Design, Synthesis And Photocatalytic Prperties Of Novel Organic-inorganic Composite Photocatalysts

In recent years, a large amount of sanitary sewage, food processing, paper and other industrial wastewater has led to serious pollution of environmental and drinking water. The waste water contains a lot of organic matter, such as carbohydrates, fats, proteins, fiber and so on. Therefore, the elimination of such organic pollutants has become the important problems. The photocatalytic strategy as a green technology has received considerable and persistent attention and great research interest in the study of its application in the energy and environmental fields. A large number of semiconductor materials like metal oxides and sulfides (TiO2, ZnO, CdS) have been identified as active photocatalysts for photodegradation of organic pollutants. These traditional semiconductor materials are widely used due to its high chemical stability, low cost and high photocatalytic activity. However, they could only respond to UV irradiation, which severely limits the development and practical application to a great extent. Therefore, it is very important to seek for an kind of effective photocatalytic materials.In this thesis, we have designed and synthesized three novel composite photocatalytic materials (g-C3N4/NiO, g-C3N4/CuO, g-C3N4Fe2O3) by a simple and controllable method of heating treatment, and then the photocatalytic activities have also been studied. The main contents of the thesis are as follows:1. A novel g-C3N4/NiO composite material with different mass fraction of NiO by calcining the g-C3N4and NiO precursors (i.e. melamine for g-C3N4and Nickelous acetate for NiO, respectively) were fabricated by a one-step route on the basis of graphitic carbon nitride (g-C3N4) which possesses the performance of with visible light response. The photocatalysts were characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HR-TEM).Their photocatalytic activities were demonstrated by the photodegradation of Methylene blue (MB) in water. Remarkably, the kinetic constant of RhB degradation catalyzed by g-C3N4/NiO is2.3times larger than that of pure g-C3N4under the same experimental conditions. This g-C3N4-based heterojunctions of composite photocatalytic materials provide an efficient strategy for the development of a novel photocatalyst which exhibits activity for the removal of organic pollutants under visible light irradiation.2. The melamine molecules are fistly adsorbed by Cu-MOF (Cu-BTC) as a template. And then, a series of g-C3N4/CuO composite materials with different mass fraction of CuO are obtained by using a simple heat treatment method. The photocatalysts were characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HR-TEM). Compared with the pure g-C3N4photocatalyst, the photocatalytic activity of the magnetically separable g-C3N4/CuO photocatalysts under visible light irradiation was increased by up to3times for MB photodegradation under visible light. Remarkably, the CuO particles could act as electron traps to facilitate the separation of photogenerated electron-hole pairs and promote the interfacial electron transfer process, which results in an efficient photocatalytic process.3. We report for the first time the fabrication of magnetically separable polymeric carbon nitride photocatalysts, i.e. g-C3N4/Fe2O3, and their enhanced photocatalytic activity for the photodegradation of an organic dye (Rhodamine B) under visible light. A series of g-C3N4/Fe2O3composites with different Fe2O3contents were facilely obtained by using a simple heat treatment method. Their photocatalytic activities were demonstrated by the photodegradation of Rhodamine B (RhB) in water. The TEM images of the sample reveal that the prepared g-C3N4/Fe2O3composites are obviously porous, and well-dispersed Fe2O3nanoparticles with a mean size of approximately5-10nm are overlaid on the surface of g-C3N4. Magnetic tests show that the g-C3N4/Fe2O3composites have excellent magnetic properties. Remarkably, the photocatalytic activity of the magnetic g-C3N4/Fe2O3photocatalysts under visible light irradiation was increased up to1.8times for the photodegradation of Rhodamine B (RhB) under visible light irradiation compared with the conventional pure g-C3N4photocatalyst. The results presented here demonstrate a new opportunity for the design of magnetically separable recycled photocatalysts with both high photocatalytic performances under visible light and excellent magnetic separation properties.