Unified approach to pore size characterization of microporous carbonaceousmaterials from N-2, Ar, and CO2 adsorption isotherms

We present a unified approach to pore size characterization of microporous carbonaceous materials such as activated carbon and carbon fibers by nitrog en, argon, and carbon dioxide adsorption at standard temperatures, 77 K for N-2 and Ar and 273 K for CO2. Reference isotherms of N-2, Ar, and CO2 in a series of model slit-shaped carbon pores in the range from 0.3 to 36 nm ha ve been calculated from the nonlocal density functional theory (NLDFT) usin g validated parameters of intermolecular interactions. Carbon dioxide isoth erms have also been generated by the grand canonical Monte Carlo (GCMC) met hod based on the 3-center model of Harris and Yung. The validation of model parameters includes three steps: (1) prediction of vapor-liquid equilibriu m data in the bulk system, (2) prediction of adsorption isotherm on graphit e surface, (3) comparison of the NLDFT adsorption isotherms in pores to tho se of GCMC simulations, performed with the parameters of fluid-fluid intera ctions, which accurately reproduce vapor-liquid equilibrium data of the bul k fluid. Pore size distributions are calculated by an adaptable procedure o f deconvolution of the integral adsorption equation using regularization me thods. The deconvolution procedure implies the same grid of pore sizes and relative pressures for all adsorbates and the intelligent choice of regular ization parameters. We demonstrate the consistency of our approach on examp les of pore structure characterization of activated carbons from adsorption isotherms of different gases and from different models (NLDFT and GCMC). S ince the CO2 isotherms measured up to 1 atm are not sensitive to pores wide r then 1 nm, the NLDFT method for CO2 has been extended to high-pressure CO 2 adsorption up to 34 atm. The methods developed are suggested as a practic al alternative to traditional phenomenological approaches such as DR, HK, a nd BJH methods.