Preparation of ground calcium carbonate-based TiO2 ...

Powder Technology 325 (2018) 568–575

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Preparation of ground calcium carbonate-based TiO2 pigment by a two-step coating method Yanru Chen a, Haijun Yu b, Lingyun Yi c, Yue Liu a,d, Lei Cao a,e, Kun Cao a, Yahui Liu a, Wei Zhao a,⁎, Tao Qi a,⁎ a

National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China Hunan BRUNP Recycling Technology Co. LTD., No.18 Jinsha EastRoad, Jinzhou New District, Changsha, Hunan 410600,China School of Minerals Processing & Bioengineering, Central South University, Changsha 410083, China d School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China e Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China b c

a r t i c l e

i n f o

Article history: Received 11 August 2017 Received in revised form 7 November 2017 Accepted 13 November 2017 Available online 21 November 2017 Keywords: Ground calcium carbonate TiO2 Pigment

a b s t r a c t A two-step coating method for preparing ground calcium carbonate-based TiO2 pigment (GCTD) was proposed and studied in this paper. The tetraethoxysilane (TEOS, C8H20O4Si) was selected as Si source. Aqueous ammonia was used as precipitant in the first coating step while titanyl sulfate (TiOSO4·2H2O) was used as Ti source in the second step. The Energy dispersive spectrometer (EDS) and X-ray fluorescence (XRF) results prove that SiO2 is coated on the surface of ground calcium carbonate (GCC) particles successfully. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results demonstrate that the coated SiO2 is in the form of amorphous. The EDS, XRD, TEM and Scanning electron microscope (SEM) results show that TiO2 is coated on the surface of SiO2 coated GCC (SiO2@GCC) and TiO2 particles are composed of mixed crystal of anatase and rutile. The hiding power of obtained GCTD is significantly improved compared with ordinary composite TiO2 pigment (CTD) and close to that of anatase TiO2 (ATD). The whiteness and lightness of this GCTD are just slightly decreased compared to that of CTD and ATD. Nevertheless, its oil absorption value is some higher than that of ATD but lower than that of CTD. © 2017 Elsevier B.V. All rights reserved.

1. Introduction TiO2 is an important white pigment. Compared with other traditional white pigments, such as lead white, zinc white and zinc barium white, TiO2 has better refractive index, achromatic force, hiding power and whiteness. Due to these excellent properties, TiO2 is usually known as the best of white pigments [1–3]. Besides, it is also widely used in coatings, plastics, paper, chemical fiber, catalyst, cosmetics and other fields [4–10]. However, the application of TiO2 has been limited because of the environment pollution caused by the waste acid produced in industry production, the shortage of titanium resource, and the high price of titanium dioxide. Therefore, the development of a TiO2 substitute with low cost and similar performance is significantly important. Many literatures have introduced methods to coat TiO2 on the surface of cheap non-metallic minerals to get a substitute for TiO2 pigment [11–16]. At present, the main methods of preparing this kind of pigment are mechanical chemical coating and chemical precipitation reaction. Mechanical chemical coating method has the advantages of simple process and less environmental pollution. The disadvantage of this method is that TiO2 easily falls off from the core particle due to the poor adhesion ⁎ Corresponding authors. E-mail address: [email protected] (W. Zhao).

https://doi.org/10.1016/j.powtec.2017.11.040 0032-5910/© 2017 Elsevier B.V. All rights reserved.

between core particle and TiO2 (The main interaction force is physic adsorption). As a result, the properties of resulting pigment are unstable. Chemical precipitation method has the advantage of uniform coating of TiO2 particles on the core surface and TiO2 particles are not easy to fall off due to the strong interaction force between core particles and TiO2 particle (The main interaction force is chemical binding). The disadvantage of this method is that the reaction process is long and some weak acid solution produced during the preparation process needs to be reused. Calcium carbonate is a kind of inorganic nonmetallic resource with abundant reserves. It has the advantages of high whiteness, low hardness and small grinding energy consumption. The ordinary calcium carbonate-TiO2 composite pigment is mostly prepared by mechanical chemical coating method. Lin et al. and Ding et al. proposed the mechano-activated mechanism for this preparation process [17] and studied the adsorption form of titanate on the surface of calcium carbonate by establishing an OH participant adsorption model [18]. Using the chemical precipitation method, Tao et al. [19] coated calcium carbonate with TiO2 using titanium sulfate as titanium source and urea as the precipitant. The resulting product CaCO3@TiO2 has a strong ultraviolet absorption capacity. The whiteness of CaCO3@TiO2 filler-containing paper sheet is 73.8%, which is similar to TiO2-incorporated paper (73.16%). Li et al. [20] prepared rutile TiO2@CaCO3 composites by an

Y. Chen et al. / Powder Technology 325 (2018) 568–575 Table 1 Chemical composition of GCC.

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Table 4 Properties of the materials.

Composition

CaO

MgO

SiO2

Al2O3

Fe2O3

SrO

SO3

K2O

Content (wt/%)

97.832

1.889

0.119

0.053

0.052

0.023

0.019

0.015

Material

Whiteness(%)

Oil absorption value(g/100 g)

Particle size (μm) D10

D50

D90

GCC ATD CTD

95.73 96.21 96.72

19.83 25.69 33.42

0.899 0.562 0.681

2.225 1.204 2.953

4.522 1.983 7.492

Table 2 Chemical composition of ATD. Composition

TiO2

P2O5

K2O

CaO

Nb2O5

ZnO

ZrO2

Content (wt/%)

99.611

0.204

0.125

0.036

0.010

0.007

0.007

in-situ synthesis method. The method comprises the following steps: mixing and stirring the TiO2 and calcium hydroxide slurry, and then introducing CO2/N2 gas mixture into the slurry. The ultraviolet absorption capacity and paint contrast ratios of resulting product are similar to that of TiO2. However, all the above mentioned calcium carbonate is precipitated calcium carbonate (PCC), not GCC. To our knowledge, using GCC as the calcium source to prepare calcium carbonate-TiO2 pigment by chemical precipitation method has not been reported. Since GCC is abundant and much cheaper than PCC in China, we explore the preparation method of GCTD using GCC as core particle via two steps chemical precipitation method in this work. The role of SiO2 coating step is to prevent the reaction between GCC and acidic Ti source and the using amount of aqueous ammonia in this step is catalytic dose to induce the hydrolysis of Si source. The Ti source is obtained from the dissolve of TiOSO4 in water. The main purpose of this research is that providing an idea to transform the low value nonmetallic mineral GCC into high value product after the suitable treatment. The obtained product could be used as high grade coatings, paints in architecture industry, whitening agent in paper making and etc. 2. Experimental 2.1. Materials The GCC used in this study was provided by the Guangxi Hezhou Kelong Micro-powder Co., Ltd. in Guangxi Province, China. The ATD was provided by Henan Billions Chemicals Co., Ltd. in Henan Province, China. CTD was purchased directly from the market. The chemical composition of GCC, ATD and CTD are shown in Tables 1, 2 and 3, respectively. The pigment properties of these materials were listed in Table 4. Chemical grade tetraethoxysilane (TEOS), ethanol, aqueous ammonia and titanyl sulfate were used in the experiment. And throughout the experiments deionized water was used. 2.2. Preparation of GCTD sample The flow diagram of GCTD preparation is shown in Fig. 1. The whole process consists of two parts: preparation of SiO2-coated GCC and preparation of TiO2-coated SiO2@GCC. The scheme illustrating the formation of ground calcium carbonate-based TiO2 pigment is illustrated in Fig. 2. 2.2.1. Preparation of SiO2-coated GCC GCC particles were dispersed in deionized water to obtain the slurry with a certain concentration and ammonia was added to adjust the pH value of this slurry. TEOS and ethanol were well mixed to a certain percentage, and then the mixture was added dropwise into above GCC slurry. The resulting slurry was stirred at a certain temperature for a certain

period of time, then filtered, washed, dried and calcined at 500 °C for 4 h to obtain the SiO2-coated GCC sample. The molar ratio of TEOS to CaCO3 is x:1, where x = 0.1–0.3. 2.2.2. Preparation of TiO2-coated SiO2@GCC Firstly, titanyl sulfate was added into deionized water to get a solution with certain concentration. Secondly, the SiO2@GCC sample was dispersed in deionized water, and then this slurry was added into above titanium solution. Thirdly, the obtained mixture was heated to 105 °C and stirred for 2 h. After the reaction, this mixture was filtered, dried and calcined at 900 °C for 2 h to obtain the GCTD product. In this step, the molar ratio of TiO2 to CaCO3 is 0.5:1. 2.3. Characterizations XRD patterns were analyzed by XRD diffractometer (X'Pert PRO MPD, PANalytical, the Netherlands) using Cu Kα radiation at 40 kV and 30 mA in the range from 5° to 90° with a 0.0263° step size. The General Structure Analysis System (GSAS)-EXPGUI [21,22] was used to refine the XRD patterns to obtain accurate crystal information. The morphological and chemical compositions of the samples were analyzed by SEM and EDS (JSM-7001F + INCA X-MAX, JEOL, Ltd., Japan and Oxford Instruments, Ltd., UK). Carbon conductive adhesive was used to prepare samples and platinum was added to increase the conductivity of samples. The samples were observed with a transmission electron microscope (JEM-2100 (UHR), JEOL Ltd., Japan). The samples were milled and dispersed in ethanol before their supported in the copper grid covered with formvar. The particle size distribution was measured by a laser granulometer (Malvern Mastersizer 2000, Malvern Instruments Ltd., UK). The sample was measured three times and the particle sizes of the materials are the average of the three measured values. The D10, D50, D90 correspond to the apertures related to 10, 50 and 90% of passing material, respectively. The chemical compositions of samples were determined by XRF (AXIOS, PANalytical B.V., Netherlands). The samples were compressed on a tabletting machine with boric acid and then were tested. The whiteness of samples was analyzed by whiteness meter (WSD3C, Beijing Kangguang Optical Instrument CO., Ltd., China). The oil absorption values of samples were examined according to GB5211.15-88 which is equivalent to ISO787/5-1980. The hiding power of samples was examined according to GB1709-79. 3. Results and discussion 3.1. The effect of hydrolysis temperature on SiO2 coating Hydrolysis temperature is a key factor for the SiO2 coating step. Fig. 3 shows the SiO2 contents of samples prepared at different hydrolysis temperatures under the conditions: TEOS/CaCO3 = 0.1:1 (molar ratio), time = 2 h and pH = 7. From Fig. 3, it can be concluded that the higher

Table 3 Chemical composition of CTD. Composition

TiO2

CaO

MgO

P2O5

Na2O

K2O

SiO2

Al2O3

SO3

Cl

Fe2O3

ZnO

Content (wt/%)

56.109

39.740

1.051

0.984

0.677

0.619

0.393

0.237

0.082

0.052

0.007

0.025

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Y. Chen et al. / Powder Technology 325 (2018) 568–575

Deionized water

GCC

Deionized water

TEOS

Slurrying

Coating

Wash filtrate

Ammonia

Ethanol

Product

Calcin ed

Grinding

Titanyl sulfate

Slurrying

Calcined

Coating

Wash filtrate

Fig. 1. Preparation flow sheet of GCTD.

Fig. 2. Scheme illustrating the formation of ground calcium carbonate-based TiO2 pigment.

the hydrolysis temperature is, the better the coating effect will be. When the hydrolysis temperature is below 70 °C, the SiO2 content just increases slowly. While, if the hydrolysis temperature is above 70 °C the SiO2 content will increase sharply corresponding to the enhancement of temperature. The reason for these results is that the hydrolysis of TEOS is an endothermic reaction, thus, high reaction temperature will benefit the equilibrium shifting to the hydrolysis direction [23]. Since the difference of SiO2 coating amount between 90 °C and 100 °C is not obvious and it is needed to avoid the boiling reaction system because it will generate irregular bubbles and local turbulent flow, and then cause the uneven coating of silica, we choose 90 °C as the optimum condition in this SiO2 coating step.

3.2. The effect of pH on SiO2 coating

than in neutral condition due to the stronger attacking force of\\OH to break the C\\O bond of TEOS. However, if the pH value is too high (above pH = 10), the depolymerization of formed SiO2 polymer will occur [24]. As a result, the coated SiO2 amount does not linearly increase with pH value. Therefore, we selected pH = 10 as the optimum condition in this SiO2 coating step. Fig. 5 shows the XRD results of samples coated with SiO2 under different pH values when the molar ratio of TEOS to CaCO3 is 0.1:1. It can be seen that there is no obvious diffraction peak of SiO2, while the diffraction peak of calcium carbonate can be found for all four samples. It can be explained that the coated SiO2 is in the form of amorphous, whose diffraction signal is weak and covered by the strong signals of rhombic crystal system for GCC. 3.3. The effect of hydrolysis time on SiO2 coating

Since GCC (CaCO3) will react with acid, the effect of pH on the SiO2 coating step above 7 has been studied. Fig. 4 shows the contents of SiO2 in samples prepared at different pH values under the conditions: TEOS/CaCO3 = 0.1:1 (molar ratio), time = 2 h and temperature = 90 °C. It can be seen that, if the pH value rises from 7 to 10, the coating amount of SiO2 increases quickly. Further increasing the pH value, the coating amount of SiO2 does not obviously increased. The reason for these results is that TEOS will be hydrolyzed faster in alkaline condition

The effect of hydrolysis time is also investigated. Fig. 6 shows the SiO2 contents of samples prepared at different hydrolysis time under the conditions: TEOS/CaCO3 = 0.1:1 (molar ratio), pH = 7 and temperature = 90 °C. Prolonging the hydrolysis time from 1 h to 5 h, the coating amount of SiO2 has slightly diminished. The reason can be attributed to the fast hydrolysis rate at a relatively high temperature (90 °C) [25], which leads to the hydrolysis reaction during a short time. Besides, further

Fig. 3. The SiO2 contents of samples prepared at different hydrolysis temperatures.

Fig. 4. The SiO2contents of samples prepared at different pH values.


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Fig. 7 is the SEM and surface sweep plot result of SiO2@GCC sample obtained at pH = 10 when the molar ratio of TEOS to CaCO3 is 0.1:1. The results show that the surface of GCC has been coated with SiO2 (Fig. 7. (a), the dark region is uncoated GCC while the light region is the GCC coated with SiO2). The silicon content of this sample is 1.37% (Fig. 7. (b)). The TEM result of the sample was shown on Fig. 8. It can be seen that the SiO2 particle is coated on the surface of core particle. From the electron diffraction result, it can be concluded that the coated SiO2 is amorphous (There is no diffraction spots in the selected region). This confirms the result of XRD (Fig. 5).

3.4. The effect of SiO2 content on TiO2 coating

Fig. 5. XRD patterns of GCC (a) and SiO2-coated GCC obtained at different pH values: pH = 7 (b), pH = 10 (c), pH = 14 (d).

Fig. 6. The SiO2contents of samples prepared at different hydrolysis time.

prolonging the hydrolysis time will induces the separation between GCC and coated Si species. Consequently we selected 1 h as the optimum condition for this parameter.

The XRD patterns of GCTD coated with different amounts of SiO2 were shown in Fig. 9. The XRD peaks appearing at 2θ = 25.270°, 37.697°, 47.977°, 54.990°, 62.570° are corresponding to (101), (004), (200), (211), (204) planes of anatase TiO2 (01-071-1166) while the 2θ values of 27.371°, 35.974°, 41.122°, 54.170°, 56.482°, 68.809° are corresponding to (110), (101), (111), (211), (220), (301) planes of rutile TiO2 (01-77-0442). The XRD peaks at 2θ = 17.919°, 27.452°, 29.732°, 34.238°, 34.506°, 55.820° are attributed to the characteristic peaks of titanite (01-87-0254). From above XRD results, there are three conclusions can be obtained. Firstly, the TiO2 particles coated on the surface of SiO2@GCC particles are in the form of the mixed crystal of anatase and rutile. The reason for the formation of mixed crystals is probably that the hydrolysis of titanyl sulfate will be disturbed by many factors, such as pH value, impurity and temperature. Usually, the lower pH value is beneficial to the formation of rutile type TiO2 since its intermediate Ti(OH)(OH)2+ 5 is easier to transform to rutile crystal phase. Yet, the higher pH value is beneficial to the formation of anatase type TiO2 since its intermediate Ti(OH)3+ is more easy to transform to anatase crystal phase [26–27]. Secondly, when the SiO2 costing amount increases from SiO2/GCC = 0.1 to SiO2/GCC = 0.3, most diffraction peaks of anatase crystals disappear in the XRD spectra except the diffraction peaks of (101) (Fig. 9(a)). It can be inferred that the decrease of SiO2 amount on the surface of GCC particles is beneficial to the formation of anatase TiO2. This is probably due to the fact that the reduction of SiO2 loading leads to imperfect coating of the GCC particle, thus, the reaction between exposed GCC and H+ will increase the pH value of system. As mentioned above, the higher pH value is beneficial to the formation of anatase crystals. Thirdly, the diffraction peaks of titanite (CaTiOSiO4) are found for all SiO2 coated samples. The titanite is a kind of silicate mineral. It will be formed when the mixture of calcium carbonate, silica and titanium dioxide are calcined at a high temperature [28–30]. The forming of titanite (also can be described as CaO·SiO2·TiO2),

Fig. 7. (a) SEM and (b) EDS spectrum of SiO2-coated GCC particles.

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Fig. 8. TEM results of SiO2-coated GCC particles.

found that there are some points that are mainly composed of TiO2, while, other points are mainly composed of CaO. This result means that TiO2 probably is coated on the surface of SiO2@GCC in the form of particle. Fig. 12 shows the TEM results of the calcium-based TiO2 pigment when the molar ratio of TEOS to CaCO3 is 0.2:1 and the molar ratio of titanyl sulfate to CaCO3 is 0.5:1. It can be seen that the TiO2 certainly has been coated on the surface of SiO2@GCC in the form of particles. The result of electron diffraction shows that the coated TiO2 is consists of mixed crystal. In order to determine the content of each component in these products, the samples with different content of SiO2 were analyzed by GSAS refinement (Fig. 13). All the observed peaks are consistent with the phase composition and lattice constants, which are presented in Table 5. When the SiO2 coating amount is low, the content of each component in the sample is anatase of 36.21%, rutile of 22.79% and titanite of 40.99%. As the SiO2 coating amount increases, the content of anatase will reduce to 4.89% while the content of titanite increase to 62.66%. By comparing the contents of anatase and rutile, it can be concluded that the high SiO2 content will inhibit the formation of anatase but promote the formation of rutile.

3.5. The effect of TiOSO4 concentration on TiO2 coating which is a sosoloid, suggests that the interaction force among GCC, SiO2 and TiO2 are chemical bond instead of physic adsorption. Fig. 10 presents the main chemical composition of GCTD coated with different SiO2 amount. It is clear that the TiO2 coating amounts for these samples have no obvious differences. This indicates that the amount of SiO2 coated on calcium carbonate does not play the main role for the hydrolysis degree of titanyl sulfate. As the rutile titanium dioxide has a better pigment performance than anatase titanium dioxide, combining with quantitative analysis results (Table 5), we selected SiO2/GCC = 0.2 as the optimum condition for this TiO2 coating step. Fig. 11 shows the composition of GCTD particles determined by the EDS analysis when the molar ratio of TEOS to CaCO3 is 0.2:1 and the molar ratio of titanyl sulfate to CaCO3 is 0.5:1. From surface sweep plot (Fig. 11. (a)), we find that TiO2 has been coated on the surface of SiO2@GCC particles successfully and the Ti content is slightly less than the original added amount, which means almost complete hydrolysis of titanyl sulfate. For the EDS point scanning results (Fig. 11. (b)), it is

As shown in Fig. 14, when the concentration of TiOSO4 solution is 1 mol/L, the size of TiO2 particles is small and mainly is less than 100 nm (Fig. 14, (a)). With the concentration of TiOSO4 solution decreasing to 0.5 mol/L, the size of TiO2 particles will increase and is mostly over 100 nm (Fig. 14, (b)). Further decreasing the concentration of TiOSO4 solution to 0.1 mol/L, the morphology of TiO2 particles cannot be distinguished (Fig. 14, (c)). These results probably attribute to that more H2TiO3 crystal nuclei that formed by the hydrolysis of TiOSO4 will be produced under the system of high concentration TiOSO4. It will cause the crystal growth rate to be more slowly than the rate of nuclei formation, thus, the crystals nuclei growth are inhibited [31] and the size of final TiO2 particles will be small. If the TiOSO4 concentration is too low, the formed H2TiO3 crystal nuclei will grow enough and the final TiO2 particles will be too large. Since the particle size of commercial rutile TiO2 is ranged from 200 to 300 nm [32], the best concentration of TiOSO4 solution is 0.5 mol/L.

Fig. 9. XRD patterns of GCTD with different amounts of SiO2: (a) n(SiO2):n(GCC) = 0.1:1, (b) n(SiO2):n(GCC) = 0.2:1, (c) n(SiO2):n(GCC) = 0.3:1.

Fig. 10. The content of TiO2, CaO and SiO2 in samples prepared at different molar ratio of SiO2/GCC.


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Table 5 The contents of the samples. Samples

Composition

Contents (wt/%)

Space group

a

b

c

α

β

γ

0.1 mol

A-TiO2a R-TiO2b Titanite A-TiO2 R-TiO2 Titanite A-TiO2 R-TiO2 Titanite

36.21 22.79 40.99 7.08 40.45 52.46 4.89 32.44 62.66

I41/amd P42/mnm P121/a1 I41/amd P42/mnm P121/a1 I41/amd P42/mnm P121/a1

3.778 4.602 7.079 3.766 4.599 7.069 3.768 4.591 7.067

3.778 4.602 8.735 3.766 4.599 8.738 3.768 4.591 8.740

9.524 2.965 6.567 9.528 2.966 6.565 9.522 2.966 6.564

90 90 90 90 90 90 90 90 90

90 90 113.93 90 90 113.93 90 90 113.93

90 90 90 90 90 90 90 90 90

0.2 mol

0.3 mol

a b

Anatase TiO2. Rutile TiO2.

4. Pigment properties The results in Table 6 show that the whiteness and lightness of GCC are reduced after the coating of silicon and titanium. The b* value of GCC is reduced greatly after the SiO2 coating. However, it will increase after the further coating of TiO2. The case of oil absorption value of GCC is just contrary to b* value after above two step coating. According to GB170979, the black-and-white grid cannot be hidden by the GCC and SiO2@ GCC no matter how many samples are used. The hiding power of GCC is significantly improved after the coating of TiO2 because of the high light-scattering indices of TiO2 [33]. The hiding power of GCTD can

reach to 23.82 g/m2 which are better than CTD pigment and close to that of ATD. In a word, the whiteness and lightness of GCTD are slightly decreased compare to ATD and CTD. Its oil absorption value is higher than that of ATD but still lower than that of CTD.

5. Conclusion GCTD was prepared successfully through a two-step coating method firstly. At the first step, the factors including hydrolysis temperature, pH value and hydrolysis time were discussed. The results of XRF, EDS and TEM show that SiO2 has been coated on the surface of GCC in the form of amorphous. The optimal coating conditions are as follows: temperature = 90 °C, pH = 10 and time = 1 h. At the second step, TiO2 particles were coated on the surface of SiO2@GCC in the form of mixed crystals of anatase and rutile. The amount of coated SiO2 will affect the distribution of Ti compounds at the TiO2 coated step. The higher SiO2 content will promote the formation of rutile. The morphology and size of coated TiO2 particles will be affected by the concentration of TiOSO4 and the optimum concentration is 0.5 mol/L. The whiteness and brightness of GCTD are reduced while its oil absorption value is increased compared to GCC. Especially, the oil absorption value and hiding power of GCTD are superior to CTD and close to ATD. The product obtained could be used as high grade coatings, paints in architecture industry, whitening agent in paper making and etc. Much detail work is still developing in our laboratory and other pigment properties are in continues improvement.

TiO2

SiO2@GCC

Fig. 11. (a) surface sweep plot and (b) point sweep plot of GCTD.

Fig. 12. TEM result of GCTD.

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Fig. 13. The experimental (crosses), calculated (solid lines), and difference (bottom) results of XRD refinement of GCTD with different amounts of SiO2: (a) n(SiO2):n(GCC) = 0.1:1, (b) n(SiO2):n(GCC) = 0.2:1,(c) n(SiO2):n(GCC) = 0.3:1.

(a)

(b) 100nm

100nm

(c) 100nm

Fig. 14. SEM results of samples with different titanium concentration: (a) 1 mol/L, (b) 0.5 mol/L, (c) 0.1 mol/L.

Y. Chen et al. / Powder Technology 325 (2018) 568–575 Table 6 Color characterization and pigment performance of different samples’ Sample

Whiteness

L*

a*

b*

Oil absorption value (g/100 g)

Hiding power (g/m2)

a b c d e

96.92 95.37 95.66 96.72 96.21

97.95 96.42 96.72 97.11 97.05

0.13 0.22 0.13 0.06 −0.22

3.69 0.41 1.04 2.78 0.30

19.83 36.45 30.37 33.42 25.69

– – 23.82 29.12 22.56

Note: a, GCC; b, SiO2@GCC; c, GCTD; d, CTD; e, ATD; L*, lightness; a*, red-green index; and b*, yellow-blue index.

Acknowledgements We are grateful for the support from the National Key Technologies R&D Program (Grant No. 2014BAC03B01), the Special Fund of Insoluble Potassium Containing Rock of Tongren City (201680), the National Science Foundation for Youth Scholars of China (Grant Nos. 51504230, 21606241 and 51402303), the Science and Technology Cooperation Project between Yunnan Province and CAS/universities (2016IB002), the Key Research Program of Frontier Sciences of Chinese Academy of Sciences (Grant No. QYZDJ-SSW-JSC021), the co-operation project of Innovation Center of ecological building materials and environmental protection equipment of Jiangsu Province (YCXT201610) and the Key Research and Development Program of Jiangxi Province (Grant No. 20161BBH80003). References [1] C.X. Tian, S.H. Huang, Y. Yang, Anatase TiO2 white pigment production from unenriched industrial titanyl sulfate solution via short sulfate process, Dyes Pigments 96 (2013) 609–613. [2] S.S. Katarzyna, N. Magdalena, K.R. Agnieszka, J. Teofil, Preparation of hybrid pigments via adsorption of selected food dyes onto inorganic oxides based on anatase TiO2, Dyes Pigments 94 (2012) 338–348. [3] Y.H. Liu, F.C. Meng, F.Q. Fang, W.J. Wang, J.L. Chu, T. Qi, Preparation of rutile titanium dioxide pigment from low-grade titanium slag pretreated by the NaOH molten salt method, Dyes Pigments 125 (2016) 384–391. [4] C. Boudot, M. Kühn, K.M. Kühn, J. Schein, Vacuum arc plasma deposition of thin TiO2 films on silicone elastomer as a functional coating for medical applications, Mater. Sci. Eng. C 74 (2017) 508–514. [5] M. Abdullaha, S.K. Kamarudin, Titanium dioxide nanotubes (TNT) in energy and environmental applications: an overview, Renew. Sust. Energ. Rev. 76 (2017) 212–225. [6] S.G. Chen, Y.J. Guo, H.Q. Zhong, S.J. Chen, J.N. Li, Z.C. Ge, et al., Synergistic antibacterial mechanism and coating application of copper/TiO2 nanoparticles, Chem. Eng. J. 256 (2014) 238–246. [7] S. Martin, B. Jan, B. Jürgen, P.J. Jansens, Experimental and theoretical investigations of the coating of capsules with TiO2, Chem. Eng. J. 160 (2010) 351–362. [8] Y.Z. Li, Y.N. Fan, Y. Chen, A novel method for preparation of nanocrystalline rutile TiO2 powders by liquid hydrolysis of TiCl4, J. Mater. Chem. 12 (2002) 1387–1390. [9] Y. Wei, R.T. Wu, Y.F. Zhang, Preparation of monodispersed spherical TiO2 powder by forced hydrolysis of Ti(SO4)2 solution, Mater. Lett. 41 (1999) 101–103. [10] Q. Sun, X.L. Hu, S.L. Zheng, Z.M. Sun, S.S. Liu, H. Li, Influence of calcination temperature on the structural, adsorption and photocatalytic properties of TiO2 nanoparticles supported on natural zeolite, Powder Technol. 274 (2015) 88–97.

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