Figure 4. Correlation between experimental and theoretical
dissolution activation energy values of (a)
MOF-CH3@CH3 and (b)
MOF-CH3@NH2 membranes. (c)E S of glucose solution, water and urea solution
for MOF-CH3@CH3 and
MOF-CH3@NH2 membranes. (d) Interaction
energy between toluene and NH2-BDC, toluene,
CH3-BDC. (e) Interaction energy between water and
NH2-BDC, water, CH3-BDC. Grey for C,
blue for N, red for O, white for H.
To further verify this hypothesis, molecule-molecule and molecule-pore
interactions were respectively adjusted. Taking water as an example,
glucose and urea solution (150 mmol L-1) were mixed
with water to strengthen and weak the interactions between water
molecules, respectively.[19,59] Figure 4c shows
that E S of glucose solution (24.23 kJ
mol-1) is higher than that of pure water (18.74 kJ
mol-1), suggesting that the enhancement of water-water
interactions elevates the energy for breaking hydrogen bonds from bulk
state, thus lifting the Es of water. In contrast, urea solution
displays weaker water-water interactions than pure water, thus the
energy for molecule arrangement is reduced and brings lowerE S (15.99 kJ mol-1). For
another, molecule-pore interactions were also adjusted. For instance,
Figure 3c reveals that MOF-CH3@NH2membrane surface with –NH2 groups on pore entrances
gives much lower E S (-4.16 kJ
mol-1) for water than that of
MOF-CH3@CH3 membrane surface with
–CH3 groups (13.70 kJ mol-1).
Moreover, compared with other nonpolar solvents, toluene and cyclohexane
display much lower E S for
MOF-CH3@NH2 membrane than that of
MOF-CH3@CH3 membrane. This is due to the
weak hydrogen bonds between –NH2 with active –H on
cyclic hydrocarbon,[60,61] which compensates for
the consumed energy considerably. This again delivers the fact that
molecule-pore interactions exert paramount impact on molecular
dissolution behaviors.