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Roussel T.J.,CSIC - Institute of Materials Science | Vega L.F.,Research Center Carburos Metalicos Air Products
Journal of Chemical Theory and Computation | Year: 2013

We present here the implementation of a code developed for the simulation of the self-assembly of nano objects (SANO). The code has the ability to predict the molecular self-assembly of different structural motifs by tuning the molecular building blocks as well as the metallic substrate. It consists in a two-dimensional grand canonical Monte Carlo (GCMC) approach developed to perform atomistic simulations of thousands of large organic molecules self-assembling on metal surfaces. By computing adsorption isotherms at room temperature and spanning over the characteristic submicrometric scales, we confront the robustness of the approach with three different well-known systems: ZnPcCl 8 on Ag(111), CuPcF16 on Au(111), and PTBC on Ag(111). We retrieve respectively their square, oblique, and hexagonal supramolecular tilling. The code incorporates generalized force fields to describe the molecular interactions, which provides transferability to many organic building blocks and metal surfaces. Ultimately, the method is versatile and can be an interesting multiscale approach if one aims to bridge quantum level calculations to the experimental scales and within a treatment in temperature. © 2013 American Chemical Society. Source

Roussel T.,CSIC - Institute of Materials Science | Vega L.F.,Research Center Carburos Metalicos Air Products
Technical Proceedings of the 2011 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2011 | Year: 2011

The self-assembly of nano-objects onto surfaces is one step toward bottom-up technique for the miniaturization of electronic devices with tunable physical properties. Finding the optimal conditions to position precisely the molecular building blocks on surfaces remains very challenging. Statistical mechanics and numerical approaches on large scales are essential to understand and eventually predict their equilibrium nanostructures, their thermodynamic properties, nucleation and growth mechanisms, which occur at sub-micrometric scalings. Atomistic simulations of thousands of these large flat organic molecules require computational efforts that become rapidly unaffordable. However, assuming the intramolecular degrees of freedom play a minor role on the resulting nanostructures, and taking advantage of grid interpolation techniques, we overcome this challenging issue and have implemented a Grand Canonical Monte-Carlo code, transferable to many transition metal surfaces and organic molecules. Source

Builes S.,Research Center Carburos Metalicos Air Products | Vega L.F.,Research Center Carburos Metalicos Air Products | Vega L.F.,Air Products Group
Journal of Physical Chemistry C | Year: 2012

It has been demonstrated that merging the inherent sorptive behavior of amorphous silica with organic groups increases the adsorption capabilities of the solid silica. However, the underlying mechanism of the adsorption process in the functionalized materials is not fully understood, limiting the possibility of designing optimal adsorbent materials for different applications; hence, the availability of complementary methods to advance in this field is of great interest. Here we present results concerning the adsorption of CO 2 in amine-functionalized silica materials, by Monte Carlo simulations, providing new insight into the capture mechanism. We propose a simulation methodology for the design of postsynthesis-functionalized silica materials in which realistic model adsorbents are generated using an energy bias selection scheme for the possible grafting sites. This methodology can be applied to different materials. In this work, we evaluate a model MCM-41 for CO 2 adsorption using grand canonical Monte Carlo simulations, and compared the results with available experimental data. A new methodology is presented, which allows accounting for the chemisorbed CO 2 on the adsorption isotherms. The results indicate that although chemisorption is an important part of this process at low pressures, physisorption also plays a significant role in the capture of CO 2 in these materials. Functionalization increases the interactions of the CO 2 molecules with the surface, whereas it decreases the available space for adsorption of CO 2; the overall efficiency of the improved adsorption lies on the availability of adsorption space versus stronger interactions. In addition to the adsorption isotherms, we studied the configurations of the amine chains during the adsorption process for different degrees of functionalization as well as the effect of the concentration of grafted amines on the adsorption isotherm. The overall results show that molecular simulations serve as a guide to quantify the CO 2 amount that can be easily sorbed for carbon capture applications, highlighting the importance of this approach. © 2012 American Chemical Society. Source

Vilaseca O.,Research Center Carburos Metalicos Air Products | Vilaseca O.,CSIC - Institute of Materials Science | Llovell F.,Research Center Carburos Metalicos Air Products | Llovell F.,CSIC - Institute of Materials Science | And 4 more authors.
Journal of Supercritical Fluids | Year: 2010

Hydrofluorocarbons (HFCs) have been used in the last years as common refrigerants, substituting the classical chlorinated compounds (CFCs and HCFCs), once it was shown that the latter ones are a major source of inorganic chlorine in the stratosphere and destroyers of the ozone layer. In this contribution, we present a thermodynamic characterization of fifteen HFCs using the extended soft-SAFT equation of state, including phase equilibria, interfacial tensions and heat capacities. A robust and transferable molecular model was developed for the description of the vapor-liquid equilibria of HFCs including the critical region and interfacial tensions. Interfacial properties were obtained by coupling the crossover soft-SAFT equation with the Density Gradient Theory of van der Waals, while near critical properties could be accurately obtained thanks to the use of a crossover term to take into account the fluctuations in the critical region. Correlations of the molecular parameters with the molecular weight of the compounds allowed predictions for new HFCs without the need of experimental data. Then, the behavior of binary mixtures of blends of refrigerants, commonly used for particular applications, was predicted with high accuracy by the theory when compared to available experimental data, without using binary data. Mixtures of refrigerants with alkanes and carbon dioxide were also investigated, showing the capabilities of the equation to capture the intermolecular interactions in these mixtures in a precise manner. The results obtained give confidence about the transferability of the model to other chemical families using the soft-SAFT equation, and provide a step towards modeling a new generation of refrigerants, such as hydrofluoroethers (HFEs). © 2010 Elsevier B.V. © 2010 Elsevier B.V. All rights reserved. Source

Builes S.,Research Center Carburos Metalicos Air Products | Builes S.,CSIC - Institute of Materials Science | Roussel T.,CSIC - Institute of Materials Science | Ghimbeu C.M.,CNRS Mulhouse Institute of Materials Science | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2011

In this study we attempt to investigate the potential use of two zeolite template carbon (ZTC), EMT-ZTC and FAU-ZTC, to capture CO2 at room temperature. We report their high pressure CO2 adsorption isotherms (273 K) that show for FAU-ZTC the highest carbon capture capacity among published carbonaceous materials and competitive data with the best organic and inorganic adsorbing frameworks ever-known (zeolites and mesoporous silicas, COFs and MOFs). The importance of these results is discussed in light of mitigation of CO2 emissions. In addition to these new experimental CO 2 adsorption data, we also present new insight into the adsorption process of the two structures by Monte Carlo simulations: we propose that two separate effects are responsible for the apparent similarity of the adsorption behaviour of the two structures: (i) pore blocking occurring on EMT-ZTC, and (ii) the change of the carbon polarizability due to the extreme curvature of FAU-ZTC. © 2011 the Owner Societies. Source

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