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)-$\textit{b}$-poly(butylmethacrylate) (PEO-$\textit{b}$-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-$\textit{b}$-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-$\textit{b}$-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

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

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