Improved piezo-photocatalytic activity by controlling the oxygen vacancy content of NaNbO3 powders

Abstract

The sintering temperature of solid-state synthesis exceeds 1000 ℃, which easily leads to the formation of oxygen vacancies. The presence of oxygen vacancies can alter the electronic/crystal structure and surface chemical properties of perovskite oxides. In this work, the content of oxygen vacancy of NaNbO₃ are controlled by adjusting the heat treatment conditions including atmosphere, temperature, and time. XPS and EPR are used to analyze the relative content of oxygen vacancies. The N₂ heat treatment time is 3 hours, and as the temperature increases from 300 ℃ to 900 ℃, the oxygen vacancy content increases from 16.4% to 18.9%. At 900 ℃, the time is extended to 5 hours, and the oxygen vacancy content increased to 26.4%. The disordered outer structure in HRTEM images confirms the existence of oxygen vacancies. The effect of the presence of oxygen vacancy on the efficiency of piezocatalysis and piezo-photocatalysis of NaNbO₃ is cleared. The NaNbO₃ sample heat-treated in N₂ for 3 hours (named NN-3h N₂) showed the best piezo-photocatalytic performance, with a rate constant (k) of 0.19175 min^-1, which is much higher than the unmodified NaNbO₃ (0.11777 min^-1). The electrochemical test results show that the NN-3h N₂ sample has better charge transfer ability and stronger photocurrent response, indicating that the presence of oxygen vacancies improves the migration and transfer efficiency of charge carriers. The volcanic trend indicates that an appropriate oxygen vacancy content is beneficial to the improvement of piezo-photocatalytic performance.