High Redox Ability Research Articles

NaBiO3/g-C3N4 Z-type heterojunction modified by Ag-anchorage to enhance the photocatalytic performance

NaBiO3/Ag/g-C3N4 photocatalyst with Z-type heterostructure was developed and synthesized using photo-deposition and hydrothermal treatment methods, yielding a composite material with high REDOX ability. Because Ag in the NaBiO3/Ag/g-C3N4 composite system served as an electron capture center, the separation efficiency of photoexcited carriers was greatly increased, and the carrier lifetime was extended, as indicated by photoelectrochemical analysis. The results show that NaBiO3/Ag/g-C3N4 had much superior photocatalytic activity than monomer materials under visible light. Under visible light irradiation, the 0.1g 6% NaBiO3/Ag/g-C3N4 photocatalyst removed 95% of tetracycline in 60min. The reaction major active components were ∙O2-, ‧OH and h+, as acquired by active species capture experiments and EPR tests. Based on this, the manufacturing pathway for active compounds showed the electron transfer pathway and photocatalytic mechanism of Z-type heterojunction.

Advancements in cobalt‐based oxide catalysts for soot oxidation: Enhancing catalytic performance through modification and morphology control

AbstractThe widespread use of diesel engines results in significant environmental contamination due to emitted pollutants, particularly soot particles. These pollutants are detrimental to public health. At present, one of the most effective ways to remove soot particles is the catalytic diesel particulate filter after‐treatment technology, which requires the catalyst to have superior low temperature activity. Compared with cerium oxide which is widely used, cobalt oxide in transition metal oxides has been widely studied in recent years because of its high redox ability and easy to control morphology. This paper elaborates on the influence of modification techniques such as doping, loading, and solid solution on the catalytic performance of cobalt‐based catalysts in soot oxidation. Along the same lines, it further reviews the research progress on cobalt‐based oxide catalysts with specific dimensional structures and morphologies in soot oxidation. Finally, it provides an outlook on the challenges faced by the theoretical basis and applied research of cobalt‐based catalysts in soot oxidation.

Fabrication of visible light responsive BaFe12O19/Ag/AgI composites with enhanced photocatalytic degradation of organic pollutants

A novel visible-light-driven (VLD) BaFe12O19/Ag/AgI photocatalysts were constructed through calcination and hydrothermal methods, in which BaFe12O19 of different mass ratios were introduced. The constructed Z-scheme heterojunction provided BaFe12O19/Ag/AgI composite catalytic with effective space carrier transport and higher redox ability. In particular, the as-prepared BaFe12O19/Ag/AgI degraded nearly 94 % of 2- mercaptobenzothiazole within 30 minutes of visible-light illumination, which was much superior to that of pure AgI (47 %) and BaFe12O19 (3 %). Moreover, BaFe12O19/Ag/AgI can be easily magnetically separated, so as to facilitate its efficient separation and recovery in practical application. Photocatalytic activity assays revealed that the as-synthesized BaFe12O19/Ag/AgI also exhibited good photodegradation capability towards Imidacloprid, Tetracycline and Carbamazepine. In particular, the complex had relatively high oxygen activation ability, and its photocatalytic H2O2 production performance was 1.29 times higher than that of the AgI monomer within 120 minutes, thus realizing rapid water disinfection. Overall, the constructed efficient Z-scheme BaFe12O19/Ag/AgI photocatalysts provide a novel insight in sewage purification.

Sonocatalytic degradation of tetracycline hydrochloride using SnO2 hollow-nanofiber decorated with UiO-66-NH2

In this study, a porous hollow nanofiber SnO2 was decorated with UiO-66-NH2 nanoparticles with straightforward solvothermal method and utilized for sonocatalytic degradation of tetracycline (TC) by ultrasonic irradiation (USI). The prepared materials were characterized using different techniques such as SEM, EDS, FTIR, XRD, BET, XPS, UV-DRS, EIS, and zeta potential. SnO2 PHNF/UiO-66-NH2 nanocomposite offered the highest apparent rate constant of 0.0397 min−1 which was 6.3 and 3.1 times higher than those obtained for SnO2 PHNF and UiO-66-NH2, respectively. The integration of nanocomposite components revealed the synergy factor of 1.58, which can be due to the created heterojunctions resulted in efficiently charge carriers separation and retaining high redox ability. The effects of different affecting parameters such as TC initial concentration, pH of the solution, catalyst dosage, trapping agents, and coexisting anions on the catalytic performance were examined. The inhibitory effects of anions were confirmed to be decreased in the sequence of Cl− > NO3− > SO42−, while the sonocatalytic efficiency of the nanocomposite improved considerably in the presence of humic acid and bicarbonate. Also, the excellent performance of the catalyst was preserved during six successive cycles, suggesting the high stability of the prepared catalyst. In addition, based on the scavenger analysis, the created O2·−, OH·, and holes were contributed to the TC degradation. In conclusion, the creation heterojunction is an impressive methodology for improving the sonocatalytic activity of a catalyst, and SnO2 PHNF/UiO-66-NH2 nanocomposite was introduced as a satisfactory catalyst in sonocatalytic degradation of organic contaminants.

Accurate construction of Cd/CdS/g-C3N4 heterojunction interface for efficient photocatalytic tetracycline degradation and Cr6+ reduction

With the increasing attention paid to environmental issues and the rapid development of photocatalytic environmental remediation technology, it is of great significance to develop catalysts with efficient photocatalytic environmental remediation capabilities. Graphite phase carbon nitride and its heterojunction are ideal choices for photocatalytic environmental remediation. Accurately constructing stable and well contacted heterogeneous interfaces is an effective means to improve catalytic efficiency. Herein, stable Cd/CdS/CN heterojunction interface was successful constructed by an in-situ synthesis method. Cd/CdS/CN photocatalysts exhibits excellent environmental remediation potential, capable of removing 88 % of high concentration TC (40 mg/L) within 60 min, and reducing over 96 % of Cr(VI) (50 mg/L) within 25 min under visible light, with good cycling stability. In addition, the reaction mechanism and TC degradation pathway of the composite photocatalyst with good photocatalytic activity were analyzed in depth. The experimental results confirmed that the synergistic effect of Z-Scheme heterojunction and Ohmic junction significantly improved the separation and migration of photogenerated carriers in the system, and maintained a high redox ability. This work provides a new reference for constructing CN based heterojunction photocatalysts with close contact.

In situ fabrication of oxygen deficient Bi2MoO6/InVO4/CeVO4 dual S-scheme ternary heterostructure for robust photocatalytic H2 and H2O2 production

Mild in situ synthesis of ternary dual S-scheme heterostructure photocatalyst with high redox ability of photo-excitons is a pragmatic approach for achieving rapid activation of tenacious atmospheric molecules. In the present study, a series of Bi2MoO6/InVO4/CeVO4 ternary heterostructures were constructed by in situ deposition of Bi2MoO6 nanoplates over one pot synthesised InVO4/CeVO4 using a facile oil bath heating method. The as-synthesised heterostructure materials were comprehensively characterised to understand their structural, optical, electrochemical and morphological properties. The ternary heterostructure displayed a distinct morphology consisting of Bi2MoO6 nanoplates, CeVO4 nanosheets and InVO4 nanorods. The significant intergrowth among the constituent phases through the in situ coupling strategy also led to the construction of tight interfacial microscopic junctions. The important attributes of the ternary heterostructures included intense photon absorption in whole UV–visible region, drastic decrease in photogenerated charge recombination and higher excited state lifetime. Both InVO4 and CeVO4 individually as well as the ternary heterostructure contained surface oxygen vacancies that further promoted efficient charge separation and activation of atmospheric molecules. The optimised ternary photocatalyst displayed 2314 μmol/g/h H2 generation and 1700 μM/g/h H2O2 production which are 12–86 and 11–27 times higher than the pristine semiconductors, respectively. Detailed band position assessment and radical entrapment analysis suggested the occurrence of a dual S-scheme charge transfer mechanism that rationally accounted for the remarkable enhancement in the photocatalytic performance.

Boosted charge separation in porphyrin-based MOFs/CdS photocatalyst via interfacial −N−Cd− bridge bond construction

The high interfacial charge transfer barrier has been a main thermodynamic obstacle for improving the catalytic efficiency of heterojunction materials. Optimizing the interfacial environment is an effective strategy to achieve high catalytic efficiency. Herein, the coordinate bond (−N−Cd−) is designed to connect the hafnium porphyrin−metal organic framework (HT) and CdS nanoparticles, which is systematically analyzed by the 1H NMR, FTIR, Raman and DRS, respectively. The optimized 15HT1.5 H/CdS6 composite featuring interfacial bridge bonds, exhibits an H2 production up to 11.9 mmol·g−1·h−1, which is 28.5, 52.8 and 7 times greater than pure CdS, HTH, and mechanically mixed sample without interfacial chemical bonds connected, respectively. Mechanistic study suggests that the coordination bonds between HT and CdS serve as the directional carrier transfer bridges, significantly improving interfacial charge separation and chemical stability. Moreover, the formed Z-scheme charge transfer mechanism also endows the composite with high redox ability. This strategic construction of interfacial chemical bonds within heterojunction provides an effective pathway for improving interfacial charge transfer in the heterojunction photocatalysts.

Visible light responsive photocatalytic fuel cell with Ce-UiO-66/g-C3N4/Bi2WO6/Ti photoanode for simultaneous degradation of rhodamine B and electricity generation

In order to enhance the carrier separation efficiency and redox ability of photoanode, a dual Z-scheme heterojunction Ce-UiO-66/g-C3N4/Bi2WO6/Ti photoanode was prepared and assembled with Cu cathode to form PFC. The characterization results show that Ce-UiO-66/g-C3N4/Bi2WO6 uniformly distributed on the Ti substrate, with average crystallite size of 9.04 nm and average particle size of 33.05 nm, which provides sufficient reactive active sites for RhB degradation. The RhB degradation rate, Pmax, Jsc, Voc and FF of the PFC were 90.9 % (90 min), 7.53 µW cm-2, 0.152 mA cm-2, 0.37 V and 0.134, respectively. The turnover frequency (TOF) for RhB degradation by the PFC reached 0.98 h-1. Fermi energy level analysis shows that a double-Z heterojunction is formed between Bi2WO6 and g-C3N4, and between Bi2WO6 and Ce-UiO-66, which not only effectively separates photogenerated e--h+, but also retains the high redox ability of the composite. Moreover, with the introduction of Ce-UiO-66, the composite photoanode has larger specific surface area and wider visible light absorption range. In addition, because of the built-in electric field, the photogenerated electrons can migrate to the surface of composite particles more easily and react with dissolved oxygen to generate more •O2- to participate in the degradation of RhB. This work provides a valuable reference for developing PFC photoanode with high efficiency and visible light response.

Indium oxide-based Z-scheme hollow core–shell heterostructure with rich sulfur-vacancy for highly efficient light-driven splitting of water to produce clean energy

Crafting an inorganic semiconductor heterojunction with defect engineering and morphology modulation is a strategic approach to produce clean energy by the highly efficient light-driven splitting of water. In this paper, a novel Z-scheme sulfur-vacancy containing Zn3In2S6 (Vs-Zn3In2S6) nanosheets/In2O3 hollow hexagonal prisms heterostructrue (Vs-ZIS6INO) was firstly constructed by an oil bath method, in which Vs-Zn3In2S6 nanosheets grew on the surfaces of In2O3 hollow hexagonal prisms to form a hollow core–shell structure. The obtained Vs-ZIS6INO heterostructrue exhibited much enhanced activity of the production of H2 and H2O2 by the light-driven water splitting. In particular, under visible light irradiation (λ > 420 nm), the rate of generation of H2 of Vs-ZIS6INO sample containing 30 wt% Vs-Zn3In2S6 (30Vs-ZIS6INO) could reach 3721 μmol g–1h−1, which was 87 and 6 times higher than those of Zn3In2S6 (43 μmol g–1h−1) and Vs-Zn3In2S6 (586 μmol g–1h−1), respectively. Meanwhile, 30Vs-ZIS6INO could exhibit the rate of H2O2 production of 483 μmol g–1h−1 through the dual pathways of indirect 2e– oxygen reduction (ORR) and water oxidation (WOR) without adding any sacrifice agents, far exceeding In2O3 (7 μmol g–1h−1) and Vs-Zn3In2S6 (58 μmol g–1h−1). The excellent photocatalytic activities of H2 and H2O2 generations of Vs-ZIS6INO sample might result from the synergistic effect of the sulfur vacancy, hollow core–shell structure, and Z-scheme heterostructure, which accelerated the electron delocalization, enhanced the absorption and conversion of solar energy, reduced the carrier diffusion distance, and ensured high REDOX ability. In addition, the possible photocatalytic mechanisms for the production of H2 and H2O2 were discussed in detail. This study provided a new idea and reference for constructing the novel and efficient inorganic semiconductor heterostructures by coordinating vacancy defect and morphology design to adequately utilize water splitting for the production of clean energy.

Enhanced charge separation via ZnIn2S4@S-doped-C3N4 S-scheme heterojunction for efficient photocatalytic water splitting under visible light

Heterojunction photocatalysts possess high efficiency in photogenerated electron-hole separation, which give significant advantages in the field of solar hydrogen production. Herein, a novel ZnIn2S4@S doped g-C3N4 (ZIS@SCN) heterojunction with mesoporous structure was prepared for photocatalytic water splitting under visible light. Characterization showed that the element of S was successfully introduced into g-C3N4 (CN) by replacing N to form C–S–C bonds and significantly enhanced the visible light absorption ability. The constructed heterojunction exhibited excellent photocatalytic hydrogen evolution under visible light. The best performance belonged to the sample of ZIS@100SCN. The corresponding H2 production rate reached 9.3 mmol h−1 g−1, which was 1.87-fold higher than that of the undoped one. More importantly, the heterojunction realized overall water splitting of H2 and O2 evolution simultaneously with good stability. The mechanism analysis indicted that introducing the element of S could regulate the band structure of CN and induce the charge transfer switching of a ZnIn2S4@g-C3N4 (ZIS@CN) photocatalyst from Ⅰ-type to S-scheme, which promoted the efficient spatial charge separation and maintained the high redox ability of the ZIS and SCN. This work provides an insight in construction high performance S-scheme heterojunction for water splitting with a doping method.

Protonated g-C3N4/oxygen-doped g-C3N4 S-scheme homojunction fabricated by electrostatic self-assembly for photocatalytic hydrogen evolution and tetracycline hydrochloride degradation

S-scheme photocatalytic systems with high redox ability and separation efficiency of photoexcited charge carriers supply considerable prospects for environmental optimization and sustainable energy development. However, coupling well-suited reduction and oxidation components for target reactions remains a challenge worth exploring. Herein, an efficient S-scheme system for H2 generation and tetracycline hydrochloride (TCH) photodegradation based on protonated g-C3N4 (PCN) coupling with oxygen-doped g-C3N4 (OCN) is fabricated via a facile electrostatic self-assembly strategy. Intimate interfacial interactions originating from the ultrathin nanostructure and staggered energy band arrangement for the S-scheme charge transfer pathway provide compelling advantages for the highly efficient separation of photoinduced electron-hole pairs in the as-designed PCN/OCN homojunction. The in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) techniques and electron paramagnetic resonance (EPR) measurements are applied to confirm the successful construction and the validity of the S-scheme charge transfer pathway. The obtained PCN/OCN composites with optimal ratio achieve a decent H2 generation rate of 6184.7 μmol g−1 h−1 outpacing the single PCN by approximately 4.8-fold, and 90.5 % TCH photodegradation efficiency is also realized within 90 min. This work provides a delicate fresh round of elevation for the exploration of an effective photocatalytic system.

CoMnOx Nanoflower-Based Smartphone Sensing Platform and Virtual Reality Display for Colorimetric Detection of Ziram and Cu2.

Transition metal doping is an ideal strategy to construct multifunctional and efficient nanozymes for biosensing. In this work, a metal-doped CoMnOx nanozyme was designed and synthesized by hydrothermal reaction and high-temperature calcination. Based on its oxidase activity, an "on-off-on" smartphone sensing platform was established to detect ziram and Cu2+. The obtained flower-shaped CoMnOx could exhibit oxidase-, catalase-, and laccase-like activities. The oxidase activity mechanism of CoMnOx was deeply explored. O2 molecules adsorbed on the surface of CoMnOx were activated to produce a large amount of O2·-, and then, O2·- could extract acidic hydrogen from TMB to produce blue oxTMB. Meanwhile, TMB was oxidized directly to the blue product oxTMB via the high redox ability of Co species. According to the excellent oxidase-like activity of CoMnOx, a versatile colorimetric detection platform for ziram and Cu2+ was successfully constructed. The linear detection ranges for ziram and Cu2+ were 5~280 μM and 80~360 μM, and the detection limits were 1.475 μM and 3.906 μM, respectively. In addition, a portable smartphone platform for ziram and Cu2+ sensing was established for instant analysis, showing great application promise in the detection of real samples including environmental soil and water.

First-principles study of direct Z-scheme GaS/WTe2 van der Waals heterostructure as photocatalyst for water splitting

The effective separation of charge carriers and the redox capacity for water splitting are two crucial factors that influence photocatalysis. Here, we studied the photocatalytic properties of GaS/WTe2 van der Waals heterostructure (vdWH) using first-principle calculations. The results show that this heterostructure acts as a direct Z-scheme with GaS as the water oxidation photocatalyst and WTe2 as the water reduction photocatalyst. Photogenerated charge carriers are efficiently separated, with electrons in GaS combining with holes in WTe2, while other charge carriers with high redox ability remain in the respective materials for water splitting. More importantly, the heterostructure exhibits excellent performance in all acid and alkali solutions (pH 0–14) and has strong light absorption in the ultraviolet (UV) and visible region. The power conversion efficiency(PCE) reaches 19.73%. This work reveals that GaS/WTe2 heterostructure is a highly promising material for photocatalytic water splitting.

Synergy of oxygen vacancies, Lewis acid sites, and interfacial chemical bonds on ZnSnO3/AgI for photodegradation of tetracycline

Chemically bonded Z-scheme ZnSnO3/AgI composites rich in oxygen vacancies (OVs) and Lewis acid sites were prepared successfully and showed excellent photocatalytic activities. Especially, ZnAg-2 degraded 96.1% tetracycline under visible light irradiation for 15 min. OVs contributed to Lewis acid sites production and interfacial chemical bonds formation through weakening the metal−O bonding. Lewis acid sites favored the adsorption of electron-rich tetracycline. Interfacial chemical bonds together with Z-scheme structure accelerated electron transfer and retained the high redox ability of ZnSnO3 and AgI. OVs contributed to singlet oxygen (1O2) production through facilitating the energy transfer from triplet exciton to O2. ZnSnO3/AgI composites possess good reusability and show great practical application potential. Based on ROSs generation and photoreduction experiment, the photocatalytic mechanism of the ZnAg composites was proposed. The possible degradation pathway was deduced and the biological toxicity was evaluated based on detected degradation intermediates. This work highlights the significant roles of OVs, Lewis acid sites, and chemical bonding in improving the photocatalytic activity of Z-scheme composites and provides new insight into designing high efficient photocatalysts.

Nanoflower-like TiO2/CoAl-layered double hydroxide direct Z-scheme for boosted photocatalytic CO2 conversion

Direct Z-scheme heterojunction (DZH) has promising potential in photocatalytic carbon dioxide reduction (PCR) owing to its unusual charge transfer pathway, exceptional charge separation efficiency, and high redox ability. Herein, ultrathin TiO2 nanosheets (NSs) have been employed as a substrate for the in-situ growth of CoAl layered double hydroxide (LDH) NSs to fabricate nanoflower-like TiO2/CoAl-LDH (TCA) DZH. The unconsolidated heterostructure is beneficial for active site exposure and mass transfer, and the inherent alkalinity of CoAl-LDH promoted the adsorption of CO2, synergistically boosting the process of PCR reaction in the TCA system. Simulated calculation and in-situ analysis jointly demonstrate the unique electron transfer processes during hybridization and photoexcitation. The resulting (-)TiO2/(+)CoAl-LDH interfacial electric field and DZH further lead to efficient separation of photogenerated charges of TCA. In the solid–gas system, the optimized TCA heterojunction exhibits a competitive PCR activity (76.18 μmol g−1h−1 for CO production rate) increase of 31.6 and 20.3 times compared to TiO2 and CoAl-LDH, respectively.

Pillar[5]arene functionalized Au NPs and BiOX (Cl/Br/I) heterojunction constructed the enhanced photo-electrochemical sensor for ultrasensitive detection of serotonin

The functional photoelectric materials based on bismuth oxyhalides (BiOX, X = Cl, Br and I) have been widely used in the field of photo-electrochemistry (PEC) due to their excellent physical, chemical and optical properties. Herein, a series of BiOX nanoflowers conjugated water-soluble pillar[5]arenes functionalized Au (Au@WP5/BiOX) modified PEC sensor are constructed and investigated for the PEC detection of serotonin. Upon exploring the physical properties, such as size, visible light absorption capacity, band gap and impedance, of the three BiOX materials, it is discovered that BiOBr is more effective in detecting 5-HT due to its high redox ability, moderate band gap (∼2.03 eV), and low impedance. BiOBr can provide a high and stable starting photocurrent compared to the other two bismuth oxyhalides. When used in acidic or neutral environments, 5-HT with a positive charge can undergo electrostatic adsorption and host-guest complexation behavior with WP5, which has a negative charge. By using WP5, the recognition ability of the material to 5-HT molecules can be enhanced, and the adsorption of 5-HT molecules on Au@WP5/BiOBr can be accelerated. The local surface plasmon resonance effect (LSPR) of gold nanoparticles (Au NPs) can accelerate the electrochemical reaction rate and charge transfer rate, which ultimately leads to the amplification of the photocurrent signal. As a result, the 5-HT detection sensor based on Au@WP5/BiOBr has a wide detection range from 0.01 to 100 μM and a low detection limit of 3 nM (S/N = 3) compared to other sensors, including Au@WP5/BiOCl and Au@WP5/BiOI. The proposed PEC sensor also exhibits good stability and selectivity, making it a promising strategy for detecting biological small molecules using pillar[5]arene functionalized PEC active materials.

Construction of B doped g-C3N4/Ni-MOF-74 porous heterojunction with boosted carrier separation for photocatalytic H2 generation

Novel heterojunction is favored to improve the separation of photogenerated carriers and maintain high redox ability. A porous heterojunction combining porous metal-organic frameworks (MOF), Ni-MOF-74, and porous B-doped g-C3N4 (BCN) was fabricated for solar-light-driven H2 generation. The permeable surface and type-I carrier transfer mode not only created more reactive sites for H2 generation but also facilitated mass transfer at the contact interphase among BCN and Ni-MOF-74 due to a slight difference in their valence bond energy, which enhanced the excellent light trapping ability and expanded spectral absorbance range and thus solving the intrinsic drawback of fast charge recombination of pristine g-C3N4. Besides that, B-doping enhanced redox ability and transport separation, and the BCN/Ni-MOF-74 composite demonstrated dramatically reduced hydrogen production overpotential. The optimal BCN-NM-3 showed outstanding H2 generation up to 2190 μmol g−1h−1, almost 11 times higher than BCN. The current study will benefit the development of new MOF-based photocatalysts and be influential in meeting environmental demands in the future.

Selective efficient photocatalytic degradation of antibiotics and direct Z-type migration pathway for hierarchical core-shell TiO2/g-C3N4 composites.

Constructing superior Z-type photocatalytic heterojunction is beneficial to effectively enlarge interface contact, improve the photo-generated carrier separation rate, and retain the high redox ability. In this work, we designed a hierarchical core-shell g-C3N4/TiO2 structure to build Z-type heterojunction via combining simple template method and pyrolysis process. A close-knit Z-type heterojunction was constructed using TiO2 as a thick core and g-C3N4 as an ultra-thin shell. The effects of lamp source, wavelength, tetracycline (TC) concentration, and photocatalyst dose on the degradation performance on TC of g-C3N4/TiO2 were inspected. 0.1TiO2/g-C3N4 photocatalyst had the best degradation rate and highest removal rate within 30min, and its degradation rate was about 49, 23, and 5 times than pure g-C3N4, TiO2, and commercial TiO2/g-C3N4 in respect. Moreover, compared with degradation ability under Xenon lamp, LED irradiation for g-C3N4/TiO2composites showed aremarkable selectivedegradation. The fast and efficient Z-type transfer pathway of 0.1g-C3N4/TiO2 was realized by forming an optimized interface and abundant surface active sites ascribed to the combined action of thick TiO2 core and ultra-thin g-C3N4 shell. In addition, the degradation intermediates were analyzed by LC-MS and suggested pathways of degradation. The work could provide novel design concept to obtain reliable Z-type photocatalysts with hierarchical core-shell structure applied in degradation of antibioticwastewater.

Improvement of separation, transfer and redox ability arising from P–N heterojuncted composite phosphate-group-intercalated g-C3N4 /Bi2WO6

Graphitic carbon (g-C3N4, CN) is a promising candidate in photosynthesis and photocatalytic fields owing to various advantages, particularly the very negative conduction band minimum. But its low transfer ability limits the application. Recently, in our early-stage work, intercalating the phosphate (P) group into the layer gap of CN resulted in better transfer properties and a transition from N- to P-type, but reduced the redox ability of the photoinduced carriers. Here, a P–N-type heterojunction-structured composite [P-group intercalated g-C3N4 (NP–CN)/Bi2WO6 (BWO), NPB] was prepared to improve redox and transfer ability in a CN-based photocatalyst. p-Nitrophenol can be photodegraded into harmless products over NPB in 120 min. The apparent constant rates (k-s) of NPB are 2.45 and 42.97 times those of pure CN and BWO, respectively. The mechanism has three effects. First, the nitrogen vacancies arising from P-group intercalation in the NP-CN layer of NPB supply a quick transfer channel for carriers. Second, the hybridization of NP-CN with BWO causes more negative ECB on the NP-CN side and more positive EVB on the BWO side, suggesting high-redox ability. Third, the generation of offsets in ECB and EVB in NPB owing to the spike offset of the energy band due to the P–N heterojunction helps maintain high-redox electrons in ECB and holes in EVB in NPB. This study provides a novel route to simultaneously improve transfer and separation ability, as well as redox ability, in a hybridized photocatalyst.

Engineering Mn–O strength in manganese oxide catalyst to enhance propane catalytic oxidation

Developing highly active and thermally stable transition-metal-oxide catalysts for light alkane catalytic oxidation is of great importance but very challenging. In the work, the catalytic performance for propane deep oxidation was significantly enhanced on the Mn1NixOy solid solution catalyst by weakening the Mn–O bond strength of manganese oxide. The characterization results combined with DFT calculations demonstrated that the introduction of Ni could create additional defect sites, resulting in a significant improvement of the adsorption and the activation of both propane and oxygen molecules. The optimal Mn1Ni0.15Oy catalyst exhibits abundant oxygen vacancies with low MnO bond strength, high redox ability and oxygen mobility, which account for its superior activity. Specifically, the specific reaction rate on Mn1Ni0.15Oy is three times higher than that on pure Mn2O3. Moreover, a Mn1Ni0.15Oy/cordierite monolithic catalyst was made by wash-coating method, and exhibited remarkable catalytic performance and stability on catalytic oxidation of propane during the 45 days (1080 h) on stream, even after tens of high temperature thermal shocks (up to 650 ℃), which declared to be satisfied for practical industrial applications. This work will shed light on designing high-efficiency and long-life environmental catalyst for VOCs elimination.