G-C₃N₄/ABO₃ Nanocomposites:Preparation And Photocatalytic Activities

In view of the global energy crisis and environmental issues, semiconductor photocatalysis is regarded as one of the green technologies, which is able to split water to produce clean hydrogen energy, to degrade organic pollutants to purify the environment, and to reduce carbon dioxide into hydrocarbon fuels. In order to effectively taking advantage of solar energy, developing new kinds of semiconductor photocatalytic materials attract much attention. Among various photocatalysts, ABO3-type(A = K, Na; B = Nb, Ta) has been attracting much attention due to its excellent properties, but they are only responsible to UV-light, which prevent further use. In other part, new-developed g-C3N4 is a 2-dimention nano semiconductor materials with a small bandgap(2.7 eV), thus it could absorb visible light. What's more, g-C3N4 has many advantages, such as easy preparation, high stability and nontoxic. But g-C3N4 behaves a low photocatalytic activity due to the easy recombination of photo-induced electrons and holes. Therefore, we want to design the g-C3N4 /ABO3 nanocomposites. One purpose is to enlarge the absorbance range. The other is to improve the photocatlytic activity by effective separate the photo-induced chargesBy using TaCl5 as Ta source and sodium carbonate as Na source,we have succeed in preparing NaTaO3 through an improved polymer complex method. We also make pure g-C3N4 by using melamine as a precursor heating under 550 ?. Finally,we prepared a series of g-C3N4/NaTaO3 composite by a facial ultrasonic bath method. From XRD results, we know that both there are no impurities in g-C3N4 and NaTaO3. From SEM and TEM results, we can conclude that NaTaO3 is like small and irregular cube and the average size is 30 nm. g-C3N4 shows typical layered platelet-like morphology. And NaTaO3 nanoparticles are deposited on the surface of g-C3N4, indicating the close connection between g-C3N4 and NaTaO3. UV-Vis results show all composites are responsible to visible light and have photocatalytic activity under visible light through the photodegradation of RhB. With the increase of content of g-C3N4, the photocatalytic activities first increase and then decrease. When the weight ratio of g-C3N4 is 70%, the composite has the best photocatalytic activity, whose rate constant is 228 times and 2.2 times high than that of pure NaTaO3 and g-C3N4. And the PL results show that g-C3N4/NaTaO3 could effectively decrease the recombination rate of photo-induced electrons and holes.To study the mechanism of photocatalysis, we use different scavengers to find the main active species. And the results show super oxygen free radicals(?O2-) plays the main role in the process of photocatalytic activitie, which comes from photo-induced electrons. Due to the negative condution band(CB), the electrons in the NaTaO3 have high potential energy. Because there is a small gap between the CB position of g-C3N4 and NaTaO3, it's not easy for the electron to transfer from g-C3N4 to NaTaO3. And compard with NaTaO3, KTaO3 and NaNbO3 prepared by using the same method have a wide gap of the CB position between them and g-C3N4. Thus the transfer from g-C3N4 becomes easier. But a lower CB position, the electrons will have less potential energy. When the content of g-C3N4 is the same, the g-C3N4/NaTaO3 composite has the best photocatalytic activity. We come the conclusion that the CB position play a more important role than the CB position gap between g-C3N4 and NaTaO3 in the g-C3N4/ABO3 composites. The more negative conduction band is, the higher photocatalytic activity the g-C3N4/ABO3 composites have.