Construction Of Heterogeneous Photocatalyst And Their Photo Degradation Performance Study On Environment Pollutants

With the continuous development and progress of the society and economy,increasing energy and environmental problems have become the key limitation of social and economic development and human health. Solar energy shows promising prospects for its abundant, clean and safe, economic and environment-friendly advantages. At present, the solar energy is mainly used in lighting, heating and photovoltaic power generation fields. In recent years, semiconductor photocatalytic technology is widely used to convert sunlight into chemical energy, to effectively remove poisonous and harmful organic pollutants in the environment, and gradually become a new way for the conversion and utilization of solar energy that attracts wide attention and in-depth study by researchers all over the world.After excitation by sunlight, the H2O and O2 molecules around semiconductor photocatalysts are activated and transformed to free radicals or negative ions with strong oxidation capability for organic pollutants degradation. Currently,a large number of semiconductor photocatalysts have been developed with different functions,and compositions. However, the photocatalytic activity of single semiconductor photocatalyst is still low and difficult to be used for practical applications due to the narrow light response range, low quantum efficiency and lacking of active sites.Therefore, it is of great significance to develop visible-light-driven heterostructure photocatalytic system to improve the light energy utilization efficiency and photocatalytic activity of single semiconductor photocatalyst. This paper is emphasized on the synthetic process and photocatalytic mechanism of several heterojunction photocatalysts with visible light response, and their photocatalytic activity of environmental pollutants (such as antibiotics, dye wastewater) degradation.X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM),X-ray photoelectron spectroscopy (XPS),UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), electrochemical Impedance Spectroscopy (EIS), electron spin resonance (ESR) were used to test the structure,composition,morphology, photoelectric performance and active species of the prepared heterojunction photocatalysts. The separation and transfer processes of the photogenerated electron-hole pairs, and the photocatalytic mechanism of the prepared heterojunction photocatalytsts were also studied.The main content are summarized below:1. Consruction of plasmonic heterojunction photocatalyst and research on photodegradation performance for antibiotics(1) Ag nanoparticles-modified cubic-like SrTiO3 (STO) are fabricated through a hydrothermal and photodeposition method. The prepared Ag-STO heterojunctions exhibit an efficient photocatalytic activity for degradation of tetracycline (?42%within 1 h reaction time) under visible-light irradiation, and Ag deposition with 8 mM AgNO3 exhibited the highest photocatalytic activity. It is considered that this excellent performance results from the surface plasmon resonance of Ag nanoparticles.Meanwhile, the mechanism of the photocatalytic process of the Ag-STO photocatalyst system is also discussed.(2) Ag/AgCl grafted AgBi(MoO4)2 ternary heterojunctions were fabricated through a anion-exchange and photo reduction method. Samples obtained by this method possess an increased specific surface area and improved photocatalytic activity for TC degradation. In our experiment, the surface Ag nanoparticles effectively increased the charge transfer and separation efficiency of photocatalysis process, and the concentration of Ag/AgCl can be easily controlled by adjusting the amount of Cl-. Moreover, insight into the photocatalytic mechanism of this photocatalytic system is also discussed based on the band structure analysis and active species trapping experimental results.(3) Ag/AgBr-grafted AgIn(MoO4)2 nanosheets were synthesized by the in situ photoreduction of AgBr/AgIn(MoO4)2 composites prepared by a precipitation-deposition method. Under visible light irradiation, the Ag/AgBr/AgIn(MoO4)2 composites exhibit a strong absorbance in the visible region because of the surface plasmon resonance absorption of the Ag nanocrystals. A dramatic enhancement in the degradation rate of tetracycline (TC) is observed over the Ag/AgBr/AgIn(MoO4)2 composites compared with bare AgIn(MoO4)2 nanosheets, Ag/AgBr nanoparticles and Ag/AgIn(MoO4)2 composites. The immense enhancement of the photocatalytic activity is attributed to the extended absorption in the visible region, effective charge separation, and the synergistic effect of surface plasmon resonance (SPR) and the heterostructure of Ag/AgBr/AgIn(MoO4)2.2. The preparation of cadmium sulfide/semiconductor heterojunction photocatalyst and photocatalytic degradation of dye molecules(1) CdS/CoWO4 heterojunction photocatalysts were fabricated by a facile hydrothermal method. Compared with the pristine CdS and CoWO4, the CdS/CoWO4 heterojunction photocatalyst showed enhanced photocatalytic activity for methylene blue (MB) degradation under visible light irradiation. Particularly, the sample with molar ratio of CdS: CoWO4 controlled at 3:5 showed the highest MB degradation ratio (83%) in 1 hour among all samples, which is about 3 times over the pure CdS and 8 times over pure CoWO4, respectively. The greatly enhanced photocatalytic activity of CdS/CoWO4 is due to the efficient separation of electron-hole pairs by the heterojunction structure and strong visible light absorption of CdS.(2) CdS/MnWO4 heterojunction was used as a high performance photocatalyst for methylene blue (MB) and methyl violet (MV) degradation under visible-light irradiation. The CdS/MnWO4 samples contend 0.3 mmol and 0.5 mmol CdS exhibited the highest photocatalytic activity for MB and MV degradation, respectively. This greatly enhanced photocatalytic activity is attributed to the efficient separation of electron-hole pairs of heterojunction structure and strong visible light absorption of CdS. The active species generated during the process of MB degradation are investigated by series of free radical scavenging experiments. Moreover, the reusability of the photocatalyst was evaluated by five consecutive catalytic runs.3. Preparation of Bi12O15C16 based heterojunction photocatalysts and the photocatalytic removal of antibiotics(1) Considering the high carrier mobility of reduced graphene oxide (rGO), a series of rGO/Bi12O15C16 photocatalysts were successfully fabricated by a facile photo reduction method with the aim to promote the charge separation of Bi12O15Cl6.Especially, 3% rGO sample showed the highest photocatalytic activity for the TC degradation under visible light irradiation. The enhanced photocatalytic performance of rGO/Bi12O15C16 heterojunction is abscribed to the strong light absorption in the visible region and fast separation of the photogenerated electron-hole pairs. The underlying photocatalytic mechanism was revealed through the photoluminescence spectra and free radical capture experiments.(2) A series of Bi2S3/Bi12O15C16 heterojunction photocatalysts were successfully fabricated via an ion-exchange method using Bi12O15C16 as template. The composition of Bi2S3/Bi12O15Cl6 can be easily controlled by adjusting the amount of thiourea. The photocatalytic activity of the prepared samples was studied based on the degradation of TC under visible light irradiation. The experimental results demonstrated superior photocatalytic rate of 0.04 S-Cl sample compared to pure Bi2S3 and Bi12O15C16 samples (enhancement of 69 % and 36.7%, respectively). The radical scavengers test demonstrated that ·O2- was the main reactive species for the degradation of TC,and holes also took part in the photodecomposition process.(3) Bi12Oi5Cl6/BiVO4 Z-scheme heterojunction photocatalyst was successfully fabricated via a facile in situ anion exchange reaction between Bi12O15C16 and VO3-ions. Compared with pristine Bi12O15Cl6 and BiVO4,the Bi12O15Cl6/BiVO4 heterojunction exhibited significantly enhanced photocatalytic activity. In addition,the 0.2 V sample (prepared by 0.2 mmol VO3- and 0.05 mmol Bi12O15Cl6) showed the optimised photocatalytic degradation toward TC (90%) within 60 min. By further studies based on the photocurrent and electrochemical impedance spectroscopy (EIS)results, this greatly enhanced photocatalytic property could be ascribed to the efficient charge carrier transfer and separation in the Bi12O15Cl6/BiVO4 heterojunctions. The active species trapping and ESR experiments indicated that superoxide radicals and holes are the major active species in which contributing to the photocatalytic process.