101 research outputs found
In silico designed microporous carbons
AbstractThis work presents a computational study on the packing of three-dimensional carbon nanostructures and their effect on gas adsorption properties. We show that it is possible to obtain intrinsically microporous materials without specifying structural properties such as surface area or pore size distribution by packing individual graphene platelets connected at a contortion site. The resulting structures can potentially represent disordered carbons and provide understanding of the relationship between pore structure and adsorption performance. The calculated CO2/CH4 selectivity of these materials at the zero coverage selectivity can be as high as 25, whilst at low finite pressures (0.05bar) is between 6 and 10, which is comparable with what is expected for most carbons. We compare the results to the ones obtained from a simple slit pore model and highlight the importance of pore morphological complexity to adsorption of industrially important gases
Solvent-induced morphological transitions in methacrylate-based block-copolymer aggregates
Poly(ethylene oxide)--poly(butylmethacrylate)
(PEO--PBMA) copolymers have recently been identified as excellent
building blocks for the synthesis of hierarchical nanoporous materials.
Nevertheless, while experiments have unveiled their potential to form
bicontinuous phases and vesicles, a general picture of their phase and
aggregation behavior is still missing. By performing Molecular Dynamics
simulations, we here apply our recent coarse-grained model of
PEO--PBMA to investigate its self-assembly in water and
tetrahydrofuran (THF) and unveil the occurrence of a wide spectrum of
mesophases. In particular, we find that the morphological phase diagram of this
ternary system incorporates bicontinuous and lamellar phases at high copolymer
concentrations, and finite-size aggregates, such as dispersed sheets or
disk-like aggregates, spherical vesicles and rod-like vesicles, at low
copolymer concentrations. The morphology of these mesophases can be controlled
by tuning the THF/water relative content, which has a striking effect on the
kinetics of self-assembly as well as on the resulting equilibrium structures.
Our results disclose the fascinating potential of PEO--PBMA
copolymers for the templated synthesis of nanostructured materials and offer a
guideline to fine-tune their properties by accurately selecting the THF/water
ratio
A facile post-synthetic modification method to improve hydrothermal stability and CO2 selectivity of CuBTC metal-organic framework
Competitive Adsorption of a Multi-functional Amine and Phenol Surfactant with Ethanol on Hematite from Non-Aqueous Solution
Surfactants, which contain phenol and amine groups, are commonly used in industries to protect metallic surfaces, and their efficiency depends strongly on factors such as pressure and temperature, solvent properties, and the presence of other surfactants in the system. In this work, we present a molecular simulation study of the competitive adsorption between a multifunctional phenol and amine surfactant model and ethanol at the oil/solid interface formed between iso-octane and a model hematite (α-Fe2O3) slab. We show that the surfactant strongly adsorbs at the iso-octane/hematite interface in the absence of ethanol at moderate temperatures. As the concentration of ethanol is increased, the ethanol molecules compete effectively for the adsorption sites on the iron oxide surface. This competition drives the surfactant molecules to remain in the bulk solution, while ethanol forms ordered and strongly coordinated layers at the oil/solid interface, despite the well-known complete miscibility of ethanol in iso-octane in bulk under standard conditions. Potential of mean force calculations show that the free energy of adsorption of the surfactant is approximately two times larger than that for a single ethanol molecule, but the simulations also reveal that a single surfactant chain needs to displace up to five ethanol molecules to adsorb onto the surface. The end result is more favorable ethanol adsorption which agrees with the experimental analysis of similar oil/iron oxide systems also reported in this work.Industr
Adsorption of Cd(II) and Pb(II) ions from aqueous solutions using mesoporous activated carbon adsorbent: Equilibrium, kinetics and characterisation studies
In this study, cadmium and lead ions removal from aqueous solutions using a commercial activated carbon adsorbent (CGAC) were investigated under batch conditions. The adsorbent was observed to have a coarse surface with crevices, high resistance to attrition, high surface area and pore volume with bimodal pore size distribution which indicates that the material was mesoporous. Sorption kinetics for Cd(II) and Pb(II) ions proceeded through a two-stage kinetic profile-initial quick uptake occurring within 30 min followed by a gradual removal of the two metal ions until 180 min with optimum uptake (qe,exp) of 17.23 mg g1 and 16.84 mg g1 for Cd(II) and Pb(II) ions respectively. Modelling of sorption kinetics indicates that the pseudo first order (PFO) model described the sorption of Pb(II) ion better than Cd(II), while the reverse was observed with respect to the pseudo second order (PSO) model. Intraparticle diffusion modelling showed that intraparticle diffusion may not be the only mechanism that influenced the rate of ions uptake. Isotherm modelling was carried out and the results indicated that the Langmuir and Freundlich models described the uptake of Pb(II) ion better than Cd(II) ion. A comparison of the two models indicated that the Langmuir isotherm is the better isotherm for the description of Cd(II) and Pb(II) ions sorption by the adsorbent. The maximum loading capacity (qmax) obtained from the Langmuir isotherm was 27.3 mg g1 and 20.3 mg g1 for Cd(II) and Pb(II) ions respectively
Mapping the Cu-BTC metal-organic framework (HKUST-1) stability envelope in the presence of water vapour for CO<sub>2</sub>Â adsorption from flue gases
Cu-BTC metal-organic framework (HKUST-1) was evaluated as the model material for CO2 capture from flue gas streams. This paper presents an optimised hydrothermal synthesis of HKUST-1 and an analysis of water stability of HKUST-1. Substantial improvements of the hydrothermal synthesis process of HKUST-1 are shown to increase the quantitative yield up to 89.4% at 100°C. Single-component adsorption experiments were carried out under conditions relevant for flue gases adsorption (45-60°C, 0-1barG) to evaluate the performance of HKUST-1 in terms of adsorption capacity, showing that the amount adsorbed of water can reach up to 21.7mmolg-1, about one order of magnitude higher than CO2 (1.75mmolg-1) and almost two orders of magnitude higher than N2 (0.17mmolg-1). The hydration process of HKUST-1 framework was investigated using dynamic vapour adsorption under the flue gas emitting conditions. HKUST-1 is sensitive to humid streams and dynamic deformation of its porous structure takes place at 40-50°C and various relative humidity values, leading to the irreversible decomposition of HKUST-1 framework and the consequent deterioration in its adsorption capacity. Under humid conditions, water displaces the organic linkers from the copper centres causing the collapse of HKUST-1 framework. These results provide fundamental knowledge to enable future material design for the modification of the hydrophilic nature of copper sites in HKUST-1 to improve its moisture stability.</p
CaSPA - an Algorithm for Calculation of the Size of Percolating Aggregates
We present an algorithm (CaSPA) which accounts for the effects of periodic
boundary conditions in the calculation of size of percolating aggregated
clusters. The algorithm calculates the gyration tensor, allowing for a mixture
of infinite (macroscale) and finite (microscale) principle moments.
Equilibration of a triblock copolymer system from a disordered initial
configuration to a hexagonal phase is examined using the algorithm.Comment: 15 pages, 10 figures. Accepted by Computer Physics Communication
Thermodynamic excess functions for mixture adsorption on zeolites
Thermodynamic excess functions have been widely used to describe liquid properties because they quantify deviations from ideal behavior. In this work, thermodynamic excess functions are used as a tool to understand and predict the behavior of mixtures in microporous materials such as zeolites. The use of excess functions for describing deviations from ideal mixing in the adsorbed phase differs from liquid solutions in several subtle but important ways. Prediction of mixture adsorption is a key factor in the design of adsorption separation processes. Measuring single-component adsorption properties is easy compared to multicomponent properties. Therefore it is important to have a reliable method of calculating mixture behavior from pure-component properties. The main obstacle to progress is a scarcity of accurate and consistent experimental data over a wide range of temperature and loading for testing theories. Almost no data are available on the enthalpy of adsorbed mixtures, even though such information is necessary for the modeling of fixed bed adsorbers. A custom-made calorimeter was used to measure mixture properties. Thermodynamic excess functions such as excess enthalpy (heat of mixing) and excess free energy (activity coefficients) provide a complete thermodynamic description of the effect of temperature, pressure and composition variables. The mixtures studied are described within experimental error by a 3-constant equation, which is thermodynamically consistent and has the correct asymptotic properties at high and low coverage for gases adsorbed in zeolites. More importantly, it is shown that pure component properties such as heats of adsorption and saturation capacity can be used to predict the magnitude of the non-idealities in mixture adsorption. Predictions of mixture properties for SF6-CH4 mixtures on silicalite using molecular simulation agree with experimental measurements. Molecular simulation results show segregation of SF6 and CH 4 molecules in different sections of the silicalite pore network. Deviations from ideal solution are consequence of a non-uniform composition of the adsorbed phase
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