Sol–gel synthesis and properties of europium–strontium copper silicates blue pigments with high near-infrared reflectance

Accepted Manuscript Sol-gel synthesis and properties of europium-strontium copper silicates blue pigments with high near-infrared reflectance Yanshuang Zhang, Yubai Zhang, Xinqiao Zhao, Yujun Zhang PII:

S0143-7208(16)30132-2

DOI:

10.1016/j.dyepig.2016.04.011

Reference:

DYPI 5189

To appear in:

Dyes and Pigments

Received Date: 30 November 2015 Revised Date:

25 March 2016

Accepted Date: 5 April 2016

Please cite this article as: Zhang Y, Zhang Y, Zhao X, Zhang Y, Sol-gel synthesis and properties of europium-strontium copper silicates blue pigments with high near-infrared reflectance, Dyes and Pigments (2016), doi: 10.1016/j.dyepig.2016.04.011. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Sol-gel synthesis and properties of europium-strontium copper silicates blue pigments with high near-infrared reflectance Yanshuang Zhanga,b, Yubai Zhanga,b, Xinqiao Zhaoc, Yujun Zhang*a,b Key Laboratory for liquid-solid Structural Evolution & Processing of Materials of

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a

Ministry of Education, Shandong University, Jinan 250061, P. R. China

Key Laboratory of Special Functional Aggregated Materials, Ministry of Education,

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b

c

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Shandong University, Jinan 250061, P. R. China

Qingdao GRX Metal Protection Technology Co., Ltd ,Qingdao 266109, P. R. China *Corresponding author. Tel / Fax: +86-531-88399760; E-mail:

Abstract Environmentally

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[email protected].

benign

near-infrared

reflective

blue

pigments

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Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4) were synthesized via sol-gel method. The

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pigment samples were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction technique, X-ray energy dispersive spectroscopy, scanning electron microscopy, UV-vis-NIR diffuse reflectance spectroscopy and the Commission Internationale de l’Eclairage 1976 L*a*b* colorimetric method. The prepared powders exhibited single-phase tetragonal crystalline structure. The color of the pigments changed from sky-blue to 1

ACCEPTED MANUSCRIPT dark blue due to the substitution of Eu for Sr in SrCuSi4O10. With increasing Eu content, the near-infrared solar reflectance increased first and then declined. Adding

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specific amount of Eu can enhance the near-infrared reflectance and solar reflectance. The prepared pigments presented an optimum near-infrared solar reflectance of 72.31% when the doping content of Eu is 20mol%.

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Keywords: Eco-friendly colorants; Europium-doped SrCuSi4O10; Near-infrared reflectance; Sol-gel; Blue pigments

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1. Introduction

Of late, cool pigments with high near-infrared (NIR) reflectance have drawn extensive attention because of their excellent performance in preserving lower

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exterior surface temperatures of buildings and decreasing power waste[1-3]. As is reported, around 5% of the solar radiation power in the Air Mass 1.5 Global (AM1.5G)

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solar irradiance spectrum is constituted by ultraviolet radiation (200-400 nm), 43% by visible radiation(400-700 nm), and 52% by the NIR radiation (700-2500 nm)[4,5].

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Thus it is significantly necessary to develop NIR reflective pigments to reduce the heat build-up on the earth and diminish energy loss. NIR reflective pigments have a wide range of applications in both civil and military fields such as architectural roof, pavements, glazing and aircraft surface pigmentation, etc[6,7]. Currently the most widely used blue pigments are Cobalt blue (CoAl2O4), Ultramarine (Na7Al6Si6O24S3), and Prussian blue (Fe4[Fe(CN)6]3). However, these 2

ACCEPTED MANUSCRIPT colorants are restricted by government legislation and regulations in many countries due to their environmental and durability issues[8,9]. Thus it has become a concern to

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investigate novel eco-friendly and durable NIR reflective blue inorganic pigments. Recently, rare earth compounds based NIR reflective pigments have been proposed as viable alternatives to conventional pigments due to their low toxicity and high

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stability. Sheethu Jose et al. [10] synthesized a series of toxic metal free intense blue

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color inorganic pigments with the general formula Sr1-xLaxCu1-yLiySi4O10 by traditional solid state routes, exhibiting a high NIR reflectance of 67%. Sheethu Jose et al. [11] synthesized intense blue nano-pigments YIn0.9Mn0.1O3-ZnO with high solar reflectance of 70% by a sol-gel combustion method. Aijun Han et al. [12] prepared

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nanocrystalline YFexMn1-xO3 pigments by modified citrate method at a certain calcination temperature, which displayed a wide range of colors from blue-green to

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pale blue and then dark blue as well as pronounced reflective performance.

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The present work is focused on the synthesis of a series of NIR reflective blue inorganic pigments with the formula Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4) by sol-gel method. Crystallization temperature, crystal structure, morphological feature, chromatic and near-infrared reflective properties of these pigments were also investigated in detail. 2. Experimental section 3

ACCEPTED MANUSCRIPT 2.1 Materials and methods A series of pigments with the general formula Sr1-xEuxCuSi4O10+δ (x =0, 0.1, 0.2,

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0.3, 0.4) were synthesized by sol-gel method. Cupric oxide (CuO, 99.0%), europium oxide (Eu2O3, 99.9%), nitric acid (HNO3, 65%), strontium nitrate (Sr(NO3)2, 99.5%), citrate acid (C6H8O7· H2O, 99.5%), ethylene glycol (C2H6O2, 99.0%), and ludox

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(SiO2·nH2O, 25%) were used as starting materials.

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Initially, stoichiometric amount of CuO and Eu2O3 were dissolved in dilute nitric acid to form transparent solution, and then Sr(NO3)2 was added in stoichiometric proportion with the total metal cation molar concentration of 2-3M. Citrate acid, which was used as the chelating agent, was weighted in the molar ratio 1.0:1.0 with

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respect to the cations (Sr, Eu and Cu), and then was dissolved in ethylene glycol solvent. Subsequently an appropriate amount of ludox was added in the citric acid

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solution under constant stirring. After pouring the mixed fluid into the nitrate solution,

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the clear precursor solution was finally obtained. The resultant solution was heated at 80˚C to induce the complexing reaction

under constant stirring for about 5 h. An organic gel was formed with evaporation of water.

Further drying was carried out in a vacuum oven at 70˚C for 24 h. Then the

dry gel was ground in an agate mortar and transferred in a muffle furnace to calcinate at different temperatures (300~1000˚C) for 2 h. The obtained pigments were triturated 4

ACCEPTED MANUSCRIPT and sieved to get fine and homogeneous powders. The pigments were pressed on boric acid substrate in a stainless die under a

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pressure of 40MPa for 3min. The final samples with a dimension of 27 mm in diameter and 5 mm in thickness were applied to the following optical test.

The

thermal

and

of

differential

precursor scanning

powders

was

calorimetry

recorded

(TG-DSC,

by

Mettler

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thermogravimetry

performance

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2.2 Characterization techniques

TG-DSC1/1600HT), in air atmosphere in the temperature range of 50-800˚C with a heating rate of 15˚C/min. Infrared spectra of samples were measured via a Fourier transform infrared spectrometer (FTIR, Vertex70, Bruker, Germany) in a

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wavenumber range from 400 to 4000 cm-1 at room temperature. The phase composition of the powders was detected by X-ray diffraction (XRD, Rigaku,

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RINT-2000) with Cu-Kα radiation (1.5405 Å), operated with voltage and current

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settings of 40 kV and 40 mA, respectively. Data were collected by step scanning over a 2θ range from 10˚ to 70˚with a step size of 0.0167˚ at scan rate of 5˚/min. The elemental composition of the sample was analyzed by X-ray energy dispersive spectroscopy (EDS, EX350, Horiba). The morphology of the powders was characterized by a field emission high-resolution scanning electron microscopy (SEM, SU-70, Hitachi), operated with an acceleration voltage of 30 kV. Before measurement, 5

ACCEPTED MANUSCRIPT the powders were coated with a thin gold layer via ion sputtering. The reflectance spectra measurements of the pigment samples was carried out by

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a UV-vis-NIR spectrophotometer (Shimadzu, UV-3600 with an integrating sphere attachment) using poly-tetrafluoroethylene (PTFE) in NIR range (700-2500 nm) and Barium sulphate (BaSO4) in visible range (380-750 nm) as a reference respectively.

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The NIR solar reflectance at wavelengths between 700 and 2500 nm is the

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irradiance-weighted average of its experimentally achieved spectral reflectance and calculated in accordance with the ASTM standard number G173-03(2012). NIR solar reflectance can be regarded as a significant indicator of heat build-up affected by the sun on the surface of a substance.

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The colorimetric values of the pigments were measured on a Color-Eye automatic differential colorimeter (X-Rite, 7000 A) using the Commission

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Internationale de l’Eclairage (CIE) 1976 L*a*b* colorimetric method. L* is the

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lightness axis (0 for black and 100 for white). The parameter a*(negative values for green and positive values for red) and b*(negative values for blue and positive values for yellow) denote the hue or color dimensions. The parameter C* (chroma) represents the chromatic saturation and is defined as C* = [(a*)2+(b*)2]1/2. The hue angle, h˚ is stated in degrees in the range of 0-360˚ and calculated by the formula h˚=tan-1(b*/a*). 6

ACCEPTED MANUSCRIPT 3. Results and discussion 3.1 TG and DSC analysis

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Fig. 1 presents the TG-DSC results of the pigment precursor sample Sr0.9Eu0.1CuSi4O10+δ. The mass loss of about 6% from 50˚C to 300˚C is owing to the removal of water and the decomposition of some nitrate and organics. The mass loss

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of approximately 59% from 300˚C to around 500˚C accompanied by an intense

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exothermic peak at 475.18˚C is ascribed to the pyrolysis of polymeric precursor, which indicates the formation of the product Sr0.9Eu0.1CuSi4O10+δ. When the temperature is above 500˚C, the weight of the sample remained stable because of the

3.2 FTIR spectra

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accomplishment of the combustion.

The optimum calcination temperature required for the crystallization of the

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pigment sample SrCuSi4O10 was investigated. The FTIR spectra of the precursor and

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SrCuSi4O10 samples calcined at different temperatures for 2 h are given in Fig. 2. As is shown, the FTIR spectra of the precursor heated at 300 °C apparently display a broad absorption band at around 3400 cm-1, which is due to the characteristic stretching vibrations of -OH. The absorption peaks at 1558 cm-1, 1461 cm-1 and 1109 cm-1 are assigned to unsymmetrical stretching vibration of O–C=O, bending vibration of C-H and stretching vibration of C–O–C respectively, caused by the 7

ACCEPTED MANUSCRIPT decomposition of carboxylate and other organics. With temperature rising up to 900˚C, the peaks of the hydroxyl groups and other organic groups are attenuated and finally disappear. Meanwhile, new absorption peaks appear below 1300 cm-1,

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including the peaks at 1161 cm-1, 1054 cm-1, 1009 cm-1 and 479 cm-1 attributed to the Si-O bond stretching vibration[13], the one at 661 cm-1 attributed to Cu-O bond

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stretching vibration[14], and the ones at 596 cm-1 and 521 cm-1 attributed to Sr-O

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bond stretching vibration[15,16]. Further heat treatment hasn’t changed the position of the absorption peaks. It can be deduced that crystallized SrCuSi4O10 has completely formed at 900˚C. 3.3 Phase and composition analysis

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Fig. 3 illustrates the XRD patterns of the pigments SrCuSi4O10 calcined at various temperatures ranging from 400˚C to 1000˚C for 2 h. The pigment sample

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calcined at 400˚C exhibits amorphous structure, and the one calcined at 700˚C is

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observed to display some weak peaks, which reveals the beginning of the phase transformation. When the temperature is higher than 800˚C, the XRD patterns can be well indexed to a tetragonal structure (JCPDS 49-1813) with lattice constants a=b=0.7366nm and c=1.5574nm. Furthermore, the peak location of the samples was not changed with the variation of heat treatment temperature at above 800˚C, but the peak intensity increases progressively resulted from the improvement of the degree of 8

ACCEPTED MANUSCRIPT crystallinity. The powder XRD patterns of Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4)

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compounds calcined at an optimal temperature of 900˚C for 2h was presented in Fig. 4. All the samples show characteristic single-phase tetragonal structure of SrCuSi4O10, hinting that the substitution of Eu for Sr does not significantly influence the phase

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composition due to the fact that the dopant ions possess similar ionic radii as the host

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ions (The ionic radius of Eu3+ = 0.112nm; Sr2+=0.118nm).

In order to confirm the percentage composition of the prepared pigments, the Sr0.8Eu0.2CuSi4O10+δ pigment sample calcined at an optimal temperature of 900˚C for 2h was chosen to perform EDS analysis and the result is shown in Fig. 5. The result

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indicates that the microcrystal of the sample is composed of 5.12 at% Strontium(Sr), 1.17 at% Europium(Eu), 5.49 at% Copper(Cu), 22.71 at% Silicon(Si) and 65.51 at%

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Oxygen(O). As is shown in Table 1, the experimental values and the theoretical

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values (calculated from the chemical formula of Sr0.8Eu0.2CuSi4O10) are very close. Combined with XRD results, EDS result demonstrates that the Sr0.8Eu0.2CuSi4O10+δ pigment sample was successfully synthesized. 3.4 Morphological analysis The

SEM

images

of

the

powdered

pigments

SrCuSi4O10

and

Sr0.9Eu0.1CuSi4O10+δ calcined at 900˚C are shown in Fig. 6. It can be figured out that 9

ACCEPTED MANUSCRIPT the particles distribution is relatively uniform and there is no remarkable morphological difference between the doped and undoped samples. Moreover, the

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images disclose the presence of agglomeration in the sample with the average particle size of about 200nm. Combined with the XRD results above, the substitution of Eu for Sr has negligible effect on the structure and morphology of the pigments.

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3.5 UV-vis diffuse reflectance and chromatic properties

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Fig. 7 depicts the UV-vis diffuse reflectance spectra of Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4) pigment samples. It can be observed that there are three broad transitions in the visible region, which are resulted from d-d transitions in the D4h symmetric crystal field at copper center owing to the vibronic coupling[10]. The

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maximum absorption occurs at 630nm due to the transition from 2B1g to 2Eg [17]. Because of the intense absorption in the region 550-700nm (red, orange and yellow),

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the pigments display visibly blue color as a complementary. The substitution of Eu for

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Sr in Sr1-xEuxCuSi4O10+δ gently influences the absorption in the visible region because it changes the substrate crystal field environment and as a result has a bearing on the d-d electronic transitions of Cu. When the x value is less than 0.2, the absorption in the region 380-500nm is insignificantly affected and the absorption in the region 500-750nm decreases. When the x value is more than 0.2, the substitution intensifies the absorption in the visible region. 10

ACCEPTED MANUSCRIPT The CIE 1976 color coordinates of the Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4) pigment samples are listed in Table 2. As is shown, all the pigments display blue

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color (a*<0, b*<0). The substitution of Eu for Sr leads to an increase in the values of -b* and L*(b* changes from -21.8 to -27.1, and L* changes from 60.2 to 64.4), and hence the intensity and the lightness of blueness of the pigment samples are

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prominently enhanced. The color of the pigments changed from sky-blue to dark blue

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as is shown in Fig. 8. On the other hand, the -a* value decreases from 6.9 to 4.6, and consequently the hue angle value h˚ increases from 252.4 to 260.4, which means the greenness of the pigment samples gets weakened. The observed hue angles of the pigments lie in the blue region of the cylindrical color space (h˚= 210-270 for blue).

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Besides, the C* value increases from 22.9 to 27.5, hinting the chromic richness of pigments intensifies with progressive Eu doping.

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3.6 Near-infrared reflectance

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Fig. 9 gives the NIR reflectance spectra of Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4) pigments calcined at 900˚C. Compared to the Eu free pigment sample, the incorporation of Eu doesn’t alter the total tendency of the NIR reflectance spectra. The maximum NIR reflectance of all pigments occurs at 1970nm. The NIR reflectance increases in the region of 810-1970nm with a peak at 1450nm, and sharply declines and then increases again in the range of 1970-2500nm. After weighting 11

ACCEPTED MANUSCRIPT treatment by multiplying the experimental spectral reflectance with the normalized spectral irradiance of the sun, the NIR solar reflectance (R*) is obtained as is shown

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in Fig. 10. The europium free sample, SrCuSi4O10 exhibits a NIR solar reflectance of 62.64%. Doping specific amount of Eu can enhance the NIR solar reflectance. When the substitution amount of Eu for Sr is 10mol% and 20mol%, the NIR solar

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reflectance can be improved up to 68.33% and 72.31%, respectively. However,

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excessive Eu is detrimental to the NIR solar reflectance. The doping amount of 30mol% and 40mol% decreases the NIR solar reflectance of pigment samples to 59.46% and 57.07%. As a result, the optimal doping content of Eu is 20mol%. 4. Conclusions

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Eco-friendly blue pigments Sr1-xEuxCuSi4O10+δ (x ranges from 0 to 0.4) with high NIR reflectance were successfully synthesized via sol-gel method. Crystalline

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SrCuSi4O10 with average particle size of about 200nm has completely formed after

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calcined at 900˚C for 2h. The substitution of Eu for Sr doesn’t change the tetragonal structure and morphology in SrCuSi4O10. The blueness of the pigments intensified with progressive Eu content. Adding specific amount of Eu can enhance the near-infrared reflectance and solar reflectance. When the doping content of Eu is 20mol%, the developed pigments reached an optimal NIR solar reflectance of 72.31%, making it a potential candidate in cool pigment industry. 12

ACCEPTED MANUSCRIPT Acknowledgements This work was financially supported by the National Nature Science Foundation of China (No. 51472146).

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References

[1] Han A, Zhao M, Ye M, et al. Crystal structure and optical properties of YMnO3

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compound with high near-infrared reflectance. Sol Energy 2013; 91: 32-6.

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[2] Hedayati HR, Alvani AAS, Sameie H, et al. Synthesis and characterization of Co1-xZnxCr2-yAlyO4 as a near-infrared reflective color tunable nano-pigment. Dyes Pigments 2015; 113: 588-95.

[3] Thongkanluang T, Limsuwan P, Rakkwamsuk P. Preparation and Application of

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High Near-Infrared Reflective Green Pigment for Ceramic Tile Roofs. Int J Appl Ceram Technol 2011; 8(6): 1451-8.

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[4] Sreeram KJ, Aby CP, Nair BU, et al. Colored cool colorants based on rare earth

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metal ions. Sol Energy Mater Sol Cells 2008; 92(11): 1462-7. [5] Malshe VC, Bendiganavale AK. Infrared reflective inorganic pigments. Recent Pat Chem Eng 2008; 1(1): 67-79. [6] Gupta KK, Nishkam A, Kasturiya N. Camouflage in the non-visible region. J Ind Text 2001; 31:27-42.

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ACCEPTED MANUSCRIPT [7] Jeevanandam P, Mulukutla RS, Phillips M, Chaudhuri S, Erickson LE, Klabunde KJ. Near infrared reflectance properties of metal oxide nanoparticles. J Phys Chem C

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2007; 111:1912-8. [8] Zayat M, Levy D. Blue CoAl2O4 particles prepared by the sol-gel and citrate gel methods.Chem Mater 2000; 12(9):2763-9.

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pigments. Angew Chem Int Ed 2002; 41:2483-7.

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[9] Berke H. Chemistry in ancient times: the development of blue and purple

[10] Jose S, Reddy ML. Lanthanum–strontium copper silicates as intense blue inorganic pigments with high near-infrared reflectance. Dyes Pigments 2013; 98(3): 540-546.

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[11] Jose S, Jayaprakash A, Laha S, et al. YIn0.9Mn0.1O3-ZnO nano-pigment exhibiting

120-129.

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intense blue color with impressive solar reflectance. Dyes Pigments 2016; 124:

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[12] Han A, Ye M, Zhao M, et al. Crystal structure, chromatic and near-infrared reflective properties of iron doped YMnO3 compounds as colored cool pigments. Dyes Pigments 2013; 99(3): 527-30. [13] Abo-Naf SM, El Batal FH, Azooz MA. Characterization of some glasses in the system SiO2, Na2O·RO by infrared spectroscopy. Mater Chem Phys 2003; 77(3): 846-52. 14

ACCEPTED MANUSCRIPT [14] Stavola M, Krol DM, Weber W, et al. Cu-O vibrations of Ba2YCu3Ox. Phys Rev B 1987; 36(1): 850.

with large surface area. Mater Lett 2004; 58: 2418–22.

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[15] Berger D, Fruth V, Jitaru I, et al. Synthesis and characterisation of La1-xSrxCoO3

[16] Pantoja AE, Pooke DM, Trodahl HJ, et al. Oxygen-isotope effect on the

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high-frequency Raman phonons in Bi2Sr2CaCu2O8+δ. Phys Rev B 1998; 58(9):

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5219-21.

[17] Kendrick E, Kirk CJ, Dann SE. Structure and colour properties in the Egyptian Blue Family, M1− xM′xCuSi4O10, as a function of M, M′ where M, M′= Ca, Sr and Ba.

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Dyes Pigments 2007; 73(1): 13-18.

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ACCEPTED MANUSCRIPT Figure captions: Fig.1. TG-DSC curves of Sr0.9Eu0.1CuSi4O10+δ precursor

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Fig.2. FTIR spectra of precursor and SrCuSi4O10 calcined at different temperatures Fig. 3. XRD patterns of SrCuSi4O10 calcined at different temperatures

Fig. 4. XRD patterns of Sr1-xEuxCuSi4O10+δ (x=0~0.4) pigments calcined at 900˚C

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Fig. 5. EDS result of the Sr0.8Eu0.2CuSi4O10+δ pigment samples prepared by sol-gel

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method

Fig. 6. SEM images of powdered pigments calcined at 900˚C (a) SrCuSi4O10 (b) Sr0.9Eu0.1CuSi4O10+δ

calcined at 900˚C

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Fig. 7. UV-vis diffuse reflectance spectra of Sr1-xEuxCuSi4O10+δ (x=0~0.4) pigments

Fig. 8. Photographs of Sr1-xEuxCuSi4O10+δ (x=0~0.4) samples calcined at 900˚C (a)

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x=0, (b) x=0.1, (c) x=0.2, (d) x=0.3, (e) x=0.4

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Fig. 9. NIR reflectance spectra of Sr1-xEuxCuSi4O10+δ (x=0~0.4) pigments calcined at 900˚C

Fig. 10. NIR solar reflectance (R*) spectra Sr1-xEuxCuSi4O10+δ (x=0~0.4) pigments calcined at 900˚C

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ACCEPTED MANUSCRIPT Table captions: Table 1 The experimental and theoretical values of the composition of the Sr0.8Eu0.2CuSi4O10+δ pigment samples prepared by sol-gel method

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Table 2 Color coordinates of Sr1-xEuxCuSi4O10+δ (x=0~0.4) pigments calcined at

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900˚C

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Fig. 1.

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20

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Fig. 5.

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Fig. 6.

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Fig. 7.

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Fig. 8.

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Fig. 9.

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Fig. 10.

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ACCEPTED MANUSCRIPT Table 1 Experimental atomic%

Theoretical atomic%

O

65.51

62.50

Si

22.71

25.00

Cu

5.49

6.25

Sr

5.12

5.00

Eu

1.17

1.25

Totals

100

100

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Element

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Table 2 Color coordinates L*

a*

b*

C*

h°

SrCuSi4O10

60.2

-6.9

-21.8

22.9

252.4

Sr0.9Eu0.1CuSi4O10+δ

68.3

-5.7

-26.7

Sr0.8Eu0.2CuSi4O10+δ

66.6

-4.9

-27.5

Sr0.7Eu0.3CuSi4O10+δ

63.7

-4.6

-28.1

Sr0.6Eu0.4CuSi4O10+δ

64.4

-4.6

-27.1

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Pigment composition

257.9

27.9

259.9

28.5

260.7

27.5

260.4

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27.3

ACCEPTED MANUSCRIPT Highlights High NIR reflective blue pigments were synthesized via sol-gel method.




The pigments have completely crystallized after calcined at 900˚C for 2h.




The color of the Sr1-xEuxCuSi4O10+δ pigments changed from sky-blue to dark

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blue.

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The developed pigments reached an optimal NIR solar reflectance of 72.31%.

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