Template-free facile preparation of mesoporous silica from fly ash for shaped composite phase change materials

Traditional sol-gel template preparation method for mesoporous silica has limited its large-scale production and applications due to low production quantity, complex preparation process and high cost. In this paper, we proposed a novel template-free process to prepare mesoporous silica-based materials by acid etching of activated fly ash to improve the support performance for shaped composite phase change materials. The mechanisms of mineral phase transformation and pore formation during preparation of mesoporous silica from fly ash were systematically investigated, and the structure, morphology and thermal properties of as-prepared shaped composite phase change materials (SCPCMs) were characterized and analyzed. The results show that stable mullite and quartz could be transformed into potassium aluminosilicate minerals after calcined with K2CO3, and mesoporous silica-based materials with different pore shapes and specific surface area ranging from 330 to 490 m2/g could be prepared from as-calcined fly ash. The PEG/MS-I (ink bottle-shaped material) achieved the largest loading efficiency of 64.88%, and the highest melting phase change enthalpy of 88.38 J/g, which is 30.7% and 57.7% higher than that of PEG/MS-S (silt-shaped material) and PEG/MS-W (wedge-shaped material), respectively. After 20 thermal cycles, the loss of melting enthalpy for PEG/MS-I was only 3%, and the thermal energy storage and release time were 23.1% and 17.0% shorter than that of pure PEG, respectively. In all, the PEG/MS-I composite exhibited reliable thermal storage performance and temperature regulation ability, which provides the feasibility of application of fly ash-derived composite phase change material in energy storage field.