Oxygen Vacancy Piezoelectric Nanosheets Constructed by a Photoetching Strategy for Ultrasound "Unlocked" Tumor Synergistic Therapy.

Piezoelectric dynamic therapy (PzDT) is an effective method of tumor treatment by using piezoelectric polarization to generate reactive oxygen species. In this paper, two-dimensional Cu-doped BiOCl nanosheets with surface vacancies are produced by the photoetching strategy. Under ultrasound, a built-in electric field is generated to promote the electron and hole separation. The separated carriers achieve O2 reduction and GSH oxidation, inducing oxidative stress. The bandgap of BiOCl is narrowed by introducing surface oxygen vacancies, which act as charge traps and facilitate the electron and hole separation. Meanwhile, Cu doping induces chemodynamic therapy and depletes GSH via the transformation from Cu(II) to Cu(I). Both in vivo and in vitro results confirmed that oxidative stress can be enhanced by exogenous ultrasound stimulation, which can cause severe damage to tumor cells. This work emphasizes the efficient strategy of doping engineering and defect engineering for US-activated PzDT under exogenous stimulation.

Oxygen Vacancy-Enhanced Centrosymmetric Breaking of SrFeO3- x for Piezoelectric-Catalyzed Synthesis of H2O2.

Normally, only noncentrosymmetric structure of the materials can potentially be piezoelectric. Thus, it is limited in the field of piezoelectricity for the centrosymmetric structure of the material. In this work, the performance of piezoelectricity is successfully achieved from centrosymmetric SrFeO3- x by modulating oxygen vacancies, which have a surface piezoelectric potential up to 93 mV by using Kelvin-probe force microscopy (KPFM). Moreover, the piezoelectric effects of SrFeO3- x are also evaluated by piezoelectric catalytic effect and density functional theory calculations (DFT). The results show that the piezo-catalytic degradation of tetracycline reaches 96% after 75 min by ultrasonic mechanical vibration and the production of H2O2 by SrFeO3- x piezoelectric synthesis could reach 1821 µmol L-1. In addition, the DFT results indicate that the intrinsic effect of oxygen vacancies effectively promotes the adsorption and activation of O2 and H2O as well as intermediates and improves the piezoelectric catalytic activity. This work provides an effective basis for realizing the piezoelectricity of centrosymmetric materials and regulating the development of piezoelectric catalytic properties.

Conferring BiVO4 Nanorods with Oxygen Vacancies to Realize Enhanced Sonodynamic Cancer Therapy.

Owing to the high depth of tissue penetration, non-invasiveness, and controllability, ultrasound (US)-mediated sonodynamic therapy (SDT) has shown broad application prospects for tumor treatment. However, the electron-hole separation inefficiency of sonosensitizers and the tumor hypoxia remain two major challenges limiting the effect of SDT. Here, ultrafine photoetched bismuth vanadate (BiVO4 ) nanorods modified with DSPE-PEG2000 (PEBVO@PEG NRs) were fabricated to achieve in situ self-supply of oxygen (O2 ) and reactive oxygen species (ROS) for hypoxic tumor therapy. The photoetching approach could enhance the charge separation by inducing enriched oxygen vacancies on the surface of BiVO4 , thereby improving the generation efficiency of ROS and O2 . The PEBVO@PEG overcome the main obstacles of traditional sonosensitizers in the SDT process and show promising sonodynamic therapeutic effects, thus providing new strategies for improving the performance of sonosensitizer and hypoxic tumor elimination.

One-Step Prepared Water-Resistant Organic-Inorganic-Hybrid Perovskite Quantum Dots with Zn-Oxygen Vacancies for Attempts at Nitrogen Fixation.

Applying organic-inorganic hybrid perovskite quantum dots (PQDs) to photocatalytic nitrogen fixation is hindered long-term by the inherent instability in water and tedious preparations. Here, to realize PQD-catalyzed photocatalytic N2 reduction reaction (NRR), water-resistant PQDs are simply prepared through one-step electrospray synthesis in microseconds. During the fast electrospray, PQDs of Zn/PbO-doped methylammonium lead bromide (Zn/PbO/PC-Zn/MAPbBr3 , MA: CH3 NH3 ) are prepared and part-encapsulated by polycarbonate. The synthesis maintains good water resistance, whose restriction on charge transport is overcome skillfully. Simultaneously, substitution of Zn with Pb on water-resistant surface is also achieved, which fabricates new Zn-oxygen vacancies (Zn-OVs) with Zn/PbO-Zn/MAPbBr3 type I heterojunction. This facilitates efficient electron transfer from internal heterojunction interface of Zn/MAPbBr3 PQDs to the surface of Zn/PbO. Demonstrated by theoretical calculations, Zn-OVs promote chemisorption and polarization of N2 . In addition, s-electrons in exposed Zn become active due to changes of electron filling of Zn orbitals under OVs' co-doping. Thus, photocatalytic N2 reduction reaction catalyzed by organic-inorganic hybrid PQDs is first achieved in aqueous phase without sacrificial agents being added. This initiates possibilities for photocatalytic applications of organic-inorganic hybrid PQDs in aqueous phase.

A novel strategy to research the mechanism of rutile TiO2with excellent photocatalytic performance.

This study reported a novel method to obtain rutile TiO2with excellent photocatalytic activity for degradation of organic dyes. In this study, the concentrated HCl was selected as the inhibitor to make TiO2precursor hardly hydrolyzed at room temperature. And a certain amount of urea was added, which results in TiO2precursor hydrolyzed to produce rutile TiO2due to urea thermally decomposed into alkaline substances to neutralize the concentrated HCl. To further explore the mechanism of excellent photocatalytic performance of rutile TiO2, a series of experiments, characterizations, and DFT computations were carried out. Based on DFT computations and experimental results, it could be concluded that the introduction of surface oxygen vacancies was the main reason for the excellent photocatalytic performance of the samples, and the concentration of surface oxygen vacancies would affect the physical and chemical properties of rutile TiO2. Meaningfully, this unique and innovative work broke the traditional preconception of rutile TiO2and provided a theoretical possibility for rutile TiO2to be applied in other research fields.

Surface Engineering of g-C3 N4 by Stacked BiOBr Sheets Rich in Oxygen Vacancies for Boosting Photocatalytic Performance.

BiOBr containing surface oxygen vacancies (OVs) was prepared by a simple solvothermal method and combined with graphitic carbon nitride (g-C3 N4 ) to construct a heterojunction for photocatalytic oxidation of nitric oxide (NO) and reduction of carbon dioxide (CO2 ). The formation of the heterojunction enhanced the transfer and separation efficiency of photogenerated carriers. Furthermore, the surface OVs sufficiently exposed catalytically active sites, and enabled capture of photoexcited electrons at the surface of the catalyst. Internal recombination of photogenerated charges was also limited, which contributed to generation of more active oxygen for NO oxidation. Heterojunction and OVs worked together to form a spatial conductive network framework, which achieved 63 % NO removal, 96 % selectivity for carbonaceous products (that is, CO and CH4 ). The stability of the catalyst was confirmed by cycling experiments and X-ray diffraction and transmission electron microscopy after NO removal.

Enriched Surface Oxygen Vacancies of Photoanodes by Photoetching with Enhanced Charge Separation.

A facile photoetching approach is described that alleviates the negative effects from bulk defects by confining the oxygen vacancy (Ovac ) at the surface of BiVO4 photoanode, by 10-minute photoetching. This strategy could induce enriched Ovac at the surface of BiVO4 , which avoids the formation of excessive bulk defects. A mechanism is proposed to explain the enhanced charge separation at the BiVO4  /electrolyte interface, which is supported by density functional theory (DFT) calculations. The optimized BiVO4 with enriched surface Ovac presents the highest photocurrent among undoped BiVO4 photoanodes. Upon loading FeOOH/NiOOH cocatalysts, photoetched BiVO4 photoanode reaches a considerable water oxidation photocurrent of 3.0 mA cm-2 at 0.6 V vs. reversible hydrogen electrode. An unbiased solar-to-hydrogen conversion efficiency of 3.5 % is realized by this BiVO4 photoanode and a Si photocathode under 1 sun illumination.

Efficient Degradation of Phenol and 4-Nitrophenol by Surface Oxygen Vacancies and Plasmonic Silver Co-Modified Bi2 MoO6 Photocatalysts.

In this work, the surface plasmon resonance effect of metallic Ag, surface oxygen vacancies (SOVs), and Bi2 MoO6 (BMO) material were rationally combined to construct new oxygen-vacancy-rich Ag/Bi2 MoO6 (A/BMO-SOVs) photocatalysts. Their synergistic effect on the photocatalytic degradation of phenol and 4-nitrophenol under visible-light irradiation (λ≥420 nm) was also investigated. TEM, EPR, and Raman spectra demonstrate the co-existence of metallic Ag nanoparticles, surface oxygen vacancies, and Bi2 MoO6 due to a controlled calcination process. The experimental results disclose that the 2 %A/BMO-SOVs-375 sample exhibited the highest photocatalytic activity for the degradation of both phenol and 4-nitrophenol under visible-light irradiation, achieving nearly 100 and 80 % removal efficiency, respectively, and demonstrated the apparent reaction rate constants (kapp ) 183 and 26.5 times, respectively, higher than that of pure Bi2 MoO6 . The remarkable photodegradation performance of A/BMO-SOVs for organic substances is attributed to the synergistic effect between the surface oxygen vacancies, metallic Ag nanoparticles, and Bi2 MoO6 , which not only improves the visible-light response ability, but also facilitates charge separation. Thus, this work provides an effective strategy for the design and fabrication of highly efficient photocatalysts through integrating surface oxygen vacancies and the surface plasmon resonance effect of nanoparticles, which has the potential for both water treatment and air purification.

Structure engineering with sodium doping for cobalt-free Li-rich layered oxide toward improving electrochemical stability.

Structure engineering of the Li-rich layered cathodes to overcome insufficient structural stability and the rapid decay of capacity and voltage is crucial for commercializing of the materials for the lithium-ion batteries. Alkali metal element doping at the lithium sites has proven to be a feasible approach to boost the performance of the Li-rich layered oxides. Herein, the Na+-doping strategy in the lithium slabs is introduced to modify the structure of the cobalt-free layered Li-rich oxide, Li1.2Ni0.2Mn0.6O2. It is revealed that the doped Na+ ions can promote the activation of the Li2MnO3 phase, endowing the materials with high initial discharge capacity of 284.2 mAh g-1 at 0.1C. Due to the pillaring effect of the doped Na+ ions in the lithium slabs and the induced formation of oxygen vacancies, the electrochemical stability of the material is significantly improved, providing a capacity retention of 94.0 % after 100 cycles at 0.5C. The voltage decay per cycle is only 2.0 mV, less than 3.2 mV of the Li1.2Ni0.2Mn0.6O2. The results suggest that the facile strategy of introducing Na+ ions into the lithium slabs is an efficient approach for optimizing structure design of the Li-rich layered oxides for the lithium-ion batteries.

Orderly Arranged Dipoles Regulate Anion-Derived Solid-Electrolyte Interphase for Stable Lithium Metal Chemistry.

Lithium (Li) metal batteries are considered the most promising high-energy-density electrochemical energy storage devices of the next generation. However, the unstable solid-electrolyte interphase (SEI) derived from electrolytes usually leads to high impedance, Li dendrites growth, and poor cyclability. Herein, the ferroelectric BaTiO3 with orderly arranged dipoles (BTOV) is integrated into the polypropylene separator as a functional layer. Detailed characterizations and theoretical calculations indicate that surface oxygen vacancies drive the phase transition of BaTiO3 materials and promote the ordered arrangement of dipoles. The strong dipole moments in BTOV can adsorb TFSI- and NO3 - anions selectively and promote their preferential reduction to form a SEI film enriched with inorganic LiF and LiNxOy species, thus facilitating the rapid transfer of Li+ and restraining the growth of Li dendrites. As a result, the Li-Li cell with the BTOV functional layer exhibits enhanced Li plating/stripping cycling with an ultra-long life of over 7000 h at 0.5 mA cm-2/1.0 mAh cm-2. The LiFePO4 || Li (50 µm) full cells display excellent cycling performance exceeding 1760 cycles and superior rate performance. This work provides a new perspective for regulating SEI chemistry by introducing ordered dipoles to control the distribution and reaction of anions.

Dual modification of BiVO4 photoanode by enriching bulk and surface oxygen vacancies for enhanced photoelectrochemical performance.

The introduction of oxygen vacancies (Ov) into photoanodes has been considered an effective method to enhance the photoelectrochemical (PEC) water splitting performance. The efficiency of water splitting is related to light absorption, charge separation to the electrode surface, and charge injection into the electrolyte. However, introducing Ov from a single level cannot meet the above objectives. In this work, we present the fabrication of BiVO4 (BVO) photoanodes with bulk and surface Ov, and their respective roles in the PEC performance have been studied. The bulk OV of the photoanode could increase the carrier density and improve the separation efficiency of photogenerated electrons and holes. The surface Ov provide abundant surface active sites, and enhance the charge injection efficiency. Charge separation efficiency of the nitrogen-treated BVO (N:BVO) (69.1 % at 0.75 V vs RHE and 85.1 % at 1.23 V vs RHE) has a noticeable increase compared with that of BVO (51.2 % at 0.75 V vs RHE and 64.6 % at 1.23 V vs RHE), nevertheless, only a minor enhancement of charge injection efficiency (from 49.1 % to 56.5 % at 1.23 V vs RHE). After the deposition of NiFeOOH, the photoanodes present superior charges injection efficiency in the whole range of applied potential. The as-synthesized N:BVO/U-NiFeOOH photoanode exhibits a photocurrent density of 5.52 mA·cm-2 at 1.23 V vs RHE with a 97 % Faradaic efficiency for O2/H2 evolution. Thus, there is a synergistic effect between the bulk OV and surface OV on the BVO photoanode, exhibiting highly promoted PEC water splitting activity relative to the individual OV decorated BVO for oxygen evolution reaction, which provides a promising strategy for fabricating efficient solar water splitting systems.

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.

Surface Oxygen Vacancies Confined by Ferroelectric Polarization for Tunable CO Oxidation Kinetics.

Surface oxygen vacancies have been widely discussed to be crucial for tailoring the activity of various chemical reactions from CO, NO, to water oxidation by using oxide-supported catalysts. However, the real role and potential function of surface oxygen vacancies in the reaction remains unclear because of their very short lifetime. Here, it is reported that surface oxygen vacancies can be well confined electrostatically for a polarization screening near the perimeter interface between Pt {111} nanocrystals and the negative polar surface (001) of ferroelectric PbTiO3. Strikingly, such a catalyst demonstrates a tunable catalytic CO oxidation kinetics from 200 °C to near room temperature by increasing the O2 gas pressure, accompanied by the conversion curve from a hysteresis-free loop to one with hysteresis. The combination of reaction kinetics, electronic energy loss spectroscopy (EELS) analysis, and density functional theory (DFT) calculations, indicates that the oxygen vacancies stabilized by the negative polar surface are the active sites for O2 adsorption as a rate-determining step, and then dissociated O moves to the surface of the Pt nanocrystals for oxidizing adsorbed CO. The results open a new pathway for tunable catalytic activity of CO oxidation.

Simultaneous acceleration of osteogenesis and angiogenesis by surface oxygen vacancies of rutile nanorods.

Advanced implants with simultaneous accelerated osteogenic and angiogenic capacities are of great importance for osteointegration. Much attention has been paid to simultaneously enhancing the osteogenesis and angiogenesis by surface decoration of bioactive molecules or ions on biomaterial surface, but the inherent physical cue of material surface down to the atomic-scale features have always been ignored. In this study, we demonstrate that regulation of surface oxygen vacancies defects of rutile nanorods are able to simultaneous accelerate the osteogenesis and angiogenesis. The concentration of surface oxygen vacancies defects of rutile nanorods can be manipulated by simple redox processing. The osteogenic differentiation of mesenchymal stem cells (MSCs), angiogenic differentiation and vessel-like tube structures of human umbilical vein endothelial cells (HUVECs) on oxygen vacancies rich surface are significantly up-regulated. This work therefore emphasizes the critical role of the inherent material atomic-scale features and provides a novel strategy to accelerate the osteogenesis and angiogenesis of Ti-based implant.

Surface oxygen vacancies and carbon dopant co-decorated magnetic ZnFe2O4 as photo-Fenton catalyst towards efficient degradation of tetracycline hydrochloride.

Carbon doped strategy has been recognized as an efficient strategy to enhance photo-Fenton degradation performance. However, the preparation of high efficiency C-doped photocatalyst has been a significant challenge. Herein, we synthesized magnetic carbon-doped ZnFe2O4 via a facile solvothermal-calcination route. The photo-Fenton activity of C-doped ZnFe2O4 under visible light (λ > 420 nm) was evaluated by degradation of tetracycline hydrochloride. C-doped sample, CZF-2 (0.5 g L-1) presented excellent removal performance for TC-HCl (20 mg L-1) in presence of H2O2 (10 mM) and could remove 90.8% of TC-HCl within 50 min. The C-doping modulates crystal defects and generates surface oxygen vacancies simultaneously, thus building a new C-doping level near valence band and a defect level under the conduction band. Meanwhile, surface oxygen vacancies bring photo-generated electrons and electrons generated from itself to surface to accelerate photo-Fenton reaction, and the holes are rapidly transferred to the surface to participate in the degradation of pollutants.

Mechanistic insights into the formation of surface oxygen vacancies with controllable concentration and long-term stability in small-molecule bonded bismuth-based semiconductor hybrid photocatalyst.

Constructing oxygen vacancies (OVs) with desired concentration and stability on the surfaces of semiconductors has been demonstrated to be a powerful tactic to enhance their photocatalytic performances. Nevertheless, forming OVs usually requires rigorous conditions, and OVs harshly suffer from deactivation during photoreaction. Herein, a facile strategy is developed to introduce surface OVs with tunable concentrations and long-term stability in bismuth-based semiconductors (BBS) through organic small-molecule surface-bonding. Taking I-doped BiOCl (I-BiOCl) as a model photocatalyst and catechol and its derivatives as ligands, a series of organic/I-BiOCl bonded hybrid photocatalysts are successfully synthesized. Compared with I-BiOCl, hybrid photocatalysts exhibited substantially enhanced catalytic activity toward multiple contaminants removal. Experimental characterizations and DFT calculations reveal a strong interfacial interaction between organic ligands and BBS through the formation of BiOC bonds, which lengthen Bi-O bonds within [Bi2O2]2+ structural units and reduce the formation energy of OVs, facilitating the escape of lattice O atoms and thus producing abundant surface OVs. More importantly, the concentration of OVs can be easily regulated by controlling the number of organic ligands, and the OVs exhibit high stability during photoreaction, attributing to the existence of high-valence-state Bi(3+x)+ that is near the OVs, which would not be re-oxidized by oxidative species like the low-valence-state Bi(3-x)+, that is, they would not be reset to original Bi3+. As a verification of its universality, the surface bonded strategy has been successfully extended to other BBS.

Insight into the Contributions of Surface Oxygen Vacancies on the Promoted Photocatalytic Property of Nanoceria.

Oxygen vacancies (OVs) have critical effects on the photoelectric characterizations and photocatalytic activity of nanoceria, but the contributions of surface OVs on the promoted photocatalytic properties are not clear yet. In this work, we synthesized ceria nanopolyhedron (P-CeO2), ceria nanocube (C-CeO2) and ceria nanorod (R-CeO2), respectively, and annealed them at 600 °C in air, 30%, 60% or pure H2. After annealing, the surface OVs concentration of ceria elevates with the rising of H2 concentration. Photocatalytic activity of annealed ceria is promoted with the increasing of surface OVs, the methylene blue photodegradation ratio with pure hydrogen annealed of P-CeO2, C-CeO2 or R-CeO2 is 93.82%, 85.15% and 90.09%, respectively. Band gap of annealed ceria expands first and then tends to narrow slightly with the rising of surface OVs, while the valence band (VB) and conductive band (CB) of annealed ceria changed slightly. Both of photoluminescence spectra and photocurrent results indicate that the separation efficiency of photoinduced electron-hole pairs is significantly enhanced with the increasing of the surface OVs concentration. The notable weakened recombination of photogenerated carrier is suggested to attribute a momentous contribution on the enhanced photocatalytic activity of ceria which contains surface OVs.

Investigation of the Kinetics and Reaction Mechanism for Photodegradation Tetracycline Antibiotics over Sulfur-Doped Bi2WO6-x/ZnIn2S4 Direct Z-Scheme Heterojunction.

The rational design of direct Z-scheme heterostructural photocatalysts using solar energy is promising for energy conversion and environmental remediation, which depends on the precise regulation of redox active sites, rapid spatial separation and transport of photoexcited charge and a broad visible light response. The Bi2WO6 materials have been paid more and more attention because of their unique photochemical properties. In this study, S2- doped Bi2WO6-x coupled with twin crystal ZnIn2S4 nanosheets (Sov-BWO/T-ZIS) were prepared as an efficient photocatalyst by a simple hydrothermal method for the removal of tetracycline hydrochloride (TCH). Multiple methods (XRD, TEM, XPS, EPR, UV vis DRS, PL etc.) were employed to systematically investigate the morphology, structure, composition and photochemical properties of the as-prepared samples. The XRD spectrum indicated that the S2- ions were successfully doped into the Sov-BWO component. XPS spectra and photoelectrochemical analysis proved that S2- served as electronic bridge and promoted captured electrons of surface oxygen vacancies transfer to the valence band of T-ZIS. Through both experimental and in situ electron paramagnetic resonance (in situ EPR) characterizations, a defined direct Z-scheme heterojunction in S-BWO/T-ZIS was confirmed. The improved photocatalytic capability of S-BWO/T-ZIS results ascribed that broadened wavelength range of light absorption, rapid separation and interfacial transport of photoexcited charge, precisely regulated redox centers by optimizing the interfacial transport mode. Particularly, the Sov-50BWO/T-ZIS Z-scheme heterojunction exhibited the highest photodegradation rate was 95% under visible light irradiation. Moreover, this heterojunction exhibited a robust adsorption and degradation capacity, providing a promising photocatalyst for an organic pollutant synergistic removal strategy.

Photocatalytic nitrogen fixation: Oxygen vacancy modified novel micro-nanosheet structure Bi2O2CO3 with band gap engineering.

As a promising ammonia synthesis approach to replace the industrial Harber method, the biggest problem restricting photocatalytic nitrogen fixation is the suboptimal efficiency. Herein, novel surface oxygen vacancies modified micro-nanosheet structure Bi2O2CO3 (namely BOC/OV) were successfully synthesized via facile formation under room temperature. These defects-rich nanosheets exhibit outstanding performance for photocatalytic nitrogen fixation under visible light. The surface oxygen vacancies provide abundant active sites for molecular N2 activation, and the effect of scattered nanometer-size could facilitate the separation of photo-generated charges. Moreover, the energy band can be consecutively tuned with the accumulation of surface oxygen vacancies by lowering the conduction band position. Among all as-prepared samples, BOC/OV3 exhibited the highest NH4+ yield, reaching 1178 µmol·L-1·g-1·h-1, which is 10 times than that of pristine Bi2O2CO3. In this work, all samples synthesis and defects formation were conducted without requiring any secondary energy, which is of great significance for realizing green and efficient artificial ammonia synthesis.

Oxygen vacancies and Lewis sites activating O3/H2O2 at wide pH range via surface electron transfer over CeOx@SiO2 for nitrobenzene mineralization.

The low efficiency of peroxone (O3/H2O2) at acidic and neutral pH restrained its application in water purification. To overcome this shortcoming, CeOX@SiO2 with large surface area, abundant surface oxygen vacancies (Vo), Lewis sites (L sites) and high Ce(III)/Ce(IV) ratio were synthesized to change the traditional electron transfer pathway between O3 and H2O2. Vo was facile in absorbing H2O2 to form Vo-H2O2 and L sites were capable of absorbing O3 to form L-O3. The electron at Vo could be donated to Vo-H2O2 and generate Vo-HO2-, which then effectively triggered the decomposition of L-O3 at CeOX@SiO2's interface and O3 in bulk solution. The electron transfer at the solid-liquid interface with the help of Ce3+/Ce4+ redox cycle and Vo was pH independent and different from the traditional electron transfer of peroxone reaction. Nitrobenzene (NB) mineralization was promoted to 92.5% in CeOX@SiO2-peroxone, but only 63.8% TOC was removed in tradition peroxone process. Moreover, CeOX@SiO2-peroxone had a wide pH application range. NB's degradation in CeOX@SiO2-peroxone process followed the co-oxidation mechanism of superoxide free (•O2-) and hydroxyl radical (•OH). The finding of this study could broaden the popularization of peroxone in water treatment and provided a strategy for catalyst design.