Alain Fuchs, head of the Physical Chemistry Laboratory in Paris-Sud, Orsay, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/
Adsorption and Separation Processes in Nano-Porous Materials
Nano-porous materials are gaining increasing importance in industrial applications (molecular sieving, ion exchange and catalysis to mention only a few of the most widespread applications). A large variety of such materials are used, ranging from disordered materials such as the conventional activated carbon to crystalline zeolites and related open-framework inorganic materials. In addition, new type of materials such as templated mesoporous materials or carbon nanotubes are attracting a great deal of interest today, from which interesting applications will presumably emerge in the near future. Whatever these materials are used for, a crucial role is played by adsorption and transport of the guest molecules. In addition, adsorption data are commonly used to characterize the porous materials (pore width and pore size distribution). While the macroscopic science of this field is well developed, there is a need for a more fundamental microscopic understanding of the phenomena, as well as means for predicting thermodynamics and transport properties in a variety of guest-host systems. Molecular simulation, in conjunction with experiments, has played an important role in the past few years in developing our understanding of the relation between microscopic and macroscopic properties of confined molecular fluids in nanoporous materials. Some of the most recent developments in this field will be reviewed in this talk.
From a fundamental point of view, if a fluid is confined to spaces of dimensions comparable to the range of intermolecular interactions, its structural, dynamic and thermodynamic behavior is altered markedly compared to the corresponding bulk behavior under identical thermodynamic conditions. Wetting is one of the unique features caused by the presence of solid substrates. Experimentally, novel techniques now permit to prepare solid substrates that are decorated with a second chemical species in a controlled manner on a nanoscopic length scale. Understanding the wetting properties of such substrates is of great importance in micro (nano)-fluidics applications. Some of the recent progress in the modeling of fluids confined by nanopatterned substrates will be presented.
The last part of the talk will be devoted to molecular sieving processes using microporous zeolitic materials. Molecular simulations have played an important role in understanding the adsorption, diffusion, chemical reactions and the synthesis in these materials. Whereas ten years ago simulations were limited to noble gases or small alkanes in purely siliceous zeolites, progress in the simulation techniques have allowed us to simulate large chain alkanes, aromatics and other polar fluids in a diversity of cationic zeolites or other open framework materials. While the chemistry of these materials used to be studied on small clusters, ab initio molecular dynamics allows nowadays the simulation of an entire unit cell of zeolite. A variety of simulation strategies have been developed in the past few years to model molecular diffusion in zeolite pores. Finally, nucleation processes during zeolite synthesis has been the subject of very recent simulation works. How far are we from being able to carry out an " in silico design" of a zeolite for a given application (such as binary mixture separation) is the question that will be addressed in reviewing the most recent progress in this field.