The precisely controlled synthesis of a specific morphology is proved to be highly effective for enhancing sensing performance of functional micro- and nano-materials. Thus, a comprehensive understanding of the effect of synthesis conditions on morphology evolution is of great importance. In this paper, by using In2O3 as an example, we demonstrate the great effect of supersaturation on the morphology evolution during the growth process. Under vapour-phase synthesis, by varying positions of product collection, the amount of the starting materials, and reaction temperatures, a continuous two-step route consisting of ammonolysis and re-oxidation processes was developed for the morphology evolution of several kinds of In2O3, including octahedron strings, nanowires, crystal chains, lollipop-like structures, and particles. The controlled supersaturation of the In2O3 vapour was eventually proved to be a decisive factor for the formation of various In2O3 morphologies. Furthermore, we evaluated the gas-sensing properties of the three kinds of one-pot synthesized In2O3, indicating a shape-dependent relationship with sensing performance. The present work not only offers a unique strategy to control supersaturation in vapour-phase synthesis, but also provides an opportunity to deeply understand the morphology-dependent sensing performance.
Jing Yang,Yingdan Cui,Mingyang Chen,Yan Wang,Shijie Xu,Songgu Wu,Jingkang Wang,Junbo Gong
Spherulitic growth, categorized as central multidirectional growth and unidirectional growth via small-angle branching, has increasingly been explored as a method to improve the flowability and bulk density of needle-like crystals. However, the formation of two categories of spherulites in solutions is still unclear. In this work, the formation mechanism of two categories of spherulite was studied in a supercooled nitroguanidine (NQ) aqueous solution with a small amount of gelatin. It is proposed that spherulitic growth depends on the initial morphology of the crystallite, wherein the gelatin concentration, temperature, and initial supersaturation play a vital role. Gelatin can significantly inhibit NQ nucleation, promote branching, and modify the morphology of NQ subunits. At high initial supersaturation and low temperatures, the aspect ratio of the crystal precursor increases and branching is accelerated, so that the lateral faces provide more branching sites than the end faces to promote the unidirectional growth. In comparison, high temperatures promoting the multipoint branching should be mainly responsible for the formation of cauliflower-like spherulites. Furthermore, the bulk densities of the cauliflower-like and compact spherulites of NQ are about triple those of needle-like crystals and their evolutions were observed. Compared with the reported methods, the macromolecule-induced spherulitic growth of NQ without an organic solvent is a green method and will have a bright future for the design and fabrication of other organic spherulites.
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