Comparison of adsorption isotherms on Cu-BTC metal organic frameworks synthesized from different routes

Due to the differences in synthesis procedures used in preparation of metal organic frameworks, surface area and pore volume of the samples usually vary from one laboratory to another. The adsorption characteristics of the frameworks are also affected. In such cases, usually a scaling factor is employed to match isotherms obtained in different laboratories (or those from experiments and simulations). In an attempt to validate the use of a scaling factor, in this work we compare adsorption properties of N2, O2, Ar, CO2, C3H8 and SF6 on Cu-BTC (HKUST-1) framework synthesized using two different procedures. It was observed that Cu-BTC sample with higher surface area and pore volume has greater adsorption capacity for all gases at the two temperatures considered (298.25 and 318.15 K). For all gases, the ratio of specific adsorption capacities of the two samples can be broadly classified into two regions. In the low loading region this ratio was about 2.03 with in a 10% uncertainty envelope. However, in the high loading region, it increases to about 2.58. Thus, the scaling factor needed to compare adsorption isotherms of Cu-BTC having different surface areas may not be unique. This value seems to be strongly affected by loading, whereas it is relatively insensitive to the type of gas used, temperature or pressure.