Preparation And Photocatalytic Activity Of Novel Visible Light Photocatalyst

Environment and energy issues are still the bottle neck for the continuable development of human being. In order to solve these problems, many researchers contribute their work to protect the environment. Semiconductor photocatalysis is an advanced technology that employs the electrons on conduction band and holes on valence band by absorbing the photons. Pollutants can be removed via oxidization or reduction and hydrogen can be obtained via water-splitting. As its essence is to convert solar energy into chemical energy, this technology may become an alternative approach to settle the environment and energy issues. TiO2 has been widely studied because of its prominent properties, such as low cost, good oxidation, chemical stability and no secondary pollution. However, its wide band gap restricts the utilization of solar energy. Thus TiO2 can only utilize a very small part of sunlight. It is a long-term issue for researchers how to utilize solar energy more efficiently. Furthermore, the research and development of new photocatalyst materials and technology, aiming the enhancement in the absorption in the visible light range, has become a hot topic in photocatalysis. Recently, Wang et al show that a simple polyer-like semiconductor, made of only carbon and nitrogen, can function as a metal-free photocatalyst for the extraction of hydrogen from water. The electronic and optical functions of polymeric C₃N₄ can be modified by metal species for the degradation of organic pollutants. For this reason, we expect that novel visible-light-actvied photocatalyst C₃N₄ and original photocatalytic materials compound to achieve better catalyst performance of the visible light response.In this dissertation, the new free-metal photocatalysts of carbon nitride were synthesized via thermolysis using the cheap urea as raw material, which is indexed as graphitic C₃N₄ (g-C₃N₄) and absorbes the visible light. Meanwhile, we prepared a series of N-doped X/C₃N₄(X=NaNbO₃, TiO₂, antimonic acid) photocatalysts and investigated their photocatalytic properties by photodegration of rhodamine B. The main contents and achievements in this dissertation are as follows:1. The N-doped NaNbO₃ samples sensitized by carbon nitrides are synthesized via heating the mixture of NaNbO₃ powders and urea at different ratios, and their photocatalytic were evaluated by the Rhodamine B under full arc Xe lamp irradiation. These samples were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscope. These investigations reveal that the samples contain N-doped NaNbO₃ and sensitizer of carbon nitride. In comparison with pristine NaNbO₃, the sample prepared at the weight ration of NaNbO₃ to urea of 1:60 shows a significantly enhanced photocatalytic activity. These results demonstrated that the metal-free carbon nitride could work as a photosensitizer, leading to an enhancement of photocatalytic activity due to the more light harvesting and efficient electron transfer between the N-doped NaNbO₃ and carbon nitride.2. The N-doped TiO₂/C₃N₄ composite samples were synthesized by heating the mixture of the hydrolysis product of TiCl4 and C₃N₄ at different weight ratios. The samples were characterized by X-ray diffraction (XRD), Raman spectrum, UV-vis absorption spectrum, photoluminescence spectrum, X-ray photon electron spectrum (XPS), and surface photovoltage spectrum (SPS). The XRD and Raman results indicate that the introduction of C₃N₄ could inhibit the formation of rutile TiO₂. The composite samples show slight visible light absorption due to the introduction of C₃N₄. The XPS result reveals that some amount of nitrogen was doped into TiO₂ and C₃N₄ exists in the composite sample. The intensities of the SPS signal in the composite samples decrease with the rise in the amount of C₃N₄ in the samples. The photocatalytic activity was evaluated from the Rhodamine B (RhB) degradation under fluorescent light irradiation. The composite samples show significantly enhanced photocatalytic activities. And the RhB self-sensitized photodegradation in this system was observed by measuring the photocurrent in the dye sensitized solar cell using the composite as the working electrode.3. The novel visible-light-response pyrochlore-type compound HSO and N-HSO with d¹⁰ configuration have been studied. The pristine and N-doped antimonic acid show higher visible light activities for Rhodamine B (RhB) degradation in comparison with the commercial product P25. The pristine antimonic acid, which is no obvious visible light absorption, exhibits the highest visible light activity for RhB degradation due to RhB-self-sensitized degradation. The N-doped antimonic acid, which could absorb the visible light, shows higher visible light activity for the phenol degradation. Furthermore, under visible light irradiation, in the presence of appropriate sacrificial reagents, the order of·OH radicals formation over the pristine and N-doped antimonic acid is consistent with that of phenol photocatalytic degradation, but opposite to that of RhB degradation. We demonstrate that whether the extent of degradation abilities is consistent with the rate of the active·OH radical formation under visible light irradiation is determined by whether the reagent has the self-sensitized degradation.