Area of Specialization
Novel Nanofiber technologies in Energy, Environment, and Health applications (Over 32 SCI papers and 7 US patents):
- Nano-Energy – Nanofiber for Perovskite Solar Cells and Nanofiber for Dye Sensitized Solar Cells.
- Nano-Environment – Nanofiber Filter for air filtration and Nanofiber photocatalysts for break-down of harmful gases in air and organics in water.
- Nano-Tissue – Nanofiber for tissue engineering.
- Nano-Innovations – Nanofibers of composite semiconductor with embedded Graphene.
- Filtration and Separation (chemicals, mining, food, industrial, water and wastewater treatment).
- Centrifugal separation/filtration (McGraw-Hill book,1998; 10 new technologies; 36 US patents).
- Centrifugal separation in Biotechnology and biopharmaceutical processing (Elsevier book, 2007).
- Flow and Mixing in micro-chambers/micro-channels (7 SCI papers).
- Health Technologies – Interactive rehab robots, Clinical decision support system, Cancer biomarkers, Osteo-arthritis smart therapy, Blind navigation (6 US patents).
- Sc.D., Mechanical Engineering, MIT, Cambridge, MA, USA (1981)
- S.M., Mechanical Engineering, MIT, Cambridge, MA, USA (1978)
- B.Sc., Mechanical & Aerospace Engineering, Cornell University, Ithaca, NY, USA (1976), GPA=4.22/4.30 (graduated first in College of Engineering, in 2-1/2 years with Cornell scholarship)
- Gold Award, Geneva Invention, 2017 (semiconductor nanofibers embedded with graphene for energy & environment) with Special congratulations from Jury
- Hong Kong Polytechnic University Distinguished Knowledge Transfer Excellence Awards (Merit Award in Research, 2017)
- Frank Tiller Award for life-time contribution in engineering and education on filtration and separations, American Filtration and Separations Society (AFS), 2015 (presented in AFS Annual Meeting Awards Luncheon, April 28, 2015, Charlotte, North Carolina, USA)
- Gold Award, Geneva Invention, 2014 (multilayer nanofiber filter and added functions)
- Special Award, Romania Ministry of Education, 2014 (multilayer nanofiber filter and added functions)
- Wells Shoemaker Award, American Filtration and Separations Society, 2006 (major contribution to the society)
- Senior Scientist Award, American Filtration and Separations Society, 2002 (technical contribution)
- Technical Achievement Award, Baker Hughes, 1992, (feed acceleration technology)
- Cedric Ferguson Medal, Society of Petroleum Engineers, 1987, (2 best papers on water influx to reservoirs, published in Soc. Pet. Eng. J. by researcher under age 33)
- Sibley Award, Cornell Mechanical & Aerospace Engineering, 1977 (highest graduating GPA)
25-year Industrial Experience:
Petroleum Engineering – In 1981, Dr. Wallace Leung joined Gulf Research & Development Company in Pittsburgh, PA, USA developing simulation model for petroleum production in naturally fractured reservoir with dual porosities and dual permeabilities. He won the 1987 Ferguson medal from the Society of Petroleum Engineers based on his two publications. In 1984, he joined Schlumberger Technology Houston, TX, USA developing finite element model on flow through 3D perforations in wellbore to optimize petroleum production, well testing models, and nodal analysis on well production.
Process Technologies and Centrifugal Separation – From 1986 to 2004, Dr. Leung joined Bird/Baker-Hughes in S. Walpole, MA, USA (largest industrial centrifuge manufacturer in the world) as Senior Research Scientist and later as Director of Process Technology responsible for R&D of all solid-liquid separation equipment (nearly 100 different types) and related applications. For 15 years, he worked closely with Prof. Ascher H. Shapiro, Institute Professor of MIT and consultant to Bird, on research relating to rotating flow and centrifugal separation. Over 10 new technologies, numerous publications, and patents have resulted from the analytical, experimental, and computational research effort of the R&D team. Dr. Leung became quickly the leading authority in the world on separation and centrifugal technologies delivering courses and keynote speeches worldwide. He authored the book – Industrial Centrifugation Technology, published in 1998 by McGraw-Hill, NY, USA. The text has been used as an important reference for all those involved in any aspects of centrifugal separation.
Biotechnology and Biopharmaceutical Separation – In 2004, Dr. Leung started his own company Advantech Company in Sherborn, MA, USA focusing on biotechnology separation of drug substances and biopharmaceutical separation of proteins in recombinant protein harvest from bacteria, yeast, and mammalian cells for production of Monoclonal Antibody. He also developed classification know-how for classification and separation of fine particle by size and mass on kaolin and calcium carbonate suspension for high-quality papers.
In Aug 2005, Dr. Leung joined Mechanical Engineering Department of The Hong Kong Polytechnic University as Chair Professor of Innovative Products and Technologies.
Research Institute of Innovative Products and Technologies:
In December 2005, he found and became Director of the Research Institute of Innovative Products & Technologies for PolyU with 20 professional staff, including 3 academic Assistant Professors, several engineers and supporting staff. Jointly with the departments of Electronics/Electrical/Mechanical/Computing Engineering, Applied Biology and Chemistry, Rehabilitation, Bioinformatics, Land Survey and Geo-Informatics, Design, and PolyU’s Industrial Centre. The Research Institute under leadership of Prof. Leung developed technologies and products related to healthcare for aged and disabled people using innovative and interdisciplinary approach to meet the unmet needs of the Society. The Research Institute has demonstrated very successful in the interdisciplinary approach led by Prof. Leung during the trial period 2005-2011 and served as road model for subsequent research institutes found subsequently in PolyU.
Since 2011, Prof. Leung continued as Chair Professor of Innovative Products and Technologies in Mechanical Engineering Department of PolyU. He has a diversified background and equally diverse research interests in science and technologies related to energy, environment, health, and innovations. Prof. Leung’s current interests are listed below:
(A) Nanofiber Technology Platform
Organic, inorganic, and biological materials can be electrospun into nanofibers 50-300 nm in diameter providing as much as 66 m2cm-3 of material. Nanofiber technologies have been applied to solar cells, air/gas filtration, air/gas purification, water purification and treatment, health applications and developing innovative technologies.
Nanofiber for Perovskite Solar Cells
Perovskite crystal structure
Graphene nanofibers have been introduced into the perovskite layer to produce perovskite crystals of large uniform size with high crystallinity, that harvest visible light from 350 to 800nm. The nanofibers provide nucleation sites and crystal growth. Further, photogenerated electrons can travel along the super highway offered by the graphene nanofiber to the electrode. As a result, the maximum power conversion efficiency reaches 19.83% and short circuit current reaches a high of 24.4mAcm-2.
Nanofiber for Dye Sensitized Solar Cells (DSSC)
DSSC is one of the most environmental friendly solar cells due to colorful, low cost, using materials that are readily available, transparent which can be used on windows and does not take up space, and good efficiency. Despite these advantages, improvements can be made on performance.
The world of colorful Dye Sensitized Solar Cells (source: Google)
Three technologies have been developed in our group to harvest light, trap light and transport electrical charges for the DSSC:
Two complimentary dyes were used to harvest light, each having their light absorption range. As a result, the entire visible light spectrum can be harvested using the dual dyes. Further, TiO2 nanofiber was used to replace the TiO2 nanoparticles for better electron transport. The first dye was coated around the nanofiber in a thin layer while the second dye, also in thin layer, wrapped around the first dye. Both dyes harvest light independently. The photogenerated electrons from the second dye is being transferred to the first dye. The photogenerated electrons from the first dye together with the electrons from the second dye are both transferred to the conduction band of the TiO2. This cascade transfer in electrons or generally in energy provides the solar cell a high PCE of 9.48%, which is 48% higher than the conventional DSSC with only a single dye.
Cascade energy transfer for cosensitizing DSSC with double core-shell structure
A second technology that has been developed for DSSC is the bilayer nanofiber photoanode. Instead of using a layer of nanofibers with small diameter (SNF) for light harvesting, a second layer of nanofibers with larger diameter (BNF) adjacent to the SNF layer is used concurrently for light scattering so that light can be scattered and trapped in the photoanode. The PCE can reach 9.5% with this technology. The work was published in Advanced Materials with high citations.
Bilayer Photoanode DSSC
A third technology that research our group have developed on DSSC was to insert carbon nanotube (CNT) completely in the truncated nanofibers (see diagram c below) such that they can be highly conductive. As such, photogenerated electrons can be transported efficiently to the electrode reducing the chance of recombination via (a) electrons recombining with sensitized dye, (b) electrolyte in the photoanode, or (c) at the TiO2 particle-particle interface. The PCE can reach a high value of 10.24%. The work was published in Advanced Materials again with high citations.
TiO2 nanorods with embedded CNT for DSSC
Alternatively, graphene can also be used and inserted in the TiO2 nanofibers with diameter 60-70nm. The PCE registered between 9 and 10%, which is 22% higher than the conventional device without graphene. Further, a thicker photoanode of over 23 micrometers can be realized as compared to conventional which is typically no more than 13-15 micrometers. This facilitates thicker photoanode for use in DSSC that can harvest more light as well as electrolytes that are more suitable for use in thicker photoanode.
TiO2 nanofibers with embedded graphene for thicker photoanode DSSC
Nanofiber Filter for air filtration
Filtration of nano-aerosols using novel nanofiber filters (from CNN News and New York Times reports)
Pollutants are largely due to vehicular emissions, power plant emissions, and atmospheric reaction. Recent measurements made in Hong Kong near the cross-harbor tunnel revealed a large amount of submicron aerosols, especially aerosols less than 100 nm (also known as nano-aerosols or ultrafine particles) which are attributed to vehicular emissions and atmospheric photochemical reactions. This is consistent with testing that our group have performed in the lab also on nano-aerosols predominantly less than 100nm with aerated sodium chloride solution.
Nano-aerosols by virus of their small size can be inhaled easily into our lung from which they enter our cardiovascular system leading to various respiratory and cardioascular problems. Filters made of
nanofiber from polymeric materials (left) can effectively filter the nano-aerosols (see right figure) up to 90%. However, the pressure drop can be very large. We have developed multilayer nanofiber technology wherein the same amount of nanofibers to achive a given eefficiency has been redistributed from a single layer into multiple layers. This ensures the pores in the fiber mat to be wide open. This is especially advantageous for producing wearable face mask that stops infiltration of viruses from infectious diseases (from common cold to more severe viruses SARS, H1N1, H5N1 etc.) as well as nanoparticle pollutants from diesel/LPG vehicle emissions. This can also be used in indoor air filter to remove submicron and ultrafine particles as well as cabin filter of motor vehicles protecting health of passengers. By engineering the nanofiber technology (design, configuration, material) accordingly, the capture target (i.e. spec filtration efficiency) of a given submicron particle size under a given challenging velocity can be achieved, see efficiency vs. size for different amount of nanofibers installed in the filter.
Novel technologies developed:
Multilayer Nanofiber technology – A quasi-3D structure with wide open pores to achieve high efficiency and low pressure drop
Charged Electret Nanofiber – Charged electret nanofiber filter that provides high efficiency while reducing pressure drop, high quality factor exceeding 0.1Pa-1 across all challenging aerosols size. Charges stay in filter for at least 3 months in humid environment without decay.
Portable filter testing – Portable filter test developed that proves nanofiber can effectively captured real nano-aerosols from vehicular emissions and atmospheric photochemical reactions
Composite filter – Filter can capture nano-aerosols over extended period with high capacity, low pressure drop, and high efficiency even during initial period.
Nanofiber photocatalysts for breaking-down harmful gases in air and harmful organics in water
As the photocatalyst, primarily TiO2 with wide-band gap, is being irradiated by light, electrons are excited and jump from the valence band to the conduction band. Electrons can combine with the oxygen in air to form super-anions, while the holes in the valence band can combine with the water vapor in air to form hydroxyl radical. Both the superanions and hydroxyl radicals break down by oxidation the harmful adsorbed onto the photocatalyst.
A suite of nanofiber-based photocatalysts have been developed targeting at effectiveness, reduction of recombinations, and operating under visible light:
TiO2 composite nanofibers with hierarchy structure reducing separated electrons-holes from recombination
Harvest UV and vis light unlike TiO2 which harvest only UV light (~5% light spectrum)
Photocatalyst integrated into flexible and rigid surfaces, washable and cleanable
3X more effective than conventional gold standard TiO2 nanoparticles of 25nm (P25) in formaldehyde breakdown
7X at least more effective than conventional gold standard TiO2 nanoparticles of 25nm (P25) in NOx conversion
Breakdown poisonous 0-xylene gas
Can be used for face mask and air purifier
Breakdown harmful organics in water (proven extremely effective for Methylene Blue dye and Rhodamine dye) much more effective than TiO2 nanoparticles of 25nm (P25)
Nanofibers of composite semiconductor with embedded Graphene
We have developed semiconductor nanofibers with embedded graphene that can be used for photonic devices such as solar cells and photocatalyst applications.
(B) Rotating Microfluidics Platform
Microfluidics can simulate many chemical and biological processes taking place at a micro-scale. This brings the lab processes to a more controlled environment requiring very small sample. It is convenient for point-of-use diagnosis. By rotating the microfluidic platform in a certain way, we can carry out further separation by centrifugal acceleration and mixing by secondary flow thus intensifying the process. When mixing is intense, this facilitates cell culture and even cell lysing. We are interested in both continuous as well as batch mixing in this research. Fig. 5a shows mixing in a rotating chamber due to continuous angular acceleration of a chamber generating complicated vortices in a 3-D manner providing effective mixing.
(Left) Batch mixing in microfluidics, (Right) mixing in continuous feed through a T-channel.
Centrifugal separation of a solid from a fluid involves rotating the bowl at high rotation speed generating centrifugal acceleration acting on the heavier phase, which gravitates toward the bowl displacing the light phase toward the axis. Unexpected phenomena and flow pattern can result in a centrifuge with complicated fluid dynamics. By understanding these phenomena, better centrifuge design and operation can be developed with improved process results.
Thin boundary layer observed on rotating pool from special illumination.
Our interest in centrifugation encompasses the following:
- Biosolid/cell/biopharmaceutical separation
- Classification of 1-2 microns for kaolin and calcium carbonate
- Separation of nanoparticles in suspension
- Deliquoring of cake consisting of fine particles
- High solids dewatering of sewage cake
- Sludge cake rheology
- Cake transport in decanter and disk centrifuge
- Feed acceleration for continuous-feed centrifuge
- Discharge of effluent liquid from a rotating pool
(D) Water and Wastewater Treatment
We are interested in innovations in water and wastewater :
Forward & Reverse osmosis
- Lamella Sedimentation
- Membrane Bioreactor
- High-Solids dewatering by centrifugation and Filter Press
(E) Healthcare Devices and Delivery
We are interested to develop healthcare devices and software that can help patients and elderly through product enabled services and process innovations. This may include but not limited to intention-driven robots, electrical stimulation devices based on pain sensing, decision support system, innovative wound dressing, etc.
Selected Recent Publications
- Y Li, WWF Leung*, “Introduction of graphene nanofibers into the perovskite layer of perovskite solar cells,” Chemsuschem, doi.org/10.1002/cssc.201800758, 2018.
- Y Li, WWF Leung*, “Conditioning Lead Iodide with Dimethylsulfoxide And Hydrochloric Acid to Control Crystal Growth Improving Performance of Perovskite Solar Cell”, Solar Energy, Vol 157, pp 328-334, Nov 2017, doi:10.1016/j.solener.2017.08.011.
- KKS Lo, WWF Leung*, Dye-Sensitized Solar Cells with Shear-Exfoliated Graphene Solar Energy, Solar Energy, 180, 16-24, 2019.
- LJ Yang, WWF Leung*, “Electrospun TiO2 Nanorod with Carbon Nanotube for Efficient Electron Collection in Dye Sensitized Solar Cell”, Advanced Materials, 25, #12, 1792-1795, Mar 25, 2013
- LJ Yang, WWF Leung*, “Application of a Bilayer TiO2 Nanofiber Photoanode for Optimization of Dye-Sensitized Solar Cells”, Advanced Materials, 23, #39, 4559-4562, Oct 18, 2011
- LJ Yang, WWF Leung*, JC Wang, “Improvement of Light Harvesting in Dye Sensitized Solar Cell Based on Cascade Charge Transfer,” Nanoscale, 2013, 5 (16), 7493-7498 DOI:10.1039/C3NR01868G, 2013
- LJ Yang, JC Wang, WWF Leung*, “Lead Iodide Thin Film Crystallization Control for High-Performance and Stable Solution-Processed Perovskite Solar Cells”, ACS Applied Materials and Interfaces, 2015, 7 (27), pp 14614–14619.
- QQ Sun and WWF Leung*, “Charged PVDF multi-layer filters with enhanced filtration performance for filtering nano-aerosols”, Sep. and Purif. Tech. J., doi.org/10.1016/j.seppur.2018.11.063, 212, pp854-876, 2019.
- WWF Leung*, Yuen Ting Chau, “Experiments on filtering nano-aerosols from vehicular and atmospheric pollutants under dominant diffusion using nanofiber filter”, Sep. and Purif. Tech. J., 10.1016/j.seppur.2018.12.021. 213, 186-198, 2019.
- WWF Leung*, WY Hau, HF Choy, “Microfiber-nanofiber composite filter for high-efficiency and low pressure drop under nano-aerosol loading”, Sep. & Purif. Tech. J, 206 (2018) 26-38, https://doi.org/10.1016/j.seppur.2018.05.033
- WWF Leung*, HF Choy, “Transition from depth to surface filtration for a low-skin effect filter subject to continuous loading of nano-aerosols”, Sep & Puri Tech, 190, 202-210, 2018.
- WWF Leung*, HF Choy, “Transition from depth to surface filtration for a high-efficiency, high-skin effect, nanofiber filter under continuous nano-aerosol loading”, Chem. Eng. Sci., 182, 67-76, 2018.
- WWF Leung*, WY Hau, “Skin layer in cyclic loading-cleaning of a nanofiber filter in filtering nano- aerosols”, Sep & Puri Tech, 188, 367-378, 2017.
- WY Hau, WWF Leung*, Experimental investigation of backpulse and backblow cleaning of nanofiber filter loaded with nano-aerosols, Sep & Puri Tech, 163, 30-38, 2016.
- WWF Leung*, WY Hau, “A model of backpulse and backblow cleaning of nanofiber filter loaded with nano-aerosols”, Sep & Puri Tech J., 169, 171-178, 2016; doi: 10.1016/j.seppur.2016.06.007
- WWF Leung*, CH Hung, “Skin effect in nanofiber filtration of submicron aerosols”, Separation and Purification Technology, 92, 174-180, 2012.
- CH Hung, WWF Leung*, “Investigating the filtration of nano-aerosol using nanofiber filter under low Peclet number regime”, Separation Purification Technology, Vol 79, Issue 1, May 2011, 34-42.
- WWF Leung*, CH Hung, and PT Yuan, “Effect of face velocity, nanofiber packing density and thickness on filtration performance of filters with nanofibers coated on a substrate” Separation and Purification Technology, 71, 30-37, 2010
- WWF Leung*, CH Hung, and PT Yuan, “Continuous filtration of sub-micron aerosols by filter composed of multi-layers including a nano-fiber layer” J. Aerosol Science and Technology, 43:1174–1183, 2009.
- WWF Leung* and CH Hung, “Investigation on pressure drop evolution of fibrous filter operating in aerodynamic slip regime under continuous loading of sub-micron aerosols”, Separation and Purification Technology, 63, pp 691-700, 2008.
- M. Kanjwal*, WWF Leung*, Titanium based composite-graphene nanofibers as high-performance photocatalyst for formaldehyde gas purification, Ceramics International, doi.org/10.1016/j.ceramint.2018.12.022
- CC Pei, KKS Lo, WWF Leung*, “Titanium-Zinc-Bismuth Oxides-Graphene Composite Nanofibers as High-Performance Photocatalyst for Gas Purification,” Sep. & Purif. Tech. J, Vol 184, pp 205-212, 2017.
- CC Pei, WWF Leung*, “Enhanced photocatalytic activity of electrospun TiO2/ZnO nanofibers with optimal anatase/rutile ratio“, Catalyst Comm., 37 (2013) 100–104, DOI:10.1016/j.catcom.2013.03.029
- CC Pei, WWF Leung*, “Photocatalytic degradation of Rhodamine B by TiO2/ZnO nanofibers under visible light irradiation,” J. of Sep. & Purif. Tech, 114 (2013) 108–116, DOI:10.1016/j.seppur.2013.04.032, 2013
- CC Pei, WWF Leung*, “Solar photocatalytic oxidation of NO by electronspun TiO2/ZnO composite nanofiber mat for enhancing indoor air quality,” J. of Chemical Technology and Biotechnology, 89, #11, 2014, 1646-1652, DOI 10.1002/jctb.4506
- CC Pei, WWF Leung*, “Photocatalytic oxidation of nitrogen monoxide and o-xylene byTiO2/ZnO/Bi2O3nanofibers: Optimization, kinetic modeling and mechanisms,” Applied Catalysis B: Environmental, 174-175 (2015), 515-525, DOI 10.1016/j.apcatb.2015.03.021
- Y Ren*, WWF Leung, “Multiplexing Diagnostic Assays Using Novel Centrifugal Microfluidic Emulsification and Separation Platform”, Micromachines, 2016, 7, 17; doi:10.3390/mi7020017
- Y Ren, WWF Leung*, “Flow and mixing in zigzag channel”, Chemical Engineering, 215-216, pp 561–578, 2013
- Y Ren, WWF Leung, “Experimental and numerical investigation on flow and mixing in batch-mode rotating microfluidics”, International Journal of Heat and Mass Transfer, 60, 95–104, 2013
- Y Ren, LMC Chow, WWF Leung*, “Pichia pastoris culture on centrifugal microfluidic platform,” Biomedical Microdevice, Volume 15, Issue 2, pp 321-337, April 2013
- Y Ren, WWF Leung*, “Vortical flow and mixing in rotating microfluidics,” Computers and Fluids, 79 (2013),
- WWF Leung* and Y Ren, “Crossflow and mixing in obstructed and width-constricted rotating radial microchannel,” International Journal of Heat and Mass Transfer, 64 (2013) 457–467, DOI: 10.1016/j.ijheatmasstransfer.2013.04.064, 2013
- WWF Leung* and Y Ren, “Scale-up on mixing in rotating microchannel under subcritical and supercritical modes“, International Journal of Heat and Mass Transfer, 77 (2014) 157-172.
- SC Fu, WWF Leung, R. So, “A Lattice Boltzmann and Immersed Boundary Scheme for Model Blood Flow in Constricted Pipes: Part 1 – Steady Flow,” in press, Comm. in computational Physics, doi: 10.4208/cicp.171011.180712a, Vol. 14, No. 1, pp. 126-152, July 2013
- SC Fu, R. So, WWF Leung, “A Lattice Boltzmann and Immersed Boundary Scheme for Model Blood Flow in Constricted Pipes: Part 2 – Pulsatile Flow,”, Comm. in computational Physics, doi: 10.4208/cicp.171011.190712a, Vol. 14, No. 1, pp. 153-173, July 2013
- SC Fu, R. So, WWF Leung, “Linearized-Boltzmann-Type-Equation-Based Finite Difference Method for Thermal Incompressible Flow”, Computers and Fluids, Vol 69, pp 67-80, Oct 30, 2012.
- SC Fu, R. So, WWF Leung, “A discrete Flux Scheme for Aerodynamics and Hydrodynamics flows”, Comm. in computational Physics, 9, pp. 1257-1283, 2011.
- SC Fu, R. So, WWF Leung, “Stochastic Finite Difference Lattice Boltzmann Method for Steady Incompressible Flows.” J. Computational Physics, 229, 17, pp 6084-6103, 2010.
- SC Fu, WWF Leung, R So, “A lattice Boltzmann Method base numerical scheme for microchannel flows” J. Fluid Engineering, vol. 131, Issue 8, Aug. 2009.
- WWF Leung, “Measurement of low yield-stress materials“, J. Chinese Inst. of Chem. Eng., vol. 39, 107-115, 2008.
50 issued US patents on, respectively, centrifugal separations, nanofibers, energy, environment, health technologies, and logistics.
- Scale-up of Solid-Liquid Separation Equipment by R. Wakeman R. and S. Tarleton, Sedimenting Centrifuges, Elsevier, 2005.
- Plant Design Handbook for Mineral Processing, pp. 1262-1288, published by Soc. of Min. Eng., 2002.
- Perry’s Chemical Engineers Handbook, 7 ed., pp. 18-106 to 18-125, McGraw-Hill, New York, NY, 1997.
- Handbook on Separation Techniques for Chemical Engineers, pp. 4-63 to 4-96, McGraw-Hill, New York, NY, 1997.
Industrial Centrifugation Technology, McGraw-Hill, NY, 1998
Centrifugal Separation in Biotechnology, Academic Press/Elsevier, UK, 2007