【作者】 孙爱武；

【导师】 汪信； 江芳；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2013， 博士

【摘要】 可见光光催化技术因具有反应条件温和、能耗低、操作简便以及可利用太阳光作为反应光源等特点,在环境污染治理和能源开发方面发挥着越来越重要的作用。可见光催化技术的关键在于新型可见光催化剂的制备及其改性,传统的可见光催化剂存在效率低且回收利用相对较难等缺点,如何提高可见光催化剂的效率,实现其可持续循环利用成为国内外光催化领域的研究热点。本论文采用石墨烯(graphene)、类石墨相氮化碳(graphite-like carbon nitride,等二维碳材料对铁酸铋和硫化镉进行修饰,制备了铁酸铋-石墨烯(Bi25Fe04o-graphene)、铁酸铋-类石墨相氮化碳(Bi25FeO40-g-C3N4)、类石墨相氮化碳-硫化镉(g-C3N4-CdS)三种新型复合光催化剂,通过不同分析手段对这些光催化剂的物理化学特性进行表征,并系统地研究了这三种催化剂的可见光催化性能。利用一步水热法制备了磁性铁酸铋-石墨烯(Bi25FeO40-graphene)可见光催化剂,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、BET比表面积分析、X射线光电子能谱(XPS)和磁滞回线测量等手段进行表征。在相同的水热条件下,加入氧化石墨制备得到的复合材料中的铁酸铋为软铋矿相的Bi25Fe040,同时,氧化石墨在水热过程中被还原为石墨烯,而不加氧化石墨得到的铁酸铋为钙钛矿相的BiFeO3。铁酸铋的晶型变化与碱浓度有一定的关系,当碱浓度降低时,得到的铁酸铋为Bi25FeO40。此外,Bi25FeO40-graphene复合材料的磁性明显优于BiFeO3,可通过外加磁场进行固液分离。氧化石墨的加入不仅影响了铁酸铋材料的晶型结构,还影响其颗粒大小。Bi25FeO4o-graphene复合光催化剂对亚甲基蓝(Methylene Blue, MB)的可见光催化降解效率优于Bi25FeO40和Bi25FeO40-graphene复合光催化剂中的o与石墨烯发挥了较好的协同效应,石墨烯可以有效地转移电子,抑制Bi25FeO4o中光生电子和空穴的复合,利于光催化活性的提高。Bi25FeO40-graphene可见光催化降解MB的过程符合Langmuir-Hinshewood模型,表明光催化反应速率与吸附在催化剂表面的MB浓度成正比。利用类石墨相氮化碳和铁酸铋复合制备得到磁性Bi25FeO40-g-C3N4复合光催化剂,采用XRD、SEM、BET比表面积分析、紫外漫反射和磁滞回线测量等进行表征。在Bi25Fe04o-g-C3N4复合光催化剂中,g-C3N4的加入使得Bi25FeO40-g-C3N4复合材料的带隙能减小。Bi25FeO40-g-C3N4复合光催化剂中g-C3Na的含量对其可见光催化降解MB的效率有较大影响,随着g-C3N4含量的增加,光催化降解效率呈现先升后降的趋势。将g-C3N4含量为50%的Bi25FeO40-g-C3N4复合材料用于MB的可见光催化降解,不仅取得了较好的去除效果,而且该催化剂具有良好的磁性特征,可通过外加磁场进行固液分离。利用类石墨相氮化碳和硫化镉复合制备得到g-C3N4-CdS复合光催化剂,采用XRD、透射电子显微镜(TEM)、BET比表面积分析、红外光谱(FT-IR)和紫外漫反射等手段进行表征。将g-C3N4-CdS复合催化剂用于MB的可见光催化降解,其降解效率明显优于g-C3N4和CdS。这主要是由于在复合催化剂中,g-C3N4表面的电子易迁移至CdS表面,有利于电子和空穴的分离；电子在CdS表面的富集使得CdS表面的空穴减少,降低了CdS光腐蚀氧化的机率；g-C3N4-CdS复合催化剂的比表面积和孔容的增大有利于MB在催化剂表面的吸附和光催化反应活性中心的增加,进而促进光催化反应的进行。对g-C3N4-CdS复合催化剂进行多次回用后发现,该复合光催化剂在回用五次后仍保持较高的催化活性,说明g-C3N4-CdS催化剂具有较高的稳定性。更多还原

【Abstract】 The visible-light-driven photocatalysis plays an important role in the field of environmental remediation and energy development due to its mild reaction conditions, low energy consumption, easy operation and utilizing visible-light. The photocatalyst is the key point of visible-light photocatalysis in the present research. However, traditional photocatalysts exhibit low photocatalytic activity under visible-light irradiation and the recycling of catalyst is relatively difficult. Therefore, it is highly desirable to develop reusable visible-light photocatalysts with high photocatalytic activity.In the present work, the2-D carbon materials, graphene and graphite-like carbon nitride (g-C3N4), were used to modify the bismuth ferrite and CdS photocatalyst. The Bi25FeO40-graphene, Bi25FeO40-g-C3N4and g-C3N4-CdS composite photocatalysts were synthesized and characterized. The photocatalytic behaviors of these composite photocatalysts were also investigated.A magnetic Bi25FeO40-graphene visible-light photocatalyst was prepared by a one-step hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Raman spectroscopy, X-ray photoelectron spectra (XPS) and magnetic hysteresis loop measurements. Under identical hydrothermal conditions, perovskite type bismuth ferrite (BiFeO3) was obtained without graphene addition, while the presence of graphene led to the formation of sillenite type bismuth ferrite (Bi25FeO40), and graphene oxide (GO) was reduced to graphene during the hydrothermal process. The crystalline of bismuth ferrite has a certain relationship with the alkali concentration. The phase of Bi2.5FeO40was formed when the alkali concentration was low. In comparison with pure BiFeO3catalyst, the Bi2.5FeO40-graphene composite showed better magnetism property. Moreover, the addition of graphene had an effect on the particle size of photocatalyst. The photocatalytic degradation of Methylene Blue (MB) demonstrated that Bi25Fe04o-graphene photocatalyst exhibited higher catalytic activity under visible-light irradiation than BiFeO3and Bi25FeO40, due to enhanced MB adsorption and synergistic effect between Bi25Fe04o and graphene. Additionally, the photocatalytic MB degradation over Bi25FeO40-graphene followed the Langmuir-Hinshelwood model, indicating an adsorption controlled reaction mechanism.Magnetic Bi25FeO40-g-C3N4visible-light photocatalysts were prepared and characterized by XRD, SEM, BET surface area analysis, UV-vis spectra and magnetic hysteresis loop measurements. The addition of g-C3N4made the band gap of Bi25Fe04o-g-C3N4composite photocatalyst decrease. Furthermore, the g-C3N4content of Bi25FeO40-g-C3N4had an impact on the photocatalytic MB degradation. The photocatalytic efficiency increased with the increase of the g-C3N4content and then decreased with the further increase of the g-C3N4content. Bi25FeO40-(50)g-C3N4showed prominently enhanced photocatalytic activity for the degradation of MB under visible-light irradiation than that of Bi25FeO40. Additionally, the Bi25FeO40-(50)g-C3N4composite was superparamagnetic, and could be readily recovered in an external magnetic field.The g-C3N4-CdS visible-light photocatalysts were prepared and characterized by XRD, TEM, BET surface area analysis, FT-IR and UV-vis spectra measurements. The CdS-g-C3N4composite photocatalyst showed prominently enhanced photocatalytic activity for the degradation of MB under visible-light irradiation than that of CdS and g-C3N4. Such enhanced photocatalytic activity could be attributed to the high adsorption capacity of MB on CdS-g-C3N4composite photocatalyst and the synergistic effect between CdS and g-C3N4. The photogenerated electrons may transfer from g-C3N4to CdS, inhibiting the combination of photogenerated electrons and holes. Meanwhile, the gathering of photogenerated electrons in the surface of CdS suppressed the photo-oxidation corrosion of CdS. Additionally, the g-C3N4-CdS catalyst had larger surface area which provided more active adsorption sites and photocatalytic reaction centers, giving rise to enhanced photocatalytic activity. Moveover, the CdS-g-C3N4composite catalyst still maintained a high photocatalytic activity after recycle for five times, which further demonstrated that the g-C3N4-CdS is a high stability catalyst.更多还原