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The ligand chemistry of colloidal semiconductor nanocrystals mediates their solubility, band gap, and surface facets. Here, selective organometallic chemistry is used to prepare small, colloidal cuprous oxide nanocrystals and to control their surface chemistry by decorating them with metal complexes. The strategy is demonstrated using small (3-6 nm) cuprous oxide (Cu2O) colloidal nanocrystals (NC), soluble in organic solvents. Organometallic complexes are coordinated by reacting the surface Cu-OH bonds with organometallic reagents, M(C6F5)2, M = Zn(II) and Co(II), at room temperature. These reactions do not disrupt the Cu2O crystallinity or nanoparticle size; rather, they allow for the selective coordination of a specific metal complex at the surface. Subsequently, the surface-coordinated organometallic complex is reacted with three different carboxylic acids to deliver Cu-O-Zn(O2CR') complexes. Selective nanocrystal surface functionalization is established using spectroscopy (IR, 19F NMR), thermal gravimetric analyses (TGA), transmission electron microscopy (TEM, EELS), and X-ray photoelectron spectroscopy (XPS). Photoluminescence efficiency increases dramatically upon organometallic surface functionalization relative to that of the parent Cu2O NC, with the effect being most pronounced for Zn(II) decoration. The nanocrystal surfaces are selectively functionalized by both organic ligands and well-defined organometallic complexes; this synthetic strategy may be applicable to many other metal oxides, hydroxides, and semiconductors. In the future, it should allow NC properties to be designed for applications including catalysis, sensing, electronics, and quantum technologies.
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The sol-gel reaction mechanism of 211 MAX phases has proven to be very complex when identifying the intermediate species, chemical processes, and conversions that occur from a mixture of metal salts and gelling agent into a crystalline ternary carbide. With mostly qualitative results in the literature (Cr2GaC, Cr2GeC, and V2GeC), additional analytical techniques, including thermal analysis, powder diffraction, total scattering, and various spectroscopic methods, are necessary to unravel the identity of the chemical compounds and transformations during the reaction. Here, we demonstrate the combination of these techniques to understand the details of the sol-gel synthesis of MAX phase V2PC. The metal phosphate complexes, as well as amorphous/nanocrystalline vanadium phosphate species (V in different oxidation states), are identified at all stages of the reaction and a full schematic of the reaction process is suggested. The early amorphous vanadium species undergo multiple changes of oxidation states while organic species decompose releasing a variety of small molecule gases. Amorphous oxides, analogous to [NH4][VO2][HPO4], V2PO4O, and VO2P2O7 are identified in the dried gel obtained during the early stages of the heating process (300 and 600 °C), respectively. They are carbothermally reduced starting at 900 °C and subsequently react to crystalline V2PC with the excess carbon in the reaction mixture. Through CHN analysis, we obtain an estimate of left-over amorphous carbon in the product which will guide future efforts of minimizing the amount of carbon in sol gel-produced MAX phases which is important for subsequent property studies.
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Layered carbides are fascinating compounds due to their enormous structural and chemical diversity, as well as their potential to possess useful and tunable functional properties. Their preparation, however, is challenging and forces synthesis scientists to develop creative and innovative strategies to access high-quality materials. One unique compound among carbides is Mo2Ga2C. Its structure is related to the large and steadily growing family of 211 MAX phases that crystallize in a hexagonal structure (space group P63/mmc) with alternating layers of edge-sharing M6X octahedra and layers of the A-element. Mo2Ga2C also crystallizes in the same space group, with the difference that the A-element layer is occupied by two A-elements, here Ga, that sit right on top of each other (hence named "221" compound). Here, we propose that the Ga content in this compound is variable between 2:2, 2:1, and 2: ≤1 (and 2:0) Mo/Ga ratios. We demonstrate that one Ga layer can be selectively removed from Mo2Ga2C without jeopardizing the hexagonal P63/mmc structure. This is realized by chemical treatment of the 221 phase Mo2Ga2C with a Lewis acid, leading to the "conventional" 211 MAX phase Mo2GaC. Upon further reaction with CuCl2, more Ga is removed and replaced with Cu (instead of fully exfoliating into the Ga-free Mo2CTx MXene), leading to Mo2Ga1-xCuxC still crystallizing with space group P63/mmc, however, with a significantly larger c-lattice parameter. Furthermore, 211 Mo2GaC can be reacted with Ga to recover the initial 221 Mo2Ga2C. All three reaction pathways have not been reported previously and are supported by powder X-ray diffraction (PXRD), electron microscopy, X-ray spectroscopy, and density functional theory (DFT) calculations.
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Single-atom catalysts have garnered significant attention due to their exceptional atom utilization and unique properties. However, the practical application of these catalysts is often impeded by challenges such as sintering-induced instability and poisoning of isolated atoms due to strong gas adsorption. In this study, we employed the mechanochemical method to insert single Cu atoms into the subsurface of Fe2O3 support. By manipulating the location of single atoms at the surface or subsurface, catalysts with distinct adsorption properties and reaction mechanisms can be achieved. It was observed that the subsurface Cu single atoms in Fe2O3 remained isolated under both oxidation and reduction environments, whereas surface Cu single atoms on Fe2O3 experienced sintering under reduction conditions. The unique properties of these subsurface single-atom catalysts call for innovations and new understandings in catalyst design.
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This work applies organometallic routes to copper(0/I) nanoparticles and describes how to match ligand chemistries with different material compositions. The syntheses involve reacting an organo-copper precursor, mesitylcopper(I) [CuMes]z (z=4, 5), at low temperatures and in organic solvents, with hydrogen, air or hydrogen sulfide to deliver Cu, Cu2 O or Cu2 S nanoparticles. Use of sub-stoichiometric quantities of protonated ligand (pro-ligand; 0.1-0.2â equivalents vs. [CuMes]z ) allows saturation of surface coordination sites but avoids excess pro-ligand contaminating the nanoparticle solutions. The pro-ligands are nonanoic acid (HO2 CR1 ), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (HO2 CR2 ) or di(thio)nonanoic acid, (HS2 CR1 ), and are matched to the metallic, oxide or sulfide nanoparticles. Ligand exchange reactions reveal that copper(0) nanoparticles may be coordinated by carboxylate or di(thio)carboxylate ligands, but Cu2 O is preferentially coordinated by carboxylate ligands and Cu2 S by di(thio)carboxylate ligands. This work highlights the opportunities for organometallic routes to well-defined nanoparticles and the need for appropriate ligand selection.
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Cobre , Nanopartículas , Ligandos , SulfurosRESUMEN
Recently, high solar-to-hydrogen efficiencies were demonstrated using La and Rh co-doped SrTiO3 (La,Rh:SrTiO3) incorporated into a low-cost and scalable Z-scheme device, known as a photocatalyst sheet. However, the unique properties that enable La,Rh:SrTiO3 to support this impressive performance are not fully understood. Combining in situ spectroelectrochemical measurements with density functional theory and photoelectron spectroscopy produces a depletion model of Rh:SrTiO3 and La,Rh:SrTiO3 photocatalyst sheets. This reveals remarkable properties, such as deep flatband potentials (+2 V versus the reversible hydrogen electrode) and a Rh oxidation state dependent reorganization of the electronic structure, involving the loss of a vacant Rh 4d mid-gap state. This reorganization enables Rh:SrTiO3 to be reduced by co-doping without compromising the p-type character. In situ time-resolved spectroscopies show that the electronic structure reorganization induced by Rh reduction controls the electron lifetime in photocatalyst sheets. In Rh:SrTiO3, enhanced lifetimes can only be obtained at negative applied potentials, where the complete Z-scheme operates inefficiently. La co-doping fixes Rh in the 3+ state, which results in long-lived photogenerated electrons even at very positive potentials (+1 V versus the reversible hydrogen electrode), in which both components of the complete device operate effectively. This understanding of the role of co-dopants provides a new insight into the design principles for water-splitting devices based on bandgap-engineered metal oxides.
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Topochemical reduction of the cation-disordered perovskite oxides LaCo0.5Rh0.5O3 and LaNi0.5Rh0.5O3 with Zr yields the partially anion-vacancy ordered phases LaCo0.5Rh0.5O2.25 and LaNi0.5Rh0.5O2.25, respectively. Neutron diffraction and Hard X-ray photoelectron spectroscopy (HAXPES) measurements reveal that the anion-deficient phases contain Co1+/Ni1+ and a 1:1 mixture of Rh1+ and Rh3+ cations within a disordered array of apex-linked MO4 square-planar and MO5 square-based pyramidal coordination sites. Neutron diffraction data indicate that LaCo0.5Rh0.5O2.25 adopts a complex antiferromagnetic ground state, which is the sum of a C-type ordering (mM5+) of the xy-components of the Co spins and a G-type ordering (mΓ1+) of the z-components of the Co spins. On warming above 75 K, the magnitude of the mΓ1+ component declines, attaining a zero value by 125 K, with the magnitude of the mM5+ component remaining unchanged up to 175 K. This magnetic behavior is rationalized on the basis of the differing d-orbital fillings of the Co1+ cations in MO4 square-planar and MO5 square-based pyramidal coordination sites. LaNi0.5Rh0.5O2.25 shows no sign of long-range magnetic order at 2 K - behavior that can also be explained on the basis of the d-orbital occupation of the Ni1+ centers.
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The research in MAX phases is mainly concentrated on the investigation of carbides rather than nitrides (currently >150 carbides and only <15 nitrides) that are predominantly synthesized by conventional solid-state techniques. This is not surprising since the preparation of nitrides and carbonitrides is more demanding due to the high stability and low diffusion rate of nitrogen-containing compounds. This leads to several drawbacks concerning potential variations in the chemical composition of the MAX phases as well as control of morphology, the two aspects that directly affect the resulting materials properties. Here, we report how alternative solid-state hybrid techniques solve these limitations by combining conventional techniques with nonconventional precursor synthesis methods, such as the "urea-glass" sol-gel or liquid ammonia method. We demonstrate the synthesis and morphology control within the V-Ga-C-N system by preparing the MAX phase carbide and nitrideâthe latter in the form of bulkier and more defined smaller particle structuresâas well as a hitherto unknown carbonitride V2GaC1-xNx MAX phase. This shows the versatility of hybrid methods starting, for example, from wet chemically obtained precursors that already contain all of the ingredients needed for carbonitride formation. All products are characterized in detail by X-ray powder diffraction, electron microscopy, and electron and X-ray photoelectron spectroscopies to confirm their structure and morphology and to detect subtle differences between the different chemical compositions.
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Molecules which exhibit thermally activated delayed fluorescence (TADF) show great promise for use in efficient, environmentally-friendly OLEDs, and thus the design of new TADF emitters is an active area of research. However, when used in devices, they are typically in the form of disordered thin films, where both the external molecular environment and thermally-induced internal variations in parameters such as the torsion angle can strongly influence their electronic structure. In this work, we use density functional theory and X-ray photoelectron spectroscopy to investigate the impact of disorder on both core and valence states in the TADF emitter 2CzPN (1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene). By simulating gas phase molecules displaying varying levels of disorder, we assess the relative sensitivity of the different states to factors such as varying torsion angle. The theoretical results for both core and valence states show good agreement with experiment, thereby also highlighting the advantages of our approach for interpreting experimental spectra of large aromatic molecules, which are too complex to interpret based solely on experimental data.
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X-ray characterisation methods have undoubtedly enabled cutting-edge advances in all aspects of materials research. Despite the enormous breadth of information that can be extracted from these techniques, the challenge of radiation-induced sample change and damage remains prevalent. This is largely due to the emergence of modern, high-intensity X-ray source technologies and the growing potential to carry out more complex, longer duration in situ or in operando studies. The tunability of synchrotron beamlines enables the routine application of photon energy-dependent experiments. This work explores the structural stability of [Rh(COD)Cl]2, a widely used catalyst and precursor in the chemical industry, across a range of beamline parameters that target X-ray energies of 8 keV, 15 keV, 18 keV and 25 keV, on a powder X-ray diffraction synchrotron beamline at room temperature. Structural changes are discussed with respect to absorbed X-ray dose at each experimental setting associated with the respective photon energy. In addition, the X-ray radiation hardness of the catalyst is discussed, by utilising the diffraction data collected at the different energies to determine a dose limit, which is often considered in protein crystallography and typically overlooked in small molecule crystallography. This work not only gives fundamental insight into how damage manifests in this organometallic catalyst, but will encourage careful consideration of experimental X-ray parameters before conducting diffraction on similar radiation-sensitive organometallic materials.
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Fotones , Sincrotrones , Rayos X , Cristalografía , Difracción de Rayos XRESUMEN
The precursor conversion chemistry and surface chemistry of Cu3 N and Cu3 PdN nanocrystals are unknown or contested. Here, we first obtain phase-pure, colloidally stable nanocubes. Second, we elucidate the pathway by which copper(II) nitrate and oleylamine form Cu3 N. We find that oleylamine is both a reductant and a nitrogen source. Oleylamine is oxidized by nitrate to a primary aldimine, which reacts further with excess oleylamine to a secondary aldimine, eliminating ammonia. Ammonia reacts with CuI to form Cu3 N. Third, we investigated the surface chemistry and find a mixed ligand shell of aliphatic amines and carboxylates (formed in situ). While the carboxylates appear tightly bound, the amines are easily desorbed from the surface. Finally, we show that doping with palladium decreases the band gap and the material becomes semi-metallic. These results bring insight into the chemistry of metal nitrides and might help the development of other metal nitride nanocrystals.
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Multilayered heterostructures comprising of In2 O3 , SnO2 , and Al2 O3 were studied for their application in thin-film transistors (TFT). The compositional influence of tin oxide on the properties of the thin-film, as well as on the TFT characteristics is investigated. The heterostructures are fabricated by atomic layer deposition (ALD) at 200 °C, employing trimethylindium (TMI), tetrakis(dimethylamino)tin (TDMASn), trimethylaluminum (TMA), and water as precursors. After post-deposition annealing at 400 °C the thin-films are found to be amorphous, however, they show a discrete layer structure of the individual oxides of uniform film thickness and high optical transparency in the visible region. Incorporation of only two monolayers of Al2 O3 in the active semiconducting layer the formation of oxygen vacancies can be effectively suppressed, resulting in an improved semiconducting and switching behavior. The heterostacks comprising of In2 O3 /SnO2 /Al2 O3 are incorporated into TFT devices, exhibiting a saturation field-effect mobility (µsat ) of 2.0â cm2 â V-1 s-1 , a threshold-voltage (Vth ) of 8.6â V, a high current on/off ratio (IOn /IOff ) of 1.0×107 , and a subthreshold swing (SS) of 485â mV â dec-1 . The stability of the TFT under illumination is also altered to a significant extent. A change in the transfer characteristic towards conductive behavior is evident when illuminated with light of an energy of 3.1â eV (400â nm).
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X-ray characterization techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray-induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever-increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complementary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray-induced effects in transition-metal catalysts and, consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.
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Lab-on-Chip is a technology that could potentially revolutionize medical Point-of-Care diagnostics. Considerable research effort is focused towards innovating production technologies that will make commercial upscaling financially viable. Printed circuit board manufacturing techniques offer several prospects in this field. Here, we present a novel approach to manufacturing Printed Circuit Board (PCB)-based Ag/AgCl reference electrodes, an essential component of biosensors. Our prototypes were characterized both structurally and electrically. Scanning Electron Microscopy (SEM) and X-Ray Photoelectron Spectroscopy (XPS) were employed to evaluate the electrode surface characteristics. Electrical characterization was performed to determine stability and pH dependency. Finally, we demonstrate utilization along with PCB pH sensors, as a step towards a fully integrated PCB platform, comparing performance with discrete commercial reference electrodes.
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Electricidad , Electrónica/métodos , Compuestos de Plata/química , Plata/química , Electrodos , Concentración de Iones de Hidrógeno , Microscopía Electrónica de Rastreo , Espectroscopía de Fotoelectrones , Polimetil Metacrilato/química , Propiedades de Superficie , Compuestos de Estaño/químicaRESUMEN
Titanium nitride is an exciting plasmonic material, with optical properties similar to gold. However, synthesizing TiN nanocrystals is highly challenging and typically requires solid-state reactions at very high temperatures (800-1000°C). Here, the synthesis of TiN nanocrystals is achieved at temperatures as low as 350°C, in just 1 h. The strategy comprises molten salt, Mg as reductant and Ca3N2 as nitride source. This brings TiN from the realm of solid-state chemistry into the field of solution-based synthesis in regular, borosilicate glassware.
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We study the photophysical stability of ensemble near-surface nitrogen vacancy (NV) centers in diamond under vacuum and air. The optically detected magnetic resonance contrast of the NV centers was measured following exposure to laser illumination, showing opposing trends in air compared to vacuum (increasing by up to 9% and dropping by up to 25%, respectively). Characterization using X-ray photoelectron spectroscopy (XPS) suggests a surface reconstruction: In air, atmospheric oxygen adsorption on a surface leads to an increase in NV- fraction, whereas in vacuum, net oxygen desorption increases the NV0 fraction. NV charge state switching is confirmed by photoluminescence spectroscopy. Deposition of â¼2 nm alumina (Al2O3) over the diamond surface was shown to stabilize the NV charge state under illumination in either environment, attributed to a more stable surface electronegativity. The use of an alumina coating on diamond is therefore a promising approach to improve the resilience of NV sensors.
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MAX phases with the general formula Mn+1AXn are layered carbides, nitrides, and carbonitrides with varying stacking sequence of layers of M6X octahedra and the A element depending on n. While "211" MAXphases (n = 1) are very common, MAX phases with higher n, especially n ≥ 3, have hardly been prepared. This work addresses open questions regarding the synthesis conditions, structure, and chemical composition of the "514" MAX phase. In contrast to literature reports, no oxide is needed to form the MAX phase, yet multiple heating steps at 1,600 °C are required. Using high-resolution X-ray diffraction, the structure of (Mo1-xVx)5AlC4 is thoroughly investigated, and Rietveld refinement suggests P-6c2 as the most fitting space group. SEM/EDS and XPS show that the chemical composition of the MAX phase is (Mo0.75V0.25)5AlC4. It was also exfoliated into its MXene sibling (Mo0.75V0.25)5C4 using two different techniques (using HF and an HF/HCl mixture) that lead to different surface terminations as shown by XPS/HAXPES measurements. Initial investigations of the electrocatalytic properties of both MXene versions show that, depending on the etchant, (Mo0.75V0.25)5C4 can reduce hydrogen at 10 mA cm-2 with an overpotential of 166 mV (HF only) or 425 mV (HF/HCl) after cycling the samples, which makes them a potential candidate as an HER catalyst.
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With the rapid development of renewable energy harvesting technologies, there is a significant demand for long-duration energy storage technologies that can be deployed at grid scale. In this regard, polysulfide-air redox flow batteries demonstrated great potential. However, the crossover of polysulfide is one significant challenge. Here, we report a stable and cost-effective alkaline-based hybrid polysulfide-air redox flow battery where a dual-membrane-structured flow cell design mitigates the sulfur crossover issue. Moreover, combining manganese/carbon catalysed air electrodes with sulfidised Ni foam polysulfide electrodes, the redox flow battery achieves a maximum power density of 5.8 mW cm-2 at 50% state of charge and 55 °C. An average round-trip energy efficiency of 40% is also achieved over 80 cycles at 1 mA cm-2. Based on the performance reported, techno-economic analyses suggested that energy and power costs of about 2.5 US$/kWh and 1600 US$/kW, respectively, has be achieved for this type of alkaline polysulfide-air redox flow battery, with significant scope for further reduction.
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A challenge in neurology is the lack of efficient brain-penetrable neuroprotectants targeting multiple disease mechanisms. Plasmonic gold nanostars are promising candidates to deliver standard-of-care drugs inside the brain but have not been trialed as carriers for neuroprotectants. Here, we conjugated custom-made peptide dendrimers (termed H3/H6), encompassing motifs of the neurotrophic S100A4-protein, onto star-shaped and spherical gold nanostructures (H3/H6-AuNS/AuNP) and evaluated their potential as neuroprotectants and interaction with neurons. The H3/H6 nanostructures crossed a model blood-brain barrier, bound to plasma membranes, and induced neuritogenesis with the AuNS, showing higher potency/efficacy than the AuNP. The H3-AuNS/NP protected neurons against oxidative stress, the H3-AuNS being more potent, and against Parkinson's or Alzheimer's disease (PD/AD)-related cytotoxicity. Unconjugated S100A4 motifs also decreased amyloid beta-induced neurodegeneration, introducing S100A4 as a player in AD. Using custom-made dendrimers coupled to star-shaped nanoparticles is a promising route to activate multiple neuroprotective pathways and increase drug potency to treat neurodegenerative disorders.
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Enfermedad de Alzheimer , Dendrímeros , Fármacos Neuroprotectores , Humanos , Fármacos Neuroprotectores/química , Péptidos beta-Amiloides , Dendrímeros/farmacología , Dendrímeros/uso terapéutico , Neuronas , Oro/química , Enfermedad de Alzheimer/tratamiento farmacológicoRESUMEN
A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.