In recent years, tantalates have been extensively studied because of their high photocatalytic activities for splitting water into H₂. However, solid state methods are always used for tantalates synthesis at high temperature of around 1000 °C over long periods, which may result in large grain growth (thus reduction in surface areas), leading to a decrease in photocatalytic activity.  

A novel approach to synthesize K_1.9Na_0.1Ta₂O₆·2H₂O (KNTO) nanocrystals with controllable crystalline facets was taken by a team of researchers lead by WANG Chuanyi from Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences (XTIPC). Researchers employed two-step synthetic approach, namely, molten salt in combination with hydrothermal processing. This strategy is highlighted by the fact that the shape and facet controlling of KNTO is achieved by simply adjusting the concentration of KOH addition in the hydrothermal reaction. Besides, photocatalytic activity of the synthesized KNTO for H₂ evolution from CH₃OH/H₂O solution was successfully tuned through the specific control of exposed facets. 

Researchers prepared selectively two distinct KNTO nanocrystals, {111}-terminated octahedra and {101}-dominated nanosheets, by varying the amount of KOH added in the hydrothermal process. They found the as-obtained crystals show high activity in photocatalytic H₂ evolution from CH₃OH/H₂O solution, and their performances mainly depend on the exposed facets. Based on test results, the rate of H₂ evolution under UV–light irradiation is about 4.4 μmol h^–1 for the KNTO nanooctahedra, which is 3 times higher than that of KNTO nanosheets dominantly exposed with {101} facets. The facet-dependent activities can be attributed to a cooperative effect of surface atomic structure (the density of undercoordinated Ta atoms) and electronic structure (the position of conduction band minimum). 

This is the first report for the facet controllable synthesis of tantalate materials with highly regular shapes. The present approach is anticipated as a general strategy for controllable synthesis of tantalate materials and also provides feasibility for rational design and activity optimization of shape-controlled photocatalysts for H₂ production.