Mechanical and adsorption properties of greenhouse gases filled carbon nanotubes

We investigate the mechanical and adsorption properties of single-walled carbon nanotubes (SWCNTs) filled with greenhouse gases through Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations using a recently developed parameterization for the cross-terms of the Lenard-Jones (LJ) potential. Carbon nanotubes interact strongly with CO$_2$ compared to CH$_4$, resulting in a CO$_2$-rich composition inside the nanotubes, with the proportion of CO$_2$ decreasing as the diameter of the nanotubes increases. Contrarily, the smallest nanotubes showed a more even balance between CO$_2$ and CH$_4$ due to gas solidification. The gas does not affect the mechanical response of the nanotubes under tension, but under compression, it presents a complex relationship with the loading direction, nanotube's diameters, chirality, and to a minor extent, the gas composition. Filled zigzag nanotubes showed to be more stable in the presence of fillers, giving the best mechanical performance compared to the filled armchairs. The study confirms carbon nanotubes as effective means of separating CO$_2$ from CH$_4$, presenting good mechanical stability

Revisiting greenhouse gases adsorption in carbon nanostructures: advances through a combined first-principles and molecular simulation approach

Carbon nanotubes and graphene are promising nanomaterials to improve the performance of current gas separation membrane technologies. From the molecular modeling perspective, an accurate description of the interfacial interactions is mandatory to understand the gas selectivity in these materials. Most of the molecular dynamics simulations studies considered available force fields with the standard Lorentz-Berthelot (LB) mixing rules to describe the interaction among carbon dioxide (CO$_2$), methane (CH$_4$) and carbon structures. We performed a systematic study in which we showed the LB underestimates the fluid/solid interaction energies compared to the density functional theory (DFT) calculation results. To improve the classical description, we propose a new parametrization for the cross-terms of the Lenard-Jones (LJ) potential by fitting DFT forces and energies. The obtained model enhanced fluid/carbon interface description showed excellent transferability between single-walled carbon nanotubes (SWCNTs) and graphene. To investigate the effect of the new parametrization on the gas structuring within the SWCNTs with varying diameters, we performed Grand Canonical Monte Carlo (GCMC) simulations. We observed considerable differences in the CO$_2$ and CH$_4$ density within SWCNTs compared to those obtained with the standard approach. Our study highlights the importance of going beyond the traditional Lorentz-Berthelot mixing rules in the studies involving solid/fluid interfaces of confined systems

Fresh Molecular Look at Calcite-Brine Nanoconfined Interfaces

Calcite-fluid interface plays a central role in geochemical, synthetic, and biological crystal growth. The ionic nature of the calcite surface can modify the fluid-solid interaction and the fluid properties under spatial confinement and can also influence the adsorption of chemical species. We investigate the structure of the solvent and ions (Na, Cl, and Ca) at the calcite-aqueous solution interface under confinement and how such environment modifies the properties of water. To properly investigate the system, molecular dynamics simulations were employed to analyze the hydrogen bond network and to calculate NMR relaxation times. Here, we provide a new insight with additional atomistically detailed analysis by relating the topology of the hydrogen bond network with the dynamical properties in nanoconfinement interfaces. We have shown that the strong geometrical constraints and the presence of ions do influence the hydrogen bond network, resulting in more extended geodesic paths. Hydrogen bond branches connect low to high dynamics molecules across the pore and hence may explain the gluelike mechanical properties observed in the confinement environment. Moreover, we showed that the surface water observed at the calcite interface is characterized by slow transversal spin relaxation time (T2) and highly coordinated water molecules. The physical and electrostatic barrier emerged from the epitaxial ordering of water results in a particular ionic distribution, which can prevent the direct adsorption of a variety of chemical species. The implications of our results delineate important contributions to the current understanding of crystallization and biomineralization processes.Fil: Kirch, Alexsandro. Universidade de Sao Paulo; BrasilFil: Mutisya, Sylvia Mueni. Universidade Federal Do Abc; BrasilFil: Sanchez, Veronica Muriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Simulación Computacional para Aplicaciones Tecnológicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; ArgentinaFil: de Almeida, James Moraes. Universidade de Sao Paulo; BrasilFil: Miranda, Caetano Rodrigues. Universidade de Sao Paulo; Brasi

CO2 Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral

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Intercalation of CO2 Selected by Type of Interlayer Cation in Dried Synthetic Hectorite

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Influence of CO2 on Nanoconfined Water in a Clay Mineral

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Eletronic properties in nanosystems based on carbono nanotubes and graphene

Neste trabalho foram realizadas simulações computacionais para investigar as propriedades eletrônicas de nanossistemas baseados em nanotubos de carbono e grafeno por meio de cálculos de primeiros princípios. Um dos nanossistemas investigados é formado por um nanotubo de carbono acoplado a eletrodos de nanofios de paládio encapsulados. Foi mostrado que estados provenientes dos eletrodos interagem fortemente com os estados do nanotubo de carbono. Cálculos de transporte eletrônico foram realizados para investigar a potencialidade desse nanossistema em aplicações como transistor de efeito de campo. Foi mostrado que a intensidade da corrente elétrica desse nanossistema pode ser variada com o campo elétrico de gate. Outro trabalho desenvolvido no presente trabalho tem como base um nanossistema formado pelo grafeno depositado nos substratos SiO2 amorfo e h-BN. Foi determinada a energia de adsorção e a quantidade de carga transferida para investigar a influênicas desses substratos na adsorção da molécula de H2 pelo grafeno. Foi mostrado que a energia de adsorção da molécula de H2 adsorivda na interface grafeno/SiO2 amorfo é menor em comparação com o grafeno suspenso ou disposto sobre o substrato h-BN. Além disso, a adsorção do H2 nessa região resulta em uma transferência de carga de uma ordem de grandeza maior em comparação com a adsorção no grafeno suspenso, sendo observado um deslocamento do Cone de Dirac em relação ao nível de Fermi. Esse estudo poderá contribuir para a construção de futuros sensores de H2 à base de grafeno.In this work, ab initio calculations were performed within DFT framework to analyse electronic properties of Carbon nanotubes and grapheme nano systems. In this work, computer simulations were performed to investigate the electronic properties of nanosystems based on carbon nanotubes and graphene within DFT framework. One of these systems studied is a Carbon nanotube semiconductor coupled to encapsulated leads of Pd nanowires. It has been shown that leads states interact strongly with the carbon nanotube states. Electronic transport calculations were performed to unfold new applications of this system, such as the field effect transistor. We noticed that charge current intensity can be tuned by electrical field. We also described the influence of amorphous SiO2 and h-BN, in H2 energy adsorption and charge transfer, where both materials are used as graphene substrates. It was shown that the latter adsorption energy in the graphene/Si02 is smaller than graphene/h-Bn and the graphene suspended itself. In fact this adsorption results in a charge transference one order greater than in the suspended graphene, which can be seen as a vertical shift of the Dirac Cone. This study may improve the construction of future H2 sensors based on graphene

Design and Characterization of Nanofluidic-Based Systems by Multiscale Molecular Simulations

As propriedades físicas incomuns exibidas por fluidos confinados em meios porosos desempenham um papel importante em diversos processos químicos, geoquímicos e ambientais. Atualmente, muitos aspectos da estrutura e dinâmica dos fluidos espacialmente confinados ainda são pouco compreendidos. Nesse contexto, fenômenos interfaciais influenciam consideravelmente os processos que ocorrem em meios nanoporosos, podendo resultar em efeitos relevantes para o desenvolvimento dos dispositivos nanofluidicos. Esses sistemas multifásicos e com fenômenos multifísicos podem apresentar propriedades eletrônicos e dinâmicos envolvendo diferentes escalas de tamanho e tempo na interface sólido/fluido. Atualmente, uma única metodologia não é capaz de resolver toda a complexidade encontrada em tais sistemas pelo fato de cada qual estar restrita a uma escala ou demanda computacional específica. Além disso, as metodologias habitualmente aplicadas para investigar as fases bulk através da modelagem computacional, em geral, não são adequadas para acessar sistematicamente os efeitos de superfície que ocorrem na interface sólido/fluido. Os desafios impostos à modelagem molecular pelos sistemas nanofluídicos requerem iniciativas inovadoras (dentre as metodologias disponíveis) para acessar as propriedades de interface. Nessa tese, desenvolvemos e aplicamos novas abordagens computacionais em nível atômico a fim de modelar e caracterizar sistemas nanofluidicos. Nesse contexto, introduzimos um método multinível hierárquico top-down, que combina simulações de dinâmica molecular com cálculos ab initio de transporte eletrônico, para abordar fenômenos de multiescala. O potencial dessa implementação foi demonstrado em um estudo de caso envolvendo o fluxo de água e o transporte de íons através de um nanotubo de carbono tipo (6,6). Mostramos que o traço iônica pode representar uma mudança na condutância elétrica do nanocanal, e levar a uma medida indireta da corrente iônica. Também implementamos uma versão modificada da análise de rede de ligações de hidrogênio baseada em teoria de grafos, a fim de fazer o estudo das propriedades estruturais e dinâmicas em diferentes regiões do poro. Com essa abordagem, nós fomos capazes de explorar sistematicamente os efeitos de interface em fluidos espacialmente confinados. Combinando-se simulações de dinâmica molecular com a análise da rede de ligações de hidrogênio em camadas, nós pudemos avaliar a extensão dos efeitos de superfície nas propriedades dinâmicas e os detalhes da interface calcita/salmoura. Com a abordagem desenvolvida, conseguimos isolar os efeitos específicas dos íons da solução aquosa na rede de ligações de hidrogênio. Mostramos que a camada superficial exibe uma topologia de rede semelhante à observada em água pura, uma vez que a barreira eletrostática e física exibida por essa região, inibe a adsorção de íons na superfície da calcita. Fora dessa faixa, os íons influenciam consideravelmente a rede de ligações de hidrogênio: observamos a formação caminhos geodésicos mais extensos em relação àqueles observados em água pura. Esses ramos, que são formados por ligações de hidrogênio contíguas, podem conectar moléculas de baixa a alta dinâmica. Tal estrutura, pode explicar as propriedades mecânicas adesivas observadas em fluidos altamente confinados. Nossas principais contribuições decorrem na descrição da estrutura do solvente, dos íons da solução aquosa na interface calcita/fluido; e suas indicações físicas, e seu potencial significado nos processos de crescimento e dissolução de cristais. Nossas implementações fornecem contribuições interessantes para a compreensão atual dos processos que ocorrem em meios porosos. Especialmente, podendo contribuir para um desenvolvimento racional de novos dispositivos nanofluidicos.The unusual physical properties exhibit by fluids within nanoscopic porous media play an important role in the plethora of chemical, geochemical and environmental processes. Currently, many aspects of the structure and dynamics of the spatially constrained fluids are still poorly understood. Additionally, the interfacial phenomena considerably influences the processes occurring in nanoporous media, which can have a major effect on nanofluidics devices. These multiphase systems and multi-physics phenomena occurs at solid/solution interfaces, with electronic and dynamic effects taking place across size and time scales. Currently, a single methodology is not capable to disentangle all the complexity find in such systems because it is restricted to a specific scale or computationally demand. In addition, the usual computational modeling methodologies applied to investigate bulk phases, they are, in general, not suitable to systematically access the surface effects occurring at solid/fluid interfaces. The challenges imposed by the nanofludics-based systems within the molecular modeling framework require innovative initiatives (among the available methodologies) to correctly access the interface properties. In this thesis, we develop and apply novel computational approaches to properly design and characterize nanofluidics-based systems at atomic level. In this context, we introduced an hierarchical top-down multilevel method by combining molecular dynamics simulations with first principles electronic transport calculations to address the multiscale phenomena problem. The potential of this implementation was demonstrated in a case study involving the water and ionic (Na, Li, and CL) flow through a (6,6) carbon nanotube. We showed that the ionic trace, observed on the electronic transmittance, it may handle an indirect measurement of the ionic current that is recorded as a sensing output. We implemented also a layered version of hydrogen bond network analysis based on graph theory. With this approach, we were able to properly explore interface effects arising on spatially confined fluids. By combining molecular dynamics simulations with the layered hydrogen bond network analysis, we evaluated the extension of surface effects on the fluids dynamics properties and the interaction details at calcite/brine interface. With the developed approach, we have been able to isolate the specific features of the aqueous solutions ions on the hydrogen bond network. We showed that the surface layer near the calcite/brine interface displays similar network topology as observed in pure water, since the electrostatic and physical barrier displayed by this layer inhibit the adsorption of ions on the calcite surface. Outside that region, these ions affect the hydrogen bond network. We observed a more extended geodesic paths with respect to that observed in pure water. Such hydrogen bond branches may connect low to high dynamics molecules across the pore and hence, it may explain the glue-like mechanical properties observed in confinement environment. Our main contributions in this work relies on describing the structure of solvent and electrolyte aqueous solution at calcite/fluid interface and their physical indications and potential significance on the crystal growth and dissolution processes. Our implementations provide interesting contributions to the current understanding of processes occurring in porous media. Specially, it may contribute on the rational design of novel nanofluidics devices

Efficient CH4/CO2 Gas Mixture Separation through Nanoporous Graphene Membrane Designs

Nanoporous graphene membranes have drawn special attention in the gas-separation processes due to their unique structure and properties. The complexity of the physical understanding of such membrane designs restricts their widespread use for gas-separation applications. In the present study, we strive to propose promising designs to face this technical challenge. In this regard, we investigated the permeation and separation of the mixture of adsorptive gases CO2 and CH4 through a two-stage bilayer sub-nanometer porous graphene membrane design using molecular dynamics simulation. A CH4/CO2 gashouse mixture with 80 mol% CH4 composition was generated using the benchmarked force-fields and was forced to cross through the porous graphene membrane design by a constant piston velocity. Three chambers are considered to be feeding, transferring, and capturing to examine the permeation and separation of molecules under the effect of the two-stage membrane. The main objective is to investigate the multistage membrane and bilayer effect simultaneously. The permeation and separation of the CO2 and CH4 molecules while crossing through the membrane are significantly influenced by the pore offset distance (W) and the interlayer spacing (H) of the bilayer nanoporous graphene membrane. Linear configurations (W = 0 Å) and those with the offset distance of 10 Å and 20 Å were examined by varying the interlayer spacing between 8 Å, 12 Å, and 16 Å. The inline configuration with an interlayer spacing of 12 Å is the most effective design among the examined configurations in terms of optimum separation performance and high CO2 and CH4 permeability. Furthermore, increasing the interlayer distance to 16 Å results in bulk-like behavior rather than membrane-like behavior, indicating the optimum parameters for high selectivity and permeation. Our findings present an appropriate design for the effective separation of CH4/CO2 gas mixtures by testing novel nanoporous graphene configurations