The correlations between the crystal structure and the photocatalytic performance of the NaNbO3 and KNbO3

Photocatalyst having a perovskite structure has attracted attention in recent years as the substrate of high performance solar cells. Perovskite structure is an ABO3 chemical composition, and the structure has been actively... [ view full abstract ]

Photocatalyst having a perovskite structure has attracted attention in recent years as the substrate of high performance solar cells. Perovskite structure is an ABO3 chemical composition, and the structure has been actively studied in various fields such as photocatalysts, piezoelectric materials, ceramic dielectric materials and etc. The performance of the photocatalyst is largely changed by substituting elements of A and B sites to the other elements. Our final purpose is to obtain a guiding principle for the synthesis of high performance photocatalysts.
In this study, we selected Nb-O based photocatalysts cause they have simple Perovskite structures and would be look forward to high photocatalytic abilities. NaNbO3(NN) and KNbO3(KN) were synthesized by modified solid-state reaction method using Na2C2O4, K2C2O4・H2O and (NH2)2CO. These powders with a molar ratio of [Na2C2O4]:[Nb2O5]:[urea] = 1:1:2 or [K2C2O4・H2O]:[Nb2O5]:[urea] = 1:1:4 were mixed for 1.5 h. The mixed powder was calcined at 560°C for 4 h. Then, we ground the calcined powder and re-calcined at 560°C for 4 h.
The sample were analyzed by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and organic decomposition measurement. Structure refinements were carried out using the Rietveld method by RIETAN-FP (Ver.2.32).
The sample was confirmed to be respectively NaNbO3 (PDF-No. 01-72-7753) and KNbO3 (PDF-No. 00-049-453). The photo activities of NN and KN was confirmed by the decomposition of acetic acid to CO2 under simulated solar irradiation(Fig. 2).
We select Na8Nb8O24 as an initial structure(space group:Pbcm). As a result, Rwp, RB and RF are shown good values 6.588%, 4.351% and 5.471%, respectively. The structural parameters from this analysis are shown in Table. 1. We select KNbO3 as an initial structure(space group:P4mm). As a result, Rwp, RB and RF are shown good values 9.521%, 4.618% and 2.703%, respectively. This structural parameters are shown in Table. 2.
NbO octahedral structure of the NN is distorted and KN show a well-equipped perovskite structure. Difference in photocatalytic performance between NN and KN of organic matter decomposition measurement was not observed. We will carry out the synthesis and analysis of the (Na, K)NbO3 and investigate the correlation between the structure and photo activities.