B(OH)4 hydration and association in sodium metaborate solutions

Significance 

In relation to the excellent performance of borohydride in storing hydrogen gas, aqueous sodium metaborate solutions have attracted attention in matters regarding their application in direct borohydride fuel cell technologies. Previous studies have already unveiled the wood preservation abilities, fire retardant attributes and the impact on the fuel performance of pressurized water nuclear reactors that borate ion hydration promulgates due to the borate mineral sedimentation and crystallization process. Despite having several techniques applied, the polyborate distribution and solid–liquid equilibrium prediction in aqueous borate solutions are still unsatisfactory. Several studies reported borate ion association in aqueous sodium metaborate solutions over a wide range of salt concentrations. However, no clear atomic/molecular level information about the borate ion association is available.

Dr. Yongquan Zhou from Qinghai Institute of Salt Lakes, Chinese Academy of Science and his colleagues at Fukuoka University in Japan studied borate ion hydration and association in sodium metaborate solutions over a wide salt concentration by X-ray diffraction and empirical potential structure refinement. Their work is currently published in the research journal, Phys. Chem. Chem. Phys.

The research team recrystallized sodium metaborate from distilled water. The x-ray scattering intensities of the empty capillary and the sample solutions were then measured under ambient conditions with an X-ray diffractometer and a curved imaging plate detector. The researchers then integrated the two-dimensional diffraction pattern of the samples recorded on an imaging plate, to one-dimensional intensities with a 2DP program. Empirical potential structure refinement modelling that utilized the Monte Carlo style approach to diminish the difference between experimental diffraction data and of those generated from the simulation of the structure was conducted. Eventually, density functional theory calculations were undertaken as a circumstantial evidence.

The authors observed that for the case of the hydrated sodium cations, the cations were seen to be surrounded by around six water molecules in an octahedral geometry in the diluted solution. Besides, octahedral hydrated geometry was observed to remain stable, while some of the water molecules were being replaced by the oxygen from borate ion to form contact ion pairs with increasing concentration.

The study successfully presented an in-depth analysis of solution structures involving borate ion hydration and sodium borate association. In addition, the effects of the bulk water in aqueous sodium metaborate solutions have been studied by X-ray diffraction and empirical potential structure refinement modelling. It has been seen that, from both X-ray diffraction and Density Functional Theory calculations of sodium metaborate clusters, there are two forms of contact ion pairs between sodium cation and borate ion in aqueous sodium metaborate solutions.

B(OH)4 hydration and association in sodium metaborate solutions by X-ray diffraction and empirical potential structure refinement.. Advances in Engineering

About the author

Yongquan Zhou graduated from Qinghai Normal University in 2007 and received his master degree at Qinghai Institute of Salt Lakes (ISL), Chinese Academy of Sciences (CAS) in 2010. Then, he became a staff of ISL, CAS and received his Ph. D. degree in 2014. In 2015, with the support from “Sakura Science Program” of Japanese Science and Technology, he did joint research at prof. Yamaguchi’s research group of Fukuoka University, Japan. He continued this joint research from 2016 to 2017 with the support from China Scholarship Council. From 2014 to 2016 he was selected as an assistant researcher, and he has been an associate professor at ISL, CAS since 2016.

His research interest focuses on the structure of solutions by X-ray/Neutron diffraction, by X-ray absorption fine structure, by ab initio and by molecular dynamics etc. his research systems have covered aqueous borate solution, ionic liquid, and electrolyte solutions in confined space etc. He has published over 30 peer-reviewed publications in the relate filed.

About the author

Dr. Toshio Yamaguchi is a professor of Department of Chemistry, Faculty of Science at Fukuoka University. In 1973 he received B.Sc. Degrees from the Nagoya Institute of Technology in Synthetic Chemistry. In 1978 he received D.Sc. Degrees in Electronic Chemistry at the Tokyo Institute of Technology. After he spent three years (1979-1982) as a postdoc at Department of Inorganic Chemistry of the University of Gothenburg in Sweden, in 1982, he returned the Tokyo Institute of Technology as an assistant professor. In 1986 he moved to Fukuoka University as an associate professor of Department of Chemistry and was promoted to a full professor in 1994 and a dean of Faculty of Science in 2013.

His research interests include water and molecular liquids in confined geometry, water and aqueous electrolyte solutions under high-temperature and high-pressure, hydration of proteins and biomolecules, and micro liquid droplets levitated in the air by X-ray and neutron scattering, X- ray absorption spectroscopy combined with Raman, NMR, and MD and MC simulations.

He has published over 270 peer-reviewed publications and received the Japan Society for Analytical Chemistry Award in 2013, The Japanese Society for Neutron Science Award in 2016, and other notable awards. He is an Editor-in-Chief of the Journal of Molecular Liquids (Elsevier) since 2013.

Reference

Yongquan Zhou, Souta Higa, Chunhui Fang, Yan Fang, Wenqian Zhang, Toshio Yamaguchi. B(OH)4 hydration and association in sodium metaborate solutions by X-ray diffraction and empirical potential structure refinement. Phys.Chem.Chem.Phys., 2017, 19, 27878

 

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