Liquid−Solid Transition of Confined Water in Silica-Based Mesopores

Liu, Xiao X.; Wang, Qiang; Huang, Xiaohong; Yang, Shu Ching; Li, Chen X.; Niu, Xiaojuan; Shi, Qin; Sun, Gang; Lü, Kun

doi:10.1021/jp909108u

Cited by 21 publications

(21 citation statements)

References 56 publications

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“…Freezing and melting of water confined in mesopores is directly relevant to many phenomena such as freeze avoidance in plants, stone weathering, and cloud glaciation . Effects of pore size, − pore geometry, − pore filling, − and nonfreezable layer − adjacent to the pore walls on the freezing and melting behavior have been extensively examined using mesoporous silicas, and general conclusions have been reached.…”

Section: Introductionmentioning

confidence: 99%

Influence of Pore Wall Hydrophobicity on Freezing and Melting of Confined Water

Morishige

2018

J. Phys. Chem. C

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To examine the influence of pore wall hydrophobicity on freezing and melting behavior of a confined water, we measured the X-ray diffraction pattern of water in the nearly cylindrical pores of ordered mesoporous carbons during cooling and heating processes. The pore walls of the ordered mesoporous carbons are crystalline and cannot form hydrogen bonds with water molecules. Capillary condensation of water in the hydrophobic mesopores takes place very slowly only close to the saturation pressure of a bulk water. Nevertheless, freezing and melting of water confined in the hydrophobic mesopores occurred almost in the same way as those in mesoporous silicas with similar pore sizes, the pore walls of which are amorphous and can form hydrogen bonds with water molecules. This clearly indicates that the pore wall hydrophobicity does not affect appreciably the freezing and melting behavior of the confined water. The existence of a thin water layer between core ice and the pore walls is responsible for it.

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Section: Introductionmentioning

confidence: 99%

Influence of Pore Wall Hydrophobicity on Freezing and Melting of Confined Water

Morishige

2018

J. Phys. Chem. C

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“…[8,37] Moreover, the major bands at 1590-1740 cm −1 can be assigned to the carbonyl group from HEA and AM units and amide from AM unit. [14,38] While the FT-IR results further prove the existence of cross-linking bonds in these polymers, they cannot be used to well explain the RTP enhancement among AM300, AM303, and AM315.…”

Section: Resultsmentioning

confidence: 99%

Water‐Induced Blue‐Green Variable Nonconventional Ultralong Room Temperature Phosphorescence from Cross‐Linked Copolymers via Click Chemistry

Liang

Zhang

Chen

et al. 2021

Advanced Optical Materials

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ground states (S 0 ). Owing to the spin-forbidden situation between singlet (S 1 ) and triplet excitation transitions and the nonradiative decay process by molecular vibration and rotation, rigorous conditions are essential to achieve RTP. [15,16] The strategies of designing RTP molecular structures can be divided into two aspects. One is to make use of heteroatoms, such as N or P, to reinforce the spin-orbit coupling for promoting the intersystem crossing (ISC). The other is the introduction of rigid matrix or cross-linking to suppress nonradiative transitions of triplet excitations. [17,18] Currently, polymer-based phosphorescent materials gain more and more important attention because of the low cost and facile preparation process as well as favorable biocompatibility compared with metal-containing materials. [19] The polymers showing RTP are usually based on their solid-state phase without water, since the dissolved oxygen in water may quench the phosphorescence. [20][21][22][23] Only a few phosphorescent systems in aqueous conditions have been reported. [22,[24][25][26][27] In these studies, the noncovalent bonding strategies such as hydrogen bonding formations [22,24] and electrostatic interactions [27] have been developed to suppress the nonradiative transition of phosphorescent molecules in order to realize RTP. [25] For the electrostatic interactions, phosphorescent molecules are usually introduced into the electrostatic matrix to obtain luminescent materials with RTP properties. Because of the noncovalent bonding nature, the stability of these materials could be easily affected by external conditions. [8] Thus, straightforward preparation of the RTP materials through covalently cross-linked networks is still desirable.Click chemistry possesses essential advantages that could be employed for polymer synthesis, including mild reaction conditions, fast reaction rate, easy purification, as well as being friendly with water, oxygen, and structurally complicated reactants. [28][29][30][31] Based on previous studies, a rigid structure can be formed by substituting boronic acid with a polymer that contains a hydroxyl group per monomer through BO click reaction. [32] Significantly, the BO covalent bond can be actualized under an ambient environment without a complicated Ultralong room temperature phosphorescence is employed in information encryption, chemical sensing, lighting, and imaging on account of its long lifetime and high signal-to-noise ratio. As the triplet excitons can be easily quenched and interfered by nonradiative transition process, it is difficult to obtain long-lived phosphorescence through conventional methods. Herein, a general design strategy to form cross-linked networks by click chemistry is presented for efficiently promoting the phosphorescence performance. Using the hydrogen bonding interactions formed between CO•••HN units and covalently cross-linked network by the BO bond, the rigidity of the entire system is greatly enhanced, so the radiative transition process is well strengthe...

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“…This salt content-independent desorption-adsorption isotherm suggests that the previously discussed adsorption and desorption models of water in Vycor glass, formulated on the basis of dielectric constant measurement and liquid-solid transition investigation, are still valid. 20,27 Particularly, water desorption in Vycor mesopores comprises of capillary decondensation and thinning of interfacial water film. As mentioned above, the first coordination shell of both cations and anions remains quite the same as in bulk solution until φ de = 35% when core water is no more available, it then becomes strongly sensitive to the filling condition.…”

Section: Resultsmentioning

confidence: 99%

Coordination variation of hydrated Cu2+/Br1− ions traversing the interfacial water in mesopores

Wang

Huang

et al. 2012

AIP Advances

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Resolution of the atomistic and electronic details about the coordination structure variation of hydrated ions in the interfacial water is still a tough challenge, which is, however, essentially important for the understanding of ion adsorption, permeation and other similar processes in aqueous solutions. Here we report the tracing of coordination structure variation for hydrated Cu2+/Br1- ions traversing the interfacial water in Vycor mesopores (ϕ = 7.6 nm) by employing both X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopies. By controlled desorption/adsorption of water, the filling fraction of the mesopores, thus the water layer thickness, can be adjusted, which in turn effects the variation of coordination structure of the ions therein. It is found that both Cu2+ and Br1- ions prefer staying exclusively in the core water, and in this circumstance no ion pairs have been detected in the solution of concentrations up to 1.0 M. Following capillary decondensation occurring at a filling fraction of ∼35% which corresponds to a water layer of about three monolayers, Br1- ions begin immediately to reconstruct their first coordination shell, characterized by ionic dehydration, shrinkage of ion-water bond length, and formation of ion pairs. In contrast, Cu2+ ions can retain a bulk-like coordination structure till being driven to bond directly to the pore surface when the filling fraction is below 20%. At the final stage of dehydration via thermal vacuum treatment at 110°C, Cu2+ ions can be completely reduced to the Cu1+ state, and recover at room temperature only when the filling fraction is above 14%. These results may be inspirable for the investigation of similar problems concerning hydrated ions in water solution under different confining conditions.

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Liquid−Solid Transition of Confined Water in Silica-Based Mesopores

Cited by 21 publications

References 56 publications

Influence of Pore Wall Hydrophobicity on Freezing and Melting of Confined Water

Influence of Pore Wall Hydrophobicity on Freezing and Melting of Confined Water

Water‐Induced Blue‐Green Variable Nonconventional Ultralong Room Temperature Phosphorescence from Cross‐Linked Copolymers via Click Chemistry

Coordination variation of hydrated Cu2+/Br1− ions traversing the interfacial water in mesopores

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