Adjacent Vacancies Research Articles

Directional Construction of Low-Coordination Fe-N3 Coupled with Intrinsic Carbon Defects for High-Efficiency Oxygen Reduction.

Regulating the coordination environment of Fe-Nx sites is an efficient but challenging approach for promoting the intrinsic catalytic activity of single-atom Fe/N-codoped carbon (Fe-N-C) toward the oxygen reduction reaction (ORR). Herein, low-coordination Fe-N3 sites coupled with carbon vacancies (Fe-N3/CV) are directionally constructed in Fe-N-C via pyrolysis of a metal-organic framework (MOF) precursor with N3-Zn-O-Fe moieties, which are delicately prefabricated by chemically anchoring Fe3+ onto a H2O-etching induced linker-missing Zn-N3 site in the MOF precursor. The optimized Fe-N-C with the Fe-N3/CV sites displays a high ORR half-wave potential of 0.92 V (vs RHE), which is attributed to the optimized electronic structure and binding strengths of the active Fe center toward the ORR intermediates stemming from the synergy of the asymmetric configuration of Fe-N3 as well as the adjacent carbon vacancies. This work could be enlightening for the design and construction of high-activity coupling sites in metal and nitrogen-codoped carbon catalysts.

Breaking scaling relation of single-atom site via energy storage-release effect from adjacent carbon vacancy for low-temperature-resistant Fenton-like catalysis

To realize efficient antibiotics degradation in low-temperature water, single-atom FeN4 sites are engineered near carbon vacancies in a porous catalyst (PCvFe1-5) via thermal-etching and pyrolysis. The high-specific-surface-area (2202.80 m2 g−1) carbon support and dispersive Fe atoms co-enrich sulfamethoxazole and peroxymonosulfate to enhance the reactant collision frequency. Carbon vacancies allow the catalyst to deform for storing the peroxymonosulfate adsorption energies at FeN4 sites, which are subsequently released to facilitate -SO4H desorption for rapid site regeneration. This breaks the scaling relation suffered by single-atom sites, thereby reducing the thermodynamic energy barrier. Consequently, a low-temperature-resistant Fenton-like system with ultralow activation energy of 9.06 kJ mol−1 is constructed for sulfamethoxazole degradation. The normalized kinetic rate constant at 2 ℃ exceeds that of reported catalysts working at 25/30 ℃ by 1–2 orders of magnitude. Moreover, due to the special site configuration, PCvFe1-5 degrades sulfamethoxazole via both long-range catalyst-mediated electron transfer and short-range direct collision oxidation.

In situ fabrication of atomically adjacent dual-vacancy sites for nearly 100% selective CH4 production

The photocatalytic CO2-to-CH4 conversion involves multiple consecutive proton-electron coupling transfer processes. Achieving high CH4 selectivity with satisfactory conversion efficiency remains challenging since the inefficient proton and electron delivery path results in sluggish proton-electron transfer kinetics. Herein, we propose the fabrication of atomically adjacent anion-cation vacancy as paired redox active sites that could maximally promote the proton- and electron-donating efficiency to simultaneously enhance the oxidation and reduction half-reactions, achieving higher photocatalytic CO2 reduction activity and CH4 selectivity. Taking TiO2 as a photocatalyst prototype, the operando electron paramagnetic resonance spectra, quasi in situ X-ray photoelectron spectroscopy measurements, and high-angle annular dark-field-scanning transmission electron microscopy image analysis prove that the VTi on TiO2 as initial sites can induce electron redistribution and facilitate the escape of the adjacent oxygen atom, thereby triggering the dynamic creation of atomically adjacent dual-vacancy sites during photocatalytic reactions. The dual-vacancy sites not only promote the proton- and electron-donating efficiency for CO2 activation and protonation but also modulate the coordination modes of surface-bound intermediate species, thus converting the endoergic protonation step to an exoergic reaction process and steering the CO2 reduction pathway toward CH4 production. As a result, these in situ created dual active sites enable nearly 100% CH4 selectivity and evolution rate of 19.4 μmol g-1 h-1, about 80 times higher than that of pristine TiO2. Thus, these insights into vacancy dynamics and structure-function relationship are valuable to atomic understanding and catalyst design for achieving highly selective catalysis.

Discovery of atomic clock-like spin defects in simple oxides from first principles

Virtually noiseless due to the scarcity of spinful nuclei in the lattice, simple oxides hold promise as hosts of solid-state spin qubits. However, no suitable spin defect has yet been found in these systems. Using high-throughput first-principles calculations, we predict spin defects in calcium oxide with electronic properties remarkably similar to those of the NV center in diamond. These defects are charged complexes where a dopant atom — Sb, Bi, or I — occupies the volume vacated by adjacent cation and anion vacancies. The predicted zero phonon line shows that the Bi complex emits in the telecommunication range, and the computed many-body energy levels suggest a viable optical cycle required for qubit initialization. Notably, the high-spin nucleus of each dopant strongly couples to the electron spin, leading to many controllable quantum levels and the emergence of atomic clock-like transitions that are well protected from environmental noise. Specifically, the Hanh-echo coherence time increases beyond seconds at the clock-like transition in the defect with 209Bi. Our results pave the way to designing quantum states with long coherence times in simple oxides, making them attractive platforms for quantum technologies.

Unlocking ethane production in photocatalytic methanol reforming based on a novel carbon–carbon coupling mechanism

Photocatalytic methanol reforming represents a promising solution to energy and environmental challenges, yet the CO2 by-product poses significant environmental concerns. Recent advancements enhance the economic and environmental sustainability of this process by yielding valuable by-products like ethylene and ethylene–glycol. However, synthesizing ethane (C2H6), a crucial material, remains unattainable through this reaction, with an unclear mechanism. Herein, we synthesized oxygen-deficient two-dimensional TiO2 nanosheets to achieve ethane production via methanol reforming. Through theoretical calculations and in situ characterization, we unveil a novel carbon–carbon (C–C) coupling mechanism driving ethane production. It is discovered that methanol preferentially adsorbs on the oxygen vacancies of the defective TiO2 surface, forming methoxy radicals (*CH3O), facilitating C–C coupling for ethane formation. Furthermore, prolonged hydrogenation creates additional oxygen vacancies, leading to more adjacent oxygen vacancies. This results in more neighboring *CH3O, facilitating C–C coupling and elevating C2H6 production. Our study clarifies ethane production feasibility in photocatalytic methanol reforming, providing valuable references for future research.

Vacancy modulation on NiTi-layered double hydroxides towards highly selective CO2 photoreduction

Photoreduction of carbon dioxide (CO2) is a promising way to achieve sustainable energy production and alleviate environmental problems. Herein, we report a NiTi-layered double hydroxides photocatalyst with bivalent and trivalent metal vacancies (denoted as NiVTiV-LDHs) via alkali-etching amphoteric metal cations (Zn and Al) from NiZnTiAl-LDHs precursor. The NiVTiV-LDHs attains a CH4 selectivity of 94% with a production rate of 2398 µmol g−1 h−1, which is preponderant to the state-of-the-art photocatalysts. Operando X-ray absorption fine structure (XAFS) and Fourier-transform infrared spectroscopy (FT-IR) characterizations combined with density functional theory (DFT) calculations corroborate that Ni2+δ−O(H)−Ti3+ζ sites modulated by adjacent vacancies exhibits a declined 3d-orbital occupancy, accelerating the charge transfer for boosting CH4 formation. Moreover, the unique adsorption configuration (Ni2+δ/Ti3+ζ−CO) not only stabilizes the key intermediate *CO for further protonation, but also induces a decreased energy barrier of the rate-determining step (hydrogenation of *OCH3), accounting for the robust photocatalytic CO2 reduction towards CH4.

Probing the sites on metal oxide cluster nodes of metal organic framework MIL-96, MIL-100 and MIL-110

Metal oxide cluster MOF nodes are a good platform to understand the reactivities and catalysis. MIL-96, MIL-100 and MIL-110 are drastically different in their node structures. Following our previous reported results for MIL-100, we report the modified synthesis and characterization of the node sites of MIL-110 and MIL-96 and their catalytic sites by using methanol dehydration as probe reaction. We show that these MOFs can be synthesized from the same solution by adding various amounts of formic acid as modulator. Herein, the chemistry of hydroxyl, formate and methoxy groups were used to probe the three MOFs’ node sites. IR data show the bonding structures of these ligands are highly diverse, with reactivities and flexibilities depending on node sites. We identified terminal OH group and various µ2-OH groups in single, paired or hydrogen bonded modes on the MOF nodes. Formate ligands were introduced to the node sites during the synthesis or by a post treatment in formic acid/DMF solution. Surprisingly, the bonding modes of formate ligands on Al3(OH)3 node structure of MIL-96 can be reversibly switched between monodentate and bidentate through a process induced by water molecules. Further, methoxy ligands—likely to be the intermediate for catalytic reaction—were also observed on the node sites under methanol dehydration conditions at 250 ℃. The activities of MIL-100 and MIL-96 for methanol dehydration determined by TOF per node were similar, both approximately 3-fold higher than that of MIL-110. The data suggests that catalytic sites incorporate adjacent vacancy and defect node sites, which constitute a minority among all observed MOF node sites. We foresee the opportunities in expanding the chemistry and understanding into other MOFs with metal oxide cluster nodes.

Disclosing the intrinsic nature of efficient removal of antibiotics in N/S dual-doped porous carbon-based materials: The manipulation of internal electric field

N/S co-doping has emerged as a prevailing strategy for carbon-based adsorbents to facilitate the antibiotic removal efficiency. Nevertheless, the underlying interplay among N, S, and their adjacent vacancy defects remains overlooked. Herein, we present a novel in situ strategy for fabricating pyridinic-N dominated and S dual-doped porous carbon adsorbent with rich vacancy defects (VNSC). The experimental results revealed that N (acting as the electron donor) and S (acting as the electron acceptor) form an internal electric field (IEF), with a stronger IEF generated between pyridinic-N and S, while their adjacent vacancy defects activate carbon π electrons, thus enhancing the charge transfer of the IEF. Density functional theory (DFT) calculations further demonstrated that the rich charge transfer in the IEF facilitated the π-π electron donor-acceptor (EDA) interaction between VNSC and tetracycline (TC) as well as norfloxacin (NOR), and thus is the key to adsorption performance of VNSC. Consequently, VNSC exhibited high adsorption capacities toward TC (573.1 mg g−1) and NOR (517.0 mg g−1), and its potential for environmental applications was demonstrated by interference, environmentally relevant concentrations, fixed-bed column, and regeneration tests. This work discloses the natures of adsorption capacity for N/S dual-doped carbon-based materials for antibiotics.

Defect Engineering of Bi2WO6 for Enhanced Photocatalytic Degradation of Antibiotic Pollutants.

Infiltration of excessive antibiotics into aquatic ecosystems plays a significant role in antibiotic resistance, a major global health challenge. It is therefore critical to develop effective technologies for their removal. Herein, defect-rich Bi2WO6 nanoparticles are solvothermally prepared via epitaxial growth on pristine Bi2WO6 seed nanocrystals, and the efficiency of the photocatalytic degradation of ciprofloxacin, a common antibiotic, is found to increase markedly from 62.51% to 98.27% under visible photoirradiation for 60min. This is due to the formation of a large number of structural defects, where the synergistic interactions between grain boundaries and adjacent dislocations and oxygen vacancies lead to an improved separation and migration efficiency of photogenerated carriers and facilitate the adsorption and degradation of ciprofloxacin, as confirmed in experimental and theoretical studies. Results from this work demonstrate the unique potential of defect engineering for enhanced photocatalytic performance, a critical step in removing antibiotic contaminants in aquatic ecosystems.

Oxygen vacancy induction strategy to regulate the evolution of valence- and free-electrons for boosting visible photodegradation of tetracycline hydrochloride

The generation, migration and reaction paths of electrons are the key steps for photodegradation of pollutants. However, efficient operation of the above pathways is still challenging. Herein, by strong coordination and slow pyrolysis, we constructed a narrow band Zn-Mn bimetallic photoactive core-shell material (Mn@Zn-N-C, Eg = 3.38 eV) with abundant oxygen vacancies for enhancing the above electronic paths. The photodegradation experiments of tetracycline hydrochloride (TCH) showed that the formation and transfer of vacancy-induced free electrons in the synthesized Mn@Zn-N-C was the key to improve the photocatalytic activity. The DFT calculation results revealed that the photogenerated electrons can transfer along the Mn-O-Zn bridge in Mn@Zn-N-C, and promote the formation of MnIV, which directly capture the free electrons and reset itself to MnII site. In this case, the introduction of Mn would enhance the separation of h+ and e-. The adjacent vacancies and defects then also trapped the above free electrons and hinder the recombination of photogenerated carriers. Simultaneously, the localized valence electron transfer between the above redox pairs (Mn4+/Mn2+ and Zn2+/Zn0) also promoted the long-term stability of the photocatalytic process. In summary, using vacancy induction strategy to regulate the evolution of valence- and free-electrons is a promising method to improve the production-transfer-utilization efficiency of photogenerated carriers.

Oxygen-doped colloidal GaN quantum dots with blue emission

Gallium nitride quantum dots (GaN QDs), as a third-generation semiconductor material, are usually synthesized through a vapor deposition method at an elevated temperature (typically ≥800 °C). Thermal injection method is rarely reported for the synthesis of GaN QDs due to the lack of active precursors and the require of harsh reaction conditions. Here, we report the fabrication of oxygen doped colloidal GaN QDs via rapid thermal injection. By screening the reaction temperature and solvent, well-dispersed GaN QDs with a size of 3.8 nm were obtained in octadecylamine (ODA) at 360 °C. The synthesized GaN QDs show blue emission, the maximum emission wavelength is about 440 nm, and the photoluminescence quantum yield is 14.3%. Furthermore, we reveal the donor-acceptor mechanism of blue emission from GaN QDs. During the growth of GaN QDs, oxygen atoms occupy some nitrogen sites and produce a shallow oxygen donor energy level (ON). A part of the ON can be combined with the adjacent gallium vacancy (VGa) to form a VGa-ON acceptor, whose energy level is about 0.98 eV above the valence band of GaN QDs. The transition of excited electrons from the donor (ON) to the acceptor (VGa-ON) is responsible for the blue emission of GaN QDs.

Modulating CO2 methanation activity on Ni/CeO2 catalysts by tuning ceria facet-induced metal-support interaction

Comprehending the metal-support interactions (MSI) as well as interface structures plays a crucial role in creating efficient interface sites. However, the interfacial nature is influenced by multiple structural factors, making it challenging to establish a direct correlation between interfacial sites and CO2 methanation activity. Herein, the CeO2 with uniform facets were used as supports to study the influence of facet-induced MSI on methanation performance. CeO2 cubes with (1 0 0) facet and octahedrons with (1 1 1) facet was fabricated over Ni/CeO2 by altering hydrothermal parameters. (HR)TEM, XPS and Raman characterizations etc. revealed that the presence of embedded MSI structures in Ni/CeO2-Cub resulted in the well-dispersed Ni0. The embedded Ni–CeO2 interaction owned a maximized interface with more surface oxygen vacancies. The FT-IR spectrum indicated that the synergistic effect of H2 dissociation on Ni NPs surfaces and CO2 activation in adjacent surface oxygen vacancies occurred in Ni–CeO2 interfaces, improving CO2 methanation activity with a large number of formates. CO2 conversion rate for Ni/CeO2-Cub was 18.4 times as high as that for Ni/SiO2 without MSI at 548 K. This study elucidated how the facet-induced interfaces impacted the methanation activity, providing new ideas for the development of efficient CO2 hydrogenation catalysts.

Should sons breed independently or help? Local relatedness matters.

In cooperatively breeding birds, why do some individuals breed independently but others have to help at home? This question has been rarely addressed despite its fundamental importance for understanding the evolution of social cooperation. We address it using 15 years of data from Tibetan ground tits Pseudopodoces humilis where helpers consist of younger males. Since whether younger males successfully breed depends critically on their chances to occupy territories nearby home, our analytic strategy is to identify the determinants of individual differences in gaining territory ownership among these ready-to-breed males. Across widowed, last-year helper and yearling males, an age advantage was evident in inheriting resident territories, occupying adjacent vacancies and budding off part of adjacent territories, which left some last-year helpers and most yearling males to take the latter two routes. These males were more likely to acquire a territory if they were genetically related to the previous or current territory owners; otherwise they remained on natal territories as helpers. The relatedness effect can arise from the prior residence advantage established in the preceding winter when younger males followed their parents to perform kin-directed off-territory forays. Our research highlights the key role of local kinship in determining younger males' territory acquisition and thus their fate in terms of independent reproduction versus help. This finding provides insight into the formation of kin-based, facultative cooperative societies prevailing among vertebrates.

Electronic Asymmetry Engineering of Fe-N-C Electrocatalyst via Adjacent Carbon Vacancy for Boosting Oxygen Reduction Reaction.

Single-atomic transition metal-nitrogen-carbon (M-N-C) structures are promising alternatives toward noble-metal-based catalysts for oxygen reduction reaction (ORR) catalysis involved in sustainable energy devices. The symmetrical electronic density distribution of the M─N4 moieties, however, leads to unfavorable intermediate adsorption and sluggish kinetics. Herein, a Fe-N-C catalyst with electronic asymmetry induced by one nearest carbon vacancy adjacent to Fe─N4 is conceptually produced, which induces an optimized d-band center, lowered free energy barrier, and thus superior ORR activity with a half-wave potential (E1/2 ) of 0.934V in a challenging acidic solution and 0.901V in an alkaline solution. When assembled as the cathode of a Zinc-air battery (ZAB), a peak power density of 218mW cm-2 and long-term durability up to 200h are recorded, 1.5 times higher than the noble metal-based Pt/C+RuO2 catalyst. This work provides a new strategy on developing efficient M-N-C catalysts and offers an opportunity for the real-world application of fuel cells and metal-air batteries.

Synergy of Paired Brønsted-Lewis Acid Sites on Defects of Zr-MIL-140A for Methanol Dehydration.

As a common defect-capping ligand in metal-organic frameworks (MOFs), the hydroxyl group normally exhibits Brønsted acidity or basicity, but the presence of inherent hydroxyl groups in the MOF structure makes it a great challenge to identify the exact role of defect-capping hydroxyl groups in catalysis. Herein, we used hydroxyl-free MIL-140A as the platform to generate terminal hydroxyl groups on defect sites via a continuous post-synthetic treatment. The structure and acidity of MIL-140A were properly characterized. The hydroxyl-contained MIL-140A-OH exhibited 4.6-fold higher activity than the pristine MIL-140A in methanol dehydration. Spectroscopic and computational investigations demonstrated that the reaction was initiated by the respective adsorption of two methanol molecules on the terminal-OH and the adjacent Zr vacancy. The dehydration of the adsorbed methanol molecules then occurred in the Brønsted-Lewis acid site co-participated associative pathway with the lowest energy barrier.

First-Principles Study of Hydrogen Dynamics in Monoclinic TiO

The existence of intrinsic vacancies in cubic (monoclinic) TiO suggests opportunity for hydrogen absorption, which was addressed in recent experiments. In the present work, based on first-principles calculations, the preferences are studied for the hydrogen absorption sites and diffusion paths between them. The oxygen vacancies are found to be the primary hydrogen traps with absorption energy of −2.87 eV. The plausible channels for hydrogen diffusion between adjacent vacancy sites (ordered in the monoclinic TiO structure) are compared with the help of calculations using the nudge elastic band method. Several competitive channels are identified, with barrier heights varying from 2.87 to 3.71 eV, that are high enough to ensure relative stability of trapped hydrogen atoms at oxygen vacancy sites. Moreover, the possibility of adsorption of molecular hydrogen was tested and found improbable, in the sense that the H2 molecules penetrating the TiO crystal are easily dissociated (and released atoms tend to proceed toward oxygen vacancy sites). These results suggest that hydrogen may persist in oxygen vacancy sites up to high enough temperatures.

X-ray Excited Optical Luminescence of Eu in Diamond Crystals Synthesized at High Pressure High Temperature

Powder diamonds with integrated europium atoms were synthesized at high pressure (7.7 GPa) and temperature (1800 °C) from a mixture of pentaerythritol with pyrolyzate of diphthalocyanine (C64H32N16Eu) being a special precursor. In diamonds prepared by X-ray fluorescence spectroscopy, we have found a concentration of Eu atoms of 51 ± 5 ppm that is by two orders of magnitude greater than that in natural and synthetic diamonds. X-ray diffraction, SEM, X-ray exited optical luminescence, and Raman and IR spectroscopy have confirmed the formation of high-quality diamond monocrystals containing Eu and a substantial amount of nitrogen (~500 ppm). Numerical simulation has allowed us to determine the energy cost of 5.8 eV needed for the incorporation of a single Eu atom with adjacent vacancy into growing diamond crystal (528 carbons).

Simulating changes of packing structures, locally loading states and mechanical behaviors for Si lattices with double vacancies at elevated temperatures

The vacancy defects in silicon matrix have important influences on processing or manufacturing novel microelectronic devices as well as their performances related to structures and mechanical properties. Molecular dynamics simulations were performed for the evolution of the atomic packing structures and locally loading states as well as tensile tests for silicon matrixes having three types of double vacancies at atomic scale. Through analysis from Young's modulus, Poisson's ratios, Lode-Nadai parameters and atomic strain energy density as well as visually packing images, the simulation results show that there exists just one type of adjacent vacancies at room temperature, and the external energy provided from high temperature results in vacancy's migration. On heating, the matrixes having vacancies present apparent different stages from elasticity to plasticity, and their temperature regimes are identified. Under applying uniaxial tension at room temperature, the strain energy density of the matrix near the vacancies is significantly higher than those in the other regions in the elasticity stage. There are differences of the elongation and tensile strength of the matrixes having different types of vacancies.

Noble-metal free Ce-Fe-Zr ternary oxides with synergistic dual active sites for accelerating NO reduction

Efficient NOx elimination is crucial for the control of air pollution but highly depends on the construction of active sites for both N–O bond activation and oxygen transfer. In this study, dual active sites were established in a highly-efficient Ce-Fe-Zr ternary catalyst in the one-step flame spray pyrolysis (FSP) method. We demonstrated that a large amount of Fe2+ species were formed and enriched on the surface of oxides, accompanied by the improvement of oxygen storage and release by Fe doping into CeO2 lattice at a limit-breaking level. Their synergistic effect greatly enhanced the kinetics of the NO reduction step, which was attributed to the activation of NO on Fe2+ active site in the form of Fe2+-(NO)2 intermediate as well as the acceleration of the oxygen transfer through the adjacent oxygen vacancies. As a result, almost 100 % NO conversion was achieved at 175 °C, and they completely transferred into N2 at low temperature (223 °C) without noble metals. The development of flame technology here will provide an efficient way for the fabrication of multi-active sites in a metastable structure, exhibiting great potential in rational catalyst design.

Efficient Nitrate Conversion to Ammonia on f-Block Single-Atom/Metal Oxide Heterostructure via Local Electron-Deficiency Modulation.

Exploring single-atom catalysts (SACs) for the nitrate reduction reaction (NO3-; NitRR) to value-added ammonia (NH3) offers a sustainable alternative to both the Haber-Bosch process and NO3--rich wastewater treatment. However, due to the insufficient electron deficiency and unfavorable electronic structure of SACs, resulting in poor NO3--adsorption, sluggish proton (H*) transfer kinetics, and preferred hydrogen evolution, their NO3--to-NH3 selectivity and yield rate are far from satisfactory. Herein, a systematic theoretical prediction reveals that the local electron deficiency of an f-block Gd single atom (GdSA) can be significantly regulated upon coordination with oxygen-defect-rich NiO (GdSA-D-NiO400) support. Thus, facilitating stronger NO3- adsorption via strong Gd5d-O2p orbital coupling and further improving the protonation kinetics of adsorption intermediates by rapid H* capture from water dissociation catalyzed by the adjacent oxygen vacancy site along with suppressed H* dimerization synergistically boosts the NH3 selectivity/yield rate. Motivated by DFT prediction, we delicately stabilized electron-deficient (strongly electrophilic) GdSA on D-NiO400 (∼84% strong electrophilic sites), which exhibited excellent alkaline NitRR activity (NH3 Faradaic efficiency ∼97% and yield rate ∼628 μg/(mgcat h)) along with superior structural stability, as revealed by in situ Raman spectroscopy, significantly outperforming weakly electrophilic Gd nanoparticles, defect-free GdSA-P-NiO400, and reported state-of-the-art catalysts.