Simulating Powder X-ray Diffraction Patterns of Two-Dimensional Materials

Selective Separation of C8 Aromatics by an Interpenetrating Metal-Organic Framework Material

O-xylene (OX) is an important chemical raw material, but it is often produced in mixtures with other C8 aromatics. Similar physicochemical properties of the C8 isomers make their separation and purification very difficult and energy intensive. There is an unmet need for an adsorbent that would be effective for the separation of OX from the other C8 isomers. This work reports a three-dimensional interpenetrated metal-organic framework, SYUCT-110, that interacts with each of the single-component C8 isomers to form. The selectivity of C8 aromatic hydrocarbons was determined through liquid-phase batch uptake experiments. The results revealed that the selectivity order was OX > PX > MX > ethylbenzene (EB). The selectivity values were found to be 2.63, 1.58, 5.51, 3.71, 1.86, and 3.02 for OX/MX, OX/PX, OX/EB, PX/MX, MX/EB, and PX/EB, respectively. The adsorption capacity of OX was 71 mg/g. Grand Canonical Monte Carlo simulations were used to study the C8 adsorption sites, revealing that π···π interactions are the main reason for the observed adsorption selectivity. The adsorption energy calculation results also verified the selectivity of SYUCT-110 for the synthesis of OX.

High-Performance Proton Field-Effect Transistor Based on Two-Dimensional Cd Vacancy-Resided Cd0.85PS3Li0.15H0.15

Ion transport is a critical phenomenon underpinning numerous biological, physical, and chemical systems. Proton transistors leveraging proton transport face significant limitations, such as a low on-off ratio and deficient carrier mobility, which restrict their applicability in biological and other scenarios. This study explores the use of two-dimensional (2D) vacancy-residing transition metal phosphorus trichallcogenide-based membranes as the active layer for proton field-effect transistors. The synthesized Cd0.85PS3Li0.15H0.15 membrane exhibits a well-organized layered structure and high hydrophilicity, with nanometer-sized interlayers containing interconnected water networks. These distinct features facilitate proton conduction, leading to a high proton conductivity value of 0.83 S cm-1 at 98% relative humidity and 90 °C, with an activation energy of 0.26 eV. The Cd0.85PS3Li0.15H0.15-based proton transistor demonstrates tunability via gate voltage, thereby enabling effective modulation of proton flow across source and drain electrodes. The transistor notably showcases superior switching characteristics, with an on/off ratio surpassing 5.51 and a carrier mobility of 8.84 × 10-2 cm2 V-1 s-1. The underlying mechanism for this performance enhancement is attributed to electric-field-induced switching in Cd vacancies. This research boosts the development of highly versatile ionotropic devices by introducing advanced 2D ion-conductive membranes.

Fabrication of Carboxylate-Functionalized 2D MOF Nanosheet with Caged Cavity for Efficient and Selective Extraction of Uranium from Aqueous Solution

The efficient removal of radioactive uranium from aqueous solution is of great significance for the safe and sustainable development of nuclear power. An ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately fabricated based on a calix[4]arene ligand. Incorporating the permanent cavity structures on MOF nanosheet can fully utilize its structural characteristics of largely exposed surface area and accessible adsorption sites in pollutant removal, achieving ultrafast adsorption kinetics, and the functionalized cavity structure would endow the MOF nanosheets with the ability to achieve preconcentration and extraction of uranium from aqueous solution, affording ultrahigh removal efficiency even in ultra-low concentrations. Thus, more than 97% uranium can be removed from the concentration range of 50-500 µg L-1 within 5 min. Moreover, the 2D nano-material exhibits ultra-high anti-interference ability, which can efficiently remove uranium from groundwater and seawater. The adsorption mechanism was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) analysis, and density functional theory (DFT) calculations, which revealed that the cavity structure plays an important role in uranium capture. This study not only realizes highly efficient uranium removal from aqueous solution but also opens the door to achieving ultrathin MOF nanosheets with cavity structures, which will greatly expand the applications of MOF nanosheets.

A key parametric study of ultrasonic exfoliation of 2D TiB2 using DI water as a unique medium

Liquid Phase Exfoliation (LPE) is a very effective technique for the synthesis of few layered two dimensional (2D) nanosheets. There is a surge to find environment friendly solvents for efficient exfoliation of layered materials to produce 2D nanosheets. TiB2 is an important layered material with very little reported work on its 2D nanosheets. The present work is about successful LPE of TiB2 using deionized (DI) water as a clean, green and low cost dispersion medium to make TiB2 nanosheets. The impact of ultrasonication conditions i.e. input power and treatment duration for efficient synthesis of few layered 2D nanosheets in DI water is studied by Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). It is found that by increasing input power, the layer thickness is reduced from bulk to 34 nm with lateral dimensions as huge as up to 5 μm. The increased treatment duration has further reduced the layer thickness to 21 nm associated with a decrease in lateral dimensions to about 1 μm. The mechanism of variation in the aspect ratio of the 2D nanosheets with ultrasonication power and treatment duration is explained. The optimum conditions for the fabrication of high aspect ratio 2D nanosheets of TiB2 owe to a greater acoustic cavitation intensity, an optimum treatment duration and a homogenous distribution of the cavitation events while using an appropriate size of the sonotrode in the sonicated volume during ultrasonication.

Structure and luminescence properties of single-component melilite Sr2MgSi2O7:Ce/Tb/Sm for n-UV wLEDs

Phosphor-converted white light-emitting diodes (pc-wLEDs) have attracted attention in the field of solid-state lighting. Selection and study of suitable single-phase phosphor and packaging modes are currently the main research hotspots. Herein, color-tunable photoluminescence (PL) and thermally stable tri-doped Melitite Sr2MgSi2O7:Ce/Tb/Sm are systematically studied via structural and static/dynamic spectral analyses. All dopants could only be accommodated in the Sr site due to similar ionic radii. Previous studies have concluded that green and red PL could be obtained from singly doped Tb and Sm phosphors with excellent reproduction, and color tunable PL can be achieved from Ce/Tb co-doped phosphors. The forbidden 4f-4f transitions of Tb/Sm cause low efficiency and Ce/Tb co-doping cannot achieve white light emissions. Alternatively, co-doping allowed 5d-4f transition sensitizer with emissions in the UV-blue region (i.e., Ce), color-tunable PL (including the white light); high efficiency of Sr2MgSi2O7:Ce/Tb/Sm could be achieved via energy transfer (ET) from Ce → Tb → Sm. The impossibly direct ET from Ce → Sm is associated with the side metal-metal charge transfer (MMCT) effect. Due to chemically nonequivalent substitutions, two positive Ce(Tb,Sm)Sr and one negative V''Sr were created to maintain the whole charge balance. To reduce the defects and allow more dopants to enter into the Sr site, Na+ was added as a charge balancer to enhance PL efficiency. Furthermore, an alkaline-earth-metal-ions blending strategy via partial replacement of Sr with Ba was investigated to regulate PL owing to the change in crystal field splitting. PL blue-shifted by Ba-co-doping, which could increase the degree of overlapping and enhance ET efficiency. As a proof-of-concept experiment, the pc-wLED fabricated via a combination of the optimal Sr(Ba)2MgSi2O7:Ce/Tb/Sm/Na and an n-UV LED chip based on a remote 'capping' packaging mode shows excellent performances, indicating its strong potential application in the field of solid-state lighting.

Silver nanoparticle enhanced metal-organic matrix with interface-engineering for efficient photocatalytic hydrogen evolution

Integrating plasmonic nanoparticles into the photoactive metal-organic matrix is highly desirable due to the plasmonic near field enhancement, complementary light absorption, and accelerated separation of photogenerated charge carriers at the junction interface. The construction of a well-defined, intimate interface is vital for efficient charge carrier separation, however, it remains a challenge in synthesis. Here we synthesize a junction bearing intimate interface, composed of plasmonic Ag nanoparticles and matrix with silver node via a facile one-step approach. The plasmonic effect of Ag nanoparticles on the matrix is visualized through electron energy loss mapping. Moreover, charge carrier transfer from the plasmonic nanoparticles to the matrix is verified through ultrafast transient absorption spectroscopy and in-situ photoelectron spectroscopy. The system delivers highly efficient visible-light photocatalytic H2 generation, surpassing most reported metal-organic framework-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic nanoparticles and organic semiconductors.

Regioselective Friedel-Crafts Acylation Reaction Using Single Crystalline and Ultrathin Nanosheet Assembly of Scrutinyite-SnO2

Peculiar physicochemical properties of two-dimensional (2D) nanomaterials have attracted research interest in developing new synthetic technology and exploring their potential applications in the field of catalysis. Moreover, ultrathin metal oxide nanosheets with atomic thickness exhibit abnormal surficial properties because of the unique 2D confinement effect. In this work, we present a facile and general approach for the synthesis of single crystalline and ultrathin 2D nanosheets assembly of scrutinyite-SnO₂ through a simple solvothermal method. The structural and compositional characterization using X-ray diffraction (Rietveld refinement analysis), high-resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and so on reveal that the as-synthesized 2D nanosheets are ultrathin and single crystallized in the scrutinyite-SnO₂ phase with high purity. The ultrathin SnO₂ nanosheets show predominant growth in the [011] direction on the main surface having a thickness of ca. 1.3 nm. The SnO₂ nanosheets are further employed for the regioselective Friedel-Crafts acylation to synthesize aromatic ketones that have potential significance in chemical industry as synthetic intermediates of pharmaceuticals and fine chemicals. A series of aromatic substrates acylated over the SnO₂ nanosheets have afforded the corresponding aromatic ketones with up to 92% yield under solvent-free conditions. Comprehensive catalytic investigations display the SnO₂ nanosheet assembly as a better catalytic material compared to the heterogeneous metal oxide catalysts used so far in the view of its activity and reusability in solvent-free reaction conditions.

Two-dimensional metal-organic layers constructed from Hf6/Hf12-oxo clusters and a trigonal pyramidal phosphine oxide ligand

Metal-organic layers (MOLs), a category of two-dimensional materials, have attracted wide interest due to their molecular tunability and the ease of surface modification. Herein, we reported the synthesis and structural determination of a free-standing MOL, {[Hf₆O₈H₄(HCOO)₂(H₂O·OH)₄]₃[Hf₁₂O₁₆H₈(HCOO)_6.8(H₂O·OH)_11.2](TPO)₈}_n, constructed from Hf₆-oxo and Hf₁₂-oxo clusters as secondary building units (SBUs) and the tris(4-carboxylphenyl)phosphine oxide (TPO) ligand. We establish a structure model of this new MOL based on the combined information from different characterization methods.

Hexagonal Layer Manganese Metal-Organic Framework for Photocatalytic CO2 Cycloaddition Reaction

A novel manganese metal-organic framework (Mn-MOF) termed UAEU-50 assembled from a benzenedicarboxylate linker (BDC) and trinuclear manganese clusters was synthesized and fully characterized using different spectroscopic and analytic techniques (e.g., X-ray powder diffraction, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy). UAEU-50 adopted a hexagonal layer structure and exhibited superior thermal stability and robust chemical stability. Photocatalytic activities of UAEU-50 were investigated using the cycloaddition of CO₂ to different epoxides, forming cyclic carbonates. Impressively, UAEU-50 can transform up to 90% photocatalytic CO₂ conversion to cyclic carbonates in the visible-light region at ambient conditions.

Tailoring Layer Number of 2D Porphyrin-Based MOFs Towards Photocoupled Electroreduction of CO2

Inspired by the success of graphene, a series of single- or few-layer 2D materials have been developed and applied in the past decade. Here, the successful preparation of monolayer and bilayer 2D porphyrin-based metal-organic frameworks (MOFs) by a facile solvothermal method is reported. The structure transition from monolayer to bilayer drives distinct electronic properties and restructuring behaviors, which finally results in distinct catalytic pathways towards CO₂ electrocatalysis. The monolayer favors CO₂ -to-C₂ pathway due to the restructuring of CuO₄ sites, while CO and HCOO^- are the major products over the bilayer. In photocoupled electrocatalysis, the Faradaic efficiency (FE) of the C₂ compounds shows a nearly fourfold increase on the monolayer than that under dark conditions (FE_C2 increases from 11.9% to 41.1% at -1.4 V). For comparison, the light field plays a negligible effect on the bilayer. The light-induced selectivity optimization is investigated by experimental characterization and density functional theory (DFT) calculations. This work opens up a novel possibility to tune the selectivity of carbon products just by tailoring the layer number of the 2D material.

Active mechanisorption driven by pumping cassettes

[Figure: see text].

Three-in-One C2 H2 -Selectivity-Guided Adsorptive Separation across an Isoreticular Family of Cationic Square-Lattice MOFs

Energy-efficient selective physisorption driven C₂ H₂ separation from industrial C2-C1 impurities such as C₂ H₄ , CO₂ and CH₄ is of great importance in the purification of downstream commodity chemicals. We address this challenge employing a series of isoreticular cationic metal-organic frameworks, namely iMOF-nC (n=5, 6, 7). All three square lattice topology MOFs registered higher C₂ H₂ uptakes versus the competing C2-C1 gases (C₂ H₄ , CO₂ and CH₄ ). Dynamic column breakthrough experiments on the best-performing iMOF-6C revealed the first three-in-one C₂ H₂ adsorption selectivity guided separation of C₂ H₂ from 1:1 C₂ H₂ /CO₂ , C₂ H₂ /C₂ H₄ and C₂ H₂ /CH₄ mixtures. Density functional theory calculations critically examined the C₂ H₂ selective interactions in iMOF-6C. Thanks to the abundance of square lattice topology MOFs, this study introduces a crystal engineering blueprint for designing C₂ H₂ -selective layered metal-organic physisorbents, previously unreported in cationic frameworks.

Inductive effects in cobalt-doped nickel hydroxide electronic structure facilitating urea electrooxidation

Electrochemical oxidation of urea provides an approach to prevent excess urea emissions into the environment while generating value by capturing chemical energy from waste. Unfortunately, the source of high catalytic activity in state-of-the-art doped nickel catalysts for urea oxidation reaction (UOR) activity remains poorly understood, hindering the rational design of new catalyst materials. In particular, the exact role of cobalt as a dopant in Ni(OH)₂ to maximize the intrinsic activity towards UOR remains unclear. In this work, we demonstrate how tuning the Ni:Co ratio allows us to control the intrinsic activity and number of active surface sites, both of which contribute towards increasing UOR performance. We show how Ni₉₀Co₁₀(OH)₂ achieves the largest geometric current density due to the increase of available surface sites and that intrinsic activity towards UOR is maximized with Ni₂₀Co₈₀(OH)₂. Through density functional theory calculations, we show that the introduction of Co alters the Ni 3d electronic state density distribution to lower the minimum energy required to oxidize Ni and influence potential surface adsorbate interactions.

Metal-organic frameworks embedded in a liposome facilitate overall photocatalytic water splitting

Metal-organic frameworks (MOFs) have been studied extensively in the hydrogen evolution reaction (HER) and the water oxidation reaction (WOR) with sacrificial reagents, but overall photocatalytic water splitting using MOFs has remained challenging, principally because of the fast recombination of photo-generated electrons and holes. Here we have integrated HER- and WOR-MOF nanosheets into liposomal structures for separation of the generated charges. The HER-MOF nanosheets comprise light-harvesting Zn-porphyrin and catalytic Pt-porphyrin moieties, and are functionalized with hydrophobic groups to facilitate their incorporation into the hydrophobic lipid bilayer of the liposome. The WOR-MOF flakes consist of [Ru(2,2'-bipyridine)₃]²⁺-based photosensitizers and Ir-bipyridine catalytic centres, and are localized in the hydrophilic interior of the liposome. This liposome-MOF assembly achieves overall photocatalytic water splitting with an apparent quantum yield of (1.5 ± 1)% as a result of ultrafast electron transport from the antennae (Zn-porphyrin and [Ru(2,2'-bipyridine)₃]²⁺) to the reaction centres (Pt-porphyrin and Ir-bipyridine) in the MOFs and efficient charge separation in the lipid bilayers.

Ultrathin water-stable metal-organic framework membranes for ion separation

Owing to the rich porosity and uniform pore size, metal-organic frameworks (MOFs) offer substantial advantages over other materials for the precise and fast membrane separation. However, achieving ultrathin water-stable MOF membranes remains a great challenge. Here, we first report the successful exfoliation of two-dimensional (2D) monolayer aluminum tetra-(4-carboxyphenyl) porphyrin framework (termed Al-MOF) nanosheets. Ultrathin water-stable Al-MOF membranes are assembled by using the exfoliated nanosheets as building blocks. While achieving a water flux of up to 2.2 mol m-2 hour-1 bar-1, the obtained 2D Al-MOF laminar membranes exhibit rejection rates of nearly 100% on investigated inorganic ions. The simulation results confirm that intrinsic nanopores of the Al-MOF nanosheets domain the ion/water separation, and the vertically aligned aperture channels are the main transport pathways for water molecules.

Understanding Powder X-ray Diffraction Profiles from Layered Minerals: The Case of Kaolinite Nanocrystals

Powder X-ray diffraction (PXRD) techniques are widely used to characterize the nature of stacking of submicrometer-wide nanometer-thick layers that form layered mineral nanocrystals, but application of these methods to infer the in-plane configuration of the layers is difficult. Line-profile-analysis algorithms based on the Bragg equation cannot describe the broken periodicity in the stacking direction. The Debye scattering equation is an alternative approach, but it is limited by the large-scale atomistic models required to capture the multiscale nature of the layered systems. Here, we solve the Debye scattering equation for kaolinite nanocrystals to understand the contribution of different layer-stacking defects to PXRD profiles. We chose kaolinite as a case study because its approximately constant composition and lack of interlayer expansion ensure that interstitial cations and/or molecules and substitutional ions can be ignored. We investigated the structure factor change as a function of crystal structural and microstructural features such as layer structure in-plane misorientation and shift (in or out of the 2D plane) and the diameter, number, and lateral indentation of the layers. Perfect and turbostratic stacking configurations bounded the range of intensity variation for hkl and 00l reflections, as well as for any scattering angle. A unique degree of disorder was computed by the average deviation from such limiting cases, and multivariate analysis was used to interpret the observed diffraction profiles. Analysis of the data for KGa-1, KGa-2, and API-9 standard kaolinites demonstrated that the estimated densities of different stacking defects are highly correlated. In addition, analysis of API-9 particle-size fractions revealed a dispersion of four or more components in the standard sample. The results illustrate that the use of a distribution of sizes, defects, and even individual kaolinite components is necessary to accurately characterize any sample of natural kaolinite.

A layered aluminum-based metal-organic framework as a superior trap for nitrobenzene capture via an intercalation role

Layered materials with porous layers are of great interest due to their intriguing structural topologies and potential applications as new adsorbents. In this study, a layered aluminum-based metal-organic framework, i.e. Al-TCPP, was successfully synthesized via a facile method for the adsorptive removal of nitrobenzene (NB). The as-synthesized Al-TCPP exhibited a typical layered structure and can be stable in water at pH = 5-7. Batch experimental results showed a superior adsorption performance towards NB with a maximum adsorption capability of 1.85 mg mg^-1, and an exceptionally rapid equilibrium within 1 min, yielding an overall adsorptive performance superior to the state-of-the-art NB adsorbents reported so far. The morphology and crystallinity of the Al-TCPP adsorbent basically retain the original status after the capture of NB. Importantly, X-ray diffraction patterns of the samples after the NB adsorption revealed that the possible NB intercalation took place in layered Al-TCPP and expanded the interlayer space during the adsorption, which greatly enriched the adsorption sites and thus achieved the outstanding performance. This work highlights new prospects in designing layered materials for use in environmental remediation.