Ultrathin Chiral Metal–Organic‐Framework Nanosheets for Efficient Enantioselective Separation

Chiral metal–organic framework (CMOF) nanosheets only a few layers thick remain a virgin land waiting for exploration. Herein, the first examples of ultrathin CMOF nanosheets are prepared by the confinement growth of two‐dimensional (2D) chiral layers, which are assembled by helical metal–organic chains within microemulsion. This convenient and easily scaled up inverse microemulsion method gives a series of 2D CMOF nanosheets composed of variable metal nodes or chiral ligands. More significantly, thanks to the exceptionally large number of chiral sites exposed on surfaces, the as‐obtained CMOF nanosheets exhibit much higher enantioselectivity in chiral separation compared with their bulk counterparts.     

S掺杂的HTiNbO5纳米片: 一种新型高效可见光催化剂

将层状HTiNbO₅剥层絮凝成HTiNbO₅纳米片, 然后与硫脲焙烧, 制得了S掺杂的HTiNbO₅纳米片. 与原始HTiNbO₅和HTiNbO₅纳米片相比, 该样品具有较大的比表面积和明显的可见光吸收. 以罗丹明B为降解物, 评价了该催化剂的吸附性能和可见光催化性能. 结果表明, HTiNbO₅纳米片和S掺杂的HTiNbO₅纳米片都具有很好的吸附能力和很高的可见光降解速率. 然而, 对于罗丹明B的矿化, S掺杂的HTiNbO₅纳米片可以达到41%矿化率, 而HTiNbO₅纳米片上矿化单几乎为零. 这说明S掺杂能有效改善纳米片的光催化效果. 最后, 对可能的光催化机理进行了探讨.     

Gas-Sensing Activity of Amorphous Copper Oxide Porous Nanosheets

In this paper, the gas-sensing properties of copper oxide porous nanosheets in amorphous and highly crystalline states were comparatively investigated on the premise of almost the same specific surface area, morphology and size. Unexpectedly, the results show that amorphous copper oxide porous nanosheets have much better gas sensing properties than highly crystalline copper oxide to a serious of volatile organic compounds, and the lowest detection limit (LOD) of the amorphous copper oxide porous nanosheets to methanal is even up to 10 ppb. By contrast, the LOD of the highly crystalline copper oxide porous nanosheets to methanal is 95 ppb. Experiments prove that the oxygen vacancies contained in the amorphous copper oxide porous nanosheets play a key role in improving gas sensitivity, which greatly improve the chemical activity of the materials, especially for the adsorption of molecules containing oxygen-groups such as methanal and oxygen.     

A Facile Steam Reforming Strategy to Delaminate Layered Carbon Nitride Semiconductors for Photoredox Catalysis

The delamination of layered crystals that produces single or few‐layered nanosheets while enabling exotic physical and chemical properties, particularly for semiconductor functions in optoelectronic applications, remains a challenge. Here, we report a facile and green approach to prepare few‐layered polymeric carbon nitride (PCN) semiconductors by a one‐step carbon/nitrogen steam reforming reaction. Bulky PCN, obtained from typical precursors including urea, melamine, dicyandiamide, and thiourea, are exfoliated into few‐layered nanosheets, while engineering its surface carbon vacancies. The unique sheet structures with strengthened surface properties endow PCNs with more active sites, and an increased charge separation efficiency with a prolonged charge lifetime, drastically promoting their photoredox performance. After an assay of a H₂ evolution reaction, an apparent quantum yield of 11.3 % at 405 nm was recorded for the PCN nanosheets, which is much higher than those of PCN nanosheets. This delamination method is expandable to other carbon‐based 2D materials for advanced applications.     

Facile Synthesis of Ultrathin Lepidocrocite Nanosheets from Layered Precursors

Ultrathin two‐dimensional nanosheets have been widely studied because of their peculiar properties and promising applications. As a typical layered material, successful exfoliation of freestanding ultrathin lepidocrocite (γ‐FeOOH) nanosheets from the bulk material has not been reported to date. Herein, we report a facile synthetic route to prepare ultrathin lepidocrocite nanosheets with a thickness of approximately 2–3 nm from FeO_x–propanediol layered precursors through weakening of the hydrogen bonds during the crystallization process. The ultrathin morphology and single‐crystal structure of the nanosheets were confirmed by transmission electron microscopy, X‐ray diffraction, and atomic force microscopy. The formation process of these nanosheets demonstrated simultaneous exfoliation and crystallization of lepidocrocite in basic aqueous solution. The obtained ultrathin nanosheets exhibited a much lower Néel temperature (18.3 K) than bulk lepidocrocite and weak ferromagnetic behavior below this temperature.     

Preconcentration of U(VI) ions on few-layered graphene oxide nanosheets from aqueous solutions

Graphene oxide nanosheets have attracted multidisciplinary attention due to their unique physicochemical properties. Herein, few-layered graphene oxide nanosheets were synthesized from graphite using a modified Hummers method and were characterized by TEM, AFM, Raman spectroscopy, XPS, FTIR spectroscopy, TG-DTA and acid-base titrations. The prepared few-layered graphene oxide nanosheets were used as adsorbents for the preconcentration of U(VI) ions from large volumes of aqueous solutions as a function of pH, ionic strength and temperature. The sorption of U(VI) ions on the graphene oxide nanosheets was strongly dependent on pH and independent of the ionic strength, indicating that the sorption was mainly dominated by inner-sphere surface complexation rather than by outer-sphere surface complexation or ion exchange. The abundant oxygen-containing functional groups on the surfaces of the graphene oxide nanosheets played an important role in U(VI) sorption. The sorption of U(VI) on graphene oxide nanosheets increased with an increase in temperature and the thermodynamic parameters calculated from the temperature-dependent sorption isotherms suggested that the sorption of U(vi) on graphene oxide nanosheets was an endothermic and spontaneous process. The maximum sorption capacities (Q(max)) of U(VI) at pH 5.0 ± 0.1 and T = 20 °C was 97.5 mg g(-1), which was much higher than any of the currently reported nanomaterials. The graphene oxide nanosheets may be suitable materials for the removal and preconcentration of U(VI) ions from large volumes of aqueous solutions, for example, U(VI) polluted wastewater, if they can be synthesized in a cost-effective manner on a large scale in the future.     

Thermal expansion-quench of nickel metal-organic framework into nanosheets for efficient visible light CO2 reduction

Metal-organic framework nanosheets (MOF NNs) offer potential opportunities for many applications,but an efficient strategy for the scalable preparation of few-layered two-dimensional (2D) MOF NNs are still a major challenge.Herein,we present an efficient top-down method for the synthesis of the Ni-BDC(Ni₂(OH)₂(1,4-BDC);1,4-BDC=1,4-benzenedicarboxylate) nanosheets utilizing a novel thermal expansionquench method of the flowerlike bulky MOFs in liquid N₂.The obtain...     

A Conductive Hybridization Matrix of RuO2 Two‐Dimensional Nanosheets: A Hybrid‐Type Photocatalyst

A universal methodology to efficiently improve the photocatalyst performance of semiconductors was developed by employing exfoliated RuO₂ two‐dimensional nanosheets as a conducting hybridization matrix. The hybridization with a RuO₂ nanosheet is easily achieved by crystal growth or electrostatically derived anchoring of semiconductor nanocrystals on the RuO₂ nanosheet. An enhanced chemical interaction of inorganic semiconductor with hydrophilic RuO₂ nanosheet is fairly effective in optimizing their photocatalytic activity and photostability by the enhancement of charge separation and charge mobility. The RuO₂‐containing nanohybrids show much better photocatalyst functionalities than do the graphene‐containing ones. The present study clearly demonstrates that hydrophilic RuO₂ nanosheets are superior hybridization matrices, over the widely used hydrophobic graphene nanosheets, for exploring new efficient hybrid‐type photocatalysts.     

一步法合成g-C3N4纳米片用作苯酚可见光降解高效催化剂

石墨相氮化碳(g-C3N4)是一种在室温条件下最稳定的氮化碳.同时g-C3N4的带隙为2.7 eV,可以利用可见光催化很多反应,例如光解水、CO2还原、有机污染物降解和有机物合成.但普通体相g-C3N4的光催化性能不尽如人意,主要是由于普通体相材料的载流子复合效率高,可见光(<450 nm)利用率低且比表面积小.众所周知,半导体的光催化性能与材料表面状态密切相关,因此可以控制合成条件来制备有利于光催化形貌的g-C3N4材料.普通体相g-C3N4材料的比表面积较小,约为10 m2/g,导致传质作用较差,光生电子-空穴复合严重,因此制备高比表面积的g-C3N4材料是目前研究的热点.我们发现在550℃下将三聚氰胺和三聚氰酸一起煅烧可以一步热合成g-C3N4纳米片,合成温度较低,对材料带隙影响小,同时可以提高材料比表面积,从而极大地提高了材料的光降解苯酚性能.XRD测试发现,随着前驱体中三聚氰酸比例增加,材料的主峰从27.38°显著偏移到27.72°.这表明三嗪环面内相连构成CN平面,同时CN层也会有堆叠最终形成g-C3N4材料.通过BET测试,g-C3N4纳米片的比表面积为103.24 m2/g.采用AFM分析得到g-C3N4纳米片的厚度为3.07 nm.研究了该g-C3N4纳米片的光降解性能,结果显示,在可见光照射30 min后,使用这种g-C3N4纳米片作为催化剂的条件下,苯酚降解率达到最优的81%.在5次循环利用后,g-C3N4(1:9)的降解率还能保持在80%以上,说明材料有良好的循环稳定性.这主要得益于材料的纳米片结构,在对苯酚吸附时不会有很复杂的吸附与脱附过程.同时纳米片结构可为有机污染物的吸附和原位降解提供传质通道.光反应体系中的产物由HPLC检测,分析苯酚的降解产物及产物的产量可以大致推测苯酚可能的降解历程.在三聚氰酸作用下,CN聚合层弯曲,减少了CN层之间的相互结合,同时不会对材料的带隙产生影响.同时整个合成过程无需引发剂,也不会导致CN层的基本单元和连接方式发生改变,同时由于二维片层结构,提高了材料的电荷分离效率.通过苯酚的降解实验得知三聚氰胺与三聚氰酸的比例为1:9,在550℃下煅烧得到的g-C3N4纳米片的光降解性能最优,同时具有很好的催化稳定性.     

Single-step synthesis of layered double hydroxides ultrathin nanosheets

A novel single-step approach was developed to prepare large-scale MgAl-LDHs ultrathin nanosheets. The key point of the successful realization was that we employed a high concentration of H(2)O(2). Oxygen molecules, derived from in situ decomposition of H(2)O(2), were speculated to be the decisive factor leading to complete separation of LDHs layers. The ultrathin nanosheets were characterized by XRD, TEM, AFM, FT-IR, and TG-DSC. The results indicated that the thickness of these nanosheets was about 1.44 nm, which was almost in perfect agreement with the theoretical thickness of two LDHs layers. From the TG-DSC curves, the weight loss of these exfoliated MgAl-LDHs ultrathin nanosheets at 500°C was 18.5%, which was much smaller compared to the 32.3% weight loss of unexfoliated MgAl-LDHs.     

Hydrogen Production on a Hybrid Photocatalytic System Composed of Ultrathin CdS Nanosheets and a Molecular Nickel Complex

The production of clean and renewable hydrogen through water splitting by using solar energy has received much attention due to the increasing global energy demand. We report an economic and artificial photosynthetic system free of noble metals, consisting of ultrathin CdS nanosheets as a photosensitizer and nickel‐based complex as a molecular catalyst. Emission quenching and flash photolysis studies reveal that this hybrid system allows for effective electron transfer from the excited CdS nanosheets to the nickel‐based complex to generate reduced intermediate species for efficient hydrogen evolution. Notably, the unique morphological and structural features of the ultrathin CdS nanosheets contribute to the highly efficient photocatalytic performance. As a consequence, the resulting system shows exceptional activity and stability for photocatalytic hydrogen evolution in aqueous solution with a turnover number (TON) of about 28 000 versus catalyst and a lifetime of over 90 h under visible light irradiation.     

Reverse Micelle Synthesis of Colloidal Nickel–Manganese Layered Double Hydroxide Nanosheets and Their Pseudocapacitive Properties

Colloidal nanosheets of nickel–manganese layered double hydroxides (LDHs) have been synthesized in high yields through a facile reverse micelle method with xylene as an oil phase and oleylamine as a surfactant. Electron microscopy studies of the product revealed the formation of colloidal nanoplatelets with sizes of 50–150 nm, and X‐ray diffraction, energy dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy studies showed that the Ni–Mn LDH nanosheets had a hydrotalcite‐like structure with a formula of [Ni₃Mn(OH)₈](Cl^?) ? n H₂O. We found that the presence of both Ni and Mn precursors was required for the growth of Ni‐Mn LDH nanosheets. As pseudocapacitors, the Ni–Mn LDH nanosheets exhibited much higher specific capacitance than unitary nickel hydroxides and manganese oxides.     

Unique Properties of 2 D Layered Titanate Nanosheets as a Building Block for the Optimization of the Photocatalytic Activity and Photostability of TiO2‐Based Nanohybrids

In comparison with the hybridization with 0D TiO₂ nanoparticle, 2D layered TiO₂ nanosheets are much more effective in the improvement of the photocatalytic activity and photostability of semiconducting compounds. The 2D TiO₂–Ag₃PO₄ nanohybrid described in this paper shows a greater decrease in the electron‐hole recombination upon hybridization and a stronger chemical interaction between the components than the 0D homologue. This result confirms the benefits of 2D layered TiO₂ nanosheets as a building block for efficient hybrid‐type photocatalyst materials.     

Anatase TiO2 nanosheet: An ideal host structure for fast and efficient lithium insertion/extraction

Anatase TiO₂ nanosheets with largely exposed (0 0 1) facets have been synthesized by a modified method. Exploitation of these nanosheets as a host structure for reversible lithium insertion/extraction has been investigated. It is found that these TiO₂ nanosheets manifest much lower initial irreversible losses compared to other anatase TiO₂ nanostructures, and excellent cycling performance at a charge–discharge rate as high as 20 C. The superior reversible lithium storage capability can be attributed to the ultrathin nanosheet structure: a large exposed effective area and a very short diffusion path. It thus attests the promising use of these anatase TiO₂ nanosheets in high-power lithium–ion batteries.     

Single- and few-layer 2H-SnS2 and 4H-SnS2 nanosheets for high-performance photodetection

The properties of two-dimensional（2D） materials are highly dependent on their phase and thickness. Various phases exist in tin disulfide（SnS₂）, resulting in promising electronic and optical properties. Hence,accurately identifying the phase and thickness of SnS₂ nanosheets is prior to their optoelectronic applications. Herein, layered 2H-SnS₂ and 4H-SnS₂ crystals were grown by chemical vapor transportation and the crystalline phase of SnS₂ w...     

Co3O4纳米催化剂催化CO的形貌效应：合成过程和催化活性

通过催化剂将CO转化为无毒气体仍然是目前减少CO污染的主要手段.随着纳米技术的快速发展,纳米催化剂因其在催化反应中呈现出的独特结构效应（如形貌效应、尺寸效应等）而受到人们的广泛关注.已有大量研究表明,纳米Co3O4作为一种非贵金属氧化物催化剂具有强烈的催化形貌效应,展现出优异的CO低温催化活性.因此,通过合理的设计来调控催化剂粒子的形貌,从而进一步改善催化剂的性能已成为近年来催化剂领域的重要研究方向.对于Co3O4纳米催化剂的可控制备,水热法具有反应温和、操作简便和产品形貌易控等特点.早期的研究主要围绕于Co3O4形貌的可控合成以及不同形貌Co3O4催化剂对其催化活性产生的影响,较少有对其形貌形成机制的报道.特别是在水热反应中,系统研究各反应参数对催化剂各异形貌的形成影响鲜有报道.
　　本文在前人的研究基础上,重点研究了水热反应过程中各主要反应参数对产品形貌控制的影响,绘制了一副不同形貌Co3O4材料的合成过程图,并研究了Co3O4纳米催化剂催化CO氧化的形貌效应.通过水热法先成功合成了三种不同形貌(纳米棒、纳米片和纳米立方)的碱式碳酸钴纳米粒子,然后将其焙烧得到了Co3O4纳米粒子.采用扫描电子显微镜(SEM),透射电子显微镜(TEM), X射线粉末衍射仪(XRD),程序升温还原(H2-TPR和CO-TPR),氮气吸附-脱附比表面积测试(BET),氧气程序升温脱附(O2-TPD), X射线光电子能谱(XPS)等表征手段研究了不同反应参数对纳米碱式碳酸钴前驱体形貌形成的作用和各异形貌Co3O4纳米粒子在催化CO氧化反应中催化性能的差异及原因.
　　结果表明, Co3O4较好地继承了碱式碳酸钴的形貌,在较低温度条件下(≤140°C),钴源(CoCl2或Co(NO3)2)是影响前驱体形貌的关键因素,反应时间只对粒子的尺寸产生较大影响.低温下, CoCl2作为钴源易诱导生产纳米棒状碱式碳酸钴,而Co(NO3)2则有利于纳米片状生成.当温度高于140°C后,无论何种钴源,最终均制得纳米立方体.表面活性剂CTAB对前驱体的均一性和粒子的分散性产生重要影响,加入CTAB后得到的产品尺寸更均一,形貌更加规整.对比于其他两种形貌的样品, Co3O4纳米片显示出更好的CO催化氧化活性.
　　 XPS结果表明,各形貌Co3O4纳米材料的表面组成存在明显差异,活性物种Co3+含量的不同是影响催化活性差异的重要原因. Co3O4纳米片具有更多的Co3+活性位,立方纳米Co3O4表面吸附氧含量较高, Co3O4纳米棒则暴露出相对更多的Co2+.因此,在三种形貌催化剂上CO氧化反应中, Co3O4纳米片表现出最优的催化活性,纳米立方次之,而纳米棒最差. H2-TPR, CO-TPR和O2-TPD等结果也表明, Co3O4纳米片拥有更强的还原性能和脱附氧能力,其次是纳米立方Co3O4.这与XPS结果一致,证实了不同形貌Co3O4纳米催化剂上暴露活性位的数量和表面氧物种的不同是造成彼此间催化CO氧化活性差异的重要原因.此外,通过稳定性测试发现Co3O4纳米片具有较高的催化稳定性,在水蒸气存在的情况下Co3O4纳米片逐渐失活,但随后在干燥条件下其催化活性又逐渐得到恢复.     

Three-in-one Fe-porphyrin based hybrid nanosheets for enhanced CO2 reduction and evolution kinetics in Li-CO2 battery

Efficient cathode-catalysts with multi-functional properties are essential for Li-CO₂ battery, while the construction of them with simultaneously enhanced CO₂ reduction and evolution kinetics is still challenging. Here, a kind of hybrid nanosheets based on Ru nanoparticles, Fe-TAPP and grapheme oxide (GO) has been designed through a one-pot self-assembly strategy. The Ru, Fe-porphyrin and GO based hybrid nanosheets (denoted as Ru/Fe-TAPP@GO) with integrated multi-components offer characteristics of ultrathin thickness (∼4 nm), high electro-redox property, uniformly dispersed morphology, and high electrical conductivity, etc. These features endow Ru/Fe-TAPP@GO with ultra-low overpotential (0.82 V) and fully reversible discharge/charge property with a high specific-capacity of 39,000 mAh/g within 2.0–4.5 V at 100 mA/g, which are much superior to Ru@GO and Fe-TAPP@GO. The achieved performance was presented as one of the best cathode-catalysts reported to date. The synergistically enhanced activity originated from the integrated hybrid nanosheets may provide a new pathway for designing efficient cathode-catalysts for Li-CO₂ batteries.     

g-C3N4纳米片制备方法研究

作为一种sp2共轭体系的非金属聚合物半导体,g-C3N4纳米片在光电化学、催化、光催化及生物医药等领域具有广泛的应用前景。本文综述了g-C3N4纳米片的制备方法,总结了各种不同方法制备g-C3N4纳米片的的优缺点,并对g-C3N4纳米片的发展进行了展望。     

Mussel‐Inspired Two‐Dimensional Freestanding Alkyl‐Polydopamine Janus Nanosheets

Mussel‐inspired two‐dimensional freestanding, alkyl‐polydopamine (alkyl‐PDA) Janus nanosheets, with a well‐controlled nanometer thickness and a lateral size of up to micrometers, have been developed. A self‐assembled octadecylamine (ODA) bilayer is used as the reactive template for the dopamine polymerization, resulting in the formation of well‐defined nanosheets. The alkyl‐PDA nanosheets show an amphiphilic nature with hydrophilic PDA and hydrophobic alkyl chains on opposing sides. The nanosheets can be used to functionalize many substrates and is dependent on the configuration of surface of the nanosheets. The nanosheets are quite stable, as the morphology is preserved after carbonization at 900 °C. Post‐modification of the nanosheets can be easily achieved because of the reactive nature of PDA. This work will provide a new strategic approach for fabricating polymeric Janus nanosheets, which can find applications for surface modifications, catalyst supports, and guided self‐assembly.     

钡掺杂中空磷酸银光催化剂的选择性及稳定性

半导体光催化材料既可以利用太阳能催化分解水制氢和降解各种有机污染物,同时还可以将温室气体CO2还原成有机低碳烷烃燃料,因此光催化是解决当今能源和环境问题最理想的途径之一.然而,目前所报道的可见光光催化材料大多具有较高的光生载流子复合率和较差的可见光吸收,导致其量子效率较低.因此,开发新型高效可见光光催化材料,拓展半导体材料光谱响应范围以及促进光生电子和空穴有效分离,成为目前光催化材料研究领域急需解决的科学问题.2010年Ye等首次报道了Ag3PO4在光催化中的应用,该材料表现出优异的光催化分解水制氧及降解有机污染物性能,在光吸收波长大于420 nm时的量子效率达到90%.然而,作为一种新型光催化材料,其组成、结构和晶面等对光催化性能的影响尚不清楚.因此,我们开展了Ag3PO4半导体纳米材料的表面微观结构调控研究,创制了一系列具有特殊形貌和选择暴露晶面的Ag3PO4基可见光催化材料,其表现出独特的光催化氧化性能.例如,利用金属络合法制备了具有(100),(110),(111),(221)和(332)等晶面的Ag3PO4晶体,发现通过调控其暴露晶面可进一步提高光催化性能.利用Ag纳米材料所具有的独特表面等离子体共振效应以及良好的导电性,构建了Ag/Ag3PO4核壳型纳米线、项链状Ag/Ag3PO4纳米线、项链状及均匀分布的Ag3PO4/PAN纳米复合纤维等异质光催化材料,提高了光生电子-空穴的分离效率,实现了有机污染物的高效催化氧化消除.然而,由于Ag3PO4在光催化反应过程中的稳定性较差以及成本较高,严重限制了其实际应用.因此,设计和制备具有高稳定性、低成本的Ag3PO4光催化材料成为目前急需开展的研究领域.本文以Ba3(PO4)2纳米片为模板和磷酸离子源,通过阳离子置换法一步制备了具有中空结构的Ba离子掺杂Ag3PO4光催化材料. 光催化结果表明, Ba离子的掺杂不但可以有效提高Ag3PO4光催化活性,并且可改变降解有机污染物甲基橙(MO)和罗丹明B(RhB)的选择性,实现优先降解MO.另外,此法制备的Ag3PO4材料经重复使用多次后仍表现出较高的光催化性能.进一步研究表明, Ba离子掺杂增强了Ag3PO4的表面电负性,因而吸附具有负电性的MO能力增加,使其光催化性能提高,此外,该法还可用于制备Ba3(PO4)2/Ag3PO4复合光催化材料,当Ag3PO4含量为40%时,该复合材料具有与纯相Ag3PO4相同的光催化剂活性.由此可见,通过合理掺杂金属离子及形成复合结构可以有效提高Ag3PO4光催化材料的活性和稳定性,降低Ag3PO4用量,这对Ag3PO4光催化材料的设计与改进具有一定指导意义.