Oxidative Intercalation for Monometallic Ni2+‐Ni3+ Layered Double Hydroxide and Enhanced Capacitance in Exfoliated Nanosheets

Monometallic Ni²⁺‐Ni³⁺ layered double hydroxide (LDH) is prepared using a simple oxidative intercalation process and may be further exfoliated into positively charged Ni(OH)₂ unilamellar sheets. The superior capacitive behavior of the unilamellar sheets stranded in carbon nanotubes (CNTs) networks is achieved because of the complete interfacial charge storage arising from the confined Faradaic reactions at the interfacial region. 3D nanosheet/CNT composites are prepared using an in situ electrostatic assembly of positive charged sheets with CNTs bearing negative charges. The restacking of active nanosheets during electrochemical cycling is effectively prohibited. Consequently, the outstanding specific capacitance and remarkable rate capability of the nanosheet/CNT hybrid electrodes are demonstrated, making them promising candidates for high performance supercapacitors, combining high‐energy storage densities with high levels of power delivery.     

Ultrathin Transition Metal Dichalcogenide/3d Metal Hydroxide Hybridized Nanosheets to Enhance Hydrogen Evolution Activity

The vast majority of the reported hydrogen evolution reaction (HER) electrocatalysts perform poorly under alkaline conditions due to the sluggish water dissociation kinetics. Herein, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS₂ and WS₂). A series of ultrathin 2D‐hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D‐TMD nanosheets. The resultant Ni(OH)₂ and Co(OH)₂ hybridized ultrathin MoS₂ and WS₂ nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The 2D‐MoS₂/Co(OH)₂ hybrid achieves an extremely low overpotential of ≈128 mV at 10 mA cm^?2 in 1 m KOH. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides.     

Alumina‐Supported CoFe Alloy Catalysts Derived from Layered‐Double‐Hydroxide Nanosheets for Efficient Photothermal CO2 Hydrogenation to Hydrocarbons

A series of novel CoFe‐based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered‐double‐hydroxide (LDH) nanosheets at 300–700 °C. The chemical composition and morphology of the reaction products (denoted herein as CoFe‐x) are highly dependent on the reduction temperature (x). CO₂ hydrogenation experiments are conducted on the CoFe‐x catalysts under UV–vis excitation. With increasing LDH‐nanosheet reduction temperature, the CoFe‐x catalysts show a progressive selectivity shift from CO to CH₄, and eventually to high‐value hydrocarbons (C₂₊). CoFe‐650 shows remarkable selectivity toward hydrocarbons (60% CH₄, 35% C₂₊). X‐ray absorption fine structure, high‐resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina‐supported CoFe‐alloy nanoparticles are responsible for the high selectivity of CoFe‐650 for C₂₊ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar‐energy to produce valuable chemicals and fuels from CO₂.     

Synthesis and characterisation of In(OH)3 and In2O3 nanoparticles by sol-gel and solvothermal methods

Indium hydroxide nanostructures were synthesised by sol-gel and hydrothermal processes from indium acetate and sodium hydroxide as precursors and polyvinyl alcohol, polyvinyl pyrrolidone or polydimethylsiloxane as stabilisers. Calcination of the In(OH)₃ nanostructures at 500°C in air yielded In₂O₃ nanoparticles. The morphology, crystallinity and thermal behaviour of the obtained products of each method were investigated by X-ray diffraction, scanning electron microscopy and thermal gravimetry analysis and differential thermal analysis.     

CaO-MgCl_2H_2O体系中一维碱式氯化镁的水热合成与表征

通过水热反应在CaO-MgCl2-H2O体系中合成了不同结构与形态特征的一维碱式氯化镁(MHCH),分析了MgCl2浓度、CaO与MgCl2的摩尔比R及水热条件对产物的影响.结果表明,当MgCl2浓度3mol/L,且R0.5时才能得到MHCH;MHCH的直径和径长比随MgCl2浓度和R的增加而增大.MHCH的最佳制备条件为[MgCl2]=4mol/L,R=0.05.MHCH的结构相与反应温度密切相关,温度低于150℃时,体系中的产物为相3(Mg2(OH)3Cl.4H2O);温度高于150℃时的产物为相9(Mg10(OH)18Cl2.5H2O).常温下体系中首先出现Mg3(OH)5Cl.3H2O和相5(Mg3(OH)5Cl.4H2O),经陈化后两者均转化为相3,经160℃水热反应后相3转化为相9.     

Synthesis of Co/SiO2 hybrid nanocatalyst via twisted Co3Si2O5(OH)4 nanosheets for high-temperature Fischer-Tropsch reaction

A cobalt-silica hybrid nanocatalyst bearing small cobalt particles of diameter ～5 nm was prepared through a hydrothermal reaction and hydrogen reduction.The resulting material showed very high CO conversion (＞82％) and high hydrocarbon productivity (～1.0 gHc·g-1cat,·h-11) with high activity (～8.5 x 10-5 molco·g-1Co·S-1) in the Fischer-Tropsch synthesis reaction.     

Metabolizable Ultrathin Bi2Se3 Nanosheets in Imaging‐Guided Photothermal Therapy

Poly(vinylpyrrolidone)‐encapsulated Bi₂Se₃ nanosheets with a thickness of 1.7 nm and diameter of 31.4 nm are prepared by a solution method. Possessing an extinction coefficient of 11.5 L g^?1 cm^?1 at 808 nm, the ultrathin Bi₂Se₃ nanosheets boast a high photothermal conversion efficiency of 34.6% and excellent photoacoustic performance. After systemic administration, the Bi₂Se₃ nanosheets with the proper size and surface properties accumulate passively in tumors enabling efficient photoacoustic imaging of the entire tumors to facilitate photothermal cancer therapy. In vivo biodistribution studies reveal that they are expelled from the body efficiently after 30 d. The ultrathin Bi₂Se₃ nanosheets have large clinical potential as metabolizable near‐infrared‐triggered theranostic agents.     

Rapid and Low‐Temperature Salt‐Templated Production of 2D Metal Oxide/Oxychloride/Hydroxide

2D materials have played an important role in electronics, sensors, optics, electrocatalysis, and energy storage. Many methods for the preparation of 2D materials have been explored. It is crucial to develop a high‐yield, rapid, and low‐temperature method to synthesize 2D materials. A general, fast (5 min), and low‐temperature (≈100 °C) salt (CoCl₂·6H₂O)‐templated method is proposed to prepare series of 2D metal oxides/oxychlorides/hydroxides in large scale, such as MoO₃, SnO₂, SiO₂, BiOCl, Sb₄O₅Cl₂, Zn₂Co₃(OH)₁₀ 2H₂O, and ZnCo₂O₄. The as‐synthesized 2D materials possess an ultrathin feature (2–7 nm) and large aspect ratios. Additionally, these 2D metal oxides/oxychlorides/hydroxides exhibit good electrochemical properties in energy storage (lithium/sodium‐ion batteries) and electrocatalysis (hydrogen/oxygen evolution reaction).     

Insight into Ca‐Substitution Effects on O3‐Type NaNi1/3Fe1/3Mn1/3O2 Cathode Materials for Sodium‐Ion Batteries Application

O3‐type NaNi_1/3Fe_1/3Mn_1/3O₂ (NaNFM) is well investigated as a promising cathode material for sodium‐ion batteries (SIBs), but the cycling stability of NaNFM still needs to be improved by using novel electrolytes or optimizing their structure with the substitution of different elements sites. To enlarge the alkali‐layer distance inside the layer structure of NaNFM may benefit Na⁺ diffusion. Herein, the effect of Ca‐substitution is reported in Na sites on the structural and electrochemical properties of Na_1?xCa_x/2NFM (x = 0, 0.05, 0.1). X‐ray diffraction (XRD) patterns of the prepared Na_1?xCa_x/2NFM samples show single α‐NaFeO₂ type phase with slightly increased alkali‐layer distance as Ca content increases. The cycling stabilities of Ca‐substituted samples are remarkably improved. The Na_0.9Ca_0.05Ni_1/3Fe_1/3Mn_1/3O₂ (Na_0.9Ca_0.05NFM) cathode delivers a capacity of 116.3 mAh g^?1 with capacity retention of 92% after 200 cycles at 1C rate. In operando XRD indicates a reversible structural evolution through an O3‐P3‐P3‐O3 sequence of Na_0.9Ca_0.05NFM cathode during cycling. Compared to NaNMF, the Na_0.9Ca_0.05NFM cathode shows a wider voltage range in pure P3 phase state during the charge/discharge process and exhibits better structure recoverability after cycling. The superior cycling stability of Na_0.9Ca_0.05NFM makes it a promising material for practical applications in sodium‐ion batteries.     

Generalized Synthesis of Metal Oxide Nanosheets and Their Application as Li‐Ion Battery Anodes

Metal oxide nanosheets have attracted great attention in various fields, such as energy storage, catalysis, and sensors. Current synthesis methods of metal oxide nanosheets are laborious and not scalable. Herein, a facile and scalable method for the synthesis of metal oxide nanosheets is presented, which requires neither hydro‐/solvothermal conditions nor postsynthesis template removal. The synthesis is versatile, as evidenced by the wide variety of metal oxide nanosheets derived. Nanosheet properties such as crystallinity, crystallite size, and carbon content can be controlled by tuning the synthesis conditions. The metal oxide nanosheets demonstrate promising performance as Li‐ion battery anodes.     

层状钙钛矿La2KMn2O7和La3KMn3O10的制备及磁、电性质的研究

采用溶胶-凝胶法制备了La2KMn2O7和La3KMn3O10两种后状钙钛矿锰氧化物多晶样品，研究了乙酸(CH3COOH)超声处理后对La2KMn2O7和La3KMn3O10结构和磁性的影响。结果表明超声取代可以提高样品的结晶度，对样品的结构及磁性能也有较大影响。本文对上述现象的可能原因也进行了初步讨论，并讨论了样品的磁电阻效应。     

表面包覆氧化镧的富锂锰基正极材料的制备及性能研究

通过溶液法在富锂锰基0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2(简称LLO)正极材料前驱体表面包覆了一层稀土氧化物--氧化镧,制备了表面包覆氧化镧的LLO正极材料。采用X射线衍射仪、能量色散谱仪、扫描电子显微镜以及电池测试仪对材料进行表征和电化学性能测试,考察表面包覆氧化镧对LLO正极材料性能的影响。研究结果表明,用摩尔分数1%的氧化镧包覆LLO正极材料,极大地改善了材料的电化学性能。电化学性能的改善归因于包覆氧化镧后有效地稳定了材料的表面结构,避免了材料在循环过程中的分解。     

Economizing Production of Diverse 2D Layered Metal Hydroxides for Efficient Overall Water Splitting

2D layered metal hydroxides (LMH) are promising materials for electrochemical energy conversion and storage. Compared with exfoliation of bulk layered materials, wet chemistry synthesis of 2D LMH materials under mild conditions still remains a big challenge. Here, an “MgO‐mediated strategy” for mass production of various 2D LMH nanosheets is presented by hydrolyzing MgO in metal salt aqueous solutions at room temperature. Benefiting from this economical and scalable strategy, ultrathin LMH nanosheets (M = Ni, Fe, Co, NiFe, and NiCo) and their derivatives (e.g., metal oxides and sulfides) can be synthesized in high yields. More importantly, this strategy opens up opportunities to fabricate hierarchically structured LMH nanosheets, resulting in high‐performance electrocatalysts for the oxygen‐ and hydrogen‐evolution reactions to realize stable overall water splitting with a low cell voltage of 1.55 V at 10 mA cm⁻². This work provides a powerful platform for the synthesis and applications of 2D materials.     

Lasing from Mechanically Exfoliated 2D Homologous Ruddlesden–Popper Perovskite Engineered by Inorganic Layer Thickness

2D Ruddlesden–Popper perovskites (RPPs) have aroused growing attention in light harvesting and emission applications owing to their high environmental stability. Recently, coherent light emission of RPPs was reported, however mostly from inhomologous thin films that involve cascade intercompositional energy transfer. Lasing and fundamental understanding of intrinsic laser dynamics in homologous RPPs free from intercompositional energy transfer is still inadequate. Herein, the lasing and loss mechanisms of homologous 2D (BA)₂(MA)_n?1Pb_nI_3n+1 RPP thin flakes mechanically exfoliated from the bulk crystal are reported. Multicolor lasing is achieved from the large‐n RPPs (n ≥ 3) in the spectral range of 620–680 nm but not from small‐n RPPs (n ≤ 2) even down to 78 K. With decreasing n, the lasing threshold increases significantly and the characteristic temperature decreases as 49, 25, and 20 K for n = 5, 4, and 3, respectively. The n‐engineered lasing behaviors are attributed to the stronger Auger recombination and exciton–phonon interaction as a result of the enhanced quantum confinement in the smaller‐n perovskites. These results not only advance the fundamental understanding of loss mechanisms in both inhomologous and homologous RPP lasers but also provide insights into developing low‐threshold, substrate‐free, and multicolor 2D semiconductor microlasers.