Preparation Of Magnetic Phase Change Material Microcapsules And Their Application In Photothermal Conversion

Facing the energy crisis,the use of renewable resources has become the best solution.As a good thermal energy storage material（PCM）,solid-fluid-phase variable material（PCM）can effectively solve the problems of low interval and low energy density of solar energy,and have spacious application landscape.Whereas,there are disadvantages to leakage and low thermal guidance rates of solid-liquid PCM.By performing microcapsule,while effectively prevent PCM leakage and improve thermal guidance,it can also be designed to the shell according to a specific application direction to improve its performance.This thesis cannot achieve the efficient use of solar energy for traditional microcapsule phase transformation materials（Me PCM）,and improves solar light thermal conversion efficiency through design and composite light thermal materials as the outer shell material of MEPCM.The results show that the prepared Me PCM has not only good thermal storage capabilities,but also high thermal guidance,light absorption capacity,and high-light heat conversion efficiency,and has huge application potential in the fields of solar light and heat conversion and seawater dilution.The specific research work is as follows:（1）The Fe₃O₄ nanoparticles（Fe₃O₄ NPs）are synthesized through the chemical precipitation method,and the MEPCM is synthesized by the self-assembly precipitated/Pickering emulsion template method with Fe₃O₄ NPs and Ca CO₃ as the composite shell,and the N-eicosane is the core material（Fe₃O₄/Ca CO₃-MEPCM）,which explores the effects of Fe₃O₄ NPs content on Me PCM performance.The results showed that the synthetic Fe₃O₄/Ca CO₃-Me PCM had a typical core shell structure.With the increase of Fe₃O₄ NPs,the phase change of the Fe₃O₄/Ca CO₃-Me PCM increased first and then decreased,and the efficiency of light thermal conversion storage continued to increase.When adding 20 ml Fe₃O₄ NPs suspension,the Fe₃O₄/Ca CO₃-Me PCM has the highest submarine heat(ΔH_C=107.2 J g^-1,ΔH_M=105.1 J g^-1);when the 25 ml Fe3O4 NPS suspension is added,the Fe₃O₄/Ca CO₃-Me PCM has the highest light thermal conversion storage efficiency（86.4%）.Under the 35 k Hz cross-magnetic field,compared with the non-additional magnetic field,the light and thermal conversion time of the Fe₃O₄/Ca CO₃-Me PCM is shortened from 106 s to 72 s indicating that the Fe₃O₄/Ca CO₃-Me PCM has the ability to shorten the light heat conversion time through the additional magnetic field.（2）MXene nanosheets were obtained by etching titanium aluminum carbide with hydrochloric acid and lithium fluoride.Two Me PCM types of Si O₂and Fe₃O₄ NPs coated with N-eicosane and N-tetradecane respectively,were successfully synthesized through in-situ polymerization;then,the surface of Me PCM was modified by self-assembly of polypyrrole and hydrogen bonding between MXene nanosheets and polypyrrole,and a multilayer Me PCM（MXene-Me PCM）with polypyrrole and MXene as shells was obtained.Due to the excellent light absorption properties of polypyrrole and MXene,the interfacial evaporator using MXene-Me PCM as a photothermal material has evaporation rates of 2.04 kg m^-2 h^-1 and 4.11 kg m^-2 h^-1 under 1 kw m^-2 and 2 kw m^-2 light intensities.In addition,due to the excellent latent heat storage and release ability of phase change core materials,the evaporation performance of interfacial evaporators has been significantly improved under no light conditions.During the continuous evaporation process with illumination intensity of 1.0 kw m^-2 for 105 min and darkness for 100 min,the water evaporation mass of the N-eicosane evaporator increased by 0.23 kg m^-2compared to the evaporator without phase change materials;During a continuous evaporation process of 105 min under 2.0 kw m^-2 illumination intensity and 120 min in darkness,the water evaporation mass of the N-tetradecane evaporator increased by 0.91 kg m^-2 compared to the evaporator without phase change materials.In addition,due to the presence of magnetism,the MXene-Me PCM has good cycle performance and salt resistance.