Nano-crystalline porous anatase TiO2 for environmental applications: Synthesis process and transport characteristics study
The topological state of entangled polymers has been analyzed recently in terms of primitive paths which allowed obtaining reliable predictions of the static (statistical) properties of the underlying entanglement network for a number of polymer melts. Through a systematic methodology that first maps atomistic molecular dynamics (MD) trajectories onto time trajectories of primitive chains and then documents primitive chain motion in terms of a curvilinear diffusion in a tubelike region around the coarse-grained chain contour, we are extending these static approaches here even further by computing the most fundamental function of the reptation theory, namely, the probability Sigma(s,t) that a segment s of the primitive chain remains inside the initial tube after time t, accounting directly for contour length fluctuations and constraint release. The effective diameter of the tube is independently evaluated by observing tube constraints either on atomistic displacements or on the displacement of primitive chain segments orthogonal to the initial primitive path. Having computed the tube diameter, the tube itself around each primitive path is constructed by visiting each entanglement strand along the primitive path one after the other and approximating it by the space of a small cylinder having the same axis as the entanglement strand itself and a diameter equal to the estimated effective tube diameter. Reptation of the primitive chain longitudinally inside the effective constraining tube as well as local transverse fluctuations of the chain driven mainly from constraint release and regeneration mechanisms are evident in the simulation results; the latter causes parts of the chains to venture outside their average tube surface for certain periods of time. The computed Sigma(s,t) curves account directly for both of these phenomena, as well as for contour length fluctuations, since all of them are automatically captured in the atomistic simulations. Linear viscoelastic properties such as the zero shear rate viscosity and the spectra of storage and loss moduli obtained on the basis of the obtained Sigma(s,t) curves for three different polymer melts (polyethylene, cis-1,4-polybutadiene, and trans-1,4-polybutadiene) are consistent with experimental rheological data and in qualitative agreement with the double reptation and dual constraint models. The new methodology is general and can be routinely applied to analyze primitive path dynamics and chain reptation in atomistic trajectories (accumulated through long MD simulations) of other model polymers or polymeric systems (e.g., bidisperse, branched, grafted, etc.); it is thus believed to be particularly useful in the future in evaluating proposed tube models and developing more accurate theories for entangled systems. [hide]
Principal Investigators
Igor Stankovic (CoPI)
Scientific Computing Laboratory Belgrade, Serbia ►
Zorana Dohcevic-Mitrovic (CoPI)
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Martin Kroger (PI)
Polymer Physics, ETH Zurich, Switzerland ►
Investigators
Zoran V. Popovic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Alexsandar Golubovic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Maja Scepanovic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Mirjana Grujic-Brojcin
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Alexsandar Belic
Scientific Computing Laboratory Belgrade, Serbia ►
Slobodan Vrhovac
Scientific Computing Laboratory Belgrade, Serbia ►
Involved Students
Sonja Askrabic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Milan Zezelj
Scientific Computing Laboratory Belgrade, Serbia ►
Dusan Vudragovic
Scientific Computing Laboratory Belgrade, Serbia ►
Jelena Smiljanic
Scientific Computing Laboratory Belgrade, Serbia ►
Jaksa Vucicevic
Scientific Computing Laboratory Belgrade, Serbia ►
Milos Radonjic
Scientific Computing Laboratory Belgrade, Serbia ►
Marko Mladenovic
Scientific Computing Laboratory Belgrade, Serbia ►
Titanium dioxide (TiO2) is an important photo catalyst due to its strong oxidizing power, non-toxicity and long-term photo stability. The interest in nano-crystalline anatase TiO2 has been driven by its potential for a variety of technological applications including photo catalysis, electrochemical solar cells, optoelectronic devices, chemical sensors, and dielectric material of thin-film capacitors. Together with cerium dioxide (CeO2), porous TiO2 is seen as a material for the production of molecular hydrogen from water using sun energy in a photo catalytic reaction process. In addition, nanocrystalline anatase TiO2 is a weak magnetic semiconductor with proven room temperature ferromagnetism. This opens the possibility for the use of TiO2 in second-generation spintronic devices. Its ferromagnetic properties can be enhanced with the addition of transition metals such as iron, cobalt, or vanadium. Approximately 4 million tons of TiO2 are consumed annually worldwide. the principle use today being that of a bright white pigment.The enumerated properties of TiO2: catalytic, porous structure, and ferromagnetism, can be fully utilized only if they are combined: (i) Applications such as pollution monitoring or leak localization in chemical plants require high sensitivity and selectivity. By discriminating between different patterns of diffusion it is possible to enable this class of sensors to recognize different molecules (ii) The distribution of TiO2 pore diameters determines the collision frequency of molecules with the pore walls and thus also the frequency of catalytic reactions. Porous media can be specifically designed and engineered so as to balance between rates of reactant inflow, chemical reaction, and outflow. (iii) In photo-hydrolysis, hydrogen is produced from solar energy. In order to achieve this ambitious goal, it is necessary not only to understand the surface interaction between TiO2 and the molecules of water, hydrogen and oxygen, but also the transport of water into the nanopores as well as the transport of oxygen and hydrogen out of them. (iv) Finally, an external magnetic field could be applied as additional parameter during the technological process in which porous TiO2 media is synthesized. If brought to application, porous structures with anisotropic geometries could be created, i.e., elongated pores in magnetic field direction. In Gräel dye solar cells, such pore geometries would lead to shorter electron diffusion paths towards the metal electrode and improve the efficiency of the whole system.
The main objectives of this project are: (1) synthesis of porous TiO2 nanocrystals through the utilization of a novel and cost effective sol-gel method and the full characterization of the obtained structural and optical properties and (2) creation of multi-scale models and simulations specifically designed for the development of environmental TiO2 based technology.
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Selected conferences (co-)organized by project members
IWNET 2009
08 Sep - 10 Sep 2009, Eternal Spring City of Cuernavaca, Mexico ►19 April 2024 mk