Oxygen Vacancy Levels Research Articles

Refining catalytic oxidation of volatile organic compounds over Gd-Sr-Co perovskite-based oxides fabricated via viscous mixture induction: Unveiling the crucial factors influencing catalytic activity

A series of Gd-Sr-Co perovskite-based oxides have been successfully synthesized by thermally driving viscous mixture, wherein only very trace amounts of water need and the metal salts powders do not need to be thoroughly mixed. By the characterization of XRD, XPS, EPR, and Raman, the levels of oxygen vacancies, lattice oxygen, and adsorbed oxygen in the catalyst are controlled by varying the amount of Sr doping. Unlike traditional conclusions, we found that the catalytic activities of the catalysts did not enhance with the increase in the contents of adsorbed oxygen and oxygen vacancies. H2-TPR and O2-TPD confirmed that the migration of lattice oxygen in catalysts determined their activities. Comparative activity of individual catalysts was evaluated by catalytic oxidation of toluene. The best active catalyst also showed superior catalytic activity for the oxidation of acetone, ethyl acetate, and chlorobenzene. The effects of humidity and weight hourly space velocity on the stability of the catalyst were also evaluated. Catalyst’s surface structural changes in toluene oxidation were also analyzed by in-situ DRIFTS. This study provides a simple approach to tailor perovskite-based oxide structures, crucial for effective catalytic oxidation of VOCs.

Oxygen vacancy-suppression strengthened the internal electric field in ZnIn2S4/BiVO4 S-scheme heterojunction to boost photocatalytic removal of aqueous pollutants

The impact of internal electric field intensity (IEF) within step-scheme (S-scheme) heterojunctions is profound on photocatalytic performance. Furthermore, the presence of oxygen vacancies in the photocatalysts has a significant influence on their photocatalytic characteristics. Thus, a ZnIn2S4/BiVO4 S-scheme heterojunction was strategically engineered for photocatalytic degradation. The modulation of oxygen vacancy levels in the oxidation photocatalyst (OP) was utilized to adjust the IEF within the S-scheme heterojunctions. BiVO4 with controlled oxygen vacancies was synthesized using a simple approach, and the impact of oxygen vacancies on the charge transfer across the heterojunction was thoroughly examined. Subsequently, various characterization results, verified that the IEF in the heterojunction with suppressed oxygen vacancy levels (10 %BV-600) was stronger, while those with elevated vacancy levels (10 %BV-400) showed weaker IEFs. Comprehensive results confirmed that the S-scheme heterojunction is formed between ZnIn2S4 and BiVO4. Under visible irradiation, the 10 %BV-600 sample demonstrated remarkable photocatalytic activity, achieving a 96.4 % degradation of methyl orange within 60 min. Intriguingly, the rate constants for methyl orange removal for the 10 %BV-600 sample were approximately 3 and 27 times greater than those of the individual ZnIn2S4 and BiVO4, respectively. Moreover, the photocatalytic performance of the 10 %BV-400 sample, which had a lower IEF, was inferior to that of the 10 %BV-600 sample. These results underscore the superior photocatalytic capabilities of heterojunctions with a strengthened IEF due to suppressing oxygen vacancy. This work provides insights into the role of oxygen vacancy in regulating IEF intensity in heterojunctions.

One-step thermal oxidation synthesis of carbon-doped TiO2 with enhanced photocatalytic activity using CO2 as the carbon source

The study proposed a simplified carbon doping synthesis strategy to enhance the photocatalytic activity of titanium dioxide (TiO2). Utilizing CO2 gas as the carbon source, the material was directly synthesized onto a titanium substrate through a one-step thermal oxidation method. Raman and XPS analyses indicated that with the increase in CO2 partial pressure, the influence of the carbon source was amplified, resulting in carbon doping in a graphite-like structure and the induction of oxygen vacancies. Electrochemical impedance spectroscopy and UV–vis spectra demonstrated that the introduced carbon species acted as a photosensitizer, augmenting the transfer of photogenerated carriers. Photoluminescence spectra suggested that oxygen vacancies could enhance the non-radiative scattering of photogenerated carriers. These two effects synergistically improved the photocatalytic activity of TiO2 significantly, although the degree of enhancement was dependent on the optimized ratio of carbon content to oxygen vacancy content. Only with optimal carbon content and oxygen vacancy levels could the undesired radiative recombination of photogenerated carriers be prevented, ensuring that the energy derived from visible light was effectively utilized to drive chemical reactions. Under these optimal conditions, the TC-O5 and TC-O10 samples exhibited excellent photocatalytic degradation performance of methyl orange under visible light, with degradation rates of 86.27% and 82.54%, respectively, and displayed outstanding cycling stability, with the degradation rate remaining above 90% for three cycles. This method proved to be simple, efficient, and easily operable, offering significant advantages for industrial-scale preparation.

Improved high voltage operation of amorphous In–Ga–Zn–O thin film transistor by carrier density enhancement

We report on improved high voltage operation of amorphous-In–Ga–Zn–O (a-IGZO) thin film transistors (TFTs) by increasing carrier density and distributing the high bias field over the length of the device which utilizes an off-set drain structure. By decreasing the O2 partial pressure during sputter deposition of IGZO, the channel carrier density of the high voltage a-IGZO TFT (HiVIT) was increased to ∼1018 cm−3. Which reduced channel resistance and therefore the voltage drop in the ungated offset region during the on-state. To further decrease the electric field in the offset region, we applied Ta capping and subsequent oxidation to locally increase the oxygen vacancy levels in the offset region thereby increasing local carrier density. The reduction of the drain field in the offset region from 1.90 V μm−1 to 1.46 V μm−1 at 200 V drain voltage, significantly improved the operational stability of the device by reducing high field degradation. At an extreme drain voltage of 500 V, the device showed an off-state current of ∼10−11 A and on-state current of ∼1.59 mA demonstrating that with further enhancements the HiVIT may be applicable to thin-film form, low leakage, high voltage control applications.

Tuning interfacial oxygen vacancy level of bismuth oxybromide to enhance photocatalytic degradation of bisphenol A

Oxygen vacancies (OVs) have garnered significant interest for their role as active sites, enhancing the catalytic efficiency of various catalysts. Despite their widespread application in environmental purification processes, the generation of OVs conventionally depends on high-temperature conditions and strong reducing agents for the extraction of surface partial oxygen atoms from catalysts. In this work, bismuth oxybromide (BiOBr) nanosheets with varying levels of OVs were synthesized via a simple and effective solvothermal method. This novel method affords precise control over the conduction band (CB) and valence band (VB) positions of BiOBr. The presence of different OVs exhibited varying photocatalytic efficiencies in the degradation of bisphenol A (BPA) under visible light irradiation, with higher levels of OVs resulting in superior photocatalytic performance. Furthermore, radical scavenger experiments demonstrated that superoxide oxides (O2•−) and holes (h+) were the primary reactive oxygen species for BPA degradation. Additionally, BiOBr-OVs exhibited excellent anti-interference and stability in water matrices containing diverse inorganic anions and organic compounds. This work provides a simple and effective approach for the fine-regulating of catalysts through interfacial defect engineering, paving the way for their practical application in environmental decontamination.

Rose-like NiCo2O4 with Atomic-Scale Controllable Oxygen Vacancies for Modulating Sulfur Redox Kinetics in Lithium-Sulfur Batteries.

The long-term stability of Li-S batteries is significantly compromised by the shuttle effect and insulating nature of active substance S, constraining their commercialization. Developing efficient catalysts to mitigate the shuttle effect of lithium polysulfides (LiPSs) is still a challenge. Herein, we designed and synthesized a rose-like cobalt-nickel bimetallic oxide catalyst NiCo2O4-OV enriched with oxygen vacancies (OV) and verified the controllable synthesis of different contents of OV. Introducing the OV proved to be an efficient approach for controlling the electronic structure of the electrocatalyst and managing the absorption/desorption processes on the reactant surface, thereby addressing the challenges posed by the LiPS shuttle effect and sluggish transformation kinetics in Li-S batteries. In addition, we investigated the effect of OV in NiCo2O4 on the adsorption capacity of LiPSs using adsorption experiments and density functional theory (DFT) simulations. With the increase in the level of OV, the binding energy between the two is enhanced, and the adsorption effect is more obvious. NiCo2O4-OV contributes to the decomposition of Li2S and diffusion of Li+ in Li-S batteries, which promotes the kinetic process of the batteries.

Photoexcitation assisted oxygen vacancy for enhancing nitrogen fixation with Fe-CeO2

Photoexcitation assisted oxygen vacancy for enhancing N2 fixation was investigated with Fe-CeO2 as photocatalysts. Fe substituted doping of CeO2 promoted the formation of oxygen vacancies (Vo). 5 % Fe-CeO2 exhibited the highest Vo concentration with photocatalytic nitrogen fixation efficiency of 176 μmol·g−1·h−1. The oxygen vacancy could induce the formation of the oxygen vacancy level, which could reduce the band gap energy, attract electrons, and hinder the electron hole recombination. More importantly, the oxygen vacancy level could be used as a springboard to reduce the energy required for N2 activation. In addition, calcination and acid-wash were used to regulate the concentration of surface oxygen vacancies (Vo-s) and bulk oxygen vacancies (Vo-b), respectively. The results showed that acid-wash only reduced the Vo-s concentration, while calcination reduced both the Vo-s and the Vo-b concentration, and the high concentration of Vo and Vo-s was beneficial for photocatalytic nitrogen fixation. The regulation strategy of Vo had guiding significance for improving the photocatalytic performance of metal oxide photocatalysts.

Oxygen vacancy–enriched Y2O3 nanoparticles having reactive facets for selective sensing of methyl ethyl ketone peroxide explosive

Methyl ethyl ketone peroxide (MEKP) is a highly-reactive and exothermically unstable compound that has caused many explosion accidents. Therefore, a simple, rapid and sensitive method for online monitoring of MEKP is urgently required to address such problems. Herein, yttrium oxide (Y2O3) nanoparticles with different levels of oxygen vacancies (OV) and exposed reactive facets were synthesised at different calcination temperatures. Gas-sensing studies revealed that a cataluminescence (CTL) sensor based on Y2O3 nanoparticles annealed at 600 °C achieved the highest response to MEKP with a limit of detection of 1 ppb at a working temperature of 80 °C. Density functional theory calculations indicated the {222} and {440} facets in Y2O3 as the most reactive sites towards MEKP. Moreover, the introduction of OV into the exposed reactive facets can considerably enhance the adsorption of O2 and MEKP on Y2O3 nanoparticles. Further sensing mechanism studies unveiled the singlet and triplet excited states of acetaldehyde produced by the catalytic oxidation of MEKP as the possible luminophores for CTL emission. This study not only offers a promising method for online monitoring of MEKP but also offers deep insights into the improved sensing mechanism caused by OV and exposed reactive facets, thus providing guidance for designing high-performance CTL sensors.

The Underlying Catalytic Role of Oxygen Vacancies in Fatty Acid Methyl Esters Ketonization over TiOx Catalysts.

Recently, interest in converting bio-derived fatty acid methyl esters (FAMEs) into added-value products has significantly increased. The selectivity of ketonization reaction in the conversion of the FAMEs has significantly hampered the efficiency of this process. Herein, this work reports the preparation of catalysts with different levels of oxygen vacancies while the crystal phase remained unchanged. The catalyst with the highest level of oxygen vacancy exhibited the maximum selectivity. The density functional theory (DFT) simulation showed an increase in interatomic distances leading to the formation of frustrated Lewis pairs (FLPs) upon the creation of oxygen vacancies. The surface measurements, type and density of acid sites of the catalysts, showed that the Lewis acid sites enhanced the selectivity for ketone production; while Bronsted acid sites increased the formation of by-products. Moreover, the ketone formation rate was directly proportional to acid density. The findings of this research provide a different approach for catalyst design, based on defects engineering and their effect on the surface activity, which could be used for enhancing the catalytic performance of novel metal oxides.

Insight into the photoluminescence and morphological characteristics of transition metals (TM = Mn, Ni, Co, Cu)-doped ZnO semiconductor: a comparative study

In this work, undoped and transition metal (TM = Mn, Ni, Co, Cu)-doped ZnO thin films were grown on Si substrate using the ultrasonic spray pyrolysis technique, adhering to the same deposition conditions to compare their morphological and photoluminescent characteristics. X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and Photoluminescence (PL) spectroscopy were used to investigate the chemical composition, morphology, and luminescence properties, respectively. XPS results indicate that Mn and Ni ions have bivalent and trivalent electronic states coexisting in the ZnO lattice, Cu ions have both monovalent and bivalent states, and Co ions have only bivalent states. Besides, there is a considerable increase in the level of oxygen vacancies observed upon TM doping. The topographic and phase-contrast AFM images, supported by their associated statistical parameters and mean height distribution histograms, reveal that TM doping increases the tendency for crystalline grains to coalesce in 3D, resulting in a more roughened surface, larger grains with prominent boundaries, increased porosity, and an inhomogeneous height distribution. PL spectra of TM-ZnO show a broadening of the ZnO band gap accompanied by different luminescence behavior compared to pure ZnO regarding both UV and visible emissions. CuZnO is characterized by a green luminescence, CoZnO and MnZnO by a red luminescence, and ZnO and NiZnO by a broad visible luminescence. The possible mechanism for defect luminescence in each TM-ZnO sample was systematically investigated. The chromaticity color coordinates of the PL emissions show that the films provide different color regions well distributed on the CIE chromaticity diagram. The findings regarding the coexistence of two valence states of TM doping, the level of oxygen vacancies, the grain coalescence process, and the luminescence characteristics are carefully correlated and discussed herein.

Combinatorial tuning of structure and optoelectronic properties of Zn-Ga-O thin films for deep ultraviolet photodetection

Ternary complex oxides exhibit strong compositional dependence on their structure and functionalities. While the profound impact of the cation stoichiometry on the physical properties of ZnGa2O4 is widely recognized, how it affects the ultraviolet photodetection behavior remains not clear. Here we apply a combinatorial pulsed laser deposition technique to establish graded composition in ZnxGa1-xO (0 ≤ x ≤ 1) across a 2-inch sapphire substrate. In combination with structural and optical characterizations, a systematic investigation of the compositional effect on the phase, crystallinity and bandgap for the ZnxGa1-xO system is performed, and their further impact on the photodetection performance is compared by fabricating multiple metal–semiconductor-metal (MSM) photodetectors based on the graded ZnxGa1-xO films. Decent photodetection behavior is seen for the photodetectors with x ≤ 0.33, above which the performance is largely limited by the conductive phase formation. An optimized compositional range of x = 0.18–0.27 is identified to deliver the best device performance, which includes a responsivity of 12.88 A/W and a photo-to-dark current ratio of 2.8 × 108. This slight zinc deficiency is considered beneficial for the formation of moderate level of oxygen vacancies or antisite defects that boosts carrier transport. This study sheds light on the composition-dependent evolution of structure and properties in ternary ultrawide-bandgap semiconductors for high-performance ultraviolet photodetection.

Dipole behavior in thin film heterostructure composed of Er-doped SnO2 and GaAs: Influence of polarization bias, temperature and stray light

The heterostructure system GaAs/SnO2 is built by resistive evaporation of Er-doped SnO2 powder on the top of GaAs semi-insulating substrate. The SnO2 powder comes from the drying of SnO2 sol-gel solution. The possible formation of dipoles in this heterostructure is investigated by the thermally stimulated depolarization current (TSDC) technique, and the possibilities for dipole formation are explored, such as the EL2 defect in the GaAs side, oxygen vacancies and Er ions in the SnO2 layer. The dipole relaxation activation energies are found in the range 0.2 eV to 0.3 eV, in good agreement with the ionization energies of these defects. The main TSDC bands: 213 meV with peak of −298 pA, for positive bias, and 218 meV with peak of 128 pA for negative bias, are modified by stray (room) light, which may correspond to the second ionization level of oxygen vacancies in SnO2, which are excited by the room lights and do not return to the original orientation.

A 3D-printed millifluidic device for triboelectricity-driven pH sensing based on ZnO nanosheets with super-Nernstian response

This paper suggests a straightforward and rapid fabrication method applying the integration of 3D printing and triboelectric nanogenerator (TENG) technologies to realize milli/microfluidic multipurpose devices. The proposed liquid-solid TENG device is served as an energy harvester and sensor at the same time with flexibility in operation modes. Accordingly, an innovative ethylene vinyl acetate (EVA)-made millifluidic pH sensor is fabricated based on zinc oxide nanosheets as a showcase of the functional adaptability of the ubiquitous device, and its performance is analyzed and compared with contemporary electrochemical pH sensors. High crystallinity of the nanosheets with an incline to (103) orientation in parallel with high levels of oxygen vacancies provides capacity for surface charge accumulation at the nanosheet-aqueous solution interface and the ensuing ultrahigh sensitivity of the triboelectric sensor. The millichannel is optimized in terms of sensing surface area, flow rate, and hydrophobicity properties by opting for appropriate geometry, TENG operation modes, and materials. Despite the finding that quasi-single-electrode mode TENG experiences a higher response (8.12 × Nernst limit) in comparison with quasi-contact-separation configuration (4.14 × Nernst limit), the latter enjoys superior linearity, stability, repeatability, reproducibility, and reliability characteristics corresponding to R2 of 98.93%, drift rate of 13 mV/h, relative standard deviation (RSD) of 1.23% in third hysteresis loop, 2.24%, and maximum standard error of ±0.2 pH units across multiple trials, respectively, in a wide pH range of 2–13. Time- and cost-effectiveness, user-friendliness, self-powering, portability, and biocompatibility of the device could be asserted as considerable advantages to open the door for feasibly realizing the new generation of real-life and point-of-care devices.

Regulation of crystallinity and defects on CoNiRuOx nanocages for enhanced oxygen evolution reaction

Amorphous/crystalline (a/c) metal-oxide nanocages with defects are promising materials towards the realization of efficient water electrocatalysis. In this work, we not only constructed a Ru doping porous nanocages (PNCs) structure, but also studied the relationship between both crystallinity of a/c degrees and oxygen vacancy (Ovac) levels in a/c CoNiRuOx PNCs catalysts and their catalytic properties. Owing to the rich mass transfer channels, optimized crystallinity and Ovac levels, and efficient catalytic model of “Ni-O-Co-O-Ru-O-Ni” for well-distributed electron density, the optimized CoNiRuOx-2 PNCs exhibited the alkaline oxygen evolution reaction (OER) properties with an overpotential of 245 mV at 10 mA cm−2 and remarkable stability for 60 h, surpassing other series of a/c CoNiRuOx and benchmark RuO2 catalysts. In addition, the electrode couple a/c CoNiRuOx-2//Pt/C only need an ultralow voltage of 1.54 V to drive overall water splitting. This work proposed the introduction and quantitative control on both a/c heterostructure degree and Ovac level, offering guidelines for OER catalysis.

Oxygen vacancies facilitated photocatalytic detoxification of three typical contaminants over graphene oxide surface embellished BiOCl photocatalysts

A conventional solvothermal way was used to synthesize graphene oxide (GO)/BiOCl photocatalytic nanomaterials with enhanced photocatalytic performance. Due to the introduction of GO, there are intuitive changes in morphology, indicating that GO can guide the growth of GO/BiOCl catalysts. The results of X-ray photoelectron spectroscopy (XPS) and Raman show that a strong chemical interaction occurs around GO and BiOCl. The results of trapping experiments show that O2– is the major active species. XPS analysis confirms that the 0.75% GO/BiOCl produces the highest level of oxygen vacancies (OVs). All the GO/BiOCl photocatalysts possess better photocatalytic properties than the neat BiOCl, and 0.5% GO/BiOCl exhibits the highest photoactivity. The photocatalytic activity of 0.5% GO/BiOCl composite for detoxification of rhodamine B (RhB) and tetracycline (TC) under visible light illumination is 4.6 and 6.3 times of that on the reference BiOCl, separately, the photocatalytic activity of 0.5% GO/BiOCl for detoxication of perfluorooctanoic acid (PFOA) is 1.25 times of that of the single BiOCl under UV light illumination, which can be credited to the high separation rate of carriers and the strong interaction between GO and BiOCl. Combining with the results, a separation and transfer mechanism of carriers was revealed.

Outstanding High Field‐Effect Mobility of 299 cm2 V−1 s−1by Nitrogen‐Doped SnO2Nanosheet Thin‐Film Transistor

AbstractRecord high field‐effect mobility (µFE) thin film transistors (TFTs) based on 5 and 7 nm thickness SnON channel layer is reported. The SnON TFT device with 7.6% nitrogen content achieves a record high µFEof 299 cm2 V−1 s−1at 7 nm thickness and 277 cm2 V−1 s−1at 5 nm thickness, compared to SnO2with µFEof 211 cm2 V−1 s−1. At the same 5 nm quasi‐2D channel thickness, this µFEof nanocrystalline SnON transistor is comparable to single crystalline Si and InGaAs metal oxide semiconductor field‐effect transistor (MOSFET) and also higher than the phonon‐scattering‐limited 2D MoS2FET. From the principle of quantum‐mechanical calculation, the high µFEof nanosheet SnON TFT is due to lower effective mass of electrons, 0.29 m0in the conduction band in contrast to 0.41 m0of SnO2. SnON can reduce the defect trap densities by introducing non‐oxide anions where the valence band can be controlled to remove or passivate the oxygen vacancy levels by substitutional alloying with nitrogen anions to circumvent instability, increase on‐current (ION) and improve the µFE. It is highly expected that the high performance quasi‐2D nanosheet SnON TFTs will be utilized in embedded DRAM and monolithic 3D integrated circuits (ICs).

Improved photoelectrocatalytic performances over electrochemically reduced WO3: implications of oxygen vacancies.

The introduction of rich oxygen vacancies into the WO3 lattice has been achieved through a facile and environmentally friendly route of electrochemical reduction. It has been shown that the electrochemical reduction treatment significantly increases the charge separation efficiency from 37.44% to 65.44% at 0.74 V vs. NHE, and charge injection efficiency from 15.06% to 58.20% at 0.74 V vs. NHE, leading to enhanced PEC performances for synergetic 4-CP degradation and H2 evolution. Various characterization results well demonstrated that the formation of W5+ species resulting from the introduction of oxygen vacancies in the WO3 lattice raises the Fermi level closer to the energy level of oxygen vacancies. The raised Fermi level achieves the substantial electron trap effect of the oxygen vacancies and further bends upward the band at the semiconductor/electrolyte interface, both of which play dominant roles in the effective interfacial transfer and separation of the photogenerated charges for enhanced PEC performances.

Oxygen vacancy levels mediated photophysical pathways of NIR-II responsive broadband upconversion

The photon upconversion (UC) is the process that has been known for a long time. Especially, lanthanide-based UC materials recently have attracted huge interest of scientific community due to their narrow visible emission bands upon near-infrared (NIR) excitation. However, the excitation in the high excitation power of NIR can cause highly bright and broad emission (B-UC). Such explosive B-UC was distinct at high excitation condition with UC wavelength encompassing the entire visible range. Previously, the proposed model of B-UC origination includes heat, multi-photon absorption, and accumulated thermal energy transfer. In this article, we will show various experimental and theoretical evidence supporting the idea that B-UC arises from photophysical pathways. Here, the key experimental evidence for photophysical pathways model of B-UC is to measure B-UC in the low-temperature environment (22 K). In addition, the density functional theory was used to regenerate energy levels which would be compared to the absorption spectral bands in Er2O3. As a result, we are confident of an electron tunneling model from 2P3/2 of Er3+ to oxygen vacancy level (VO) of Er2O3. Then, VO electrons are sequentially excited to the conduction band of Er2O3 by energy transfer from 4F9/2 of Er3+. Finally, the electrons return to the VO of Er2O3 with concomitant B-UC.

Pair vacancy defects in β-Ga2O3 crystal: Ab initio study

Despit many studies dedicated to the defects in β-Ga2O3, information about formation processes of complex “donor-acceptor” defects in β-Ga2O3 and their energetic characteristics is still very scarce. Meanwhile, complex defects, such as pair vacancies, are often indicated as electrically active centers that can play the role of acceptor defects. We have carried out comparative ab initio study of formation energies, as well as optical and thermodynamic transition levels of single and pair vacancies in β-Ga2O. It was confirmed that single gallium and oxygen vacancies are deep acceptors and deep donors, respectively. In this case, the optical transition levels of single gallium and oxygen vacancies are located in such a way that electrons can easily pass from donors to acceptors. Unlike single vacancies, a pair vacancy has a neutral state due to the location of the acceptor levels above the donor ones. However, if pair vacancies were thermally excited, the transition levels are shifted to ∼2.0 eV above the top of the valence band, at which the recombination of electrons and holes become possible, as is observed in the case of single vacancies.

Enhanced activation of peroxymonosulfate using ternary MOFs-derived MnCoFeO for sulfamethoxazole degradation: Role of oxygen vacancies

Herein, ternary metal-organic frameworks (MOFs)-derived MnCoFeO with different levels of oxygen vacancies (Ov) were designed by adjusting the doping amount of Mn and employed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. The MnCoFeO-2 with the largest Ov content exhibited the highest SMX degradation efficacy. Almost 100% of SMX was removed within 5 min using the MnCoFeO-2/PMS system. The reaction rate constant (kobs) was 1.7321 min−1, which was 4.1 times that of CoFeO (0.4195 min−1). Both the SO4•− and 1O2 were the dominant reactive oxygen species. Significantly, the relationship among Ov, radical pathways, and non-radical pathways was explored for the first time. The results showed that Ov could regulate the radical pathways by promoting the adsorption of PMS onto MnCoFeO-2. Ov was positively correlated with 1O2 (P < 0.05) and facilitated the direct electron transfer. The superior catalytic activity of MnCoFeO was attributed to the Fe, Co, Mn active sites, Lewis basic sites and Ov in MnCoFeO. Mn(II) not only contributed to the formation of Ov, but also facilitated the reduction of Fe(III). Additionally, Ov was mainly concentrated near the low-valent metal ions, thus the synergistic effect between the metal active sites and Ov promoted the activation of PMS.