Molecular simulation of carbon dioxide adsorption in chemically and structurally heterogeneous porous carbons

Capture of carbon dioxide from fossil fuel power plants via adsorption and sequestration of carbon dioxide in unmineable coal seams are achievable near-term methods of reducing atmospheric emissions of this greenhouse gas. To investigate the influence of surface heterogeneity upon predicted adsorption behavior in activated carbons and coal, isotherms were generated via grand canonical Monte Carlo simulation for CO 2 adsorption in slit-shaped pores with underlying graphitic structure and several variations of chemical heterogeneity (oxygen and hydrogen content), pore width, and surface functional group orientation. Adsorption generally increased with increasing surface oxygen content, although exceptions to this trend were observed on structurally heterogeneous surfaces with holes or furrows that yield strongly adsorbing preferred binding sites. Among the heterogeneous pore structures investigated, those with coal-like surfaces adsorbed carbon dioxide more strongly than planar, homogeneous graphitic slit pores of comparable width. Electrostatic adsorbate–adsorbent interactions significantly influenced adsorption onto model surfaces. © 2006 American Institute of Chemical Engineers Environ Prog, 25: 343–354, 2006Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55883/1/10168_ftp.pd

Abstract Competition

Articlehttp://deepblue.lib.umich.edu/bitstream/2027.42/97009/1/UMURJ-Issue09_2012-StudentAbstractCompetition.pd

University of Michigan Undergraduate Research Journal, Issue 9, Winter 2012

Articlehttp://deepblue.lib.umich.edu/bitstream/2027.42/97010/1/UMURJ-Issue09_2012.pd

Exploring the Thermodynamic Criteria for Responsive Adsorption Processes

We describe a general model to explore responsive adsorption processes in flexible porous materials.This model combines mean field formalism of the osmotic potential, classical density functional theory of adsorption in slit pore models and generic potential functions which represent the Helmholtz free energy landscape of a porous system.Using this model, we focus on recreating flexible adsorption phenomena observed in prototypical metal-organic frameworks, especially the recently discovered effect of negative gas adsorption (NGA).We identify the key characteristics required for the model to generate unusual adsorption processes and subsequently employ an extensive parametric study to outline conditions under which gate-opening and NGA are observed.This powerful approach will guide the design of responsive porous materials and the discovery of entirely new adsorption processes.</div

Interactions of CO2 with various functional molecules

The CO2 capturing and sequestration are of importance in environmental science. Understanding of the CO2-interactions with various functional molecules including multi-N-containing superbases and heteroaromatic ring systems is essential for designing novel materials to effectively capture the CO2 gas. These interactions are investigated using density functional theory (DFT) with dispersion correction and high level wave function theory (resolution-of-identity (RI) spin-component-scaling (scs) Moller-Plesset second-order perturbation theory (MP2) and coupled cluster with single, double and perturbative triple excitations (CCSD(T))). We found intriguing molecular systems of melamine, 1,5,7-triazabicyclo[4.4.0]dec-5- ene (TBD), 7-azaindole and guanidine, which show much stronger CO2 interactions than the well-known functional systems such as amines. In particular, melamine could be exploited to design novel materials to capture the CO2 gas, since one CO2 molecule can be coordinated by four melamine molecules, which gives a binding energy (BE) of similar to 85 kJ mol(-1), much larger than in other cases.open2

10.1098/rsta.2004.1455 Connectivity, clusters, and transport:

use of percolation concepts and atomistic simulation to track intracellular ion migratio

Performance and Long Term Stability of Mesoporous Silica Membranes for Desalination

This work shows the preparation of silica membranes by a two-step sol-gel method using tetraethyl orthosilicate in ethanolic solution by employing nitric acid and ammonia as co-catalysts. The sols prepared in pH 6 resulted in the lowest concentration of silanol (Si–OH) species to improve hydrostability and the optimized conditions for film coating. The membrane was tested to desalinate 0.3–15 wt % synthetic sodium chloride (NaCl) solutions at a feed temperature of 22 °C followed by long term membrane performance of up to 250 h in 3.5 wt % NaCl solution. Results show that the water flux (and salt rejection) decrease with increasing salt concentration delivering an average value of 9.5 kg m–2 h–1 (99.6%) and 1.55 kg m–2 h–1 (89.2%) from the 0.3 and 15 wt % saline feed solutions, respectively. Furthermore, the permeate salt concentration was measured to be less than 600 ppm for testing conditions up to 5 wt % saline feed solutions, achieving below the recommended standard for potable water. Long term stability shows that the membrane performance in water flux was stable for up to 150 h, and slightly reduced from thereon, possibly due to the blockage of large hydrated ions in the micropore constrictions of the silica matrix. However, the integrity of the silica matrix was not affected by the long term testing as excellent salt rejection of >99% was maintained for over 250 h

Fate factors and emission flux estimates for emerging contaminants in surface waters

Pharmaceuticals, personal care products, hormones, and wastewater products are emerging environmental concerns for manifold reasons, including the potential of some compounds found in these products for endocrine disruption at a very low chronic exposure level. The environmental occurrences and sources of these contaminants in the water, soil, sediment and biota in European nations and the United States are well documented. This work reports a screening-level emission and fate assessment of thirty compounds, listed in the National Reconnaissance of the United States Geological Survey (USGS, 1999–2000) as the most frequently detected organic wastewater contaminants in U.S. streams and rivers. Estimations of the surface water fate factors were based on Level II and Level III multimedia fugacity models for a 1000 km2 model environment, the size of a typical county in the eastern United States. The compounds are categorized into three groups based upon the sensitivity of their predicted surface water fate factors to uncertainties in their physicochemical property values and the landscape parameters. The environmental fate factors, mass distributions, and loss pathways of all of the compounds are strongly affected by their assumed modes of entry into the environment. It is observed that for thirteen of the thirty organic wastewater contaminants most commonly detected in surface waters, conventional treatment strategies may be ineffective for their removal from wastewater effluents. The surface water fate factors predicted by the fugacity models were used in conjunction with the surface water concentrations measured in the USGS reconnaissance to obtain emission flux estimates for the compounds into U.S. streams and rivers. These include estimated fluxes of 6.8 × 10−5 to 0.30 kg/h km2 for the biomarker coprostanol; 1.7 × 10−5 to 6.5 × 10−5 kg/h km2 for the insect repellent N,N-diethyltoluamide; and 4.3 × 10−6 to 3.1 × 10−5 kg/h km2 for the steroid estriol

Pore Size Heterogeneity and the Carbon Slit Pore: A Density Functional Theory Model

We present model isotherms predicted by nonlocal density functional theory for adsorption of simple fluids in carbon slit pores. The effects of pore size, temperature, and solid-fluid potential interaction strength are examined. Our results are summarized into a classification scheme based upon regimes of continuous pore filling, capillary condensation, and 0 -1 layering transitions. The descriptions we have devised depart from the IUPAC convention in that the filling behavior, rather than the physical width of the pore, is used as a guide to classification. Our results suggest that while the magnitude of the solid-fluid interactions dictates the pressure at which pore filling occurs, the type of filling depends primarily upon the ratio of pore width to adsorbate molecular diameter. The critical pore widths that denote the boundaries between various regimes of filling behavior are strongly dependent upon the temperature. To confirm the accuracy of the theoretical results, we compare adsorption isotherms and density profiles calculated from nonlocal theory and Gibbs ensemble simulation. The results from theory and simulation are found to be in good agreement. We conclude with a discussion of the problems associated with estimating solid-fluid potential parameters from experiment for use in theoretical computations. A comparison of nonlocal theory model isotherms and experimental nitrogen uptake measurements on nonporous carbon is presented