Higher Oxidation Efficiency Research Articles

Heterostructure Co3O4@NiO as bifunctional electrocatalyst for high efficient urea oxidation and hydrogen evolution reaction

Herein, the synergetic effect developed between two metal oxide nanostructure mixture Co3O4@NiO is described. The result demonstrates that composite has a promising catalyst for UOR (urea oxidation reaction) and HER (hydrogen evolution reaction). XRD, SEM, TEM and FT-IR, and XPS studies reveal the formation of Co3O4@NiO. For the electrochemical study, Co3O4@NiO displayed lower onset potential −0.123 V for HER and 1.18 V vs. RHE for UOR to deliver a standard current density of 10 mA cm−2. Importantly, with a low Tafel slope of 141 and 340 mV dec−1 for UOR and HER, respectively. Thus, this present dual incorporation Co3O4@NiO catalyst could be the potential catalyst for practical-level applications.

Controllable Modulation of Defects for Layered Double Hydroxide Nanosheets by Altering Intercalation Anions for Efficient Electrooxidation Catalysis.

Hydrazine (N2 H4 ) is considered as one of the most potential energy storage materials in liquid fuel cells, as it contains high energy and power density, and the high-efficiency oxidation of N2 H4 in fuel cells has drawn great attention. However, the most used catalysts are expensive noble metal catalysts, thus the development of highly efficient non-noble metal catalysts is crucial to reduce the cost of hydrazine oxidation in practical industry. Herein, we synthesized a series of CoFe-layered double hydroxides (CoFe-LDHs) intercalated with different anions via a simple one-step co-precipitation method for the electrooxidation of hydrazine. Through altering the intercalated anions of CoFe-LDHs, the defects and the electronic structure can be well controlled, and the catalytic performance for the electrooxidation of hydrazine were well promoted by using NO3 - intercalated into CoFe-LDH compared with other anions (like Cl- , BO3 3- , CO3 2- ). This work developed a series of hydrazine electrooxidation catalysts and established the relationship between the intercalated anions, the fine structure of the catalyst and the electrocatalytic performance.

Algae-containing raw water treatment and by-products control based on ClO2 preoxidation-assisted coagulation/precipitation process.

Eutrophication has become a great concern in recent years with the algae blooms in source water resulting in a serious threat posing to the safety of drinking water. Chlorine dioxide (ClO2) has been served as an alternative oxidant for preoxidation or disinfection during drinking water treatment process due to its high oxidation efficiency and low risk of organic by-products formation. However, the generation of inorganic by-products including chlorite (ClO2-) and chlorate (ClO3-) has become a potential problem when applied in drinking water treatment. In this study, ClO2 preoxidation-assisted coagulation/precipitation process was applied to improve the raw water quality, especially algae, turbidity, chemical oxygen demand (CODMn), and UV254, and explore the formation mechanisms of inorganic by-products. It was found that the polymeric aluminum chloride (PAC) and ClO2 have shown the best raw water treatment performance with the optimal dosage of 10mg/L and 0.8mg/L, respectively. Moreover, the initial pH also has exhibited a notable influence on pollutants treatment and by-products generation. Due to the adverse influence of algae and natural organic matters (NOM) and the generation of by-products, it was significant to investigate their inhibition effect on the water quality and the production of ClO2- and ClO3- in the ClO2 preoxidation-assisted coagulation/precipitation process. Moreover, it was applicable of this process to apply for the algae-containing raw water (calculated as Chl.a lower than 50μg/L) treatment with the ClO2 dosage of less than 0.8mg/L to achieve optimum treatment performance and minimum by-products generation.

Ultrasound-assisted decoration of CuOx nanoclusters on TiO2 nanoparticles for additives free photocatalytic hydrogen production and biomass valorization by selective oxidation

• Ultrasound-assisted ultra-wet (US-UWet) impregnation synthetic method is presented. • Mixed cupric and cuprous oxides nanoclusters (< 4 nm) were decorated on TiO 2 P25. • The nanocomposite showed H 2 formation capability under low power UV irradiation. • The additive free oxidation of biomass derived model platform chemicals was studied. • Nanocomposite revealed higher selectivity comparing to P25 for HMF and BnOH oxidation. The herein presented ultrasound-assisted ultra-wet (US-UWet) impregnation synthetic approach was followed in order to avoid the drawbacks of the conventional wet impregnation synthesis. The goal was to homogeneously decorate the surface of the TiO 2 nanoparticles with nanometric sized (< 4 nm) clusters of mixed cupric and cuprous oxides. The physicochemical features of the nanocomposite (TiO 2 CuO x ) were determined by high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and Diffuse reflectance (DR) spectroscopy. TiO 2 CuO x showed an enhanced and continuous capability to generate molecular hydrogen upon low power ultraviolet irradiation. The benchmark commercial TiO 2 P25 did not reveal any H 2 formation under these conditions. TiO 2 CuO x presented also a high efficiency for the additives-free selective partial oxidation of two well established biomass derived model platform chemicals/building blocks, 5-hydroxymethylfurfural (HMF) and benzyl alcohol (BnOH) to the value-added chemicals 2,5-diformylfuran (DFF) and benzyl aldehyde (PhCHO), respectively. The nanocomposite showed higher DFF and PhCHO yield compared to P25.

Covalent Triazine Framework as an Efficient Photocatalyst for Regeneration of NAD(P)H and Selective Oxidation of Organic Sulfide.

Covalent triazine frameworks (CTFs), belonging to the super-family of covalent organic frameworks, have attracted significant attention as a new type of photosensitizer due to the superb light-harvesting ability and efficient charge transfer originating from the large surface area. However, the wide optical band gap in CTFs, which is larger than 3.0 eV, hinders the efficient light harvesting in the visible range. To overcome this limitation, we developed the new type CTFs photocatalyst based on the donor-acceptor conjugation scheme by using melamine (M) and 2,6-diaminoanthraquinone (AQ) as monomeric units. The melamine-2,6-diaminoanthraquinone-based covalent triazine frameworks (M-AQ-CTFs) photocatalyst shows the excellent light-harvesting capacity with high molar extinction coefficient, and the suitable optical band gap involving the internal charge transfer character. Combination of M-AQ-CTFs and artificial photosynthetic system including the organometallic rhodium complex, acting as an electron mediator, exhibited the excellent photocatalytic efficiency for the regeneration of the nicotinamide cofactors such as NAD(P)H. In addition, this photocatalyst showed the high photocatalytic efficiency for the metal-free aerobic oxidation of sulfide. This study demonstrates the high potential of CTFs photocatalyst with the donor-acceptor conjugated scheme can be actively used for artificial photosynthesis.

Influence of syngas composition on combustion and emissions in a homogeneous charge compression ignition engine

Homogeneous charge compression ignition (HCCI) is a promising combustion concept that can simultaneously achieve high efficiency and low nitrogen oxides (NOx) emissions. Synthesis-gas (syngas)-fueled HCCI engines can be adapted for a wide range of fuel compositions. The aim of this study was to investigate the combustion and emissions of an HCCI engine with various syngas compositions. The baseline syngas contained 30% H2, 25% CO, and 45% CO2 by volume, which provided a low heating value (LHV) of 6.08 MJ/Nm3. The fuel composition varied from hydrogen-rich to lean. It was found that syngas with an LHV of 3.34 MJ/Nm3 could be auto-ignited by implementing intake boosting with sufficient intake heating. The intake temperature required to achieve autoignition was reduced at higher loads. The start of combustion temperature mainly relied on the intake temperature and fueling rate, regardless of the fuel composition. A higher H2 content in the fuel facilitated fast burning with good combustion stability, even under lean conditions. It was revealed that a higher CO fraction deteriorated the combustion stability on the lean side with slow burning. The gross indicated thermal efficiency (ITEg) increased with an increase in the LHV of the syngas, with an ITEg of 38.1% realized at a low load of 0.3 MPa for the base fuel, while maintaining engine stability. The combustion efficiency was greater than 90% for the fuels examined at a higher fuel rate. The NOx emissions were very low because of the ultra-lean, diluted charge used for HCCI combustion.

High-efficiency oxidation of norfloxacin by Fe3+/H2O2 process enhanced via vacuum ultraviolet irradiation: Role of newly formed Fe2+

Fluoroquinolones in water environments have caused worldwide concern due to negative effects on human health and ecological environment. Heretofore, synergistic mechanisms of Fe3+/H2O2 process enhanced via vacuum ultraviolet (VUV) irradiation for fluoroquinolones removal, and generation ways and contribution evaluations of reactive oxygen species (ROS) in integrated VUV/Fe3+/H2O2 were not reported systematically. This work comparatively investigated norfloxacin (NOR, typical fluoroquinolones) degradation in VUV/Fe3+/H2O2 and its sub-processes. Compared with its sub-processes, VUV/Fe3+/H2O2 process could not only increase degradation rate constant by 2.1–10.2 times and increase mineralization rate by 14.5%–49.5%, but also reduce energy consumption by 53.1%–89.9% and reduce economic cost by 33.3%–68.0%. Effect mechanisms of Fe3+ and H2O2 doses on decontamination capability of VUV/Fe2+/H2O2 were elaborated, and 3 mM H2O2 and 90 μM Fe3+ were determined as optimal doses. The synergetic factor in integrated VUV/Fe3+/H2O2 was 3.33, which was mainly ascribed to VUV photons accelerating iron cycle. In VUV/Fe3+/H2O2 process, superoxide radical and hydroxyl radical were confirmed as primary ROS, contributing 20.86% and 76.32% to NOR oxidation, separately. Organic and inorganic products of NOR and its degradation pathways in integrated VUV/Fe3+/H2O2 were also investigated. Besides, the synergistic reaction pathways in VUV/Fe3+/H2O2 were elaborated. Effects of water matrices on decontamination capability of VUV/Fe3+/H2O2 were also studied. All results indicated VUV/Fe3+/H2O2 as an efficient and cost-effective process suitable for NOR removal.

High-efficiency oxidation of fluoroquinolones by the synergistic activation of peroxymonosulfate via vacuum ultraviolet and ferrous iron

Fluoroquinolones in aquatic environments have caused worldwide concern due to the negative effects on human health and ecological environment. So far, the performance and mechanism for fluoroquinolones removal by the synergistic activation of peroxymonosulfate (PMS) via vacuum UV (VUV) irradiation and Fe2+ are still blank. Herein, compared with its sub-processes, VUV/Fe2+/PMS process significantly improved the degradation and mineralization efficiencies of three fluoroquinolones. Effect mechanisms of typical parameters (Fe2+ and PMS doses, initial pH) on norfloxacin (NOR) removal by VUV/Fe2+/PMS were elaborated and VUV/Fe2+/PMS showed excellent performance at wide initial pH (3−10). The results of fluorescence molecular probe and radical trapping experiments proved that hydroxyl radical, singlet oxygen, and sulfate radical were primary reactive oxygen species in VUV/Fe2+/PMS. The degradation pathways of NOR in VUV/Fe2+/PMS were mainly defluorination, piperazine ring transformation and quinolone group transformation, and its main inorganic by-products were F-, NO3−, and NH4+. Besides, the synergistic reaction pathways in integrated VUV/Fe2+/PMS process were elaborated. Furthermore, inorganic anions (such as Cl-, NO3-, SO42-, CO32-) hardly affected NOR removal by VUV/Fe2+/PMS, while dissolved organic matter showed slight inhibition. Finally, well-pleasing results of fluoroquinolones removal by VUV/Fe2+/PMS in actual waters highlighted its superiority in the advanced treatment of secondary effluent.

A novel layer-layer crossed structure of bentonite/g-C3N4 for enhanced photocatalytic oxidation of arsenic(III) in a wide pH range

In this work, a novel 2-dimentional (2D)-2D bentonite/g-C3N4 composite (B/g-C3N4), with a layer-layer cross structure and large surface area, was synthesized by a self-assembly process, with the aim for the photocatalytic oxidation of arsenic (As(III)) in wastewater. The structure and properties of the mineral-based composite were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), and photocurrent measurements. The photocatalytic activity of 2D-2D B/g-C3N4 for As(III) removal was further investigated under visible light. The results reveal that the As(III) oxidation rate by 2D-2D B/g-C3N4 composite was three times higher than that by pure g-C3N4, owing to the enlarged specific surface area and the suppressed electron–hole recombination by the incorporated bentonite. Moreover, the composite exhibited a high photocatalytic oxidation efficiency in a wide pH adaptability from 3 to 8.5. Through electron spin resonance (ESR) technique and radical quenching experiments, the photocatalytic mechanism of As(III) oxidation was proposed, where superoxide radicals played a critical role in the photo-oxidation of As(III) in both acid and basic conditions. This work paved a new way to design the mineral-based photocatalyst for treatment of pollutants in a wide pH range.

Superparamagnetic core‐shell metal–organic framework Fe3O4@Ni‐MOF as efficient catalyst for oxidation of 1,4‐dihydropyridines using hydrogen peroxide

AbstractA facile and efficient method was described for oxidation of some 3,5‐diacyl or 3,5‐diester 1,4‐dihydropyridines using H2O2 in the presence of superparamagnetic core‐shell metal–organic framework Fe3O4@Ni‐MOF. The Fe3O4@Ni‐MOF has been obtained by Step‐by‐Step method in which magnetic Fe3O4 magnetic nanoparticles were coated with Ni‐MOF using a mercaptoacetic acid linker. The synthesized catalyst was characterized using thermogravimetric analysis, FT‐IR spectroscopy, powder X‐ray diffraction, field emission scanning electron microscopy and energy‐dispersive X‐ray analysis. The novel superparamagnetic core‐shell metal–organic framework Fe3O4@Ni‐MOF revealed high efficiency for oxidation of various 1,4‐dihydropyridines using hydrogen peroxide. The Box–Behnken design matrix and the response surface method were applied to investigate the optimization of the reaction conditions. The conditions for optimal reaction yield and time were: amount of catalyst ≈17 mmol, temperature ≈78°C and amount of hydrogen peroxide ≈ 1 ml. A variety of 3,5‐diacyl or 3,5‐diester 1,4‐dihydropyridines with different substituted functional groups have been converted to corresponding pyridines with good to excellent isolated yields using H2O2 and Fe3O4@Ni‐MOF. The catalyst was reused up to five times for the oxidation of 1,4‐dihydropyridines without a significant loss in catalytic activity. The short reaction times, simplicity of method, good to excellent yields and reusability of catalyst were some advantages of the proposed procedure.

Performance and mechanism of photocatalytic degradation of tetracycline by Z–scheme heterojunction of CdS@LDHs

Z–scheme heterojunction has the advantages of high carrier separation efficiency and strong oxidation ability, which is a potential material for photodegradation. In this paper, CdS@Zn,Cr-layered double hydroxides (CdS@LDHs) Z–scheme heterojunction was synthesized and used for photocatalytic degradation of tetracycline (TC). The effects of the amount of catalyst, pH value of the solution, initial concentration of TC, light intensity, and reaction temperature were studied. The degradation kinetics and mechanism were also discussed in detail. Under the optimal conditions (initial concentration of TC 50 mg/L, pH 9, light intensity 500 W, the amount of the catalyst 25 mg, and reaction temperature 45 °C), the highest removal percentage and the corresponding activity of CdS@LDHs was 93.04% and 37.09 mg g−1 h−1, respectively. In addition, DFT calculation confirmed the existence of built–in electric field (BIEF) in the heterojunction, which promotes the electron transfer from CdS to LDHs. The amount of electron transfer was accelerated, and the recombination of electron and hole was obviously inhibited, so that they were more involved in oxidation and reduction. Thus, it makes CdS@LDHs heterojunction as a highly efficient catalyst for photodegradation of TC.

Co-regulation of dispersion, exposure and defect sites on CeO2 (111) surface for catalytic oxidation of Hg0

The additional cost of Hg0 capture in coal-fired power plants has facilitated the demand for environmental pollutants mitigation material for Hg0 oxidation to Hg2+ for an ultra-low Hg emission technology. Herein, a suite of CeO2-based catalysts were investigated aiming at ultra-low gaseous Hg0 emission at coal-fired power stations. Gaseous elemental mercury is feasible to be catalytically oxidized to Hg2+. The co-regulated dispersion, exposure and defect sites on CeO2 (111) surface with 2 wt% Ce and 8 wt% Mo compositions on γ-Al2O3 was found to be the most promising catalyst demonstrating a high catalytic oxidation efficiency, a broad operating temperature range and a low activation energy. Specifically, it is shown that the oxidation of Hg0 on the Ce-based catalysts can be enhanced by the addition of Mo (up to 8 wt%) via promoting the CeO2 (111) surface dispersion and exposure. Moreover, insights into the Ce and Mo synergistic interactions showed that it facilitated the formation of defect-containing surface sites. Besides, the co-regulation of dispersion, exposure and defect sites on CeO2 (111) surface was further studied by DFT calculations. This study provides a feasible approach in optimization of CeO2-based catalysts for catalytic oxidation of Hg0 to achieve efficient removal of environmental pollutants.

Engineering surface oxygen vacancy of mesoporous CeO2 nanosheets assembled microspheres for boosting solar-driven photocatalytic performance

Surface oxygen vacancy defects of mesoporous CeO2 nanosheets assembled microspheres (D-CeO2) are engineered by polymer precipitation, hydrothermal and surface hydrogenation strategies. The resultant D-CeO2 with a main pore diameter of 9.3 nm has a large specific surface area (~102.3 m2/g) and high thermal stability. The mesoporous nanosheets assembled microsphere structure prevents the nanosheets from aggregation, which is beneficial to effective mass transfer and shortens the migration distance of charge carriers. After surface hydrogenation, the photoresponse extends to long wavelength region, combing with the band gap from 2.63 eV reduced to 2.39 eV. Under AM 1.5 G radiation, the photocatalytic degradation rate of tetracycline (TC) can be up to 99.99%, which is three times as high as that of pristine CeO2 microspheres. The excellent solar-driven photocatalytic performance can be attributed to the efficient surface oxygen vacancy engineering and the mesoporous nanosheets assembled microsphere structure, which narrows the band gap, shortens the migration distance of carriers, promotes the spatial separation of photogenerated electron-hole pairs and favors mass transfer. The strategy provides new insights for fabricating other high-efficient oxide photocatalysts .

Fast photocatalytic polypropylene degradation by nanostructured bismuth catalysts

Every year millions of tons of polymeric waste are discarded by human activities due to its low production cost; the landfills are littered with plastic waste without any recycling value. This class of garbage exhibits a very low degradation rate under environmental conditions, occupying a lot of space in landfills for a long time, which is costly for society and harmful to environment. Photocatalysis has become a quite interesting tool to oxidize organic pollutants as dyes, drugs, and some polymers, representing a potential alternative for reducing the environmental pollution. In this work, we report an ecofriendly method for polypropylene (PP) degradation by catalytic bismuth nanoparticles (Bi2O3 or BiFeO3) assisted by ionizing radiation. The effect of catalyst load and applied radiation dose on photo-degradation rate were studied. High oxidation efficiencies were detected even at both low catalyst load nd irradiation dose. Oxidized propylene was detected by infrared spectroscopy (FTIR-ATR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (SEM-EDS). All those instrumental techniques confirmed the successful oxidation of PP in few hours of reaction and 1% weight of the catalyst. 2,3 butane-dione, 4-hydroxy-4-methyl pentane-2-one, and ethyl-9-acetoxynonanoate were the main degradation products identified mainly by nuclear magnetic resonance (NMR 1H, 13C).

Miniaturized TOC analyzer using dielectric barrier discharge for catalytic oxidation vapor generation and point discharge optical emission spectrometry

Total organic carbon (TOC) is an important parameter describing organic pollution degree of waters. Due to the increasing need of field analysis and drawbacks of conventional TOC analytical instruments, miniaturized TOC analyzers are still demanding. In this work, a dielectric barrier discharge (DBD) microplasma was utilized for catalytic oxidation vapor generation (COVG) of organic compounds into CO2, and a point discharge (PD) microplasma was employed to excite the carbon atomic emission spectra for quantification. Sample solution with phosphoric acid and persulfate solution was injected into the DBD-COVG reactor by a syringe to convert organic compounds into CO2 efficiently and quickly, which was subsequently transported into the point discharge optical emission spectrometer (PD-OES) for detecting carbon at 193.09 nm. Under optimal experimental conditions, high oxidation efficiencies for several organic compounds were achieved, i.e., 96.4%, 95.1% and 94.3% for 50 mg L−1 potassium hydrogen phthalate (KHP), sodium laurylsulfonate and phenol, respectively. A limit of detection (LOD) of 0.02 mg L−1 (as C) was obtained, with a precision of 3.9% (relative standard deviation, RSD) at 15 mg L−1 TOC standard (as C). The possible catalytic oxidation mechanism was proposed with the characteristic results of electron paramagnetic resonance (EPR). Its potential environmental application was demonstrated by successfully analyzing TOC in underground water, surface river water and surface sedimentary water samples from oil fields, with analytical results agreed well with those obtained by the commercial high-temperature combustion coupled nondispersive infrared absorption (HTC-NDIR) technique.

Theoretical study on iron and nitrogen co-doped graphene catalyzes CO oxidation

• A novel CO oxidation reaction with trimolecular co-adsorption mechanism has been first proposed on FeN-SV. • The CO reaction on FeN-SV favor 2*CO+*O 2 →*OOCO+*CO→*O+*CO+CO 2 →*CO 2 1 →*CO 2 2 , with barrier as 0.525 eV. • For FeN-SV and FeN-DV, the LH mechanism was also very favorable for CO oxidation, and the energy barriers were 0.604 eV and 0.660 eV, respectively. Carbon monoxide oxidation is a famous typical polyphase catalytic reaction, which can convert toxic gases into non-toxic substances, thus reducing environmental pollution. The traditional catalytic reaction has high energy barriers and low energy efficiency, while the single metal atom was inserted into the thin graphene with excellent electronic properties to form a special structure, which has extraordinary catalytic properties. Based on the first principle calculation method, the different reaction mechanism of CO oxidation in nitrogen co-doped single vacancy and double vacancy (FeN-SV and FeN-DV) was studied systematically, and its stable structure was analyzed to find the optimal catalytic reaction path. For FeN-SV, the energy barriers of a new trimolecular co-adsorption mechanism (2*CO+*O 2 →*OOCO+*CO→*O+*CO+CO 2 →*CO 2 1 →*CO 2 2 ), which has not been reported yet, was only 0.525 eV. The rate-determining step (RDS) for FeN-SV (FeN-DV) is *CO+*O 2 →*OOCO→*O+CO 2 →*O+CO→CO 2 , which is also very beneficial to CO oxidation, was 0.604 eV (0.660 eV). The findings revealed FeN-SV and FeN-DV can be used as a low cost, high efficiency for CO catalytic oxidation. Conversion of toxic CO to non-toxic CO 2 on FeN-SV by trimolecular co-adsorption mechanism.

Influence of plasma-assisted ignition on flame propagation and performance in a spark-ignition engine

Lean-burn is an attractive concept for reasons of high thermal efficiency and low nitrogen oxide (NOx) emissions, however, successful implementation in spark-ignition (SI) engines turned out to be challenging because of misfire or partial burn caused by attenuated flame propagation. In order to overcome this issue, microwave-assisted plasma ignition system (MAPIS) has been applied in combustion systems. The MAPIS consists of a conventional ignition coil, a non-resistor spark plug, a mixing unit, a waveguide, and a magnetron (2.45GHz, 3kW). A series of experiments was carried out to understand discharge characteristics and to validate its performance in a constant volume vessel as well as in a single-cylinder spark-ignition engine. The fundamental investigation based on optical emission spectroscopy and flame imaging showed that the ejection of the microwave was beneficial to produce more reactive species such as OH and O radicals thanks to higher electron temperature than conventional spark ignition. The lean limit was able to be extended up to an equivalence ratio of 0.5 based on a larger initial flame kernel size with MAPIS in the vessel test. Meanwhile, in the engine test, combustion stability was noticeably improved showing smaller cycle-to-cycle fluctuations in in-cylinder pressure. Improvement in fuel efficiency up to 6% could be achieved by stable operation under fuel-lean conditions. In terms of emissions, MAPIS was advantageous to reduce carbon monoxide (CO) emissions by promoting more complete combustion.

ZSM-5-supported V-Cu bimetallic oxide catalyst for remarkable catalytic oxidation of toluene in coal-fired flue gas

A close-coupled catalytic oxidation module after the NH3-SCR section has been constructed that employs catalytic materials to achieve high-efficiency oxidation of toluene (a surrogate for VOCs stemming from coal combustion) during flue gas purification. The V-Cu bimetallic bifunctional catalyst supported on ZSM-5 zeolite (V-Cu/ZSM-5) not only efficiently removed VOCs but also tolerated to complex flue gas. The catalytic material that removed the toluene was easily fabricated via the impregnation method. Results showed that, compared with single metal-supported catalysts, the V-Cu/ZSM-5 catalyst exhibited enhanced performance. This superior performance was attributed to improved reducibility at lower temperatures, higher electron transfer efficiency, more abundant Oα species and lower C7H8 activation temperature. The material also exhibited excellent flue gas tolerance and COx selectivity. The suppression mechanism of VOCs oxidation under complex coal-fired flue gas has been elucidated for the first time. There was competitive adsorption between the toluene and NH3 and/or NO. SO2 in the flue gas would cause chemical poisoning of the catalyst. Finally, in-situ DRITFS studies gave insights on the reaction mechanism. In short, this work provides new ideas and strategies for removing VOCs from complex coal-fired flue gas.

Fe-N/C single-atom catalysts with high density of Fe-Nx sites toward peroxymonosulfate activation for high-efficient oxidation of bisphenol A: Electron-transfer mechanism

A high-efficient iron-based heterogeneous catalyst is desired to active peroxymonosulfate (PMS). Due to a large catalytic contribution of atomically dispersed Fe-Nx sites, single-atom iron–nitrogen-carbon catalysts exhibit superior performance in the catalytic activation of PMS. Herein, a sequence of Fe-N-C SACs with atomically dispersed Fe-Nx sites, FeSA-N-C and FeSA-N/C, were prepared from Fe-doped ZIF-8 and FePc@ZIF-8, respectively. Single-atom Fe-Nx sites were confirmed to be the main active sites for PMS activation. FeSA-N/C-20 with a higher density of Fe-Nx sites exhibited superior catalytic performance to N/C, FeSA-N-C, FeSA-N/C-15, and FeSA-N/C-25 for BPA degradation. Integrated with chemical quenching experiments, electron spin resonance (ESR), in-situ Raman spectra, and electrochemical analysis, a nonradical pathway was demonstrated to dominate the degradation of BPA in the PMS + FeSA-N/C-20 system. More importantly, the nature of this nonradical pathway was found to be an electron-transfer regime instead of a high-valent iron or singlet oxygenation process. The BPA was adsorbed onto the Fe-Nx site by a “donor–acceptor complex” mechanism to form a nonradical PMS* intermediate during the process. Benefiting from this mechanism, the PMS + FeSA-N/C-20 system showed wide pH adaptation and high resistance to inorganic anions.

Surface defects induced charge imbalance for boosting charge separation and solar-driven photocatalytic hydrogen evolution

Low charge separation efficiency of semiconductor materials is the main obstacle for high-performance photocatalyst. Herein, we report surface defects engineered uniform mesoporous TiO2 nanospheres (DMTNSs) through surfactant-mediated self-assembly solvothermal approach combined with hydrogenation strategy to promote charge separation. The surface defects induced charge imbalance result in the formation of built-in field, which can promote photogenerated charge separation efficiently and be confirmed by experimental and density functional theory (DFT) calculations. Under AM 1.5G irradiation, the photocatalytic hydrogen evolution of DMTNSs is ~3.34 mmol h−1 g−1, almost 3.5 times higher than that of pristine non-defective TiO2 nanospheres (0.97 mmol h−1 g−1), due to the engineered surface defects narrowing the bandgap (~3.01 eV) and inducing charge imbalance to boost spatial charge separation and extend visible-light response. The defect induced charge imbalance strategy opens a new valuable perspective for fabricating other high-efficient oxide photocatalysts.