The high variability and low heat of fusion of composite shape-stabilized phase change materials is a considerable challenge to their widespread application. Here we present the synthesis of shape-stabilized phase change materials composed of lauric acid and mesoporous silica with high heat of fusion through evaporative solution impregnation. Two hexagonal ordered silica with 2.8 and 6.3 nm pores (MCM-41, SBA-15) and two disordered mesocellular foams with 27 -34.9 nm spherical pores connected by 10.4 -14.9 nm "windows" are employed.The thermal properties and stability, heat storage efficiency, crystallization, textural and chemical properties are investigated using DSC analysis, small-and wide-angle XRD, nitrogen adsorption-desorption isotherms, optical and electron microscopy, as well as FT-IR spectroscopy. MCF-based materials with up to 83% wt. fatty acid show large latent heat (124 Jg -1 ), almost 90% efficiency with respect to the acid content and two melting -crystallization temperature ranges associated with nanoconfined and bulk phases. Up to 53 Jg -1 enthalpy change for the nanoconfined phase can be obtained. The melting point depression, heat storage efficiency and the physical state of lauric acid at the mesopore level are correlated with theoretical considerations of thermodynamic and geometric factors, revealing a non-melting interface layer of one organic molecule thickness. This approach provides a facile methodology to estimate the relevant properties of mesoporous silica phase change materials with useful dual temperature ranges.

The enhancement of the Raman scattering in Cs3Bi2I9 is evaluated by the ratio IT/I300 K between the relative intensities of the Raman line peaked at 146 cm−1, when the spectra are recorded in the temperature range of 88–300 K, as a signature of exciton–phonon interactions. In the resonant and nonresonant conditions, excitation wavelengths 476, 561, and 660 nm, respectively, are used in order to overlap with great accuracy the bands disclosed by diffuse reflection, photoconductivity (PC), photoluminescence (PL), and photoluminescence excitation (PLE) spectra. Based on the experimental analyses, the strength of exciton–phonon interaction is dependent on the defects in the crystal and the type–range interaction of the excitations in an independent Bi2I93− cluster. The noticeable PL band, attributed to excitons trapped on different stacking faults, manifests some defects in crystal that diminish the movement of excitons. This effect significantly decreases the overlaps of excitons with the phonons, resulting in a reduced exciton–phonon coupling.

Phase change materials (PCMs) can store thermal energy as latent heat through phase transitions. PCMs using the solid-liquid phase transition offer high 100–300 J g−1 enthalpy at constant temperature. However, pure compounds suffer from leakage, incongruent melting and crystallization, phase separation, and supercooling, which limit their heat storage capacity and reliability during multiple heating-cooling cycles. An appropriate approach to mitigating these drawbacks is the construction of composites as shape-stabilized phase change materials which retain their macroscopic solid shape even at temperatures above the melting point of the active heat storage compound. Shape-stabilized materials can be obtained by PCMs impregnation into porous matrices. Porous silica nanomaterials are promising matrices due to their high porosity and adsorption capacity, chemical and thermal stability and possibility of changing their structure through chemical synthesis. This review offers a first in-depth look at the various methods for obtaining composite PCMs using porous silica nanomaterials, their properties, and applications. The synthesis and properties of porous silica composites are presented based on the main classes of compounds which can act as heat storage materials (paraffins, fatty acids, polymers, small organic molecules, hydrated salts, molten salts and metals). The physico-chemical phenomena arising from the nanoconfinement of phase change materials into the silica pores are discussed from both theoretical and practical standpoints. The lessons learned so far in designing efficient composite PCMs using porous silica matrices are presented, as well as the future perspectives on improving the heat storage materials.

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