可见光辐射下新型可循环石墨烯-铁酸铋杂化催化剂高效光催化降解氨氮（英文）

发布时间：2019-04-22 15:15

【摘要】：近年来,本课题组利用简单的一步水热法,将石墨烯和铁酸锰、铁酸镍进行掺杂,先后制备出石墨烯铁酸锰和活性炭铁酸镍纳米光催化材料,并发现在可见光辐射作用下,这两种光催化剂均能利用可见光能量催化分解过氧化氢产生活性因子,从而有效地降解氨.基于此,本文采用简单的水热法成功制备出新型的高效多相石墨烯铁酸铋(rG-BiFeO_3)催化剂,并尝试在不添加H_2O_2的条件下进行光降解氨氮实验.结果表明,该复合光催化剂仍可接受可见光辐射,在rG和BiFeO_3的协同作用下高效地光分解氨氮.由X射线衍射结果计算出rG-BiFeO_3的平均粒径约为18.5 nm.通过清晰的rG-BiFeO_3的透射电镜图可以观察到,BiFeO_3纳米颗粒物较均匀地分散在r G的二维表面上.对比BiFeO_3和rG-BiFeO_3的傅里叶变换红外光谱可以发现,rG和BiFeO_3之间可能形成了化学键.拉曼光谱结果表明,相对于纯的GO,rG-BiFeO_3拉曼谱线的D带和G带发生了蓝移,表明石墨烯铁酸铋复合材料中的GO被充分还原成石墨烯.对比BiFeO_3和rG-BiFeO_3的紫外-可见漫反射光谱发现,rG-BiFeO_3的漫反射光谱发生了红移,表明rG-BiFeO_3光催化材料对可见光的响应程度进一步提高.比表面积测定表明,BiFeO_3的比表面积为21.0 m~2/g,而rG-BiFeO_3催化剂的比表面积则增加到48.6 m~2/g,说明rG-BiFeO_3的吸附性能将得到很大提高.可见光催化反应结果表明,在不添加H2O2,p H=11的条件下,0.2 g rG-BiFeO_3对50 mg/L NH_3-N的降解率达到91.2%.动力学研究表明,BiFeO_3光催化剂氧化氨氮反应遵循一级反应动力学规律.另外,由于BiFeO_3纳米材料本身具有一定的弱磁性,所以BiFeO_3和r G的复合材料也具有一定的磁性,较易回收.催化剂经过7次循环使用后,仍然具有很高的光催化活性.根据已有文献报道,吸附在催化剂表面的氨氮被氧化的路径有两条:(1)氨在被氧化为NH_2,NH和N_2H_x+y(x+y=0,1,2)等一系列中间产物后,最终被分解为氮气;(2)氨被氧化为中间产物HONH_2,最终分解为硝酸盐和亚硝酸盐.本文利用紫外-可见分光光度计对rG-BiFeO_3光降解体系下的氨溶液进行了全波长扫描,在206和211 nm处未检测到任何吸光度,从而排除了氨氮最终分解产物为硝酸盐和亚硝酸盐的可能性.这意味着rG-BiFeO_3可见光降解氨体系符合第一种氧化路径.进一步的机理研究表明,反应过程中石墨烯与铁酸铋之间的协同作用所产生的空穴、超氧阴离子自由基和羟自由基共同将NH_3直接氧化成N_2,其中羟基自由基在整个氧化分解过程中起着最主要的作用.
[Abstract]:In recent years, graphene, manganese ferrate and nickel ferrate were doped with graphene, manganese ferrate and nickel ferrate by a simple one-step hydrothermal method, and nanometer photocatalysis materials of manganese ferrate and nickel ferrate on activated carbon were prepared successively, and it was found that under the action of visible light radiation, nano-photocatalysis materials of manganese ferrate and nickel ferrate were prepared. Both of these photocatalysts can catalyze the decomposition of hydrogen peroxide with visible light energy to produce active factors, thus effectively degrade ammonia. Based on this, a new type of polyphase bismuth graphene ferrate (rG-BiFeO_3) catalyst was successfully prepared by a simple hydrothermal method, and the photodegradation of ammonia-nitrogen was carried out without the addition of H_2O_2. The results show that the composite photocatalyst can still accept visible light radiation and efficiently decompose ammonia nitrogen under the synergistic action of rG and BiFeO_3. The average particle size of rG-BiFeO_3 is about 18.5 nm. calculated from the results of X-ray diffraction. It can be observed that nano-particles of BiFeO_3 dispersed uniformly on the two-dimensional surface of rG by clear transmission electron microscope of rG-BiFeO_3. Compared with the Fourier transform infrared spectra of BiFeO_3 and rG-BiFeO_3, the chemical bond between rG and BiFeO_3 may be formed. Raman spectra show that the blue-shift of D-band and G-band of the pure GO,rG-BiFeO_3 Raman line indicates that the GO in the bismuth graphene ferrate composite is fully reduced to graphene. Compared with the UV-visible diffuse reflectance spectra of BiFeO_3 and rG-BiFeO_3, it was found that the diffuse reflectance spectra of rG-BiFeO_3 shifted red, indicating that the response of rG-BiFeO_3 photocatalytic materials to visible light was further improved. The specific surface area measurement showed that the specific surface area of BiFeO_3 was 21.0 mg ~ 2 g, while the specific surface area of rG-BiFeO_3 catalyst was increased to 48.6 mg ~ 2 g, which indicated that the adsorption performance of rG-BiFeO_3 would be greatly improved. The results of visible light catalytic reaction showed that the degradation rate of 50 mg/L NH_3-N was 91.2% under the condition of 0.2 g rG-BiFeO_3 without adding H 2O 2 and p H 2O 11. The kinetic study showed that the oxidation of ammonia nitrogen over BiFeO_3 photocatalyst followed the first order reaction kinetics. In addition, due to the weak magnetic properties of BiFeO_3 nano-materials themselves, the composites of BiFeO_3 and r-G also have certain magnetic properties and are easy to be recovered. After 7 cycles of recycling, the catalyst still has high photocatalytic activity. According to previous reports, there are two pathways for the oxidation of ammonia nitrogen adsorbed on the surface of the catalyst: (1) ammonia is decomposed into nitrogen after being oxidized to a series of intermediate products such as NH_2,NH and N_2H_x y (x y 0, 1, and 2); (2) ammonia was oxidized to the intermediate product HONH_2, and finally decomposed to nitrate and nitrite. In this paper, all-wavelength scanning of ammonia solution in rG-BiFeO_3 photodegradation system was carried out by UV-vis spectrophotometer. No absorbance was detected at 206and 211nm. Thus, the possibility that the final decomposition product of ammonia nitrogen is nitrate and nitrite is excluded. This means that the rG-BiFeO_3 visible light degradation system conforms to the first oxidation pathway. Further study on the mechanism shows that the hole produced by the synergistic action between graphene and bismuth ferrate, superoxide anion radical and hydroxyl radical can directly oxidize NH_3 to N ~ (2 +) _ (2) in the reaction process. Hydroxyl radical plays the most important role in the whole process of oxidative decomposition.
【作者单位】：上海交通大学环境科学与工程学院;苏州科技大学环境科学与工程学院;
【基金】：supported by the National Natural Science Foundation of China (21347006, 21576175, 51478285, 51403148) the Opening Project of Key Laboratory of Jiangsu Province Environmental Science and Engineering of Suzhou University of Science and Technology (zd131205) the Collaborative Innovation Center of Technology and Material of Water Treatment~~
【分类号】：O643.36

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