Synergistic Effect Of Oxygen Vacancies Research Articles

Modulation mechanism of Mn-O strength in α-MnO2 catalyst for high-efficiency catalytic combustion of propane

The cleavage of C-H with high energy impedes the catalytic combustion of propane. Herein, α-MnO2 with modulation of Mn-O strength by changing the calcination temperature was applied in propane catalytic combustion. α-MnO2 calcinated at 350 °C (α-MnO2-350) exhibited superior performance (T20=150 °C, T90= 220 °C) in propane oxidation due to the synergistic effect of oxygen vacancies (OVs) and Lewis acidity. Density functional theory (DFT) calculations revealed that the lowest o-vacancy formation energy on α-MnO2-350 (Evo=0.74 eV) with its lowest Mn-O strength prompted the existence of abundant OVs and propane oxidation. Moreover, the highest Lewis acidity in α-MnO2-350 displayed the strongest propane adsorption, promoting the activation of C-H. The mineralization of propane on α-MnO2-350 dropped steeply after 68 h while could recover to 90 % in long-term water vapor stability test owing to the H2O adsorbed at OVs and the carbonaceous intermediates adsorbed at the Lewis acid sites.

Internal electric field and oxygen vacancies synergistically boost S-scheme VO/BiOCl-TiO2 heterojunction film for photocatalytic degradation of norfloxacin

Sluggish interfacial dynamics and weak redox properties make the degradation of antibiotics by photocatalysts still a great challenge. Herein, constructing S-scheme heterojunction between BiOCl and TiO2 nanorod arrays (TNA) by hydrothermal method, and the synergistic effect of oxygen vacancies (VO) and Internal Electric Field (IEF) on improving the performance of the photocatalysts was revealed by adjusting the VO. The VO modified BiOCl-TiO2 (VBiTNA) exhibited excellent photocatalytic activities for norfloxacin, achieving a degradation efficiency of up to 90.2 % in just 60 min, and the rate constant was as high as 3.67 × 10-2 min−1. In addition, it also showed great photocatalytic degradation performance of NOR in a wide pH range, complex ionized water environment and real water source. The degradation intermediates and degradation pathway of NOR were predicted with LC-MS technology and Fukui function. Combined with free radical capture, electron paramagnetic resonance, relevant electrochemical testing, and DFT calculations reveals the mechanism of the enhanced photocatalytic performance of VBiTNA. The performance enhancement can be attributed to the expansion of the light absorption range, enhanced adsorption of O2 and effective activation to generate ·O2–, while improving the separation efficiency of electron-hole pairs and maintaining a strong redox capacity. This research focusing on VO and IEF mechanisms will help to advance the rational design of high-performance defective photocatalysts.

Fabrication of (H2PO4−, Ni2+) – α-Fe2O3/Bi2S3 heterojunction photocatalysts with improved visible-light catalytic activity

In this work, the (H2PO4−, Ni2+) – α-Fe2O3(PNF) with abundant oxygen vacancies (OVs) was synthesized, and PNF/Bi2S3 heterojunction photocatalysts were then prepared by hydrothermal process. The obtained PNF showed higher photo-Fenton degradation activity. In comparison with PNF and Bi2S3, the prepared PNF/Bi2S3 composites significantly improved the photocatalytic degradation of p-nitrophenol (p-NP) under visible-light illumination. The production of active species was accelerated in the composite system through the synergistic effect of OVs, heterojunction, and photo-Fenton, resulting in high p-NP degradation efficiency. The PNF/B-2 composite exhibited the highest photocatalytic-Fenton degradation activity, which could be used as a high-performance visible-light-driven photocatalyst for the degradation of difficult-to-degrade pollutants.

ZIFs material-derived bimetallic oxide heterojunctions activate perodisulfate to degrade chlortetracycline rapidly: The synergistic effects of oxygen vacancies and rapid electron transfer

The bimetallic oxides heterojunction structure from new 3D-ZIF was prepared to degrade the chlortetracycline by PDS activation. The system achieved more than 95 % degradation of chlortetracycline within 40 min. Theoretical calculations and physicochemical characterization of the NiZnCo-N-C proved that the material had better electron transfer properties and multi-site reactivity, and the presence of Zn provided an effective intermediate medium for the reaction of Co and Ni, while the non-metallic N-C component also constituted good electron reaction sites. Meanwhile, the existence of abundant oxygen vacancies established the good foundation for the formation of oxygen radicals in the material, and the rapid electron transfer processes speeded up non-radical processes such as electron transfer and 1O2.The combination of two degradation pathways reduced the impact of environmental factors, the PDS + NiZnCo-N-C system exhibited relatively stable or even better performance in the existence of inorganic anions. Furthermore, the structure of the NiZnCo-N-C had the smallest d-band center, which efficiently adsorbed PDS molecules and broke the O-O bond in PDS. DFT Conclusion and LC-MS of CTC suggested the various reaction processes in the system. Our study provided new solutions and insights for the organic pollutions in the aquatic environment.

Construction of MoS42− intercalated NiAl-layered double hydroxide by solvent-free method for promoting photocatalytic degradation of antibiotics: Synergistic effect of oxygen vacancies and electron-rich groups

MoS42− intercalated NiAl-layered double hydroxides (LDH) were prepared by solvent-free techniques, which possessed oxygen vacancies and efficient electron transfer channels. Oxygen vacancies were increased with increasing of the MoS42− intercalation amount. Through X-ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR), Kelvin Probe Force Microscopy (KPFM), and Density Functional Theory (DFT), the presence of oxygen vacancies and electron transfer channels were confirmed. In the meantime, the formation mechanisms of electron transfer channels and the synergistic mechanisms involving oxygen vacancies and electron transfer channels were illustrated. Electrochemical characterization revealed that compared with LDH, the electron lifetime of LDH-WM-0.5 increased from 1.70 ns to 2.88 ns, and the recombination efficiency of electron holes was reduced by about 6 times. Degradation experiments demonstrated that the degradation rate of tetracycline by LDH-WM-0.5 increased from 19.0 % to 90.0 % in 3 h, representing a 4.5-fold improvement compared to LDH photocatalysts. This study contributed novel insights into developing advanced photocatalysts by strategically manipulating the presence of oxygen vacancies and constructing the electron transfer channels.

Synergistic effect of oxygen vacancies and doped sulfur over BiOBr for efficient visible photocatalytic removal of dyes

Herein, the BiOBr co-modified with oxygen vacancies (Vo) and doped by sulfur was a promising photocatalyst (Vo-BiOBr-S), which was synthesized by a one-pot solvothermal approach. The TEM showed that Vo-BiOBr-S is a sea urchin-shaped microsphere with a diameter of about 4 μm. The photocatalytic efficiency of Vo-BiOBr-S was studied by removing rhodamine B and methylene blue, which were higher than that of BiOBr, Vo-BiOBr and BiOBr-0.8S, respectively. Additionally, the photocatalyst exhibits high degradation of aqueous solutions containing both rhodamine B and methylene blue. The photocurrent and photoluminescence tests showed that the improved photocatalytic performance of Vo-BiOBr-S was due to the accelerated charge transfer and separation by the internal electric field, which extended the visible light absorption range. Furthermore, experiments free radical trapping revealed that superoxide radicals were the principal active species in this system, contributing to the superior degradation performance of Vo-BiOBr-S. The density of states of the samples was calculated via DFT to analyse the energy band structure. The effectiveness of Vo-BiOBr-S in mineralising RhB under LED light was demonstrated through total organic carbon tests. This study presents a method to design efficient photocatalysts for use in environmental preservation.

Synergistic effects in ZnO nanorod films by pulsed electrodeposition on graphene oxide towards enhanced photocatalytic degradation

In this work the synthesis, characterization and photocatalytic activity of novel graphene oxide-supported ZnO nanostructured film are reported. The ZnO film was deposited onto GO layer in a two-step procedure varying the deposition mode. The electrodeposited ZnO films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform Infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The effect of the electrodeposition mode and GO presence on the properties of the ZnO nanostructured film was assessed. The applicability towards the adsorption, photodegradation of methylene blue (MB) for the obtained films was analyzed. The results indicated the electrodeposition pulses result in a strong interaction between ZnO and GO results, lower c-axis strain of the deposited ZnO and higher oxygen vacancies. Synergistic effect of oxygen vacancies and morphology towards degradation performance was indicated. Both adsorption and photocatalysis towards the degradation of MB on the modified ZnO films were observed, 52 % degradation efficiency being recorded in 90 min with a rate constant of 0.00171 min−1 under low UV irradiation, with respect to 5 % corresponding to ZnO film obtained in single step by direct mode and in absence of GO layer. A recycling experiment indicated excellent stability of the photocatalyst, the degradation efficiency reaching 98 % after 3 successive runs.

Preparation of a Novel Ag/CFOOVs Composite Catalyst and Efficient Degradation of Phenol in a H2O2-based Fenton-like System

Although CuFe2O4 has been widely used in the field of Fenton-like wastewater treatment, its ability to activate H2O2 still needs to be further improved. In this context, a novel Agx/CFOOVs (x represents the theoretical mass percentage of Ag) composite catalyst was prepared by the tartaric acid reduction method for the first time, and its degradation performance and degradation mechanism of Phenol in a H2O2-based Fenton-like system were investigated. Through a series of characterizations, the successful preparation of the catalyst was confirmed. The degradation experiment showed that the degradation rate of 50mg/L Phenol by Ag2/CFOOVs/H2O2 system was 98.55% within 15min, which was a significant improvement in the degradation efficiency compared with that of CuFe2O4 and CFOOVs. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) confirmed the successful introduction of oxygen vacancies (OVs). Electrochemical impedance spectroscopy (EIS) showed that Ag2/CFOOVs had the lowest impedance, and the synergistic effect of OVs and Ag effectively enhanced the degradation capability of the catalysts for Phenol. The capture experiments of active species and ESR tests showed that the main active species of the Ag2/CFOOVs/H2O2 system were 1O2 and •OH. This study provides a new reference for the introduction of OVs and Ag in Fenton-like catalysts and their application to wastewater treatment.

Oxygen vacancies-modified S-scheme heterojunction of Bi-doped La2Ti2O7 and La-doped Bi4Ti3O12 to improve the NO gas removal avoiding NO2 product

Monoclinic phase La2Ti2O7 and orthorhombic phase Bi4Ti3O12 with layered crystal structure constructed by the perovskite slab were widely used in photocatalysis. Their electronic structures are the most crucial factor in high photocatalytic activity. Bi-doped La2Ti2O7 gradually converts to La-doped Bi4Ti3O12 with the incorporation of bismuth ions, and the two phases build an S-scheme heterojunction. More oxygen vacancies were introduced into the S-scheme heterojunction after heat treatment in a nitrogen atmosphere. The 0.1BTO/LTO-OV sample exhibits the largest NO removal efficiency of 52% and only 5.6 ppb NO2 intermediate generation. The improved NO removal efficiency was ascribed to the synergistic effect of oxygen vacancies, doping and heterojunction, providing a new insight into the photocatalytic NO removal. The photocatalytic mechanism was eventually proposed on the basis of trapping experiments.

The synergistic effect of oxygen vacancies and acidic properties of SO42−/CexZr1−xO2 on enhancing the Electro-Fenton performance in antibiotics wastewater treatment

Recently, bi-functional catalysts have emerged as an effective approach for enhancing the performance of electro-Fenton in degrading antibiotics by simultaneously improving H2O2 generation and Fe circulation. Herein, we prepared a SO42- modified CexZr1-xO2 bi-functional catalyst to construct an efficient e-Fenton system for degrading norfloxacin. Results display that the fabricated catalyst exhibited superior performance in degrading norfloxacin owing to durative generated ⋅OH, which was proved to be the dominant active species. The H2O2 generation capacity of that catalyst was twice higher than the pure e-Fenton and its faradaic efficiency even came up to 75%. The amount of soluble total Fe and Fe2+ ions of that catalyst were both increased twofold compared to the blank system, declaring the acceleration of Fe recycling process. Characterizations and density function theory calculations proposed a synergistic mechanism that attributed the simultaneously improvement in H2O2 generation and Fe2+ circulation to the multiple regulated interface properties, the promoted 2e- ORR activity caused by enriched oxygen vacancies at Ce sites, and the accelerated electrons transfer owing to the strengthened acidic sites for the coordination between Zr sites and S species. Furthermore, that catalyst is also proved to be feasible, well-recycled and practical for application in wastewater purification.

Revealing the effect of crystallinity and oxygen vacancies of Fe-Co phosphate on oxygen evolution for high-current water splitting

Strategically tuning the composition and structure of transition metal phosphates (TMPs) holds immense promise in the development of efficient oxygen evolution reaction (OER) electrocatalysts. However, the effect of crystalline phase transformation for TMPs on the catalytic OER activity remains relatively uncharted. In this study, we have deftly orchestrated the reaction process of anion-etched precursor to induce the amorphization process of FeCo-POx from crystalline to amorphous states. The as-obtained amorphous FeCo-POx (A-FeCo-POx) exhibited an optimized OER performance with a low overpotential of 270 mV at a current density of 10 mA cm−2, which could be attributed to the flexibility of its amorphous structure and the synergistic effect of oxygen vacancies. Moreover, when incorporated into an overall water splitting (OWS) device configured as A-FeCo-POx(+)||Pt/C(–), it displayed long-term solid stability, sustaining operation for 300 h at a current density of 200 mA cm−2. This work not only provides valuable insights into understanding the transformation from crystalline to amorphous states, but also establishes the groundwork for the practical utilization of amorphous nanomaterials in the field of water splitting.

In situ construction of Z-type defective Al2O3/BiPO4 for efficient photocatalytic degradation of organic dyes

In this study, we synthesize an Al2O3/BiPO4 heterojunction via a straightforward in-situ coprecipitation technique. An examination of the catalyst specimen reveals that Al2O3 nanoparticles are uniformly distributed on the surface of the hexagonal BiPO4, achieved through the formation of sturdy chemical bonds. This process leads to the creation of an Al2O3/BiPO4 heterojunction with an elevated concentration of oxygen vacancies. This, in turn, contributes to a notable decrease in the photocatalyst's energy band gap while enhancing the absorption spectrum for visible light. Additionally, the Al2O3/BiPO4 complex showcases a unique internal electric field, giving rise to a direct Z-type heterostructure. This heterostructure can drive the selective migration of photogenerated electrons and holes, achieve effective separation of photogenerated charges under the synergistic effect of oxygen vacancies, and maintain the strong redox abilities of BiPO4 and Al2O3. Consequently, there has been a marked improvement in the efficiency of photocatalytic degradation of organic pollutants in dyes.

Photothermal‐boosted polaron transport in Fe2O3 photoanodes for efficient photoelectrochemical water splitting

AbstractIntroduction of the photothermal effect into transition‐metal oxide photoanodes has been proven to be an effective method to improve the photoelectrochemical (PEC) water‐splitting performance. However, the precise role of the photothermal effect on the PEC performance of photoanodes is still not well understood. Herein, spinel‐structured ZnFe2O4 nanoparticles are deposited on the surface of hematite (Fe2O3), and the ZnFe2O4/Fe2O3 photoanode achieves a high photocurrent density of 3.17 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (VRHE) due to the photothermal effect of ZnFe2O4. Considering that the hopping of electron small polarons induced by oxygen vacancies is thermally activated, we clarify that the main reason for the enhanced PEC performance via the photothermal effect is the promoted mobility of electron small polarons that are bound to positively charged oxygen vacancies. Under the synergistic effect of oxygen vacancies and the photothermal effect, the electron conductivity and PEC performance are significantly improved, which provide fundamental insights into the impact of the photothermal effect on the PEC performance of small polaron‐type semiconductor photoanodes.

Synergistic effect of oxygen vacancies and edging/corner-connected MnO6 structural motifs in multi-dimensional manganese oxides to enhance OVOCs catalytic oxidation

The structure-activity relationships for vinyl acetate catalytic oxidation are challenging to explore at the atomic scale due to the ambiguity of the structural defect types and sites of manganese oxides. Our work elaborates, at the atomic level, through in-situ experimental and theoretical methods, the synergistic effects of two types of structural defect sites of VO-e (edge-sharing oxygen) and VO-c (corner-sharing oxygen) and MnO6 structural motifs of manganese oxides. Multi-dimensional manganese oxides, namely those with corner-connected MnO6 structural motifs and VO-c structural oxygen defect sites, significantly improved the activation of vinyl acetate. Enhancement of enol structure formation, acetate and formate intermediate species, and tautomerism between enol structure and acetaldehyde were detected when oxygen vacancies of manganese oxides were present in combination with corner/edge-connected MnO6. Moreover, the activation of chemical bonds and deep catalytic oxidation of vinyl acetate depend on the presence of a redox couple, surface oxygen species, and weakened MnO bonds. It provides a valuable notion for investigating and designing catalytic systems and reaction processes for the purpose of emission reduction and the management of environmental contaminants.

Synergistic effect of oxygen vacancies and built-in electric field in GdCrO3/BiVO4 composites for boosted photocatalytic reduction of nitrate in water

As a promising approach for nitrate nitrogen removal in water, photocatalysis required sufficient photogenerated charges to achieve a high photocatalytic efficiency. Herein, a novel GdCrO3/BiVO4 composite was prepared by the solid-state combustion method combined with hydrothermal treatment. The synergistic effect of oxygen vacancies introduced by chemical reduction method and built-in electric field formed in GdCrO3/BiVO4 heterostructures suppressed the charge recombination, which eventually improved the photocatalytic activity. Effects of photocatalyst composition, HCOOH dosage and oxygen vacancy concentration on photocatalytic activity were investigated. It was found that 0.30-GdBiOVs composites exhibited highest photocatalytic activity with nitrate removal ratio of 97.05% and N2 selectivity of 92.76% in 40 min. Moreover, end-products of nitrate nitrogen elimination and stability of photocatalysts were revealed. The existences of oxygen vacancies and built-in electric field were confirmed by EPR and HRTEM analyses. Ultimately, the possible mechanisms of nitrate nitrogen elimination were clarified.

Tailoring high-index-facet and oxygen defect of black In2O3−x/In2O3 as highly photothermal catalyst for boosting photocatalytic hydrogen evolution and contaminant degradation

Defect engineering and the high index surface (HIF) can be regarded as two effective methods to tuning the microstructure of catalysts and photocatalytic activities. So far, the integration of the synergistic effects of oxygen vacancies and HIF advantages into semiconductors to enhance photocatalytic performance has received little attention. Herein, Black In2O3−x/In2O3 with oxygen vacancy and exposed (321) surface active crystal plane has been synthesized as excellent photocatalysts via a facile method. The catalysts of Black In2O3−x/In2O3 can reach the highest photocatalytic hydrogen evolution rate (1046 μmol h−1 g−1) and degradation efficiency of MB (0.017 min−1) with 120 min, respectively. As a special phase junction, Black In2O3−x/In2O3 could effectively boost the separation and transfer of photogenerated charges because of unique defect homojunction microstructure resulting in exposing abundant photocatalyst redox active sites. The experiment characterization and density functional theory (DFT) calculations can further employ to unveil mechanism of enhanced hydrogen evolution reaction (HER) activity. It is obvious that enhanced HER activity was attributed to synergy of oxygen defect and exposed (321) surface active crystal planes due to electron distribution and lower Gibbs free energy of H adsorption. This work might open up new avenues to integrate exposed facets and oxygen vacancy for enhancing the photocatalytic hydrogen evolution with renewable energy sources and environmental remediation.

Fe-polyoxometalate nanodots decorated Bi2MoO6 nanosheets with dominant {0 1 0} facets for photo-Fenton degradation of antibiotics over a wide pH range: Mechanism insight and toxicity assessment

It remains challenging to rationally design ultra-efficient and reusable heterogeneous photo-Fenton catalysts with a wide pH working range for environmental remediation. Here, Fe-polyoxometalate (Fe-POM)-modified Bi2MoO6 with dominant {010} facets, denoted as Fe-POM/BMO, was elaborately designed and synthesized for the degradation of typical antibiotics. Benefiting from the synergistic effect of oxygen vacancies and the Fe3+/Fe2+ redox couple, the Fe-POM/BMO heterojunctions exhibited remarkable photo-Fenton degradation performance at a wide pH range of 3.0–11.0. Based on the density functional theory calculations and intermediates analysis, the probable degradation pathways of TC were unraveled. In addition, the QSAR prediction and the Microtox test (Photobacterium phoshoreum T3 spp. as the luminescent bacteria) proved that the degradation process of tetracycline could effectively alleviate the ecotoxicity. According to the findings, the application of Fe-POM/BMO in the photo-Fenton degradation process of antibiotics is eco-friendly and exhibits high application potential in environmental remediation.

Synergistic effect of oxygen vacancies and Ni particles over the ZnWO4/CdS heterostructure for enhanced photocatalytic reduction and oxidation activities

A hybrid photocatalyst of oxygen vacancies-decorated ZnWO4/CdS–Ni greatly boosts the photocatalytic reduction and oxidation activities, which is due to the Z-scheme heterojunction after introducing oxygen vacancies and bifunctional Ni particles.

Plasma-assisted CO2 decomposition catalyzed by CeO2 of various morphologies

Plasma-assisted catalytic decomposition of CO2 over CeO2 nanocatalysts was investigated in this study. CeO2 nanocatalysts with different morphologies (i.e., cube, rod, and hexagon were prepared by hydrothermal method) were evaluated in a dielectric barrier discharge reaction at room temperature and atmospheric pressure. Among the above catalysts, commercial CeO2 and quartz sands, CeO2 nanorods (CeO2-R) exhibited the highest CO2 conversion under an applied voltage of 8 kV. When the discharge voltage was increased to 9 and 11 kV, all CeO2 catalysts showed increased CO2 conversion with little difference, but when the applied voltage was larger than 11 kV, the difference in catalytic performance became negligible. The better performance of CO2 activation over CeO2-R was attributed to the abundant oxygen vacancies on its exposed (110) crystal plane, which was further confirmed by XPS characterization. Oxygen vacancies on CeO2-R led to twice CO2 adsorption amount compared with the other CeO2 catalysts, and presented a more significant synergistic effect of oxygen vacancies and plasma on CO2 decomposition. The CO2 molecules adsorbed on oxygen vacancies over CeO2-R were partly activated and more easily decomposed in the plasma, resulting in higher CO2 conversion. Meanwhile, the minimum discharge voltage for CO2 decomposition over CeO2-R was 5.0 kV, which was 8.3 kV for commercial CeO2 due to its lowest oxygen vacancy density. However, due to the higher electron density and increased probability for free CO2 splitting under high discharge voltage, most CO2 molecules were activated by the plasma alone, thus less catalyst effect was observed.

Efficient catalytic ozonation over Co-ZFO@Mn-CN for oxalic acid degradation: Synergistic effect of oxygen vacancies and HOO-Mn-NX bonds

Co-ZFO@Mn-CN with 1O2 and O2•− as main reactive oxygen species was synthesized for catalytic ozonation, which could efficiently degrade organic pollutants. EPR and XPS analysis indicated that lattice doping of Co induced formation of abundant of OVs, which could provide localized electrons for O3 activation with the generation of HO2•/O2•−. 1O2 and H2O2 were produced by the recombination of HO2•/O2•−. DFT calculation demonstrated that H2O2 was deprotonated to generate HOO−, which preferred to form HOO-Mn-NX bonds with Co-ZFO@Mn-CN. Under the attack of O3, HOO-Mn-NX bonds were broken with the generation of HO2• and HO3•/O3•−, not only accelerating 1O2 production for organics degradation but also avoiding Mn(Ⅱ) sites oxidation. Combining advantages of OVs and HOO-Mn-NX, Co-ZFO@Mn-CN achieved 70–100% mineralization for different organic pollutants. Thus, this work provided a simple and efficient way for enhancing the utilization of O3 by the synergistic effect of OVs and HOO-Mn-NX bonds, also improving ROS transformation.