【作者】 王敏；

【导师】 王里奥；

【作者基本信息】 重庆大学 ， 环境工程， 2009， 博士

【摘要】 半导体光催化技术作为一项新的环境净化技术越来越为人们所重视,其中光催化剂是光催化过程的关键部分。在众多的光催化剂中,TiO2以优良的抗化学和光腐蚀性能、价格低廉等优点而成为过去几十年来最重要的光催化剂,然而其实用化研究进程长期以来却未有较大的突破,主要由于其带隙较宽,只能利用紫外光和难以回收利用等原因。因此,研究和开发非TiO2新型光催化体系已成为光催化领域的热点之一,具有宽广的前景和挑战性。其中钒酸盐作为新型可见光催化剂之一,近年来逐渐引起学者的关注。但目前研制的钒酸盐光催化剂种类较少,且大都应用于光分解水方面,少数用于光催化降解有机污染物。为此,论文采用一种简单合成路线制备钒酸铁(FeVO4)光催化剂用于降解染料,并用不同金属进行掺杂改性,对其微观结构和光催化性能进行探索和研究。论文的研究成果进一步拓宽了钒酸盐光催化剂的研究领域,为探索钒酸盐光催化剂及其掺杂改性提供一定的理论基础和依据。论文采用液相沉淀法,制备了钒酸铁(FeVO4)光催化剂,并用Ag、Ba、Cu、Fe和Eu掺杂改性FeVO4光催化剂。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、比表面积(BET)、X射线光电子能谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)等技术研手段研究了样品的制备工艺、形貌、结构和光吸收性能与催化性能的关系。实验以甲基橙为模型反应,评价各样品光催化活性。以硝酸铁和偏钒酸铵为原料,在不同n(V)/n(Fe)摩尔比,不同pH值和不同温度条件下制备了系列样品,优化了三斜型FeVO4的工艺制备条件。实验发现,不同n(V)/n(Fe)摩尔比、不同pH值对物相形成有一定的影响。n(V)/n(Fe)摩尔为1时制备的样品为纯相,高于或小于1时有V2O5或Fe2O3相; pH高于或低于8时,有Fe2O3或V2O5相,杂相均影响样品的活性。温度对样品的结晶程度和晶粒大小影响较大。实验结果表明:n(V)/n(Fe)摩尔比为1,pH值为8,800℃下煅烧4h时,样品活性相对最高。在此条件下制备的样品为非化学计量比物质:Fe2x2 + Fe3 +1-2 xV5+O4-x,晶体中存在氧空位;晶体粒径约74nm左右,对光的吸收阈为605nm左右,禁带宽度约为2.05eV,比表面积为:2.265m2/g。样品在可见光下具有活性,且其沉降性好而有利于回收,重复使用5次左右能保持活性基本不变。同时确定了FeVO4光催化降解甲基橙的反应条件。银掺杂钒酸铁光催化剂:对比三种掺杂方法后,确定混合钒酸银和钒酸铁前躯体共同热处理的方法效果最佳。采用该法掺杂后:FeVO4晶型仍然为三斜型,但部分Ag+进入FeVO4晶格中,使FeVO4晶格产生了畸变和膨胀,并加大了晶体中非化学计量比,增大了表面吸附氧量;晶体表面形貌发生了显著变化,但未增大比表面积。当掺杂量大于10 wt%时,出现Ag4V2O7相,主要分布在针状物上。最佳掺杂量为1wt%,800℃下煅烧4h时。采用钒酸铁+钒酸钡前驱体混合后热处理方法,制备了掺杂Ba2+/FeVO4光催化剂。掺杂Ba2+后,未改变FeVO4晶型;但Ba进入FeVO4晶格中,导致晶格缺陷和晶胞体积增大,晶粒度增大,并加大了FeVO4晶体的非化学计量比及增加了表面吸附氧量;当掺杂量大于12 wt%时,出现BaV2O6相,主要分布在FeVO4晶体表面的片状物质上;增强了光的吸收能力。掺杂后形貌发生了显著变化,但仍没有增大其比表面积。最佳掺杂量为12wt%,750℃下煅烧4h。采用液相沉淀法制备Fe2O3/FeVO4光催化剂:当n(Fe)/n(V)摩尔比为1.01:1时,煅烧温度为750℃时制得的Fe2O3/FeVO4光催化剂,生成的Fe2O3相抑制了晶粒粒径的增加,并起到捕获电子的作用,使其较纯FeVO4活性提高。采用钒酸铁+钒酸铜前驱体混合后热处理方法制备Cu2+掺杂FeVO4光催化剂。掺杂Cu2+后,未改变FeVO4晶型,但晶粒增大。当掺杂量大于5wt%时有新相Cu3Fe4(VO4)6出现。掺杂后,加大了FeVO4晶体的非化学计量比,氧空位增加,表面吸附氧增加。但其比表面积变化较小。形成的新相和FeVO4之间类似复合半导体作用而提高了其活性。最佳掺杂量为5wt%的钒酸铜,在700℃下煅烧4h时。Eu/FeVO4光催化剂制备:对比几种掺杂方法,确定浸渍法制备的Eu/ FeVO4光催化剂光催化效果优于其他方法。FeVO4负载Eu后,晶型和晶粒径大小未有改变,但表面附着较多细小颗粒,比表面积增大。光吸收性能增强。最佳掺杂量为0.5wt%,回烧温度为250℃。本论文制备的FeVO4及其掺杂改性光催化剂,在可见光下具有活性,便于回收,能重复利用,具有很好的应用前景。但其比表面积却较小,如何提高比表面积值得进一步研究。采用不同金属离子对其掺杂改性,均能有效提高其活性。但存在最佳掺杂量,高于或低于此值,活性不能得到很好提高。在最佳掺杂量下,煅烧温度也影响活性的提高。更多还原

【Abstract】 Semiconductor-based phtotocatalysis has become increasing promising technology in environmental remediation. Photocatalyst was a key part in photocatalytic process. Of various types of photocatlysis, TiO2 has been identified as the most effective and useful photocatalyst because of its photostable, nontoxic, cheap and active properties in the past decades. However, the study of TiO2 has not larger breakthrough because it has wide energy gap, was only effective under ultra-violet light and difficult to recycle. Therefore, the research and development of new non-TiO2 photocatalytsts has become one of the hot fields, with broad prospects and challenging. Recently, vanadate, as one of the new photocatalyst, is gaining more attention of scholars. However, few vanadate has been developed,most of which being used in water splitting, only a few of which for the photocatalytic degradation of organic pollutants. So, pure iron(III) vanadate (FeVO4) photocatalyst and doped FeVO4 photocatalyst were prepared with simple synthesis methods in the paper. Its structure and photocatalytic properties were explored and researched, broadening the vanadate photocatalysts research field. It may provide a theoretical basis and foundation for further exploring vanadate photocatalyst and doping.In paper, FeVO4 photocatalyst was synthesised with liquid phase precipitation method . As well as Ag, Ba, Cu, Fe and Eu-doped photocatalyst FeVO4 were prepared. The relationships between preparation, sturcure, morphologies and photocatalytic of samples were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectra (DRS). The photocatalytic activities of the samples were determined by oxidative decomposition of methyl orange in aqueous under UV light and visible light irradiation.Using Iron Nitrate and Vanadium Ammonium as raw materials, series samples were synthesised. The different factors’(n (V) / n (Fe) molar ratio, precipitation pH and calcination temperature) effects on the characterization of FeVO4 were discussed and the optimum preparation conditions of triclinic FeVO4 was concluded. The results showed that the different n (V) / n (Fe) molar ratio and different pH value had impact on the phase formation. The pure FeVO4 was prepared when n (V) / n (Fe) molar ratio was 1 and Fe2O3 or V2O5 phase appeared when n (V) / n (Fe) molar ratio was higher or lower than 1.00 and pH value be higher or lower than 8. Calcining temperature greatly affected the crystallization and the grain size of samples.It was found that the samples prepared with the n (V) / n (Fe) moral ratio be 1,pH=1 and calcinated under 800℃for 4 hours had the best photocatalytic ability. The sample prepared under these conditions was triclinc phase and oxygen-deficient lattice structure due to deviation from oxgen stoichiometric material. The structure was Fe2x2 + Fe3 +1-2 xV5+O4-x, with the particle size be about 74nm. The absorption edge was around 605nm and its band gap was about 2.05eV. But it had small specific surface area: only 2.265m2/g. FeVO4 photocatalyst shows the photocatalytic activity under the visible ligh and it is easy to recovery from the suspension beacause of its good sedimentation ability.The effects of catalyst loading, initial MO concentration, light intensity and pH value on the degree of photo degradation had been investigated.Ag+ doped FeVO4: it was conclued that the method of calcining silver vanadate and iron vanadate mixtures worked best on the basis of comparison of three doping methods. It was found that Ag doping led to distoration and expansion of crystal lattice due to a few of Ag being into the FeVO4 crystal lattice, which increased the degree of oxgen stoichiometric. Ag doping changed crystal surface morphology dramatically, but didn’t change the specific surface area. And Ag4V2O7 phase appeared when the doping amount was greater than 10wt%, mainly be on the needle-like material. In the experimental conditions used, the optimal photocatalytic activity for all the prepared samples was reached when the Ag doping was 1 wt% calcined at 800℃for 4h.Ba2+ doped FeVO4 photocatalyst was prepared through calcining silver vanadate and iron vanadate mixtures. It was found that Ba doping had little effect on the grain size of FeVO4, but led to distoration and expansion of crystal lattice due to a few of Ba being into the FeVO4 lattice, which increased the degree of oxgen stoichiometric. BaV2O6 phase appeared when the doping amount was greater than 12wt%, mainly be on the flake-like material. Ba doping changed crystal surface morphology dramatically with almost the same specific surface area .The light absorption ability was intensitied after Ba2+ doping . In the experimental conditions used, the optimal photocatalytic activity for all the prepared samples is reached when the Ag doping was 1 2wt% and the samples calcined at 750℃.Fe2O3/FeVO4 photocatalysts were successfully prepared by liquid phase precipitation. It was found that the samples prepared with the Fe/V moral ratio be 1.01:1 and calcinated under 750℃had the best ability of photodegradation of MO. Doping Fe2O3 maybe inhibit the growth of FeVO4 and increase the surface area which can improve the photo-activity. Also the Fe2O3 can act as electron traps promoting the electron-hole separation and then increase the photo-activity.Cu2+ doped FeVO4 photocatalyst was prepared through calcining cupper vanadate and iron vanadate mixtures. It was found that Cu doping made particle size increased and led to distoration and expansion of crystal lattice, which increased the degree of oxgen stoichiometric. Cu3Fe4(VO4)6 phase appeared when the doping amount was greater than 5wt%. Cu doping changed crystal surface morphology dramatically with almost the same specific surface area. In the experimental conditions used, the optimal photocatalytic activity for all the prepared samples is reached when the Ag doping was 5wt% and the samples calcined at 700℃.Eu/ FeVO4 photocatalysts were prepared by the impregnation method on the basis of comparison of four methods. The results indicated that the Eu/ FeVO4 photocatalysts consist of triclinic phase without signifcant changes of crystalline size. SEM images showed that after loading with Eu,many fine particles were observed on the surface of the FeVO4 particles which maybe greatly increase their specific surface area. The DRS measurements showed that the light absorption of Eu/ FeVO4 novel photocatalyst was greatly increased during 200-500nm.. The photocatalyty activity of Eu/ FeVO4 sample was significantly enhanced when doping content was 0.5wt % and calcined at 250℃.In this paper, pure FeVO4 and the doped FeVO4 have good application prospects because they had photocatalytic activity under visible light irradiation and can be easy to recovery from the suspension and be reused at least 5 times without reducing photocatalytic efficiency. But it was pitful for its small surface area . How to improve the specific surface area is worthy to further study. Using different metal ions doping can effectively enhance its activity. However, there exists an optimum doping amount, higher or lower than this value, the activity should not be very good. In the optimum doping amount, the calcination temperature also affected the activity improved.更多还原