Neighboring Oxygen Atoms Research Articles

First-principle study origin of ferromagnetism in non-magnetic perovskite BaSnO3 doped with 2p-X (X=C, N)

In this study, our goal is to analyze the origin of magnetization in non magnetic cubic structure perovskite BaSnO3 doped with 2p-X (X=C, N) using the full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For the exchange and correlation potential we have applied the generalized gradient approximation (GGA) and the GGA plus-modified Becke-Johnson potential (mBJ-GGA). The results show that BaSnO3 doped with C then with N and finally with C and N exhibit half-metallic ferromagnetism behavior with the integer magnetic moment of 1, 2 and 3 μB per cell respectively. The origin of the ferromagnetism that occurs within these compounds is mainly caused by the p-p hybridization between 2p-impurities and its neighboring oxygen atoms. These results allowed to conclude that doped perovskite could provide a new type of materials, called half-metallic for future spintronic devices.

A New Type of Acidic OH-Groups in the LTL Zeolite

Acidic properties of ion-exchanged LTL zeolites have been studied using FTIR spectroscopy, complemented by X-ray powder diffraction, SEM-EDX, XRF and N2 physisorption. Infrared spectra of the ion-exchanged zeolites show the presence of two intense bands of the bridging OH-groups: a narrow band at ~3640 cm−1 that is attributed to Si(OH)Al groups freely vibrating in 12 MR and a broad, intense band at ~3250 cm−1 that is assigned to bridging OH groups forming hydrogen bond with neighbouring oxygen atoms, e.g., in six-membered rings. The former can be selectively removed by caesium or rubidium cations with up to 3 Cs+ or Rb+ per unit cell readily ion-exchanged into the LTL zeolite, replacing an equivalent number of acidic OH-groups or K+ cations within the structure. The cation migration of the larger cation, evaluated by the Rietveld refinement method, occurs mostly via the main 12 MR channels. By contrast, less than 1 Li+ or Na+ cation per unit cell can be introduced under similar conditions. Accordingly, the concentration of Si(OH)Al groups in back-exchanged NH4-K-LTL with smaller cations (Li+, Na+) does not differ considerably from the concentration of Brønsted acid sites in the original NH4-K-LTL. Lower concentrations of acid sites have been detected in the samples back-exchanged with Cs+, Rb+ and K+. In addition, the acidic properties of NH4-LTL samples have been compared with a structurally related NH4-MAZ zeolite.

Chemical reduction-induced defect-rich bismuth oxide-reduced graphene oxide anode for high-performance supercapacitors

We prepare bismuth oxide-reduced graphene oxide (Bi2O3-rGO) composite anode using a one-step chemical precipitation/reduction method. Under a reducing atmosphere, oxygen atoms on the surface of Bi2O3 are gradually removed and neighboring oxygen atoms migrate to the surface, leaving oxygen vacancies. Defective Bi2O3 enhances the number of active sites, providing additional pseudocapacitive performance. The transition metal oxide-based Bi2O3 acts as an anode, providing capacitive performance that far exceeds that of conventional carbon materials. Moreover, the introduction of rGO forms a conductive network for Bi2O3, improving capacitive contribution and ion diffusion capabilities for the electrode. The Bi2O3-rGO-100 (GO added at 100 mg) exhibits a high specific capacitance of 1053F/g at 1 A/g, significantly higher than that of Bi2O3 (866F/g). The Bi2O3-rGO-100 anode and Ni3Co2-rGO cathode are assembled into a battery-type supercapacitor. The coin-cell device achieves an energy density of 88.2 Wh kg−1 at a power density of 850 W kg−1. The Ni3Co2-rGO//Bi2O3-rGO-100 pouch-cell device demonstrates an extremely low Rct of 0.77 Ω. At a power density of 850 W kg−1, the energy density reaches 118.5 Wh kg−1, and remains 67.4 Wh kg−1 at 8500 W kg−1.

Basic Sites on Alumina with Preadsorbed Ethanol and Ammonia-An IR Study.

The adsorption of ethanol and ammonia changes the basic properties of alumina, and new basic sites are created. Ethanol reacts with surface Al-OH groups, forming ethoxy group Al-O-C2H5. The substitution of Al-OH by Al-O-C2H5 increases the negative charge of neighbouring oxygen atoms, and they became sufficiently basic to react with adsorbed CO2 forming carbonate species CO32-. These carbonates were found to be monodentate and bidentate species. Preadsorption of ammonia also increases the basicity of alumina, but the mechanism is different than for ethanol adsorption. Adsorbed ammonia interacts with surface Lewis acid sites being three-coordinated aluminium atoms. This interaction is accompanied by an electron transfer from ammonia molecules to surface sites, and increases the basicity of the neighbouring oxygens, which can react with the absorbed CO2. The carbonate species formed are polydentate ones.

Hydrogenation conversion of CO2 molecules on monolayer MoS2 supported (TiO2)n clusters: A first-principles investigation

Adsorption and hydrogenation reaction of CO2 molecules on the surfaces of monolayer MoS2 supported (TiO2)n clusters were investigated using the first principles calculations. Calculation results reveal that small (TiO2)n clusters can be bounded firmly on monolayer MoS2 surface through the formation of chemical bonds between Ti and S atoms. (TiO2)n clusters on the surface of MoS2 can significantly improve the capabilities for CO2 capture. Due to the existence of dangling oxygen atoms of (TiO2)n clusters, CO2 molecules are likely to adsorb on MoS2/(TiO2)n surfaces as bent configurations. H atoms and CO2 molecules co-adsorb stably on the surfaces of MoS2/(TiO2)n, and then realize the hydrogenation conversion of adsorbed CO2 to *COOH through H adatoms migrations. The results suggest that H adatoms can migrate along several specific reaction pathways with relative lower energy barriers. Especially, for MoS2/(TiO2)4 substrate, distal H adatoms could firstly migrate to neighboring oxygen atoms with a lower energy barriers of about 1.12 eV, and further hydrogenation reaction occurs with an activation barrier of about 0.59 eV. These results may provide some useful proposals of catalyst design for hydrogenation conversion of CO2.

Spectroscopic and Theoretical Studies on Conformational Stability of Benzyl Methyl Ether.

Conformer-selected electronic and vibrational spectra of benzyl methyl ether and its terminal methyl group-substituted derivative in a supersonic jet have been measured using ultraviolet (UV)-UV hole burning and fluorescence-detected infrared spectroscopy to investigate the conformational stability of flexible molecules. Various quantum chemical calculations as well as experimental observations reveal the coexistence of three conformers with different CCOC dihedral angles and side-chain orientations relative to the benzene ring plane. Vibrational analysis in the excited state with time-dependent density functional theory and IR simulations containing anharmonic coupling sufficiently reproduce the experimental results, suggesting that these three conformers can be distinguished into one gauche-conformer and two trans-ones with respect to the CCOC dihedral angle. We also observe that the gauche conformer exhibits higher-frequency CH2 modes. The natural bond orbital analysis indicates that this phenomenon is attributed to the electron delocalization from the non-bonding orbitals and the C-O orbitals associated with the neighboring oxygen atom, which leads to a conformer dependence of the methylene C-H bond strength.

A Heterogeneous Single Atom Cobalt Catalyst for Highly Efficient Acceptorless Dehydrogenative Coupling Reactions.

A fundamental understanding of metal active sites in single-atom catalysts (SACs) is important and challenging in the development of high-performance catalyst systems. Here, a highly efficient and straightforward molten-salt-assisted approach is reported to create atomically dispersed cobalt atoms supported over vanadium pentoxide layered material, with each cobalt atom coordinated with four neighboring oxygen atoms. The liquid environment and the strong polarizing force of the molten salt at high temperatures potentially favor the weakening of VO bonding and the formation of CoO bonding on the vanadium oxide surface. This cobalt SAC achieves extraordinary catalytic efficiency in acceptorless dehydrogenative coupling of alcohols with amines to give imines, with more than 99% selectivity under almost 100% conversion within 3h, along with a high turnover frequency (TOF)of 5882h-1 , exceeding those of previously reported benchmarking catalysts. Moreover, it delivers excellent recyclability, reaction scalability, and substrate tolerance. Density functionaltheory(DFT) calculations further confirm that the optimized coordination environment and strong electronic metal-support interaction contribute significantly to the activation of reactants. The findings provide a feasible route to construct SACs at the atomic level for use in organic transformations.

Atomically dispersed single ruthenium sites anchored on bismuth tungstate with synergistic geometric and electronic effects for epoxidation of trans-stilbene

The feasibility of elegantly tuned geometric structures and electronic environments of metal active sites in single atom catalysts (SACs) is crucial for developing highly robust and efficient catalytic materials. Here we report a straightforward and efficient approach to accessing single ruthenium (Ru) atoms over a Bi2WO6 assemblage, with each Ru atom coordinated with four neighboring oxygen atoms. This Ru catalyst, exhibits synergistic geometric and electronic effects, resulting in a significantly enhanced catalytic performance for epoxidation of trans-stilbene to give trans-stilbene oxide. The reaction takes place under mild conditions, with high conversion (>99 %) and selectivity (>99 %) within a mere 2 h and a high turnover frequency (TOF) of 558 h−1. The theoretical calculations demonstrate that the high catalytic activity originates from the strong electronic metal-support interaction and the charge state of ruthenium sites in Bi2WO6. This work opens an avenue to engineer SACs on Aurivillius (perovskite) phase materials at the atomic level and serves as a promising platform for further studies of many other organic transformations.

New properties of boron-oxygen dimer defect in boron-doped Czochralski silicon

Silicon doped with boron is the most widely used material in modern microelectronic devices based on p-Si. Therefore, it is important to thoroughly understand boron’s role in the processes of defect-impurity interaction in Si both on growing the material and during operation of devices. In this work, interactions of boron with oxygen in Si are investigated by studying boron absorption intracenter transitions, which are known to be highly sensitive to the local environment. In boron-doped Si, two lines with maxima at 228 and 261.3 cm−1 were detected. The linear dependence of lines intensity on boron concentration and the quadratic on oxygen content testifies that the defect responsible for the lines can be identified as BsO2i. The observed absorption lines correspond to the transitions from the ground to the excited states of boron, which are shifted toward lower frequencies relative to the main transitions due to a deformation perturbation from neighboring oxygen atoms. The activation energy of annealing and ionization energy of defect are determined. The properties of the registered ВsO2i defect differ from the known ВsO2 associated with the light-induced degradation of solar cells by local configuration. The data obtained testify that the ВsO2i defects with different properties can be formed in Si and must be taken into account when developing Si:B-based devices because they can play an important role in charge carrier transfer and affect the electrical and optical parameters of the material.

Adsorption of toxic and non-toxic metals with new model of CX[4]: Experimental and computational investigation, Spectroscopic, QTAIM, and Antibacterial activity analyses

The presence of toxic metals in the environment is a big problem because it can be harmful to human health. Consequently, it is necessary to control the percentage of metals (for example, magnesium) in human body. In this paper, a very efficient model was proposed to detect the toxic or know the presence of the non-toxic metals at the same time. The selected models are capable of adsorbing cations in all active sites, even if they are present in different positions. The structural stability, adsorption sites and charge transfer have been investigated. The models, where all adsorption sites are filled involving azo-ethoxycarbonylmethoxy-calix[4]arene-X2+,3+ (Pb, Cd, Mg, and Eu), are stable and selective for toxic or non-toxic cations. The Hirshfeld surfaces (HS) have been computed at the active sites, where Mg2+, Pb2+ and Cd2+ cations are adsorbed. Theoretical and experimental investigations of the luminescence properties have demonstrated that when adding the three cations in the acceptor sites a very high charge transfer is observed, indicating that the compound is well selective for the three cations. According to the QTAIM theory, a toxic or non-toxic metal may be fixed through strong hydrogen bonding interactions between the guest and its neighboring oxygen atoms. The molecular docking simulation showed that the most stable system azo-ethoxycarbonylmethoxy-CX[4]-Eu3+ exhibits a potential anti-bacterial activity.

Strong electronic interaction of indium oxide with palladium single atoms induced by quenching toward enhanced hydrogenation of nitrobenzene

The realization of efficient and fully controllable synthesis of single atom catalysts is an exciting frontier, yet still challenging in the modern catalysis field. Here we describe a straightforward high-temperature quenching approach to precisely construct isolated palladium atoms supported over cubic indium oxide, with individual palladium atoms coordinated with four neighboring oxygen atoms. This palladium catalyst achieves exceptional catalytic efficiency in the selective hydrogenation of nitrobenzene to aniline, with more than 99% chemoselectivity under almost 100% conversion. Moreover, it delivers excellent recyclability, anti-CO poisoning ability, storage stability, and substrate tolerance. DFT calculations further reveal that the high catalytic activity stems from the optimized electronic structure and the charge states of palladium atoms in the defect-containing indium oxide. Our findings provide an effective approach to engineering single atom catalysts at the atomic level and open the door to a wide variety of catalytic reactions.

In English

By the method of density functional theory with exchange-correlation functional B3LYP and basis set 3‑21G (d), the structural and energy characteristics have been considered of the molecular models of SnO2 nanoclusters of different size and composition with the number of Sn atoms from 1 to 10. Incompletely coordinated surface tin atoms were terminated by hydroxyl groups. It has been shown that the Sn–O bond length in nanoclusters does not depend on the cluster size and on the coordination number of Sn atoms, but is determined by the coordination type of neighboring oxygen atoms. Namely, the bond length Sn–O(3) (@ 2.10 Å) is greater than that of Sn–O (2) (@ 1.98 Å). The calculated values of Sn–O (3) bond lengths agree well with the experimental ones for crystalline SnO 2 samples (2.05 Å). The theoretically calculated width of the energy gap decreases naturally with increasing cluster size (from 6.14 to 3.46 eV) and approaches the experimental value of the band gap of the SnO 2 crystal (3.6 eV). The principle of additivity was used to analyze the energy characteristics of the considered models and to estimate the corresponding values for a cassiterite crystal. According to this principle, a molecular model can be represented as a set of atoms or atomic groups of several types that differ in the coordination environment and, therefore, make different contributions to the total energy of the system. The calculated value of the atomization energy for SnO2 is 1661 kJ/mol and corresponds satisfactorily to the experimentally measured specific atomization energy of crystalline SnO2 (1381 kJ/mol). It has been shown that a satisfactory reproduction of the experimental characteristics of crystalline tin dioxide is possible when using clusters containing at least 10 state atoms, for example, (SnO2)10×14H2O.

IR-Spectroscopic Study of Complex Formation of Nitrogen Oxides (NO, N2O) with Cationic Forms of Zeolites and the Reactivity of Adsorbed Species in CO and CH4 Oxidation.

The formation of complexes and disproportionation of nitrogen oxides (NO, N2O) on cationic forms of LTA, FAU, and MOR zeolites was investigated by diffuse-reflectance IR spectroscopy. N2O is adsorbed on the samples under study in the molecular form and the frequencies of the first overtone of the stretching vibrations ν10–2 and the combination bands of the stretching vibrations with other vibrational modes for N2O complexes with cationic sites in zeolites (ν30–1 + ν10–1, ν10–1 + δ0–2) are more significantly influenced by the nature of the zeolite. The presence of several IR bands in the region of 2400–2600 cm−1 (the ν10–1 + δ0–2 transitions) for different zeolite types was explained by the availability of different localization sites for cations in these zeolites. The frequencies in this region also depend on the nature of the cation (its charge and radius). The data can be explained by the specific geometry of the N2O complex formed, presumably two-point adsorption of N2O on a cation and a neighboring oxygen atom of the framework. Adsorption of CO or CH4 on the samples with preliminarily adsorbed N2O at 20–180 °C does not result in any oxidation of these molecules. NO+ and N2O3 species formed by disproportionation of NO are capable of oxidizing CO and CH4 molecules to CO2, whereas NOx is reduced simultaneously to N2 or N2O. The peculiarities in the behavior of cationic forms of different zeolites with respect to adsorbed nitrogen oxides determined by different density and localization of cations have been established.

Harnessing Intramolecular Chalcogen-Chalcogen Bonding in Merocyanines for Utilization in High-Efficiency Photon-to-Current Conversion Optoelectronics.

A novel series of donor (D)-π-acceptor (A) merocyanine molecules harnessed with intramolecular chalcogen bonding (ChaB) is designed, synthesized, and characterized. ChaB comprises periodic chalcogen atoms, S, Se, and Te, and a neighboring oxygen atom of a carbonyl moiety. Compared to the D-π-A merocyanine dye with nontraditional intramolecular hydrogen bonding, the novel molecules with an intramolecular ChaB exhibit remarkably smaller absorption spectral widths and higher absorption coefficients attributed to their cyanine-like characteristics approaching the resonance parameter (c2) ∼0.5; furthermore, they exhibit better thermal stabilities and electrical charge-carrier transport properties in films. These novel D-π-A merocyanines harnessed with intramolecular ChaB networks are successfully utilized in high-performance color-selective organic photon-to-current conversion optoelectronic devices with excellent thermal stabilities. This study reports that the unique intramolecular ChaB plays an essential role in locking the molecular conformation of merocyanine molecules and enhancing the optical, thermal, and optoelectronic properties of high-performance and high-efficiency organic photon-to-current conversion devices.

Hydrogen Bonds Dominate Brønsted Acid Sites in Zeolite SSZ-42: A Classification of Their Diversity.

The zeolite catalyst SSZ‐42 shows a remarkable high abundance (≈80 %) of hydrogen‐bonded Brønsted acid sites (BAS), which are deshielded from the 1H chemical shift of unperturbed BAS at typically 4 ppm. This is due to their interaction with neighboring oxygen atoms in the zeolite framework when oxygen alignments are suitable. The classification and diversity of hydrogen bonding is assessed by DFT calculations, showing that oval‐shaped 6‐rings and 5‐rings allow for a stronger hydrogen bond to oxygen atoms on the opposite ring side, yielding higher experimental chemical shifts (δ (1H)=6.4 ppm), than circular 6‐rings (δ(1H)=5.2 ppm). Cage‐like structures and intra‐tetrahedral interactions can also form hydrogen bonds. The alignment of oxygen atoms is expected to impact their role in the stabilization of intermediates in catalytic reactions, such as surface alkoxy groups and possibly transition states.

Formation of a macrocycle from di-chloro-dimethyl-silane and a pyridoxalimine Schiff base ligand.

The reaction of di-chloro-dimethyl-silane with a polydentate Schiff base ligand derived from pyridoxal and 2-ethano-lamine yielded the macrocyclic silicon compound (8E,22E)-4,4,12,18,18,26-hexa-methyl-3,5,17,19-tetra-oxa-8,13,22,27-tetra-aza-4,18-disilatri-cyclo-[22.4.0.010,15]octa-cosa-1(24),8,10,12,14,22,25,27-octa-ene-11,25-diol, C24H36N4O6Si2. The asymmetric unit contains the half macrocycle with an intra-molecular O-H⋯N hydrogen bond between the imine nitro-gen atom and a neighbouring oxygen atom. The crystal structure is dominated by C-H⋯O and C-H⋯π inter-actions, which form a high ordered mol-ecular network.

Structural, Spectroscopic, Antiferromagnetic and in vitro antiproliferative studies of copper (II) pyrophosphate complex against Human breast cancer cell lines

In purpose to search for compounds of biological interest, we have succeeded in synthesizing a copper complex with polypyridine ligands. The architecture of the compound consists of O, N-donor entities, the pyrophosphate anion HP2O73− and the two heterocyclic molecules, 1,10-phenanthroline and 2,2′-bipyridine. X-ray diffraction study proves that our compound crystallizes in a monoclinic cell of space group P21/n. The atomic arrangement can be described by the aggregation of [(C10H8N2)(C12H10N2)Cu2(H2O)2(HP2O7)]+ cation, which contributes to the macrocyclic compound-complex. The second sphere of the cationic complex is localized the anion ClO4− to complete the neutrality. Magnetic studies show an antiferromagnetic coupling exchange between metal copper ions which mediated throw neighboring oxygen atom belonging from the pyrophosphate anion. The biological antiproliferative activity of the sample shows a relatively high cytotoxicity IC50 respectively toward MCF-7 breast cancer cell lines.

The Features of Infrared Absorption of Boron‐Doped Silicon

Herein, the influence of heat treatment at 400 °C on the spectrum of boron intracenter transitions in silicon using IR absorption spectroscopy is investigated. In the transition region from the ground 1Γ8+ state associated with the p3/2 valence band of Si to the odd‐parity excited states of boron, a new absorption line with its maximum at 261.3 cm−1 is observed in the thermally treated boron‐doped Cz‐Si. Oxygen is a component of defect that is responsible for the detected absorption line. Perturbation of boron atoms due to the inhomogeneous stress effect from neighboring oxygen atoms results in a frequency shift in the main boron transition. The defect associated with 261.3 cm−1 line is also observed in as‐grown silicon. The defect disappears during annealing at 550 °C. The concentration of defects and binding energy of the 1Γ8+ ground state are estimated assuming that the line observed belongs to the transition of boron 1Γ8+ → 2Γ8−, subjected to the perturbation from a neighboring oxygen atom.

Engineering Manganese Defects in Mn3O4 for Catalytic Oxidation of Carcinogenic Formaldehyde.

Formaldehyde (HCHO) is a priority pollutant in the indoor environment, which is irritative and carcinogenic to humans. The non-noble metal oxides have a wide application prospect in the decomposition of HCHO. Defects in metal oxides have been widely accepted as active sites in heterogeneous catalysis. Compared with the extensive study of oxygen defects, the effect of cation defects has not been clearly addressed. Herein, Mn defect-rich Mn3O4 was synthesized by pyrolysis of Ce-doped MnCO3. It is found for the first time that the content of Mn defects in Mn3O4 can be adjusted by introducing Ce. The introduction of Ce resulted in the higher contents of Mn defects, which significantly enhances the HCHO decomposition. Moreover, Mn defect can effectively narrow the half-metallic gap of Mn3O4, regulate the electronic structure and coordination environment of surrounding oxygen, and further improve the activity and mobility of neighboring oxygen atoms. Importantly, Mn defects are not only beneficial to the generation of neighboring oxygen vacancy but also conducive to enhancing the activation ability of oxygen vacancy for O2. The advantages resulting from Mn defects significantly enhance the HCHO decomposition. This research proposes a strategy to adjust cation defects and deepens the comprehension of the function of cation defects.

Modulating oxygen electronic orbital occupancy of Cr-based MXenes via transition metal adsorbing for optimal HER activity

Modulating the surface electronic properties of the 2D MXenes is of significant importance to boost their hydrogen evolution reaction (HER) activity. Herein, a series of transition metal adatoms are employed to tune the surface electronic properties of Cr-based MXenes with oxygen function group for realizing impressive HER performance. The Results show that the charge of surface oxygen atoms, which is affected by both the host metal atoms and the adsorbed transition metal atoms, play critical role in the adsorption strength of hydrogen. The optimal performance is achieved by depositing Cr atom on the Cr2TiC2O2 MXene, which results in the adsorption free energy of hydrogen very close to zero (0.03 eV). Systematic electronic structure analyses confirm that the charge transfer from the adsorbed transition metals to the neighboring surface oxygen atoms could tune the orbital occupancy of oxygen and their adsorption strength to hydrogen atom and therefore the HER activity. These findings and concepts may be useful for the design of advanced MXene-based HER catalysts.