Sol-gel synthesis and properties of novel inorganic chromophore based on tetrahedral coordination of Cu2+in A(1-x)CuxMoO4:(A=Co, Mn)

This paper reports synthesis and characterization of a series of novel and environment-friendly color pigments based on Cu doped cobalt and manganese molybdate with the general formula A1-xCoxMoO4 (A = Co, Mn; 0 <= x <= 0.075). The synthesized pigments exhibited blue-green/purple (Co, Cu) and different beige-yellows (Mn, Cu). The obtained powders through the sol gel route are characterized using thermal analysis (TGA-DTA), X ray diffraction (XRD), Infrared (IR) and UV visible spectroscopies. Morphology of obtained powders was examined by scanning electron microscopy (SEM). The surface specific area was calculated using the Bru-nauer-Emmett-Teller analysis. Colorimetric parameters (CIE L*a*b*) are measured to study the color evolution with rate substitution (x). All compounds crystallize in the monoclinic system with C2/m space group Belong to beta-AMoO4. A(1-x)CuxMoO4 (A = Co, Mn) powders are formed of small juxtaposed with platelets dimensions and residual porosity is presented. The specific surface area (BET) of powders increases as a function of the substi-tution of Cu2+ in AMoO4, with the highest value found for the Co0.925Cu0.075MoO4 powder at around 14.05 m2/g. Colorimetric parameters (L*a*b*) of Co(1-x)CuxMoO4 powders present a maximum value of (-b*) parameter for a rate of 0.05, which is responsible of the blue-purple color. While for Mn(1-x)CuxMoO4 compounds, these parameter is not changed. By introducing element Cu into the CoMoO4 matrix, the color of the pigment was successfully changed from purple to green and from beige to yellow into the MnMoO4 matrix, indicating that doping can control the color of the pigment. Based on the results of optical properties (Eg between 2.36 and 2.88 eV), A(1-x)CuxMoO4 solid solutions can be considered as semiconducting materials.