Fundamental study on the synthesis of transition metal nanoparticles for the environmentally benign process using supercritical water

2019 Fiscal Year Research-status Report

• Project/Area Number: 19K15348
• Research Institution: Tohoku University
• Principal Investigator: 成 基明 東北大学, 未来科学技術共同研究センター, 助教 (30747259)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: metal / nanoparticle / EOS / flow reactor / Thermodynamics / kinetics / fugacity / supercritical

Outline of Annual Research Achievements

The purpose of this study is to develop an environmentally benign process that can present a new paradigm on the synthesis of metal nanoparticles. Specifically, this study analyzes the factors contributing to the reaction through statistical thermodynamics and molecular simulations along with classical equation of state. It applies them to actual reaction system to establish the underlying technology for metal nanoparticle synthesis.
In 2019, the first goal was to calculate reliable values for the chemical potential between water and the reducing agent, hydrogen. Even if there is no specific experimental data, each fugacity can be obtained under supercritical conditions with Predictive Soave-Redlich-Kwong Equation of State or Volume-Translated Peng-Robinson EOS, which provides interaction parameters and group contribution technique between molecules. Using the Dortmund Data Bank Software Package, the fugacity of water and hydrogen according to the temperature and pressure of subcritical-supercritical conditions was determined, and the reduction potential of hydrogen in the reaction was estimated through the ratio of two fugacities. The corresponding reference values published in the past were confirmed using those estimated data. In particular, even in a system in which little hydrogen was loaded, the reaction was performed until the equilibrium state was reached so that a pure metal phase without oxides was obtained. Thus, the calculations and experimental results satisfy both thermodynamic and kinetic theory, so the basic concept of this study was satisfied.

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

This study is going smoothly as initially planned. The first goal is to calculate the chemical potential between hydrogen and water, which was easily obtained using PSRK and VTPR EOS. Statistical thermodynamic approaches were also planned, and now it is currently in preparation. Second, based on the above results, those parameters are applied to the real reaction system using a batch-type reactor and further evaluated by kinetic analysis. Lastly, it is to find an organic modifier that fits well with the metal nanoparticles, which has led to the selection of candidate groups by organizing reported references.

Strategy for Future Research Activity

In order to accomplish the purpose of this study, the detailed plan of the research is divided into three categories as follows.
1) Thermodynamics: In 2020, more complicated reaction system will be analysed. First of all, the system concerning Co or Fe which needs to suppress the secondary oxidation further will be examined. Moreover, calculation and analysis will be attempted in the presence of organic modifiers or co-solvents. The use of statistical thermodynamic approaches or molecular simulations, which are non-classical interpretations, will also be considered when it is difficult to predict those reactions with a classical approach.
2) Kinetics: A flow-type reactor capable of in-situ modification will be set up based on the results obtained from the equilibrium condition, and a non-equilibrium reaction will be tried to obtain nano-sized metal particles. Finally, the reaction mechanism will be studied at the final stage for the optimization of the process.
3) In-situ modification: In 2020, it will be examined the stability of the organically modified metal nanoparticles with the analysis of the adsorption and desorption behavior of the modifiers., and finally, dispersion of the nanoparticles in the media such as polymers or organic solvents will be performed.