Seminar - Nanofiber Photocatalyst in Purifying Air and Water by Prof. Wallace Woon-Fong LEUNG
日期：2018 年 03 月 05 日 ( 星期一)
Time：11:00 am – 12:00 pm
Harmful exhausted gases, such as NOx, hydrocarbon gases, emitted from vehicles from combustion, can be photo-chemically reacted in presence of sunlight to smog and haze affecting our health and well-being. For indoor environment, harmful gases such as formaldehyde and others, when under high concentration can cause headache and even more serious health threats. Photocatalyst is one effective means to reduce these harmful gases by converting them to harmless substances, water vapor and carbon dioxide. Existing photocatalysts mostly use titanium dioxide nanoparticles, which can only be activated by ultraviolet light that makes up only 5-6% of the light spectrum. In addition, there are concerns of inhaling these nanoparticles that can easily be detached. We have developed composite nanofibers of titanium dioxide (TiO2), 70 nanometer in diameter that is 1/1000 times of a fine human hair. These nanofibers are not easily detachable and can harvest both ultraviolet and visible light that encompass 50% of the entire light spectrum. We will discuss the use of TiO2-ZnO nanofibers in degradation of organics in polluted water as well as oxidation of harmful NOx. The optimal ratio of the TiO2 crystals, anatase-to-rutile phase, can be achieved and controlled during fabrication. Further, we will discuss enhancement in light harvesting using additive of Bismuth oxide in the composite nanofibers for synergistic function. A model for the kinetics on photocatalysis has also been developed to interpret the test results. The major drawback in photocatalyst is due to recombination of the electrons with the holes, and this problem has been solved by use of embedded graphene in nanofibers for transporting the electrons quickly away from the photo-generated holes. Moreover, these electrons are transported along the “graphene superhighways” to sites where the polluted gas molecules are adsorbed; and once combined with oxygen in air generating super-anions, the harmful molecules are oxidized. We will illustrate how the new photocatalyst can effectively convert formaldehyde and NOx. Viruses and bacteria can be killed by these powerful photocatalysts that serve also as disinfection agents. Finally, we will discuss p-type photocatalyst being developed and a means of affixing the photocatalyst on a flexible surface for practical applications.
Prof. Wallace W-F Leung received his BS in Mechanical and Aerospace from Cornell University, and MS and ScD both in Mechanical Engineering from MIT. For the past 40 years, he has worked on filtration and separation from ultrafiltration of protein solution, centrifugation of process stream, vacuum filtration of minerals, to air filtration. For 18 years, he was with Bird/Baker Hughes as Senior Research Scientist and Director of Process Technologies directing centrifugal separation/filtration. Earlier, he has worked for Gulf Oil and Schlumberger on production/testing of petroleum reservoirs and wells. For the past 14 years, he is Chair Professor of Innovative Products and Technologies at The Hong Kong Polytechnic University. Besides air filtration, he is also interested in applications of nanofiber technologies in renewable energy (photovoltaics, and recently hydrogen production using water splitting), air and water purification (photocatalysis), and health technologies (wound dressing). He is a fellow of American Institute of Chemical Engineers, American Society of Mechanical Engineers, American Filtration and Separations Society, Hong Kong Institute of Engineers, and Hong Kong Academy of Engineering Sciences. He has 48 US patents and two books to his credit. He is the Chair of International Delegation on Filtration with 13 member countries, including US, UK, Germany, France, Scandinavia, Austria, Hungary, Japan, Australia, Taipei, China, S. Korea, and India. He is also the chair of the World Filtration Congress, San Diego, CA, USA, 2020.