Preparation And Performance Research Of Ag₃PO₄ Ultrasound Assisted Ion Exchange Method

In this thesis, ultrasonic assisted ion exchange method is used to prepare Ag₃PO₄ particles, and systematic study of the samp le size, morphology, light absorption properties, photocatalytic activity and mechanism of photocatalysis are systematically investigated. The main contents and results obtained are as follows:（1） Investigate the effect of ultrasonic frequency on the prep aration of Ag₃PO₄ particles. It is found that the application of ultrasonic irradiation at a frequency of 40 k Hz leads to the production of uniform spherical particles with an average size of ³00 nm. However, at a higher ultrasonic frequency of 60 k Hz, th e prepared sample presents polyhedron-shaped particles in the size range of 6-8 μm, which are constructed from small grains with a size of several hundred nanometers. In the ultrasonic frequency is 0 k Hz, the samples prepared at room temperature or under 5 0 oC water-bath condition are composed of spherical particles and large-sized agglomerative particles. The photocatalytic activity of Ag 3PO4 samples was evaluated by degrading Rh B under simulated-sunlight irradiation. Among these samples, the one prepared at 40 k Hz exhibits the highest photocatalytic activity, where the degradation percentage of Rh B reaches 96% after irradiation for 60 min.（2） At 40 k Hz frequency, the effects of p H value, reaction temperature and reaction time on the preparation of Ag₃PO₄ particles was investigated. It is found that the samples prepared at neutral（p H=7） and alkaline（p H=11） environments exhibit a similar particle morphology and size. The particles are shaped like spheres with a size distribution majorly focusing on a range of 200-450 nm, and the average particle size is about 300 nm. The sample prepared at acidic environment（p H=3） is composed of polyhedral microparticles with size of 5-8 μm. At relatively low temperatures of 20-50 oC, the spherical nanoparticles do not undergo ob vious morphology/size changes; however, when the temperature is increased up to 80 oC, the nanoparticles are aggregated to form large-sized polyhedral microparticles in the size range of 4-7 μm. Compared to the p H value and reaction temperature, the reaction time has a minor effect on the morphology of Ag₃PO₄ particles. Rh B was chosen as the target pollutant to evaluate the photocatalytic activity of the as-prepared Ag₃PO₄ samples under simulated-sunlight irradiation. It is shown that the samples consisting of spherical nanoparticles exhibit an extremely high photocatalytic activity, and the degradation percentage of Rh B after reaction for 50 min reaches over 90%. The samples of polyhedral microparticles have a relatively low photocatalytic activity, which i s possibly due to their large particle size. Hydroxyl（?OH） radical was detected by spectrofluorimetry using terephthalic acid as a ?OH scavenger and was not found to be produced over the simulated-sunlight-irradiated Ag₃PO₄ catalyst. The effect of ethanol, benzoquinone and ammonium oxalate on dye degradation was also investigated. Based on experimental results, the direct oxidation by h+ is suggested to the dominant mechanism toward the dye degradation.（3） At 40 k Hz frequency, the effect of mineralization agent Na3 Cit, glacial acetic acid and auxiliary agent KH2PO4 on the preparation of Ag₃PO₄ particles are investigated. In the course of the experiment, a set of Ag₃PO₄ samples are prepared by varying certain conditions. SEM image observation obtained that KH2PO4 is 2 mmol, Na3 Cit to 1 mmol, stock solution of acetic acid 3 m L, synthetic Ag₃PO₄ particles exhibit porosity coralline; when mineralizing agent glacial acetic acid is not added, Ag₃PO₄ particles produced have a smooth surface; at relatively high KH2PO4 concentration（3 mmol） and the holding other conditions remain unchanged, Ag 3PO4 particles obtained are uneven surface and spherical,which is the largest particle size in the products; under the relatively low Na 3Cit concentration（0.1/0.5 mmol）, the Ag₃PO₄ samples were prepared by the combination of spherical, tetrahedral and cubic particles. The synthesized samples have similar optical absorption properties. The absorption edge is at ⁴95 nm, and the corresponding band gap is about 2.50 e V. Under the simulation-sunlight irradiation, the dye Rh B is taken as target degradation to explore the photocatalytic properties of Ag₃PO₄ catalyst preparation. Experimental results show that the Ag₃PO₄ samples with pore structure have a relatively poor photocatalytic activity.