Preparation And Photo-thermal Conversion Performance Of LaB₆-based Nanofluids

With the development of society,the energy problem has attracted more and more attention.Solar energy has attracted the interest of researchers due to its wide source,no pollution to the environment,and inexhaustible use.Among them,the application of nanofluids formed by nanoparticles based on the localized surface plasmon resonance effect in the field of photo-thermal conversion can effectively alleviate the problem of energy shortage.The premise of high photothermal conversion efficiency is to improve the solar light absorption properties of nanofluids.It has shown that the localized surface plasmon resonance properties of materials can be controlled by controlling the size of nanoparticles,dielectric constant,and other factors,thereby improving their light absorption properties.Therefore,lanthanum hexaboride(LaB₆)as the main research object to investigate the light absorption properties and photo-thermal conversion properties of LaB₆ with different sizes in this work.And explore the effect of Ce and Y elements doping lanthanum hexaboride on its light absorption properties and photo-thermal conversion properties.Using lithium borohydride as boron source and anhydrous lanthanum chloride as lanthanum source,pure phase cubic structure LaB₆ nanoparticles with different sizes was synthesized by solid-phase method.The synthesis temperature affects the size of the products,and the average particle size of LaB₆ nanocrystals synthesized at 400?,600? and 800? increases from 8.6 nm to 15.4 nm with increasing synthesis temperature.The stability,light absorption properties and photothermal conversion properties of LaB₆/water nanofluids prepared by LaB₆ nanoparticles with different sizes were also explored.The results show that the LaB₆/water nanofluids prepared based on the electric double layer principle exhibits good stability under weak alkaline conditions.Zeta potential values greater than 30 m A at p H=9.5.The particle size of LaB₆ nanoparticles affects the light absorption properties and photo-thermal conversion properties of the prepared LaB₆/water nanofluids.The LaB₆/water nanofluids with different LaB₆ sizes have different absorption valley wavelengths,and the LaB₆/water nanofluids with small-sized LaB₆ display relatively stronger light absorption properties for solar radiation.The LaB₆/water nanofluids prepared by small-sized LaB₆ exhibit relatively better photo-thermal conversion performance.The mass fraction concentration of LaB₆ in the prepared LaB₆/water nanofluids also affects the light absorption performance and photo-thermal conversion performance of the nanofluids.The photo-thermal conversion performance is enhanced when the mass fraction concentration increases from 0.002%to 0.020%.The photo-thermal conversion efficiency of the LaB₆/water nanofluids prepared in the small-sized LaB₆with a mass fraction concentration of 0.020%can reach 99.78%,and the temperature of the LaB₆/water nanofluids can be increased from 20? to 63? when irradiated by a simulated solar light.Using sodium borohydride as boron source,anhydrous lanthanum chloride as lanthanum source,and anhydrous cerium chloride as cerium source,single-phase La_1-xCe_xB₆ nanoparticles with cubic structure were synthesized.The effects of Ce doping concentration on the light absorption properties and photo-thermal conversion properties of the as-prepared La_1-xCe_xB₆ nanoparticles were studied.The results show that the size of La_1-xCe_xB₆ nanoparticles increases with the increase of Ce doping amount.The La_1-xCe_xB₆/water nanofluids showed excellent stability,and the nanofluid did not settle after standing for two weeks.The wavelength of absorption valley of La_1-xCe_xB₆/water nanofluids appeared red-shifted phenomenon with the increase of Ce doping concentration,confirming that the plasmonic regulation of La_1-xCe_xB₆/water nanofluid can be achieved by controlling the amount of Ce doping.The La_0.75Ce_0.25B₆/water nanofluids has stronger photothermal conversion performance than the other samples.Under simulated sunlight irradiation,the temperature of the La_0.75Ce_0.25B₆/water nanofluids can be increased from 20? to 60.0? and its photo-thermal conversion efficiency can reach 96.85%.Using sodium borohydride as boron source,anhydrous lanthanum chloride as lanthanum source,and anhydrous yttrium chloride as yttrium source,the pure phase La_1-xY_xB₆ nanocrystals with cubic structure were synthesized by solid-phase method.The absolute values of the zeta potential values of the La_1-xY_xB₆/water nanofluid were greater than 30 m A under weakly aikaline conditions,indicating its good stability.The influence of Y doping amount on the structure of the La_1-xY_xB₆ nanocrystals,and the light absorption properties and photo-thermal conversion properties of the La_1-xY_xB₆/water nanofluids were also investigated.The results show that the absorption valley wavelength of the La_1-xY_xB₆/water nanofluids appears red-shifted with the increase of the doping amount of Y,indicating that the doping concentration of Y can controlled the plasmonic regulation of La_1-xY_xB₆nanoparticles.The La_0.75Y_0.25B₆/water nanofluids show strongest photo-thermal conversion performance than other nanofluids.Under simulated sunlight irradiation,the temperature of the La_0.75Y_0.25B₆/water nanofluids with the mass fraction concentration of La_0.75Y_0.25B₆nanoparticles is 0.020%can be increased from 20? to 59.3?,and its photo-thermal conversion efficiency can reach 94.65%.