The aim of my research is to develop a rational design strategy for advanced engineering materials based on the understanding of molecular-level processes that govern the synthesis and performance of these materials.
Research Areas
(1) Synthesis of advanced materials for inorganic membrane applications in separation and reaction,
(2) Chemical reaction engineering: Design, analysis and implementation of hybrid reactors and microreactors,
(3) Nanostructured materials for environmental and biological applications.
My research has grown and matured over the years. Our group has made important contributions in the fabrication, microstructuring and incorporation of zeolites as active functional elements (i.e., catalyst and membrane) in microreactors and microseparators. Our work has been highlighted by the Lab-on-a-Chip (2003) and frequently cited by other researchers in the field (citations=370 as of August 25, 2009). Early works focused on the incorporation of microstructured zeolite catalysts in microreactor channels for reaction studies. The aim is to create roughness to introduce in-channel mixing to enhance reactions [“TS-1 zeolite microrengineered reactors for 1-pentene epoxidation,” Chem. Commun., (2002) 878, citations=24]. We proposed the use of membrane and catalytic membrane microreactors for fine chemical syntheses, where the coupling of reaction and separation resulted in an important increase in the product yield and purity as well as the catalyst life [“An investigation of Knoevenagel condensation reaction in microreactors using a new zeolite catalyst,” Appl. Catal., A 261 (2004) 109, citations=37; “TS-1 oxidation of aniline to azoxybenzene in a microstructured reactor,” Appl. Catal. A 281 (2005) 285, citations=14]. The successful fabrication of thin, freestanding zeolite micromembranes and the use of ozone for the controlled removal of the organic structure directing agent from zeolite pores at low temperatures enabled the preparation of low-defect membranes that are rich in surface hydroxyls. Our work on the use of zeolite micromembranes as proton conducting membrane for miniature fuel cell was awarded the HOT ARTICLE status by the Royal Society of Chemistry Chemical Communication (2008) and I was invited to contribute a chapter on Zeolites and Molecular Sieves in Fuel Cell Application in a new book Zeolites and Catalysis: Synthesis, Reactions and Application to be published by Wiley-VCH Verlag. Also, an invention patent was awarded by the U.S. patent office for the zeolite micromembranes (“Methods for fabricating zeolite micromembranes,” US Patent No. 7494610). Our works are extensively cited by leading researchers in the area of zeolite membranes including the groups of Michael Tsapatsis (University of Minnesota), Freek Kapteijn (Delft University of Technology) and Jesus Santamaria (University of Zaragoza). Our paper “Engineering the shape of zeolite crystal grain in MFI membranes and their effects on the gas permeation properties,” Microporous Mesoporous Mater., 47 (2001) 203 was cited in Lai et al. “Microstructural optimization of a zeolite membrane for organic vapor separation,” Science, 300 (2003) 456-460. The recent state-of-the-art reviews by Caro et al. “Zeolite membranes-Recent developments and progress,” Microporous and Mesoporous Mater. 115 (2008) 215 cited 22 of our papers; Snyder et al. “Hierarchical nanomanufacturing: From shaped zeolite nanoparticles to high performance separation membranes,” Angew. Chem. Int. Ed. 46 (2007) 7560 cited 5 of our papers; and McLeary et al. “Zeolite based films, membranes and membrane reactors: Progress and prospects,” Microporous Mesoporous Mater. 90 (2006) 198 cited 8 of our papers. Our research had been presented as a plenary lecture at the 1st International Conference on Materials Processing for Properties and Performance (2002) in Singapore, keynote lecture at the 9th International Conference on Inorganic Membrane (2006) in Norway, plenary lecture at the 4th International Zeolite Membrane Meeting (2007) in Spain and keynote lecture at the 9th International Conference on Catalysis in Membrane Reactors (2009) in France.
My Ph.D. background is on fundamental catalysis, specifically on the use of scanning probe microscopy (SPM) for visualizing catalyst surfaces. My catalyst research in Hong Kong focused mainly on environmental catalysis for the remediation of indoor pollution. The work was initiated as collaboration between our group and Spanish CSIC to conduct fundamental studies of photocatalytic activity of nanostructured TiO2. Our papers “Size effects in gas-phase photo-oxidation of trichloroethylene using nanometer-sized TiO2 catalysts,” J. Catal., 192 (2000) 185 clarified the effects of particle and ensemble sizes on the photocatalytic oxidation reaction and is widely cited (citation = 114); “Gas-phase photo-oxidation of toluene using nanometer-size TiO2 catalysts,” Appl. Catal. B 29 (2001) 327 explores the generation reactive species and their role in the reaction received 96 citations; and “The influence of surface properties on the photocatalytic activity of nanostructure TiO2,” J. Catal. 219 (2003) 107 examines the role of surface hydroxyls and received 45 citations. The knowledge gained is vital for our later researches into nanotextured TiO2, aerogel-immobilized nano-TiO2 and Au/TiO2 catalysts that resulted in well cited papers including the “An investigation of trichloroethylene photocatalytic oxidation on mesoporous titania-silica aerogel catalysts,” Appl. Catal. B 76 (2007) 64 cited 12 times and “Effects of ozone pretreatment on the performance of Au/TiO2 catalyst for CO oxidation,” J. Catal., 242 (2006) 131 cited 14 times. The efforts also resulted in four patent inventions that were successfully transferred to industry (Chiaphua Industries Ltd. and Artenano) and commercialized. Our works in catalysis also led to a review paper “Scanning probe microscopy in catalysis,” J. Nanosci. Nanotechnol., 4 (2004) 647, a report on “Advances in characterization of microporous catalysts,” for The Catalyst Group, a leading international chemical technology consulting firm, and an invited paper “Properties of TiO2 support and the performance of Au/TiO2 catalyst for CO oxidation reaction,” Gold Bull., 40 (2007) 15 (journal impact factor=2.00). Our work was also reported in the local Radio Television Hong Kong (RTHK) television series on Engineering (March 2005) as an example of industry-academia partnership and technology transfer.
I have established a network of research partners in Europe and Asia. Our research into microreactor design and modeling was carried out with the group of Prof. A. Gavriilidis at University College, London. Prof. R. Martin-Aranda (UNED, Spain) provided expert knowledge in base catalysis and fine chemical synthesis that enabled us to investigate the possible use of microreactor for fine chemical production. We are interested in the potential application of various zeolite “microstructures” including zeolite micropattern, zeolite microneedles and hollow zeolite microspheres for immobilization of biomolecules, transdermal delivery of drug and study of cell signaling. The latter was done with Prof. H.B. Peng of the Biology Department at HKUST. The faculty spent his sabbatical learning more about drug delivery at Prof. R. Langer’s group in MIT and nanomedicine at Prof. J. Santamaria’s group in University of Zaragoza, Spain. Our research on ambient temperature catalysts benefited from the spectroscopic studies by Dr. M.A. Bañares and Dr. J. Soria of the Institute of Catalysis and Petrochemistry, Spain and from the contributions of Prof. P. L. Yue (HKUST, HK) on photoreactor designs. Dr. M. Djafer (Veolia, HK), Dr. J. C. Schrotter (Anjou Recherche, France), Dr. A. Julbe (IEM, France), Prof. A. Ayral (IEM & U. Montpellier, France) are our partners in developing new membrane technology for the treatment of recalcitrant and refractory organic pollutants in water. I have learned a lot about adsorption from my collaboration with Prof. G. McKay (HKUST) and used the knowledge to design highly selective adsorbents based on mesoporous materials with single site system.
