Moscow Technological University (Institute of Fine Chemical Technologies), Moscow, Russia:

K. A. Smirnova, Leading Engineer of the Department of Chemistry and Technology of Rare and Dispersed Elements, Nanoscale and Composite Materials named after K. A. Bolshakov, e-mail: smirnova_xenia@mail.ru

D. V. Drobot, professor of the Department of Chemistry and Technology of Rare and Dispersed Elements, Nanoscale and Composite Materials named after K. A. Bolshakov, e-mail: dvdrobot@mail.ru

V. Yu. Musatova, postgraduate student of the Department of Chemistry and Technology of Rare and Dispersed Elements, Nanoscale and Composite Materials named after K. A. Bolshakov

National Research Center “Kurchatov Institute”, Moscow, Russia:
R. D. Svetogorov, engineer of the Department of Synchrotron Experimental Stations of the Kurchatov Synchrotron-Neutron Research Complex

The authors of the article set forth scientific results of developing a new method of controlled (particle size and shape, specific surface) synthesis of copper niobate (I) — CuNb₃O₈, which has photocatalytic properties and is a p-type semiconductor. Information on the production of CuNb₃O₈ by Supercritical AntiSolvent technology using SCF-CO₂ was not found in the literature. SСF are the substances which are in supercritical condition, at temperatures and pressure exceeding their critical values (respectively, Tcr, Rcr). SСF unite in a unique way property of liquid and gas. The speeds of the proceeding processes considerably increase in the conditions of SСF, the quality of the received products improves, energy consumption decreases, essentially (and sometimes completely act) problems with ecological safety of productions, in tens otherwise are solved, and at times and in hundreds of times the sizes of reactors and production constructions decrease. Copper (I) niobate was prepared by SAS technology using bimetallic methylate (M_x¹M²_{1 – x})₂(OMe)₁₀(M¹ — Nb, M² — Cu), as the precursor. It is shown that amorphous copper niobate (I) is a macro porous adsorbent with a specific surface area of 7.9 m²/g and contains macro pores with a volume of 0.018 cm³/g, the proportion of which is 49 % of their total number. Amorphous copper niobate (I) has 138 nm particles. Annealing of copper niobate (I) for 24 hours at T = 700 ^оC leads to crystallization of CuNb₃O₈ with monoclinic syngony and particle size 285 nm.
The work was carried out with the financial support of the Russian Foundation for Basic Research (project No. 18-03-00671) and in the framework of the state assignment No. 11.9872.2017/8.9.

1. Nico C., Monteiro T., Graça M. P. F. Niobium Oxides and Niobates physical properties: review and prospects. Progress in Materials Science. 2016. Vol. 80. pp. 1–37.
2. Marinder B. O., Werner P. E., Wahlstrom E., Malmros G. Investigations on a New Copper Niobium Oxide of LiNb₃O₈ Type Using Chemical Analysis and X-Ray Powder Diffraction Profile Analysis. Acta Chemica Scandinavica. 1980. Vol. 34. pp. 51–56.
3. Maggard P. A. Heterometallic Solids for Solar Photoconversion. Proceedings of the 32 nd DOE Solar Photochemistry Research Meeting. Annapolis, USA, June 2010. p. 153.
4. Joshi U. A., Maggard P. A. CuNb₃O₈: A p-Type Semiconducting Metal Oxide Photoelectrode. The Journal of Physical Chemistry Letters. 2012. Vol. 3. pp. 1577–1581.
5. Sullivan I., Sahoo P. P., Fuoco L., Hewitt A. S., Stuart S., Dougherty D., Maggard P. A. Copper Deficiency in the p-Type Semiconductor Cu_{1 – x}Nb₃O₈. Chemistry of Materials. 2014. Vol. 26. pp. 2095–2104.
6. Vaswanathan B., Subramanian V. R., Lee J. S. Materials and Processes for Solar Fuel Production. New York : Springer Science, Business Media, 2014. 237 p.
7. Zalepugin D. Yu., Tilkunova N. A., Chernyshova I. V., Polyakov V. S. The development of technology based on the use of supercritical fluids. Supercritical Fluids Theory and Practice. 2006. Vol. 1, No. 1. pp. 27–51.
8. Zalepugin D. Yu., Tilkunova N. A., Chernyshova I. V. The use of supercritical fluids for obtaining nano- and microforms of pharmaceutical substations. Supercritical Fluids Theory and Practice. 2008. Vol. 3, No. 1. pp. 5–23.
9. Parenago O., Pokrovskiy O., Ustinovich K. Supercritical fluids for creating nanomaterials. Nanoindustry. 2013. Vol. 5, No 43. pp. 62–72.
10. GOST 8050–85. Gaseous and liquid carbon dioxide. Specifications. Introduced: 01–01–1987.
11. Smirnova K. A., Fomichev V. V., Drobot D. V., Nikishina E. E. Production of nanosized niobium and tantalum pentoxides by supercritical antisolvent technology. Fine Chemical Technologies. 2015. Vol. 10, No. 1. pp. 76–82.
12. Turova N. Ya., Korolev A. V., Tchebukov D. E., Belokon A. I. Tantalum (V) alkoxides: electrochemical synthesis, mass-spectral investigation and oxoalkoxocomplexes. Polyhedron. 1996. Vol. 15, No. 21. pp. 3869–3880.
13. Krzhizhanovskaya M. G., Firsova V. A., Bubnova R. S. Application of the Rietveld method for solving powder diffractometry problems. URL : http://crystal.geology.spbu.ru/files/books/MGK-rietveld.pdf (accessed 14.04.2017).
14. Petricek V., Dusek M., Palatinus L. Crystallographic computing system JANA2006: general features. Zeitschrift für Kristallographie — Crystalline Materials. 2014. Vol. 229, Iss. 5. pp. 345–352.
15. Open-access collection of crystal structures of organic, inorganic, metalorganics compounds and minerals, excluding biopolymers. URL : http://www.crystallography.net/cod/ (accessed 14.04.2017).
16. Sing K. S. W., Everett D. H., Haul R. A. W., Moscou L., Pierotti R. A., Rouquerol J., Siemieniewska T. Reporting Physisorption Data for Gas/Solid Systems with Special Reference to the Determination of Surface Area and Porosity. Pure and Appllied Chemistry. 1985. Vol. 57, No. 4. pp. 603–619.
17. Evstratova K. I., Kupina N. A., Malakhova E. E. Physical and colloidal chemistry. Moscow : Vysshaya shkola, 1990. 487 p.