Synthesis of the Zn1.9Cu0.1SiO4 pigment via the sol–gel and coprecipitation methods

The Zn1.9Cu0.1SiO4 pigment was obtained by two variants of “soft” chemistry methods: using sol–gel synthesis in ethanol from TEOS and zinc and copper acetates and by coprecipitation of hydroxosilicate from an aqueous solution of zinc acetate and copper formate with sodium silicate. Thermal behavior of precursors, characterization of intermediate and final synthesis products were carried out by DSC, XRD, electron microscopy, colorimetry, IR, and UV-Vis-NIR spectroscopy. It is shown that the sequence of the phase formation of the synthesis product is determined by the characteristics of the initial solutions. It was established for the first time that when using the sol–gel method, the sequence of structural transformations is caused by the removal of the organic components and the destruction of the three-dimensional polymer network ≡Si–O–Si≡. In the coprecipitation method, crystallization occurs after the removal of the organic components and structurally bound water. It is shown that a feature of this method is the simultaneous crystallization of two structural modifications Zn1.9Cu0.1SiO4, the metastable phase transforms into the willemite structure with a further increase in the temperature. It was found that well-crystallized single-phase Zn1.9Cu0.1SiO4 samples synthesized by these methods can be obtained by annealing at 800 °C for 10 h. The differences in the shape of the samples depend on the morphological and dimensional variations of the particles. UV-Vis-NIR spectra show the broad band with a maximum at about 760 nm corresponding to two electronic d–d transitions: 2B1g → 2Eg and 2B1g → 2B2g.