Preparation And The Near-Infrared Absorption Properties Of LaB₆ Nanoparticles

LaB6 nanoparticles have strong absorption of near-infrared light and thus can be used as thermal insulation and photothermal material.However,the synthesis of LaB6 nanoparticles is difficult due to the lack of active boron sources.In this paper,LaB6 nanopowder was synthesized by using LiBH4 and La(OH)3 or La2O3.In order to obtain LaB6 nanopowder with desirable size,the sythesis conditions were optimized.With the increase of ball milling time,the particle size decreased,and became uniform.The addition of TiF3 further reduced the particle size of the reaction product,resulting in LaB6 nanoparticles of 20 to 50 nm.After the addition of TiF3,the reaction temperature was lowered accordingly.The hydrogen release temperature of 6LiBH4 + La(OH)3 was lowered by about 25 ?,and that of 12LiBH4 + La2O3 was lowered by about 10 ?.The dispersion of LaB6 in ethanol was prepared by bead milling with ZrO2 beads(0.3 mm).Increasing the milling time helped to refine the LaB6 particles,but long-term bead milling reduced the near-infrared absorption properties of LaB6 nanoparticles.The near-infrared absorption performance of LaB6 powders was found to decrease with the increase of oxygen content.Therefore,LaB6 nanoparticles should be prevented from oxidation during its synthesis,dispersion and storage.The LaB6@SiO2 core-shell nanoparticles were successfully prepared by the Slobber method,and their near-infrared light absorption property was not significantly reduced compared to that of bare LaB6 nanoparticles.The photothermal test results of LaB6@SiO2/ethanol dispersion showed that the photothermal effect of LaB6@SiO2 was remarkable.The temperature of the dispersion reached 65.1 ? after 3 min illumination when the concentration of LaB6@SiO2/ethanol dispersion was 100 ?g/mL and the output density of 980 nm laser was 0.43 W/cm2.The standard MTT assay showed that there was no obvious cytotoxicity and the cell viability remained at a high level,when the concentrations of LaB6 and LaB6@SiO2 were below 200 ?g/mL.LaB6 and LaB6@SiO2 both showed high photothermal treatment effects in photothermal therapy experiments of vitro tumor cell.The tumor cells were all completely apoptotic in the illumination area after 5 min illumination,when the material concentration was 100?g/mL and the 980 nm laser output density was 0.81 W/cm2.These results indicate that LaB6 is a promising photothermal material for biomedical applications.