(70bi) Absolute assessment of adsorption-based characterisation methods

Vapour adsorption is used extensively for characterization of microporous particulate solids to facilitate their design, synthesis and utilization. These characterization methods are necessarily founded on significant simplifications with regards both the structure of the adsorbent and the behaviour of the adsorbate, with these simplifications varying from method to method. These varying simplifications give rise to uncertainties over what is actually being measured, differences between methods for the same characteristics, and measurements that at times defy commonsense. We have used Grand Canonical Monte Carlo (GCMC) simulations on Virtual Porous Carbons (VPCs) to assess a host of characterisation methods on an absolute basis to gain greater understanding of what these methods are measuring and the reasons for any failures. GCMC simulations of nitrogen adsorption VPCs were performed and different types of adsorption isotherms have been obtained. These isotherms were inverted using a range of adsorption-based characterisation methods to obtain the pore surface areas and volumes, pore size distributions, fractal dimension, energy distribution and pore system connectivity. These ?experimentally determined' characteristics were finally compared with values determined directly via geometric analysis of the pore space as defined by the adsorbed molecules ? it is this comparison with the exact directly determined values that makes this assessment absolute rather than relative in nature, the latter being the standard method of assessment where typically results from two or more methods are compared. In this presentation, we will report a review of this work including details of the VPCs, the geometry-based methods used for their direct characterisation, and an overview of the absolute assessment of many of the standard methods used to determine the characteristics outlined above including reasons for failure.