Preparation And Photocatalytic Properties Of Bismuth - Based / Magnetic Semiconductor Composite Micro - Nano Materials

Energy shortage and environmental pollution are the major challenges which mankind facing. Photocatalytic technology is a popular technology in recent years. It can transform the solar energy into solar energy with high density and electric energy. It can use solar energy to degrade mineralized water, air pollutants and organic pollutants directly and with good removal rate. In this paper, the micro-nano-BiOI, Fe₃O₄@Bi₂O₃ and Fe₃O₄/BiOI magnetic composites were synthesized according a novel composite soft template method, which was constructed by PEG4000 and DL-asparaginic acid. Using this composite soft template, not only flowerlike BiOI nanomaterial with uniform morphology and size was successfully synthesized, but also Bi₂O₃ and BiOI nanomaterials can be combined with Fe₃O₄ nanoparticles to form their magnetic composites. After amplification synthesis, their formation mechanisms, physical and chemical properties and their application in photocatalysis were also studied. In the process of material synthesis, the experimental conditions such as the additive concentration and reaction time were investigated to explore their effects on structures, shapes and sizes of materials. The effectiveness and feasibility of bismuth-based semiconductor to degrade organic pollutants and the changes of magnetic properties after the Fe₃O₄ microspheres combined with bismuth-based semiconductor were discussed. FE-SEM, TEM. XPS, BET, XRD. VSM. FT-IR and UVDRS were used in characterizing and analyzing the materials and their applications.The main research content of this paper is as follows:1. The monodisperse Fe₃O₄ nanospheres were prepared with solvothermal method by using hexahydrated ferric chloride （FeCl3·6H2O） as single source of iron, succinic acid （C4H6O4） as connection agent and dispersing agent, sodium acetate （CH3COONa） as homogeneous precipitation agent, and 1,2-propylene glycol C3H8O4 as the reducing agent. The prepared Fe₃O₄ has high magnetization intensity reached to 88 emu/g. Then taking PEG4000-DL-asparaginic acid as the composite soft template, Fe₃O₄ as core, Bi（NO3）3·5H2O as bismuth source and urea as the homogeneous precipitating agent, Fe₃O₄@Bi（OH）3 with homogeneous morphology and size were obtained by simple atmospheric refluxing. This Fe₃O₄@Bi（OH）3 core-shell structure was composed of 200 nm Fe₃O₄ core and 50～100 nm Bi（OH）3 shell. The brown precursor was calcined at 35O℃ to get red brown core-shell structure Fe₃O₄@BiO3 The effects of PEG-4000, DL-asparaginic acid, and refluxing time on the size and morphology of Fe₃O₄@Bi（OH）3 were explored. Low temperature N:adsorption desorption experiment showed that the specific surface area of the Fe₃O₄@Bi₂O₃ with a core-shell structure is 19.8 m2/g. Then we used the above magnetic Fe₃O₄@Bi₂O₃ nanomaterials as catalysts, and studied their catalyzed degradation on methyl violet under the visible light irradiation and ultraviolet radiation, respectively. The result showed that it has good photocatalytic degradation activity.2. Bi（NO3）2·5H2O and KI as main raw material, PEG4000-DL-asparaginic acid as composite soft template and urea as a homogeneous precipitation agent were added respectively to the system to prepare uniform flower-shaped and ring-shaped BiOI micro-nano-structure under atmospheric pressure refluxing condition. The outer diameter of the flower-shaped BiOI structure was about 1 μm, and the thickness was about 20 nm. UV-Vis diffuse reflectance spectroscopy test showed the absorption band edge of BiOI located at 670 nm in the visible region, then the bandgap energy of 1.77eV was calculated by the formula and the value of the bandgap energy was significantly less than that of the most photocatalyst. In a XRD pattern, there were differences at （101） crystal surface between the flower-like and ring-shaped BiOI, which showed that the ring-shaped BiOI was hollow structure. Low temperature N2 adsorption desorption experiment indicated that the specific surface area of the flower-like BiOI micro-nano-structure was 22.8 m2/g. According to the test results of UV-Vis diffuse reflectance spectra and low temperature N2 adsorption desorption experiment, the flower-like BiOI micro-nano-structure performed good visible light catalytic ability. The experimental results showed the flower-like BiOI micro-nano-structure indeed expressed very good photocatalytic activity in the degradation reaction of the methyl violet under visible light irradiation.3. We can successfully synthesize 10 nm Fe₃O₄ nanoparticles with uniform morphology and size by large quantities and economic energy-saving coprecipitation method, using powdered hexahydrated ferric chloride （FeCl3-6H2O） and ferrous sulfate （FeSO4） as source of iron, sodium hydroxide （NaOH） or ammonia as alkali source and homogeneous precipitation agent. The 10 nm Fe₃O₄ nanoparticles were characterized by vibrating sample magnetometer （ADE company. America）. The saturation magnetization （MS） was 66.7 emu/g. The magnetic composite photocatalyst Fe₃O₄/BiOI were obtained by simple refluxing under the control of innovative PEG4000-DL-asparaginic acid composite soft template, with Bi（NO3）3·5H2O as source of bismuth, KI as source of iodine.10 nm and 200 nm Fe₃O₄ nano/microspheres as core, urea as homogeneous precipitation agent. The UV-Vis diffuse reflectance spectra showed the smaller band gap width than that of pure Fe₃O₄ which meant the heterogeneous structure Fe₃O₄/BiOI nano-spheres were formed. We use Fe₃O₄/BiOI as heterojunction photocatalyst in the process of degradation of methyl violet pollutants. The results displayed the better activity than that using flower-like BiOI as photocatalyst under the irradiation of visible light. In this chapter, we also explored the capacity of degradation and activity retention of degradating phenol and other industrial pollutant under visible light irradiation with heteroj unction structure Fe₃O₄/BiOI as photocatalyst after several times usage.