MOLECULAR SIMULATION OF SIMPLE FLUIDS AND WATER IN POROUS CARBONS

We report Grand Canonical Monte Carlo (GCMC) molecular simulation stud ies of argon, nitrogen and water in model porous carbons. Adsorption i n ''buckytubes'' is studied for argon and nitrogen, We calculate adsor ption isotherms, density profiles, phase transitions and heats of adso rption for model tubes of 1.05 and 4.8 nm diameter at 77 and 60 K. The smaller buckytube is too small to exhibit phase transitions. For the larger tube we observe layering transitions, capillary condensation an d hysteresis for both argon and nitrogen. Fluid molecules are modelled as Lennard-Jones spheres, and an averaged fluid-wall potential, depen dent only on the distance of the adsorbed molecule from the centre of the tube, is used. Results are reported for water in model graphitic a nd activated carbons with slit pores. Water is modelled using the TIP4 P potential, and COOH groups are used as the active sites, the water-C OOH interaction being the OPLS potential. The structure of the carbon walls is taken into account. We study the effect of varying the densit y and arrangement of active groups on the surface. For these carbons t he adsorption is generally greater than for graphitic carbons, and is strongly dependent on the arrangement of the active groups on the surf ace.