Green complex pigments with TiO2@CoTiO3 core–shell structure were prepared through calcination of precursors obtained from the precipitation of Co2+ on TiO2 particles. The synthesized pigments were characterized by colorimetry, near-infrared diffuse reflectance spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet–visible (UV–vis) spectroscopy. The pigments were found to consist of a rutile TiO2 core and outer ilmenite CoTiO3 shell. The green pigments with good color properties could be obtained via calcination of the precursors at 800 °C. The pigments with Co/Ti ratio of 0.4 had the highest green component value and exhibited good color properties (L*=49.51, a*=−34.58, b*=5.53). The color properties could be tuned by just changing the Co/Ti ratio. The as-prepared complex pigments exhibited an enhanced near-infrared reflectance compared with pure CoTiO3 pigments and also exhibited better color properties than the mixed pigments of TiO2 and CoTiO3. Further, the complex pigments had much lower consumption of cobalt compared to pure CoTiO3 and Co2TiO4 pigments. The special core–shell structure was found to be responsible for the enhanced near-infrared reflectance and good color properties.

Blue TiO2/CoAl2O4 complex pigments were prepared through calcination of precursors from the precipitation of Al3+ and Co2+ on TiO2 particles in sequence. The synthesized powders were characterized by colorimetry, near-infrared diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and ultraviolet-visible spectroscopy. The pigments were found to have composite phases composed of rutile TiO2 and spinel CoAl2O4. The bright blue pigments having good color properties could be obtained via calcination of the precursors at 1000 °C. As the mass of CoAl2O4 increased to 40 wt% of TiO2, the pigments presented good color properties (L* = 53.43, a* = −4.75, b* = −41.78) and the results showed little variation with an increase in the CoAl2O4 content. In comparison to the pure CoAl2O4 pigments, the as-prepared pigments with a CoAl2O4/TiO2 mass ratio of 0.4 exhibited an enhanced near-infrared reflectance and also showed better color properties relative to the mixed pigments of TiO2 and CoAl2O4.

•Pigments had regular morphology and narrow size distribution ranging from 0.5 to 1 μm.•The pigments had high luminosity values and good color properties.•Pigment showed homogeneous dispersion without any milling and sieving.•Pigments had high NIR reflectance.•The existence of Cr6+ would reduce significantly color properties and NIR reflectance.Highly dispersed (Cr, Sb)-co-doped rutile nonwhite pigments with high near-infrared (NIR) reflectance were prepared by introducing dispersants during precursor hydrolysis. The pigment properties were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoemission spectroscopy, diffuse reflectance spectroscopy, Raman spectroscopy, and colorimetry. The pigments had rutile phase composition and narrow size distributions of 0.5 μm–1 μm after calcination at 700 °C. Co-doping with Cr and Sb restrained the generation of hexavalent chromium in the rutile lattice. The co-doped pigments had good color properties and high NIR reflectance because of the absence of Cr6+. The pigments had high tinting strength, and a good hue for PE flake was attained by adding 1% pigments. An approximately 10 °C decrease in temperature was obtained for the inner surface of ceramic tiles coated with the co-doped pigments under 30 min of irradiance.

Monodisperse Fe3O4@SiO2 nanoparticles are prepared using hydrazine as a catalyst via a biphase approach without any alcohols or surfactants. Fe3O4 seeds can be dispersed well in this system. The sizes of Fe3O4@SiO2 nanoparticles with a single core could be regulated from 20 nm to 50 nm corresponding to SiO2 shell thickness from 3 nm to 17 nm. Core-free SiO2 nanoparticles are not observed in this system. The coating process can be implemented at a temperature greater than 90 °C, which results in a short coating duration from 2 h to 8 h for different shell thicknesses. Hydrazine can prevent the Fe3O4 core from oxidization during coating at this temperature. Fe3O4@SiO2 nanoparticles have high chemical stability and magnetic saturation. A plausible formation mechanism of these nanoparticles is also presented.

Monoclinic vanadium dioxide (VO2) particles are prepared via the thermolysis of a vanadyl ethylene glycolate precursor in an atmosphere of air. Monoclinic VO2 particles can be obtained at temperatures above 170 °C in an oven. The synthetic VO2 product exhibits high crystallinity and features a pure monoclinic phase and composition. The expected metal–insulator transition at around 68 °C is revealed by differential scanning calorimetry, variable-temperature X-ray diffraction and temperature-dependent resistance curves. The exothermic decomposition of the precursor elevates the temperature of the sample and results in a final sample consisting of monoclinic VO2 and having a high crystallinity at room temperature.

Cr-doped rutile pigments were prepared by calcination of doped rutile precursors resulting from the hydrolysis-precipitation method. The pigment properties were investigated by X-ray diffraction, Thermogravimetry–differential scanning calorimetry, scanning electron microscopy, energy dispersive spectroscopy, diffuse reflection spectroscopy, Raman spectroscopy, and colourimetry. The pigments were found to have a rutile phase composition. Rutile pigments with good colour properties can be acquired by calcination from 500 °C to 900 °C. The pigment with 1.25% dopant and calcination at 700 °C presented optimal colour properties (L* = 75.46, a* = 15.24, b* = 39.46). The pigments presented high dispersion and could be dispersed directly into polyurethane paint and polyurethane epoxy resin without further modification.Highlights► Rutile was used as a precursor to prepare a Cr-doped rutile pigment. ► Calcination was implemented at low temperature (500–900 °C). ► The pigments presented good colour properties. ► The pigments showed homogeneous dispersion without any milling and sieving. ► The pigments were photocatalytically inert.

An amorphous free-impurity TiO2 sol was synthesized only by means of ultrasonic dispersing of Ti(OH)4 precipitation without any peptizing agents. Anatase sol was obtained by hydrothermally treating the amorphous TiO2 sol. Photocatalytic tests showed that the amorphous sol exhibited higher photocatalytic activity for the photodegradation of methylene blue (MB) under visible light and UV irradiation than anatase sol and P25 TiO2. The photocatalysts were characterized by UV–visible spectroscopy, Raman spectrometer, photoluminescence (PL), FTIR, TEM, XRD, and XPS. The results showed the peroxide titanium complexes were formed on TiO2 sol particles sensitized with H2O2. More peroxide complexes and stronger vis absorption were observed for the amorphous TiO2 sol sensitized with H2O2.The sensitization of H2O2 would completely quench PL of the amorphous sol, but little impact on the anatase sol. The surface structure with fewer physisorbed water molecules facilitated the sensitization of H2O2 to the amorphous TiO2 sol particles, which resulted in the generation of more OH radicals and higher photocatalytic activity under both visible light and UV irradiation.

Monoclinic vanadium dioxide (VO2) particles are prepared via the thermolysis of a vanadyl ethylene glycolate precursor in an atmosphere of air. Monoclinic VO2 particles can be obtained at temperatures above 170 °C in an oven. The synthetic VO2 product exhibits high crystallinity and features a pure monoclinic phase and composition. The expected metal–insulator transition at around 68 °C is revealed by differential scanning calorimetry, variable-temperature X-ray diffraction and temperature-dependent resistance curves. The exothermic decomposition of the precursor elevates the temperature of the sample and results in a final sample consisting of monoclinic VO2 and having a high crystallinity at room temperature.