Interfacial Reaction Mechanism Research Articles

Interface Reaction Mechanism During Laser Brazing of Zn–Mg–Al-Coated Steel To Aa 6061 Aluminum Alloy

Interface Reaction Mechanism During Laser Brazing of Zn–Mg–Al-Coated Steel To Aa 6061 Aluminum Alloy

Investigations of interfacial reaction and toughening mechanisms of Ta fiber-reinforced TiAl-matrix composites

Continuous fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. Ta fiber with outstanding plasticity and toughness is regarded as a promising reinforcement. In this work, a 10 vol% Ta fiber-reinforced TiAl composite was prepared by combining slurry casting and vacuum hot pressing under condition of 1150 °C/ 35 MPa/ 2 h. Microstructure of interfacial reaction zone of the composite was investigated; meanwhile, thermodynamic calculation and theoretical analysis were conducted to explain the formation mechanisms of the reaction products. Three types of reaction products σ-Ta 2 Al, B2 and α 2 phases were formed between Ta fiber and TiAl matrix. σ phase was adjacent to Ta fiber with a fine grain structure, which was formed due to the lowest formation free energy. The aggregation of β stabilizers in Ti-rich region resulted in the formation of B2 phase that was close to σ phase. α 2 phase relied on B2 phase to nucleate and grow based on the Burgers relationship and their structure symmetry. Three-point bending tests show the fracture toughness (K IC ) of the Ta f /TiAl composite was 58% higher than that of pure TiAl matrix. The main toughening mechanism of the Ta f /TiAl composite was plastic deformation of the Ta fiber, meanwhile the interfacial debonding also had a contribution to toughening the TiAl alloy. The interfacial debonding location was mainly at the Ta / L I -σ interface due to the existence of thermal residual stress. • The interfacial reaction products from Ta fiber to TiAl matrix in turn were σ-Ta 2 Al, B2 and α 2 phases. • The fracture toughness (K IC ) of Ta f /TiAl composite has increased by 58% than that of pure TiAl matrix. • Plastic deformation of the Ta fiber was the main toughening mechanisms, and interfacial debonding also had a contribution to toughening TiAl alloy. • Interfacial debonding location was mainly at the Ta/L I -σ interface due to the existence of thermal residual stress.

Interfacial reaction of aluminum borate whisker reinforced Mg-10Gd-3Y-1Zn-0.4Zr (wt%) alloy matrix composite

Magnesium matrix composites usually possess high strength and stiffness as well as low coefficient of thermal expansion, which makes them promising in lightweight and energy-saving strategies. Although the interfacial bonding state has a crucial influence on the properties of magnesium matrix composites, the interfacial reaction mechanism of Mg-RE alloy matrix composites is still unclear. Herein, the interfacial reaction and microstructure of Mg-10Gd-3Y-1Zn-0.4Zr (wt%) alloy matrix composite reinforced with aluminum borate whisker (Al18B4O33w) were reported by heating the matrix to a semisolid region and inducing the interfacial reaction to continue. After heat treatment at 600 °C for 6 h, the thickness of the interface layer increased from 50‐120 nm to about 335 nm, and the main interfacial reaction product was (Mg0.4Al0.6)Al1.8O4. With the increase of heating time to 12 h, a new double interface layer with (Mg0.4Al0.6)Al1.8O4 in the inner layer and MgO in the outer layer was formed. The difference of interfacial reaction products during isothermal heat treatment was related to the concentration gradient of Mg atoms along the radial direction of the whiskers and the hindrance of the migration of Mg atoms by reaction products formed in the early stage. These findings provide a further understanding of the interfacial reaction of Al18B4O33w reinforced Mg-RE alloy matrix composites.

The Gnps Evolution and Interface Reaction Mechanism of Gnps/Ta15 Composites by Pre-Sintering and Canned Hot Extrusion

The Gnps Evolution and Interface Reaction Mechanism of Gnps/Ta15 Composites by Pre-Sintering and Canned Hot Extrusion

Effects of Different Types of Interlayers on the Interfacial Reaction Mechanism at the Cu Side of Al/Cu Lap Joints Obtained by Laser Welding/Brazing.

The influence of tin foil and Ni coatings on microstructures, mechanical properties, and the interfacial reaction mechanism was investigated during laser welding/brazing of Al/Cu lap joints. In the presence of a Zn-based filler, tin foil as well as Ni coating strengthened the Al/Cu joints. The tin foil only slightly influenced the joint strength. It considerably improved the spreading/wetting ability of the weld filler; however, it weakened the bonding between the seam and the Al base metal. The Ni coating considerably strengthened the Al/Cu lap joints; the highest tensile strength was 171 MPa, which was higher by 15.5% than that of a joint without any interlayer. Microstructure analysis revealed that composite layers of Ni3Zn14–(τ2 Zn–Ni–Al ternary phase)–(α-Zn solid solution)–Al3Ni formed at the fusion zone (FZ)/Cu interface. Based on the inferences about the microstructures at the interfaces, thermodynamic results were calculated to analyze the interfacial reaction mechanism. The diffusion of Cu was limited by the Ni coating and the mutual attraction between the Al and Ni atoms. The microstructure comprised Zn, Ni, and Al, and they replaced the brittle Cu–Zn intermetallic compounds, successfully strengthening the bonding of the FZ/Cu interface.

Surface sulfur vacancies enhanced electron transfer over Co-ZnS quantum dots for efficient degradation of plasticizer micropollutants by peroxymonosulfate activation

Peroxymonosulfate (PMS) activation in heterogeneous processes is a promising water treatment technology. Nevertheless, the high energy consumption and low efficiency during the reaction are ineluctable, due to electron cycling rate limitation. Herein, a new strategy is proposed based on a quantum dots (QDs)/PMS system. Co-ZnS QDs are synthesized by a water phase coprecipitation method. The inequivalent lattice-doping of Co for Zn leads to the generation of surface sulfur vacancies (SVs), which modulates the surface of the catalyst to form an electronic nonequilibrium surface. Astonishingly, the plasticizer micropollutants can be completely degraded within only tens of seconds in the Co-ZnS QDs/PMS system due to this type of surface modulation. The interfacial reaction mechanism is revealed that pollutants tend to be adsorbed on the cobalt metal sites as the electron donors, where the internal electrons of pollutants are captured by the metal species and transferred to the surface SVs. Meanwhile, PMS adsorbed on the SVs is reduced to radicals by capturing electrons, achieving effective electron recovery. Dissolved oxygen (DO) molecules are also easily attracted to catalyst defects and are reduced to O 2 •− , further promoting the degradation of pollutants. A new strategy is reported to generate electron-rich/poor reaction sites on the catalyst surface by constructing sulfur vacancies through Co doping into the ZnS QDs lattice. PMS and DO are captured by sulfur vacancies and reduced to reactive oxygen species, thus rapidly degrading organic pollutants.

Carbonized MOF-Coated Zero-Valent Cu Driving an Efficient Dual-Reaction-Center Fenton-like Water Treatment Process through Utilizing Pollutants and Natural Dissolved Oxygen

Excessive consumption of resources and energy is inevitable in a classical Fenton reaction due to the demand for electron donors or electron acceptors (H2O2) and the existence of reaction rate-limiting steps. In this work, we propose an innovative strategy to solve this key scientific problem by utilizing the organic pollutants and the dissolved oxygen (DO) naturally present in the wastewater through a newly developed carbonized metal–organic framework-coated zero-valent Cu catalyst (ZVC@CMOF). It has been found that the formation of a C–O–Cu bond bridge on the catalyst induces electron polarization distribution to form a non-equilibrium surface with electron-rich or electron-poor microareas based on a series of characterization techniques. This typical non-equilibrium surface feature leads to excellent performance for pollutant conversion and a new interfacial reaction mechanism. Various types of refractory organic pollutants can be rapidly degraded in a few minutes in the ZVC@CMOF Fenton-like systems, accompanied by good stability and a wide pH adaptation range. The interfacial reaction processes are revealed by experimental analysis and theoretical calculations, in which pollutants and DO act as electron donors and electron acceptors in the electron-poor and electron-rich microareas, respectively, which greatly reduce the consumption of H2O2 and improve the reaction efficiency and catalytic performance for pollutant removal.

Ab initio -based approach for the oxidation mechanisms at SiO2 /4H-SiC interface: Interplay of dry and wet oxidants during interfacial reaction

Effects of the coexistence of dry and wet oxidants on the reaction process at ${\mathrm{SiO}}_{2}$/4H-SiC(0001) and ($000\overline{1}$) interfaces during SiC oxidation are systematically investigated by performing ab initio calculations. We find characteristic features of the interfacial reaction mechanisms, which are dependent on the plane orientation and wet oxidation condition. The incorporation of wet oxidants leads to lower barrier heights for the reaction of ${\mathrm{O}}_{2}$ molecules, resulting in the promotion of interfacial reaction at the ${\mathrm{SiO}}_{2}$/4H-SiC(0001) interface. In contrast, the coexisting ${\mathrm{O}}_{2}$ molecule assists the reactions by ${\mathrm{H}}_{2}\mathrm{O}$ molecule and OH groups at the ${\mathrm{SiO}}_{2}$/4H-SiC($000\overline{1}$) interface. Furthermore, we estimate the linear rate constants in the Deal-Grove model using the calculated barrier heights and reveal that the preferable wet ambient condition at the ${\mathrm{SiO}}_{2}$/4H-SiC(0001) interface is different from that at the ${\mathrm{SiO}}_{2}$/4H-SiC($000\overline{1}$) interface. The difference in the rate constants is caused by the difference in the rate-limiting reaction pathway between ${\mathrm{SiO}}_{2}$/4H-SiC(0001) and ($000\overline{1}$) interfaces. These calculated results offer better understanding of the atom-scale mechanisms for the significant enhancement of SiC oxidation by the interplay of dry and wet oxidants.

All-Solid-state Lithium Battery with Sulfide Electrolyte: From Interface Design to Full Cell

All-solid-state lithium batteries (ASSLBs) have gained intensive attention because of their intrinsic safety and high energy density.1 However, significant interfacial challenges such as detrimental interfacial reactions, poor solid-solid ionic contact, and lithium dendrite growth have stymied the development of ASSLBs. Besides that, the large gap between fundamental research and practical engineering design has slowed down ASSLBs commercialization. Over the past five years, our group has been dedicated to the research and development of ASSLBs, with the aims of overcoming the interfacial challenges and pushing ASSLBs closer to commercialization. First, we have regulated the interfacial ion and electron transport via increasing the ionic conductivity of interfacial buffer layers,2 manipulating interfacial nanostructures,3, 4 using single-crystal cathodes,5 deciphering interfacial reaction mechanisms,6 and constructing artificial solid electrolyte interphases (SEI).7 Based on these advanced and innovative strategies, the large interfacial resistance was successfully eliminated. As a result, ASSLBs with sulfide electrolytes demonstrated both ultra-long cycling stability and high-rate performance. To transfer these viable technologies into practical application and bridging the large gap between laboratory research and practical full cells, we are committed to engineering solid-state pouch cells with competitive energy density and low cost. Recently, a solvent-free and cost-effective process was developed for fabricating ultra-thin inorganic solid electrolyte membranes as well as solid-state thick electrodes. Furthermore, a solid-liquid interface and a plastic crystal electrolyte were engineered to enable practical solid-state pouch cells with high energy density and excellent safety.8, 9 These works not only provide an in-depth understanding of interfacial mass and charge transport but also offer feasible strategies to commercialize practical solid-state pouch cells. References C. Wang, J. Liang, Y. Zhao, M. Zheng, X. Li, X. Sun*, Energy Environ. Sci. , 2021, doi:10.1039/d1ee00551k.C. Wang, J. Liang, S. Hwang, X. Li, Y. Zhao, K. Adair, C. Zhao, X. Li, S. Deng, X. Lin, X. Yang, R. Li, H. Huang, L. Zhang, S. Lu, D. Su and X. Sun*, Nano Energy , 2020, 72, 104686.C. Wang, X. Li, Y. Zhao, M. N. Banis, J. Liang, X. Li, Y. Sun, K. R. Adair, Q. Sun, Y. Liu, F. Zhao, S. Deng, X. Lin, R. Li, Y. Hu, T.-K. Sham, H. Huang, L. Zhang, R. Yang, S. Lu and X. Sun*, Small Methods , 2019, 3, 1900261.C. Wang, J. Liang, M. Jiang, X. Li, S. Mukherjee, K. Adair, M. Zheng, Y. Zhao, F. Zhao, S. Zhang, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, C. V. Singh and X. Sun*, Nano Energy, 2020, 76, 105015.C. Wang, R. Yu, S. Hwang, J. Liang, X. Li, C. Zhao, Y. Sun, J. Wang, N. Holmes, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, D. Su and X. Sun*, Energy Storage Mater ., 2020, 30, 98-103.C. Wang, S. Hwang, M. Jiang, J. Liang, Y. Sun, K. Adair, M. Zheng, S. Mukherjee, X. Li, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, J. Wang, C. V. Singh, D. Su, X. Sun*. Adv. Energy Mater., 2021, 2100210. doi:10.1002/aenm.202100210.C. Wang, Y. Zhao, Q. Sun, X. Li, Y. Liu, J. Liang, X. Li, X. Lin, R. Li, K. R. Adair, L. Zhang, R. Yang, S. Lu and X. Sun*, Nano Energy, 2018, 53, 168-174.C. Wang, Q. Sun, Y. Liu, Y. Zhao, X. Li, X. Lin, M. N. Banis, M. Li, W. Li, K. R. Adair, D. Wang, J. Liang, R. Li, L. Zhang, R. Yang, S. Lu and X. Sun*, Nano Energy, 2018, 48, 35-43.C. Wang, K. R. Adair, J. Liang, X. Li, Y. Sun, X. Li, J. Wang, Q. Sun, F. Zhao, X. Lin, R. Li, H. Huang, L. Zhang, R. Yang, S. Lu and X. Sun*, Adv. Funct. Mater. , 2019, 29, 1900392.

Recent progress in the function of redox mediators on the electrode/electrolyte interfaces of lithium–oxygen batteries

The nonaqueous lithium–oxygen batteries have attracted considerable interest because of the ultrahigh theoretical capacity. However, the overpotential and cyclability issue of lithium–oxygen battery caused by interfacial issue limits its commercialization. To overcome these challenges, redox mediators, which are capable of charge transport on the electrode/electrolyte interfaces, are introduced to lithium–oxygen batteries to reduce overpotential. This review provides a detailed summary of the interfacial reaction mechanism and the influence of redox mediators on the electrode/electrolyte interfaces. Researches on suppressing redox mediators’ shuttle effect are also beneficial to enhance the electrochemical performance of lithium–oxygen batteries.

Enhanced Fenton-like process via interfacial electron donating of pollutants over in situ Cobalt-doped graphitic carbon nitride

The heterogeneous Fenton process suffers from low efficiency because of the low electron transfer cycle rate of Fe3+/Fe2+, which often consumes enormous amounts of hydrogen peroxide (H2O2) or other energy. Herein, we report a novel Co-based Fenton-like catalyst (in-situ-Co-g-C3N4) synthesized via the surface complexation method, in which Co species were modified in situ into the framework of the graphitic carbon nitride (g-C3N4) substrate through C–O–Co chemical bonding. The catalyst exhibited higher Fenton-like catalytic activity than pure g-C3N4 in the degradation of various pollutants under neutral conditions, as evidenced by the approximately 150-fold higher Fenton-like reaction rate constant of in-situ-Co-g-C3N4 than that of g-C3N4. Density functional theory (DFT) calculations and a series of experimental and characterization analyses revealed the interfacial reaction mechanism between H2O2, pollutants and in-situ-Co-g-C3N4. During the Fenton-like reaction, the electron-poor C center on the aromatic ring of g-C3N4 could capture the electrons deprived from pollutants, and subsequently deliver them to around the electron-rich Co center to efficiently reduce H2O2 to hydroxyl radicals (•OH), enabling H2O2 to be used efficiently for the degradation of pollutants. This study provides a strategy for improving Fenton-like degradation efficiency by effectively utilizing the energy of organic pollutants.

Enhanced Cyclability of Cr8O21 Cathode for PEO-Based All-Solid-State Lithium-Ion Batteries by Atomic Layer Deposition of Al2O3

Cr8O21 can be used as the cathode material in all-solid-state batteries with high energy density due to its high reversible specific capacity and high potential plateau. However, the strong oxidation of Cr8O21 leads to poor compatibility with polymer-based solid electrolytes. Herein, to improve the cycle performance of the battery, Al2O3 atomic layer deposition (ALD) coating is applied on Cr8O21 cathodes to modify the interface between the electrode and the electrolyte. X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, and Fourier transform infrared spectroscopy, etc., are used to estimate the morphology of the ALD coating and the interface reaction mechanism. The electrochemical properties of the Cr8O21 cathodes are investigated. The results show that the uniform and dense Al2O3 layer not only prevents the polyethylene oxide from oxidization but also enhances the lithium-ion transport. The 12-ALD-cycle-coated electrode with approximately 4 nm Al2O3 layer displays the optimal cycling performance, which delivers a high capacity of 260 mAh g−1 for the 125th cycle at 0.1C with a discharge-specific energy of 630 Wh kg−1.

Oxygen electrochemistry in Li‐O2 batteries probed by in situ surface‐enhanced Raman spectroscopy

AbstractSurface‐enhanced Raman spectroscopy (SERS), as a nondestructive and ultra‐sensitive single molecular level characterization technique, is a powerful tool to deeply understand the interfacial electrochemistry reaction mechanism involved in energy conversion and storage, especially for oxygen electrochemistry in Li‐O2 batteries with unrivaled theoretical energy density. SERS can provide precise spectroscopic identification of the reactants, intermediates and products at the electrode|electrolyte interfaces, independent of their physical states (solid and/or liquid) and crystallinity level. Furthermore, SERS's power to resolve different isotopes can be exploited to identify the mass transport limitation and reactive sites of the passivated interface. In this review, the application of in situ SERS in studying the oxygen electrochemistry, specifically in aprotic Li‐O2 batteries, is summarized. The ideas and concepts covered in this review are also extended to the perspectives of the spectroelectrochemistry in general aprotic metal‐gas batteries.

Layered double hydroxide photocatalysts for solar fuel production

Splitting water or reducing CO2via semiconductor photocatalysis to produce H2 or hydrocarbon fuels through the direct utilization of solar energy is a promising approach to mitigating the current fossil fuel energy crisis and environmental challenges. It enables not only the realization of clean, renewable, and high-heating-value solar fuels, but also the reduction of CO2 emissions. Layered double hydroxides (LDHs) are a type of two-dimensional anionic clay with a brucite-like structure, and are characterized by a unique, delaminable, multidimensional, layered structure; tunable intralayer metal cations; and exchangeable interlayer guest anions. Therefore, it has been widely investigated in the fields of CO2 reduction, photoelectrocatalytic water oxidation, and water photolysis to produce H2. However, the low carrier mobility and poor quantum efficiency of pure LDH limit its application. An increasing number of scholars are exploring methods to obtain LDH-based photocatalysts with high energy conversion efficiency, such as assembling photoactive components into LDH laminates, designing multidimensional structures, or coupling different types of semiconductors to construct heterojunctions. This review first summarizes the main characteristics of LDH, i.e., metal-cation tunability, intercalated guest-anion substitutability, thermal decomposability, memory effect, multidimensionality, and delaminability. Second, LDHs, LDH-based composites (metal sulfide-LDH composites, metal oxide-LDH composites, graphite phase carbon nitride-LDH composites), ternary LDH-based composites, and mixed-metal oxides for splitting water to produce H2 are reviewed. Third, graphite phase carbon nitride-LDH composites, MgAl-LDH composites, CuZn-LDH composites, and other semiconductor-LDH composites for CO2 reduction are introduced. Although the field of LDH-based photocatalysts has advanced considerably, the photocatalytic mechanism of LDHs has not been thoroughly elucidated; moreover, the photocatalytic active sites, the synergy between different components, and the interfacial reaction mechanism of LDH-based photocatalysts require further investigation. Therefore, LDH composite materials for photocatalysis could be developed through structural regulation and function-oriented design to investigate the effects of different components and interface reactions, the influence of photogenerated carriers, and the impact of material composition on the physical and chemical properties of the LDH-based photocatalyst.

Wettability and interfacial reaction mechanism between Ag–Cu alloy and Si3N4 ceramics in air atmosphere

The wetting behaviour and interfacial reaction mechanism between Ag–Cu alloy fillers (with varying copper contents) and Si3N4 ceramics using reactive air brazing at 970 °C were systematically investigated. As the copper content increased, the contact angles of the Ag–Cu filler on the Si3N4 ceramics decreased. A violent boiling-like interfacial reaction was observed during the experiment, and mass spectrometry analysis identified the gaseous products as N2, NO and NO2. The solid products SiO2 and Cu–O formed at the interface, and the interfacial reactions improved the wettability of the Ag–Cu filler on the Si3N4 ceramics. Owing to buoyancy and the pushing of the gases, the interfacial products floated to the surface of the filler and their distribution increased along with the increasing copper content. Two different microstructures were formed at the interface near the triple line. Thick and thin SiO2 layers were respectively formed on the triple line interface of the fillers with low (Ag–3Cu/Ag–5Cu) and high (Ag–6.6Cu/Ag–16Cu) copper content. The interfacial bonding zones formed in Ag–5Cu, Ag–6.6Cu, and Ag–16Cu samples indicated that the corresponding Ag–Cu fillers were effectively brazed with the Si3N4 ceramics.

Reactive wetting and interfacial reaction mechanism of ZrC-SiC ceramic and Ag-Zr filler

In this study, the isotherm wetting and spreading behaviors of molten Ag-Zr filler on ZrC-SiC ceramic surface was investigated using a sessile drop method in vacuum. The effect of Zr content in Ag-Zr filler on the wetting behavior was studied, and the wetting mechanism was revealed in details. The results showed that the contact angle of Ag-Zr filler on the ZrC-SiC surface decreased from 140 ° to 20 ° with the Zr content varied from 0 to 8 wt.%, and the Zr was the key factor to the wetting process. The wetting dynamic analysis illustrated that the interfacial reaction controlled the wetting of Ag-Zr filler on the ZrC-SiC surface. Due to the Zr activity difference at Ag-Zr/ZrC interface, the ZrC released C into Ag-Zr filler, and reacted with Zr to form new-born ZrC with higher Zr content. The formation of the new-born ZrC promoted wetting and spreading of Ag-Zr filler on ZrC-SiC surface.

Mechanisms of Si Nanoparticle Formation by Molten Salt Magnesiothermic Reduction of Silica for Lithium‐ion Battery Anodes

AbstractMolten salt methods enable the synthesis of Si nanostructures by moderating the thermal energy evolved in highly exothermic magnesiothermic reduction reactions (MRR) of silica. Due to their cost‐effectiveness and scalability, these techniques are well suited for producing nanoscale Si for a number of applications, including energy storage. To control the microstructure morphology and particle size, it is necessary to understand the formation mechanism of the Si produced. By evaluating the time‐resolved phase evolution, when NaCl moderates the thermal energy generated by MRR of SiO2, we elucidate 3 parallel interfacial reaction mechanisms yielding Si nanoparticles – via Mg vapor, Mg‐rich eutectic liquid, and Mg ions dissolved in molten NaCl. These individual Si nanoparticles offer a striking contrast to the typical by‐product of MRR of SiO2 with and without NaCl, which yields a 3‐dimensional (3‐D) porous network of sintered Si nanoparticles. Lithium‐ion battery half‐cells with electrodes composed of individual Si nanoparticles showed a greater first‐cycle irreversible discharge capacity and faster capacity loss over the first 5 cycles at a current density of 200 mA g−1 compared to half‐cells with electrodes of a porous 3‐D Si network–indicative due to thicker solid electrolyte interphase (SEI) formation on individual particles. At a higher current rate of 400 mA g−1, once SEI formation and activation of Si are established, both cells exhibit a similar capacity retention rate over 100 cycles.

Unraveling the multiple roles of Ag species incorporation into OMS-2 for efficient catalytic ozonation: Structural properties and mechanism investigation

Silver incorporated manganese oxide octahedral molecular sieves (Ag-OMSX-T) were successfully synthesized via a hydrothermal-calcination method. Due to the multiple roles of Ag species doping, the optimal Ag-OMS0.2-180 nanocatalyst with the Ag/Mn molar ratio of 0.2 had the highest TOF value (2.94 × 10−5 mol g−1 h−1), which could completely degrade 50 mg L−1 OA at pH 5.0 in 30 min much higher than those of OMS-2 (22.3%) in catalytic ozonation system. The results of systematic characterization (such as XRD, XPS, Py-IR, and O2-TPD) and catalytic performance tests of Ag-OMS0.2-180 clearly demonstrated that the proper amount of Ag incorporation not only facilitated the electron transfer but also induced more formation of Lewis acid sites in Ag-OMS0.2-180 as well as metals (Ag and Mn) as activation sites to collectively favor the catalytic ozonation degradation of OA. In addition, the higher mineralization rate has been achieved (79.6%) and the Ag-OMS0.2-180 exhibited the satisfactory stability and reusability with low metal release during multiple consecutive cycles (≥ 5). Meanwhile, the electron spin resonance spectra and radical scavenger tests confirmed that superoxide radical and singlet oxygen were the main reactive oxygen species in catalytic process. The mechanism of solid-liquid interface reaction and the pathway of cycling of oxygen vacancies were also elaborated, which present a new insight for water decontamination.

Enhanced photocatalytic reduction of Cr(VI) by the novel hetero-system BaFe2O4/SnO2

In this study, BaFe2O4 nanoparticles with a crystallite size of 86 nm were produced using the sol–gel method and applied in the photoreduction of chromate. The spinel phase was identified by X-ray diffraction and scanning electron microscopy-energy-dispersive X-ray analysis. The structure was refined in orthorhombic symmetry by Rietveld analysis. A forbidden band (Eg) of 2.03 eV was extracted from the diffuse reflectance data and the optical transition was directly permitted. The thermal dependence of the electrical conductivity (σ) followed an exponential law with an activation energy of 0.23 eV. In addition, photo-electrochemical characterization of the spinel was conducted to establish the energy diagram for the hetero-system BaFe2O4/SnO2/HCrO4− solution in order to assess the interfacial reaction mechanism. Similar to most spinels, BaFe2O4 exhibits p-type behavior with a flat band potential (Efb) of 0.52 VSCE. Therefore, the potential of the conduction band (ECB) is sufficiently negative to be involved in an electronic injection with SnO2. The photoluminescence spectrum obtained for the rutile contained an intense peak at 590 nm and its intensity was substantially reduced in the hetero-system. Electrochemical impedance spectroscopy detected a depressed arc assigned to a constant phase element and its resistance (1.64 kΩ cm2) decreased to 1.05 kΩ cm2 under visible light, thereby confirming the semiconductor behavior. The reduction of Cr(VI) was successfully achieved with the BaFe2O4/SnO2 hetero-system under visible light as an application. Photocorrosion was prevented by using oxalate (C2O42−) as a scavenger to captures the holes and improve the photo-activity. The quasi-total chromate reduction had a reduction efficiency of 99% with a concentration of 30 mg L−1 under a light flux of 16 mW cm−2. The kinetics followed a first-order model with a photocatalytic half-life of 38 min and the results were fitted in an appropriate manner to the Langmuir–Hinshelwood model. Moreover, BaFe2O4/SnO2 exhibited photocatalytic efficacy for five successive runs and the final reduction efficiency was still 92%.

Doping and facet effects synergistically mediated interfacial reaction mechanism and selectivity in photocatalytic NO abatement

The surface atomic coordination and arrangement largely determine photocatalytic properties. Whereas, the intrinsic impact of surface microstructures on the reaction mechanism and pathway is still unclear. Herein, via constructing N-doped Bi2O2CO3 photocatalysts with diverse exposed facets, (1 1 0) and (0 0 1) facet, we testify that the pivotal roles of crystal facet and doping effect on the intermediate production and reactivity for photocatalytic nitric oxide (NO) abatement. The photoreactivity of N-doped Bi2O2CO3 is documented to be higher than that of the pure samples because of the enhanced light absorption and charge transfer. Further in situ probing experiments and theoretical calculations verify that the unique adsorption patterns and activated intermediates on the (1 1 0) facet facilitate the formation of final products and inhibit the generation of toxic NO2 by-product in terms of thermodynamics. More importantly, we found that the selective and nonselective oxidation processes are emerged over (1 1 0) and (0 0 1) facets of Bi2O2CO3, respectively.