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题名: 强化 BiOX(X=Br,Cl)基材料催化氧化有机污染物机制研究
作者: 李文涛1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 王东升
关键词: 可见光催化材料,类 Fenton技术,有机污染物,活性物种,水处理 ; Visible-light catalyst, Fenton-like technology, active species,organic contaminants, wastewater
其他题名: Enhanced the Oxidation of Orgainc Contaminants by Based-BiOX (X=Br, Cl) Visbile-Light-Catalytic Materials
学位专业: 环境工程
中文摘要: 饮用水水质风险已经成为中国乃至全球性的重大环境与健康问题。近年来, 世界各地饮用水源(包括长江、黄河、海河、辽河、太湖等主要流域)中均发现持 久性有机污染物(POPs)、内分泌干扰物、医药及个人护理品等新型污染物。饮用 水源中新型有机污染物主要来源于污水处理厂的出水排放。因为污水处理厂中传 统水处理工艺技术不能完全去除它们,而会随着出水进入水体环境,给水生态系 统和人类健康带来潜在的风险。高级氧化技术是去除新型有机污染物的最有效手 段之一,其中光催化和类 Fenton技术具有绿色环保的特性,但都存在一定的缺 陷,如电子-空穴复合率高,Fe(III)还原效率低等。基于二者的优势与缺陷互补, 本论文设计一系列可见光催化剂,构造可见光/H2O2体系内高效快速降解新型有 机污染物,并深入探讨活性物种产生途径与新型有机污染物降解机制,具体研究 成果如下: 1)利用溶剂热合成法,以十六烷基溴化铵(CTAB)为模板剂与乙醇、盐酸为 还原剂,制备 CTAB-Bi/BiOCl异质结光催化材料。XRD、HRTEM、FTIR与 UV –Vis DRS、Zeta电位等结果表明,BiOCl本体上有单质 Bi纳米颗粒产生,CTAB 促使 Bi/BiOCl最大吸收波长发生红移,Bi/BiOCl与 CTAB间存在某种化学作用 力(如 N-Cl和 N-O等)。单波长可见光催化降解罗丹明 b与甲基橙(两种不同电荷 的染料,前者为阴离子型,后者为阳离子型)实验结果显示,与 Bi/BiOCl相比, CTAB显著强化 Bi/BiOCl催化降解有机污染物效率,如罗丹明 B降解效率提高 3.72倍左右,而甲基橙去除效果更为显著。通过吸附实验、FTIR与 zeta电位测 试,CTAB强化 Bi/BiOCl可见光催化性能的原因是(1)增强可见光区域内的吸收 范围,能够快速形成空穴、超氧自由基等活性物种; (2)对有机污染物去除起着 一定的分配作用。 2)采用溶剂热合成法,以 CTAB、乙二醇分别为溴源、还原剂,制备金属 离子(Ag-/Zn-/Ni-/Cu-/Fe-)改性 BiOBr催化材料。XRD表征表明 Ag单质与 Bi单 质分别在 Ag-BiOBr和 Fe-BiOBr中, FESEM与 BET表明 Ag-BiOBr、Fe-BiOBr 与 Cu-BiOBr孔径与比表面积有较大变化。通过金属离子的氧化还原电位对比, 发现合成过程中 Cu(II)、Fe(III)很容易被乙二醇还原为 Cu(I)、Fe(II)。2-氯酚与 罗丹明 b可见光-类 Fenton催化降解实验表明,H2O2促使有机污染物高效降解, 并且 Cu-BiOBr与 Fe-BiOBr呈现出更强催化活性。羟基自由基定量分析实验表 明,其自由基产生速率大小: Fe-BiOBr >> BiOBr > Zn-BiOBr = Ni-BiOBr =Ag-BiOBr > Cu-BiOBr,而 H2O2分解速率大小:Cu-BiOBr > Fe-BiOBr >> BiOBr = Zn-BiOBr = Ni-BiOBr > Ag-BiOBr。ESR测定 DMPO-OH实验进一步表明, Vis/Fe-BiOBr/ H2O2反应体系中羟基自由基信号最强,Vis/Cu-BiOBr/ H2O2反应体 系中羟基自由基信号几乎未检测到,存着超氧自由基的信号。通过 XPS价态谱 分析,不同金属改性 BiOBr可见光-类 Fenton催化降解机制存在很大差异,大致 分为三类:Ni-BiOBr/Zn-BiOBr反应机制与 BiOBr类似,H2O2仅起着电子捕捉剂 的作用;Ag-BiOBr/Fe-BiOBr反应机制类似,H2O2发生类 Fenton反应,对电子 捕获作用很弱而 Ag(I)或 Fe(III)担任捕获电子的角色;Cu-BiOBr反应机制尤为复 杂,H2O2不仅仅捕获电子释放羟基自由基氧化 Cu(II),还发生类 Fenton反应生 成 Cu(III)与超氧自由基。活性物种猝灭实验证实,空穴与羟基自由基(Cu(III))对 有机物降解起着重要作用。 3)以溴化钾、乙二醇分别为溴源、还原剂,制备 Fe(II)/Fe(III)改性 Bi/BiOBr(FBB)催化材料。Bi单质异质结与 Fe(II)/Fe(III)存在分别被 XRD、XPS 一一验证。FESEM与 BET结果显示,Fe离子掺杂显著改变了 BiOBr表面积与 孔径分布。罗丹明 b降解实验表明,Fe/Bi摩尔比为 0.2-0.3时,其光催化效果最 为显著。双酚 A(BPA)可见光-Fenton催化降解实验表明,与单一可见光、Fenton 催化相比,0.25-FBB体系对双酚 A氧化效率显著(20min内全部 BPA被降解)。 经表面 Fe(II)捕获实验发现,与单一可见光催化、Fenton反应相比,确实存在有 更多 Fe(II)形成。此外,羟基自由基生成数量与 H2O2分解速率有显著增加。 Fe(II)/Fe(III)改性 Bi/BiOBr可见-Fenton催化机制与(3)中 Fe-BiOBr体系机制基本 一样。另外,0.25-FBB对多氯酚降解效果也尤为显著,大约 20min内全部降解, 矿化度高达 70-80%。 4)以 CTAB、乙二醇分别为溴源、还原剂,制备 Cu(I)/Cu(II)改性 Bi/BiOBr(CBB)催化材料。Bi单质异质结与 Cu(I)/Cu(II)存在分别被 XRD、XPS 所证实。FESEM与 BET结果显示,Cu离子掺杂显著改变了 BiOBr表面积与孔 径分布。铜含量、pH、H2O2浓度对 CBB可见光-类 Fenton催化性能进行研究. 磺胺甲恶唑降解实验结果表明,中性或酸性条件下,少量 H2O2浓度对 0.01-CBB 可见光-类 Fenton降解效率最高。pH、H2O2浓度、或铜含量过高时,会对活性 物种有抑制作用。ESR对该反应体系自由基进行检测,发现仅有超氧自由基信号 出现。Vis/CBB/H2O2体系氧化降解有机物机制有待进一步研究。
英文摘要: The drinking water quality problem has been a potential risk on the environment and health. Recently, various new contaminants (i.e., POPs, EDCs, PPCPs.), mainly from sewage treatment plant, have been detected in the potable water sources all over the world, including Yangtze River, Yellow River, Hai River, Liao River, Tai Lake. The conventional treatment methods cannot meet potable water standard that people demand. The advanced oxidation processes (AOPs) have been applied for the treatment of drinking water and wastewater containing new pollutants. Photocatalysis and Fenton-like technologies with friendly-environmental characteristic are widely concerned, although they have some drawbacks, such as high recombination rate of electron-hole pairs and low reduction rate of Fe(III).On the basis of complementary advantages, this paper design a series of visible-light catalysts, construct the visible light/catalyst/H2O2 system to highly efficient degradation for new pollutants, and deeply discuss the pathway of active species and mechanisms of new contaminants degradation, specific findings as following: 1) Bi/BiOCl heterojunction was prepared via a hydrothermal method, using cetyltrimethylammonium bromide (CTAB) as a stabilizing agent. The structure and chemical properties of Bi/BiOCl with the three different CTAB contents were thoroughly analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), UV-vis diffuse reflectance spectra (UV-vis DRS), zeta potential, and carbon element analysis, The results indicates that there are some important interactions between CTAB and Bi/BiOCl, resulting in decreasing the band gap of Bi/BiOCl with the increase of CTAB content. Two typical dyes, Rhodamine B (RhB) and methyl orange (MO) which has different surface charges, were choosed as the target pollutants. Under the visible light (λ=420 nm), the photocatalytic efficiency of Bi/BiOCl with a higher CTAB (Bi/BiOCl-a) was 3.72-fold more than that of Bi/BiOCl with a lower CTAB (Bi/BiOCl-c) to remove RhB. Bi/BiOCl heterojunction alone exhibited a poor degradation capability for the MO such as 5% of MO photodegradation with Bi/BiOCl-c. In contrast, MO removal efficiency by the Bi/BiOCl-a was 100%. Hence, the CTAB could play an important role to enhance the removal of dyes. Firstly, CTAB could absorb the target pollutants near the surface of Bi/BiOCl due to the electrostatic attraction and dispersion interaction; then Bi/BiOCl could degrade the pollutants via the in-situ h+ or • O2− under the visible light. The proposed mechanism was supported by the FTIR and adsorption analysis. 2) The BiOBr-based hierarchical microspheres was prepared by a simple solvothermal method. The phase structure, morphology and optical properties of catalysts were well characterized by XRD, FESEM, FTIR, UV-DR spectra, XPS valence band and BET surface area analysis. Among the Vis/catalyst/H2O2 system, Cu-BiOBr is found to be the most effective for rhodamine b degradation while Fe-BiOBr exhibits the highest catalytic activity for the mineralization of 2-chlorophenol. Hydroxyl radicals generation rate and H2O2 decomposition rate follow: Fe-BiOBr > BiOBr > Zn-BiOBr = Ni-BiOBr = Ag-BiOBr > Cu-BiOBr, and Cu-BiOBr> Fe-BiOBr > BiOBr = Zn-BiOBr = Ni-BiOBr > Ag-BiOBr, respectively. The catalytic mechanisms under Vis/catalyst/H2O2 systems are proposed and compared, as following: (1) for BiOBr/Zn-BiOBr/Ni-BiOBr, the activation of H2O2 by photoelectrons to generate hydroxyl radical; (2) for Ag-BiOBr/Fe-BiOBr, the reaction of Ag0 (Fe(II)) with H2O2 to produce hydroxyl radical and Ag(I)(Fe(III)) that is reduced by photoelectrons to Ag0 (Fe(II)); (3) for Cu-BiOBr, the activation of H2O2 by photoelectrons to generate hydroxyl radical that probably oxides Cu(II) to Cu(III), and the reaction of Cu(I) with H2O2 to generate Cu(III). The trapping experiments display that holes and hydroxyl radicals (or Cu(III)) have dominant roles. 3) The novel Fe(II)/Fe(III) doped Bi/BiOBr (FBB) visible-light- Fenton-like catalyst was successfully synthesized by using the solvothermal method. The morphological and structural features of FBB were analyzed by XRD, FESEM, TEM, BET, and XPS. The results revealed that the presence of Fe could promote the growth of Bi metal nanoparticles, and increase the specific surface areas of FBB. The rhodamine b (RhB) photodegradation experiments indicated that FBB with the Fe/Bi molar ratio (0.2-0.3) exhibited the higher photocatalytic activities. In the photo-Fenton-like reaction, the degradation efficiency of bisphenol a (BPA) over FBB-25 was increased to 100% within 30min while 3% and 12% in the Fenton-like and photocatalytic reaction. Moreover, 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) were completely degraded within 30min over FBB-25. The presence of visible light can promote the rapid propagating reaction rate between Fe(II) and Fe(III) over FBB with H2O2, producing more hydroxyl radicals (•OH) and more holes. The radical scavenger experiments demonstrated that holes and hydroxyl radicals (•OH) were mainly active species. FBB-25 is still stable after five cycles. Therefore, FBB-25 has a great potential in the wastewater treatment. 4) Novel Cu(I)/Cu(II) doped Bi/BiOBr (CBB) visible-light-Fenton-like catalyst was successfully synthesized by a facile solvothermal method. The morphological and structural features of CBB were analyzed by XRD, FESEM, TEM, BET, and XPS. The results revealed the formation of Bi metal nanoparticles, the reduction of Cu(II) and the increase of the specific surface areas when Cu addition. Effects of Cu content, pH and H2O2 concentration on the visible-light-Fenton-like catalytic performance of CBB were carried out, finding that the optimized reaction conditions of SMX degradation in visible light/catalyst/H2O2 system were low Cu content (1% of Cu/Bi molar ratio), neutral or acid atmosphere (not more than 7.0) and low H2O2 concentration (less than 5mM), whereas active species were inhibited. By ESR technology, the free radical signal in visible light/catalyst/H2O2 system was defined as superoxide radical rather than hydroxyl radical, probably the formation of high valence state of Cu. The reaction mechanism of contaminants needs to be further investigated.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38647
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
李文涛. 强化 BiOX(X=Br,Cl)基材料催化氧化有机污染物机制研究[D]. 北京. 中国科学院大学. 2017.
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