دانلود رایگان مقاله روش درمان واکنسی ساده و تاثیر خواص فتوشیمیایی

Abstract

Recently, an increasing attention is paid to crystal defects due to the significant influence on the catalytic properties of material. Herein, the WO3 and fluorinated WO3 (F-WO3) samples have been prepared by an in situ hydrothermal method. On one hand, we have found that under visible light irradiation (λ ≥ 420 nm), the photocatalytic activities of F-WO3 samples are obviously reduced, which has been mainly attributed to the generation of W vacancies by fluorination. This finding is obviously distinct from the previous reports, in which the photocatalytic activities of semiconductors can be effectively improved by fluorination. On the other hand, after being further processed by H2O2 again, the generated W vacancies by fluorination can be remedied easily; moreover, the WO3/WO3·0.333H2O heterojunctions have formed with a novel flower shape (H2O2-F-WO3). It is amazing that under visible light irradiation (λ ≥ 420 nm), the activity of H2O2-F-WO3 sample is 4.3 and 3.0 times higher than that of F-WO3 and WO3, respectively. The significantly improved activity is mainly attributed to the remedy of W vacancy and the formation of the WO3/WO3·0.333H2O heterojunction. Compared with conventional defect remedy method (e.g., calcination), this vacancy remedy method with H2O2 is facile, energy-saving, which could be extended to develop the other efficient photocatalysts.

3. Results and discussion

3.1. Physico-chemistry and vacancy property of the samples 3.1.1. UV-DRS spectra Fig. 1 shows the Ultraviolet–visible diffuse reflection spectra (UV-DRS) of the samples at different RF. Compared with pure WO3, all the F-WO3 samples show obvious light absorptions above 450 nm (Fig. 1a), which may originates from the surface defect states of F-WO3 [22,23]. Typically, the inset of Fig. 1a shows the Tauc plots ((˛h)2 vs. energy) ofWO3 at RF = 0 and F-WO3 at RF = 1.0. Their band gaps are determined to be 2.86 and 2.97 eV for WO3 and F-WO3, respectively. Moreover, the presence of surface defects can also be confirmed by their different apparent colors. The WO3 sample prepared at RF = 0 is yellow, but the F-WO3 sample at RF = 1 is grayish green (Fig. 1b). The weak absorption above 420 nm has also been observed for the other fluorinated photocatalysts [10,15,16]. This result also confirms the presence of defects in the F-WO3 sample. It is obvious that the fluorination has a significant influence on the light absorption of the sample.