A holmium molybdate ceramic pigment with ‘allochroic effect’ was prepared via mechanical activation-assisted solid-state reaction. The effects of mechanical activation mode and time as well as sintering temperature on the properties of synthesized holmium molybdate pigment were investigated by laser particle size analysis, simultaneous thermal analysis, X-ray diffraction and scanning electron microscopy, respectively. The color properties and allochroic effect of the synthesized pigments were evaluated by ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis) and colorimetry. In addition, the high-temperature stability and chemical stability of the pigments were also investigated. The results show that a sole phase of holmium molybdate can be obtained from mixed precursors ground at 1 h and sintered at 900 ℃ for 3 h, and the sintering temperature is reduced by 100 ℃ , compared to that from each precursor ground separately for 2 h and then mixed or the mixed precursors unground. This is because mechanical activation pretreatment can effectively reduce the size and crystallinity of mixed precursor particles and enhance its solid-phase reaction activity, thus leading to the decrease of solid-phase reaction temperature. In addition, the pigment obtained from mixed precursors ground for 2 h has better color performance and allochroic effect under different illuminants. It is indicated that the allochroic effect of holmium molybdate pigment occurs due to the rich energy level structure of holmium ions in the visible range and the difference between relative spectral power distributions under different light sources. Meanwhile, holmium molybdate pigment can be used as a potential functional pigment in ceramic decoration and other related fields due to its high-temperature stability and chemical stability.

SrTiO₃ nanoparticle (NP) photocatalyst was synthesized with a facile and environmental-friendly hydrothermal method using tetrabutyltitanate, strontium oxide, and ethanolamine as precursors at low temperature without alkali as mineralizer for the first time. The SrTiO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and N₂ Brunauer–Emmett–Teller (BET) method. The SrTiO₃ catalyst synthesized at 120 ℃ (STO-120) exhibited the highest photocurrent intensity among the samples synthesized at different hydrothermal temperatures. The high photocatalytic performance of STO-120 was mainly attributed to the more homogeneous and minimum nanoparticle size, the highest surface area, and the maximum light absorption property among the four different samples. This work presented an applicable and facile method to fabricate a highly active and stable SrTiO₃ photocatalyst for organic pollutant degradation.