Preparation And Properties Of Rare Earth Inorganic Pigments With High Near Infrared Reflection

The use of environmentally friendly and green inorganic pigments with high near-infrared reflection is an effective measure to mitigate the"urban heat island effect",and can save energy at the same time.It has great application value in construction,paint,ink and other industries.In recent years,in the research of near-infrared reflective pigments,there are problems such as toxic formulations or single color that need to be solved.Generally,pigments with bright colors have poor near-infrared reflection properties,such as bismuth yellow;and pigments with good reflection properties are not rich enough in color,such as rare earth bismolybdate.Single-color,toxic and low-performance inorganic pigments cannot meet people’s growing needs for a better life.The development of environmentally friendly inorganic composite pigments with low toxicity to non-toxicity and high near-infrared reflection function has become a research hotspot at home and abroad.In this paper,yellow pigment[(Li_0.4RE_0.6Al_0.6)_x/2Bi_1-x][Mo_xV_1-x]O₄（RE=La-Lu;x=0-0.4）,and multicolor pigment Li Al_1-xM_x（Mo O₄）₂（M=Fe,Pr,Ho,Nd,Er,Ce;x=0-0.4）was synthesized at the same time.The structure,chemical composition,morphology and particle size of the samples were characterized by XRD,XPS,SEM,particle size analyzer and other tests,and the effects of doping concentration and doping elements on the color and reflection properties of the pigment were studied.The results of the study are as follows:（1）The doping concentration（x）has a great influence on the structure,morphology,color properties and reflection properties of the synthesized[(Li_0.4La_0.6Al_0.6)_x/2Bi_1-x][Mo_xV_1-x]O₄ pigments.The structure of the pigment changes from the monoclinic scheelite phase to the tetragonal scheelite phase from x=0.2,and the impurity peak of V₄O₉ appears when x=0.4;with the increase of doping concentration,the particles are gradually transformed from regular ellipse to irregular shape,accompanied by agglomeration;different doping concentrations make the pigment show different yellow hues,and the color properties are improved;doping can improve the near-infrared reflectance（R%）of[(Li_0.4La_0.6Al_0.6)_x/2Bi_1-x][Mo_xV_1-x]O₄pigments,which can reach up to 97.14%;in addition,the synthesized pigments have excellent acid and alkali resistance,and have excellent thermal insulation properties in practical applications.[(Li_0.4RE_0.6Al_0.6)_0.1Bi_0.8][Mo_0.2V_0.8]O₄（RE=La-Lu）pigments doped with different rare earth elements are all tetragonal scheelite phase bismuth vanadate structure,from Sm began to appear the impurity peak of REVO₄;the morphology of all samples showed rough surface,irregular shape and agglomeration;the color of the pigment[(Li_0.4RE_0.6Al_0.6)_0.1Bi_0.8][Mo_0.2V_0.8]O₄ varies from dark yellow to bright yellow,mainly due to the difference in the forbidden band width;different rare earth element doping improves the near-infrared reflectance of the pigment,and when RE is Gd or Lu,the R%can reach more than 97%.（2）The Li Al_1-xFe_x(Mo O_4+δ)₂ pigment samples show a triclinic lithium aluminum molybdate structure,the space group is P-1,and the increase of x makes the grains grow in orientation;Fe in the sample exists as Fe³⁺and a small amount of Fe²⁺;pigment particles are irregular polyhedrons with different particle sizes;the color of the pigment gradually changed from white to yellow,and the forbidden band width（Eg）decreased;the near-infrared solar reflectance R*%of the prepared Li Al_1-xFe_x(Mo O_4+δ)₂ pigment can reach up to 94.19%.By introducing rare earth elements Pr,Ho,Nd,Er,Ce into the Li Al（Mo O₄）₂ matrix,the color of the pigment was successfully changed from white to green,lavender,pink,and yellow,indicating that doping can control the color of the pigment;as the doping concentration of rare earth ions increases,the color of the pigment gradually deepens;in addition,the prepared pigments have high near-infrared solar reflectance（>87%）,indicating that the pigment samples have excellent thermal insulation properties and can be widely used as a new type of reflective thermal insulation coatings.In summary,the inorganic pigments synthesized by the solid-phase reaction method in this paper have good near-infrared reflection properties,which can be used as a new type of environmentally friendly and green building energy-saving materials.The requirements for visual perception have huge application potential.