Structure of Ice in Confinement: Water in Mesoporous Carbons

Abstract

In this study, the structure of nanoconfined ice and its behavior during the melting process have been investigated. For this purpose, deionized water was inserted into the pores of the ordered carbon structures CMK-3 and CMK-8 having pores of different diameters. The first set of experiments was performed using differential scanning calorimetry (DSC), from which the melting transition temperature of the confined ice was determined. In order to investigate the structure of ice formed inside the mesopores, wide-angle X-ray scattering was used. The measurements were performed at temperatures from 173 K up to and above the pore melting point for each system. The results of the XRD experiments showed features characteristic of both hexagonal, I h , and cubic, I c , ice at temperatures below the melting point. The structure of the confined ice corresponds to disordered stacking ice layers, ice I sd , and our results agree well with recent simulations of X-ray diffraction of such ice crystals by Murray and co-workers.

Structure of ice confined in carbon and silica nanopores

“…Ice confined in nanopores becomes more cubic as the pore size decreases [14,15]. A similar dependence was shown by Domin et al [55]; when water is confined in smaller pores, the calculated percentage composition of the cubic form of ice increases. Malkin et al [38] showed that the ice produced from homogeneous nucleation in pure water droplets at around 230 K was fully random, with 50% cubic and 50% hexagonal stackins.…”

“…Such a defective structure of the cubic ice was also observed in previous experiments on confined ice formation [15,18,25]. Recently published results of X-ray diffraction studies for water confined in nanopores [55,56] and the theoretical studies by Malkin et al [31,38] suggest that the obtained profile can be a hybrid of both hexagonal and cubic ice forms that were formed as a result of stacking faults. The theory [38] predicts that when a water droplet freezes, a two-dimensional nucleation process occurs.…”

“…Our diffraction data show the existence of features (such as diffraction profile broadening) of stacking disorder ice I sd confined in pores. The asymmetric profile that has been associated with the presence of some defects or disorders in the confined ice structure was also observed in previous studies which concern the ice in nanopores [23,25,26,55]. We evaluated the percentage contribution of cubic and hexagonal ice inside silica and carbon mesopores.…”

Surface Properties of Al-Functionalized Mesoporous MCM-41 and the Melting Behavior of Water in Al-MCM-41 Nanopores

“…48 The second branch, at 10 −6 s, appears immediately below the pore melting point and can be related to the cubic I c form of ice confined in the pores. 48 As follows from the recent work of Domin et al, 49,50 the metastable ice formed in pores is a combination of cubic sequences intertwined with hexagonal sequences stabilized by the confinement. The theory 51 predicts that when a water droplet freezes, a two-dimensional nucleation process occurs.…”

Competitive adsorption and reduced mobility: N-octane, CO2 and H2S in alumina and graphite pores

“…The results are reported in Table 1. These data should only be considered as tentative guidelines, as it is known that confinement in pores alters the thermodynamic properties of fluids [37][38][39][40]. In particular, extended Peng-Robinson equations of state have been used to predict fluid behaviour in cylindrical and slit pores [41][42][43].…”