利用FraGen程序预测沸石分子筛的骨架结构

沸石分子筛是一类广泛应用于各种化工领域的微孔材料. 利用计算机方法搭建理论上合理的沸石骨架模型, 即沸石分子筛的结构预测, 不仅可以用来对已合成的沸石材料进行结构解析, 而且可以用来设计尚未被合成的具有新颖结构的沸石材料, 为未来实现沸石分子筛的定向合成提供靶向结构. 目前, 沸石材料的结构预测面临着许多亟待解决的难题, 其中最突出的问题是现有的结构预测方法产生合理结构的效率仍然非常低. 针对这一问题, 我们课题组开发了一套专门用于预测无机晶体结构的计算机程序——FraGen. FraGen程序可以在指定的晶胞内产生原子, 并根据平行回火的Monte Carlo 原理调整晶胞内原子的位置, 以产生合理的晶体结构. 在本文中, 我们首次利用FraGen 程序, 以已知的AET沸石结构为模板, 通过单独控制每个原子的Wyckoff点对称性, 预测出一系列新颖的沸石结构. 对比已有的结构预测方法, 我们的新方法在相同的条件下能够预测出更多化学上合理的沸石结构.     

Hexagonite: A Hypothetical Organic Zeolite

Elaborating the discrete hydrocarbon molecule bicyclo[2.2.2]-2,5,7-octatriene in three-dimensions, a unique, hypothetical allotrope of carbon is produced. Such a structure possesses a principal 6-fold axis; along this axis are hexagonal, organic tunnels with about a 5.70 Å outside tunnel diameter across opposite vertices, and an actual, inside diameter of 4.16 Å when taking into account the covalent radius of tetrahedral carbon. Across opposite edges, the outside hexagonal tunnel diameter is 4.94 Å, and the inside tunnel diameter is 3.61 Å. These tunnels are lined alternately with hexagonally disposed ethane-like functions and hexagonally disposed ethene-like functions that stack along the tunnel axis. The lattice lies in space group P6/mmm, and it has the Schläfli symbol given by (6, 3^2/5), it is therefore topologically related to the graphite–diamond hybrids. Because of the hexagonal symmetry of the unit cell, and also due to the fact that its polygonality is six, the structure has been given the name hexagonite. There are 10 carbon atoms in the unit of pattern, and the density is 2.50 g/cm³; bordered by the densities of graphite at 2.27 g/cm³ and diamond at 3.56  g/cm³. Its large organic channels, lined with π organic functions, may make it particularly useful as an organic zeolite material, or alternatively as a host lattice for ionic conduction. The electronic band structure of the empty, hexagonal host lattice is described.     

Porous Carbon Nitride Frameworks Derived from Covalent Triazine Framework Anchored Ag Nanoparticles for Catalytic CO2 Conversion

Porous carbon nitride frameworks (PCNFs) with uniform and rich nitrogen dopants and abundant porosity were successfully fabricated through the direct carbonization of the covalent triazine frameworks (CTFs) at different pyrolysis temperatures and used as supports to anchor and stabilize Ag nanoparticles (NPs) for catalytic CO₂ conversion. Importantly, the pyrolysis temperature plays a crucial role in the properties of porous carbon nitride frameworks. The material carbonized at 700 °C showed the highest surface area and micro- and mesoporous structure with a certain interlayer distance. Taking advantage of their unique surface characteristics, PCNF-supported Ag NP catalysts (Ag/PCNF-T, T=pyrolysis temperature) were prepared by a simple chemical method. A series of characterizations revealed that Ag NPs are embedded in the porous carbon nitride frameworks and confined to a relatively small size with high dispersion owing to the assistance of the abundant surface groups and porous structures. The as-obtained Ag/PCNF-T catalysts, especially Ag/PCNF-700, showed excellent catalytic activity, selectivity, and stability for the carboxylation of CO₂ with terminal alkynes under mild conditions. This can be due to the existence of abundant nitrogen atoms and diverse porosity, which resulted in highly efficient catalytic activity and stability.     

金属有机框架衍生的多孔碳修饰电极同时检测邻苯二酚和对苯二酚

本文运用金属有机框架(MOFs)作为模板,在惰性气体下热处理,合成金属有机框架衍生多孔碳材料(Metal Organic Frameworks Derived Porous Carbon,MDPC)。采用扫描电子显微镜(SEM)和X射线粉末衍射(XRD)分别对MDPC进行形貌和相纯度的表征。采用滴涂法将MDPC修饰在玻碳电极表面,运用循环伏安法(CV)、差分脉冲伏安法(DPV)、交流阻抗法(EIS)等电化学方法对该电极进行电化学表征,研究邻苯二酚(CC)和对苯二酚(HQ)在MDPC修饰电极上的电化学行为。结果表明,该修饰电极对CC和HQ这两种异构体表现出优异的氧化还原电活性和区分效果。在最佳实验条件下,CC和HQ的浓度在0.5~80μmol/L的范围内与氧化峰电流呈现良好的线性关系。CC和HQ的检测限分别为0.031μmol/L和0.11μmol/L。该方法电流响应大、灵敏度高、检测限低,具有实际应用前景。     

Electrochemical Aptasensor Based on Au Nanoparticles Decorated Porous Carbon Derived from Metal-Organic Frameworks for Ultrasensitive Detection of Chloramphenicol

A facile and sensitive electrochemical aptamer sensor (aptasensor) based on Au nanoparticles-decorated porous carbon (AuNPs/PC) composite was developed for the efficient determination of the antibiotic drug chloramphenicol (CAP). AuNPs modified metal-organic framework (AuNPs/ZIF-8) is applied as a precursor to synthesize the porous carbon with homogeneous AuNPs distribution through a direct carbonization step under nitrogen atmosphere. The as-synthesized AuNPs/PC exhibits high surface area and improved conductivity. Moreover, the loading AuNPs could enhance the attachment of the aptamers on the surface of electrode through the Au–S bond. When added to CAP, poorly conductive aptamer-CAP complexes are formed on the sensor surface, which increases the hindrance to electron transfer resulting in a decrease in electrochemical signal. Based on this mechanism, the developed CAP aptasensor represents a wide linear detection range of 0.1 pM to 100 nM with a low detection limit of 0.03 pM (S/N = 3). In addition, the proposed aptasensor was employed for the analysis of CAP in honey samples and provided satisfactory recovery.     

Functionalized Carbon Nanomaterials Derived from Carbohydrates

A tremendous growth in the field of carbon nanomaterials has led to the emergence of carbon nanotubes, fullerenes, mesoporous carbon and more recently graphene. Some of these materials have found applications in electronics, sensors, catalysis, drug delivery, composites, and so forth. The high temperatures and hydrocarbon precursors involved in their synthesis usually yield highly inert graphitic surfaces. As some of the applications require functionalization of their inert graphitic surface with groups like ? COOH, ? OH, and ? NH₂, treatment of these materials in oxidizing agents and concentrated acids become inevitable. More recent works have involved using precursors like carbohydrates to produce carbon nanostructures rich in functional groups in a single‐step under hydrothermal conditions. These carbon nanostructures have already found many applications in composites, drug delivery, materials synthesis, and Li ion batteries. The review aims to highlight some of the recent developments in the application of carbohydrate derived carbon nanostructures and also provide an outlook of their future prospects.     

A Stable Extra-Large Pore and High-Silica Zeolite Derived from Ge-Rich Precursor

A multidimensional extra-large pore zeolite with highly hydrothermal stability, denoted as −IRT−HS , has been developed successfully, starting from Ge-rich germanosilicate precursor hydrothermally directed by a small and commercially available piperidinium-type organic structure-directing agent (OSDA). −IRT−HS , with the supermicropores, is structurally analogues to 28-membered ring −IRT topology as confirmed by various spectroscopic techniques. And it is the high-silica (Si/Ge=58) zeolite with the largest pore size as well. Notably, using acid-washed as-made Ge-rich −IRT precursor as the silicon source is crucial to restore partially collapsed structure into a stable framework by OSDA-assisted recrystallization. The calcined −IRT−HS maintains a high crystallinity, even when stored in a humid environment for extended periods or directly exposed to water. Additionally, high silica Al-containing analogue is also readily synthesized, serving as an active solid-acid catalyst in 1,3,5-triisopropylbenzene cracking reaction, yielding an impressive initial conversion up to 76.1 % much higher than conventional large-pore Beta zeolite (30.4 %). This work will pave the way for the designed synthesis of targeted high-silica zeolites with stable and extra-large pore frameworks, mimicking the structures of existing Ge-rich counterparts.     

Porous Nitrogen‐Doped Carbon Microspheres Derived from Microporous Polymeric Organic Frameworks for High Performance Electric Double‐Layer Capacitors

This research presents a simple and efficient method to synthesize porous nitrogen‐doped carbon microspheres (PNCM) by the carbonization of microporous poly(terephthalaldehyde‐pyrrole) organic frameworks (PtpOF). The common KOH activation process is used to tune the porous texture of the PNCM and produce an activated‐PNCM (A‐PNCM). The PNCM and A‐PNCM with specific surface area of 921 and 1303 m² g^?1, respectively, are demonstrated as promising candidates for EDLCs. At a current density of 0.5 A g^?1, the specific capacitances of the PNCM and A‐PNCM are 248 and 282 F g^?1, respectively. At the relatively high current density of 20 A g^?1, the capacitance remaining is 95 and 154 F g^?1, respectively. Capacity retention of the A‐PNCM is more than 92 % after 10 000 charge/discharge cycles at a current density of 2 A g^?1.     

含氮金属有机框架衍生的铜基催化剂电催化还原二氧化碳

With the development of human society and economy, the demand for energy resources has also increased rapidly. However, the use of traditional fossil energy leads to high amounts of carbon dioxide emissions, causing severe greenhouse effects. This, in turn, triggers a series of environmental problems. Harnessing renewable energy such as solar energy, wind energy, and hydropower to replace the traditional energy sources is very urgent. Conversion CO₂ into value-added fuels and chemicals could be a useful strategy to mitigate the current energy and environmental crisis. It is well known that Cu-based materials are good electrocatalysts for the electrochemical reduction of CO₂ (ECR-CO₂). However, they suffer from some disadvantages such as high overpotential and poor selectivity and durability. Therefore, the development of copper based electrocatalysts with high activity and selectivity is essential.     

由含铝金属有机骨架材料制备的多孔碳在锂硫电池中的应用

采用水热法制备了一种含铝金属有机骨架材料, 其在高温下发生炭化得到多孔碳, 最后与硫复合制得锂硫电池正极材料. XRD图谱显示在高温炭化时多孔碳样品出现了部分石墨化. N₂等温吸附-脱附测试分析显示合成的多孔碳材料含有微孔和介孔结构. 对不同载硫量的锂硫电池进行了充放电性能测试, 结果显示S质量分数为46.3%的样品在0.01 C倍率下首次放电容量达到1272 mA·h/g; 在0.1 C倍率下首次放电容量为934 mA·h/g, 循环性能良好.     

二维层状分子筛前驱体的合成、改性及催化应用

二维层状分子筛前驱体具有三维分子筛的层结构单元,具备母体分子筛的特性,其开放二维片层骨架结构给合成新分子筛以及基于其改性得到新衍生结构分子筛提供新机遇,是近年来分子筛研究领域一个新热点。大量二维片层前驱体可直接合成或通过三维分子筛后处理获得,基于二维片层前驱体人们发展了溶胀、剥层、柱撑、原子扩孔、层重组等层操纵的策略,通过这些策略一些常规方法难以合成或不符合理论规则的分子筛被合成出来,这极大地丰富了二维层状分子筛前驱体的研究领域,扩展了其应用范围。本文概述了二维层状分子筛前驱体的结构特点,系统总结了近年来二维层状分子筛前驱体的合成方法,在此基础上着重阐述了其改性获得新结构分子筛的新策略,并介绍了在多相催化反应中的应用。     

Graphene-Like Carbon Derived from Macadamia Nut Shells for High-Performance Supercapacitor

The graphene-like carbon was obtained from macadamia nut shells by an activated hydrothermal method and applied for high-performance supercapacitors. The morphologies and microstructures are investigated by X-ray diffractometer, Raman spectrometer, scanning electron microscopy and transmission electron microscopy. The experimental results show that the obtained carbon exhibits perfect graphene-like structure filled with more micropores and mesopores. The graphene-like carbon displays high surface areas of 1057 m² g^?1. The graphene-like carbon delivers an impressive specific capacitance of 251 F g^?1 and has no capacitance loss at the current density of 1 A g^?1 after 1000 cycles, which demonstrates the excellent cycle stability and high specific capacitance. The graphene-like carbon derived from macadamia nut shells can be expected for the widespread application of supercapacitors.

     

Microscopic and Mesoscopic Dual Postsynthetic Modifications of Metal–Organic Frameworks

We report the dual postsynthetic modification (PSM) of a metal–organic framework (MOF) involving the microscopic conversion of C?H bonds into C?C bonds and the mesoscopic introduction of hierarchical porosity. MOF crystals underwent single‐crystal‐to‐single‐crystal transformations during the electrophilic aromatic substitution of Co₂(m‐DOBDC) (m‐DOBDC^4?=4,6‐dioxo‐1,3‐benzenedicarboxylate) with alkyl halides and formaldehyde. The steric hindrance caused by the proximity of the introduced functional groups to the coordination bonds reduced bond stability and facilitated the transformation into hierarchically porous mesostructures by etching with in situ generated protons (hydroniums) and halides. The numerous defect sites in the mesostructural MOFs are potential water‐sorption sites. However, since the introduced functional groups are close to the main adsorption sites, even methyl groups are able to considerably decrease water adsorption, whereas hydroxy groups increase adsorption at low vapor pressures.     

Carbon Dioxide Sensitivity of Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks of zinc, cobalt, and cadmium, including the framework ZIF‐8 commercially sold as Basolite Z1200, exhibit surprising sensitivity to carbon dioxide under mild conditions. The frameworks chemically react with CO₂ in the presence of moisture or liquid water to form carbonates. This effect, which has been previously not reported in metal–organic framework chemistry, provides an explanation for conflicting reports on ZIF‐8 stability to water and is of outstanding significance for evaluating the potential applications of metal–organic frameworks, especially for CO₂ sequestration.     

Nanostructure Engineering of Metal–Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient ORR Catalyst

Heteroatom doping is considered an efficient strategy when tuning the electronic and structural modulation of catalysts to achieve improved performance towards renewable energy applications. Herein, we synthesized a series of carbon-based hierarchical nanostructures through the controlled pyrolysis of Co-MOF (metal organic framework) precursors followed by in situ phosphidation. Two kinds of catalysts were prepared: metal nanoparticles embedded in carbon nanotubes, and metal nanoparticles dispersed on the carbon surface. The results proved that the metal nanoparticles embedded in carbon nanotubes exhibit enhanced ORR electrocatalytic performance, owed to the enriched catalytic sites and the mass transfer facilitating channels provided by the hierarchical porous structure of the carbon nanotubes. Furthermore, the phosphidation of the metal nanoparticles embedded in carbon nanotubes (P-Co-CNTs) increases the surface area and porosity, resulting in faster electron transfer, greater conductivity, and lower charge transfer resistance towards ORR pathways. The P-Co-CNT catalyst shows a half-wave potential of 0.887 V, a Tafel slope of 67 mV dec⁻¹, and robust stability, which are comparatively better than the precious metal catalyst (Pt/C). Conclusively, this study delivers a novel path for designing multiple crystal phases with improved catalytic performance for energy devices.     

Metal Organic Frameworks Derived Catalysts for the Upgrading of Platform Chemicals

Biomass plays a significant role in replacing fossil resources, and catalytic transformation of platform chemicals to high-value chemicals is an effective approach to maximize the utilization of biomass. Among of which, efficient and durable catalysts are the heart for upgrading of these platform chemicals, and metal–organic frameworks (MOFs)-derived catalysts have attracted much attentions due to their suitable and versatile physicochemical properties. In this work, we present a short review on the applications of MOFs-derived catalysts in upgrading of platform chemicals. The design and synthetic strategies of MOFs-derived catalysts were summarized in detail, and their application in the catalytic upgrading of glycerol, ethanol, furanic compounds, levulinic acid and vanillin were addressed. The final section outlines the potential industrial applications of MOFs-derived catalysts for upgrading platform chemicals.     

Two-Dimensional Mesoporous Carbon Materials Derived from Fullerene Microsheets for Energy Applications

Porous carbon materials rich in defects are promising candidates in energy storage and conversion applications. Herein, a facile template-free approach is reported for the synthesis of a two-dimensional (2 D) mesoporous carbon material derived from fullerene (C₆₀) microsheets (FMSs) through simple heat treatment. The sample obtained at 1000 °C (FMS1000) shows a large surface area of 1507.6 m² g⁻¹ owing to the presence of mesopores and rich defects, which promote electron and mass transfer in the electrocatalytic process of the oxygen reduction reaction (ORR), showing an excellent performance with an onset potential of 0.95 V, a half-wave potential of 0.85 V, and long-term durability of 2000 cycles, comparable to the performance of commercial Pt/C. Moreover, FMS1000 displays a remarkable supercapacitive property with a specific capacitance of 330.7 F g⁻¹ at 0.2 A g⁻¹ and good long-term stability with a capacitance retention of 97 % over 50 000 cycles. Thus, a practical strategy for the production of mesoporous carbon materials with different morphological structures and porous defects as high-performance energy materials is advanced.