| In this paper, photocatalytic technology has been studied because of the energy shortage and environmental pollution. It's the photocatalytic reaction that photocatalyst can utilize solar energy directly to degrade the organic pollutants. So, there are two key points on photocatalytic technology: the first is the development of a novel photocatalyst, the second is a photocatalyst for solar energy utilization. Generally, semiconductor photocatalysis is easier to utilize ultraviolet light that account for only 4%, or visible light which about 47% of solar energy in photocatalysis. Years ago, researchers discovered TiO2 semiconductor with high performance in photodegradaion of organic compounds, but it only can utilize ultraviolet light. Subsequently, researchers successfully prepared some highly efficient visible-light-responsive photocatalyst, such as Ag3PO4, AgI and so on, but they are prone to corrosion under irradiation of visible light in the process, so that the photocatalytic performance is greatly weakened. Therefore, the target of this research work is to prepare visible-light-responsive photocatalysts, especially with high performance and high stability, to fully utilize solar energy in photocatalysis. In this work, we prepared three new visible-light-responsive photocatalysts, AgIO4, HgI2 and HgO, through a facile precipitation method, respectively. These samples were characterized by scanning electron microscopy(SEM), energy dispersive spectormeter(EDS), X- ray diffraction(XRD), ultraviolet-visible diffuse reflectance spectrum( UV-VIS DRS) techniques, etc. The photodegradation activity of AgIO4, HgI2 and HgO, respectively, were tested in degradation of rhodamine B, methylene blue and methyl orange under irradiation of visible light with ? > 420 nm. To identify the major active species in the rhodamine B degradation, we conducted radical-trapping experiment over the three photocatalysts by using disodium ethylenediaminetetraacetate, tert-butanol and benzoquinone, respectively. Moreover, to test the reusability of them, we performed the recycling experiments of degradation. Ultimately, the results of the study are as follows:(1)Prepared a novel visible-light-responsive photocatalyst, AgIO4. It is yellow and mostly has rhombic shape. It can absorbs visible light, and the absorption band edge is around the wavelength of 468 nm and its band gap is about 2.65 eV, EVB and ECB of AgIO4 were 3.61 eV and 0.96 eV, respectively. The ECB of AgIO4 is much higher than the LUMO potential of the rhodamine B molecule, and interestingly the HOMO potential of rhodamine B is very close to the ECB of AgIO4, and it is a process of the self-photosensitization of rhodamine B in degradation. Besides, It exhibited much higher activity than Ag3PO4 or Ag3AsO4 in photodegradation of rhodamine B under visible-light irradiation. The generation of AgO in degradation of rhodamine B under visible-light irradiation, which is attributed to the strong oxidizing-ability of photogenerated holes of AgIO4, this is because of that its VB potential is very high.Although the generation of AgO led photodegradation activity of AgIO4 to decrease, but if the used AgIO4 photocatalyst was washed with a dilute nitric acid, the ultrahigh degradation activity recovered. Therefore, AgIO4 semiconductor is a novel visible-light-responsive photocatalyst with ultrahigh photodegradation activity and can be recycled.(2) Prepared a novel visible-light-responsive photocatalyst, HgI2. It is brown red. Its absorption band edge is around the wavelength of 600 nm, which is broader than Ag3PO4( about 530 nm) and AgI( about 440 nm). Its photocatalytic activity is as high as that of Ag3PO4, and is significantly higher than that of AgI in degradation of rhodamine B dyes under irradiation of visible light, which may be attributed to its low recombination rate of the photogenerated carriers. superoxide anion radicals are the dominant reactive species contributing to the photocatalytic degradation of rhodamine B. Moreover, it can be reused for at least three cycles in the degradation experiments, and that its activity and crystal structure is just the same as that of fresh HgI2. Therefore, HgI2 semiconductor is a novel visible-light-responsive photocatalyst with excellent photocatalytic performance and ultrahigh stability.(3) Prepared a novel visible-light-responsive photocatalyst, HgO. It is dark yellow. Its absorption band edge is around the wavelength of 550 nm and its band gap is about 2.25 eV, EVB and ECB of HgO were 3.69 eV and 1.44 eV, respectively. The main active species of HgO are photogenerated holes in photocatalytic degradation of rhodamine B. Because the VB potential of HgO is very high, hence resulting in strong oxidizing-ability of its photogenerated holes, which prompts its ultrahigh photocatalytic activity in degradation of rhodamine B, and even its photocatalytic activity is higher than that of the highly efficient photocatalyst Ag3PO4 in degradation of methylene blue or methyl orange as well. Additionally, it reused for three cycles without obvious loss of its activity and change of crystal structure in degradation of rhodamine B. Therefore, HgO semiconductor is a novel visible-light-responsive photocatalyst with ultrahigh activity and ultrahigh stability. |
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