石蜡/Fe-MIL-101-NH2金属有机骨架定形复合相变材料制备

该研究采用石蜡为相变芯材，Fe-MIL-101-NH2金属有机骨架为载体材料，旨在解决石蜡芯材在固-液相变过程中体积变大，从而出现泄漏现象的问题。通过溶剂蒸发法制备了质量分数为40%～70%的石蜡/Fe-MIL-101-NH2定形复合相变材料。采用扫描电子显微镜（Scanning Electron Microscope, SEM）、X射线衍射仪（X-ray Diffraction, XRD）、傅里叶变换红外光谱（Fourier Transform Infrared Spectroscopy, FTIR）对定形复合相变材料的形貌和结构进行观察；用热重分析（Thermogravimetric Analysis, TGA）对定形复合相变材料的热稳定性进行分析；通过差示扫描量热（Differential Scanning Calorimetry, DSC）仪对样品的相变温度、相变焓和热循环稳定性进行测试；SEM结果表明，石蜡的最高负载量为70%，且其均匀分布于Fe-MIL-101-NH2孔道中。XRD、FTIR分析发现石蜡与Fe-MIL-101-NH2之间只是物理混合，没有化学变化；DSC分析可知，质量分数为70%的石蜡/Fe-MIL-101-NH2储能量最大，为51.3 J/g，且质量分数为70%的石蜡/Fe-MIL-101-NH2经过50次循环后，其储能量为47.6 J/g，无明显下降，说明质量分数为70%的石蜡/Fe-MIL-101-NH2具有良好的热循环稳定性，可为相变材料在建筑领域应用研究提供参考。

Shape-stable phase change materials preparation of composite of paraffin/Fe-MIL-101-NH2 as metal-organic framework

Phase change materials (PCMs) can widely be used to absorb and release large amounts of latent heat at temperatures when the physical state changes. Heat storage systems depend mainly on the high latent heat density and small temperature intervals in PCMs during phase transition. However, there is a great leakage of current solid-liquid PCMs in the liquid phase, resulting from a large volume change above the melting point. Alternatively, the porous metal-organic frameworks (MOFs) have been investigated as solid support for a variety of storage purposes. A MOFs matrix material can also be expected to deal with the leakage of a shape-stabilized composite PCM in the most practical way. It is highly demanding for the extremely large surface area, large pore volume, and chemical tunability in the MOFs as the ideal matrix for PCMs. In particular, MOFs can also be designed for several aspects, such as pore shape and size, framework topology, and surface properties in the inner channels. A combination of fatty acids and porous MOF supports can be utilized to maintain the solid shape in the liquid PCM composite, where the phase change temperature of paraffin is within the range of normal human environments. Paraffin also presents high latent heat, suitable melting temperature range, non-corrosivity/non-toxicity, excellent chemical stability, and easy availability. The outstanding energy storage density and suitable phase change temperature also allow for the paraffin highly practical in the building materials. In this study, a facile solution impregnating approach was proposed to access a novel type of shape-stabilized PCM with metal-organic frameworks as the matrix. As such, a paraffin/MOF composite PCM was developed for heating storage, where paraffin was used as a phase change core, while Fe-MIL-101-NH2 was the supporting matrix. Solvent evaporation was finally conducted to successfully prepared 40 wt%~70 wt% paraffin/Fe-MIL-101-NH2 shape-stable phase change material (ss-PCM). Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy were also conducted to characterize the morphology and structure of ss-PCM composites. Thermal gravimetric analysis (TGA) was used to determine the thermal stability, while differential scanning calorimetry (DSC) to the supercooling, the energy storage, and thermal cycle stability of ss-PCM. SEM images showed that the maximum loading of paraffin wax was 70%, mostly distributed in the interior and external core of Fe-MIL-101-NH2. XRD and FTIR showed that the paraffin wax and Fe-MIL-101-NH2 were physically combined in the ss-PCM. DSC analysis indicated that the highest energy storage capacity (51.3 J/g) was achieved in the 70 wt% paraffin/ Fe-MIL-101-NH2. In addition, there was no significant decrease in the thermal enthalpy of 70 wt% paraffin/Fe-MIL-101-NH2 (47.6 J/g) after 50 cycles, indicating an excellent heat cycle stability. Consequently, a novel paraffin/Fe-MIL-101-NH2 composite PCM can be expected to serve as the heat storage application. This finding can also provide a novel approach to access the shape-stabilized composite PCMs, which can potentially be extended to a variety of solid-liquid phase change materials.