohibiting the growth of Escherichia coli and therefore can be used as a promising kind of antibacterial coatings. Considering the high mechanical and chemical stability of the matrix titanium phosphate film used, the silver-doped titanium phosphate film can be used in a wide range as catalyst and antibacterial coatings. The high ion exchange capacity of the titanium phosphate film as exemplified by silver ions and its easy deposition on substrates with complicated morphologies will make titanium phosphate films excellent candidates in removing heavy metals from water.In chapter 5, we show that tris(2,2'-bipyridine)-ruthenium(II) complex (Rubpy) and water-insoluble tris(4,7-diphenyl-1,10- phenanthroline)ruthenium(II) complex (Rudpp) can be successfully incorporated into zirconium phosphate (ZrPS) films during the layer-by-layer adsorption and reaction process for the fabrication of ZrPS films. Because of the large dimension of Rubpy and Rudpp, the direct incorporation of them into ZrPS films through ion-exchange process was unsuccessful. By mixing Rubpy with phosphate solution, the Rubpy was incorporated into ZrPS films during the formation of ZrPS films. By adding ethanol into phosphate solution, Rudpp becomes soluble and can be incorporated into ZrPS films through the formation of ethanol pre-intercalated ZrPS layers. While the incorporated Rubpy can be stabilized in the Rubpy@ZrPS/ZrPS alternate films, the Rudpp@ZrPS films are stable in water because of the water-insoluble property of the Rudpp. The Rudpp@ZrPS films are particularly suitable for the fabrication of oxygen sensors of high sensitivity because the porous structure of the Rudpp@ZrPS films enable the quick permeation of oxygen into and out of the film. The present method for the incorporation of guest organic molecules into ZrPS films is characterized by its simplicity and effectiveness in controlling the amount of Rubpy or Rudpp incorporated by simply tailoring the concentration of the mixture ratio of Rubpy or Rudpp to phosphate salt. Compared with organic or polymeric matrix films, ZrPS films fabricated by layer-by-layer adsorption and reaction method present the characters of excellent mechanical and chemical stability and can widen the application window of the ZrPS matrix films functionalized with guest materials. We believe that other cationic organic molecules of both water-soluble and water-insoluble could be also incorporated into ZrPS or titanium phosphate (TiPS) films by the present method to prepare various kinds of functionalized film materials.