A neutron spin echo study of low-temperature water confined in the spherical silica pores of SBA-16.

The dynamic properties of heavy water (D2O) and light water (H2O) confined in porous silica SBA-16 were studied over a temperature range of 210-290 K by neutron spin echo measurements. SBA-16 has predominant spherical pores (7.1 nm in pore size), channels interconnecting the spherical pores, and micropores (corona). The coherent intermediate scattering function on D2O filled SBA-16 showed the rotational dynamics of confined water without significant translational motion over the temperature range measured. This finding is due probably to collective entities of water due to cooperativity of hydrogen-bonds among water molecules in SBA-16 pores. The relaxation time of the collective entities followed the Vogel-Fulcher-Tammann relation at temperatures down to the freezing temperature of 235 K, suggesting a behavior of fragile water in the spherical pore. A comparison with previous NSE measurements of D2O in MCM-41 showed that the collective entities of water in the SBA-16 spherical pores have higher rotational mobility than those in the MCM-41 cylindrical pores. On the other hand, the incoherent intermediate scattering function on H2O filled SBA-16 revealed the translational motion of individual water molecules in the collective entities. It has been found that water in micropores is not frozen and is mobile down to 210 K from data of both D2O and H2O in SBA-16. Phase changes of various water confined in SBA-16 with decreasing and increasing temperatures are discussed based on the obtained dynamic properties.

An NMR study on the mechanisms of freezing and melting of water confined in spherically mesoporous silicas SBA-16.

Thermodynamic and dynamic properties of water confined in mesoporous silica glass SBA-16 were investigated by DSC, and (1,2)H NMR spectroscopy and (2)H NMR spin-lattice relaxation time (T1) as a function of pore size. SBA-16 possesses the main spherical pores, interconnecting channels and micropores (corona). Water in the characteristic spherical pores of SBA-16 freezes at the homogeneous nucleation temperature of water. Between room and freezing temperatures, the correlation time of the isotropic rotation of water in the pores of SBA-16 followed the Vogel-Fulcher-Tammann (VFT) relation, which reflects the formation and growth of clusters of fragile water for changing to the strong water. The vitrification of water in micropores around 200 K was observed by (2)H NMR. Above 200 K, the correlation time of the rotation of water in micropores exhibited non-Arrhenius behavior, which is correlated with the gradual decrease in the mobility of water due to the growth of hydrogen bonding, forming low density water before vitrification. After vitrification, the activation energy of the rotation of water in micropores was 25-33 kJ mol(-1), which was similar to that in ice Ih for all samples. The freedom of cluster formation and water rotation increased with the increasing the pore size.

Different behavior of water in confined solutions of high and low solute concentrations.

Water-glycerol solutions confined in 21 Å pores of the silica matrix MCM-41 C10 have been studied using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The results suggest a micro-phase separation caused by the confinement. Likely the water molecules coordinate to the hydroxyl surface groups of the pores, leaving most of the glycerol molecules in the centre of the pores. This makes the dynamics of glycerol almost concentration independent up to water concentrations of about 85 wt%. However, at higher water concentrations no substantial clustering of glycerol molecules should occur and the glass transition related dynamics exhibit an anomalous behaviour. Instead of a common plasticization effect of water, as for the corresponding bulk solutions (when no ice is formed), it is evident that water acts as an anti-plasticizer in the confinement at high water concentrations. We propose that the increased water concentration slows down the glass transition related dynamics in the deeply supercooled regime due to that a rigid hydrogen bonded network structure of water molecules is formed at low temperatures and low glycerol concentrations. This is in contrast to the situation in a homogenously mixed bulk solution of a high solute concentration where the water molecules will be less hydrogen bonded, and therefore are typically more mobile than the surrounding solute molecules. An almost complete hydrogen bonded network of water molecules may, even in confinements, be sufficiently rigid to slow down the relaxation of embedded solute molecules. It can also be expressed the other way around, i.e. small amounts of glycerol act as a plasticizer for water, due to its breaking up of the nearly tetrahedral network structure. From the here observed concentration dependent behaviour of the deeply supercooled bulk and confined solutions it seems, furthermore, evident that the Tg value of bulk water cannot be estimated from extrapolations of aqueous solutions.

Low temperature phase properties of water confined in mesoporous silica MCM-41: thermodynamic and neutron scattering study.

The phase properties of water confined in mesoporous silica MCM-41 were investigated over a temperature range of 100-298 K as a function of pore size by specific heat capacity and inelastic neutron scattering (INS) measurements. The water content of the samples was carefully controlled to ensure the capillary filled state and no overloading of water. The values of heat capacity of the pore water are higher than those of bulk ice and liquid water over the whole temperature range measured. The contribution of water in the inner part of pores (abbreviated as the internal water) was elucidated by using the heat capacity data of monolayer water measured. The entropy of the internal water was then estimated from integration of the heat capacity of the internal water. The entropy values of the internal water increase by confinement in the pores of MCM-41 in both liquid and frozen regions, indicating an increase in the deformation of the structure and∕or a change in the dynamics in both regions. The INS spectra show the density of states for the librational motion of water frozen at 50 K, suggesting that the confined water is similar to amorphous ice rather than to crystalline ice. When the sample is warmed to melt, the band edge of the librational motion for water frozen in large pores (diameter of 3.6 nm) shifts to a lower energy side, indicating the weakening of intermolecular hydrogen bonds. For water in small pores (2.1 nm), on the contrary, the librational band shifts slightly to a higher energy side, suggesting the low density liquid to high density liquid transition (L-L transition) at 225-250 K. A plausible mechanism of the L-L transition of water in confinement is proposed in terms of incomplete growth of homogeneous nucleation of ice due to an interfacial free energy effect to inhibit crystallization of water confined in small pores.

Visible-light-derived photocatalyst based on TiO(2-δ)Nδ with a tubular structure.

We succeeded in achieving visible-light responsiveness on a tubular TiO(2) sample through the treatment of a tubular TiO(2) that has a large surface area with an aqueous solution of ammonia or triethylamine at room temperature and subsequent calcination at 623 K, which produced a nitrided tubular TiO(2) sample. It was found that the ease of nitridation is dependent on the surface states; washing the tubular TiO(2) sample with an aqueous acidic solution is very effective and indispensable. This treatment causes the appearance of acidic sites on the tubular TiO(2), which was proved by the following experiments: NH(3) temperature-programmed desorption and two types of organic reactions exploiting the acid properties. The prepared samples, TiO(2-δ)N(δ), efficiently absorb light in the visible region, and they exhibit a prominent feature for the decomposition of methylene blue in an aqueous solution at 300 K under irradiation with visible light, indicating the achievement of visible-light responsiveness on the tubular TiO(2) sample. This type of tubular TiO(2-δ)N(δ) sample has merit in the sense that it has a large surface area and a characteristic high transparency for enabling photocatalytic reactions because it has a tubular structure and is composed of thin walls.

Mechanism of freezing of water in contact with mesoporous silicas MCM-41, SBA-15 and SBA-16: role of boundary water of pore outlets in freezing.

The freezing mechanism of water contacted with mesoporous silicas with uniform pore shapes, both cylindrical and cagelike, was studied by thermodynamic and structural analyses with differential scanning calorimetry (DSC) and X-ray diffraction (XRD) together with adsorption measurements. In the DSC data extra exothermic peaks were found at around 230 K for water confined in SBA-15, in addition to that due to the freezing of pore water. These peaks are most likely to be ascribed to the freezing of water present over the micropore and/or mesopore outlets of coronas in SBA-15. Freezing of water confined in SBA-16 was systematically analysed by DSC with changing the pore size. The freezing temperature was found to be around 232 K, close to the homogeneous nucleation temperature of bulk water, independent of the pore size when the pore diameter (d) < 7.0 nm. Water confined in the cagelike pores of SBA-16 is probably surrounded by a water layer (boundary water) at the outlets of channels to interconnect the pores and of fine corona-like pores, which is similar to that present at the outlet of cylindrical pores in MCM-41 and of cylindrical channels in SBA-15. The presence of the boundary water would be a key for water in SBA-16 to freeze at the homogeneous nucleation temperature. This phenomenon is similar to those well known for water droplets in oil and water droplets of clouds in the sky. The XRD data showed that the cubic ice I(c) was formed in SBA-16 as previously found in SBA-15 when d < 8.0 nm.

Effect of water on structure of hydrophilic imidazolium-based ionic liquid.

The state of water in room-temperature ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI(+)BF(4)(-)), has been investigated by measurements of absorption and desorption isotherms, attenuated total reflectance infrared (ATR-IR) spectroscopy, and (2)H NMR relaxation method. The absorption enthalpies of water for the ionic liquid were estimated from the absorption isotherms. The enthalpies in the water mole fraction range of x(w) approximately 0.3. In addition, the activation energies for the rotational motion of a water molecule estimated from the (2)H NMR relaxation rates have indicated that the motion of water molecules in EMI(+)BF(4)(-)-D(2)O solutions gradually becomes freer with increasing water content from x(w) = 0.10 to 0.30, but is retarded again at x(w) = 0.33. Therefore, all the present findings have suggested that the state of water molecules in EMI(+)BF(4)(-) significantly changes at x(w) approximately 0.3. On the other hand, to directly observe the effect of water on structure of EMI(+)BF(4)(-), LAXS experiments have been made on EMI(+)BF(4)(-)-water solutions. It has been suggested that the interactions between the C(2) atom within the imidazolium ring of EMI(+) and BF(4)(-) are strengthened with increasing water content, while those at the C(4) and C(5) atoms weaken. Thus, the present LAXS experiments have clarified the beginning of formation of ion pair in EMI(+)BF(4)(-) by adding water at the molecular level.

Thermodynamic and FTIR studies of supercooled water confined to exterior and interior of mesoporous MCM-41.

The thermal properties of water confined to both exterior and interior of cylindrical mesoporous MCM-41 (pore diameter d = 1.8-3.6 nm) were analysed by differential scanning calorimetry and FTIR spectroscopy. A three-step freezing of the exterior water was observed just above 233 K, the homogeneous nucleation temperature of bulk water, before the interior water was frozen. The first freezing of water was ascribed to the outermost bulk water, the second one to water between bulk and water bound to the exterior wall, and the third one to the bound exterior water. With decreasing pore size, the second freezing water decreased in magnitude. This stepwise freezing of the exterior water has been found in porous zeolite materials. The exothermic peak of the interior water confined in MCM-41 was observed at 227.5 K before freezing, ascribed probably to a high-density liquid-low-density liquid phase change. FTIR data of the interior water confirmed this finding. The present results substantiate the static and dynamic crossover of supercooled water in MCM-41 reported from previous neutron scattering and NMR data.

Thermodynamic, structural, and dynamic properties of supercooled water confined in mesoporous MCM-41 studied with calorimetric, neutron diffraction, and neutron spin echo measurements.

Thermodynamic, structural, and dynamic properties of heavy water (D(2)O) confined in mesoporous silica glass MCM-41 C10, C12, and C14 were investigated by differential scanning calorimetry, neutron diffraction, and neutron spin echo (NSE) measurements, respectively. The DSC data showed that no crystallization of D(2)O confined in C10 occurs in a temperature range between 298 and 180 K, and that crystalline ice is formed at 204 and 221 K for C12 and C14, respectively. For C10, the neutron radial distribution functions of confined D(2)O suggested a structural change in the supercooled state between 223 and 173 K. For C10 sample, it has been found that the tetrahedral-like water structure is partially enhanced in the central part of pores at 173 K. For all the samples, the intermediate scattering functions from the NSE measurements are fitted by the Kohlrausch-Williams-Watts stretched exponential function which implies that confined supercooled D(2)O exhibits a wide distribution of relaxation times. For C10, C12, and C14 samples, between 298 and 240 K, the relaxation times of supercooled D(2)O follow remarkably well the Vogel-Fulcher-Tamman equation; for C10 sample, below 240 K, the relaxation times of nonfreezing D(2)O show an Arrhenius type behavior. From the present experimental results on calorimetric, structural, and dynamic properties, it has been concluded that supercooled D(2)O confined in MCM-41 C10 experiences a transition from high-density to low-density hydrogen-bonded structure at around 229 K.

Tubular nitrogen-doped TiO2 samples with efficient photocatalytic properties based on long-lived charge separation under visible-light irradiation: synthesis, characterization and reactivity.

A nitrogen-doped TiO2 sample was prepared at 413 K by direct hydrothermal treatment of titanium isopropoxide in an aqueous solution of NH3. This new material has a large specific surface area of ca. 220 m2 g-1 because of its tubular structure and it exhibits a prominent absorption feature in the region between 400 and 650 nm. It responds strongly to light in the visible region, which is key to its potential performance as a photocatalyst that may improve the efficiency for utilization of solar energy. Actually, this sample exhibits very efficient activity in the decomposition of CH3COOH under visible light among the samples prepared. This effective photocatalysis of the present sample was substantiated by characteristic spectroscopic features, such as: (1) an optical absorption band with λ > 400 nm because of the doped nitrogen species; (2) the formation of EPR-active, long-lived N˙ and O2- species, as well as N2- species, under visible-light irradiation in the O2 or N2 adsorption process at 300 K by way of the monovalent nitrogen ions in the bulk (both substitutional and interstitial); (3) the existence of IR-active O2 species adsorbed on the nitrogen-doped TiO2 sample even without light irradiation; and (4) an XPS N1s band around 399.6 eV that is assignable to the N- species. The amounts of N˙ and O2- species formed in the nitrogen-doped TiO2 sample under visible-light irradiation correlated well with the levels of reactivity observed in the decomposition of CH3COOH on the samples with varying amounts and types of doped nitrogen species. We conclude that the photoactive N˙ and O2- species created in the present sample are responsible for the decomposition of organic materials assisted by visible light irradiation. These features may be attributable to the interface between the sample's tubular structure and anatase with poor crystallinity, which probably causes the resistance to the recombination of electron-hole pairs formed by irradiation.

Structure of methanol confined in MCM-41 investigated by large-angle X-ray scattering technique.

Large-angle X-ray scattering (LAXS) measurements over a temperature range from 223 to 298 K have been made on methanol confined in mesoporous silica MCM-41 with two different pore diameters, 28 A (C14) and 21 A (C10), under both monolayer and capillary-condensed adsorption conditions. To compare the structure of methanol in the MCM-41 pores with that of bulk methanol, X-ray scattering intensities for bulk methanol in the same temperature range have also been measured. The radial distribution functions (RDFs) for the monolayer methanol samples showed that methanol molecules are strongly hydrogen bonded to the silanol groups on the MCM-41 surface, resulting in no significant change in the structure of adsorbed methanol with respect to the pore size and temperature. On the other hand, the RDFs for the capillary-condensed methanol samples showed that hydrogen-bonded chains of methanol molecules are formed in both pores. However, the distance and number of hydrogen bonds estimated from the RDFs suggested that hydrogen bonds between methanol molecules in the pores are significantly distorted or partly disrupted. It has been found that the hydrogen bonds are more distorted in the smaller pores of MCM-41. With decreasing temperature, however, the hydrogen-bonded chains of methanol in the pores were gradually ordered. A comparison of the present results on methanol in MCM-41 pores with those on water in the same pores revealed that the structural change with temperature is less significant for confined methanol than for confined water.

Neutron scattering study on dynamics of water molecules in MCM-41. 2. Determination of translational diffusion coefficient.

Quasielastic neutron scattering (QENS) spectra of water-filled MCM-41 samples (pore diameters: 21.4 and 28.4 Angstrom) were measured over the temperature range 238-298 K and the momentum transfer range 0.31-0.99 A(-1) to investigate the dynamics of confined water molecules. The spectra, which consist mainly of contributions from the translational diffusion of water molecules, were analyzed by using the Lorentzian and the stretched exponential functions. Comparison of the fits indicated that the latter analysis is more reliable than the former one. The fraction of immobile water molecules located in the vicinity of the pore walls, which give an elastic component, was found to be 0.044-0.061 in both pores. The stretch exponent beta was determined as 0.66-0.80. It was shown that the translational diffusion of water molecules in the pores is decelerated by confinement and that the deceleration becomes marked with a decrease in pore size. The ratios of the translational diffusion coefficient D(T) of confined water to that of bulk water at room temperature were within a range of 0.47-0.63.

Low temperature properties of acetonitrile confined in MCM-41.

The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C[triple bond]N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 A (C14), below which it is not frozen. In addition, phase changes between alpha-type and beta-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Deltagamma(l/alpha) = 22.4 mJ m(-2) for the liquid/pore surface (ps) and alpha-type/ps, and Deltagamma(alpha/beta) = 3.17 mJ m(-2) for alpha-type/ps and beta-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol(-1) compared to the bulk value of 12.7 kJ mol(-1). The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.

Highly compressed nanosolution restricted in cylindrical carbon nanospaces.

We shed light on the specific hydration structure around a zinc ion of nanosolution restricted in a cylindrical micropore of single-wall carbon nanotube (SWNT) by comparison with the structure restricted in a cylindrical mesopore of multi-wall carbon nanotube (MWNT) and that of bulk aqueous solution. The average micropore width of open-pore SWNT was 0.87 nm which is equivalent to the size of a hydrated zinc ion having 6-hydrated water molecules. We could impregnate the zinc ions into the micropore of SWNT with negligible amounts of ion-exchanged species on surface functional groups by the appropriate oxidation followed by heat treatment under an inert condition. The results of X-ray absorption fine structure (XAFS) spectra confirmed that the proportion of dissolved species in nanospaces against the total adsorbed amounts of zinc ions on the open-pore SWNT and MWNT were 44 and 61%, respectively, indicating the formation of a dehydrated structure in narrower nanospaces. The structure parameters obtained by the analysis of XAFS spectra also indicate that the dehydrated and highly compressed hydration structure can be stably formed inside the cylindrical micropore of SWNT where the structure is different from that inside the slit-shaped micropore whose pore width is less than 1 nm. Such a unique structure needs not only a narrow micropore geometry which is equivalent to the size of a hydrated ion but also the cylindrical nature of the pore.

High physisorption affinity of water molecules to the hydroxylated aluminum oxide (001) surface.

The adsorption mechanism of water on the hydroxylated (001) plane of α-Al(2)O(3) was studied by measuring adsorption isotherms and GCMC simulations. The experimental adsorption isotherms for three α-Al(2)O(3) samples from different sources are typical type II, in which adsorption starts sharply at low pressures, suggesting a high affinity of water to the Al(2)O(3) surface. Water molecules are adsorbed in two registered forms (bilayer structure). In the first form, water is registered at the center of three surface hydroxyl groups by directing a proton of the water. In the second form, a water molecule is adsorbed by bridging two of the first-layer water molecules through hydrogen bonding, by which a hexagonal ring network is constructed over the hydroxylated surface. The network domains are spread over the surface, and their size decreases as the temperature increases. The simulated adsorption isotherms present a characteristic two-dimensional (2D) phase diagram including a 2D critical point at 365K, which is higher than that on the hydroxylated Cr(2)O(3) surface (319 K). This fact substantiates the high affinity of water molecules to the α-Al(2)O(3) surfaces, which enhances the adsorbability originating from higher heat of adsorption. The higher affinity of water molecules to the α-Al(2)O(3) (001) plane is ascribed to the high compatibility of the crystal plane to form a hexagonal ring network of (001) plane of ice Ih.

Pore size dependent behavior of hydrated Ag+ ions confined in mesoporous MCM-41 materials under synchrotron X-ray irradiation.

The behavior of hydrated Ag+ ions in a 1.5 mol dm(-3) AgNO3 aqueous solution confined in mesoporous silica MCM-41 with different pore sizes was characterized by synchrotron X-ray absorption spectroscopy. The hydrated Ag+ ions are stabilized in 4-fold coordination down to 195 K in the pores (21 Å in diameter), whereas in the larger pores (28 Å) the hydrated Ag+ ions are reduced to Ag0 to form nano clusters with the Ag-Ag interactions of 2.80 Å.

Effect of confinement on the fluid properties of ammonia in mesopores of MCM-41 and SBA-15.

The effect of pore size on capillary condensation and solid-liquid phase changes of ammonia in MCM-41 and SBA-15 was studied by adsorption and FTIR measurements of condensed phases at low temperatures. Adsorption isotherms are all typical type IV on the fully hydroxylated surfaces, without hysteresis loops in the smaller pores (d < 2.4 nm). In the larger pores, hysteresis loops appear at lower temperatures and disappear with increasing temperature, i.e., the capillary critical phenomenon was detected (hysteresis critical point). The criticality of the adsorption hysteresis loop is very similar to that for nonpolar nitrogen in mesopores of various shapes, suggesting that this is a universal phenomenon among fluids in mesopores. Freezing and melting of capillary-condensed ammonia were observed by FTIR spectroscopy. The melting temperature of capillary-condensed ammonia decreased with decreasing pore size, which is similar in the behavior of freezing. In the smaller pores (d < 2.4 nm); however, ammonia was not frozen. It is suggested that the capillary-condensed inner part, i.e., inside the ammonia monolayer, is affected too much by the pore wall and/or is too small in volume to crystallize. In the larger pores of SBA-15, crystallization is remarkably segregated from ammonia molecules strongly coordinated to surface hydroxyls.

Investigating hydration dependence of dynamics of confined water: monolayer, hydration water and Maxwell-Wagner processes.

The dynamics of water confined in silica matrices MCM-41 C10 and C18, with pore diameter of 21 and 36 A, respectively, is examined by broadband dielectric spectroscopy (10(-2)-10(9) Hz) and differential scanning calorimetry for a wide temperature interval (110-340 K). The dynamics from capillary condensed hydration water and surface monolayer of water are separated in the analysis. Contrary to previous reports, the rotational dynamics are shown to be virtually independent on the hydration level and pore size. Moreover, a third process, also reported for other systems, and exhibiting a saddlelike temperature dependence is investigated. We argue that this process is due to a Maxwell-Wagner process and not to strongly bound surface water as previously suggested in the literature. The dynamics of this process is strongly dependent on the amount of hydration water in the pores. The anomalous temperature dependence can then easily be explained by a loss of hydration water at high temperatures in contradiction to previous explanations.

Aggregation of imidazolium ionic liquids in molecular liquids studied by small-angle neutron scattering and NMR.

The aggregation of two imidazolium-based ionic liquids, 1-ethly-3-methylimidazolium chloride (EMI(+)Cl(-)) and EMI(+) bis-(trifluoromethanesulfonyl)amide (EMI(+)TFSA(-)), in molecular liquids, water, methanol, acetonitrile, and benzene, has been studied by using the small-angle neutron scattering (SANS) technique. The SANS results have shown that the heterogeneity of EMI(+)Cl(-)-acetonitrile mixtures is significant at high acetonitrile contents, thus, EMI(+)Cl(-) forms clusters in acetonitrile solutions. On the other hand, it has been revealed that EMI(+)Cl(-) is homogeneously dissolved in water and methanol. EMI(+)TFSA(-) remarkably aggregates in methanol solutions, while the mixtures of EMI(+)TFSA(-) with acetonitrile and benzene are homogeneous. Furthermore, aggregation of EMI(+)Cl(-) and EMI(+)TFSA(-) in acetonitrile and methanol, respectively, has been examined by using (1)H NMR spectroscopy. The mechanism of aggregation of the ionic liquids in the molecular liquids has been discussed on the basis of the properties of cations, anions, and molecular liquids.

Phase separation of acetonitrile-water mixtures and minimizing of ice crystallites from there in confinement of MCM-41.

The effect of confinement of an acetonitrile-water mixture, whose correlation length was comparable to the pore size of the mesopores of MCM-41 (d=2.4-3.6 nm), on the phase changes was studied. Used techniques were low temperature differential scanning calorimetry and Fourier transform infrared spectroscopy, where the phase separation, lowering of the freezing and melting temperatures, and phase transitions of the acetonitrile were detected. The latter occurred in the mesopores at temperatures similar to that of the pure liquid, while the melting temperature of the water in the mesopores<3.1 nm decreased markedly at higher acetonitrile contents, suggesting a marked lowering of ice crystallite size.