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题名: 新型多相类芬顿催化降解水中有机污染物机理
作者: 吕 来1
学位类别: 博士
答辩日期: 2017-06
授予单位: 中国科学院大学
授予地点: 北京
导师: 胡春
关键词: 多相芬顿催化,羟基自由基,富电子中心,有机污染物,水质净化 ; Heterogeneous Fenton catalysis, Hydroxyl radicals, Electron-rich center, Organic pollutants, Water purification
其他题名: Mechanism of Novel Heterogeneous Fenton-like Catalysis for Organic Pollutant Degradation in Water
学位专业: 环境科学
中文摘要: 多相芬顿催化技术是一种有效的处理难生物降解有机污染物的方法。由于其可循环利用、易固液分离且不产生铁泥等优点,近年来成为环境领域研究热点。然而,多相芬顿催化体系主要依靠固载的金属物种的价态反复变化来实现H2O2活化,导致其主要存在中性条件下催化活性差、催化剂稳定性差以及H2O2利用率低等问题。笔者主要针对这三个问题,从经典芬顿反应的速率限制步骤入手,深入研究新型多相类芬顿催化降解水中有机污染物机理,从而探究其解决方案。主要工作内容和结果摘要如下: 首先,在用单一铜反应中心芬顿催化体系γ-Cu-Al2O3/H2O2催化降解含芳环的污染物的过程中发现了多相芬顿反应的-Cu2+-ligand络合促进机理。H2O2对于有机自由基加合物的直接攻击促进OH的产生而极大抑制HO2/O2−和O2的生成,避免了H2O2的无效分解,使H2O2的有效利用率提升。γ-Cu-Al2O3在中性条件下对于芳环类有机污染物的降解和矿化表现出高的活性、稳定性和H2O2的利用率(~90%)。在此单一铜反应中心催化机制的基础上,进一步优化催化剂结构,开发出两种不同构型的高效芬顿催化剂——铜掺杂介孔二氧化硅纳米微球(Cu-MSMs)和铜掺杂铝强化的蒲公英状二氧化硅纳米纤维球(DCAS Ns)。Cu-MSMs中骨架内铜物种比骨架外铜物种具有更高的催化效率和稳定性。DCAS Ns中掺杂的金属物种形成了Cu-O-Si键和Cu-O-Al键,且活性组分被极大地暴露于催化剂的表面。由于其特殊的蒲公英构型,反应过程中,污染物和H2O2很容易接触到这些大量暴露出来的活性位点,并与之进行高效芬顿反应,遵循-Cu2+-ligand络合促进机理。因此DCAS Ns在去除各种难降解的有机污染物过程中表现出极佳的催化活性、稳定性和高的过氧化氢利用率。 由于单一铜反应中心机制强烈依赖于具有酚羟基的芳环类物质,且没有实质性脱离经典芬顿反应中金属离子自身的氧化还原。鉴于此,笔者在最优构型催化剂(蒲公英状纳米纤维球)的基础上创造性地开发出钛、铜和铝三金属共晶格掺杂蒲公英状二氧化硅纳米纤维球(d-TiCuAl-SiO2 Ns)双反应中心芬顿催化剂。三金属共晶格掺杂形成Cu-O-Si、Cu-O-Al和Cu-O-Ti键,进而诱发靠近铜的晶格O2-的富电子中心和靠近Ti和Al的晶格O2-的缺电子中心形成,使催化剂表面产生无数类原电池。芬顿反应时,污染物及其有机自由基中间体(R)占据阳极缺电子中心同时提供电子,阻止H2O2亲核位点与之接触而发生反应,避免其无效分解为O2−和O2;而H2O2则主要以其亲电端吸附在阴极富电子铜中心,并被该中心大量的电子不断还原为OH。整个过程避免H2O2的氧化而促进H2O2的还原,使得H2O2被最大限度地用于降解有机污染物。 为了发挥反应体系中水的供电子作用,依据双反应中心芬顿体系的研究思路,笔者利用表面有机配体络合手段,通过g-C3N4在Cu和Co共掺杂的介孔γ-Al2O3基体上原位生长而合成出一种性能更加优异的双反应中心芬顿催化剂OH-CCN/CuCo-Al2O3。OH-CCN与CuCo-Al2O3之间通过C-O-Cu键桥呈σ型键连,从而诱发了富电子铜中心和大π键上缺电子氮中心的形成。芬顿反应中,H2O2在富电子铜中心还原为OH;同时,H2O在OH-CCN的缺电子氮中心被氧化OH。此过程相当于每消耗1分子H2O2产生了2分子的OH。因此该芬顿体系体现出很高的OH转化率,是经典芬顿反应的85倍,并对于各类有机污染物的降解都表现出极佳的催化活性、稳定性和过氧化氢利用率。 以上研究发现金属物种的引入只是一种诱发双反应中心产生的手段,但是金属物种的存在却是导致芬顿反应主要问题产生的根源。因此在本论文最后章节,笔者利用分子掺杂和共聚合手段,创造性地开发出无金属双反应中心催化剂——氧掺杂还原性氧化石墨烯纳米杂化体(O-rGO Nhs)。O-rGO Nhs中本征C-O-C的形成导致引入的氧原子周围电子密度增加、其相邻碳原子周围电子密度减少以及邻近大π键的电子非均匀分布,进而产生无数富电子中心和缺电子中心。此双中心对于H2O2的还原和氧化以产生活性自由基遵循类原电池反应机理,因此O-rGO Nhs催化体系对于机污染物的降解表现出很好的性能。这为无金属催化体系的研究和多相芬顿催化技术的开发用于水中污染物降解提供了一个全新的视野。
英文摘要: Heterogeneous Fenton catalytic technology is a powerful method for degradation of various kinds of non-biodegradable pollutants. It has been received increasing attention in recent years because of its recyclability, easy solid-liquid separation and non-production of iron sludge. However, the heterogeneous Fenton system mainly relies on the valence change of the immobilized metal species to achieve the activation of H2O2, which often leads to poor activity under neutral condition, poor stability of the catalyst and low utilization efficiency of H2O2. Therefore, we try to explore the solutions of these problems through the in-depth research of the novel heterogeneous Fenton-like catalysis mechanism from the rate-limiting step of the classical Fenton reaction. The work and results are summarized as follows: Firstly, -Cu2+-ligand complexes-associated mechanism of the heterogeneous Fenton reaction was found during the degradation of the aromatic pollutants using a Cu-containing one-center Fenton-like system (γ-Cu-Al2O3/H2O2). H2O2 directly attacked the -Cu2+-complexes aromatic ring with the phenolic OH group, which enhanced the formation of OH and prevented from oxidizing H2O2 to form HO2/O2− or O2, and enhanced the utilization efficiency of H2O2. γ-Cu-Al2O3 was found to be highly effective and stable for the degradation and mineralization of aromatic pollutants in the presence of H2O2 under neutral pH conditions. Based on the reaction mechanism of the one-center Fenton-like system, two efficient one-center catalysts with different configurations were we developed. They were Cu-doped mesoporous silica microspheres (Cu-MSMs) and Cu & Al co-doped dandelion-like silica nanospheres (DCAS Ns). The framework copper species of Cu-MSMs exhibited a higher catalytic efficiency and stability than the extraframework copper species. DCAS Ns possessed an unique fibrous structure arranged in three dimensions to form nanospheres, just like dandelion flowers. Cu and Al were co-incorporated into the framework of the fibrous silica nanospheres with Si-O-Cu and Al-O-Cu, resulting in great exposure, significant accessibility and high stability of the surface Cu, which were mainly responsible for the outstanding Fenton catalytic performance of DCAS Ns. The one-center Fenton system strongly depends on the aromatic pollutants with phenolic hydroxyl groups and is not substantially free from the redox of the metal ions. Therefore, based on the optimal configuration of the catalyst (dandelion-like nanospheres), an efficient dual-center Fenton-like catalyst consisting of Cu, Ti and Al lattice-doped dandelion-like silica nanospheres (d-TiCuAl-SiO2 Ns) was developed. The lattice substitution of Cu, Ti and Al for Si initiated countless surface galvanic-like cells formed between the electron-rich Cu center (cathode) and the electron-deficient Ti and Al center (anode) on the nanospheres. This kind of surface structure facilitated the reduction of H2O2 to OH at the cathode and induced the oxidation of organic radical intermediates (R) on the anode through the delivery of the electron of R to the cathode during the Fenton reaction, which resulted in almost all of the energy of H2O2 being applied to the degradation of pollutants. To take advantage of H2O as electron-donor during the Fenton reaction, according to the research idea of the dual-center Fenton-like systems, a more efficient dual-center Fenton-like catalyst OH-CCN/CuCo-Al2O3 was developed by the co-incorporated Cu and Co in γ-Al2O3, and the sequential complex formation of σ-type Cu-O-C linker between the surface Cu and the hydroxyl group of the tri-s-triazine ring in C-g-C3N4. An electron-rich Cu center and an electron-deficient N center formed due to the Cu-π interaction and the different electronegativity of Cu with Co and Al. During the Fenton-like reaction, two electron transfer processes occurred. One process is from the electron-rich Cu center to H2O2 to form OH, the other is from H2O to the N atom of OH-CCN to produce OH. As a result, the catalyst shows extremely high activity for the degradation of various refractory organic pollutants in water under mild conditions with a high utilization efficiency of H2O2 (~90%) and high TOF of the OH yield (1.30 s−1), which is 85 times higher than that of the classical Fenton reaction. Introduction of metal species is just a means for inducing dual-centers. Unfortunately, the existence of metal species is also the source of the main problems for the Fenton system. Therefore, a metal-free dual-center catalyst consisting of oxygen-doped reduced graphene oxide nanohybrids (O-rGO Nhs) was developed through molecular doping and copolymerization. The formation of intrinsic C-O-C in O-rGO Nhs resulted in an increase and decrease in the electron density around the introduced O atoms and the adjacent C atoms, respectively, which led to the formation of numerous electron-rich centers around O and electron-deficient centers around C. The reduction and oxidation of H2O2 in the dual-centers to produce OH and HO2/O2− followed the galvanic-like cell reaction mechanism. O-rGO Ns presents good activity for degradation of pollutants under mild conditions with a high utilization efficiency of H2O2 and a favorable cycling stability. It could be anticipated that this work would open up new insights into the design of the metal-free catalytic systems and the development of the heterogeneous Fenton techniques for water purification.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38676
Appears in Collections:环境水质学国家重点实验室_学位论文

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作者单位: 1.中国科学院生态环境研究中心
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