Adsorption isotherms of condensable vapors on solids: Determination of monolayer points from isothermal plots based on the temperature of the vapor source

DeBoer and Broekhoff have proposed that inflections occur in adsorption isotherms at one-third of a monolayer if the adsorbent is homogeneous and the adsorbate does not undergo two-dimensional condensation. This concept has been applied to data for furan, thiophene, and 1,4-cyclohexadiene adsorbed on Graphon carbon black. The method needs only sample weight and thermocouple readings from which to compute the inflection corresponding to one-third of a monolayer. It is shown that this method can agree with the Brunauer-Emmett-Teller method for determining monolayer points only if the BET constant c has a value near 10.