The Preparation And Study On Properties Of CDs-Composited PEG Photothermal Phase Change Materials

The research of solar energy has never stopped.Solar energy is rich,clean and sustainable,which is the green source.However,because of the instability and dispersion,the utilization of solar energy is discontinuous and the overall utilization efficiency is low.Storing solar energy before use is a powerful means to improve the efficiency of solar energy utilization.Phase change heat storage materials are referred to as thermal phase change materials,which store and release more heat than sensible heat in the form of latent heat through phase change of materials.However,the general phase change materials have poor light absorption and cannot realize the absorption,storage and release of solar energy.Therefore,it is necessary to reform them.Moreover,the traditional phase change materials have various defects,such as the mutual transformation of solid to liquid phases during the operation of solid-liquid phase change materials will lead to leakage,corrosion and other problems.Therefore,the material structure of phase change materials generally also needs to be designed.Carbon dots(CDs)are zero-dimensional carbon-based nanomaterials with rich functional groups on the surface,which have excellent optical properties,large specific surface area and small size effect.At the nanometer scale,unexpected interactions(called small size effect of nanomaterials)can occur between different materials,which makes the characteristics of materials increase or decrease in some aspects,thus realizing the transformation of materials.By constructing a composite system of coal tar pitch CDs and organic solid-liquid phase change material polyethylene glycol(PEG),this paper discusses the feasibility of using CDs for solar energy storage from the aspects of material structure,interaction mechanism between materials,heat energy management and application.The main research conclusions are as follows:Firstly,CDs were dissolved into PEG through solution mixing to obtain CDs@PEG hybrids.It was found that the interaction between CDs and PEG could affect each other through the interface,which maks the phase change enthalpy of CDs@PEG differ from PEG.After adjusting the ratio,the phase change enthalpy of CDs@PEG is 13.7% higher than the theoretical value,and the introduction of CDs does not damage the original crystallization characteristics and thermal conductivity structure of PEG.Secondly,hybrids of CDs and PEG are impregnated into the melamine sponge modified with CDs and polydimethylsiloxane through vacuum induced infiltration technique to prevent the liquid leakage.The obtained composite shows the long heat storage duration and achieves 82.57% of solar-to-thermal storage efficiency as well as 92.27% of the heat release efficiency.In particular,its outstanding hydrophobicity and stability in shape and heating-cooling cycles allows it to practically apply in solar-thermal energy conversion and storage.Finally,it is envisaged that the prepared composite phase change materials will be used in the traditional solar greenhouse.The results show that using phase change materials for heating can save about 73% of the cost over a five-year period compared to traditional coal-fired heating methods.Further prospects for the laying and system construction of composite phase change materials in practical applications are also made.