MolybdatesZn1-xCoxMoO4(0≤ x ≤0.3) were elaborated by the Sol-Gel method with pH=3.The results obtained by DRX show a single-phase domain startingfrom 500°C for x ≤ 0.3 isostructural to ZnMoO4.The powder ofZn0.7Co0.3MoO4treated at 500°C and 700°C is formed by nano-sized primary crystallitesof size between 80 and 160nm. The colorimetric parameters (L a* b*) of powders obtained at 700°C present adegree of high bluing

Benchikhi, Mohamed

Durand, Bernard

El Ouatib, Rachida

Er-Rakho, Lahcen

Guillemet, Sophie

Lakhlifi, H.

International audienceMolybdatesZn1-xCoxMoO4(0≤ x ≤0.3) were elaborated by the Sol-Gel method with pH=3.The results obtained by DRX show a single-phase domain startingfrom 500°C for x ≤ 0.3 isostructural to ZnMoO4.The powder ofZn0.7Co0.3MoO4treated at 500°C and 700°C is formed by nano-sized primary crystallitesof size between 80 and 160nm. The colorimetric parameters (L a* b*) of powders obtained at 700°C present adegree of high bluing

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Synthesis and physicochemical characterization of
pigments based on molybdenum “ZnO-MoO3: Co2+”
H. Lakhlifi, Mohamed Benchikhi, Rachida El Ouatib, Lahcen Er-Rakho,
Sophie Guillemet, Bernard Durand
To cite this version:
H. Lakhlifi, Mohamed Benchikhi, Rachida El Ouatib, Lahcen Er-Rakho, Sophie Guillemet, et al.. Syn-
thesis and physicochemical characterization of pigments based on molybdenum “ZnO-MoO3: Co2+”.
Journal of Materials and Environmental Science , Mohammed Premier University, 2015, 6, pp.3465-
3469. ￿hal-02091210￿
  
 
 
OATAO is an open access repository that collects the work of Toulouse 
researchers and makes it freely available over the web where possible 
Any correspondence concerning this service should be sent  
to the repository administrator: tech-oatao@listes-diff.inp-toulouse.fr 
This is a Publisher’s version published in: http://oatao.univ-toulouse.fr/23620 
 
To cite this version:  
Lakhlifi, H. and Benchikhi, Mohamed and El Ouatib, Rachida and Er-Rakho, 
Lahcen and Guillemet, Sophie  and Durand, Bernard  Synthesis and 
physicochemical characterization of pigments based on molybdenum «ZnO-
MoO3: Co2+». (2015) Journal of Materials and Environmental Science - JMES, 
6. 3465-3469. ISSN 2028-2508  
Official URL: https://www.jmaterenvironsci.com/Document/vol6/vol6_N12/396-Lakhlifi.pdf 
 
J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. 
ISSN : 2028-2508 
CODEN: JMESCN 
 
3465 
 
 
 
 
Synthesis and physicochemical characterization of pigments based on 
molybdenum « ZnO-MoO3: Co
2+
» 
 
H. Lakhlifi
1
, M. Benchikhi
1
, R. El Ouatib
1*
, L. Er-Rakho
1
,  
S. Guillemet-Fritsch
2
 and B. Durand
2 
1
 Laboratoire de Physico-Chimie des Matériaux Inorganiques, Département de chimie, Faculté des Sciences Ain Chock, 
Université Hassan II Casablanca, Maroc 
2 
Institut Carnot CIRIMAT, CNRS Université de Toulouse, 118 route de Narbonne, 31062 Toulouse Cedex 9, France. 
 
*
Corresponding Author. E-mail: elouatib@yahoo.fr; Tel: (+212661170710) 
 
Abstract  
Molybdates Zn1-xCoxMoO4 (0≤ x ≤0.3) were elaborated by the Sol-Gel method with pH=3.The results obtained 
by DRX show a single-phase domain starting from 500°C for x ≤ 0.3 isostructural to ZnMoO4.The powder of 
Zn0.7Co0.3MoO4 treated at 500°C and 700°C is formed by nano-sized primary crystallites of size between 80 and 
160 nm. The colorimetric parameters (L a* b*) of powders obtained at 700°C present a degree of high bluing. 
 
Keywords: Molybdate, Sol–gel, Nanometric, Chromophore, Morphology, Pigment. 
 
Introduction 
The molybdates of divalent elements AMoO4, exhibits numerous structural varieties and especially, 
polymorphisms with phase transition [1, 2]. These compounds train a big family of oxides being the object of 
search both in the field of the applied sciences and that of the fundamental sciences. The intrinsically 
luminescent colorless molybdates, MgMoO4, ZnMoO4 and PbMoO4 [3, 4], are doped with rare earth in order to 
obtain phosphors [5-7]. Molybdates AMoO4 with A=Ni2 +, Co2 +, Fe2+, Mn2 +, are very studied as catalysts for 
oxidation of organic compounds [8,9]. Recent studies show that, in tungsten doped copper molybdate CuMo1-
xWxO4, the temperature of the structural transition α     γ is dependent upon the tungsten content [10,11]. These 
two polymorphs have different colors, respectively green and brown-red. It is thus possible to envisage the use 
of this pigment as marker of temperature. 
The objective of our work, is to elaborate Zn1-xCoxMoO4 pigments. The element cobalt appears to us to be a 
very promising chromophore for the synthesis of new pigments. The element cobalt appears to us to be a very 
promising chromophore for the synthesis of new pigments. Indeed, this element is responsible for different tints 
following the environment which it occupies. In tetrahedral site, it is at the origin of the blue color [11, 12]. In 
octahedral regular site, it is responsible for a pink colorb [12,13], while a purple tint seems to be obtained when 
the octahedral site is deformed [10].  
The literature also mentions the possibility of the cobalt to take a trigonal bipyramidal based coordination. In 
molybdate ZnMoO4, the Zn2+ ions are located both in octahedral and in triangular bipyramidals sites [14]. The 
presence of cobalt in these sites would induce distinguishable colors resulting of the transitions between cobalt 
d-levels. 
Several synthesis methods have been developed to obtain the zinc molybdate, such as the solid method 
involving solid state reactions between copper and molybdenum oxides. Powders obtained by this method are 
generally constituted of large-sized particles with low specific surface [15]. The Co-precipitation method has the 
disadvantage of adsorption at the surface of the particles of foreign ions difficult to remove [16]. To elaborate 
J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. 
ISSN : 2028-2508 
CODEN: JMESCN 
 
3466 
 
our samples of Zn1-xCoxMoO4 (x ≤ 0.3), we opted for the polymerizable complex method, that we have already 
used to prepare the cobalt molybdate [17]. 
 
2. Materials and Methods 
Commercial reagents used for the synthesis of our compounds are: ammonium heptamolybdate (NH4) 6Mo7O24, 
4H2O (Acros, 99%), metal nitrates ((Zn, Co) (NO3)2, 6H2O) (Aldrich, 98%), citric acid (Acros, 98%) and 
ammonia (NH4OH 28% pure, density = 0.91).The aqueous solutions of metals salt0.2M and ammonium 
hyptamolybdate 0.2M are mixed in stoichiometric proportions. The citric acid is then introduced so that the 
molar report A/M is equal 3 and the pH is fixed to 3. The precursors are obtained after evaporation and drying at 
120 ° C for 12 h. These precursors are pre-calcined at 300 °C for 12 hours under air. The black powders 
obtained were treated at temperature ranging from 500 to 800 °C. The various steps of this synthesis are given 
in the Figure 1. 
The obtained powders were characterized by thermal analysis ATD-ATG (SETARAM TG-DTA 92), by X-rays 
diffraction (Brucker AXS D4λCu Kα = 1.5418 Å), by scanning (JEOL-JSM6400) and transmission (JEOL 
2010) electronics microscopies. The colorimetric parameters (L a * b *) were measured in the system CIE Lab 
by means of a colorimeter CR-400 / 410. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 1: Flowchart of the synthesis of Zn1-xCoxMoO4 0≤ x ≤0.3 by the polymerizable complex method 
 
3. Results and discussion 
3. 1. Structural characterization 
The thermally decomposion from precursor Zn0.7Co0.3MoO4 obtained by the drying the gel at 120 ° C was 
followed by thermal analysis (TGA/DTA). The measures were carried out under air flux at a temperature rate of 
2.5°C min-1. Figure 2 shows the typical thermal behavior of the precursor gel. The whole mass loss is about 
69%. 
The thermogram obtained can be divided into two parts: 
- The first weight loss about, 11.5 %, occurring in the range from room temperature to 130°C, is characterized 
by an endothermic phenomenon. It is attributed to the dehydration of surface water 
- The second weight loss about 57.5 % occurs in the range from 300°C to 450°C. It is characterized by two 
exothermic peaks, one at 424 °C, attributed to the combustion of organic matter and the other at 460 °C 
attributed to the combustion of the residual carbon and crystallization of molybdate. Beyond 500°C no loss of 
mass is observed what indicates that the decomposition is finished. 
M-Mo-cit 
 (NH
4
)
6
Mo
7
O
24
4H
2
O 
(Zn, Co)(NO3)
2
,6H
2
O 
 Citric acid (CA) 
pH =3 
Xerogel 
Calcination 
Powders Zn(1-x)CoxMoO4 
Evaporation / drying 
Precursor 
 
Pre -calcination  
J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. 
ISSN : 2028-2508 
CODEN: JMESCN 
 
3467 
 
 
Figure 2: TGA–DTA curves of the Zn0.7Co0.3MoO4 precursor 
 
X-ray diffraction patterns of powders treated at 500 °C for 2 hours are shown in Figure 3a. These diagrams 
show for x < 0.35 a mono-phased powder, isostructural with ZnMoO4 (ASTM: 01-070-5387).  
For x=0.35, we note the appearance of an additional phase isostructural with ß-CoMoO4 (ASTM 00-021-
0868).The Figure 3b shows the XRD patterns of Zn0.7Co0.3MoO4 treated at temperatures above 500 ° C. These 
diagram shows that this composition is stable above 500°C. 
 
  
Figure 3a: XRD patterns of Zn1-xCoxMoO4       Figure 3b: XRD patterns of Zn0.7Co0.3MoO4 
      (x ≤ 0.35) treated at500°C                     treated at different temperatures 
 
In the rest of the characterization, we considered only the Zn0.7Co0.3MoO4 compound. 
 
3.2. Infrared spectroscopy analysis (FTIR) 
The FT-IR spectrum of Zn0.7Co0.3MoO4 precursor powder treated at 500°C during 2 hours Figure 4 show the 
presence of the characteristic bands of Mo-O (749 - 948 cm-1) [18,19] the characteristic strips of vibration of the 
connection Zn-O (617-692 cm-1) [20], as well as that of Co-Mo observed at 435 cm-1 [21]. These results confirm 
that the cobalt is successfully incorporated in to the ZnMoO4 crystal structure.  
J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. 
ISSN : 2028-2508 
CODEN: JMESCN 
 
3468 
 
 
Figure 4: FT-IR spectra of Zn0.7Co0.3MoO4 precursor powders treated at 500°C 
 
 3.3. Microstructural characterization 
The Zn0.7Co0.3MoO4 powders obtained by calcination for 2h of precursor at 500 , 700 and 800 °C, were 
examined by scanning (SEM) and transmission (TEM) electron microscopy. The SEM micrographs (Figure 5) 
show that the powders obtained at 500 and 700°C are formed of agglomerates which size increases with 
increasing temperature. Examination of the surface of these agglomerates by transmission electron microscopy 
TEM (Figure 6) shows that these latter are formed of more or less spherical particles of sizes between 80 and 
160 nm. These agglomerates become more compact at 800 °C, which shows a certain degree of sintering of the 
powders at this temperature. According to these results, we note that the best morphology of Zn0.7Co0.3MoO4 is 
obtained by treatment at 500°C for 2 hours. 
 
 
 
 
 
 
 
 
 
Figure 5: SEM micrograph of Zn0.7Co0.3MoO4 treated at 500° C (a) / 700°C (b) and 800°C (c). 
 
 
 
 
 
 
 
 
 
Figure 6: TEM Micrographs of Zn0.7Co0.3MoO4 treated at 500 ° C (a) / 700 ° C (b) and 800 ° C (c). 
 
3.4. Characterization of the color of Zn0.7Co0.3MoO4 powders prepared at 500°C 
The variation of the colorimetric parameters (L a* b*) of Zn0.7Co0.3MoO4 according to the calcination 
temperature is given in the Figure 7.The evolution of the component (-b*) which characterizes the blue color 
presents a maximum at 700°C. The component (-b*) coupled with a relatively low value of the red component 
(a*) would translate the quality of Zn0.7Co0.3MoO4 with the aim of an application as blue pigment in the ceramic 
tint. 
J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. 
ISSN : 2028-2508 
CODEN: JMESCN 
 
3469 
 
 
Figure 7: Evolution of the colorimetric parameters of Zn0.7Co0.3MoO4 with the temperature. 
 
Conclusion 
During this work, we have been able to develop molybdates Zn1-xCoxMoO4 (0 ≤ x ≤ 0.3) by sol-gel method at 
500°C during 2 hours. The Zn0.7Co0.3MoO4 powders obtained at 500 and at 700°C are formed by grains of size 
between 80 and 160 nm. The colorimetric parameters (L, a*, b*) of this composition shows a high degree of 
bluing at 700 °C. Polymerizable complex method appears as a simple and reproducible method for preparing 
Zn1-xCoxMoO4 based pigments suitable for the coloring of tiles. 
 
References 
1. Wang B., Zhou K., Jiang S., Hu Y., and Gui Z., Poly. Adv. Technol. 25 (2014) 1419-1425. 
2.  Matar S.F., Largeteau A., Demazeau G., Solid State Sci. 12 (2010), 1779–1785. 
3. Mikhailik V. B., Kraus H., Wahl D., Ehrenberg H., Mykhaylyk M.S., Nucl. Instrum. Methods Phys. Res., 
Sect. A, 562 (2006) 513–516. 
4. Mikhailik V. B., Kraus H., Itoh M., Iri D. and Uchida M., J. Phys. Condens. Matter. 17 (2005) 7209 –7218. 
5. Zhou L.Y., Wei. J.S., Gong F. Z., Huang J. L., Yi L. H., J. Solid State Chem.181 (2008) 1337-1341. 
6. Zhou L.Y., Wei. J.S., Gong F. Z., Huang J.L., Yi L. H., Huang, W. Wang, Mater. Res. Bull., 44 (2009) 1411. 
7 Junjun Z., Tianqi Z., Lianchun Z., Shucai G., J. Photochem. Photobiol., A 314 (2016) 35–41. 
8. Sarkar B., Heavy Metals In The Environment, New York, (2002) 446-447. 
9. Daturi A M., Savary L., Costentin G., Lavalley J. C., Catal. Today 61 (2000) 231–236. 
10.  Schalkwijk W. A., Scrosati B., Advances in lithium-ion batteries, New York, (2002) 121-122. 
11. Maoine A., Devillers M., J. Solid State Chem. 177 (2004) 2339–2349. 
12. Rehren T., Archaeometry 43 (2001) 483–489.  
13. Wahba A. M., Imam N.G., Mohamed M. B., J. Mol. Struct. 1105 (2016) 61-69. 
14. Robertson L., Duttine M., Gaudon M., Demourgues A., Chem. Mater., 23 (9) (2011) 2419–2427 
DOI: 10.1021/cm200795p.  
15. Ehrenberg H., Weitzel H., Paulus H., Wiesmann M., Wltschek G., Geselle M., Fuess H., J. Phys. Chem. 
Solids 58 (1997) 153–160. 
16. Fontaine M. L., thesis of Toulouse University III, France (2004). 
17. Lakhlifi H., El Ouatib R., Er-Rakho L., Durand B., Guillemet-Fritsch S., MATEC Web of Conferences 5 
(2013) 03001. 
18. Bhattacharya S., Kar T., Bar A.K., Roy D., Graca M.P.F., Valente M.A., Sci. Adv. Mater. 3 (2011) 284–288. 
19 Keereeta Y., Thongtem T., Thongtem S., Mater. Lett. 68 (2012) 265–268. 
20. Sabet M., Salavati-Niasari M., Davar F., Mic. Nano Lett. 6 (2011) 904–908. 
21. Kianpour G., Niasari M. S. and Emadi H., Superlattices Microstruct. 58 (2013) 120–129. 
 
 
(2015) ; http://www.jmaterenvironsci.com 


English

Synthesis and physicochemical characterization of pigments based on molybdenum «ZnO-MoO3: Co2+»

Open Archive Toulouse Archive Ouverte

    OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible Any correspondence concerning this service should be sent  to the repository administrator: tech-oatao@listes-diff.inp-toulouse.fr This is a Publisher’s version published in: http://oatao.univ-toulouse.fr/23620  To cite this version:  Lakhlifi, H. and Benchikhi, Mohamed and El Ouatib, Rachida and Er-Rakho, Lahcen and Guillemet, Sophie  and Durand, Bernard  Synthesis and physicochemical characterization of pigments based on molybdenum «ZnO-MoO3: Co2+». (2015) Journal of Materials and Environmental Science - JMES, 6. 3465-3469. ISSN 2028-2508  Official URL: https://www.jmaterenvironsci.com/Document/vol6/vol6_N12/396-Lakhlifi.pdf  J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. ISSN : 2028-2508 CODEN: JMESCN  3465     Synthesis and physicochemical characterization of pigments based on molybdenum « ZnO-MoO3: Co2+»  H. Lakhlifi1, M. Benchikhi1, R. El Ouatib1*, L. Er-Rakho1,  S. Guillemet-Fritsch2 and B. Durand2 1 Laboratoire de Physico-Chimie des Matériaux Inorganiques, Département de chimie, Faculté des Sciences Ain Chock, Université Hassan II Casablanca, Maroc 2 Institut Carnot CIRIMAT, CNRS Université de Toulouse, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.  *Corresponding Author. E-mail: elouatib@yahoo.fr; Tel: (+212661170710)  Abstract  Molybdates Zn1-xCoxMoO4 (0≤ x ≤0.3) were elaborated by the Sol-Gel method with pH=3.The results obtained by DRX show a single-phase domain starting from 500°C for x ≤ 0.3 isostructural to ZnMoO4.The powder of Zn0.7Co0.3MoO4 treated at 500°C and 700°C is formed by nano-sized primary crystallites of size between 80 and 160 nm. The colorimetric parameters (L a* b*) of powders obtained at 700°C present a degree of high bluing.  Keywords: Molybdate, Sol–gel, Nanometric, Chromophore, Morphology, Pigment.  Introduction The molybdates of divalent elements AMoO4, exhibits numerous structural varieties and especially, polymorphisms with phase transition [1, 2]. These compounds train a big family of oxides being the object of search both in the field of the applied sciences and that of the fundamental sciences. The intrinsically luminescent colorless molybdates, MgMoO4, ZnMoO4 and PbMoO4 [3, 4], are doped with rare earth in order to obtain phosphors [5-7]. Molybdates AMoO4 with A=Ni2 +, Co2 +, Fe2+, Mn2 +, are very studied as catalysts for oxidation of organic compounds [8,9]. Recent studies show that, in tungsten doped copper molybdate CuMo1-xWxO4, the temperature of the structural transition α     γ is dependent upon the tungsten content [10,11]. These two polymorphs have different colors, respectively green and brown-red. It is thus possible to envisage the use of this pigment as marker of temperature. The objective of our work, is to elaborate Zn1-xCoxMoO4 pigments. The element cobalt appears to us to be a very promising chromophore for the synthesis of new pigments. The element cobalt appears to us to be a very promising chromophore for the synthesis of new pigments. Indeed, this element is responsible for different tints following the environment which it occupies. In tetrahedral site, it is at the origin of the blue color [11, 12]. In octahedral regular site, it is responsible for a pink colorb [12,13], while a purple tint seems to be obtained when the octahedral site is deformed [10].  The literature also mentions the possibility of the cobalt to take a trigonal bipyramidal based coordination. In molybdate ZnMoO4, the Zn2+ ions are located both in octahedral and in triangular bipyramidals sites [14]. The presence of cobalt in these sites would induce distinguishable colors resulting of the transitions between cobalt d-levels. Several synthesis methods have been developed to obtain the zinc molybdate, such as the solid method involving solid state reactions between copper and molybdenum oxides. Powders obtained by this method are generally constituted of large-sized particles with low specific surface [15]. The Co-precipitation method has the disadvantage of adsorption at the surface of the particles of foreign ions difficult to remove [16]. To elaborate J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. ISSN : 2028-2508 CODEN: JMESCN  3466  our samples of Zn1-xCoxMoO4 (x ≤ 0.3), we opted for the polymerizable complex method, that we have already used to prepare the cobalt molybdate [17].  2. Materials and Methods Commercial reagents used for the synthesis of our compounds are: ammonium heptamolybdate (NH4) 6Mo7O24, 4H2O (Acros, 99%), metal nitrates ((Zn, Co) (NO3)2, 6H2O) (Aldrich, 98%), citric acid (Acros, 98%) and ammonia (NH4OH 28% pure, density = 0.91).The aqueous solutions of metals salt0.2M and ammonium hyptamolybdate 0.2M are mixed in stoichiometric proportions. The citric acid is then introduced so that the molar report A/M is equal 3 and the pH is fixed to 3. The precursors are obtained after evaporation and drying at 120 ° C for 12 h. These precursors are pre-calcined at 300 °C for 12 hours under air. The black powders obtained were treated at temperature ranging from 500 to 800 °C. The various steps of this synthesis are given in the Figure 1. The obtained powders were characterized by thermal analysis ATD-ATG (SETARAM TG-DTA 92), by X-rays diffraction (Brucker AXS D4λCu Kα = 1.5418 Å), by scanning (JEOL-JSM6400) and transmission (JEOL 2010) electronics microscopies. The colorimetric parameters (L a * b *) were measured in the system CIE Lab by means of a colorimeter CR-400 / 410.                   Figure 1: Flowchart of the synthesis of Zn1-xCoxMoO4 0≤ x ≤0.3 by the polymerizable complex method  3. Results and discussion 3. 1. Structural characterization The thermally decomposion from precursor Zn0.7Co0.3MoO4 obtained by the drying the gel at 120 ° C was followed by thermal analysis (TGA/DTA). The measures were carried out under air flux at a temperature rate of 2.5°C min-1. Figure 2 shows the typical thermal behavior of the precursor gel. The whole mass loss is about 69%. The thermogram obtained can be divided into two parts: - The first weight loss about, 11.5 %, occurring in the range from room temperature to 130°C, is characterized by an endothermic phenomenon. It is attributed to the dehydration of surface water - The second weight loss about 57.5 % occurs in the range from 300°C to 450°C. It is characterized by two exothermic peaks, one at 424 °C, attributed to the combustion of organic matter and the other at 460 °C attributed to the combustion of the residual carbon and crystallization of molybdate. Beyond 500°C no loss of mass is observed what indicates that the decomposition is finished. M-Mo-cit  (NH4)6Mo7O244H2O (Zn, Co)(NO3)2,6H2O  Citric acid (CA) pH =3 Xerogel Calcination Powders Zn(1-x)CoxMoO4 Evaporation / drying Precursor  Pre -calcination  J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. ISSN : 2028-2508 CODEN: JMESCN  3467   Figure 2: TGA–DTA curves of the Zn0.7Co0.3MoO4 precursor  X-ray diffraction patterns of powders treated at 500 °C for 2 hours are shown in Figure 3a. These diagrams show for x < 0.35 a mono-phased powder, isostructural with ZnMoO4 (ASTM: 01-070-5387).  For x=0.35, we note the appearance of an additional phase isostructural with ß-CoMoO4 (ASTM 00-021-0868).The Figure 3b shows the XRD patterns of Zn0.7Co0.3MoO4 treated at temperatures above 500 ° C. These diagram shows that this composition is stable above 500°C.    Figure 3a: XRD patterns of Zn1-xCoxMoO4       Figure 3b: XRD patterns of Zn0.7Co0.3MoO4       (x ≤ 0.35) treated at500°C                     treated at different temperatures  In the rest of the characterization, we considered only the Zn0.7Co0.3MoO4 compound.  3.2. Infrared spectroscopy analysis (FTIR) The FT-IR spectrum of Zn0.7Co0.3MoO4 precursor powder treated at 500°C during 2 hours Figure 4 show the presence of the characteristic bands of Mo-O (749 - 948 cm-1) [18,19] the characteristic strips of vibration of the connection Zn-O (617-692 cm-1) [20], as well as that of Co-Mo observed at 435 cm-1 [21]. These results confirm that the cobalt is successfully incorporated in to the ZnMoO4 crystal structure.  J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. ISSN : 2028-2508 CODEN: JMESCN  3468   Figure 4: FT-IR spectra of Zn0.7Co0.3MoO4 precursor powders treated at 500°C   3.3. Microstructural characterization The Zn0.7Co0.3MoO4 powders obtained by calcination for 2h of precursor at 500 , 700 and 800 °C, were examined by scanning (SEM) and transmission (TEM) electron microscopy. The SEM micrographs (Figure 5) show that the powders obtained at 500 and 700°C are formed of agglomerates which size increases with increasing temperature. Examination of the surface of these agglomerates by transmission electron microscopy TEM (Figure 6) shows that these latter are formed of more or less spherical particles of sizes between 80 and 160 nm. These agglomerates become more compact at 800 °C, which shows a certain degree of sintering of the powders at this temperature. According to these results, we note that the best morphology of Zn0.7Co0.3MoO4 is obtained by treatment at 500°C for 2 hours.          Figure 5: SEM micrograph of Zn0.7Co0.3MoO4 treated at 500° C (a) / 700°C (b) and 800°C (c).          Figure 6: TEM Micrographs of Zn0.7Co0.3MoO4 treated at 500 ° C (a) / 700 ° C (b) and 800 ° C (c).  3.4. Characterization of the color of Zn0.7Co0.3MoO4 powders prepared at 500°C The variation of the colorimetric parameters (L a* b*) of Zn0.7Co0.3MoO4 according to the calcination temperature is given in the Figure 7.The evolution of the component (-b*) which characterizes the blue color presents a maximum at 700°C. The component (-b*) coupled with a relatively low value of the red component (a*) would translate the quality of Zn0.7Co0.3MoO4 with the aim of an application as blue pigment in the ceramic tint. J. Mater. Environ. Sci. 6 (12) (2015) 3465-3469                                                    Lakhlifi et al. ISSN : 2028-2508 CODEN: JMESCN  3469   Figure 7: Evolution of the colorimetric parameters of Zn0.7Co0.3MoO4 with the temperature.  Conclusion During this work, we have been able to develop molybdates Zn1-xCoxMoO4 (0 ≤ x ≤ 0.3) by sol-gel method at 500°C during 2 hours. 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Synthesis and physicochemical characterization of pigments based on molybdenum «ZnO-MoO3: Co2+»

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