Research On The Photocatalytic And Reflective Thermal Insulation Property Of ZnO/Bismuth Oxyhalides Coated Hollow Glass Microspheres

Nowadays,energy depletion and environmental pollution have become the serious challenges for all mankind.Nanomaterials provides a new way in solving energy shortages and environmental problems.Nano-zinc oxide and bismuth oxyhalide can degradate water pollutants and harmful gases with the help of ultraviolet or visible light,which show great potentials in environmental protection.Besides,the zinc oxidebased pigments have a high near-infrared reflectance,which can be applied in reflective insulation coatings to reduce the energy consumption of air conditioning in southern hot areas.However,due to the problem of nanoparticle agglomeration,the reflective property and photocatalytic performance of the nanomaterials was greatly undermined in practical application.Futhermore,few studies about multifunctional composites that can solve both energy and environment problems have been reported.In this paper,nano-zinc oxide and bismuth oxychloride were coated on the surface of hollow glass microspheres as multifunctional composites with solar reflective and photocatalytic property.Our study solved the problem of dispersibility and recovery of nanoparticles,and expanded the application of hollow glass microbead composite functional materials in solving energy shortages and environmental pollution.In this paper,nano-zinc oxide and bismuth oxychloride particles with different compositions and microstructures were coated on the surface of hollow glass microspheres by heterogeneous precipitation method.The effects of compositions and microstructures on the photocatalytic performance and reflective thermal insulation property of zinc oxide and bismuth oxide were systematically studied.The main points could be summarized as following.The effect of synthesis conditions on the morphology and loading of zinc oxide on the surface of glass microspheres were investigated.The growth mechanism of zinc oxide with different morphology and the binding mechanism between nanometer zinc oxide and glass beads were studied.When the concentration of zinc oxide is 0.0105~0.0175mol/L,the reaction time is 4~6h,the reaction temperature is 80~90?,the concentration of zinc nitrate is 0.035~0.05mol/L,ZnO/HGM composites with high ZnO loading and different morphology can be prepared.The nano-zinc oxide is anchored to the surface of the hollow glass microbeads by Zn-O-Si bonds.(2)The effects of nano-ZnO with different morphology on the reflective properties,thermal insulation properties and photocatalytic properties were studied.It was found that the morphology of nanometer zinc oxide on the surface of the hollow glass microspheres have a great influence on the reflective insulation and ultraviolet photocatalytic property.Near infrared reflectance : ZnO nanoparticles> ZnO nanosheets> ZnO nanoplates.The maximum near infrared reflectance of the composite pigment reaches 95.7% and the maximum insulation temperature difference is 11.1°C.Ultraviolet photocatalytic activity:ZnO nanoplates> ZnO nanosheets> ZnO nanoparticles.The degradation rate of ZnO nanoplates coated HGM was 91.9% in 3 hours.(3)The effects of the synthesis conditions on the morphology and composition of bismuth oxychloride on the surface of glass microspheres were studied.We found that rhodamine B was decomposed by BiOCl/HGM through visible photodegradation.The band gap of the composite particles decrease with the incorporation of Br and I elements.When the molar ratio of Cl to Br was 1:3,the degradation rate reached 99.8% within 10 min.The near infrared reflectivity of bismuth oxyhalide coated hollow glass microspheres is 92.05 ~ 95.19%.Compared with the blank sample,5.1~9.4 C decrease in outer surface temperature and 1.8~4? decrease in the inner temperature was obtained for the heat box coated with composite pigments.