Nanotechnology & Catalysis Research
The research programs in Nanotechnology & Catalysis Group of SCBE cut across multi-disciplinary boundaries in chemistry, chemical engineering, material sciences and physics. The research activities are mainly focused on i) heterogeneous catalysis and reaction engineering; ii) inorganic membranes, functionalized polymeric materials and nanocomposite materials; and iii) functional nanostructured materials for pharmaceutical, medical and other advanced applications.
In particular, metal incorporated mesoporous silica-based catalysts such as MCM-41, SBA-15, etc. have been synthesized for different catalytic applications including production of carbon nanotube with controlled chirality using CVD method, Fischer-Tropsch reaction and isomerization for clean energy, etc. Fundamental studies are also conducted to investigate the chirality control mechanism of carbon nanotube, and the controlling factors of metal incorporation and structural order of the catalysts.
Hollow nanostructured semiconductor materials synthesis is another research interest in the group. These materials are evaluated as photocatalysts for production of hydrogen from water and degradation of organic pollutants in waste water. Nanoscale electrocatalyst development for proton exchange membrane fuel cells and direct methanol fuel cells is another focus of the group. Immobilization of enzymes on solid support to generate active and reusable biocatalysts for chemical transformation is also carried out. Computational heterogeneous catalysis approach is used within the group to provide information about complex catalytic reaction networks, probing factors whose synergy shapes the activity and selectivity of a heterogeneous catalyst, and the mechanism of the catalytic reaction, based on which researchers are able to rationally design and optimize catalysts.
Furthermore, development of synthesis strategies of zeolite and zeolite/polymer functional membranes for key applications like gas separations, membrane reactors, membrane distillations, fuel cells, and chemical sensors is another focus of the group. The properties of zeolites, including their internal pore structure, crystal size and morphology, and the interactions between zeolite and polymers are studied in details and controlled carefully in order to generate high performance membranes.
The group has also developed spectroscopic techniques, including solid-state NMR and FTIR, to study the structure-processing-property relationships of polymers and polymer/nanoclay composite materials at interfaces and in bulk. The understanding of conformation, orientation, spatial distances, main chain and side group reorientation motion as well as stress at the molecular level is important for design of polymers with desired molecular properties.
Last but not the least, the research activities on design and engineering of multifunctional nanomaterials for targeting, bio-imaging, drug delivery, drug separation and self-cleaning surface are actively going on.
Separation and Analysis – Nanoparticles in Achiral and Chiral Separation
One of the main priorities of analytical laboratory is to develop efficient and rapid procedures for performing qualitative and quantitative analyses of large number of complex, low concentration samples in a short period of time. The strategy to decrease analysis time is to use shorter column and higher flowrate. However, one of the problems associated with shorter column is the reduction of separation efficiency. In order to overcome the lack of chromatographic efficiency afforded by decreasing column length, we propose the use of small particles as the support for stationary phase as particle size is inversely proportional to separation efficiency. With the use of smaller particles, chromatographic efficiency is improved by reducing the diffusion distance of the sample molecules in the stationary phase. Currently, there are no commercially available submicron particles used as stationary phase. In addition, there is limited research done on the use of submicron particles in liquid chromatography.
We have developed highly monodispersed non-porous and porous C18-functionalizaed silica submicron particles (500 nm) and have successfully applied these particles in Ultra Performance Liquid Chromatography (UPLC). We have compared the separation efficiency of our particles with commercially available columns, and found our particles to have superior separation efficiency. Our submicron particles are envisioned to have great potential as chiral stationary phase (CSP). Currently we are developing sub-micron and nanosize CSPs for a range of applications such as Capillary Electrochromatography (CEC), Capillary Electrophoresis (CE), and Supercritical-Fluid Chromatography (SFC). We are also seeking commercialization potentials.
Nanocomposites for Self-Cleaning and Antibacterial Surface Coatings
The emphasis on Green Architecture has provided great impetus for the applications of self-cleaning surface. Self-cleaning and/or antibacterial surfaces have great commercial potential and also wide area of applications such as the exterior coatings for buildings and structures, hydrophilic and anti-bacterial ceramic tiles of hospital interiors and antibacterial refrigerators etc.
We are developing permanent self-cleaning and antibacterial surface coatings which are applicable to different substrates such as glass, plastics and aluminum. The coating materials will have the ability to harvest visible light to destroy organic compounds and pathogens. Permanent surface characteristics such as permanent superhydrophilicity and bactericidal activities will render the coated surface self-cleaning and antibacterial all the time. In addition, the coating will be engineered to be mechanically sound to withstand abrasion and scratching.
Printed electronics is predicted to be a $ 300 billion market within two decades. Printing is a versatile enabling technology for electronic products that can not be made achieved with Si microelectronics technology. The applications of printed electronics are diverse and pervasive, including macroelectronics products (e.g. large active display pixel drivers and solar panels), conformal electronics for implantable medical sensors, wearable or textile electronics, biosensors, single-use electronics, low-cost sensors, and Radio Frequency Identification (RFID) tags. Printed electronics will also lead to completely new products such as sophisticated diagnostic tools and smart packaging and inventory labels. It is believed that printed electronics will revolutionize our lifestyle within the next two decades just as Si microelectronics has done in past decades.
One of our school’s focuses is on materials and technology which benefit the total printed electronics industry. Our faculties have developed (1) novel one-dimensional nanomaterials, and (2) suitable printing techniques.
In recent years, single walled carbon nanotubes (SWNTs) which carrier mobilities and stabilities much higher than those of polymers, as well as those of Si and ZnO nanowires, have emerged as alternative candidates for printable transistors. SWNTs can be thought of rolled-up cylinders of graphene monolayer with ~ 1 nm diameter and tens of nanometers to several centimeters length. Depending on their chirality, SWNTs can be either metallic (met-) or semiconducting (sem-). Due to their nearly one-dimensional and defect-free electronic structure, electronic transport in SWNTs is ballistic, allowing them to carry high current with essentially no heating. Also, the electron transport in semiconducting SWNTs manifests superior field-effect behavior. Current synthesis approaches inevitably produce SWNTs which are electrically heterogeneous. Our faculties focus on novel synthesis and enrichment technologies to obtain electrically homogeneous products.
We have developed novel catalysts Co-MCM-41to stabilize sub-nanometer scale metal clusters. We have achieved the best ever-reported chirality control results in synthesizing only specific (n,m) types of SWNT (i.e. (7,5) at 35 mol % or (6,5) at 50 mol %) through precise control of sub-nanometer scale metal clusters using our novel catalysts and precise carbon decomposition control. Our as-synthesized SWNTs are enriched with 10-20 (n,m) types. We also developed a mild purification procedure to obtain low-defect density SWNTs nearly free of contaminants. Our nanotubes have measured purity index among the highest in comparison with other published results.
After purification, SWNTs mixture will still be composed of both met- and sem- nanotubes. We have developed various techniques to further enrich specific type of tubes. Using co-surfactant extraction without density-gradient, the chirality diversity can be reduced to ≤ 8 species. We have synthesized various surfactants with sem- or met-SWNT and high solubility for excellent metallicity-based selectivity with minimum disruption of nanotube intrinsic electronic properties. Chitosan and its various neutral pH water-soluble derivatives were also investigated to obtain SWNT solutions which are suitable for printing. We are also developing virus-based nanotechnology with specific applications in separation of SWNTs according to their chirality, and subsequent viral-directed SWNT assembly for applications in nano-circuitry.
Our faculties are also developing printing techniques to achieve printed highly aligned nanomaterial based FETs with high performance and yield. There are several processes we have developed to achieve the desired high device performance including microfluidic alignment technique, magnetic patterning and UV nanoembossing method.
We have shown, for the first time, which with pre-alignment of the nanotubes, flows in microchannels can align the SWNTs in patterns with widths down to sub-micron over mm-scale area.
Printing techniques (e.g. inkjet, offset or gravure printing) commonly applied for low-cost, large-area printed electronics circuits can only typically achieve 20-50 µm resolution. We have demonstrated that a novel ultraviolet (UV) nanoembossing method can print conducting channels with sub-micron (600 nm) lengths so as to achieve high charge mobility and drain current for the network. Further UV nanoembossing can achieve transfer of sintered Au electrodes whilst physical contact printing used by others typically transfers Au nanoparticles which need high-temperature post-print sintering. Our UV nanoembossing is fast and is done at ambient temperature.