Brilliant IR Reflecting Yellow Colorants in Rare Earth Double Molybdate Substituted BiVO₄ Solid Solutions for Energy Saving Applications

Abstract

Brilliant IR reflecting yellow colorants are developed in rare earth double molybdate substituted BiVO 4 solid solutions. Li 0.10 RE 0.10 Bi 0.8 Mo 0.2 V 0.8 O 4 (RE = La, Pr, Sm, Gd, Tb, Dy, Y, Yb and Lu) pigments are prepared by a conventional solid-state reaction route and their optical, structural and morphological properties are analyzed. X-ray diffraction analysis confirms the tetragonal scheelite phase formation in the series. These pigments have a strong optical absorption in the UV-blue light wavelength region. CIE LAB color analysis shows that different hues of yellow shades are obtained in these solid solutions. The color characteristics are comparable to commercial BiVO 4 pigment. Incorporation of double rare earth molybdates of La, Gd, Tb, Y and Lu into BiVO 4 results in nontoxic IR reflecting cool pigments. The applicability of the developed pigment was tested on a concrete cement surface as well as on a metal panel. These pigments are composed of less toxic elements that make them favorable for energy saving surface coating formulations for buildings and automotives.The urban heat island effect emerging in metropolitan cities produces elevated urban air temperatures. Solar radiation consists of about 5% ultraviolet radiation, 46% visible radiation and 49% infrared radiation. A major contribution of heat comes from the IR radiation, which transfers heat to the underlying structure in buildings and automotives causing thermal discomfort and health problems. A substantial amount of energy is consumed to cool buildings, thus increasing energy demand. 1 Cool paints absorb less solar energy, which keeps the surface at a lower temperature and decreases energy transfer by radiation. Passive cooling of buildings helps reduction in air pollution due to low energy usage and power plant emissions. Therefore, current interest in the pigment industry is focused on developing nontoxic cool pigments that aid in energy savings. 2 Bright yellow shades are particularly challenging, with preferential reformulation away from cadmium pigments and lead chromates within the plastics and surface coating markets. 3 There is an urgent need for developing IR reflecting nontoxic yellows, which are limited in the current market.Recently, BiVO 4 has attracted wide attention for its photocatalytic, 4 ferroelastic, 5 dielectric, 6 ionic and electronic conductive properties, 7 which makes it attractive for use in gas sensors, 8 microwave resonator devices, 6 wastewater treatment 9 and water splitting. 9 BiVO 4 has been identified as an ideal candidate for pigmentary applications. 10 Recently, many researchers, including our group, have reported BiVO 4 based pigments such as (Bi, La)VO 4, 11 (Bi, Ca, Zn)VO 4, 12 (Bi, Ca, Zn, La)VO 4, , 13 Y and Nb doped BiVO 4 14 and SiO 2 coated BiVO 4. 15 So, development of nontoxic IR reflecting BiVO 4 based pigments can lead to cool surface coating formulations for buildings and automobile shells.Double alkali rare earth molybdates and tungstates of the type ARE(XO 4 ) 2 ; X = Mo, W 16 have a va...

Visible‐Light‐Activated C−C Bond Cleavage and Aerobic Oxidation of Benzyl Alcohols Employing BiMXO5 (M=Mg, Cd, Ni, Co, Pb, Ca and X=V, P)

“…The observed color coordinates (L*, a*, and b* parameters) were compared with BiVO 4 , which is also a yellow colored compound. [29] The data are presented in Table S5, S6. The BiMgVO 5 and BiCdVO 5 compounds compare well with the reported BiVO 4 .…”

High Near-Infrared Reflectance Orange Pigments of Fe-Doped La2W2O9: Preparation, Characterization, and Energy Consumption Simulation

“…Al 2 O 3 was used as a white reference and the test range was 300–2500 nm. ASTM G173-03 was taken as a reference for calculating the NIR reflectance ( R ) of the pigments and their coatings in the wavelength range from 700 to 2500 nm, and the main formula is: , where i (λ) is the solar spectral irradiance (w·m –2 ·nm –1 ) and r (λ) is the spectral reflectance obtained from the experiment.…”

Synthesis and Characterization of Yellow Pigments of Bi1.7RE0.3W0.7Mo0.3O6 (RE = Y, Yb, Gd, Lu) with High NIR Reflectance

“…Recently, the yellow pigments based on iron and tungsten codoped La 2 Ce 2 O 7 and BiVO 4 -coated mica–titanium oxide pigment have been reported. Notably, Rao et al also reported a suite of BiVO 4 -based brilliant yellow pigments − and Y-doped Bi 2 MoO 6 yellow pigments, , which are friendly alternatives to toxic pigments (PbCrO 4 -based pigment and PbSbO 3 pigment). , These pigments with high near-infrared reflectance can serve as cold pigments.…”

“…Differently, the occupied 4f band in Yb oxide locates above the O 2p band; hence, the band-gap energy can be determined by 4f−d transition. Rao et al 18 stated that the increase of atomic number of the rare earth became gradually lowered to the 4f electronic level, finally approaching the valence band, which resulted in an increase of the band-gap energy. Whereas the band-gap energy of Gddoped pigment is 2.40 eV, it is higher than 2.37 eV of Yb (with a higher atomic number than Gd-doped pigment in this study).…”

“…All of the pigments possess high NIR reflectances (>95%), which are higher than those of yellow pigments of Li 0.1 La 0.1 Bi 0.8 Mo 0.2 V 0.8 O 4 (R = 90%), (LiLaZn) 1/3 MoO 4 −BiVO 4 (R = 89−95%), and irondoped La 2 Mo 2 O 7 pigments (R = 71−93%). 18,19,38 Not only does the doping of additives into pigments possess high NIR reflectance but also the colors of the pigments are switched from faint yellow to yellow-orange, which contributes to satisfying the public demands for colors. In accordance with the ASTM standard G173-03, the NIR solar reflectance spectra of Bi 1.7 RE 0.3 W 0.7 Mo 0.3 O 6 (RE = Y, Yb, Gd, Lu) pigments are computed and displayed in Figure 7.…”