Abundant Surface Oxygen Vacancies Research Articles

Oxygen vacancy for boosted alkaline oxygen evolution under AC magnetic field

Reducing the overpotential of oxygen evolution reaction (OER) with slow kinetics is important to realize commercial hydrogen production from water electrolysis. Here, ZnCo2O4 with abundant surface oxygen vacancies is employed to clarify the influence of oxygen vacancies on OER performance under AC magnetic field. The additional active sites as well as enhanced reaction activity of each active sites resulting from oxygen vacancies enable N–ZnCo2O4-δ-350 to exhibit outstanding OER performance, where the overpotential is 406 mV at 10 mA cm−2. Furthermore, double exchange interaction between Co2+-O2--Co3+ ignited by oxygen vacancies produces ferromagnetism in N–ZnCo2O4-δ, which can directly promote OER under ACMF. And the mass transport at additional active sites active sites provided by oxygen vacancies is also accelerated under ACMF due to magnetohydrodynamic convection. As a result, non-iR-corrected overpotential at 10 mA cm−2 of N–ZnCo2O4-δ-350 is reduced to 243 mV when the ACMF intensity is 4.752 mT, which is a 44.5% reduction compared to no ACMF. These findings provide a novel and efficient perspective for realizing efficient electrocatalysis.

Elucidating the effect of Ce with abundant surface oxygen vacancies on MgAl2O4-supported Ru-based catalysts for ammonia decomposition

Ammonia is a promising COx-free hydrogen (H2) carrier because of its high volumetric H2 density. However, developing highly active/stable ammonia decomposition catalysts for H2 production remains challenging. In this study, the role of ceria (CeO2) as a promoter for Ru-based catalysts was investigated. Ru/Cex/MgAl(y00) catalysts were prepared by the incipient wetness impregnation (IWP) and deposition–precipitation (DP) methods. The surface oxygen vacancy (OV) concentration was controlled by the Ce loading and calcination temperature. By evaluating the surface reaction behavior of the ammonia decomposition catalysts, this study proposes that CeO2 effectively improves the recombination/desorption of N and H atoms. The optimal catalyst Ru/Ce5/MgAl(600) achieved a high H2 formation rate (27.4 mmolH2·gcat−1∙min−1 at 30,000 mL·gcat−1·h−1, 450 °C) and stable performance after exposure at 650 °C for 20 h. This study provides insight into the effect of abundant surface OVs in CeO2 on the physicochemical properties and ammonia decomposition performance of the catalysts.

One-step conversion of acidified oil to biodiesel by novel bifunctional SrZr1-xFexO3 catalyst

The novel heterogeneous catalysts of SrZr1-xFexO3 (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 or 0.40) with acid-base bifunctional property are prepared through the sol-gel method and applied in catalyzing transesterification and esterification from acidified oil to produce biodiesel. The substitution of Zr by Fe in the SrZrO3 perovskite results in the lattice distortion to generate abundant surface oxygen vacancies. Also, the enhancement of electron density on active sites improves the acidity and basicity of catalyst to construct the acid-base pair sites for high efficiency of biodiesel production. The SrZr0.75Fe0.25O3 catalyst shows the strongest catalytic activity and the maximum FAME yield of 99.5% is achieved at the reaction temperature of 178 °C, catalyst amount of 4.5 wt%, methanol to oil molar ratio of 19:1 and reaction duration of 3.4 h through optimizing reaction parameters by convolutional neural network. The catalyst exhibits strong acid resistance and the FAME yield of 93.9% is achieved with 30 wt% oleic acid addition, where methanol is readily adsorbed to Sr site for transesterification and free fatty acids are readily adsorbed to Fe site for esterification. In addition, the SrZr0.75Fe0.25O3 catalyst shows satisfactory reusability and the FAME yield of 96.2% is maintained for the fifth reused cycle.

Morphology effect of Pd/In2O3/CeO2 catalysts on methanol steam reforming for hydrogen production

Catalyst support morphology strongly influences its surface and structural properties, therefore, may have a significant impact on their reactivity in heterogeneous catalysis. Herein, the Pd/In2O3/CeO2-x (loaded with 1 wt% Pd and In2O3) catalysts with different morphologies of rods(r), cubes(c) and irregularity(w) shapes were prepared by hydrothermal method and impregnation method. At temperature of 275–425 °C, as-prepared catalysts were evaluated for hydrogen production from methanol steam reforming (MSR). The activity data showed the outstanding performance of the rod-shaped Pd/In2O3/CeO2 catalysts, exhibiting the complete conversion of methanol and particularly low CO (1.3%) at 375 °C. The structural properties and physicochemical of Pd/In2O3/CeO2-x with different morphologies were characterized by means of X-ray diffraction (XRD), high resolution transmission microscopy (HR-TEM), CO pulse chemisorption, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of methanol (CH3OH-TPD). Activity data and catalyst characterization results correlated, and indicated that the excellent reactivity for the rod-shaped Pd/In2O3/CeO2 catalysts in MSR is ascribed to the large particle size of palladium nanoparticles and the abundant oxygen vacancies induced by the strong interaction between Pd, In and Ce. HR-TEM results revealed that rod-like CeO2 mainly expose (110) crystalline surface with high mobility of surface oxygen and possess the most abundant surface oxygen vacancies with the low formation energy, facilitating the formation of active species of Pd0 on catalyst surface, and promoting the activation and adsorption of methanol and water molecules. Furthermore, the rod-shaped Pd/In2O3/CeO2 catalysts showed excellent reactivity and stability in MSR for 30 h, demonstrating its potential of being used as catalysts in methanol steam reforming in PEMFC systems.

Achieving High Selectivity in Photocatalytic Oxidation of Toluene on Amorphous BiOCl Nanosheets Coupled with TiO2.

The inert C(sp3)-H bond and easy overoxidation of toluene make the selective oxidation of toluene to benzaldehyde a great challenge. Herein, we present that a photocatalyst, constructed with a small amount (1 mol %) of amorphous BiOCl nanosheets assembled on TiO2 (denoted as 0.01BOC/TiO2), shows excellent performance in toluene oxidation to benzaldehyde, with 85% selectivity at 10% conversion, and the benzaldehyde formation rate is up to 1.7 mmol g-1 h-1, which is 5.6 and 3.7 times that of bare TiO2 and BOC, respectively. In addition to the charge separation function of the BOC/TiO2 heterojunction, we found that the amorphous structure of BOC endows its abundant surface oxygen vacancies (Ov), which can further promote the charge separation. Most importantly, the surface Ov of amorphous BOC can efficiently adsorb and activate O2, and amorphous BOC makes the product, benzaldehyde, easily desorb from the catalyst surface, which alleviates the further oxidation of benzaldehyde, and results in the high selectivity. This work highlights the importance of the microstructure based on heterojunctions, which is conducive to the rational design of photocatalysts with high performance in organic synthesis.

The enhancement of benzene total oxidation over RuxCeO2 catalysts at low temperature: The significance of Ru incorporation

Catalytic oxidation is considered to be the most efficient technology for eliminating benzene from waste gas. The challenge is the reduction of the catalytic reaction temperature for the deep oxidation of benzene. Here, highly efficient RuxCeO2 catalysts were utilized to turn the number of surface oxygen vacancies and Ce–O–Ru bonds via a one-step hydrothermal method, resulting in a preferable low-temperature reducibility for the total oxidation of benzene. The T50 of the Ru0.2CeO2 catalyst for benzene oxidation was 135 °C, which was better than that of pristine CeO2 (239 °C) and 0.2Ru/CeO2 (190 °C). The superior performance of Ru0.2CeO2 was attributed to its large surface area (approximately 114.23 m2·g−1), abundant surface oxygen vacancies, and Ce–O–Ru bonds. The incorporation of Ru into the CeO2 lattice could effectively facilitate the destruction of the CeO bond and the facile release of lattice oxygen, inducing the generation of surface oxygen vacancies. Meanwhile, the bridging action of Ce–O–Ru bonds accelerated electron transfer and lattice oxygen transportation, which had a synergistic effect with surface oxygen vacancies to reduce the reaction temperature. The Ru0.2CeO2 catalyst also exhibited high catalytic stability, water tolerance, and impact resistance in terms of benzene abatement. Using in situ infrared spectroscopy, it was demonstrated that the Ru0.2CeO2 catalyst can effectively enhance the accumulation of maleate species, which are key intermediates for benzene ring opening, thereby enhancing the deep oxidation of benzene.

Boosting catalytic activity of Cu-Ce solid solution catalysts by flame spray pyrolysis with high Cu+ concentration and oxygen vacancies

Cu-Ce solid solution catalysts are remarkable in catalytic oxidation. However, the traditional synthesis methods struggle to prevent severe phase separation at high Cu concentration. In this study, a stable Cu-Ce solid solution with a Cu content>30% was synthesized by flame spray pyrolysis (FSP). Flame synthesis process with a high reaction temperature of 2000 K and rapid cooling characteristics of over 100 K cm−1 resulted in the enrichment of Cu elements on the catalyst's surface as Cu+. The high Cu content fostered abundant surface oxygen vacancies on the catalyst. The catalyst surface has more CO activation sites due to the high Cu+ concentration, and the abundant oxygen vacancies bring greater oxygen activation ability to the catalyst. It was found that Cu-30 had a reaction rate of 0.48 μmolCO g−1 s−1 at 60 °C, dozens of times higher than other catalysts, and achieved complete conversion of CO at 120 °C. The mechanism suggests that the active site of CO is the surface Cu+, and the oxygen vacancies provide active oxygen species, which facilitate the CO catalytic reaction's rapid progress.

Effective Atomic N Doping on CeO2 Nanoparticles by Environmentally Benign Urea Thermolysis and Its Significant Effects on the Scavenging of Reactive Oxygen Radicals.

Atomic nitrogen doping on CeO2 nanoparticles (NPs) by an efficient and environmentally benign urea thermolysis approach is first studied, and its effects on the intrinsic scavenging activity of the CeO2 NPs for reactive oxygen radicals are investigated. The N-doped CeO2 (N-CeO2) NPs, characterized by X-ray photoelectron and Raman spectroscopy analyses, showed considerably high levels of N atomic doping (2.3-11.6%), accompanying with an order of magnitude increase of the lattice oxygen vacancies on the CeO2 crystal surface. The radical scavenging properties of the N-CeO2 NPs are characterized by applying Fenton's reaction with collective and quantitative kinetic analysis. The results revealed that the significant increase of surface oxygen vacancies is the leading cause for the enhancements of radical scavenging properties by the N doping of CeO2 NPs. Enriched with abundant surface oxygen vacancies, the N-CeO2 NPs prepared by urea thermolysis provided about 1.4-2.5 times greater radical scavenging properties than the pristine CeO2. The collective kinetic analysis revealed that the surface-area-normalized intrinsic radical scavenging activity of the N-CeO2 NPs is about 6- to 8-fold greater than that of the pristine CeO2 NPs. The results suggest the high effectiveness of the N doping of CeO2 by the environmentally benign urea thermolysis approach to enhance the radical scavenging activity of CeO2 NPs for extensive applications such as that in polymer electrolyte membrane fuel cells.

Thermocatalytic Degradation of Gaseous Formaldehyde Using Transition Metal-Based Catalysts.

Formaldehyde (HCHO: FA) is one of the most abundant but hazardous gaseous pollutants. Transition metal oxide (TMO)-based thermocatalysts have gained much attention in its removal due to their excellent thermal stability and cost-effectiveness. Herein, a comprehensive review is offered to highlight the current progress in TMO-based thermocatalysts (e.g., manganese, cerium, cobalt, and their composites) in association with the strategies established for catalytic removal of FA. Efforts are hence made to describe the interactive role of key factors (e.g., exposed crystal facets, alkali metal/nitrogen modification, type of precursors, and alkali/acid treatment) governing the catalytic activity of TMO-based thermocatalysts against FA. Their performance has been evaluated further between two distinctive operation conditions (i.e., low versus high temperature) based on computational metrics such as reaction rate. Accordingly, the superiority of TMO-based composite catalysts over mono- and bi-metallic TMO catalysts is evident to reflect the abundant surface oxygen vacancies and enhanced FA adsorptivity of the former group. Finally, the present challenges and future prospects for TMO-based catalysts are discussed with respect to the catalytic oxidation of FA. This review is expected to offer valuable information to design and build high performance catalysts for the efficient degradation of volatile organic compounds.

To be support or promoter: the mode of introducing ceria into commercial V2O5/TiO2 catalyst for enhanced Hg0 oxidation

Ce-modified commercial vanadium-based catalysts are still in a rapid development stage in terms of optimizing Hg0 oxidation performance. Due to the universal property of ceria, it can act as either support or promoter to supported vanadium-based catalysts. However, the introduction mode of Ce on the Hg0 oxidation is still unclarified. Herein, introducing Ce to vanadium-based catalysts as a promoter (VCe/Ti) plays a more effective role in the Hg0 oxidation than only doping Ce into TiO2 support (V/CeTi). It is revealed that the strong interaction between V and Ce increases the orbital hybridization, and reduces the lowest unoccupied molecular orbital (LUMO) of V, which is conducive to adsorbing and activating HCl. The excellent performance of the VCe/Ti catalyst can be ascribed to its superior redox ability, stronger HCl adsorption capacity, abundant surface oxygen vacancies, and the redox equilibrium (Ce3+ + V5+ ↔ Ce4+ + V4+), which improves electron transfer, and thus the catalytic activity. This work provides the potential application of Ce-modified V-based catalysts for the simultaneous control of NOx and Hg0 in stationary sources.

Plasma-catalytic CO2 methanation over NiFen/(Mg, Al)Ox catalysts: Catalyst development and process optimisation

Plasma-assisted catalytic carbon dioxide (CO2) methanation is a promising approach to valorise CO2 under mild conditions, and the system requires rational design regarding both catalysts and processes to advance it towards practical applications. Herein, the bimetallic NiFen/(Mg, Al)Ox catalysts were developed for plasma-catalytic CO2 methanation, and the effect of atomic ratio of Ni and Fe and reduction temperature on the catalysts was investigated systematically. The findings show that a higher reduction temperature was beneficial to the formation of Ni3Fe alloy and abundant surface oxygen vacancies, and increased CO2 adsorption ability. As a result, the NiFe0.1/(Mg, Al)Ox-800 catalyst led to a good catalytic performance in the plasma-assisted catalysis with about 84.7% CO2 conversion and 100% methane (CH4) selectivity. In addition, this study also employed response surface methodology (RSM) to explore the optimisation of plasma-catalytic CO2 methanation for the first time. Results from RSM show that in the plasma-catalytic system the selective CO2 hydrogenation to CH4 was favoured by higher applied voltage, lower gas flow rate and higher gas ratio (H2: CO2).

Low-energy production of a monolithic catalyst with MnCu-synergetic enhancement for catalytic oxidation of volatile organic compounds

Producing a low-cost catalyst by a low-cost method is one of the hottest topics in the field of catalytic oxidization of volatile organic compounds (VOCs). In this work, a catalyst formula with a low-energy requirement was optimized in the powdered state, and verified in the monolithic state. An effective MnCu catalyst was synthesized at a temperature as low as 200 °C. Removals were all bigger than 88% for toluene, ethyl acetate, hexane, formaldehyde, and cyclohexanone at a low temperature of 240 °C. The MnCu catalyst was then loaded on a honeycomb cordierite, which was also effective for toluene removal at 240 °C. After characterizations, active phases were Mn3O4/CuMn2O4 in both the powdered and monolithic catalysts. The enhanced activity was attributed to balanced distributions of low-valence Mn and Cu, as well as abundant surface oxygen vacancies. The obtained catalyst is produced by low energy and effective at low temperature, which suggests a perspective application.

CO2 Hydrogenation to Methanol over a Pt-Loaded Molybdenum Suboxide Nanosheet with Abundant Surface Oxygen Vacancies

Hydrogenation of carbon dioxide (CO2) using CO2-free hydrogen (H2) to produce methanol (CH3OH) is a promising reaction that can alleviate both carbon emissions and the dependence on fossil fuels. Nonstoichiometric molybdenum suboxide coupled with Pt nanoparticles (NPs) acts as a promising catalyst for this reaction, in which surface oxygen vacancies (VO) and the redox ability of Mo in molybdenum suboxide are the keys to transforming CO2 into the CO intermediate and further to afford CH3OH. In this study, a series of molybdenum oxides with different morphologies, including bulk, nanosheet, nanobelt, and rod morphologies, are used as catalysts, and the effects of particle morphologies on the catalytic performance toward CO2 hydrogenation are examined. A Pt-loaded molybdenum suboxide nanosheet (Pt/HxMoO3–y(Sheet)) with a high specific surface area affords 1.35 times greater CO2 conversion and CH3OH yield in liquid-phase CO2 hydrogenation compared with the corresponding bulk analog under relatively mild reaction conditions (total 4.0 MPa, 200 °C). Experiments and comprehensive analyses, including X-ray diffraction and in situ X-ray absorption fine structure studies, reveal that the enhanced activity of Pt/HxMoO3–y(Sheet) is attributable to a high concentration of surface-exposed VO sites, which are introduced in the (010) plane during the H2 reduction due to the high surface-to-volume ratio of the nanosheet-structured MoO3. In addition, the nanosheet-structured catalyst exhibits better reusability because of its antiaggregation behavior for Pt NPs compared with the conventional bulk analog.

A mesh cladding-structured Sr-doped LaFeO3/Bi4O5Br2 photocatalyst: Integration of oxygen vacancies and Z-scheme heterojunction toward enhanced CO2 photoreduction

Solar-driven conversion of CO2 into beneficial chemical fuels using photocatalysts is a sustainable approach for obtaining renewable energy. However, the poor photoabsorption, low charge separation efficiency, and sluggish interfacial reaction due to a paucity of active sites limit the photocatalytic activity. Herein, a mesh cladding structure of Sr-doped LaFeO3/Bi4O5Br2 (Sr-LFO/BOB) Z-scheme heterojunction with abundant surface oxygen vacancies (OVs) is developed to improve the CO2 photoreduction. Sr doping in LFO introduce OVs, which captures more photoinduced electrons contributing to the surface adsorption of CO2 molecules and narrows the LFO band gap extending the light absorption range to the whole visible spectrum. Particularly, the unique mesh cladding heterostructure composed of Sr-LFO particles wrapped with BOB nanowires provides ample Z-scheme charge-transfer pathways at the Sr-LFO/BOB and sufficiently exposes Sr-LFO surface for CO2 adsorption. Benefiting from the OVs and design of Z-scheme, the optimized photocatalyst (0.05Sr-LFO/BOB(2)) with appropriate Sr doping (5%) and BOB content demonstrates a considerable CH4 generation of 10.14 μmol g−1, which is approximately 48.3-fold higher than that of the pristine LFO. This study provides an insight into the design and fabrication of high-performance perovskite oxide-based photocatalysts by constructing a Z-scheme heterojunction with abundant active sites for CO2 photoreduction.

Efficient degradation of ciprofloxacin by activated peroxymonosulfate using OV-rich NiCo4-LDH: Insights into radical production pathway and catalytic mechanism

In this study, the NiCo4-LDH with abundant surface oxygen vacancies (SOVs) was synthesized by a simple solvent thermal method, and was used to activate peroxymonosulfate (PMS) through heterogenous catalysis for ciprofloxacin (CIP) degradation. The OV-rich NiCo4-LDH/PMS system exhibited excellent CIP removal efficiency and rapid kinetics, as 95.0 % of the CIP was degraded within 10 min and the COD removal rate was 71.2 %. SO4•−, •OH, O2•− and 1O2 were involved in the degradation of CIP, with O2•− contributing the most, followed by SO4•−, •OH and 1O2. Ethanol, as solvent, could modulate the intrinsic electron properties and produce abundant OVs on the surface of NiCo4-LDH, which enhanced the generation of O2•−. This study shed new light on the skillful design and application of heterogeneous catalysts for environmental remediation.

Insights into the enhanced hydrogen adsorption on M/La2O3 (M = Ni, Co, Fe).

Lanthanum oxide (La2O3) possesses superior reactivity during catalytic hydrogenation, but the intrinsic activity of La2O3 toward H2 adsorption and activation remains unclear. In the present work, we fundamentally investigated hydrogen interaction with Ni-modified La2O3. Hydrogen temperature programmed desorption (H2-TPD) on Ni/La2O3 shows enhanced hydrogen adsorption with a new hydrogen desorption peak at a higher temperature position compared to that on the metallic Ni surfaces. By systematically exploring the desorption experiments, the enhanced H2 adsorption on Ni/La2O3 is due to the oxygen vacancies formed at the metal-oxide interfaces. Hydrogen atoms transfer from Ni surfaces to the oxygen vacancies to form lanthanum oxyhydride species (H-La-O) at the metal-oxide interfaces. The adsorbed hydrogen at the metal-oxide interfaces of Ni/La2O3 results in improved catalytic reactivity in CO2 methanation. Furthermore, the enhanced hydrogen adsorption on the interfacial oxygen vacancies is ubiquitous for La2O3-supported Fe, Co, and Ni nanoparticles. Benefiting from the modification effect of the supported transition metal nanoparticles, the surface oxyhydride species can be formed on La2O3 surfaces, which resembles the recently reported oxyhydride observed on the reducible CeO2 surfaces with abundant surface oxygen vacancies. These findings strengthen our understanding of the surface chemistry of La2O3 and shed new light on the design of highly efficient La2O3-based catalysts with metal-oxide interfaces.

A-site defective La2-xCuO4 perovskite-type oxides for efficient oxidation of cyclohexylbenzene.

Phenol production through the oxidation of cyclohexylbenzene (CHB) and the subsequent decomposition of tertiary hydroperoxide has attracted more and more attention. In this study, defective La2-xCuO4 perovskite-type oxide catalysts with tunable A-site deficient structures and abundant surface oxygen vacancies were developed for the liquid phase oxidation of CHB to produce cyclohexylbenzene-1-hydroperoxide (CHBHP). By tuning the amount of A-site La ions in the perovskite structure, more surface oxygen vacancies and Cu+ species were formed in catalysts. The A-site-deficient La1.9CuO4 catalyst achieved significant catalytic efficiency along with a high CHBHP yield of 27.6% at 48.6% CHB conversion under reaction conditions (i.e., 120 °C and 12 h), outperforming those of other transition metal-based catalysts previously reported in the literature. A series of structural characterization methods and catalytic reactions highlighted the crucial roles of surface oxygen vacancies and metal La and Cu ions in the oxidation process. It was revealed that metal ions favored CHB adsorption and activation, while surface oxygen vacancies facilitated the creation of active adsorbed oxygen species. The present study offers an opportunity for the future design of new high-efficiency heterogeneous catalyst systems for CHB oxidation to obtain phenol.

Green structure orienting and reducing agents of wheat peel extract induced abundant surface oxygen vacancies and transformed the nanoflake morphology of NiO into a plate-like shape with enhanced non-enzymatic urea sensing application.

Researchers are increasingly focusing on using biomass waste for green synthesis of nanostructured materials since green reducing, capping, stabilizing and orientation agents play a significant role in final application. Wheat peel extract contains a rich source of reducing and structure orienting agents that are not utilized for morphological transformation of NiO nanostructures. Our study focuses on the role of wheat peel extract in morphological transformation during the synthesis of NiO nanostructures as well as in non-enzymatic electrochemical urea sensing. It was observed that the morphological transformation of NiO flakes into nanoplatelets took place in the presence of wheat peel extract during the preparation of NiO nanostructures and that both the lateral size and thickness of the nanostructures were significantly reduced. Wheat peel extract was also found to reduce the optical band gap of NiO. A NiO nanostructure prepared with 5 mL of wheat peel extract (sample 2) was highly efficient for the detection of urea without the use of urease enzyme. It has been demonstrated that the induced modification of NiO nanoplatelets through the use of structure-orienting agents in the wheat peel has enhanced their electrochemical performance. A linear range of 0.1 mM to 13 mM was achieved with a detection limit of 0.003 mM in the proposed urea sensor. The performance of the presented non-enzymatic urea sensor was evaluated in terms of selectivity, stability, reproducibility, and practical application, and the results were highly satisfactory. As a result of the high surface active sites on sample 2, the low charge transfer resistance, as well as the high exposure to the surface active sites of wheat peel extract, sample 2 demonstrated enhanced performance. The wheat peel extract could be used for the green synthesis of a wide range of nanostructured materials, particularly metal/metal oxides for various electrochemical applications.

Enriched Surface Oxygen Vacancies of Fe2(MoO4)3 Catalysts for a PDS-Activated photoFenton System

The environmentally benign Fe2(MoO4)3 plays a crucial role in the transformation of organic contaminants, either through catalytically decomposing oxidants or through directly oxidizing the target pollutants. Because of their dual roles and the complex surface chemical reactions, the mechanism involved in Fe2(MoO4)3-catalyzed PDS activation processes remains obscure. In this study, Fe2(MoO4)3 was prepared via the hydrothermal and calcine method, and photoFenton degradation of methyl orange (MO) was used to evaluate the catalytic performance of Fe2(MoO4)3. Fe2(MoO4)3 catalysts with abundant surface oxygen vacancies were used to construct a synergistic system involving a photocatalyst and PDS activation. The oxygen vacancies and Fe2+/Fe3+ shuttle played key roles in the novel pathways for generation of •O2-, h+, and 1O2 in the UV-Vis + PDS + FMO-6 photoFenton system. This study advances the fundamental understanding of the underlying mechanism involved in the transition metal oxide-catalyzed PDS activation processes.

SnO2 grains with abundant surface oxygen vacancies for the Ultra-sensitive detection of NO2 at low temperature

N-type metal oxide semiconductors are widely used in the field of gas sensors, but achieving high sensor response at low temperatures with low concentrations is challenging. In this paper, we report a high-performance gas sensor for NO2. SnO2 grains with different sizes and oxygen vacancies were prepared by a simple hydrothermal method followed by high-temperature calcination, and the electronic and chemical properties of the SnO2 grains were significantly changed. The results demonstrate that the sensor prepared from SnO2 grains hydrothermally grown at 180 °C has the optimal gas sensing performance with a response up to 4358.8 for 1 ppm NO2 at a low temperature of 80 °C, a rapid response recovery (7 s), and a detection limit down to 9 ppb. Together with some series characterization, an empirical factor F between the sensor response and the influencing factors is proposed. In addition, through experimental and density generalization studies, the oxygen vacancies are distinguished into surface oxygen vacancies and subsurface oxygen vacancies. The dominance of the surface oxygen vacancies in dictating the gas response is demonstrated. The excellent sensor characteristics demonstrated and the elucidation of the gas-sensitive mechanism provide a clear framework for the preparation of high-performance gas sensors.