Preparation of bismuth oxycarbodiimide Bi2O2NCN by a liquid-phase process

Bismuth oxychalcogenides such as Bi 2 O 2 Ch ( Ch = S, Se, and Te) have attracted significant attention in the field of materials science because of their unique structure, chemical stability, and high carrier mobility, which make them potential candidates as novel functional materials for various applications. Recently, it was reported that an analogous material of Bi 2 O 2 Ch , bismuth oxycarbodiimide (Bi 2 O 2 NCN), can be synthesized and used in photoelectrodes. Bi 2 O 2 NCN contains the carbodiimide ion (NCN 2− ), which is a well-known pseudochalcogenide ion, instead of a chalcogenide ion. However, the preparation of metal (oxy)carbodiimides, including Bi 2 O 2 NCN, is limited to a few methods such as solid-phase metathesis. In this study, a simple liquid-phase preparation method for Bi 2 O 2 NCN was developed. Bi(NO 3 ) 3 ·5H 2 O, which was used as the Bi precursor, formed insoluble basic bismuth nitrate clusters when reacted with water under neutral pH conditions. Strong acidic conditions were required for the complete dissolution of these clusters. When the Bi precursor and H 2 NCN were homogeneously dissolved under strongly acidic conditions, and ammonia water was added, Bi 2 O 2 NCN was obtained with impurities. In contrast, when basic bismuth nitrate was undissolved, and ammonia water was added in the presence of H 2 NCN in an inhomogeneous system, basic bismuth nitrate clusters were rapidly converted to Bi 2 O 2 NCN with high crystallinity and purity. This method can be potentially applied to the preparation of various metal (oxy)carbodiimides by the liquid-phase process because of its simplicity, low cost, and low energy consumption. Graphical Abstract Highlights Bismuth oxycarbodiimide was prepared using bismuth nitrate pentahydrate and cyanamide as precursors. Bismuth oxycarbodiimide, which was obtained from a homogeneous solution in which the Bi precursor was completely dissolved, contained impurities. In an inhomogeneous system that contained dispersions of insoluble basic bismuth nitrate clusters, bismuth oxycarbodiimide was rapidly obtained via basification in the presence of cyanamide. The bismuth oxycarbodiimide prepared via an inhomogeneous liquid-phase process showed high purity and crystallinity.