Xie Bo, Numako Chiya, Naka Takashi, Takami Seiichi
Department of Materials Process Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
Department of Chemistry, Graduate School of Science, Chiba University, Chiba 263-8522, Japan.
Dalton Trans. 2023 Nov 14;52(44):16285-16296. doi: 10.1039/d3dt03086e.
Spinel-type inorganic pigments with intensive color and chemical/thermal stability are showing extensive applications that could be further broadened by color manipulation and improvement of the material properties through nanosizing. In this study, we report the supercritical hydrothermal synthesis of nonstoichiometric spinel-type cobalt gallate nanoparticles (Co-Ga NPs) with controlled color. Without the conventional calcination procedure, NPs with greenish-blue, blue, and yellowish-green colors were synthesized from precursor solutions at pH 7, 9, and 11, respectively, with a low Co/Ga molar ratio of 0.25. X-ray diffraction, scanning/transmission electron microscopy, and inductively coupled plasma-atomic emission spectroscopy methods suggest that the products were spinel-type cobalt gallate NPs with high crystallinity and a nonstoichiometric composition. Based on an X-ray absorption fine structure investigation, the prepared nonstoichiometric Co-Ga NPs were found to have different cationic configurations from stoichiometric CoGaO produced by a solid-state reaction during calcination. Meanwhile, the degrees of distortions at tetrahedral and octahedral sites in the NPs were evaluated by Raman spectroscopy. In particular, nonstoichiometric Co-Ga NPs with a blue color were prepared without calcination for the first time and were found to have lower tetrahedral cobalt occupancy but comparable octahedral cobalt occupancy and larger polyhedral distortions at tetrahedral sites when compared to calcined CoGaO. We also discuss strategies that could realize Co-Ga NPs with a more brilliant blue color using the present technique based on an investigation of the growth process.
具有强烈颜色和化学/热稳定性的尖晶石型无机颜料展现出广泛的应用，通过纳米尺寸调控颜色和改善材料性能，其应用范围可能会进一步拓宽。在本研究中，我们报道了具有可控颜色的非化学计量尖晶石型钴镓酸盐纳米颗粒（Co-Ga NPs）的超临界水热合成。无需传统的煅烧程序，分别在pH值为7、9和11的前驱体溶液中，以0.25的低Co/Ga摩尔比合成了蓝绿色、蓝色和黄绿色的纳米颗粒。X射线衍射、扫描/透射电子显微镜和电感耦合等离子体原子发射光谱法表明，产物为具有高结晶度和非化学计量组成的尖晶石型钴镓酸盐纳米颗粒。基于X射线吸收精细结构研究，发现制备的非化学计量Co-Ga NPs与煅烧过程中通过固态反应生成的化学计量CoGaO具有不同的阳离子构型。同时，通过拉曼光谱评估了纳米颗粒中四面体和八面体位点的畸变程度。特别是，首次在无煅烧的情况下制备了蓝色非化学计量Co-Ga NPs，发现与煅烧后的CoGaO相比，其四面体钴占有率较低，但八面体钴占有率相当，且四面体位点的多面体畸变较大。基于对生长过程的研究，我们还讨论了使用本技术实现具有更鲜艳蓝色Co-Ga NPs的策略。
