Development of layered Titanate nanomaterials for environmental applications

• Main Author: Tang, Yuxin.
• Other Authors: Dong Zhili
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials; DRNTU::Engineering::Materials::Functional materials
• Online Access: http://hdl.handle.net/10356/51352
• Institution: Nanyang Technological University

Nanosized materials with exceptional properties have already led to breakthroughs in various fields of science and technology. This project aims to explore new routes to design functional titanate nanomaterials with tailored structure to achieve low cost and efficient titanate materials for environmental cleanup, particularly water treatment methods and applications. Since the properties and applications of the nanomaterials greatly depend on their size, composition, crystal structure, morphology, as well as the surface functionality, the synthesis of the titanate materials and their hybrids with controlled structure, size, shape, and composition is very important to their various promising applications. In order to study the influence of crystal structure, the morphology and the surface area on the adsorption performance, different dimensional titanate materials are prepared. Firstly, we have developed an ultrafast and template-free method to synthesize three-dimensional (3D) hierarchical layered titanate microspherulite (TMS) particles with high surface area. The synthesis makes use of an electrochemical spark discharge spallation (ESDS) process, during which fast anodic reaction on titanium surface creates a layer of titanium dioxide that instantly breaks down by the applied electrical field into the solution in the form of titanium oxide particles. The spalled particles readily react with the heated NaOH electrolyte to form the titanate particles. After hydrogen ion exchange, the surface area can reach as high as ~ 406 m2g-1. Secondly, we study the adsorption performance and mechanisms based on the as-prepared different dimensional titanate materials (TMP, TNT, TNW and TMS) for waste water treatment. The methylene blue (MB) and PbII ions are used as representative organic and inorganic pollutants. The result show that the titanate micro-spherulite particle (TMS) powders possess excellent ion-exchange ability and high adsorption rate with toxic PbII ion and the MB dye due to its high surface area and crystal structure compared with sodium trititanate bulk particle, titanate nanowires and nanotube. The adsorption mechanisms of the removal of MB dye and PbII ions are proposed. Apart from the adsorption application of the titanate materials, we also develop an efficient photocatalyst for photocatalytic degradation. Three-dimensional TiO2 microsphere photocatalysts with different hierarchical nanostructures are synthesized by the synergistic strategies of ultrafast electrochemical spark discharge spallation process and thermal treatment. The nanostructure of hierarchical microspheres undergoes three evolution steps, which includes the change from nanosheets into hybrid nanoflakes/nanoparticles and finally to nanoparticles as the calcination temperature increases, in line with the predicable trend of increase in crystallinity and decrease in specific surface area. Compared to other forms of calcined TiO2 samples (nanosheets and nanoparticles), the hybrid TiO2 nanoflakes/nanoparticles hierarchical porous structure exhibits a higher photocatalytic activity for the degradation of organic compounds (methyl orange and bisphenol A). This is attributed to their relatively larger specific surface area (~ 116 m2/g), more abundant porosity and good crystallinity. Based on this hybrid structure, a visible light sensitive Ag/TiO2 microsphere photocatalyst is designed and it shows higher degradation rate under the visible light illumination (> 420 nm). The porous microsphere photocatalyst does not lose its activities after recycled use. Moreover, the emergence of titanate nanomaterials, as the new building blocks for designing new and high efficient nanohybrid materials, has opened up new ways to utilize the solar energy for different applications. In our work, dense and uniform silver halides AgX (X = Cl, Br, I) nanoparticles were successfully fabricated on layered titanate nanowired honeycomb (THC) support. The honeycomb structure is composed of vertically grown, intertwined one dimensional (1D) titanate nanowires from its side walls. This unique morphology of the THC surface structure was prepared by a modified hydrothermal approach within a short autoclave treatment time. The growth of AgX nanocrystals was carried out through two steps. Firstly, the growth of AgX crystals on the THC firstly makes use of a facile ion-exchange process by soaking the as-prepared THC in HNO3 solution and AgNO3 in sequence, during which Na+ ion in the interlayer of titanate is consequently replaced by H+ and Ag+ ions without changing its morphology. Secondly, the obtained Ag-THC then readily reacts with gas or liquid HX compound to form the nanosized AgX particles on THC. Followed by light-irradiation, the optimized Ag/AgX thin films exhibited excellent degradation performance of methyl orange under visible light due to localized surface plasmon resonance effect.