Adsorption Of O2 Molecules Research Articles

Spontaneous Production of Ultrastable Reactive Oxygen Species on Titanium Oxide Surfaces Modified with Organic Ligands

AbstractThe spontaneous formation and long‐term surface stabilization of superoxide radicals are observed on specific TiO2 hybrid materials in which titanium is coordinated to an organic ligand. Here the rationale for this uncommon phenomenon is investigated by a synergistic theoretical and experimental approach involving density functional theory (DFT) calculations and spectroscopic techniques. Stoichiometric and reduced anatase (101) surfaces modified with acetylacetone, dibenzoylmethane, and catechol are comparatively examined. These results reveal that the interaction between organic ligands and adsorbed O2 molecules improves when O vacancies are present on the external layer of the surface, promoting O2 reduction. The electronic features of the ligand play a pivotal role for both an effective electronic interaction with the surface and the stabilization of the generated reactive oxygen species. These results agree with experimental data showing that sol–gel‐derived Ti‐diketonate hybrid oxides spontaneously produce very persistent superoxide radicals under ambient conditions, thus holding a high intrinsic oxidative activity.

Two-dimensional Nb3Cl8 memristor based on desorption and adsorption of O2 molecules

Two-dimensional Nb3Cl8 memristor based on desorption and adsorption of O2 molecules

Excellent sulfur and water resistance for CO oxidation on Pt single-atom-catalyst supported by defective graphene: The effect of vacancy type

The competitive adsorption of sulfur dioxide and water molecules will degrade the performance for CO oxidation catalyst in some processes such as automobile exhaust cleaning or Claus tail gas treatment. In order to study the effect of carbon vacancy on the sulfur and humidity resistance, the adsorption of CO, O2, SO2 and H2O molecules on Pt single-atom-catalyst supported by graphene with single carbon vacancy (Pt-SG) and double carbon vacancy (Pt-DG) have been comparatively investigated by using density functional theory calculations. It shows that the active site of Pt-SG can be blocked by the SO2 and H2O molecules due to their strong affinity towards Pt-SG. However, the carbon divacancy makes Pt atom less attractive towards SO2 and H2O molecules on Pt-DG compared with that on Pt-SG, where the pre-adsorbed SO2 and H2O molecules will be substituted by the CO molecule with larger adsorption energy on Pt-DG, which finally achieves the sulfur and water resistance for Pt-DG. In addition, an efficient Termolecular Eley-Rideal reaction path with a low energy barrier of 0.49 eV for CO oxidation is found on Pt-DG. The significant downshift of CO-5σ orbital levels plays an important role in the formation of new O-C bonds in OCOOCO intermediate on Pt-DG, where the O2-1π orbital is weakened due to its interaction with CO-5σ and CO-1π orbital, which finally facilitates the break of O-O bond and the production of CO2 molecules along the TER mechanism. Overall, the double carbon vacancy can enhance the selective adsorption for CO molecule other than the SO2 and H2O molecules on Pt atom, making the Pt-DG to be an efficient CO oxidation catalyst even in sulfur and humid environment.

Investigation for oxidation mechanism of CrN: A combination of DFT and ab initio molecular dynamics study

Density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD) are combined to investigate the CrN oxidation mechanism. The surface energy, adsorption configuration and electronic structure of oxygen molecule and atom on the CrN (100) surface are investigated through DFT calculation. AIMD calculation is used to investigate the geometric configuration and electronic structure evolution of O2 molecule adsorption and dissociation process at 1073 K. Results show that the (100) surface has the lowest surface energy. The top site of Cr atom is the most stable adsorption site for oxygen molecules and atoms, and the adsorption energy values are −4.276 eV and −4.975 eV, respectively. Charge density difference results show that both oxygen molecule and atom undergo charge transfer with the Cr atom. The O atom gains electrons while the Cr atom loses electrons. Results of partial density of states show that the CrO bond is formed due to the hybridization between the O-p and Cr-d orbitals. At 1073 K, AIMD results show that the O2 molecule automatically dissociates into O atoms, and the dissociated O atoms form stable covalent bonds with the surface Cr atom. The hybridization between the O-p and Cr-d orbitals gradually increases, thereby forming stable adsorption.

Boron and nitrogen co-doped carbon dots for boosting electrocatalytic oxygen reduction

Carbon dots (CDs) have become an emerging carbon nanomaterial for use in energy-conversion systems because of their large surface area and rapid electron transfer. Carbon dots (BN-CDs) doped with both boron and nitrogen were synthesized by a simple one-step electrochemical etching approach using low-cost petroleum coke as precursor. Compared with CDs doped with only B or N, BN-CDs showed an excellent four-electron oxygen reduction reaction (ORR) activity with a positive onset potential of 0.958 V and a large diffusion-limited current density of −4.32 mA cm−2. Furthermore, the long-term stability and methanol tolerance of BN-CDs were better than those of a commercial Pt/C catalyst. It was found by density functional theory (DFT) calculation that the co-doping of N and B promoted the adsorption of O2 molecules in the ORR process. This work provides new insight into the rational design of carbon nanomaterials and their use in energy conversion.

Uncovering the synergy between Mn substitution and O vacancy in ZnAl-LDH photocatalyst for efficient toluene removal

Metal-substituted layered double hydroxide (LDH) photocatalysts are considered to have potential advantages in air pollution control. However, the current understanding of effect mechanism of metal substitution on microstructure and photocatalytic performance is still poor. Herein, we prepared Mn-substituted ZnAl-LDH and found that Mn substitution can effectively promote the surface O vacancy formation. Combining experiments and theoretical calculations, it was confirmed that the synergy between Mn substitution and O vacancy is the essential reason for the enhanced photocatalytic performance of LDH. The main function of Mn substitution is to regulate the band gap structure and improve the separation efficiency of photogenerated carriers, while the contribution of O vacancy is focused on strengthening the adsorption and activation of O2 molecules, thereby promoting the formation of reactive oxygen species. During the photocatalytic degradation of toluene, the synergistic effect not only promotes the absorption of pollutants, but also intensifies the ring-opening reaction.

Single Co Atoms Implanted into N-Doped Hollow Carbon Nanoshells with Non-Planar Co-N4-1-O2 Sites for Efficient Oxygen Electrochemistry.

Facile synthesis of cost-effective carbon-supported Co single atoms (Co-SAs) exhibits huge potential applications in energy storage and conversion devices. We here report the implantation of Co-SAs into hollow carbon spheres (Co-SAs-HCS) via a facile wet-chemistry strategy followed by controlled pyrolysis. Electron-rich histidine acted as a Lewis base effectively immobilizing Co2+ (Lewis acid) via the electrostatic effect and hydrogen bonds, thus achieving the scalable synthesis of Co-SAs-HCS. We constructed a series of histidine-Co2+ structure models to elucidate the formation of histidine-Co2+ complexes by analyzing their binding energy. X-ray absorption fine-structure results verify that central Co atoms with four N coordination atoms possess a non-planar Co-N4 structure. Electrochemical results indicate that the as-prepared Co-SAs-HCS catalyst shows a low potential difference (0.809 V) between the oxygen evolution reaction potential at 10 mA cm-2 and the oxygen reduction reaction half-wave potential, outperforming the commercial Pt/C catalysts (0.996 V). Moreover, an assembled Zn-air battery based on Co-SAs-HCS exhibits an unexpected long-term durability. We have demonstrated that non-planar Co-N4-1-O2 sites are the source for highly efficient adsorption and dissociation of O2 molecules and then reduction of the free energy of desorption of the intermediates by density functional theory. Our findings provide a new design insight into the exploration of advanced electrocatalysts, which will be applied in the design of green energy devices in the future.

Selective gas sensor based on bilayer armchair graphene nanoribbon

Abstract Detection and sensing of toxic gases are vital in many areas such as in environmental and safety monitoring, industrial applications and etc. Fundamental requirements for modern gas sensors typically are small size, low power consumption, high sensitivity and good selectivity towards various gases. Recently, graphene-based gas sensors have attracted significant attention due to their potential applications. Based on published works, the energy band gap of monolayer graphene nanoribbon (GNR) varies by changing its ribbon width. However, in the case of bilayer GNR, the energy band gap varies via three ways: the ribbon width, the layers separation and the symmetry between the layers. Therefore, it is interesting to investigate the characteristics of bilayer armchair graphene nanoribbon (B-AGNR) as gas nanosensor in presence of CO, O2 and CO2 gas molecules. In this study, we report a theoretical investigation and numerical simulation of the electronic properties of monolayer and bilayer AGNR (with 10 atoms in width) and study their sensitivities in presence of CO, O2 and CO2 gas molecules. Using Quantum espresso-5.3.0 package, the structure optimizations are done based on density functional theory (DFT). Moreover, we have evaluated the current-voltage (I-V) characteristics of the aforementioned structures using the open source package TRAN SIESTA which is based on non-equilibrium Green's function (NEGF) method. The obtained results show that the adsorption of CO, O2 and CO2 gas molecules onto AGNR can be modified significantly in bilayer AGNR with respect to the monolayer. These gas molecules show weak interaction with the AGNR atomic structure due to large interaction distances. Thus, it is deduced that the graphene nanoribbon (AGNR) shows weak gas sensing in presence of CO, O2 and CO2 molecules. Meanwhile, bilayer AGNR shows different electronic properties compared to monolayer AGNR which makes it highly sensitive and selective to the presence of O2 and CO gases.

Atomistic insights into interactions between oxygen and α–Zr (101-1) surface

Abstract The oxidation corrosion is a crucial challenge for zirconium (Zr) alloys as cladding materials in fission power reactors. In the present study, a first-principles approach is employed for understanding behaviors of oxygen adsorbed on the Zr ( 10 1 - 1 ) surface. It is found that the Zr substrate is reactive to O species. Electrons in the 4d band of the metallic substrate tend to migrate to antibonding orbitals of the adsorbed O2 molecule, leading to breaking the O-O bond and releasing energy. Several diffusion paths for an adsorbed O atom migrating to the subsurface interstitial site are proposed. It is found that the lowest diffusion barrier is only 0.08 eV. Therefore, it can be inferred that the Zr ( 10 1 - 1 ) surface suffers fast oxidation kinetics.

Influence of adsorbed oxygen concentration on characteristics of carbon-doped indium oxide thin-film transistors under bias stress

To clarify a factor on the reliability, we investigated the characteristics of carbon-doped indium oxide (InO1.16C0.04) thin-film transistors by varying the O2 concentration from 0.001% to 100% at atmospheric pressure under negative bias stress (NBS) and positive bias stress (PBS). A positive threshold voltage (V th) shift was observed when the bias stress was changed from NBS to PBS. The positive V th shift increased with increasing bias voltage irrespective of the O2 concentration. This behavior was attributed to the reaction between adsorbed O2 molecules on the back side of the InO1.16C0.04 channel and the electrons in the channel being strongly enhanced under PBS. We have found the magnitude and direction of the bias stress play an important role in the positive V th shift under environments included O2 at concentrations as low as 0.001%.

DFT study on the interaction of H2O and O2 with α-Fe2O3 (001) surface

The interactions of H2O and O2 with α-Fe2O3 (001) surface were studied using density functional theory (DFT). The surface structures of α-Fe2O3 changed a lot after H2O and O2 molecules adsorption, and the O–Fe bonds of α-Fe2O3 surface are weakened. The oxygen atom of H2O molecule are bonded to iron atom of α-Fe2O3 surface, and one H–O bond is broken to form hydroxyl group (−OH). Two oxygen atoms of O2 molecule are bonded the same iron atom of α-Fe2O3 surface. The adsorption energy of O2 on the α-Fe2O3 surface is −170 kJ/mol, which is larger than that of H2O on the α-Fe2O3 surface (−130 kJ/mol). The charge transfers occur from H2O molecule to α-Fe2O3 surface during H2O molecule adsorption, while from α-Fe2O3 surface to O2 molecule for O2 molecule adsorption. The value of charge transfer from α-Fe2O3 surface to O2 molecule (−0. 47 e) is larger than that from H2O to α-Fe2O3 surface (+0.06 e). This study provides a microcosmic explanation for the effect of H2O and O2 on α-Fe2O3 surface, and thus on the photocatalytic mechanism, which has important guiding significance for the industrial application of α-Fe2O3 as a photocatalyst.

Piezotronic effect and oxygen vacancies boosted photocatalysis C‒N coupling of benzylamine

Photocatalytic selective oxidation of benzylamine into high-value-added organic intermediates holds great promise. Herein, to achieve the goal of efficient separation of photo-generated electrons/holes and regulation of abundant active sites, we systematically investigated the synergistic impact of piezotronic effect and oxygen vacancies on selectively aerobic oxidation of benzylamine into N-benzylidenebenzylamine with Bi4NbO8Br single-crystalline nanosheets (BNO). We found that piezotronic effect and oxygen vacancies could collaboratively enhance the separation of photogenerated electrons and holes. Furthermore, theoretical calculations and experimental results demonstrated that oxygen vacancies can also optimize the adsorption and activation of O2 and benzylamine molecules to favor the efficient conversion of which. As a result, the conversion rates of benzylamine increased by about 2.1 times owing to the presence of piezotronic effect and oxygen vacancies. The present work opens an avenue for enhancing photocatalytic activity in selective oxidation of organic pollutant into value-added products, and also shed light on an understanding for the design of a highly efficient multi-field catalytic system in the future.

Surface Lattice Oxygen Activation on Sr2Sb2O7 Enhances the Photocatalytic Mineralization of Toluene: from Reactant Activation, Intermediate Conversion to Product Desorption.

Transition-metal oxide photocatalysis has attracted increasing attention in environmental remediation and solar energy conversion. Surface lattice oxygen is the key active site on the metal oxide, but its role and activation mechanism in the photocatalytic VOC mineralization are still unclear. In this work, we have demonstrated that Sr2Sb2O7 exhibits an excellent photocatalytic activity and stability compared to TiO2 (P25) in gaseous toluene mineralization because the lattice oxygen on Sr2Sb2O7 can be activated efficiently. The lattice oxygen of Sr2Sb2O7 promotes the adsorption and activation of O2 and H2O molecules and enhances the production of •O2- and •OH radicals, as confirmed by the electron spin resonance and DFT calculations. The in situ diffuse reflectance infrared Fourier transform spectroscopy spectra are applied to dynamically monitor the intermediate activation and selective conversion. Combined with DFT calculation, the role and the mechanism of lattice oxygen in photocatalysis have been revealed. Owing to the promoted surface lattice oxygen, the selectivity for benzoic acid formation is enhanced and final product desorption is promoted, which could largely advance the ring opening and mineralization of toluene. This work reveals the origin of lattice oxygen activation and the role for efficient VOC degradation at the atomic scale.

Catalytic activity of PtCu intermetallic compound for CO oxidation: A theoretical insight

To understand the microscopic mechanism of the CO oxidation reaction at PtCu nanoparticles, which have unique geometric and electronic structures compared to their component metals, we present here a theoretical study, based on density functional theory calculations, of the main reaction steps of this reaction. We examine the O2 dissociation, the CO adsorption and the CO + O2 reaction at an atomic level and use the computed geometries, Bader charges, and vibrational frequencies to rationalize the role of the intermetallic nanoparticles surface structure on the experimentally observed much higher activity of these nanoparticles as catalysts of the preferential oxidation of CO. By comparing with clean Pt (111) surface and with different Cu-doped models of this same surface, our results show that, at the surface, the presence of Cu induces the segregation of CO molecules at Pt sites and of O2 molecules at Cu sites. Contrarily to Pt surfaces, the unassisted O2 dissociation has a high barrier at the intermetallic nanoparticle surface and proceeds through a CO-assisted mechanism in which the new CO bond is formed while the OO bond is broken with a kinetic barrier much lower than on either Pt (111) or in Pt-doped surfaces. The particular structure of the intermetallic surface is shown to have a significant role in the low kinetic barrier for the reaction, allowing for an easy approach of the CO to the adsorbed O2 molecule that permits an early transition state with a low energetic barrier.

A DFT-D study on the reaction mechanism of selective catalytic reduction of NO by NH3 over the Fe2O3/Ni(111) surface

The adsorption and SCR reaction mechanism of NH3, NO, and O2 molecules on the Fe2O3/Ni(111) catalyst surface was revealed.

Переход металл-полупроводник в нанопленках иттербия, индуцированный адсорбированными молекулами кислорода

The influence of nondissociative adsorption of oxygen molecules on the electronic structure of ytterbium films with the thickness of 16 monolayers (6.08 nm) has been studied for the first time by using scanning tunneling spectroscopy. It is established that the adsorption of O2 molecules induces the metal-semiconductor transition in ytterbium. As a result of this transition, the quantum states have disappeared in the films, which evidences for a change of bonding type in the ytterbium crystal lattice, as well as the band gap of ~0.72 eV has opened.

Plasmon induced dual excited synergistic effect in Au/metal-organic frameworks composite for enhanced antibacterial therapy.

Efficient antibacterial therapy holds great promise for human health. However, it is often limited by the insufficient activity of antibacterial agents. Herein, we demonstrate that the localized surface plasmon resonance (LSPR) excitation of gold nanostars (AuNSs) can dramatically improve the antibacterial activity of a Zn-metal-organic frameworks (Zn-MOFs) nanosheet, which exhibits higher ability to generate reactive oxygen species (ROS) (∼2.5-fold) for bacterial inactivation under light irradiation. Mechanistic investigations demonstrate that the enhancement is closely related to a plasmon-induced "dual excited synergistic effect". On the one hand, the Zn-MOFs nanosheets as photosensitive agents can be excited to generate ROS with bacterial toxicity. More importantly, abundant plasmonic hot electrons are generated on the surface of AuNSs upon LSPR excitation, which are then transferred from AuNSs into the Zn-MOFs due to the energy matching. As a result, the Zn-MOFs nanosheet presents an electron-rich condition, which activates the adsorbed O2 molecule into a transition state followed by its decomposition into ROS for bacterial inactivation. This study highlights the superiority of LSPR excitation on improving the antibacterial activity of MOFs and provides a novel strategy for effective antibacterial therapy.

Synergistic degradation mechanism of chlorobenzene and NOx over the multi-active center catalyst: The role of NO2, Brønsted acidic site, oxygen vacancy

Development of an efficient synergistic degradation technology to prevent the emission of chlorinated organics and NOx from industrial sources without forming harmful by–products, is a major challenge in environmental chemistry. The designed multi–active center catalyst (PdV/TiO2) showed excellent CB/NO synergistic removal conversion efficiency and target product selectivity. Experimental and DFT calculation results indicated that Pd was the common center for adsorption of CB, O2, NH3 and NOx molecules. The O vacancies (VOx–1 and TiOx–1) generated during the CB ring opening process was conducive to adsorption of reaction gas molecules, accelerating CBCO and NH3–SCR reaction. The adsorbed NH3 species would dissociate H protons to provide Brønsted acidic sites necessary for Cl conversion. O vacancies structure was easier to be restored by reoxidation with the participation of NO2. Certain synergistic effect in the removal of CB and NO on the multi–active center catalyst surface was found.

Novel green synthesis of S-doped TiO2 nanoparticles using Malva parviflora plant extract and their photocatalytic, antimicrobial and antioxidant activities under sunlight illumination

Visible-light-responsible S-doped TiO2(GST) nanoparticles (NPs) are synthesized via sol-gel process, and an aqueous extract of Malva parviflora (MP) plant is used as the green and versatile medium with excellent reducing and capping properties to facilitate the S-doping and crystal growth of anatase. Compared with the counterpart (CST) derived from the conventional organic solvent. GST show a smaller average particle size (20.3 vs. 29.5 nm) with a larger surface area (135 vs 95 m2/g), together with the more significant red shift to longer wavelength in the visible light region. XPS analysis shows Ti4+ cations are substituted by S6+ ions into the lattice structure of TiO2 for both samples. The photodynamics of CST and GST catalysts are examined by electron paramagnetic resonance (EPR) spectroscopy, which shows the surface Ti3+ sites can be oxidized easily by the surface adsorbed O2 molecules, forming O2− radicals. Their photocatalytic activities (PCA) are evaluated by degrading methyl orange (MO) dye under the visible light irradiation. GST exhibit higher PCA in MO bleaching and chemical oxygen demand (COD) reduction. In addition, antimicrobial and antioxidant assays of CST and GST NPs also show that the irradiated NPs samples show higher antibacterial activities. GST NPs have a higher antibacterial activity than CST NPs against all tested bacteria and the minimum inhibitory concentration (MIC) is optimized to 25 μg/mL. The in-vitro antioxidant activity evaluated by the radical cation de-colorization test using 1,1-diphenyl-2-picrylhydrazyl (DPPH) further demonstrates that GST NPs give a better antioxidant activity.

Photoinduced Adsorption and Oxidation of SO2 on Anatase TiO2(101).

Adsorption of molecules is a fundamental step in all heterogeneous catalytic reactions. Nevertheless, the basic mechanism by which photon-mediated adsorption processes occur on solid surfaces is poorly understood, mainly because they involve excited catalyst states that complicate the analysis. Here we demonstrate a method by which density functional theory (DFT) can be used to quantify photoinduced adsorption processes on transition metal oxides and reveal the fundamental nature of these reactions. Specifically, the photoadsorption of SO2 on TiO2(101) has been investigated by using a combination of DFT and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The combined experimental and theoretical approach gives a detailed description of the photocatalytic desulfurization process on TiO2, in which sulfate forms as a stable surface product that is known to poison the catalytic surface. This work identifies surface-SO42– as the sulfate species responsible for the surface poisoning and shows how this product can be obtained from a stepwise oxidation of SO2 on TiO2(101). Initially, the molecule binds to a lattice O2– ion through a photomediated adsorption process and forms surface sulfite, which is subsequently oxidized into surface-SO42– by transfer of a neutral oxygen from an adsorbed O2 molecule. The work further explains how the infrared spectra associated with this oxidation product change during interactions with water and surface hydroxyl groups, which can be used as fingerprints for the surface reactions. The approach outlined here can be generalized to other photo- and electrocatalytic transition metal oxide systems.