Progress made on synthesis of two dimensional materials via the molten salts method
On May 30th, the new findings by Professor Jun Zhou’s research group of Wuhan National Lab of Optoelectronics was published on-line in Nature Communications (Nature Communications 2017, DOI: 10.1038 / ncomms15630). The title of this paper is “Rapid mass production of two dimensional metal oxides and hydroxides via the molten salts method”. Zhimi Hu, Xu Xiao and Huanyu Jin are the co-first authors, and prof. Jun Zhou is the corresponding author of the paper.
Two-dimensional (2D) materials with atomic layer thickness have received extensive attention due to their unique physical and chemical properties. Previously, scientists reported a variety of methods to prepare two-dimensional materials, including exfoliation ((mechanical exfoliation, liquid phase exfoliation, electrochemical exfoliation, etc.), chemical vapor deposition and wet chemistry. But how to achieve efficient, fast, low cost, large-scale two-dimensional materials preparation remained a conundrum for the researchers.
In the previous research, Professor Jun Zhou and Professor Jiang Tang worked with Professor Yury Gogotsi of Drexel University in the United States by using crystal salt (NaCl, KCl, etc.) as template to synthesize non-layer structure two dimensional transition metal oxide and nitride (Nat. Commun. 2016, 7, 11296; ACS Nano 2017, 11, 2180). They noted that salt exists in the form of "bare ions" when in molten state so as to avoid the ion desolvation in traditional chemical synthesis and reduce the activation energy of reaction, thus rendering possibility for achieving the rapid synthesis of materials. According to this characteristic, Professor Jun Zhou’s research group designed salt reaction system (LiNO3、NaNO3、KNO3, etc.) at a low melting point, which is adding the reaction precursor under the salt molten state for one minute and then simply washing with water (without centrifugation), the target product can be obtained (in the above picture). At the same time, the type of intercalation ion can be regulated simply by changing the type of the cation or anion of salt. In this way, the research group successfully prepared a variety of cation intercalation type of two dimensional transition metal oxides (including Na0.55Mn2O4·1.5H2O, K0.27MnO2·0.54H2O, Li2WO4 and Na2W4O13) and anionic intercalation transition metal hydroxide (including Zn5(OH)8(NO3)2·2H2O and Cu2(OH)3NO3), the synthesized materials show significant application prospects in some fields such as electrochemical energy storage devices and ion adsorption of heavy metal. This method is simple, rapid (minute-level), high yield (~ 62%) and has the potential of synthesizing two-dimensional material in large-scale. In the follow-up study, the group will further expand the universality of the method in the synthesis of two-dimensional material system and continue to study the synthesis mechanism in depth.
The research was supported by projects such as the National Natural Science Foundation of China (NSFC), the "10,000 Talent Plan", etc.. The research also received the support and help from Dr. Liang Huang, lecturer of Wuhan National Lab of Optoelectronics, Feng Guang, Professor of School of Energy and Power Engineering, Yanrong Zhang, Professor of Institute of Environmental Science, etc..
The paper link: https: //www.nature.com/articles/ncomms15630