Oxygen Activation Ability Research Articles

Construction of surface oxygen vacancy active sites upon MnOx/AC composite catalysts for efficient coupling adsorption and oxidation of toluene

Activated carbon (AC) has been widely used as adsorbent and support of noble metal catalysts for the elimination of VOCs, owing to its high specific surface area and effective regulation of interfacial properties of catalysts via metal-support interaction. Herein, a series of MnOx/AC composite catalysts are prepared by in-situ redox precipitation method using KMnO4 as manganese source, ethylene glycol (EG) as reducing agent and coconut shell-based AC as active carrier. The obtained MnOx/AC catalysts have been fully characterized by XRD, SEM, TEM, N2 adsorption-desorption, FT-IR, XPS, EPR, H2-TPR, TPD-MS and toluene-TPSR-Ms (with and without O2) and their catalytic properties are evaluated for low temperature oxidation of toluene. It is found that the introduction of AC support significantly enhanced the adsorption capacity of toluene upon the MnOx/AC composite catalysts. Amongst, the MnOx/AC-0.3 shows excellent low-temperature catalytic activity (T90 = 193 °C), which can be related to highly efficient synergy of AC and MnOx species in toluene combustion. Especially, the construction of efficient MnOx/AC interfaces with more oxygen vacancy active sites, better lattice oxygen mobility, and stronger molecular oxygen activation ability, makes MnOx/AC-0.3 composite catalyst possess the best coupling adsorption oxidation capacity of toluene, and thus resulting in significant improvement in catalytic performance. Additionally, the obtained MnOx/AC-0.3 catalyst has also exhibited good catalytic stability and water resistance (5 vol%). This work deepens the understanding of the metal-support interaction in MnOx/AC composite catalysts and provides new ideas for the design of environmentally friendly catalysts.

Atomically Dispersed Pt-Doped Co3 O4 Spinel Nanoparticles Embedded in Polyhedron Frames for Robust Propane Oxidation at Low Temperature.

This study adopts a facile and effective in situ encapsulation-oxidation strategy for constructing a coupling catalyst composed of atomically dispersed Pt-doped Co3 O4 spinel nanoparticles (NPs) embedded in polyhedron frames (PFs) for robust propane total oxidation. Benefiting from the abundant oxygen vacancies and more highly valent active Co3+ species caused by the doping of Pt atoms as well as the confinement effect, the optimized 0.2Pt-Co3 O4 NPs/PFs catalyst exhibits excellent propane catalytic activity with low T90 (184 °C), superior apparent reaction rate (21.62×108 (mol gcat -1 s-1 )), low apparent activation energy (Ea = 17.89kJ mol-1 ), high turnover frequency( 811×107 (mol gcat -1 s-1 )) as well as good stability. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations indicate that the doping of Pt atoms enhances the oxygen activation ability, and decreases the energy barrier required for CH bond breaking, thus improving the deep oxidation process of the intermediate species. This study opens up new ideas for constructing coupling catalysts from atomic scale with low cost to enhance the activation of oxygen molecules and the deep oxidation of linear short chain alkanes at low temperature.

Fabrication of Hierarchical Porous Metal Oxides by the HPMC-Assisted Gel Combustion Strategy: Incorporation of Nanoceria into Cookie-like Mn2O3 with Enhanced Oxidation Activity and Excellent Water Resistance

Constructing nonprecious metal oxide catalysts with a hierarchical porous structure by a simple method for the deep catalytic oxidation of toxic volatile organic compounds at low temperatures is of great value and significance. In this work, a porous manganese trioxide catalyst (Mn2O3-H) was prepared by a hydroxypropyl methylcellulose-assisted combustion synthesis strategy for catalytic complete oxidation of gaseous toluene. Benefiting from the rich porous nanostructure, Mn2O3-H has much higher specific surface area and active site density, resulting in better low-temperature reducibility and oxygen activation ability than blank Mn2O3 formed by direct calcination. With this sol–gel combustion process, CeO2 nanoparticles could be successfully introduced to form cookie-like Ce–Mn composite oxide with a hierarchical porous nanostructure, which builds the strong interaction of CeO2–Mn2O3 to weaken Mn–O with more active defects. Among Ce-doped catalysts, 5%CeMn-H shows the best catalytic activity in toluene oxidation with 90% conversion temperature at 242 °C under a weight hour space velocity of 60,000 mL·g–1·h–1, which is about 30 and 133 °C lower than that of Mn2O3-H and Mn2O3-B, respectively. This advantage is also shown in other typical hydrocarbons such as propylene and propane. Moreover, the as-prepared Ce-doped catalyst exhibits excellent stability and water resistance ability. This simple robust sol–gel combustion method will provide valuable enlightenment for designing porous catalysts with high performance for related catalytic reactions.

Metal-free N-GQDs/P-g-C3N4 photocatalyst with broad-spectrum response: Enhanced exciton dissociation and charge migration for promoting H2 evolution and tetracycline degradation

Graphitic carbon nitride (g-C3N4) is a promising candidate for solving energy and environmental problems. However, narrow photoresponse range, difficult exciton dissociation, and high charge recombination rate severely restrict its activity. Herein, a novel ultrathin porous N-GQDs/P-g-C3N4 (PG-CNS) nanocomposite was fabricated by combining P-element doping, N-doped graphene quantum dots (N-GQDs) coupling, and morphology regulation strategies. The optimal sample (PG-CNS-0.2) was found to extend the photoresponse range over 780 nm due to the combination of midgap state induced by P-doping and excellent upconversion performance of N-GQDs, achieving a fuller utilization of solar energy. Photoluminescence and electrochemical tests confirmed that both exciton dissociation and charge transfer within PG-CNS-0.2 were dramatically enhanced, as reflected by a 3.0-fold increase in carrier density. This enhancement was attributed to reduced exciton binding energy resulting from P-doping, superior electron conduction ability of N-GQDs, as well as larger specific surface area and shorter migration paths provided by the 2D porous structure. Besides, the trapping experimental result indicated that targeted regulation of reactive oxygen species was achieved by changing the addition amount of N-GQDs, thereby enhancing the controllability of photocatalytic reactions. Compared with g-C3N4 nanosheets (CNS), the H2 production rate and tetracycline degradation rate of PG-CNS-0.2 under visible light were improved by 15.7 and 6.9 times, respectively. Meanwhile, the molecular oxygen activation ability of PG-CNS-0.2 was also significantly increased, as reflected by the generation of O2– and H2O2 at concentrations 2.5 and 3.5 times higher than that of CNS, respectively. This work not only comprehensively reveals the exciton and carrier behaviors in g-C3N4-based reaction systems, but also provides a new strategy for designing low-cost, environmentally friendly, and efficient broad-spectrum responsive photocatalysts.

A readily available and efficient Pt/P25 (TiO2) catalyst for glycerol selective oxidation

AbstractIn this work, a commercial P25 (TiO2) with phase junctions between (101) and (110) faces supported Pt catalyst was prepared for glycerol selective oxidation, giving a decent 76.8% glyceric acid (GLYA) yield, and good stability. The kinetic experiments calculated apparent activation energy, turnover frequency (TOF), and reaction rates, demonstrating Pt/P25 could facilitate glyceraldehyde (GLYAD) formation and inhibit GLYA over‐oxidation. Series of structural techniques confirmed the 101/110 junctions in P25 contributed electronic effect on Pt through metal‐support interface, which improved the oxygen activation ability and optimized the GLYAD/GLYA adsorption modes. Furthermore, progressive scale‐up reactions were tested and the mass transfer limitations under different conditions were thoroughly studied. The obtained mass transfer factors suggested the gas–liquid and liquid–solid mass transfer were severely limited. Finally, through optimizing the conditions, Pt/P25 catalyst achieved 75.8% GLYA yield at 300 ml‐scale reaction, realizing equivalent magnification with the 5 ml‐scale experiment.

A Stable Zn-MOF for Photocatalytic Csp3–H Oxidation: Vinyl Double Bonds Boosting Electron Transfer and Enhanced Oxygen Activation

Molecular oxygen activation has always been a difficult issue and challenge in heterogeneous photocatalytic aerobic oxidations due to the kinetically persistent or spin-forbidden nature of O2. In this work, a highly delocalized interpenetrated 3D MOF photocatalyst with high stability, Zn-TACPA (H3TACPA = tris(3-carboxybiphenyl)amine), based on vinyl-functionalized triphenylamine and bipyridine ligands has been fabricated and employed as a reactive oxygen species (ROS) generator to catalyze the photooxidative CDC/aromatization tandem reaction of glycine esters and styrenes. In comparison to a similar triphenylamine MOF (Zn-TCA), DFT calculations and extensive control experiments reveal that the introduction of functional vinyl double bonds not only optimizes the visible-light absorption and photoredox potential of triphenylamine ligand to powerfully activate O2 via a single-electron-transfer process but also improves the conjugation degree, charge-carrier separation, and migration efficiency of the MOF semiconductor for rapid O2 activation. Such an oxygen activation ability endows Zn-TACPA with a catalytic yield of up to 91%, 2.6 times higher than that of Zn-TCA. Furthermore, the crucial intermediates and activation processes were also properly captured and monitored by a series of experiments including ESI-MS, ESR, IR, and fluorescence analyses to better understand the possible catalytic mechanisms.

Low-Temperature Combustion of Toluene over Cu-Doped SmMn2O5 Mullite Catalysts via Creating Highly Active Cu2+-O-Mn4+ Sites.

Catalytic combustion of volatile organic compounds (VOCs) at low temperatures is still an urgent issue to be solved. Herein, low-temperature combustion of toluene over Cu-doped SmMn2O5 mullite catalysts via creating highly active Cu2+-O-Mn4+ sites has been originally demonstrated. Cu-doped SmMn2O5 mullite catalysts exhibited 90% conversion of toluene at 206 °C and displayed robust stability even in the presence of water. It has been demonstrated that Cu doping created Cu2+-O-Mn4+ active composite sites that were more exposed after removing surface Sm species via acid-etching. Benefiting from this, the redox and oxygen activation ability of catalysts was significantly enhanced. The consumption of benzaldehyde and benzoic acid as intermediate species and the CO2 generation ability were apparently promoted, which were the direct reasons for the enhanced low-temperature combustion of toluene. This work provides novel ideas for the development of high-performance catalysts for low-temperature VOC combustion, which has great industrial application prospects.

The role of Cs dopants for improved activation of molecular oxygen and degradation of tetracycline over carbon nitride

Molecular oxygen (O2) is activated to reactive oxygen species (ROS) by transferring energy and carriers in the photocatalytic process, which plays an important role in environmental remediation. Herein, Cs-doped carbon nitride (CN-xCs, x = 0.2, 0.8, 1) was prepared by CsCl directly inducing the structural reconstruction of carbon nitride (CN), which had obvious molecular oxygen activation ability to promote tetracycline (TC) degradation. Besides, we explored the influence of Cs doping concentration. As a consequence, the doping concentration of Cs was an important factor affecting the activation of O2, which could cause changes in the physical and chemical structure of CN, make O enter the CN structure, form N vacancy defects and cyano groups. In addition, a proper amount of Cs doping could reduce the band gap value, increase the light absorption range, have better charge separation and transfer performance, which could remarkably promote the activation of O2. Benefiting from these advantages, CN-0.8Cs could generate a higher concentration of superoxide radicals (•O2−, 179.30 µmol/L), which was much higher than CN (6.22 µmol/L). Therefore, it exhibited excellent TC degradation photocatalytic performance, and the rate constant k of TC degradation was 0.020 min−1, which was 6.7 times the degradation rate of CN (k = 0.0030 min−1). Furthermore, the possible degradation pathways of TC were proposed based on the results of HPLC-MS.

Integrating the Z-scheme heterojunction and hot electrons injection into a plasmonic-based Zn2In2S5/W18O49 composite induced improved molecular oxygen activation for photocatalytic degradation and antibacterial performance

The semiconductor-based photocatalysts with local surface plasmon resonance (LSPR) effect can extend light response to near-infrared region (NIR), as well as promote charge-carriers transfer, which provide a novel insight into designing light-driven photocatalyst with excellent photocatalytic performance. Here, we designed cost-effective wide-spectrum Zn2In2S5/W18O49 composite with enhanced photocatalytic performance based on a dual-channel charge transfer pathway. Benefiting from the synergistic effect of Z-scheme heterostructure and unique LSPR effect, the interfacial charge-carriers transfer rate and light-absorbing ability of Zn2In2S5/W18O49 were enhanced significantly under visible and NIR (vis-NIR) light irradiation. More reactive oxygen species (ROS) were formed by efficient molecular oxygen activation, which were the critical factors for both Escherichia coli (E. coli) photoinactivation and tetracycline (TC) photodegradation. The enhancement of molecular oxygen activation (MOA) ability was verified via quantitative analyses, which evaluated the amount of ROS through degrading nitrotetrazolium blue chloride (NBT) and p-phthalic acid (TA). By combining theoretical calculations with diverse experimental results, we proposed a credible photocatalytic reaction mechanism for antibiotic degradation and bacteria inactivation. This study develops a new insight into constructing promising photocatalysts with efficient photocatalytic activity in practical wastewater treatment.

Metal-free porous phosphorus-doped g-C3N4 photocatalyst achieving efficient synthesis of benzoin.

Photocatalytic organic synthesis is mostly limited by the shortcomings of insufficient light absorption, high photogenerated electron–hole recombination rate and inadequate reactive sites of photocatalysts. To solve these problems, phosphorus-doped g-C3N4 with a porous structure was constructed. Benefiting from enhanced light absorption and electron–hole separation efficiency, PCNT has intensive oxygen activation ability to generate superoxide radicals, and is highly active in organic synthesis. In addition, PCNT has enhanced surface nucleophilicity, which is conducive to the carbon–carbon coupling process of the intermediate product benzaldehyde molecules and benzyl alcohol molecules in the benzoin condensation reaction. Metal-free PCNT is expected to replace the previously used highly toxic cyanide catalysts and provide a new way for the low-cost and efficient photocatalytic synthesis of benzoin.

Effect of the A-site cation over spinel AMn2O4 (A = Cu2+, Ni2+, Zn2+) for toluene combustion: Enhancement of the synergy and the oxygen activation ability

To investigate the underlying mechanism of the tetrahedral A2+ cations and the octahedral Mn3+ cations in AMn2O4 spinel catalysts for toluene oxidation, a series of structure-controlled AMn2O4 spinel catalysts were prepared through substituting A2+ and Mn3+ with Cu2+, Ni2+, Zn2+, and Fe3+, respectively. The evaluation results demonstrated that the catalytic activities arrange in the sequence of CuMn2O4 > NiMn2O4 > ZnMn2O4 > CuFe2O4, and the temperature required for 90% conversion of toluene is 205 °C for the CuMn2O4 catalyst. The physical properties of these samples were well characterized by XRD, TEM, N2 adsorption–desorption isotherms. The influences of crystal type, micro structure and specific surface area were successfully eliminated by using KIT-6 as the hard template method. The influence mechanism of A-site metal was further explored by analyzing the results of XPS, H2-TPR and O2-TPD. Results showed that the catalytic activity of the samples was highly affected by the substitution of highly electronegative A-site metal due to the enhancement of low-temperature reducibility and chemisorption oxygen activity. In particular, it was found that the incorporation of A-site metal can improve the ability of the catalyst to activate molecular state O2– to O-, which was highly related to the catalytic activity of the catalyst. The results hold guidance for the design of manganese spinel catalysts on the removal of VOCs.

Oxidative Esterification of 5-Hydroxymethylfurfural with an N-doped Carbon-supported CoCu Bimetallic Catalyst.

The direct fabrication of furan-2,5-dimethylcarboxylate (FDMC), a promising renewable monomer, from biomass-derived 5-hydroxymethylfurfural (HMF) is a cutting-edge process. In this contribution, an elaborately designed N-doped carbon-supported CoCu bimetallic catalyst (Cox Cuy -NC; x/y=9:1, 7:3, 4:6, which represents the designed molar ratio of Co and Cu in the catalyst), which could offer a desirable FDMC yield of 95 % under mild and base-free conditions (Co7 Cu3 -NC, 2 bar O2 , 80 °C, 4 h) is described for the oxidative esterification of HMF. Notably, an FDMC formation rate of 6.1 molFDMC molCo -1 h-1 was achieved over Co7 Cu3 -NC, which represents the highest catalytic efficiency so far among Co-based catalytic systems. It has been demonstrated that Cu-doping in Co7 Cu3 -NC catalyst brings about more active sites (Co-Nx species) with stronger molecular oxygen activation ability. The increase of surface N content of Co7 Cu3 -NC also improves basicity of the catalyst, which favors the hydrogen abstraction process during the HMF oxidative esterification reaction. These findings may pave an efficient and green way for the synthesis of sustainable bio-based polymer monomers.

CeO2-Supported Pt Catalysts Derived from MOFs by Two Pyrolysis Strategies to Improve the Oxygen Activation Ability.

Functional metal organic framework (MOF) derivatives have attracted tremendous attention as promising catalysts for various reactions. The thermal decomposition strategies have a vital effect on the structures and physicochemical properties of functional MOF derivatives. Nevertheless, what effect does the pyrolysis strategy have on MOF derivatives need further study. In this work, one-step (under dry air) and two-step (first under N2 and then dry air) pyrolysis are chosen to prepare the functional ceria-based MOF derivatives with novel hierarchical pore structure. In comparison with the derivatives prepared by one-step pyrolysis, the two-step pyrolysis composites exhibit better catalytic activity for toluene oxidation due to the higher contents of surface absorbed oxygen species and surface oxygen vacancies. The reusability and durability test demonstrates perfect stability of such functional MOF derivatives. The in-situ UV Raman reveals that two-step strategy is favorable for enhancing the gaseous oxygen activation ability of the functional MOF derivatives. Those findings may instruct the synthesis of functional MOF derivatives via different pyrolysis strategies as well as afford a further understanding of the crucial role of oxygen vacancies.

Insight into photocatalytic nitrogen fixation on graphitic carbon nitride: Defect-dopant strategy of nitrogen defect and boron dopant

Designing efficient semiconductors for photocatalytic nitrogen reduction reaction (N2RR) is an urgent challenge for artificial ammonia (NH3) production under ambient condition. Graphitic carbon nitride (GCN) shows fascinating potential in conversion of inert chemical bonds into high-value-added products. However, the low NH3 conversion efficiency in GCN leads to unsatisfied practical application. Herein, a defect-dopant strategy through introduction of nitrogen defects and boron (B) heteroatoms is proposed to boost NH3 production. The optimal catalyst shows enhanced photocatalytic activity with NH3 conversion rate of 435.28 μmol g−1 h−1 under visible light illumination. The boosting NH3 production is owing to the synergistic effect of nitrogen defect and B dopant. The nitrogen defect is favorable for promoting the optical harvesting ability, charge carrier separation efficiency as well as N2 adsorption ability. B dopant not only enhances N2 adsorption and activation ability, but also maintains the high reduction ability of BNUCNx. Density functional theory (DFT) calculation shows that high adsorption energy for N2 and longer N–N bond length of N2 are simultaneously obtained in BNUCNx, contributing to NH3 production. Furthermore, the high molecular oxygen activation ability in BNUCNx shows great potential for environmental remediation. This work provides a pioneering perspective for enhancing photocatalytic N2RR through defect-dopant strategy.

Modification of Au nanoparticles electronic state by MOFs defect engineering to realize highly active photocatalytic oxidative esterification of benzyl alcohol with methanol

Defect modified UiO-66 supported Au nanoparticles exhibited excellent catalytic performance in the oxidative esterification of benzyl alcohol with methanol under mild conditions. The defects were generated by introducing HCl during the preparation procedure. The defects exposed the Lewis acid of coordinatively unsaturated metal sites, which is benefit for Au loading and changing Au nanoparticles (NPs) to a negative electron state. The negatively charged Au nanoparticle promoted the reaction by strong oxygen activation ability. The present study could help to unravel the synergistic effect of support and metal interaction and provides an efficient photocatalytic route for synthesis high-value esters in terms of sustainable chemistry.

Mesoporous cobalt monoxide-supported platinum nanoparticles: Superior catalysts for the oxidative removal of benzene

Mesoporous Co3O4 (meso-Co3O4)-supported Pt (0.53 wt.% Pt/meso-Co3O4) was synthesized via the KIT-6-templating and polyvinyl alcohol (PVA)-assisted reduction routes. Mesoporous CoO (meso-CoO) was fabricated through in situ reduction of meso-Co3O4 with glycerol, and the 0.18–0.69 wt.% Pt/meso-CoO samples were generated by the PVA-assisted reduction method. Meso-Co3O4 and meso-CoO were of cubic crystal structure and the Pt nanoparticles (NPs) with a uniform size of ca. 2 nm were well distributed on the meso-Co3O4 or meso-CoO surface. The 0.56 wt% Pt/meso-CoO (0.56Pt/meso-CoO) sample performed the best in benzene combustion (T50% = 156 °C and T90% = 186 °C at a space velocity of 80,000 mL/(g h)). Introducing water vapor or CO2 with a certain concentration led to partial deactivation of 0.56 Pt/meso-CoO and such a deactivation was reversible. We think that the superior catalytic activity of 0.56 Pt/meso-CoO was intimately related to its good oxygen activation and benzene adsorption ability.

Self‐assembly of Atomically Dispersed Ag Catalysts on Polyhedral Co3O4 at Elevated Temperatures: A Top‐Down Nanofabrication of High‐Loading Atomically Dispersed Catalysts

AbstractCatalysts based on atomically dispersed noble metal catalysts have attracted considerable attention due to their enhanced reactivity and selectivity. However, to prevent the formation of metal nanoparticles and to keep the dispersity of isolated single atoms on surface, the loading concentration of the noble metal must be kept low (usually below 0.5 %). Here, we report a self‐assembly approach for synthesizing a stable atomically dispersed silver‐cobalt oxide catalyst on polyhedral Co3O4 nanoparticles containing Ag up to 10 wt % at elevated temperature. The sample‐averaged extended X‐ray absorption fine structure (EXAFS) analysis revealed the presence of highly dispersed Ag species along with small Ag clusters. The coordinatively unsaturated Co3+ centers present on the {110} facets of the Co3O4 surface were shown to be crucial for anchoring catalytically active single Ag atoms. Control experiments showed that polyhedral Co3O4 was more effective than Co3O4‐cube and Co3O4‐octahedron at anchoring Ag atoms. The oxidized nature of the atomically dispersed Ag sites was revealed by X‐ray absorption near‐edge structure (XANES) Ag−L3‐edge spectra. From the H2‐temperature programmed reduction and CO oxidation test, it was discovered that downsizing catalytically active components from nanocrystals to single atoms not only enhanced the catalytic activity, but also endowed single‐atom catalysts with exceptional oxygen activation ability at low temperature.

A dual transfer strategy for boosting reactive oxygen species generation in ultrathin Z-scheme heterojunction driven by electronic field

Reactive oxygen species (ROS), which are generated from molecular oxygen activation and oxidization of H2O/OH− in photocatalysis process, are vital for environmental remediation. In this study, a dual strategy for boosting ROS generation is proposed by construction of ultrathin Z-scheme heterojunction of Bi5O7I/g-C3N4. The charge-carrier-quenching effect is inhibited attributed to the prepared ultrathin 2D/2D heterojunction. Profiting from the interfacial charge properties, the boosting molecular oxygen activation and oxidization ability are obtained in the heterojunction. In comparison with pristine catalysts, the yield amount of superoxide (O2−) in Bi5O7I/g-C3N4 case shows enhancement. Furthermore, controllable experiments demonstrate that the generation of hydrogen peroxide (H2O2) is through two-step electron reduction strategy, and it can decompose into hydroxyl radicals (OH) assisted with photoelectrons. The singlet oxygen (1O2) is produced by two transfer pathways including charge transfer and energy transfer. Through DFT calculation, the built-in electronic field (IEF) is formed owing to the electron configuration. The IEF in the heterojunction tunes the charge transfer from type-II to Z-scheme model. Simultaneously, the short charge transfer distance enables more high energy charge carriers to reach the surface of solid catalyst for catalytic reactions. Owing to the boosting ROS generation, the novel composite shows enhanced photocatalytic performance for ciprofloxacin (CIP) degradation. This study gives a proof-of-concept perspective on fabrication of 2D/2D Z-scheme heterojunction with boosting ROS generation for environmental remediation and energy conversion.

Oxygen Vacancy-rich Porous Co3O4 Nanosheets toward Boosted NO Reduction by CO and CO Oxidation: Insights into the Structure-Activity Relationship and Performance Enhancement Mechanism.

Oxygen vacancy-rich porous Co3O4 nanosheets (OV-Co3O4) with diverse surface oxygen vacancy contents were synthesized via facile surface reduction and applied to NO reduction by CO and CO oxidation. The structure-activity relationship between surface oxygen vacancies and catalytic performance was systematically investigated. By combining Raman, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and O2-temperature programmed desorption, it was found that the efficient surface reduction leads to the presence of more surface oxygen vacancies and thus distinctly enhance the surface oxygen amount and mobility of OV-Co3O4. The electron transfer towards Co sites was promoted by surface oxygen vacancies with higher content. Compared with the pristine porous Co3O4 nanosheets, the presence of more surface oxygen vacancies is beneficial for the catalytic performance enhancement for NO reduction by CO and CO oxidation. The OV-Co3O4 obtained in 0.05 mol L-1 NaBH4 solution (Co3O4-0.05) exhibited the best catalytic activity, achieving 100% NO conversion at 175 °C in NO reduction by CO and 100% CO conversion at 100 °C in CO oxidation, respectively. Co3O4-0.05 exhibited outstanding catalytic stability and resistance to high gas hour space velocity in both reactions. Combining in situ DRIFTS results, the enhanced performance of OV-Co3O4 for NO reduction by CO should be attributed to the promoted formation and transformation of dinitrosyl species and -NCO species at lower and higher temperatures. The enhanced performance of OV-Co3O4 for CO oxidation is due to the promotion of oxygen activation ability, surface oxygen mobility, as well as the enhanced CO2 desorption ability. The results indicate that the direct regulation of surface oxygen vacancies could be an efficient way to evidently enhance the catalytic performance for NO reduction by CO and CO oxidation.

Novel CNT/PbBiO2Br hybrid materials with enhanced broad spectrum photocatalytic activity toward ciprofloxacin (CIP) degradation

In this work, novel multiwalled carbon nanotube (CNT)/PbBiO2Br composite photocatalysts have been prepared using reactable ionic liquid (IL) assisted solvothermal method. On the surface of PbBiO2Br ultrathin nanosheets, the CNT are uniform distribution. The obtained CNT/PbBiO2Br materials exhibit markedly enhanced photocatalytic performance for the photodegradation efficiency of antibiotic agent CIP under ultraviolet, visible and above 580 nm light irradiation. The introduction of CNT plays vital role in promoting the photocatalytic activity of CNT/PbBiO2Br composite catalysts. The CNT promote light absorbance, reduce the impedance and act as photoinduced electron separation center as well as pollutant degrading activity center. The electron spin resonance and active species trap experiments reveal that the O2− and holes are the main active species during the photocatalytic process. Compared with pure PbBiO2Br, the molecular oxygen activation ability of CNT/PbBiO2Br composite photocatalyst is evident promotion. A possible photocatalytic mechanism of CNT/PbBiO2Br materials has been proposed based on a series of experimental analysis. The strategy for the preparation of high-performance photocatalysts can be extended to design and tune other advanced broad spectrum photocatalytic materials.