Adsorption of water vapors and the micropore structure of carbon adsorbents. Communication 14. Differential heats of adsorption of water vapors by active carbons

Polyurethane Aerogels Based on Cyclodextrins: High-Capacity Desiccants Regenerated at Room Temperature by Reducing the Relative Humidity of the Environment

“…Q 0 for α-CDPU-2.5 was calculated via eq (see the Experimental Section) using the coefficients of the Q st vs N plot (see Table S.5), and it was found at about 18 kJ mol –1 , which is a typical value for H-bonding between water and urethane groups that decorate the surfaces of cyclodextrin-based polyurethane aerogels (refer to Figure ). As noted in Figure C, Q st increases rapidly with the quantity of water adsorbed and reaches a value of about 55 kJ mol –1 , which is higher than the heat of condensation of water (44.0 kJ mol –1 ) . This kind of “overshooting” in the Q st plots of water adsorption has been noted before, , and the consensus is that it is an artifact. , Instead, the average asymptotic value of Q st with increasing N is a better indicator of the interactions that lead to the total water uptake .…”

“…81 As noted in Figure 8C, Q st increases rapidly with the quantity of water adsorbed and reaches a value of about 55 kJ mol −1 , which is higher than the heat of condensation of water (44.0 kJ mol −1 ). 82 This kind of "overshooting" in the Q st plots of water adsorption has been noted before, 82,83 and the consensus is that it is an artifact. 31,83 Instead, the average asymptotic value of Q st with increasing N is a better indicator of the interactions that lead to the total water uptake.…”

“…31,83 Instead, the average asymptotic value of Q st with increasing N is a better indicator of the interactions that lead to the total water uptake. 82 That average asymptotic value (see dotted horizontal line in Figure 8C) was near the condensation heat of water, indicating multilayer adsorption of water on water. It is also important to note that the average asymptotic value of Q st is reached at the early stages of water uptake, and thereby the overall water uptake was due to pore filling.…”

Heterogeneous Do–Do model of water adsorption on carbons

“…1 and 2 are usually decreasing with adsorbed amount. In fact, this type of plots has been observed recently for some experimental data determined for a series of microporous activated carbons, usually for the unmodified chemically adsorbents [3,4,6,7,9,10,[17][18][19][20] and also in some theoretical studies [4,[6][7][8][9][10]. It should be mentioned here that also different kind (i.e., the increasing one) of the plot of adsorption enthalpy can be easily generated from the original DD model.…”

Adsorption and Mobility of Water and Benzene Molecules in Carbon and Polymer Adsorbents

“…1. ) It was found that the heat of water adsorption on PASs in the area of low relative filling occurred to be less than the heat of water condensation (Vartapetyan et al, 1986(Vartapetyan et al, , 1987Dubinin et al, 1987). This is the main difference of water adsorption from the adsorption of nonpolar molecules such as benzene adsorbing on the surface or in pore volume of AC due to dispersion interactions (Dubinin, 1982(Dubinin, , 1983 with the heat of benzene vapor adsorption always exceeding the heat of benzene condensation (Babaev et al, 1977).…”