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N-oxide ligands, combined with pyridinic N groups, are predicted to offer attractive La(iii)/Ln(iii) selectivities for rare-earth separations.

Atomically precise nanoclusters play an important role in nanoscaled catalysis, photonics, and quantum information science.

ConspectusHexagonal boron nitrides (h-BNs) are attractive two-dimensional (2D) nanomaterials that consist of alternating B and N atoms and layered honeycomb-like structures similar to graphene. They have exhibited unique properties and promising application potentials in the field of energy storage and transformation. Recent advances in utilizing h-BN as a metal-free catalyst in the oxidative dehydrogenation of propane have triggered broad interests in exploring h-BN in catalysis. However, h-BN-based materials as robust nanocatalysts in heterogeneous catalysis are still underexplored because of the limited methodologies capable of affording h-BN with controllable crystallinity, abundant porosity, high purity, and defect engineering, which played important roles in tuning their catalytic performance. In this Account, our recent progress in addressing the above issues will be highlighted, including the synthesis of high-quality h-BN-based nanomaterials via both bottom-up and top-down pathways and their catalytic utilization as metal-free catalysts or as supports to tune the interfacial electronic properties on the metal nanoparticles (NPs). First, we will focus on the large-scale fabrication of h-BN nanosheets (h-BNNSs) with high crystallinity, improved surface area, satisfactory purity, and tunable defects. h-BN derived from the traditional approaches using boron trioxide and urea as the starting materials generally contains carbon/oxygen impurities and has low crystallinity. Several new strategies were developed to address the issues. Using bulk h-BN as the precursor via gas exfoliation in liquid nitrogen, single- or few-layered h-BNNS with abundant defects could be generated. Amorphous h-BN precursors could be converted to h-BN nanosheets with high crystallinity assisted by a magnesium metallic flux via a successive dissolution/precipitation/crystallization procedure. The as-fabricated h-BNNS featured high crystallinity and purity as well as abundant porosity. An ionothermal metathesis procedure was developed using inorganic molten salts (NaNH

Inspired by a recently reported metal-organic framework (MOF), V

Constituting the bulk of rare-earth elements, lanthanides need to be separated to fully realize their potential as critical materials in many important technologies. The discovery of new ligands for improving rare-earth separations by solvent extraction, the most practical rare-earth separation process, is still largely based on trial and error, a low-throughput and inefficient approach. A predictive model that allows high-throughput screening of ligands is needed to identify suitable ligands to achieve enhanced separation performance. Here, we show that deep neural networks, trained on the available experimental data, can be used to predict accurate distribution coefficients for solvent extraction of lanthanide ions, thereby opening the door to high-throughput screening of ligands for rare-earth separations. One innovative approach that we employed is a combined representation of ligands with both molecular physicochemical descriptors and atomic extended-connectivity fingerprints, which greatly boosts the accuracy of the trained model. More importantly, we synthesized four new ligands and found that the predicted distribution coefficients from our trained machine-learning model match well with the measured values. Therefore, our machine-learning approach paves the way for accelerating the discovery of new ligands for rare-earth separations.

Atomically dispersed catalysts such as single-atom catalysts have been shown to be effective in selectively oxidizing methane, promising a direct synthetic route to value-added oxygenates such as acetic acid or methanol. However, an important challenge of this approach has been that the loading of active sites by single-atom catalysts is low, leading to a low overall yield of the products. Here, we report an approach that can address this issue. It utilizes a metal-organic framework built with porphyrin as the linker, which provides high concentrations of binding sites to support atomically dispersed rhodium. It is shown that up to 5 wt% rhodium loading can be achieved with excellent dispersity. When used for acetic acid synthesis by methane oxidation, a new benchmark performance of 23.62 mmol·gcat-1·h-1 was measured. Furthermore, the catalyst exhibits a unique sensitivity to light, producing acetic acid (under illumination, up to 66.4% selectivity) or methanol (in the dark, up to 65.0% selectivity) under otherwise identical reaction conditions.

The hydration structure of protons has been studied for decades in bulk water and protonated clusters due to its importance but has remained elusive in planar confined environments. Two-dimensional (2D) transition metal carbides known as MXenes show extreme capacitance in protic electrolytes, which has attracted attention in the energy storage field. We report here that discrete vibrational modes related to protons intercalated in the 2D slits between Ti3C2Tx MXene layers can be detected using operando infrared spectroscopy. The origin of these modes, not observed for protons in bulk water, is attributed to protons with reduced coordination number in confinement based on Density Functional Theory calculations. This study therefore demonstrates a useful tool for the characterization of chemical species under 2D confinement.

Perovskite oxyhydrides such as BaTiO2.5H0.5 have been found to be able to catalyze NH3 synthesis, but the mechanism and the role of the catalyst’s lattice hydrides in the catalytic reaction remain unknown. Here we employ first principles density functional theory to investigate the mechanism of ammonia synthesis and the role of lattice hydrides on a prototypical perovskite oxyhydride, BaTiO2.5H0.5. Two mechanistic hypotheses, the distal and alternating pathways, have been tested on the Ti2O2 termination of the BTOH (210) surface, previously determined to be the most stable surface termination at the reaction conditions considered. In the distal pathway, H atoms hydrogenate N2 to form the *N-NHx key intermediates, followed by N-N bond breaking. In the alternating pathway, H atoms hydrogenate N2 in an alternating fashion to form the *NHx-NHy intermediates, before N-N bond breaking and formation of co-adsorbed *NHx/*NHy on the surface. We find that the subsurface hydride vacancy formed after reaction of *N2 with the lattice hydride is key to the distal pathway, leading to surface nitride formation after breaking the *N-NH3 bond, while the neighboring surface Ti sites are key to bridging and stabilizing the *NNH intermediate in the alternating pathway. In both pathways, desorption of NH3 is the most uphill process in energy. Our results provide important insights into the role of hydrides and surface vacancies in hydrogenation reactions over BTOH that will be useful to guide future spectroscopic experiments such as operando IR and inelastic neutron scattering to verify the key intermediates.

We report the first all-alkynyl-protected Au2Ag8Cu5 cluster, which adopts a M@M8@M6 core configuration similar with Au7Ag8/Ag9Cu6 clusters. The three clusters exhibited strong metal core effect toward CO2RR, which was understood by DFT calculations.

First principles molecular dynamics reveals how Mg2+ influences Cl coordination around U and the U–Cl network in UCln–MgCl2 (n = 3,4).

The broad employment of water electrolysis for hydrogen (H2) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a Cu3Ag7 electrocatalyst. Such a strategy not only produces more valuable anodic product than O2 but also releases H2 at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7 than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(–) can produce H2 at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2 with a cell voltage of only 0.60 V.

The role of counterions in molecular recognition of lanthanides is underexplored, especially when they exhibit weak interactions with the metal cations. Here, we report a complementary and comprehensive investigation integrating theoretical calculations with X-ray absorption fine structure spectroscopy, dynamic light scattering, and small-angle X-ray scattering to reveal atomic-scale structural features beyond the immediate coordination sphere of a system used for rare-earth element separations. Our results indicate the formation of an unusual T-shaped outer-sphere lanthanide complex, containing two ligands and two nitrate ions in the first coordination sphere, whereas the third nitrate is weakly coordinated and resides in the second shell. This unique structural arrangement causes inhomogeneous charge distribution, leading to self-assembly of the complexes into larger nanoclusters through sterically directed electrostatic interactions in the nonpolar medium. Our findings point to the importance of "noncoordinating" anions in defining the degree of supramolecular aggregation and ion cluster assembly.

The last decade has witnessed significant advances in the synthesis and structure determination of atomically precise metal nanoclusters. However, little is known about the condensed matter properties of these nanosized metal nanoclusters packed in a crystal lattice under high pressure. Here using density function theory calculations, we simulate the crystal of a representative superatomic gold cluster, [Au25(SR)18]0 (R = C2H5), under various pressures. At ambient conditions, [Au25(SC2H5)18]0 clusters are packed in a crystal via dispersion interactions; being a 7e superatom, each cluster carries a magnetic moment of 1μB or one unpaired electron. Upon increasing compression (from 10 to 110 GPa), we observe the formation of inter-cluster Au-Au, Au-S, and S-S covalent bonds between staple motifs, thereby linking the clusters into a network. The pressure-induced structural change is accompanied by the vanishment of the magnetic moment and the semiconductor-to-metal transition. Our work shows that subjecting crystals of atomically precise metal nanoclusters to high pressures could lead to new crystalline states and physical properties.

Single-atom catalysts are a relatively new type of catalyst active for numerous reactions but mainly for chemical transformations performed at low or intermediate temperatures. Here we report that singly dispersed Rh1O5 clusters on TiO2 can catalyze the partial oxidation of methane (POM) at high temperatures with a selectivity of 97% for producing syngas (CO + H2) and high activity with a long catalytic durability at 650 °C. The long durability results from the substitution of a Ti atom of the TiO2 surface lattice by Rh1, which forms a singly dispersed Rh1 atom coordinating with five oxygen atoms (Rh1O5) and an undercoordinated environment but with nearly saturated bonding with oxygen atoms. Computational studies show the back-donation of electrons from the dz2 orbital of the singly dispersed Rh1 atom to the unoccupied orbital of adsorbed CHn (n > 1) results in the charge depletion of the Rh1 atom and a strong binding of CHn to Rh1. This strong binding decreases the barrier for activating C-H, thus leading to high activity of Rh1/TiO2. A cationic Rh1 single atom anchored on TiO2 exhibits a weak binding to atomic carbon, in contrast to the strong binding of the metallic Rh surface to atomic carbon. The weak binding of atomic carbon to Rh1 atoms and the spatial isolation of Rh1 on TiO2 prevent atomic carbon from coupling on Rh1/TiO2 to form carbon layers, making Rh1/TiO2 resistant to carbon deposition than supported metal catalysts for POM. The highly active, selective, and durable high-temperature single-atom catalysis performed at 650 °C demonstrates an avenue of application of single-atom catalysis to chemical transformations at high temperatures.

Superbase-derived task-specific ionic liquids (STSILs) represent one of the most attractive and extensively studied systems in carbon capture via chemisorption, in which the obtained CO

Molten chlorides are a preferred choice for fast-spectrum molten salt reactors. Molten MgCl

Although anionic N and O sites have been widely used in chemisorption of CO

Identifying and understanding charge storage mechanisms is important for advancing energy storage, especially when new materials and electrolytes are explored. Well-separated peaks in cyclic voltammograms (CVs) are considered key indicators of diffusion-controlled electrochemical processes with distinct Faradic charge transfer. Herein, we report on an electrochemical system with separated CV peaks, accompanied by surface-controlled partial charge transfer, in 2D Ti3C2Tx MXene in water-in-salt electrolytes. The process involves the insertion/desertion of desolvation-free cations, leading to an abrupt change of the interlayer spacing between MXene sheets. This unusual behavior increases charge storage at positive potentials, thereby increasing the amount of energy stored. This also demonstrates new opportunities for the development of high-rate aqueous energy storage devices and electrochemical actuators using safe and inexpensive aqueous electrolytes.

The top-performing perovskite solar cells (efficiency > 20%) generally rely on the use of a nanocrystal TiO2 electron transport layer (ETL). However, the efficacies and stability of the current stereotypically prepared TiO2 ETLs employing commercially available TiO2 nanocrystal paste are far from their maximum values. As revealed herein, the long-hidden reason for this discrepancy is that acidic protons (∼0.11 wt %) always remain in TiO2 ETLs after high-temperature sintering due to the decomposition of the organic proton solvent (mostly alcohol). These protons readily lead to the formation of Ti–H species upon light irradiation, which act to block the electron transfer at the perovskite/TiO2 interface. Affront this challenge, we introduced a simple deprotonation protocol by adding a small amount of strong proton acceptors (sodium ethoxide or NaOH) into the common TiO2 nanocrystal paste precursor and replicated the high-temperature sintering process, which wiped out nearly all protons in TiO2 ETLs during the sintering process. The use of deprotonated TiO2 ETLs not only promotes the PCE of both MAPbI3-based and FA0.85MA0.15PbI2.55Br0.45-based devices over 20% but also significantly improves the long-term photostability of the target devices upon 1000 h of continuous operation.

Introducing transition-metal components to ceria (CeO

Metallic-state gold nanorods are well known to exhibit strong longitudinal plasmon excitations in the near-infrared region (NIR) suitable for photothermal conversion. However, when the size decreases below ∼2 nm, Au nanostructures become nonmetallic, and whether the longitudinal excitation in plasmonic nanorods can be inherited is unknown. Here, we report atomically precise rod-shaped Au

Covalent triazine framework (CTF)-based membranes have shown unique properties and wide applications in energy-related fields, but there is still no efficient strategy capable of affording CTF memb...

Cr cation doping in the support of the Ru/CeO2 catalyst with a Cr/Ce molar ratio of 1:9 dramatically improved the CO2 methanation activity at low temperatures, with the turnover frequency value on ...

Although the coordinates of the metal atoms can be accurately determined by X-ray crystallography, locations of hydrides in metal nanoclusters are challenging to determine. In principle, neutron crystallography can be employed to pinpoint the hydride positions, but it requires a large crystal and a neutron source, which prevents its routine use. Here, we present a deep-learning approach that can accelerate determination of hydride locations in single-crystal X-ray structure of metal nanoclusters of different sizes. We demonstrate the efficiency of our method in predicting the most probable hydride sites and their combinations to determine the total structure for two recently reported copper nanoclusters, [Cu25 H10 (SPhCl2 )18 ]3- and [Cu61 (St Bu)26 S6 Cl6 H14 ]+ whose hydride locations have not been determined by neutron diffraction. Our method can be generalized and applied to other metal systems, thereby eliminating a bottleneck in atomically precise metal hydride nanochemistry.

Pore size is a crucial factor impacting gas separation in porous separation materials, but how to control the pore size to optimize the separation performance remains a challenge. Here, we propose a design of graphene/ionic liquid composites with tunable slit pore sizes, where cations and anions of ionic liquids are intercalated between graphene layers. By varying the sizes of the ions, we show from first-principles density functional theory calculations that the accessible pore size can be tuned from 3.4 to 6.0 A. Grand canonical Monte Carlo simulations of gas sorption find that the composite materials possess high CO2 uptake at room temperature and 1 bar (up to ∼8.5 mmol/g). Further simulations of the sorption of gas mixtures reveal that high CO2/N2 and CO2/CH4 adsorption selectivities can be obtained when the accessible pore size is

Ultrathin transition-metal oxides (TMOs) from nonlayered bulk structures are emerging 2D materials. Here we investigate the reactivity of a 2D TMO of varying thickness from first principles. We find that the band gap of the 2D nL-TiO2(110) shows a strong linear correlation with its surface reactivity: the smaller the band gap, the more reactive the surface oxygen; 3L-TiO2(110) has the smallest band gap and the highest reactivity. We further design Pt1 single-atom catalysts (SAC) by substituting a Pt single atom for a surface Ti atom. We find that the band gap of nL-TiO2(110) dictates both chemisorption and dissociation of CH4 on Pt1-nL-TiO2(110): the smaller the band gap, the stronger the adsorption of CH4 and the lower the barrier of heterolytic C-H activation of CH4. We propose that band gap can be a novel and direct descriptor for the reactivity of 2D TMOs and their supported SACs.

Strong metal–support interactions (SMSIs) and catalyst deactivation have been heavily researched for decades by the catalysis community. The promotion of SMSIs in supported metal oxides is commonly...

The synthesis of heterostructures of different two-dimensional (2D) materials offers an approach to combine advantages of different materials constituting the heterostructure and ultimately enhance their performance for applications such as electrochemical energy storage, achieving high energy, and high-power densities. Understanding the behavior of ions and solvents in confinement between these dissimilar layers is critical to understand their performance and control. Considering aqueous electrolytes, we explore the heterostructure of 2D lepidocrocite-type TiO2 (2D-TiO2) and hydroxylated or O-terminated Ti3C2 MXene using ReaxFF molecular dynamics simulations and elastic/quasielastic neutron scattering techniques. Simulating a bilayer water intercalation, we find that the extent of interlayer hydration is impacted most by the surface terminations on the MXene and is marginally affected by 2D-TiO2. However, the introduction of 2D-TiO2 decreases the water self-diffusion due to the notch sites (i.e., surface oxygen ridges) entrapping water molecules. Intercalating alkali cations into the heterostructures, we find that Li+ is predominantly adsorbed at the 2D-TiO2 surface instead of the MXenes with the preferential occupation of the notch sites. In contrast, Na+ forms a planar solvation with water, while K+ is adsorbed both at the O-terminated MXene and 2D-TiO2. This behavior is altered when OH-terminated MXene is involved-the repulsion from the protons on the MXene surface forces the K+ ions to be adsorbed exclusively to 2D-TiO2, while Na+ retains some of its solvation in the water layer due to its smaller size. In OH-terminated MXenes, we see a consistent transfer of protons from the MXene surface toward 2D-TiO2, implying a greater capacity to store protons in the heterostructures. Of the three cations simulated, Na+ hinders the proton migration the least and Li+ the most because of its position near the 2D-TiO2 surface. Therefore, 2D-TiO2/MXene heterostructures are likely to exhibit a higher energy density but lower power density, especially with Na+ intercalation.

Doping metal nanoclusters (NCs) with another metal usually leads to superior catalytic performance toward CO

The construction of heterogeneous frustrated Lewis pairs (FLPs) with performance comparable to or surpassing the homogeneous counterparts in H