Preparation Of Titanium Oxide Nanoparticles And Study On Photothermal Conversion Performance

With the rapid development of society and economy,the traditional energy sources have a large consumption,then the environmental pollution has become one of the most prominent issues facing the world.Solar energy is one of the most widely used renewable resources today,providing an effective way to alleviate the energy crisis.Converting light energy into thermal energy is an important aspect of realizing solar applications.Therefore,finding excellent light absorption and heat transfer materials is a hot spot for many researchers.As a multifunctional semiconductor material,titanium oxide has the characteristics of low cost,non-toxicity and corrosion resistance,and has certain applications in the field of photocatalysis.However,it has not been involved in the field of photothermal materials.This paper focuses on solar light-to-heat conversion,and it is divided into the following three parts:1.Titanium dioxide and titanium pentoxide with different sizes were prepared by ball milling.The Ti₂O₃ and Ti₃O₅ nanomaterials were ground from 100-mesh size raw material balls to a size of 100-400 nm.Subsequently,it was characterized in detail by XRD,SEM and UV-Vis-NIR.The effects of ball milling time on the particle size,crystallinity and light absorption of the material were studied.The results show that with the increase of ball milling time,the light absorption increases regularly.Compared with raw materials,the dispersibility of nanofluids has gradually improved.Then,under the test of a solar simulation system simulated in the laboratory,the Ti₂O₃/water and Ti₃O₅/water nanofluids also increased in temperature with the increase of the ball milling time,and the light-to-heat conversion efficiency also improved significantly.2.Searching for direct absorption solar collector(DASC)nanofluids with better absorption in the full spectral range has become the first task of today.In the current work,the anoxic TiO₂(TiO_2-x)obtained by the NaBH₄ reduction method improves the defects of traditional titanium dioxide,and the obtained materials have great absorption in the full spectrum of sunlight.The higher the reduction temperature,the stronger the absorption capacity of solar energy.From the results of XRD and UV-Vis-NIR,600?is a suitable reduction temperature.In addition,in order to investigate the dispersion stability of nanofluids,dispersing TiO_2-x in two kinds of base liquids,such as high-temperature heat-conducting oil and dimethyl silicone oil,showed good stability and excellent solar thermal conversion at 80-200?.Au nanoparticles with LSPR effect further improve the spectral absorption performance of anaerobic TiO₂.100 ppm 5%Au/TiO_2-x can reach a high temperature of 91?,which is26.6?higher than the base liquid dimethyl silicone oil.At the same time,it also shows enhanced photothermal conversion efficiency,and its excellent full-spectrum absorption performance brings a new paradigm to the working fluid of medium temperature DASC.3.Three-dimensional graphene-reinforced structural materials with excellent solar heat conversion and heat transfer properties provide attractive prospects for the preparation of high-performance composite phase change materials(PCM).Here,a graphene oxide dispersion,P25,black titanium dioxide,sodium borohydride solution,and ethylenediamine were used to prepare a lightweight porous structure hydrogel using a one-step hydrothermal method,followed by freeze drying to obtain P25-graphene gels and different percentages of TiO_2-x-graphene aerogels.The composite phase change material was obtained after absorbing paraffin in a vacuum drying box.After a series of characterization and performance tests,it was found that the black titanium dioxide-graphene aerogel has the best thermal storage performance,cycle stability,and light-to-heat conversion performance.The temperature rises of TiO_2-x-graphene aerogels with different loadings were compared and it was found that the optimal loading for current work is 80%.When the load exceeds 80%,the photothermal effect is not improved.Light intensity is also one of the main factors affecting its heat storage performance.Under the light intensity of 3000W/m²,phase change composites show the best performance.This research expands the application of PCM in the field of solar thermal energy.