| 초록 |
Hydrogen energy is one of the clean energy that is possible to develop new generation energy. Ideal method producing hydrogen can be chemical decomposition methods of water using photocatalyst. Recently, tantalum oxides have been introduced for the new photocatalysts. Especially, tantalum oxides with the layered perovskite structure have an advantage to occur photocatalytic reaction without supporting co-catalyst because layered structure acts as active sites. This research initiated with assumption that a change of electron structure enhances the mobility of electron-hole pair and suppresses recombination of electron-hole pair exited by light in photocatalyst. A change of electron structure will be achieved by the distortion of crystal structure. In the concrete, Sr2Ta2O7 with layered perovskite structure, known as promising photocatalyst, was used as a main material. Barium was doped on strontium site of Sr2Ta2O7 in order to give structural variation. Photocatalytic activity of Sr2Ta2O7 was successfully enhanced about three ~ four times higher than that of undoped Sr2Ta2O7 . Using X-ray diffraction, SEM, UV-visible absorption spectra, and BET method, the characterization of each sample was performed to investigate the reason to improve the photocatalytic activity in terms of specific surface area and crystal size. Based on the results, the photocatalytic activity was improved with increasing Ba content on Sr2Ta2O7. In 20 mol% of Ba dope, the photocatalytic activity of Sr2Ta2O7 (~6374 mmol/hour) increased three time higher than that of undoped Sr2Ta2O7 (~2800 mmol/hour). Raman spectroscopy and Rietveld analysis were performed to investigate the improvement of photocatalytic activity of Sr2Ta2O7 due to Ba dope in terms of structural distortion. The unit cell volume of Sr2Ta2O7 increased up to 30mol% of Ba-dope and became almost constant after 30mol%. On the other hand, mass fraction of Sr2Ta2O7 was almost constant up to 30mol% of Ba dope and started to decrease after 30mol%. This relationship was explained with the lever rule. Moreover, all lattice parameters in a, b, c axes of Sr2Ta2O7 were increased anisotropically with Ba dope up to 30mol%. Based on these, it was confirmed that the distortion occurred in the structure of Sr2Ta2O7 due to Ba dope. According to these results, distortion of structure of Sr2Ta2O7 was one of the reasons to improve the photocatalytic activity. |
