• Ph.D., 2004, Hebrew University of Jerusalem
• M.Sc., 1999, Hebrew University of Jerusalem
• B.Sc., 1997, Hebrew University of Jerusalem
Catalysis play a central role in the chemical industry and academic research. It is applied in a wide range of fields such as preparation of fine and bulk chemicals, energy production and environmental protection. There are two types of catalysis, homogeneous catalysis and heterogeneous catalysis. The homogeneous catalysts require mild operating conditions and they can usually offer excellent reactivity and high selectivity. However, this type of catalysts has limited application in the chemical industry due to the difficulties in their separation and recovery, which can increase the costs of their application in industrial processes. On the other hand, the heterogeneous catalysts can be separated and recovered easily, but they need harsh operating conditions due to their reduced reactivity and they usually give less selective transformations. Our research aims at developing new catalytic materials by nanotechnology that can bring about bridging between homogeneous and heterogeneous catalysis.
Bridging homogeneous and heterogeneous catalysis is a major challenge in the modern catalysis that requires extensive multidisciplinary studies to achieve it. To address this challenge, we focus on two main strategies. The first relies on the development of new micro- and nano-reactors that contain in their cores non-volatile solvent dissolving or dispersing the desired catalyst. Due to this approach the substrates can react with the catalysts in the core of the micro and nano-reactors under homogeneous or semi-homogeneous conditions. The second strategy is based on the design and construction of nanocatalytic systems with well-defined structures and large surface area.
In the first strategy, we develop methods for preparing catalytic silica and polymeric micro- and nanoreactors. For Example, silica microreactors containing in their core ionic liquids are created by emulsification of ionic liquids in water and then confining the resulted ionic liquid droplets with silica shells by interfacial polycondensation of silane monomer. These silica microreactors containing different types of catalysts are utilized in various organic transformations. The results of this work indicate a unique possibility to tune reactivity and selectivity of catalysts by this approach.
In the second strategy we construct new catalytic nano-materials with large surface area using nanoemulsification methods and sol-gel chemistry. For instance, periodic mesoporous organosilica (PMO) nanoparticles with a surface area up to 2000 m2/g are prepared by nanoemulsification of different bridged silanes such as 1,2-bis(trimethoxysilyl)ethane and their polycondensation under basic or acidic conditions. These materials are utilized as nanosupports for metal nanoparticles, organometallic complexes or organocatalysts.
1. Immobilization of Palladium Catalyst on Magnetically Separable Polyurea Nanosupport, S. Natour and R. Abu-Reziq, RSC Adv. 2014, 4, 48299-48309.
2. BMIm-PF6@SiO2 Microcapsules: Particulated Ionic Liquids as A New Material for the Heterogenization of Catalysts. E. Weiss, B. Dutta, A. Kirschning and R. Abu-Reziq,Chem. Mater. 2014, 26, 4781-4787 .
3. Palladium Nanoparticles Encapsulated in Magnetically Separable Polymeric Nanoreactors. E. Weiss, B. Dutta, Y. Schnell, and R. Abu-Reziq, J. Mater. Chem. A 2014, 2, 3971-3977.
4. Palladium Nanoparticles Supported on Magnetic Organic-Silica Hybrid Nanoparticles. S. Omar, and R. Abu-Reziq, J. Phys. Chem. C 2015, 118, 30045-30056.
5. Homogeneous and semi-heterogeneous magnetically retrievable bis-N-heterocyclic carbene Rh(I) based catalysts for selective hydroaminomethylation reactions.B. Dutta, R. Schwarz, S. Omar, S. Natour, and R. Abu-Reziq, Eur. J. Org. Chem. 2015, 1961-1969.
1. Model heterogeneous catalysis is studied under ultra-high vacuum (UHV) conditions on top of alloy bimetallic nano-clusters (e.g. Au-Cu and Cu-Pd) grown via buffer layer assisted growth method in UHV. In situ Auger and thermal desorption methods are used to follow reactivity and selectivity. High pressure-low pressure apparatus is uniquely used to study the thermal and photo-excited catalysis.
2. Local (transient) electric field effect on photo-induced and electron-induced reactivity of caged molecules on surfaces is studied near sharp edges and by growing model
in-vacuum nano-capacitors by trapping electrons in ice.
3. The role of plasmonic giant field enhancement near metallic (Ag) nano-particles on photo-reactivity vs. the effect of hot excited electrons on surface photochemistry has
been investigated. Its potential enhancement in photo-catalysis when embedded within TiO2 films has been investigated.
1. Photoinduced desorption of Xe from porous silicon: Evidence for selective and highly effective optical activity, Toker, G., Asscher, M., Phys. Rev. Lett., 107, 167402-16406 (2011).
2. Reduced Oxide Sites and Surface Corrugation Affecting the Reactivity, Thermal stability, and Selectivity of Supported Au–Pd Bimetallic Clusters on SiO2/Si(100) ; Gross, E., Sorek, E., Murugadoss, A., Asscher, M., Langmuir , 29 (20), 6025–6031 (2013).
3. Electron-induced chemistry of methyl chloride caged within amorphous solid water Horowitz, Y. and Asscher, M., J. Chem. Phys., 139, 154707 (2013).
4. Structure and Composition of Au-Cu and Pd-Cu Bimetallic Catalysts ffecting Acetylene Reactivity, Murugadoss, A., Sorek, E., and Asscher, M., Topics in Catalysis, 57 (10), 1007-1014 (2014).
5. Enhanced Photo Chemistry of Ethyl Chloride on Ag Nanoparticles,Toker, G., Bespaly A., Zilberberg, L., Asscher, M. Nano Letters, 15(2), 936-42 (2015);
6. Buffer Layer Assisted Growth of Ag Nanoparticles in Titania Thin Films Zilberberg, L., Mitlin, S., Shankar, H., Asscher, M., J. Phys. Chem. C, 119(52), 28979-28991 (20155).
Ratner Family Chair in Chemistry
Postdoc,1998, Chemistry, University of California, Berkeley, CA.
Ph.D.1996, Chemistry, The Hebrew University of Jerusalem.
M.Sc.1993, Chemistry, Summa Cum Laude, The Hebrew University of Jerusalem.
B.Sc.1982, Mathematics and Physics, The Hebrew University of Jerusalem.
A theoretical chemist, developing new theories and computational methods to predict the properties of molecules, nanocrystals and in general materials directly from the basic laws of quantum physics. His research focuses on the search of new mathematical and computational ways for describing the molecular processes behind efficient production of sustainable energy, including conversion of sunlight to electricity via solar-cells and production of clean and efficient fuels from natural gas. Baer's recent research involves development of new computational techniques for studying the behavior of charge carriers in nanocrystals and polymers.
D. Neuhauser, E. Rabani, Y. Cytter and R. Baer "Stochastic Optimally-Tuned Ranged-Separated Hybrid Density Functional Theory", J. Phys. Chem. in press (2016).
V. Vlček, H. R. Eisenberg, G. Steinle-Neumann E. Rabani, D. Neuhauser and R. Baer, "Spontaneous charge-carrier localization in extended one-dimensional systems", Phys. Rev. Lett. 116, 186401 (2016).DOI:http://dx.doi.org/10.1103/PhysRevLett.116.186401
Q. Feng, A. Yamada, R. Baer & B. D. Dunietz, "Deleterious effects of exact exchange functionals on predictions of molecular conductance", Submitted (2016).
R. E. Hadad and R. Baer "Minimally-corrected partial atomic charges that reproduce the dipole moment", submitted (2015).
E. Rabani, R. Baer, and D. Neuhauser, "Time-dependent Stochastic Bethe-Salpeter Approach", Phys. Rev. B 91, 235302 (2015).
Y. Gao, D. Neuhauser, R. Baer, E. Rabani, "Sublinear scaling for time-dependent stochastic density functional theory", J. Chem. Phys. 142, 034106 (2015).
• Postdoc, 1994-97, University of California, Berkeley
• Ph.D., 1994, Hebrew University of Jerusalem, Summa Cum Laude
• B.Sc., 1989, Hebrew University of Jerusalem, Summa Cum Laude
Our research concerns the chemistry, physics and applications of nanocrystals focusing on the unique tuning of chemical, optical, electrical and thermodynamic properties afforded by control of size, shape, composition and organization on the nanometer scale. We study colloidal semiconductor nanocrystals that are a class of nanomaterials that manifest the transition from the molecular limit to the solid state, as well as hybrid semiconductor-metal nanoparticles. The tunable properties along with the chemical processibility also lead to significant potential for using nanocrystals as building blocks of nano-devices in diverse applications such as solid state lighting, flat panel displays, solar energy conversion, opto-electronic devices and biomedical applications.
We work on dimensionality effects in semiconductor nanocrystals. Stemming from our ability to control shape of the nanocrystals we study using both ensemble and single nanocrystal based optical spectroscopy, the dependence of nanocrystals optical and electronic properties on the evolution from 0D quantum dots to 1D nanowires as manifested in particular in the intermediate nanorods structure. This is also a basis for applying semiconductor nanocrystals in displays, utilizing their unique emission properties.
An additional focus of our work in recent years concerns hybrid nanoparticles, composed of two components of different material types that represent a frontier area of research in nanomaterials. This addresses a key goal of nanocrystal research in the development of experimental methods to selectively control the composition and shape of nanocrystals over a wide range of material combinations. A particular combination which we pioneered in 2004, concerns the growth of metal (Au) tips onto the apexes of semiconductor (CdSe) nanorods creating ‘nanodumbbells’. Since this discovery, we have been studying hybrid metal-semiconductor nanoparticle systems extensively. The ability to selectively arrange nano-sized domains of metallic, semiconducting and magnetic materials into a single “hybrid” nanoparticle offers an intriguing route to engineer nanomaterials with multiple functionalities or the enhanced properties of one domain. Such semiconductor-metal hybrid nanoparticles manifest a synergistic effect of light induced charge separation opening the path for their application in solar energy harvesting with focus on photocatalysis. Visible light photocatalysis is a promising route for harnessing of solar energy to perform useful chemical reactions and to convert light to chemical energy. Our systems offer possibility for visible light photocatalysis using highly controlled hybrid metal-semiconductor nanoparticles. Under visible light irradiation, charge separation takes place between the semiconductor and metal parts of the hybrid particles. The charge separated state can then be utilized for ensuing oxidation-reduction reactions.
We are also aiming efforts towards development and study of doped nanocrystals. Doping of semiconductors by impurity atoms enabled their widespread technological application in micro and optoelectronics. However, for strongly confined colloidal semiconductor nanocrystals, doping has proven elusive. This arises both from the synthetic challenge of how to introduce single impurities and from a lack of fundamental understanding of this heavily doped limit under strong quantum confinement. We develop methods to dope semiconductor nanocrystals with impurities providing control of the band gap and Fermi energy. Successful control of doping and its understanding provide n- and p-doped semiconductor nanocrystals which greatly enhance the potential application of such materials in the field of printed electronics for solar cells, thin-film transistors, and optoelectronic devices.
1. U. Banin, Y.W. Cao, D. Katz, and O. Millo, “Identification of atomic-like states in InAs nanocrystal quantum dots”, Nature 400, 542-544 (1999).
2. N. Tessler, V. Medvedev, M. Kazes, S.H. Kan, and U. Banin, “Efficient 1.3m Light Emitting Diodes Based On Polymer-Nanocrystal Nanocomposite”,Science 295, 1506-1508 (20022).
3. S. Kan, T. Mokari, E. Rothenberg, and U. Banin, “Synthesis and properties of semiconductor quantum rods with cubic lattice”, Nature Materials 2, 155-158 (20033).
4. T. Mokari, E. Rothenberg, I. Popov, R. Costi and U. Banin, "Selective Growth of Metal Tips Onto Semiconductor Quantum Rods and Tetrapods", Science 304 (5678), 1787-1790 (20044).
5. T. Mokari, C. G. Sztrum, A. Salant, E. Rabani and U. Banin, "Formation of asymmetric one-sided metal tipped semiconductor nanocrystal dots and rods",Nature Materials 4, 855 (20055).
6. R. Costi, A.E. Saunders, U. Banin, “Colloidal Hybrid Nanostructures: A New Type of Functional Materials”, Angewandte Chemie International Edition 49, 4878 - 4897 (20100).
7. J.E. Macdonald, M. Bar Sadan, L. Houben, I Popov, U. Banin, “Hybrid nanoscale inorganic cages”, Nature Materials 9, 810-815 (2010).
8. D. Mocatta, G. Cohen, J. Schattner, O. Millo, E. Rabani, U. Banin, “Heavily Doped Semiconductor Nanocrystal Quantum Dots”, Science 332, 77-81 (2011)
9. A. Sitt, I. Hadar, and U. Banin “Band-gap engineering, optoelectronic properties and applications of colloidal heterostructured semiconductor nanorods “,Nano Today 8, 494-513 (2013).
10. G. Jia, A. Sitt, G. B. Hitin, I. Hadar, Y. Bekenstein, Y. Amit, I. Popov, U. Banin, “Colloidal Semiconductor Nanorod Couples Via Self-Limited Assembly”, Nature Materials 13, 301-307 (20144).