Synthesis of Self-Modified Black BaTiO_3-x Nanoparticles and Effect of Oxygen Vacancy for the Expansion of Piezocatalytic Application

Piezocatalysis has been considered a promising green and sustainable technology because of its ability to promote the passive conversion of natural mechanical energy into electrochemical energy. Among various piezoelectric materials, barium titanate (BaTiO₃) nanoparticles have been actively studied as a piezocatalyst due to their non-toxicity, physicochemical stability, and high piezoelectric potential. However, the low carrier concentration of BaTiO₃ is a significant drawback that limits their applicability as piezocatalyst only in ultrasonic systems, which can thermally excite BaTiO₃ via cavitation. Although the ultrasonic system can simultaneously supply thermal energy for the generation of carriers and high pressure as the driving force for chemical reactions, this system requires bulky, and expensive facilities that result in space constraints. Therefore, a novel strategy that can overcome the limitation of material is still necessary for the development of a high-performance piezocatalyst that convert the various natural low mechanical energy.<br/>Self-modification is a useful technique to modulate the electrochemical properties of oxide materials via the introduction of atomic defects such as oxygen vacancies and/or low valence metal ions. However, only a few reports on the synthesis of self-modified black BaTiO_3-xare available, and investigations on the piezocatalyst performance of black BaTiO_3-x nanoparticles have not yet been reported. Moreover, the conventional synthesis methods of black metal oxides depend on the post-treatment methods to form the atomic vacancies. Since these methods require complicated and prolonged processes that are inappropriate for practical application, it is still necessary to develop facile and versatile synthesis methods for the synthesis of black metal oxide.<br/>In this study, the self-modified black BaTiO_3-x nanoparticles were successfully synthesized by a simple solid-state reaction using defective raw materials in a reducing atmosphere. From these results, the initial atomic defects in raw material were demonstrated as the critical factor to determine the size and defect concentration of final products. Therefore, the synthesis mechanism of black BaTiO_3-x was systematically investigated in terms of the initial defect concentration of raw material. In order to study the effect of atomic defects on piezocatalytic performance, the piezocatalytic performance of self-modified BaTiO_3-x nanoparticles was evaluated under an ultrasonic system and stirring system compared with commercial white BaTiO₃ nanoparticles. The piezocatalytic performance of self-modified BaTiO_3-x nanoparticles showed a higher degradation efficiency of about 4.28 times than white BaTiO₃ under the stirring system, and the effect of self-modification was clearly identified. This study demonstrated a pioneering strategy that can promote the practical applications of BaTiO₃ as a piezocatalyst in an environment that requires low energy harvesting.