Adsorption Of Molecular Oxygen Research Articles

From waste to treasure: Synthesis of Ag3PO4/TiO2/r-SiC composite photocatalysts with efficient photocatalytic performance using waste photovoltaic silicon wafers

The conversion of low-value waste into high-value-added photocatalysts for pollution removal is considered a promising approach for waste utilization. In this work, regenerated SiC (r-SiC) nanowires were synthesized using waste photovoltaic silicon wafers through a mechanochemical-carbothermal reduction method. The prepared filamentary structure of r-SiC nanowires as a substrate for an Ag3PO4/TiO2/r-SiC (APO/TIO/r-SiC) ternary photocatalyst was prepared by immobilizing TiO2 and Ag3PO4 on r-SiC nanowires. The 30%APO/TIO/r-SiC (loaded with 30 wt%Ag3PO4) achieved more than 90% degradation rate for six organic dyes, and 80% for tetracycline (TC) within 15 min, respectively. The loading of TiO2 and Ag3PO4 improved the adsorption of molecular oxygen in the aqueous environment, which facilitated the generation of reactive oxygen species and enhanced the photocatalytic performance of 30%APO/TIO/r-SiC. The Z and II dual-scheme electron transfer mechanism for 30%APO/TIO/r-SiC was demonstrated to promote effectively carrier separation. Three potential pathways of RhB degradation were proposed, and the disruption of the conjugated structure (chromophore) was the main cause of RhB degradation. The radical quenching experiments revealed that the degradation process was more significantly influenced by •O2- and •OH than h+. The research proposed a promising 'win-win' treatment approach for waste photovoltaic wafers and delved into the photocatalytic performance and enhancement mechanism of SiC-based composite catalysts.

Electron Structure Tuned Oxygen Vacancy-Rich AuPd/CeO2 for Enhancing 5-Hydroxymethylfurfural Oxidation.

The design of high activity catalyst for the efficiently conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) gains great interest. The rationally tailoring of electronic structure directly affects the interaction between catalysts and organic substrates, especially molecular oxygen as the oxidant. This work, the bimetallic catalysts AuPd/CeO2 were prepared by the combining method of chemical reduction and photo-deposition, effectively concerting charge between Au and Pd and forming the electron-rich state of Au. The increasing of oxygen vacancy concentration of CeO2 by acidic treatment can facilitate the adsorption of HMF for catalysts and enhance the yield of FDCA (99.0 %). Moreover, a series of experiment results combining with density functional theory calculation illustrated that the oxidation performance of catalyst in HMF conversion was strongly related to the electronic state of interfacial Au-Pd-CeO2. Furthermore, the electron-rich state sites strengthen the adsorption and activation of molecular oxygen, greatly promoting the elimination of β-hydride for the selective oxidation of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) to FDCA, accompanied with an outgoing FDCA formation rate of 13.21 mmol ⋅ g-1 ⋅ min-1 at 80 °C. The perception exhibited in this research could be benefit to understanding the effects of electronic state for interfacial sites and designing excellent catalysts for the oxidation of HMF.

Nitrogen-doped carbon-coated Cu0 activates molecular oxygen for norfloxacin degradation over a wide pH range

The Fenton-like activated molecular oxygen technology demonstrates significant potential in the treatment of refractory organic pollutants in wastewater, offering promising development prospects. We prepared a N-doped C-coated copper-based catalyst Cu0/NC3-600 through the pyrolysis of Mel-modified Cu-based metal–organic framework (MOF). The results indicate that the degradation of 20 mg/L norfloxacin (NOR) was achieved using 1.0 g/L Cu0/NC3-600 across a wide pH range, with a removal rate exceeding 95 % and total organic carbon (TOC) removals approaching 70 % after 60 min at pH 5–11. The nitrogen doping enhances the electronic structure of the carbon material, facilitating the adsorption of molecular oxygen. Additionally, the formed carbon layer effectively prevent copper leaching,contributing to increased stability to a certain extent. Subsequently, we propose the catalytic reaction mechanism for the Cu0/NC/air system. Under acidic conditions, Cu0/NC3-600 activates molecular oxygen to produce the •O2–, which serves as the primary active species for NOR degradation. While in alkaline conditions, the high-valent copper species Cu3+ is generated in conjunction with •O2–, both working simultaneously for NOR degradation. Furthermore, based on the LC-MS results, we deduced four possible degradation pathways. This work offers a novel perspective on expanding the pH range of copper-based catalysts with excellent ability to activate molecular oxygen for environmental water treatment.

Molybdenum carbide nanoclusters with ultrafast electron transfer ability promotes molecular oxygen selective electrocatalytic reduction to hydroxyl radicals for pollutant control

A treatment strategy of in situ generation and activation of hydrogen peroxide to degrade pollutants by the heterogeneous Fenton-like technology is promising for water pollution. However, the selective activation of oxygen to hydroxyl radicals (OH) by cathode materials is still challenging. Here, molybdenum carbide (MoC) supported on a heteroatoms-doped (N, P, S) carbon carrier catalyst was successfully prepared, which rapidly produced OH and degraded paracetamol (APAP) pollutants. A high APAP degradation efficiency with a specific energy consumption of 0.24 kWh g−1 TOC was achieved. After 10 sets of continuous operations, the APAP degradation rate remains unchanged. Combined with density functional theory calculations, molecular oxygen adsorption obtains one electron with proton hydrogen transfer to hydroperoxyl (OOH) on the MoC surface, and the adsorbed OOH directly activate into OH due to the ultrafast electron transfer ability of MoC. Differential charge density analysis also shows that Mo transfers electrons to O. This strategy provides a new idea for optimizing catalysts to improve the heterogeneous Fenton-like performance.

Adsorption of Molecular Oxygen on N-graphene

Adsorption of Molecular Oxygen on N-graphene

Carbon-shell-encapsulated gold–palladium nanoreactors for highly efficient 5-hydroxymethylfurfural oxidation: Confinement and alloy effects study

Encapsulating noble metal nanoparticles in carbon nanoshells is an emerging and efficient way to enhance the activity and stability of noble metal species. A novel type of hollow rod-shaped carbon-shell-encapsulated gold–palladium (AuPd) alloy nanoreactor (AumPdn@CT) was designed and constructed. The Au2Pd1@C800 nanoreactor afforded a satisfactory 2,5-furandicarboxylic acid (FDCA) yield of 99.9 % from 5-hydroxymethylfurfural (HMF) oxidation using O2 as the oxidant in water. Remarkably, carbon-shell-encapsulated only 1.0 wt% AuPd alloy could offer an outstanding FDCA formation rate of 2003.6 mmol·g−1·h−1. Mechanistic studies demonstrated that the generated confinement and AuPd alloy species not only improved the adsorption capacity of the HMF substrate and the key intermediate 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), but also facilitated the adsorption and activation of molecular oxygen to generate oxygen active species of superoxide radicals. Constructing a carbon shell around AuPd alloy active sites provided effective physical protection for the metal core, thus enhancing the catalyst stability and reusability.

Copper-doped bismuth oxychloride nanosheets assembled into sphere-like morphology for improved photocatalytic inactivation of drug-resistant bacteria

The devastating microbiological contamination as well as emerging drug-resistant bacteria has posed severe threats to the ecosystem and public health, which propels the continuous exploitation of safe yet efficient disinfection products and technology. Here, copper doping engineered bismuth oxychloride (Cu-BiOCl) nanocomposite with a hierarchical spherical structure was successfully prepared. It was found that due to the exposure of abundant active sites for the adsorption of both bacteria cells and molecular oxygen in the structure, the obtained Cu-BiOCl with nanosheets assembled into sphere-like morphology exhibited remarkable photocatalytic antibacterial effects. In particular, compared to the pure BiOCl, composite Cu-BiOCl possessed improved antibacterial effects against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Methicillin-resistant Staphylococcus aureus (MRSA). The combination of physicochemical characterizations and theoretical calculations has revealed that copper doping significantly promoted the light absorbance, inhibited the recombination of electron-hole pairs, and enhanced molecular oxygen adsorption, which resulted in more generation of active species including reactive oxygen species (ROS) and h+ to achieve superior photocatalytic bacterial inactivation. Finally, transcriptome analysis on MRSA pinpointed photocatalytic inactivation induced by Cu-BiOCl may retard largely the development of drug-resistance. Therefore, the built spherical Cu-BiOCl nanocomposite has provided an ecofriendly, economical and robust strategy for the efficient removal of drug-resistant bacteria with promising potentials for environmental and healthcare utilizations.

Tuning the Magnetic and Catalytic Properties of Manganese Ferrite through Zn2+ Doping: Gas Phase Oxidation of Octanol

Spinel ferrites, ZnFe2O4, MnFe2O4, and ZnMnFe2O4, were synthesized using the sol–gel method and thoroughly investigated for their potential as catalytic and magnetic materials. Experiments unveiled that ZnMnFe2O4 exhibited excellent catalytic and magnetic properties, whereas the Density Functional Theory (DFT) calculations provided insight into the excellent performance of ZnMnFe2O4 compared with ZnFe2O4 and MnFe2O4. The catalytic efficiencies of the synthesized spinel ferrites were evaluated against a model reaction, i.e., the gas-phase oxidation of octanol to a corresponding aldehyde, utilizing molecular oxygen as an oxidant. The results indicated that the order of catalytic activity was ZnMnFe2O4 > MnFe2O4 > ZnFe2O4. The reaction was found to follow Langmuir Hinshelwood’s mechanism for dissociative adsorption of molecular oxygen. Owing to their superb catalytic and magnetic properties, mixed ferrites can be extended to a variety of organic transformation reactions.

Screening and Discovery of Metal Compound Active Sites for Strong and Selective Adsorption of N2 in Air.

Photocatalytic nitrogen fixation has the potential to provide a greener route for producing nitrogen-based fertilizers under ambient conditions. Computational screening is a promising route to discover new materials for the nitrogen fixation process, but requires identifying "descriptors" that can be efficiently computed. In this work, we argue that selectivity toward the adsorption of molecular nitrogen and oxygen can act as a key descriptor. A catalyst that can selectively adsorb nitrogen and resist poisoning of oxygen and other molecules present in air has the potential to facilitate the nitrogen fixation process under ambient conditions. We provide a framework for active site screening based on multifidelity density functional theory (DFT) calculations for a range of metal oxides, oxyborides, and oxyphosphides. The screening methodology consists of initial low-fidelity fixed geometry calculations and a second screening in which more expensive geometry optimizations were performed. The approach identifies promising active sites on several TiO2 polymorph surfaces and a VBO4 surface, and the full nitrogen reduction pathway is studied with the BEEF-vdW and HSE06 functionals on two active sites. The findings suggest that metastable TiO2 polymorphs may play a role in photocatalytic nitrogen fixation, and that VBO4 may be an interesting material for further studies.

Oxygen vacancy-driven strong metal-support interactions on AuPd/TiO2 catalysts for high-efficient air-oxidation of 5-hydroxymethylfurfural

The regulation ofstrong metal-support interactions (SMSI) has emerged as a powerful strategy in boosting catalytic activity and controlling product selectivity. However, directly tuning the metal-supportinteractions in oxide supported metal nanocatalysts remains challenging. Herein, citric acid (CA)‑assisted synthesized TiO2 layer on halloysite nanotubes (HNTs) with varied oxygen vacancies (Ov) concentrations was designed for loading AuPd nanoparticles. SMSI between the AuPd nanoparticles and the TiO2-xCA@HNTs support was successfully induced by adjustable Ov concentrations. The synthesized catalyst was employed for air-oxidation of bio-based 5-hydroxymethylfurfural (HMF) to bioplastic monomer 2,5-furandicarboxylic acid (FDCA) in water. A satisfactory FDCA yield of 98.4 %, accompany with an outstanding FDCA formation rate of 900.9 mmol·g−1·h−1 and an excellent TOF value at 441.2 h−1 was afforded. Based on catalysts characterizations and experimental studies, the catalytic performance was significantly affected by Ov concentrations. The kinetic study showed that the supported gold nanoparticles in alkaline environment had strong aldehyde oxidation activity but weak alcohol oxidation ability. On the contrary, supported palladium nanoparticles were more conducive to alcohol oxidation. This imbalance was overcome by the loading of AuPd nanoparticles, which enhanced the activity for air-oxidation of HMF. Mechanistic studies demonstrated that the stronginteractions between noble metal nanocatalysts and supports were regulated by Ov, which not only increased the adsorption capacity of the substrate and crucial intermediate, but also facilitated the adsorption and activation of molecular oxygen to generate oxygen active species of superoxide radicals. The possible catalytic mechanism for air-oxidation of HMF over Ov-driven SMSI on the obtained catalysts was proposed. This work sheds lights on the design of supported metal catalysts with SMSI for the catalytic upgrading of biomass-derived platform chemicals.

Efficient Catalytic Production of Hydrogen Peroxide Using Tin‐containing Zeolite Fixed Palladium Nanoparticles with Oxidation Resistance

AbstractThe metal surfaces tend to be oxidized in air through dissociation of the O−O bond of oxygen to reduce the performances in various fields. Although several ligand modification routes have alleviated the oxidation of bulky metal surfaces, it is still a challenge for the oxidation resistance of small‐size metal nanoparticles. Herein, we fixed the small‐size Pd nanoparticles in tin‐contained MFI zeolite crystals, where the tin acts as an electron donor to efficiently hinder the oxidation of Pd by weakening the adsorption of molecular oxygen and suppressing the O−O cleavage. This oxidation‐resistant Pd catalyst exhibited superior performance in directly synthesizing hydrogen peroxide from hydrogen and oxygen, with the productivity of hydrogen peroxide at ≈10,170 mmol gPd−1 h−1, steadily outperforming the catalysts tested previously. This work leads to the hypothesis that tin is an electron donor to realize oxidation‐resistant Pd within zeolite crystals for efficient catalysis to overcome the limitation of generally supported Pd catalysts and further motivates the use of oxidation‐resistant metal nanoparticles in various fields.

Efficient Catalytic Production of Hydrogen Peroxide Using Tin-containing Zeolite Fixed Palladium Nanoparticles with Oxidation Resistance.

The metal surfaces tend to be oxidized in air through dissociation the O-O bond of oxygen to reduce the performances in various fields. Although several ligand modification routes have alleviated the oxidation of bulky metal surfaces, it is still a challenge for the oxidation resistance of small-size metal nanoparticles. Herein, we fixed the small-size Pd nanoparticles in tin-contained MFI zeolite crystals, where the tin acts as an electron donor to efficiently hinder the oxidation of Pd by weakening the adsorption of molecular oxygen and suppressing the O-O cleavage. This oxidation-resistant Pd catalyst exhibited superior performance in directly synthesizing hydrogen peroxide from hydrogen and oxygen, with the productivity of hydrogen peroxide at ~10,170 mmol gPd-1 h-1, steadily outperforming the catalysts tested previously. This work leads to the hypothesis that tin is an electron donor to realize oxidation-resistant Pd within zeolite crystals for efficient catalysis to overcome the limitation of generally supported Pd catalysts, and further motivates the use of oxidation-resistant metal nanoparticles in various fields.

Surface oxygen vacancy-dependent molecular oxygen activation for propane combustion over α-MnO2

Oxygen vacancies (OV), as the sites of molecular oxygen adsorption and activation, play an important role in the catalytic combustion process of volatile organic compounds (VOCs). Revealing the relationship between OV concentration and molecular oxygen activation behavior is of significance to construct the efficient catalysts. Herein, α-MnO2 with different OV concentrations was prepared to investigate the molecular oxygen activation for C3H8 combustion. It is disclosed that the enhanced OV concentration in α-MnO2 induced the reconfiguration of surface metal atoms, resulting in the transformation of oxygen activation configuration from end-on mode to side-on mode. Oxygen molecules in side-on mode possessed more localized electron density and weaker coordination bond strength with surrounding Mn atoms, which were more favorable to adsorb C3H8 molecules and activate C-H bond for the improved combustion performance. This work provides a new understanding to reveal that the increased OV concentration contributes to more efficient VOCs combustion.

Bismuth oxysulfide thin films for light and humidity sensing

Bismuth oxysulfide (BOS) films were formed on dielectric glass substrates by the chemical bath deposition. They have a high sensitivity to moisture content and demonstrate the decrease in the electrical resistance up to three orders of magnitude when the relative humidity reaches 85% and more. The high sensitivity of resistive structure representing 0.65 µm thick film between two Ag contacts is associated with randomly oriented thin nanoplate crystals. The presence of a great number of intergrain boundaries restricts electron transport (both in the dark and under illumination), which is desirable for resistive humidity sensors. The BOS films possess a high surface-to-volume ratio making them ultra-sensitive to adsorption of water. It is supposed that ionic conductivity in a thin layer of adsorbed water plays a crucial role in fast response of sensing structure (1–3 s) to adsorption-desorption cycles. High dark resistance and low photoconductivity of BOS films make them practically insensitive to processes of molecular oxygen adsorption and action of light when they are used as humidity sensing structure.

Synergistic photocatalytic degradation mechanism of BiOClxI1-x-OVs based on oxygen vacancies and internal electric field-mediated solid solution

The easy recombination of photoexcited electron-hole pairs is a serious constraint for the application of photocatalysts. In this work, a range of BiOClxI1-x solid solutions with abundant oxygen vacancies (BiOClxI1-x-OVs) were synthesized. In particular, the optimal BiOCl0.5I0.5-OVs sample exhibited almost 100% removal of bisphenol A (BPA) within 45 min visible light exposure, which was 22.4, 3.1 and 4.5 times greater than BiOCl, BiOCl-OVs and BiOCl0.5I0.5, respectively. Besides, the apparent quantum yield of BPA degradation reaches 0.24%, better than some other photocatalysts. Benefiting from the synergism of oxygen vacancies and solid solution, BiOCl0.5I0.5-OVs gained an enhanced photocatalytic capacity. Oxygen vacancies induced an intermediate defective energy level in BiOClxI1-x-OVs materials, promoting the generation of photogenerated electrons and the molecular oxygen adsorption to produce more active oxygen radicals. Meanwhile, the fabricated solid solution structure enhanced the internal electric field between BiOCl layers, achieving rapid migration of photoexcited electrons and effective segregation of photoinduced charge carriers. Thus, this study provides a viable idea to solve the problems of poor visible light absorption of BiOCl-based photocatalysts and easy reorganization of electrons and holes in the photocatalysts.

Controlled synthesis of hollow carbon ring incorporated g-C3N4 tubes for boosting photocatalytic H2O2 production

H2O2 production through solar-driven photocatalytic route has received increasing attention. Herein, a carbon ring incorporated hollow g-C3N4 tubes (CHCN) was successfully fabricated via a novel supramolecular self-assembly strategy, co-inducing by hydrogen bond and covalent bond. The optimum H2O2 yield over the CHCN-0.02 reached up to 1.58 mmol L−1 h−1 (AQE= 28.10%, 420 nm), which was 5.4 times significantly higher than that of bulk g-C3N4 (0.29 mmol L−1 h−1) under visible light irradiation. Experimental and density functional theory (DFT) calculations revealed that the CHCNs not only expedited the charge carrier transfer/separation but also favored molecular oxygen adsorption and regulated bandgap structure under the in-plane electronic field induced by continuous π-conjugated Cring, which boosted the ORR efficiency for photocatalytic H2O2 synthesis. The optimized CHCN catalyst demonstrated adequate hybrid ORR routes, consisting of a dominated selective one-step two-electron ORR pathway and highly efficient two-step single-electron ORR for H2O2 production. Therefore, this work not only provides a new strategy for an efficient H2O2 formation using a g-C3N4-based photocatalyst but also explores the functionary mechanism of the ORR process and enlightens the way to highly efficient H2O2 generation.

Single-atom Cu anchored on N-doped graphene/carbon nitride heterojunction for enhanced photocatalytic H2O2 production

Photocatalytic production of H2O2 by polymeric carbon nitride has been regarded as a promising approach for the conversion of solar energy into valuable chemicals. However, the efficiency of pristine carbon nitride is limited by the rapid charge recombination and the lack of suitable active sites. Herein, we introduce single-atom Cu anchored on N-doped graphene (Cu-NG) as a cocatalyst coupled with carbon nitride via covalent bonding to enhance photocatalytic H2O2 production. The Cu-NG/carbon nitride could broaden the light absorption from UV to near-infrared region, contributing to the photocatalytic process. Moreover, NG containing electron-rich N atoms could serve as anchoring sites for stabilizing single-atom Cu. Importantly, the single-atom Cu acts not only as an electron sink to steer the interfacial charge separation but also as an active site for molecular oxygen adsorption and activation. With the synergistic effect of the enhanced interfacial charge separation and suitable active sites, Cu-NG/carbon nitride exhibits improved photocatalytic performance with an H2O2 generation rate of 2856 µmol g−1 h−1, which is 2.6 times that of pristine carbon nitride. This work provides a protocol for high-performance photocatalytic H2O2 production using a single-atom cocatalyst.

Reactivity of diamanes against oxidation: A DFT study

Diamanes, ultrathin diamond films represent a very promising class of two-dimensional carbon materials that attracts attention due to broad potential applications starting from sensing and optics and finishing with mechanical applications. We investigate here the ability of diamanes with hydrogenated and fluorinated surfaces to confront oxidation by performing density functional calculations. Simulations for adsorption of atomic and molecular oxygen show greater oxidation resistance for fluorinated diamanes in comparison with hydrogenated ones making these 2D materials promising for various applications where intensive oxidation is present.

Stability and activity of PdCu clusters embedded on pyridinic N-doped graphene: a density functional theory investigation

The stability and reactivity of Pd6-nCun (n = 0−3) clusters supported on pyridinic N-doped graphene (PNG) were investigated using the auxiliary density functional theory method. First, the stability of Pd6-nCun (n = 0−3) clusters supported on PNG was analyzed using charge transfer, interaction energy, and electron density critical point calculations. Then, the reactivity of these clusters supported on PNG was computed using frontier molecular orbitals and oxygen adsorption energies. According to the calculated interaction energy, as the Cu content increased, the interaction energy between Pd6-nCun (n = 0−3) clusters and PNG increased. The charge transfer indicated that the clusters donate charge to the PNG. Based on the energy of the frontier orbitals, the Pd5Cu cluster supported on PNG exhibits the smallest HOMO–LUMO gap inferring that this system is the most reactive, whereas the less reactive system corresponds to the Pd4Cu2 cluster supported on PNG. Finally, the oxygen adsorption energies on Pd6 (−3.86 eV) and Pd5Cu (−3.87 eV) clusters supported on PNG were similar. However, the Pd5Cu cluster has a lower Pd content than the Pd6 cluster. Therefore, this work reveals that PdCu systems supported on PNG could be cheap and efficient catalysts for the oxygen reduction reaction.

Oxygen vacancies-mediated CuO@N-doped carbon nanocomposites for non-radical-dominated photothermal catalytic degradation of contaminants

Efficient molecular oxygen activation (MOA) is a critical step for most of the environmental catalysis applications for generating reactive oxygen species (ROS), which is often limited by the lack of energy to excite electrons. The emergence of photothermal catalyst provides an opportunity to make effective use of solar energy to energize electrons for boosting activation of molecular oxygen. Herein, CuO nanoparticles wrapped into nitrogen-doped carbon nanocomposites (CuO@NCs) with abundant oxygen vacancies (OVs) were prepared through a facile one-step synthesis using carboxymethyl chitosan hydrogel as a template. The as-obtained CuO@NCs exhibited excellent photothermal catalytic properties under visible-light irradiation to achieve efficient molecular oxygen activation, thus allowing the effective degradation of bisphenol F (BPF) in complex aqueous environments and actual water matrices. Density functional theory (DFT) calculations reveal that both the enhanced properties of OVs for molecular oxygen adsorption and the accelerated properties of graphitic N for electron transfer contribute significantly to the MOA and charge separation efficiency, resulting in a large amount of ROS. Molecular oxygen is converted to superoxide (·O2−) and ultimately to singlet oxygen (1O2), which is the dominant ROS responsible for contaminants degradation. Additionally, a photothermal catalytic degradation pathway of BPF was proposed based on the product detection and theoretical calculations. This study provides an effective method for the in-situ fabrication of metal@N-doped carbon nanocomposite photothermal catalysts and elucidates the mechanism of the photothermal catalytic activation of molecular oxygen for contaminants degradation, providing a promising approach for making effective use of solar energy for environmental remediation.