Changing Water Affinity from Hydrophobic to Hydrophilic in Hydrophobic Channels

Abstract

The behavior of water at hydrophobic interfaces can play a significant role in determining chemical reaction outcomes and physical properties. Carbon nanotubes and aluminophosphate materials have one-dimensional hydrophobic channels, which are entirely surrounded by hydrophobic interfaces. Unique water behavior was observed in such hydrophobic channels. In this article, changes in the water affinity in one-dimensional hydrophobic channels were assessed using water vapor adsorption isotherms at 303 K and grand canonical Monte Carlo simulations. Hydrophobic behavior of water adsorbed in channels wider than 3 nm was observed for both adsorption and desorption processes, owing to the hydrophobic environment. However, water showed hydrophilic properties in both adsorption and desorption processes in channels narrower than 1 nm. In intermediate-sized channels, the hydrophobic properties of water during the adsorption process were seen to transition to hydrophilic behavior during the desorption process. Hydrophilic properties in the narrow channels for both adsorption and desorption processes are a result of the relatively strong water-channel interactions (10-15 kJ mol(-1)). In the 2-3 nm channels, the water-channel interaction energy of 4-5 kJ mol(-1) was comparable to the thermal translational energy. The cohesive water interaction was approximately 35 kJ mol(-1), which was larger than the others. Thus, the water affinity change in the 2-3 nm channels for the adsorption and desorption processes was attributed to weak water-channel interactions and strong cohesive interactions. These results are inherently important to control the properties of water in hydrophobic environments.

Fast Water Relaxation through One‐Dimensional Channels by Rapid Energy Transfer

“…Water vapor was fully introduced into the internal nanospaces in response to the water vapor adsorption isotherms at 303 K (Figure ). Here, the adsorbed amounts of water vapor corresponded to nanopore volumes evaluated from the N 2 ‐adsorption isotherms at 77 K . Significant adsorption hysteresis loops in the 2 and 3 nm CNTs indicate a change between hydrophobicity and hydrophilicity, associated with a change in assembled structure, as reported elsewhere .…”

“…Water vapor was fully introduced into the internal nanospaces in response to the water vapor adsorption isotherms at 303 K( Figure 2). Here, the adsorbed amounts of water vapor corresponded to nanopore volumes evaluated from the N 2 -adsorptioni sotherms at 77 K. [16] Significant adsorptionh ysteresis loops in the 2a nd 3nmC NTsi ndicateachange between hydrophobicity and hydrophilicity,a ssociated with ac hange in assembled structure, as reported elsewhere. [3c, 16] The adsorption hysteresis was clearly observed as forbidden structure changes of water adsorbed in carbon nanospaces during adsorptiona nd desorption processes, and the adsorbed water formed clusters and layers, respectively.…”

Effect of H2O on Slurry‐Phase Fischer–Tropsch Synthesis over Alumina‐supported Cobalt Catalysts

“…The intensity of the band around 1600 cm −1 , which represents the deformation of physisorbed water (δ(HOH)), decreases in the order of Co/Zr/γ‐Al 2 O 3 > Co/Zn/γ‐Al 2 O 3 > Co/γ‐Al 2 O 3 > Co/P/γ‐Al 2 O 3 . Partial formation of AlPO 4 containing hydrophobic interfaces as reported earlier is proposed to justify this observation, which also suggests that addition of P in the alumina support can lower the H 2 O adsorption capacity of Co catalyst. It is also noted that the hydrothermal stability of the Co catalysts with Zn and Zr in the modified support is comparable to Co/γ‐Al 2 O 3 even though the adsorption capacity of H 2 O increases (Table and Figure ).…”

“…The intensity of the band around 1600 cm −1 , which represents the deformation of physisorbed water (δ(HOH)), 43,44 decreases in the order of Co/Zr/γ-Al 2 O 3 > Co/Zn/γ-Al 2 O 3 > Co/γ-Al 2 O 3 > Co/P/γ-Al 2 O 3 . Partial formation of AlPO 4 containing hydrophobic interfaces as reported earlier 45,46 is proposed to justify this observation, which also suggests that addition of P in the alumina 22 where an increase in the catalytic activity of SiO 2 and TiO 2supported cobalt catalysts was observed with~20% water addition, but at higher concentration of water the catalytic activity was found to decrease. The product distribution over the Co catalysts at 230 C and 2.0 MPa is listed in Table 3.…”

Surface Effect on Oil Transportation in Nanochannel: a Molecular Dynamics Study

“…The channel size of oil shale ranges from 2 to 100 nm in width [4, 5], which generates a large specific surface area and many kinds of surface effect. Under the influence of surface interaction between fluid and substrate, lots of new physical phenomena may be aroused, for example, water flows much faster inside nanotubes than in a classical macroscale tube [6, 7], anomalous increase is found in carbon capacitance at pore sizes less than 1 nm [8], water affinity in carbon nanotube changes from hydrophobic to hydrophilic as the width decreases [9]. Being located in oil shale, with the strong surface interaction between fluids and shale substrate, the fluid exhibits a lot of different characters from that in macroscopic channel, such as the density distribution, wettability, and diffusion coefficient [10–12], resulting in different transportation properties of fluids through such nanochannel from those in macroscale channel.…”