A Study of the Mechanism of Micropore Filling. I. Molecular Sieve Effects

The adsorptive properties of two microporous carbons and a microporous silica have been investigated and compared using argon and benzene. The micropore volumes determined using the Theory for Volume filling of Micropores (TVFM) agreed to within 40/o of the total micropore volumes determined from the a8 method of pore analysis. Adsorption data of argon at 77 °K and benzene at 298 °K on the microporous carbons were interpreted in terms of the Dubinin-Astakhov and Dubinin-Radushkevich equations, and Weibull and Gaussian distributions of the adsorption free energy with pore volume, respectively. The Weibull distribution was found to apply better than the Gaussian distribution, although variations from linear D-A plots occurred. The adsorption data on the silica sample were best interpreted as a two-term D-R equation. Plots of the distribution of adsorption energy with pore volume of the silica sample for each term of the D-R equation and their effective contribution to the cumulative distribution curve gave conclusive evidence of the ordering of the adsorption process within micropores of varying dimensions

Uncertainty in pore size distribution derived from adsorption isotherms: I. classical methods

Procedures for propagation of uncertainty in pore size distribution calculation based on classical methods for both micro and mesoporous materials are described. Uncertainty in experimental adsorption isotherm data and uncertainty in temperature are introduced as the main sources for uncertainty in height and position of peaks of PSD determined via classical mesopore size distribution determination method. Uncertainty in PSD derived from classical micropore size distribution methods mainly arises from uncertainty in experimental isotherm data. Calculation step size is shown to have some effects on magnitude of uncertainty in micropore calculation. Micropore size distribution calculations are also highly sensitive to the adsorptive molecular diameter

Uncertainty in pore size distribution derived from adsorption isotherms: II. adsorption integral approach

Uncertainty in the amount adsorbed in manometric adsorption isotherm measurements is well established. Here, we extend uncertainty methodologies from adsorption isotherm data uncertainty and apply them to calculate pore size distributions based on adsorption integral methods. The analyses consider as variables: uncertainty in adsorption isotherm data, regularization parameter, molecular potential model, and the number of single pore isotherms calculated with an associated quadrature interval. We demonstrate how the calculated pore size distribution is quite insensitive to the uncertainty in experimental data, but in contrast, the uncertainty in the experimental data affects the calculated value of the optimized regularization parameter which, in turn, leads to considerable variation in the calculated pore size distribution. The calculated pore size distribution is also shown to be highly dependent on the potential model selected and on the number of single pore isotherms applied to the inversion process. We conclude and suggest a quantitative comparison between calculated pore size distributions should be discouraged unless the uncertainty in the experimental data is relatively small and, default values for regularization parameters, potential models, the number of single pore isotherms and their distribution are exactly the same for each pore size distribution evaluation

A Study of the Mechanism of Micropore Filling. I. Molecular Sieve Effects

The adsorptive properties of two microporous carbons and a microporous silica have been investigated and compared using argon and benzene. The micropore volumes determined using the Theory for Volume filling of Micropores (TVFM) agreed to within 40/o of the total micropore volumes determined from the a8 method of pore analysis. Adsorption data of argon at 77 °K and benzene at 298 °K on the microporous carbons were interpreted in terms of the Dubinin-Astakhov and Dubinin-Radushkevich equations, and Weibull and Gaussian distributions of the adsorption free energy with pore volume, respectively. The Weibull distribution was found to apply better than the Gaussian distribution, although variations from linear D-A plots occurred. The adsorption data on the silica sample were best interpreted as a two-term D-R equation. Plots of the distribution of adsorption energy with pore volume of the silica sample for each term of the D-R equation and their effective contribution to the cumulative distribution curve gave conclusive evidence of the ordering of the adsorption process within micropores of varying dimensions

Control of the pore size distribution and its spatial homogeneity in particulate activated carbon

There are circumstances where it is desirable to achieve a particular, optimal, pore size distribution (PSD) in a carbon, including in the molecular sieving, gas storage, CO2-capture and electrochemical energy storage. Activation protocols that cycle a carbon a number of times between a low-temperature oxygen chemisorption process and a higher temperature pyrolysis process have been proposed as a means of yielding such desired PSDs. However, it is shown here that for PFA-based char particles of ∼100 μm in size, only the super-micropores are substantially developed under such an activation protocol, with the ultra-micropores being substantially un-touched. It is also shown that a typical CO2-activation process yields similar control over PSD development. As this process is nearly 15 times faster than the cyclic-O2 protocol and yields larger pore volumes and areas for a given level of conversion, it is to be preferred unless spatial homogeneous porosity within the particles is also desired. If such homogeneity is desired, it is shown here that CO2 activation should continue to be used but at a rate of around one-tenth the typical; this slow rate also has the advantage of producing pore volumes and areas substantially greater than those obtained using the other activation protocols.CH acknowledges a joint scholarship provided by China Scholarship Council (CSC) and the University of Adelaide. SS acknowledges the award of International Postgraduate Research Scholarship (IPRS) from the University of Adelaide. SHM acknowledges the award of a President’s Scholarship from the University of South Australia. The support of the Australian Research Council Discovery Program (DP110101293) is also gratefully acknowledged

Raman spectroscopy study of the transformation of the carbonaceous skeleton of a polymer-based nanoporous carbon along the thermal annealing pathway

We report a multi-wavelength Raman spectroscopy study of the structural changes along the thermal annealing pathway of a poly(furfuryl alcohol) (PFA) derived nanoporous carbon (NPC). The Raman spectra were deconvoluted utilizing G, D, D′, A and TPA bands. The appropriateness of these deconvolutions was confirmed via recovery of the correct dispersive behaviours of these bands. It is proposed that the ID/IG ratio is composed of two parts: one associated with the extent of graphitic crystallites (the Tuinstra–Koenig relationship), and a second related to the inter-defect distance. This model was used to successfully determine the variation of the in-plane size and intra-plane defect density along the annealing pathway. It is proposed that the NPC skeleton evolves along the annealing pathway in two stages: below 1600 °C it was dominated by a reduction of in-plane defects with a minor crystallite growth, and above this temperature growth of the crystallites accelerates as the in-plane defect density approaches zero. A significant amount of transpolyacetylene (TPA)-like structures was found to be remaining even at 2400 °C. These may be responsible for resistance to further graphitization of the PFA-based carbon at higher temperatures

Early changes in visuospatial episodic memory can help distinguish primary age‐related tauopathy from Alzheimer’s disease

From Wiley via Jisc Publications RouterHistory: received 2021-02-08, rev-recd 2021-03-19, accepted 2021-05-01, pub-electronic 2021-05-29Article version: VoRPublication status: PublishedFunder: Alzheimer's Research Trust; Id: http://dx.doi.org/10.13039/501100000319Funder: Medical Research Council; Id: http://dx.doi.org/10.13039/501100000265Funder: Unilever; Id: http://dx.doi.org/10.13039/100007190Funder: Economic and Social Research Council; Id: http://dx.doi.org/10.13039/501100000269Funder: Alzheimer's Society; Id: http://dx.doi.org/10.13039/501100000320Funder: Wellcome Trust; Grant(s): 00388

Structure, Chemistry and Energy of Carbon Surfaces

In this paper, the graphene layer is considered as the basic structural unit in a range of carbon materials. The effects of 2D and 3D order in defining the microstructures and macrostructures of carbons are reviewed along with the related concept of graphene layer orientation within the structure and the resulting ratio of basal plane to edge site as well as its effects on surface chemical reactivity and energy. Both non-specific and specific surface forces and the resulting potentials are considered. Theoretical physical models based on the Lennard–Jones potential applied to the basic structural units, either as an ideal, i.e. perfect, single graphene layer or as multiple layers of varied inter-layer spacing and size, are presented. Mention is then made of non-ideal surfaces (stepped or containing vacancies) and their resulting enhanced potential. The effects of incorporating chemical heterogeneity into the surfaces of these structures are also considered: carbon oxidation mechanisms are discussed in terms of bond energy and disruption of the (conjugated) graphene structure and the resulting polar functional groups are shown to increase interactivity with molecules that possess permanent dipoles or multipoles. The resulting increases in the polar component of surface-free energy can be used to control properties of adhesion, adsorption and wettability