Adsorption Of Oxygen Molecules Research Articles

Engineering oxygen vacancy of MoOx nanoenzyme by Mn doping for dual-route cascaded catalysis mediated high tumor eradication

There is an urgent need to develop photosensitive nanoenzymes with better phototherapeutic efficiency through simple processes. By exploiting semiconductor catalysis and defect chemistry principles, herein, a MnMoOx composite semiconductor nanoenzyme was developed to achieve a fully integrated theranostic nanoenzyme for highly efficient photo/chemo-enzyme-dynamic eradication of deep tumors. Relative to iron oxides, manganese oxides offer ideal catalytic performance under near-neutral conditions, which helps to broaden the suitable pH range of the MnMoOx nanoenzyme for antitumor therapy. Furthermore, with the assistance of glutathione depletion, Mn4+/Mo6+ was successfully converted to Mn2+/Mo5+, inhibiting the scavenging of reactive oxygen species (ROS) and promoting cycling. Therefore, MnMoOx has favorable catalase (CAT)-like activity and oxidase (OXD)-like activity in the tumor microenvironment (TME) for promoting the “H2O2O2O2−” and “H2O2OH” cascade reactions. The abundant oxygen vacancy defects also promote the surface plasmon resonance (SPR) effect in the second near-infrared (NIR-II) window of MnMoOx, which significantly enhanced its photothermal therapy (PTT) effect and catalytic activity. In detail, ROS production was significantly enhanced due to the adsorption of water and oxygen molecules by the rich oxygen vacancies of MnMoOx. MnMoOx also exhibited excellent multi-modal imaging activity (including computed tomography (CT), magnetic resonance imaging (MRI), and photoacoustic (PA)), which can be exploited to better guide the administration of medication.

Tribocatalysis of homogeneous material with multi-size granular distribution for degradation of organic pollutants

Recently, tribocatalysis driven by mechanical energy has been developed by rubbing two kinds of different materials. In this work, we firstly demonstrated that the friction of the single material also could initiate the tribocatalysis for degrading organic dyes. Under magnetic stirring, the multi-size granular polytetrafluoroethylene (PTFE) particles were triboelectrically charged, among which the collision between large and small particles would cause high energy electrons on large particles to transfer to small ones. These triboelectric charges on PTFE particles could react with adsorbed oxygen molecules or water to generate reactive oxygen species, and then promoted the degradation process of organic dyes together with oxidant holes. We further investigated the experimental parameters, such as stirring speed, size and quantity of stirring bar, to optimize the tribocatalytic performance. What’s more, the PTFE tribocatalysis possessed high durability for multiple recycling runs with > 90% degradation efficiency of Rhodamine B, as well as well universality for eliminating other pollutants. Finally, we proposed a plausible tribocatalytic mechanism of multi-size granular PTFE according to the detected reactive oxygen species and the determined intermediates. This study provides new insights into tribocatalysis, and demonstrates that the single material with different particle sizes can also be used as catalyst to drive tribocatalytic process.

Density Functional Investigation on α-MoO3 (100): Amines Adsorption and Surface Chemistry.

The (100) surface of α-MoO3 should possess overwhelmingly more exposed Mo atoms than the (010), and the exposed Mo has been extensively considered as an active site for amine adsorption. However, α-MoO3 (100) has drawn little attention concerning the amine sensing mechanism. In this research, adsorption of ammonia (NH3), monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) is systematically investigated by density functional theory (DFT). All four of these molecules have high affinity to α-MoO3 (100) through interaction between the N and the exposed Mo, and the affinity is mainly influenced by both the characteristics of the molecules and the geometric environment of the surface active site. Adsorption and dissociation of water and oxygen molecule on stoichiometric and defective α-MoO3 (100) surfaces are then simulated to fully understand the surface chemistry of α-MoO3 (100) in practical conditions. At low temperature, α-MoO3 (100) must be covered with a large number of water molecules; the water can desorb or dissociate into hydroxyl groups at high temperature. Oxygen vacancy (VO) can be generated through the annealing process during sensor device fabrication; VO must be filled with an O2 molecule, which can further interact with adsorbed water nearby to form hydroxyl groups. According to this research, α-MoO3 (100) must be the active surface for amine sensing and its surface chemistry is well understood. In the near future, further reaction and interaction will be simulated at α-MoO3 (100), and much more attention should be paid to α-MoO3 (100) not only theoretically but also experimentally.

Zn2SnO4 Thin Film Based Nonvolatile Positive Optoelectronic Memory for Neuromorphic Computing

An optoelectronic synaptic device based on the ITO/Zn2SnO4(ZTO)/ITO structure is fabricated which integrates the electronic memory and optical sensing properties along with synaptic functions. The fabricated device shows over 80% optical transparency for the entire visible region (400–800 nm). Post-oxide annealing treatment is performed in a nitrogen environment at 200 °C. Significant improvements in bipolar resistive switching properties of the device with low SET voltage (+0.93 V) and long DC endurance cycles (∼12000) are observed in the annealed device. The linearity of such memristive synapse is improved for 350 training epochs with a total number of 175000 pulses. The spike time dependent plasticity learning rule for the annealed device is demonstrated through the electric field. The optical sensing capabilities of this device including photonic potentiation (responsivity: 0.52 μA/W), photonic paired pulse facilitation by adjusting time interval between two identical light pulses, learning experience behavior, and multilevel memory feature by the repetition of optical pulse for ∼103 s are demonstrated under the blue light (wavelength “λ” = 405 nm) illumination at 50 mW/cm2. Photonic potentiation and electric depression behavior of the device mimic its nonvolatile synaptic plasticity. The linear fitting of I–V curve illustrates the dominance of Schottky emission and Poole–Frenkel conduction mechanisms at high and low resistance states, respectively. The electric response of the device is explained by the oxygen vacancy based filamentary model. The trapping and detrapping of electrons during the adsorption and desorption processes of atmospheric oxygen molecules on the ITO surface are responsible for the photoconduction phenomenon. To train the Hopfield neural network (HNN) model for image processing of 28 × 28 pixels, the normalized experimental data of long-term potentiation/depression are employed to mimic the learning behavior of the human brain. The convergence of electronic data storage and optical sensor has high potential which provides a path toward the future smart invisible optoelectronics for artificial intelligence.

Incorporating Boron into Niobic Acid Nanosheets Enables Generation of Multiple Reactive Oxygen Species for Superior Antibacterial Action.

Photocatalytic therapy is an alternative antibacterial pathway but most photocatalysts are limited by light absorption, charge transfer and insufficient production of reactive oxygen species (ROS). Herein, the authors utilize boron doped niobic acid nanosheets (B-HNbO3 NSs) as a superior photocatalytic antibacterial platform. The experimental results and density functional theory (DFT) confirm that superior photocatalytic therapy activity is mainly due to boron doping, which not only promotes the generation and separation of electrons and holes, but also enhances the adsorption of water and oxygen molecules on B-HNbO3 NSs. Consequently, multiple ROS including hydroxyl radicals (•OH), superoxide radicals (•O2- ), and singlet oxygen (1 O2 ) are generated under light irradiation, resulting in outstanding bacterial killing ability of B-HNbO3 NSs. Besides, oxygen is produced during the therapy process, thus alleviating the inflammatory response caused by hypoxia. Furthermore, molecular dynamics (MD) simulations verify that the nanosheet structure makes it possess strong electrostatic attraction for bacterial cell membranes, leading to physical insertion and damage to bacterial cells. Therefore, bactericidal rates for four types of bacteria are all more than 99%, proving its excellent and broad-spectrum antibacterial capacity. Moreover, B-HNbO3 NSs could be applied to treat biofilm-coated medical devices in vivo, suggesting its possibility in practical application.

Elucidating the Ambient Stability and Gas Sensing Mechanism of Nickel-Decorated Phosphorene for NO2 Detection: A First-Principles Study.

In the field of layered two-dimensional functional materials, black phosphorus has attracted considerable attention in many applications due to its outstanding electrical properties. It has experimentally shown superior chemical sensing performance for the room temperature detection of NO2, highlighting high sensitivity at a ppb level. Unfortunately, pristine black phosphorus demonstrated an unstable functionality due to the fast degradation of the material when exposed to the ambient atmosphere. In the present work, a deepened investigation by density functional theory was carried out to study how nickel decoration of phosphorene can improve the stability of the material. Further, an insight into the sensing mechanism of nickel-loaded phosphorene toward NO2 was given and compared to pristine phosphorene. This first-principles study proved that, by introducing nickel adatoms, the band gap of the material decreases and the positions of the conduction band minimum and the valence band maximum move toward each other, resulting in a drop in the conduction band minimum under the redox potential of O2/O2–, which may result in a more stable material. Studying the adsorption of O2 molecules on pristine phosphorene, we also proved that all oxygen molecules coming from the surrounding atmosphere react with phosphorus atoms in the layer, resulting in the oxidation of the material forming oxidized phosphorus species (POx). Instead, by introducing nickel adatoms, part of the oxygen from the surrounding atmosphere reacts with nickel atoms, resulting in a decrease of the oxidation rate of the material and in subsequent long-term stability of the device. Finally, possible reaction paths for the detection of NO2 are given by charge transfer analyses, occurring at the surface during the adsorption of oxygen molecules and the interaction with the target gas.

Interface engineering of iron sulfide/tungsten nitride heterostructure catalyst for boosting oxygen reduction activity

• An ion migration approach is reported for preparing the Fe 1-x S/WN heterostructure. • The electron depletion of iron centers caused by WN promotes the O 2 protonation. • WN component promotes the reversible Fe 2+/3+ redox couple during catalysis. • An exceptional durability is demonstrated in the setups of RDE and half-cell GDL. • Zn-air battery driven by Fe 1-x S/WN delivers a stable and outstanding performance. Herein, we demonstrate an ion migration approach for constructing iron sulfide/tungsten nitride heterostructure supported over carbon nanoboxes as an efficient and robust electrocatalyst toward the oxygen reduction reaction. Tungsten nitride decorated at iron sulfide induces the electron delocalization of iron sites for facilitating the electron/proton transfer into adsorbed oxygen molecules that is generally proposed as the rate-determining step over the sulfides. It also greatly promote the reversible Fe 2+/3+ redox transition during catalysis that determines the durability performance. Therefore, the iron sulfide/tungsten nitride heterostructure catalyst shows much superior activity and long-term stability to pristine iron sulfide, as evidenced in the setups of rotating disk electrode and half-cell gas diffusion electrode. It is explored as an exceptional air cathode of rechargeable zinc-air battery that stably operates for over 140 h without the performance loss. This work offers a novel synthetic strategy for designing transition–metal nitride/sulfide heterostructure and provides an insight into optimized electron configuration via interface engineering.

A Facile Synthesis of Noble-Metal-Free Catalyst Based on Nitrogen Doped Graphene Oxide for Oxygen Reduction Reaction.

A simple method for the mechanochemical synthesis of an effective metal-free electrocatalyst for the oxygen reduction reaction was demonstrated. A nitrogen-doped carbon material was obtained by grinding a mixture of graphene oxide and melamine in a planetary ball mill. The resulting material was characterized by XPS, EPR, and Raman and IR spectroscopy. The nitrogen concentration on the N-bmGO surface was 5.5 at.%. The nitrogen-enriched graphene material (NbmGO has half-wave potential of −0.175/−0.09 V and was shown to possess high activity as an electrocatalyst for oxygen reduction reaction. The electrocatalytic activity of NbmGO can be associated with a high concentration of active sites for the adsorption of oxygen molecules on its surface. The high current retention (93% for 12 h) after continuous polarization demonstrates the excellent long-term stability of NbmGO.

Рентгеновские фотоэлектронные спектры молекул кислорода, адсорбированных на нанопленках иттербия

The adsorption of oxygen molecules on ytterbium nanofilms of various thicknesses has been studied by X-ray photoelectron spectroscopy and contact potential difference measurements. It has been established that the maximum number of O2 molecules that can be adsorbed on the films increases with the film thickness. Such behavior is observed at thicknesses less than 10 monolayers. This size effect is ultimately due to the fact that an indispensable condition for the adsorption process at high doses of oxygen is the electron transfer from the film to molecules, and that the maximum number of electrons that can participate in this process depends on the nanolayer thickness. Localization of a negative charge on O2 molecules occurring in at high doses of adsorbate, causes a weakening of the bonding of 1s electrons in these molecules. In addition, it should lead to a weakening of the bond between oxygen atoms in O2 molecules.

X-ray photoelectron spectra of oxygen molecules adsorbed on ytterbium nanofilms

The adsorption of oxygen molecules on ytterbium nanofilms of various thicknesses has been studied by X-ray photoelectron spectroscopy and contact potential difference measurements. It has been established that the maximum number of O2 molecules that can be adsorbed on the films increases with the film thickness. Such behavior is observed at thicknesses less than 10 monolayers. This size effect is ultimately due to the fact that an indispensable condition for the adsorption process at high doses of oxygen is the electron transfer from the film to molecules, and that the maximum number of electrons that can participate in this process depends on the nanolayer thickness. Localization of a negative charge on O2 molecules occurring in at high doses of adsorbate, causes a weakening of the bonding of 1s-electrons in these molecules. In addition, it should lead to a weakening of the bond between oxygen atoms in O2 molecules. Keywords: oxygen, ytterbium, adsorbed molecules, nanofilms, X-ray photoelectron spectroscopy, work function.

Engineering of Single Atomic Cu-N3 Active Sites for Efficient Singlet Oxygen Production in Photocatalysis.

Photocatalytic generation of singlet oxygen (1O2) is an attractive strategy to convert organic chemicals to high value-added products. However, the scarcity of suitable active sites in photocatalysts commonly leads to the poor adsorption and activation of oxygen molecules from a triplet state to a singlet state. Here, we report single atomic Cu-N3 sites on tubular g-C3N4 for the production of singlet oxygen. X-ray absorption fine spectroscopy, in combination with high-resolution electron microscopy techniques, determines the existence of atomically dispersed Cu sites with Cu-N3 coordination mode. The combined analysis of electron spin resonance and time-resolved optical spectra confirmed that a single atomic Cu-N3 structure facilitates a high concentration of 1O2 generation due to charge transport, electron-hole interaction, and exciton effect. Benefiting from the merits, a single atomic photocatalyst yields nearly 100% conversion and selectivity from thioanisole to sulfoxide within 2.5 h under visible light irradiation. This work deeply reveals the design and construction of catalysts with specific active sites, which are helpful to improve the activation efficiency of oxygen.

Influence of sulfur vacancy on pyrite oxidization by water and oxygen molecules

Pyrite (FeS2) is one of the widely existed sulfide minerals, which plays a very significant role in acid mine drainage (AMD) and other aspects. Natural and synthetic pyrite has often been found to contain vacancy and impurity defects. Nevertheless, the effect of S-vacancy on pyrite oxidization by water and oxygen molecules has not been researched in detail. In this work, the adsorption of water and oxygen molecules is simulated based on density functional theory (DFT). It is found that the adsorption energy of water molecules on S-vacancy surface is relatively low and the dissociative adsorption of water molecules does not occur readily. When oxygen molecules are adsorbed, it is shown that the adsorption is stronger than that of water molecules and a SO specie is formed. And through the change of density of states (DOS), charges and magnetic moments of Fe1 and Fe2 on the S-vacancy surface before and after oxygen molecule adsorption, this indicated that due to the adsorption of oxygen molecule, the property of the S-vacancy surface is changed. Furthermore, the co-adsorption of water and oxygen molecules on S-vacancy surface is calculated. It is manifested that the Fe-OH and S-O species are formed. When the filling of O atom (captured from water molecules) at S-vacancy site restores the surface and the O atom bonds to the surrounding two Fe atoms and one S atom, the adsorption configuration is the most stable.

Enhanced gas sensing performance of Bi2MoO6 with introduction of oxygen vacancy: Coupling of experiments and first-principles calculations

Bismuth molybdate (Bi2MoO6) is a multi-elemental metal oxide of the molybdate series, which could show great potentials for the application of gas sensors with outstanding sensitivity. Oxygen vacancy is a ubiquitous defect in this class of materials, and their introduction may be an effective strategy to regulate gas sensing performance. In this work, coupling investigations of experiment and first-principles calculations were performed to gain insight into the effect of oxygen deficiency on the gas-sensitive properties of Bi2MoO6. The oxygen vacancies existed in surface lattice changes the adsorption reaction pathway of the gas by modifying the coordination state and geometry of lattice oxygens, which is more favorable for the adsorption or dissociation of target gas and oxygen molecule. Further, the oxygen-deficient Bi2MoO6 was synthesized experimentally by a one-step solvothermal method. The gas sensor based on the oxygen-deficient Bi2MoO6 could respond to NH3 gas sensitively and selectively, with a high response value of 53.97 (5 ppm) at the optimal temperature of 75 °C. Combining the clarifications by first-principles calculations, the satisfactory sensing performance exhibited experimentally could be understood based on the promotion of adsorption activity and adsorption capability.

Ga-doped Pd/CeO[formula omitted] model catalysts for CO oxidation reactivity: A density functional theory study

Ceria-supported Pd single-atom catalysts (SACs) are important catalysts to catalyze the CO oxidation, often used in three-way catalysts to treat automobile exhaust gases. This paper uses density functional theory (DFT) calculations and transition state theory to systematically study the effect of Ga atom doping on the performance of the Pd/CeO2 SACs system. Noticeably, the results of DFT calculations reveal that the stability of Pd single atoms supported on the surface of CeO2(111) was significantly augmented by doping Ga. An oxygen vacancy generated easily near the Ga and Pd site will act as a crucial role for activating the adsorbed oxygen molecule. Most importantly, the climbing image nudged elastic band (CINEB) calculations show that the doping of Ga remarkably reduces the highest energy barrier during the CO oxidation reaction, meaning that the catalytic performance of the CO oxidation reaction is promoted effectively. This work provides a new perspective for SACs modification.

Influence of galvanic interaction between chalcopyrite and galena on electrochemical and flotation behaviour of chalcopyrite

Chalcopyrite is often associated with galena in nature, which brings great difficulties to the flotation recovery of chalcopyrite. One of the main reasons for these difficulties is that galvanic interaction between chalcopyrite and galena has a significant effect on the oxidation and flotation behavior of chalcopyrite. In this paper, density functional theory and cyclic voltammetry measurement were used to study galvanic interaction between chalcopyrite and galena and its effect on the adsorption of oxygen and xanthate molecules on chalcopyrite (001) surface. The results show that the galvanic interaction inhibits the dissociation of oxygen molecules on the surface of chalcopyrite (001), and it also weakens the bonding DOS of O-Fe bonds, S-Cu bonds and S-Fe bonds, which may be detrimental to the adsorption of xanthate and oxygen molecules on the surface of chalcopyrite (001). The cyclic voltammetry measurements results show that compared with pure chalcopyrite and pure galena electrode, the oxidation peak intensity of the electrode with a mass ratio of chalcopyrite and galena of 1:1 near 0.4 V is weaker at pH 9.18 and a butyl xanthate concentration of 0.001 mol/L, which is consistent with the results of DFT studies.

Galvanic interaction between different grinding media and galena (1 0 0) surface and its influence on galena flotation behavior: A DFT study

Galena has different electrostatic potentials from grinding medium. Collision and friction occur between them in the grinding process, which lead to electron transfer and charge redistribution on galena surface, affecting surface oxidation and galena recovery. In this paper, the galvanic interaction between galena and eight different grinding media including low carbon steel (carbon content 0.1 wt%), medium carbon steel (carbon content 0.3 wt%), high carbon steel (carbon content 0.9 wt%), and grinding medium containing 0.1 wt% Ce, 0.1 wt% La, 0.1 wt% Y, 4.6 wt% Cr, or 1.5 wt% Mn has been studied using DFT method. The effects of those galvanic interactions on the surface structure, surface activity and adsorption of oxygen and xanthate molecules on galena surface have been investigated. The results show that the adsorption of oxygen and xanthate molecules on the surface of galena is the strongest with medium carbon steel (carbon content is 0.3 wt%), followed by low carbon steel and high carbon steel. In addition, compared with the grinding media containing chromium, cerium, yttrium and manganese, the grinding medium containing lanthanum (lanthanum content is 0.1 wt%) is more conducive to the adsorption of oxygen and xanthate molecules on the surface of galena.

Mechanism of methanol decomposition on the Cu-Embedded graphene: A DFT study

The methanol decomposition reaction has gained substantial attention due to the wide range of applications that its intermediates offer. In this work, methanol (CH3OH) decomposition on Copper-embedded graphene (CuG) surface has been investigated via density functional theory with Grimme-D2 dispersion correction. The charge density of the CuG surface has been analyzed and the redistribution of the electron density of the surface has been represented via the electron density difference (EDD) map. Moreover, the decomposition reaction mechanism of CH3OH on the CuG surface through the cleavage of C–H, O–H and C–O bonds has been investigated in detail. In the initial state, the C–O and O–H bonds of CH3OH have similar activation barriers, thereby the adsorption and degradation mechanism of the intermediate states arising through O–H bond cleavage on the CuG surface has been investigated. In addition, the charge density calculations of the transition state geometries have been conducted and examined with EDD maps. The results have revealed that the previously adsorbed oxygen molecule exhibited high catalytic activity towards O–H decomposition compared to the bare surface. The CuG surface has offered higher activity on the C–H bonds compared to the C–O bonds of the intermediate states generated by CH3OH decomposition. The results revealed that the proposed CuG structure can be utilized as an alternative electrode catalyst that can prevent the CO poisoning issue in direct methanol fuel cells.

Metal–Semiconductor Transition Induced by Adsorbed Oxygen Molecules in Ytterbium Nanofilms

Metal–Semiconductor Transition Induced by Adsorbed Oxygen Molecules in Ytterbium Nanofilms

Heat-Treated Electrolytic Manganese Dioxide as an Efficient Catalyst for Oxygen Reduction Reaction in Alkaline Electrolyte

We developed an oxygen depolarized cathode (ODC) catalyst that can be employed for industrial chlor-alkali electrolysis by improving the oxygen reduction reaction (ORR) activity of commercially available electrolytic manganese dioxide (EMD). The ORR activity of EMD was systematically investigated by rotating disc electrode (RDE) measurements for EMD samples having different particle sizes and heat-treated at different temperatures. We found that the ORR activity of EMD became comparable to commercially available platinized carbon (Pt/C) when EMD with a median diameter of 0.5 μm was heat-treated at 500 °C. From XPS analysis, the EMD heat-treated at 500 °C contains many surface oxygen vacancies that were advantageous for adsorption of oxygen molecules. The obtained EMD sample was assembled into an ODC electrode and its ORR performance was evaluated under chlor-alkali electrolysis conditions (32.5 wt% NaOH, 88 °C). The heat-treated EMD showed an overpotential of ∼0.1 V smaller (at a current density of −1.0 A cm−2) than the benchmark catalyst, i.e., Ag particles. The catalyst we developed is therefore a most promising candidates to replace precious metal catalysts, owing to industrially valuable features such as low cost, simple synthesis method, and high ORR activity.

Revisiting the Role of the Triple‐Phase Boundary in Promoting the Oxygen Reduction Reaction in Aluminum–Air Batteries

AbstractThe decomposition, electron transfer, and protonation of oxygen molecules are typically assumed to be the rate‐limiting steps of the oxygen reduction reactions (ORR), and the activation energy barriers of these reactions can be surmounted using catalysts. In this study, the physical rate‐limiting step of the ORR consists of the adsorption of gaseous oxygen molecules at the liquid–solid phase boundary, indicating that the formation of a gas–liquid–solid triple‐phase boundary (TPB) is important for accelerating the ORR kinetics. This is experimentally confirmed by analyzing the ORR in aluminum–air batteries. Moreover, the formation of a TPB using the hierarchical pores of sparked reduced graphene oxide is demonstrated, which serve as the cathode, and the remarkable electrochemical performance of the fabricated battery is presented. These findings can be used to accelerate the ORR kinetics by maximizing the TPB, particularly in aluminum–air batteries.