Covalent Organic Frameworks: A Sustainable Photocatalyst toward Visible-Light-Accelerated C3 Arylation and Alkylation of Quinoxalin-2(1H)-ones

A practical and scalable protocol for visible-light-accelerated arylation and alkylation of quinoxalin-2(1H)-ones with hydrazines is reported. In this protocol, a hydrazone-based two-dimensional covalent organic frameworks (2D-COF-1) was employed as the heterogeneous photocatalyst (PC). Due to its excellent photocatalytic properties, good chemical stability and heterogeneous nature, the present method exhibits high efficiency, good functional group tolerance, easy scalability and remarkable catalyst reusability. More importantly, it provides an alternative way that allows rapid access to various C3 arylated or alkylated quinoxalin-2(1H)-ones in a greener and sustainable manner.     

酰胺连接的共价有机骨架的制备及其在水中高效光催化性能

光催化是将太阳能转换为化学能的绿色可持续发展途径,有望解决日益严重的能源危机和环境污染问题.在光催化过程中,半导体材料作为光催化剂,负责可见光的捕获、光生载流子的生成和传输以及氧化还原反应,在整个光催化系统中起着决定性的作用.共价有机骨架材料(COFs)是一类新兴的半导体光催化剂,已被证明在可见光诱导的水分解、二氧化碳还原、有机转化反应和水中污染物降解方面具有应用前景.然而,大部分COFs是通过可逆反应构筑的,在水中及苛刻条件下的稳定性差.因此,提升基于COFs的光催化剂在水相中的光催化活性和循环稳定性仍然面临巨大挑战.本文提出了一种新策略,即通过实现多重协同效应,设计和开发2D-COFs作为在水中的高效非均相光催化剂.通过后合成策略将亚胺键连接的2D-COFs氧化,制备了两种具有丰富三嗪结构单元的以酰胺键连接的2D-COFs(命名为COF-JLU18和COF-JLU19).结果表明,COF-JLU18和COF-JLU19具有高比表面积和孔体积,其比表面积分别为1156和541 m2/g;COF-JLU19具有比相似拓扑结构的亚胺COF-JLU17更好的水蒸气吸附性能.此外,COF-JLU19表现出了极高的化学稳定性,在水中、盐酸和氢氧化钠溶液中浸泡两天,其结构和结晶性均没有发生明显变化.由此可见,酰胺键不仅可以增加材料骨架的亲水性,还能够提高COFs对水的稳定性.本文制备的酰胺键连接的COF-JLU19材料,在光降解罗丹明B水溶液(RhB)反应中可以获得高达0.69 min?1的光降解速率常数,活性明显优于其他光催化剂,如C3N4等.COF-JLU19具有较好的催化活性主要归因于以下两方面:一方面,良好的亲水性和固有孔隙率之间的协同效应可以增强COFs在水中对染料的吸附能力,使其光催化活性得到有效提升;另一方面,高的结晶度和优秀的稳定性使酰胺键连接的COFs在多相光催化中实现稳定循环利用.为了扩展COFs的应用前景,本文还制备了一种基于酰胺键连接COFs的静电纺丝膜,在以太阳光为光源的光降解罗丹明B水溶液实验中表现出较高的光催化活性和重复使用性.综上,本文提出的多重协同效应为基于COFs的高效光催化剂的设计提供了一种有效策略.     

Synthesis of visible-light-driven TiO2 yolk-shell spheres with {0 0 1} facets dominated mesoporous shells

Anatase phase visible-light-driven TiO2 yolk-shell spheres with the size of ca. 1-2 μm have been synthesized with the combination of solvothermal and heat treatment method. XRD, SEM, TEM, XPS, and PL analysis were used to examine structure and properties of the photocatalyst. The N species and Ti3+ centers introduced into the as-prepared photocatalyst can enhance the visible light absorption significantly. The mesoporous shell of the prepared photocatalyst, which promotes the pollutant adsorption ability, consists of the high-reactive {0 0 1} facets dominated nanocrystals. Due to the unique structure, it is also observed that the as-prepared visible-light-driven TiO2 yolk-shell spheres exhibit a superior photocatalytic activity for organic dyes decomposition than the well-known P25.     

Fabrication of Cu/rGO/MoS2 nanohybrid with energetic visible-light response for degradation of rhodamine B

A novel visible-light-driven Cu/rGO/MoS₂ ternary nanostructure as a photocatalyst with high catalytic activity towards degradation of rhodamine B was successfully synthesized through a facile solvothermal method.     

Fabrication of Cu/rGO/MoS2 nanohybrid with energetic visible-light response for degradation of rhodamine B

A novel visible-light-driven Cu/rGO/MoS₂ (CRM) ternary nanostructure as a photocatalyst with high catalytic activity towards environmental purification using solar energy was successfully synthesized through a facile solvothermal method. It was found that the nanoflower structure of MoS₂ increased the number of its exposed edges. Meanwhile rGO as a catalytic substrate played a role of charge-carrier channel to improve the separation of holes and electrons, which originated from the band gap absorption of MoS₂. The content of Cu in photocatalyst affected photocatalytic performance obviously. And the optimal 30% Cu/rGO/MoS₂ possessed the highest photocatalytic performance, which could be attributed to the improved separation of charges and synergistic effects among Cu, rGO and MoS₂. The removal efficiency of Rhodamine B (RhB) over CRM was up to 100% in 5 min. CRM as a photocatalyst maintained good reproducibility and stability during 3 times of the recycle experiments. These results indicate CRM is a promising photocatalyst for degrading organic pollutants in wastewater.     

Photocatalytic Oxidative [3+2] Cycloaddition for Pyrrolo[2,1-a]isoquinoline Synthesis Using a Porphyrin-Based Covalent Organic Framework

By using a catalytic amount of a porphyrin-based covalent organic framework (Por-Ad-COF) as the efficient recyclable photocatalyst, the photocatalytic oxidative [3+2] cycloaddition reaction between tetrahydroisoquinolines and N-substituted maleimides was developed under aerobic conditions at room temperature. Various substituted pyrrolo[2,1-a]isoquinolines were obtained in moderate to good yields via the dipolar [3+2] cycloaddition and oxidative aromatization cascade process under visible light irradiation. This was the first example to employ the covalent organic framework as the heterogeneous photocatalyst to perform the photocatalytic dipolar [3+2] cycloaddition reaction for the synthesis of pyrrolo[2,1-a]isoquinolines.     

A new efficient visible-light-driven photocatalyst Na0.5Bi1.5VMoO8 for oxygen evolution

A new visible-light-driven photocatalyst Na_0.5Bi_1.5VMoO₈ was developed by making a solid solution of BiVO₄ and (NaBi)_0.5MoO₄. The prepared powders were confirmed crystallizing in the tetragonal scheelite crystal structure by the XRD patterns and Raman spectra. Different from that of the tetragonal BiVO₄, Na_0.5Bi_1.5VMoO₈ showed a high activity for photocatalytic O₂ evolution under visible light irradiation, which is even better than that of monoclinic BiVO₄, a well-known efficient visible-light-driven photocatalyst. The mechanism of the improved activity of Na_0.5Bi_1.5VMoO₈ was discussed.     

双功能S-型g-C3N4/Bi/BiVO4复合光催化剂驱动人工碳循环（英文）

长期以来,陆地、大气和海洋之间的碳循环维持了大自然碳平衡.随着密集人类活动和高度工业发展,碳燃料、碳化学品和碳材料广泛应用于各个领域,导致碳排放过量,碳平衡已被严重破坏,碳污染已成为一个严峻问题.例如,持久性有机污染物和挥发性有机化合物过量排放到环境中,威胁着人类的健康和生态平衡.人们陆续开发出各种先进的环境技术,如微生物分解,去除空气和水中的碳基污染物,将有毒有害的有机化合物转化为无害CO2.但是,CO2本身是大气中的主要温室气体,它在大气中的浓度早超过了天然碳循环所能维持的环境自洁净能力.基于先进催化技术建立人工碳循环,将有机污染物矿化生成的CO2进一步转化为有价值的有机化学品(如太阳能燃料)是一种理想的低碳方法.光合作用是自然碳循环中核心过程之一,是降低大气中CO2浓度的关键.受到光合作用启发,科学家们积极开发人工光合成技术推动CO2资源化.人工光合成技术本质上基于半导体光催化过程.半导体光催化过程具有双重作用.一方面,基于有氧光催化氧化过程,有机污染物可以矿化生成无毒CO2.另一方面,基于缺氧光催化还原过程,CO2可以转化为碳氢化合物太阳能燃料.理论上,结合上述两个过程,为建立人工碳循环奠定基础,但是,至今很少有人成功建立有氧氧化-无氧还原串联光催化工艺,实现人工碳循环.难点在于有机污染物的有氧氧化反应和CO2的无氧还原反应的操作条件与反应机制是完全不同的,目前缺乏同时适用于上述两种反应的双功能光催化剂.本文成功构建了具有双功能的g-C3N4/Bi/BiVO4三元复合光催化剂,它不仅在降解有机污染物方面表现出优异的有氧光催化氧化性能(以降解染料罗丹明B为例),而且还表现出优异的缺氧CO2光催化还原性能.此外,基于“一锅法”厌氧耦合氧化-还原反应,g-C3N4/Bi/BiVO4三元复合光催化剂成功实现同步罗丹明B降解与太阳能燃料生成,构建了从毒害有机污染物到高品质太阳燃料的碳循环.结合牺牲剂实验分析与密度泛函理论理论计算,作者提出g-C3N4/Bi/BiVO4复合光催化剂的双功能性与g-C3N4与BiVO4界面内建S-型复合异质结有关.S-型复合异质结既促进界面电荷转移与分离,又维持了最佳电荷氧化还原电位.此外,S型g-C3N4/Bi/BiVO4复合光催化剂中原位生成的具有等离子体效应的Bi纳米颗粒具有双重作用,既促进界面电荷定向转移,又促进可见光吸收.本文开发的新型双功能S-型g-C3N4/Bi/BiVO4复合光催化剂系统为进一步开发集成式有氧-缺氧光催化碳循环反应系统奠定基础.     

Magnetic retrievable Ag/AgBr/ZnFe2O4 photocatalyst for efficient removal of organic pollutant under visible light

In the present work, a visible-light-driven Ag/AgBr/ZnFe₂O₄ photocatalyst has been successfully synthesized via a deposition–precipitation and photoreduction method. The crystal structure, chemical composition, morphology and optical properties of the as-prepared nanocomposites were characterized by X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscope, UV–vis diffuse reflectance spectroscopy and photoluminescence. The photocatalytic activities of the Ag/AgBr/ZnFe₂O₄ nanocomposites were evaluated through the photodegradation of gaseous toluene and methyl orange (MO) under visible light. The results revealed that the as-prepared Ag/AgBr/ZnFe₂O₄ nanocomposite exhibited excellent photocatalytic activity. The degrading efficiency of MO could still reach 90% after four cycles, and the Ag/AgBr/ZnFe₂O₄ nanocomposite could be recycled easily by a magnet. Additionally, the enhanced photocatalytic mechanism was discussed according to the trapping experiments, which indicated that the photo-generated holes (h⁺) and •O₂⁻ played important roles in photodegradation process. At last, a possible photocatalytic oxidation pathways of toluene was proposed based on the results of GC–MS. The Ag/AgBr/ZnFe₂O₄ composites showed potential application for efficient removal of organic pollutant.     

光催化有机物偶联/芳构化放氢反应研究进展

光催化氧化还原反应具有绿色、高效、安全等优势,已经在有机化学中得到广泛关注.介绍了基于光催化的偶联/芳构化放氢反应,通过使用光催化剂/催化剂的双催化体系,可用于光催化有机碳-碳和碳-杂原子成键反应,且反应中氢气是唯一的副产物.强调了有机光氧化还原体系的构建与催化机理.     

Visible-Light-Enabled C−H Functionalization by a Direct Hydrogen Atom Transfer Uranyl Photocatalyst

The development of the uranyl cation as a powerful photocatalyst is seriously delayed in comparison with the advances in its fundamental and structural chemistry. However, its characteristic high oxidative capability in the excited state ([UO₂]²⁺* (+2.6 V vs. SHE; SHE=standard hydrogen electrode) combined with blue-light absorption (hv=380 – 500 nm) and a long-lived fluorescence lifetime up to microseconds have reveals that the uranyl cation approaches an ideal photocatalyst for visible-light-driven organic transformations. Described herein is the successful use of uranyl nitrate as a photocatalyst to enable C(sp³)−H activation and C−C bond formation through hydrogen atom transfer (HAT) under blue-light irradiation. In particular, this operationally simple strategy provides an appropriate approach to the synthesis of diverse and valuable diarylmethane motifs. Mechanistic studies and DFT calculations have provided insights into the detailed mechanism of the photoinduced HAT pathway. This research suggests a general platform that could popularize promising uranyl photocatalytic performance.     

Reduced graphene oxide as capturer of dyes and electrons during photocatalysis: surface wrapping and capture promoted efficiency

To elucidate the roles of graphene in photoelectric events and mass transfer during photocatalytic process is important for engineering graphene-semiconductor hybrid photocatalyst. Here, we demonstrated reduced graphene oxide (RGO) capturing dyes and photoinduced electrons during photocatalytic degradation of organic dyes in water. It captures dyes from water through adsorption and desorption irreversible hysteresis, and captures photoinduced electrons from semiconductor through surface junction. The RGO was attached to the surface of TiO(2) in the form of surface wrapping. After one-step photocatalytic reduction of graphene oxide (GO) and TiO(2) in ethanol-water solvent under UV irradiation, the RGO wrapped TiO(2) hybrid (graphene-w-TiO(2)) photocatalyst was obtained. Using visible absorption spectroscopy, we also demonstrated these captured dyes were degraded during photocatalysis. The photocatalytic test showed the RGO significantly improved the photocatalytic activity of this hybrid photocatalyst.     

光催化剂Bi1-xGdxVO4的制备和表征及其光催化分解水

通过高温固相法合成了不同组分的光催化剂Bi1-xGdxVO4(x=0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1.0), 并用X射线衍射(XRD)、紫外-可见漫反射光谱(DRS)、比表面积分析(BET)、扫描电子显微镜(SEM)对催化剂Bi1-xGdxVO4进行了表征和分析. XRD结果表明, 在Bi1-xGdxVO4中存在两种结构, 当0.3≤x≤1.0时, Bi1-xGdxVO4为四方晶系硅酸锆型结构; 当x=0时, 为单斜晶系白钨矿结构BiVO4; 当0相似文献   

Reticular Synthesis of One-Dimensional Covalent Organic Frameworks with 4-c sql Topology for Enhanced Fluorescence Emission

Covalent organic frameworks (COFs) have been extensively investigated due to their unique structure, porosity, and functionality. However, at the topological level, COFs remain as two-dimensional (2D) or three-dimensional (3D) structures, while COFs with one-dimensional (1D) topology have not been systematically explored. In this work, we proposed a synthetic strategy for the construction of 1D-COFs based on non-linear edges and suitable high-symmetry vertices. Compared with their 2D-COFs counterparts, the 1D-COFs with AIEgens located at the vertex of the frame exhibited enhanced fluorescence. The density functional theory (DFT) calculations revealed that the dimensional-induced rotation restriction (DIRR) effect could spontaneously introduce additional non-covalent interactions between the strip frames, which could substantially diminish non-radiative transitions. This work also provides protocols for the design of 1D-COFs and a guidance scheme for the synthesis of emitting COFs.     

Fe2O3掺杂对WO3光催化降解有机染料X3B的影响

发展高效的可见光催化剂是太阳能化学利用的一个挑战. 本文采用简单的混合方法, 制备了WO₃和Fe₂O₃的混合物, 研究了该复合氧化物在H₂O₂存在下光催化降解有机染料X3B的活性. 实验表明, 催化剂的光催化活性与其煅烧温度和Fe₂O₃含量有关. 最佳煅烧温度和Fe₂O₃含量分别等于400 °C 和1.0% (w). 根据自由基捕获电子顺磁共振(EPR)波谱分析, 复合氧化物产生羟基自由基的量远高于Fe₂O₃和WO₃. 我们推测, 这种协同效应来源于WO₃和Fe₂O₃之间的电荷转移, 从而加快半导体光生载流子的分离和X3B的光催化降解.     

基于可见光催化分解水制氢的物理化学综合实验设计

将可见光催化分解水制氢引入物理化学综合实验,系统介绍了催化剂制备、表征及光催化反应性能评价等实验内容.以无毒、易制备的g-C3N4作为实验用可见光催化剂,考查了制备温度对催化剂的结构及光催化性能的影响.     

TiO2薄膜光催化降解4-(2-吡啶偶氮)间苯二酚的研究

为了探索有机物４－（２－吡啶偶氮）间苯二酚（ＰＡＲ）,在固定光催化剂上的降解行为,采用溶胶一凝胶法,在玻璃表面制得均匀透明的纳米ＴｉＯ２薄膜,并以其作光催化剂,在２５４ｎｍ紫外光照射下,进行ＰＡＲ水溶液的光催化降解研究。研究了ＰＡＲ光催化降解率与溶液ｐＨ值、ＰＡＲ初始浓度、助催化剂（Ｈ２Ｏ２）浓度和不同光照条件的变化关系,得出了ＴｉＯ２薄膜的光催化降解ＰＡＲ的有利条件。     

A Porphyrin-Based Covalent Organic Framework for Metal-Free Photocatalytic Aerobic Oxidative Coupling of Amines

Imines are important intermediates in drug synthesis. Photocatalytic aerobic oxidative coupling of amines has been considered as a clean and promising way to produce imines and has attracted great attention. Herein, we designed and synthesized a novel two-dimensional porphyrin-based covalent organic framework (Por-BC-COF) which adopts an AA stacking mode with excellent crystallinity, high Brunauer–Emmett–Teller surface areas (1200 m² g⁻¹), wide light absorption range (200–1300 nm) and good stability in a variety of organic solvents. Por-BC-COF can be used as a metal-free heterogeneous photocatalyst for the photocatalytic oxidation of amines to imines under visible light and red light with a high yield (97 %). This work presents a novel and efficient COF photocatalyst in the application of light-driven organic synthesis.     

Development of TiO<Subscript>2</Subscript> photocatalysts suitable for practical use and their applications in environmental cleanup

Recently, environmental disruption is proceeding on a global scale through the consumption of huge amounts of fossil fuels and the emission of various chemical substances. However, these substances resist bio-treatment. TiO₂ generates electrons and holes by irradiation with light. Most organic micro-pollutants, including dioxins, are decomposed into carbon dioxide and water by the effect of the holes with high oxidative potential. By using such a photocatalytic reaction, various applications are feasible for environmental cleanup. In general, TiO₂ powder has been utilized as photocatalyst, although TiO₂ powder photocatalyst has several disadvantages: (1) it is difficult to handle, (2) photocatalytic reaction is slow and it takes a lot of time for treatment and (3) it is difficult to apply to plastics and textiles, because the photocatalyst decomposes them. We have developed a photocatalyst suitable for practical use and have developed high-activity photocatalysts such as TiO₂ photocatalytic transparent film, photocatalytic silica-gel, apatite-coated TiO₂ photocatalyst usable for plastics and textiles, photocatalytic paper, photocatalytic blue charcoal and photocatalytic oxygen scavenger. The application of these high-activity photocatalysts has been studied in deodorization, anti-bacterial, self-cleaning, anti-stain, water treatment, air purification such as photocatalytic decomposition of dioxins and VOC, and NO _x removal. Now various photocatalytic articles using these new photocatalyst materials are on the market in Japan. Photocatalytic technology can create many valuable products for environmental use all over the world.     

Fe/Ti/Si复合纳米微粒光催化降解NO-2

采用溶胶－凝胶法制备了Ti/Si和不同浓度Fe^3 掺杂的Fe/Ti/Si复合纳米粉末,并利用XRD、BET、UV－vis等技术手段研究了Ti/Si复合微粒的表面结构形态变化,以及对污染物NO2^-光催化降解的影响。研究表明,Fe/Ti/Si复合微粒的催化活性高于Ti/Si体系,并且Fe/Ti/Si[ω（Fe^3 )=1.5%,m(Ti):m(Si)=2:1]具有最佳活性,样品呈晶化度较低的锐钛矿结构。Fe^3 掺杂导致晶粒的增大,稳定性降低,大大提高了半导体的光催化活性,有利于对低浓度NO2^-的光催化降解。