Preparationg And Transparent Thermal-Insulating Properties Of Mo-doped Tungsten Bronze And Photo/Thermo Responsive Tungsten Bronze-PNIPAM Composites

As the main channel for solar energy entry,windows with special optical properties have a significant effect on the comfortable living of buildings.For instance,a window,with excellent near-infrared absorbing ability and simultaneously high visible transparency,can depresses solar heat gain for the building in hot climate remarkably,and reduces energy consumption and corresponding CO₂ emission.Currently,spectral selective materials for this application include low-emissivity（low-E）coatings,indium/antimony doped tin oxide（ITO/ATO）,and rare-earth hexaborides（LaB₆）.In general,silver-based low-E coatings exhibit excellent thermal insolating ability,but usually need a complex stack structure of different functional layers to ensure binding strength onto substrates and oxidization resistance.ITO/ATO and rare-earth hexaborides typically shield NIR light in a limited range of 750-1300 and 600-1500 nm,respectively.Tungsten bronze materials is a good transparent thermal-insulating material obviously superior to the above materials.The wide-range NIR shielding ability of tungsten bronze should be ascribed to the appearance of small-polaron absorption and a strong LSPR absorption.The photothermal simulation evaluation showed that the tungsten bronze thermal-insulation coting can reduce the indoor temperature by 3-10°C,which significantly reduce air conditioning energy consumption and improve comfortable living.In this paper,Mo is doped in tungsten bronzes lattice by replace W atom to adjust microstructure band gap and optical properties of tungsten bronze.Both Mo and W belong to VIB-sub-group,and have similar ionic radii,electronegativity and oxide lattice configuration.Their oxides can form a series of solid solution with each other.The microstructure and near-infrared shielding properties of Mo-doping tungsten bronzes were characterized by XRD,XPS,SEM,TEM and UV-Vis-NIR spectrophotometer.Furthermore,based on the photothermalconversioncharacteristicsoftungstenbronze,A photo-/thermo-dual-responsive PNIPAM-Cs_xWO₃ hydrogels were synthesized according to PNIPAM temperature sensitivity.When the infrared light is absorbed by Cs_xWO₃,causing a temperature rise of polymer,the PNIPAM hydrogel undergoes a hydrophilic-hydrophobic phase transition that regulates sunlight transmission.The photo-/thermo dual responsive,visible light control and near infrared shielding property of PNIPAM-Cs_xWO₃ hydrogels composite were tested.The main results are as follows:（1）Mo-doped（0-80 at.%）tungsten bronzes,M_xWO₃,were was prepared by hydrothermal method to systematically explore the effects of Mo-doping on their microstructure and optical properties.The products adopted a hexagonal（NH₄）_xWO₃ within 6 at.%Mo-doping,and transformed into a monoclinic W₁₈O₄₉ with higher Mo-doping content.When Mo/（Mo+W）is 1.5%,The nanorods tungsten bronze（6-9 nm in diameter and 60-80 nm in length）have excellent near-infrared light shielding performance and high visible light transmittance,which can be used as energy saving glass coatings.（2）The PNIPAM-Cs_xWO₃ hydrogels composite were obtained by milling Cs_xWO₃ and PNIPAM by the zirconia bead.The transmittance of visible light decreased from 60%to 20%,that’s to say,it has a control range of 40%.The transmittance of near infrared is always around 10%meaning the nanocomposites have a good near infrared shielding performance.And the infrared light is absorbed by Cs_xWO₃ converted into heat,causing a temperature rise of polymer.The dual-intelligent window is able to dynamically regulate solar radiations and adapt surrounding temperature simultaneously,leading to a much better energy-saving performance.In this photo-/thermo-dual-responsive system,the energy of solar is used to control its transmittance without additional device.