ZHAO, Xiu Song George

Associate Professor

PhD (Chem. Eng.) Queensland, 1999
BSc (Chem.) Shandong Uni , 1987

Contact information
Blk E5, 4 Engineering Drive 4, #03-17, Singapore 117576
Tel: (65) 6516 4727    Fax: (65) 6779 1936
Email: chezxs@nus.edu.sg

Research Group Website

RESEARCH

Fabrication and simulation of 3D PBG materials

Photonics is the technology of molding the flow of light. It is envisioned photonic technology will play a revolutionary role in the 21th century, which will outperform current electronic technology. The key to photonics is the fabrication of photonic bandgap (PBG) materials or photonic crystals, which are periodic dielectric structures with lattice parameters comparable to the wavelength of electromagnetic waves. This project aims to fabricate PBG materials with self assembly approach. Self-assembled colloidal crystals are employed as the templates to structurally direct the formation of 3D PBG materials. Recently, a flow-controlled vertical deposition (FCVD) and an inward growing self assembly methods have been developed to grow colloidal crystal templates. High-refractive-index materials like Si are being fabricated to make 3D photonic crystals with a full PBG. In addition, a method in combination with self assembly and photolithography for insertion of defects in the 3D PBG materials has been developed. It allows us to create line, point, and plannar defetcs embedded in a 3D photonic crystal for photonic device applications. In the mean time, simulation of the band structures and optical properties of the PBG materials is performed to support experimental data.

Zeolites as acidic catalyst and ion exchanger

Zeolites are microporous crystalline materials with many interesting properties such as surface acidity, ion exchange property, and molecular sieving property. They have found wide applications in shape-selective catalysis and adsorption. Our current research interest focuses on design and synthesis of nano-sized zeolite crystals with special characteristics such as chrality, high ion-exchange capacity and tailored acidity for applications of (1) enantioselective catalysis/separation, (2) heterogeneous catalysis, and (3) removal of heavy metal ions present in waters.

Template synthesis of novel porous carbon materials

The development of a hydrogen storage material capable of meeting the U.S. Department of Energy storage target of 6.5% would speed the commercialization of fuel cell vehicles, which in turn could alleviate the dependence on fossil fuels while reducing air emissions. The last couple of years have seen a great deal of research interest dealing with carbon materials such as nanotubes and fibers as hydrogen storage media, fuel cell electrodes, and supercapacitors. This research project is aimed to synthesize new porous carbon structures using template synthesis strategies. Zeolites, mesoporous silicas, and colloidal crystals have been employed as the template. it has been observed that templated-synthesized carbon with a graphitic pore wall nature performs better for low-temperature hydrogen storage and for room-temperature methanol oxidation.

Functionalization of mesoporous materials for catalyst immobilization

In our research group, a great deal of effort has been made at synthesis, processing, characterization, and application of mesoporous materials, ranging from pure silica to organosilia, from metals to semiconductors, from inorganics to composites. Surafce functionalization via post-treatment and in-situ synthesis has been carried out. Immobilization of biocatalysts (enzymes) and Lewis catalysts such as aluminum trichloride on surface-functionalized materials has been recent focus. Immobilzied penicillin G acylase (PGA) has been observed to display a higher enzymatic activity than free PGA while offers the advantages of easy operation and possible reuse. Immobilized aluminum trichloride has been found to outperform AlCl3 catalyst in terms of selectivity in the reaction of isopropylation of naphthalene to produce 2,6-DIPN.

Molecularly imprinted inorganic adsorbents

Separation and purification of biological compounds is highly desired in industry, especially those processing food and pharmaceuticals. Molecular imprinting (MI) is a technique to incorporate specific recognition sites into a substrate. These sites display high affinity and selectivity towards a given molecule, from which the substrate was prepared. The objectives of this project are to synthesize molecularly imprinted porous silica materials by using a combined technique of surfactant template and molecular imprinting, and to evaluate their performance in separation and purification of biological compounds presented in food, drug and beverage, etc.

Fundamental study on self assembly of colloidal particles

Self assembly of particles in colloidal and biological systems plays an important role in fabrication of functional nanomaterials such as bilayered membranes and photonic crystals. it has been a great challenge of understanding the forces driven self assembly in a colloidal system. The objective of this project is to model and simulate self assemly processes by considering the interparticle forces such as van der Waals force, DLVO and non-DLVO forces, electrostatic force.

NEWS & EVENTS

1. Prof Zhao serves on the editorial board of Journal of Porous Materials since 2006.

2. Nature Nanotechnology highlighted our work on fabrication of colloidal spheres with nanoholes, which is a hot communication paper published in Journal of Materials Chemistry and enjoyed Top Ten most downloaded article in both May and June of 2006.

3. The work on 3D colloidal crystals with a dual periodicity published in Langmuir is highlighted by Nature Publishing Group Materials Update (see the highlight).

4. A themed issue of Journal of Materials Chemistry on Novel Porous Materials for Emerging Applications edited by Professor George Zhao contains 6 review articles from leading researchers which cover a range of types and applications of porous materials (see the editorial).

5. Our work on fabrication of 3D linear defects within a self-assembled photonic crystal published in Chem. Mater. 2005, 17: 3069 is highlighted by MRS Bulletin, 2005, issue 8 (see the highlight).

6. The work on fabrication line defects embedded in a 3D photonic crystal published in Advanced Materials is highlighted as the inside cover of the issue (see the cover).

7. The work of preparation of novel nanostructured carbon combining micro-, meso- and macropores, published in International Journal of Nanoscience, is highlighted in the front cover of the issue. (Click to see the cover)

For more information, see List of Publications