Quantitative Analysis of Degree of Nitridation of Ta₂O₅ to TaON Particles and their Photocatalytic Oxygen Evolution Properties

Abstract

Oxynitride or nitride photocatalysts are typically synthesized by heating oxide precursor particles at high temperatures under NH3 flow. Although there are numerous reports on optimizing the nitridation conditions for different materials, the detailed nitridation mechanism is still unclear. In this study, the nitridation of Ta2O5 to TaON was investigated. The degree of nitridation was quantitatively analyzed using the change in the weight of a powder after nitridation. Three regions were identified in the nitridation process for different nitridation times and NH3 flow rates. Moreover, the initial stage of the nitridation process (linear region) was formulated for the first time. Structural analysis, absorption properties, and oxygen evolution activity were combined with the degree of nitridation to reveal the relationship between the nitridation process and photocatalytic activity. The results of this work are useful for understanding and improving the photocatalytic properties of oxynitrides.

Development of a Deposition Method of IrOx Cocatalysts on SrTaO2N Photocatalysts for Higher Oxygen Evolution Activities under Visible-Light Irradiation

“…The optimum flow rate was 20 mL min –1 , indicating that one-fifth of the flow rate occurred during the STON synthesis. It has been reported that the flow rate and nitridation time are both linearly proportional to the degree of nitridation in TaON . Therefore, higher flow rates may have caused overnitridation, resulting in a reduced activity.…”

“…It has been reported that the flow rate and nitridation time are both linearly proportional to the degree of nitridation in TaON. 13 Therefore, higher flow rates may have caused overnitridation, resulting in a reduced activity. The loading amount was also optimized to 0.3 wt % (Ir base), although the activity did not significantly change in the range of the investigated conditions, whereas the STON particles without the cocatalyst produced only a negligible amount of oxygen.…”

Metallic Powder Promotes Nitridation Kinetics for Facile Synthesis of (Oxy)Nitride Photocatalysts

“…[11] First, thermal ammonolysis requires high temperature and involves multiple diffusion steps. [12] Second, the partial decomposition of ammonia gas into hydrogen and nitrogen at high temperatures may cause Scheme 1. Schematic of metallic-powder-assisted nitridation route used in this study.…”

“…[ 11 ] First, thermal ammonolysis requires high temperature and involves multiple diffusion steps. [ 12 ] Second, the partial decomposition of ammonia gas into hydrogen and nitrogen at high temperatures may cause undesired side reactions. [ 13 ] Third, the exchange kinetics of reactive nitrogen species with the lattice oxygen of the oxide precursor is usually sluggish, which generally leads to weak or limited nitrogen substitution for oxygen atoms and causes nitridation to occur only on the surface of the sample.…”