Photocatalytic Oxygen Production Research Articles

Photocatalytic Oxygen Evolution under Visible Light Mediated by Molecular Heterostructures.

Due to their structural and property tunability, semiconductive conjugated polymers (CPs) have emerged as promising candidates for photocatalytic water splitting. Compared with inorganic materials, the photocatalytic performance of mono-component polymers was limited by the fast recombination of photoexcited charge carriers, and they always needed to catch up to expectations. To this end, researchers established molecular donor-acceptor heterostructures, which could notably promote oxygen production efficiency due to their more effective charge carrier separation. In this work, easy Schiff base reactions between side-chain -CHO groups and terminal -NH2 groups were used to introduce benzene and perylene diimide (PDI) into the molecular heterostructure to serve as electron donors (D) and electron acceptors (A). In particular, for the first time, we employed the molecular heterostructures of CPs to promote photocatalytic O2 production. One prepared molecular heterostructure was demonstrated to improve oxygen generation rate (up to 0.53 mmol g-1 h-1) through visible light-driven water splitting. Interestingly, based on the photoelectric properties, a stepwise two-electron/two-electron pathway constituted the photocatalytic mechanism for oxygen production with the molecular heterostructure. These results provide insights into designing and fabricating high-performance molecular heterostructures for photocatalytic oxygen production.

Microbial‐Enabled Photosynthetic Oxygenation for Disease Treatment

AbstractOxygen as one of the most critical substances in living organisms has attracted ever‐increasing attention in disease treatment, which is important in regulating metabolic activities. However, the hypoxia arising from disease is a prevalent problem, leading to observably reduced therapeutic effectiveness in photodynamic therapy, radiotherapy, sonodynamic therapy, etc. Therefore, the reversion of hypoxia becomes the basis for enhancing the disease treatment. Thanks to the development of nanotechnology, various nanomaterials with oxygen‐production capacity are explored to recover the function of oxygen in tissue, but there are still some limitations. The photosynthetic microorganisms (PSMs) are extensively applied for improving hypoxia in diseases due to their highly efficient photocatalytic oxygen production efficacy and desirable biocompatibility. In this review, the up‐to‐date research progress on therapeutic modalities of microbial‐based photosynthetic oxygenation (e.g., cancer treatment, wound healing, and tissue engineering) are summarized and highlighted. In addition, the key issue of biocompatibility/biosafety of microbial‐based treatment that is fundamental to apply in vivo is further emphasized and clarified. Finally, the present critical issues are discussed and the future evolution of microbial‐based treatment based on photosynthetic oxygenation is predicted, promoting further development and clinical applications.

Simultaneous Photocatalytic Oxygen Production and Hexavalent Chromium Reduction in Ag3PO4/C3N4 S-scheme Heterojunction

Simultaneous Photocatalytic Oxygen Production and Hexavalent Chromium Reduction in Ag3PO4/C3N4 S-scheme Heterojunction

Enhancement of the Photocatalytic Oxygen Production by Tantalum Nitride Supported Fe Atom Embedded N‐Doped Graphene Oxide†

Comprehensive SummaryEnergy crises and environmental pollution have become urgent problems with human civilization development. Photocatalysis technology is a green method to deal with these challenges. The key to improve photocatalytic efficiency lies in the effective separation of photogenerated electron–hole pairs. In this work, we designed the Fe atom embedded N‐doped graphene oxide (Fe‐NGO) supporting on tantalum nitride (Ta3N5) catalyst, which was employed to improve the photocatalytic oxygen production activity. The oxygen production of 5 wt% Fe atom embedded N‐doped graphene oxide supporting on tantalum nitride (Fe‐NGO/Ta3N5) was 184.7 μmol·g−1, about 3.5 times higher than that of the pure Ta3N5. The introduction of the cocatalyst Fe‐NGO acting as an electron conductor in the Fe‐NGO/Ta3N5 accelerates the carrier migration of Ta3N5 and further enhances the photocatalytic oxygen production activity. N‐doping increases the conductivity of graphene oxide (GO), and Fe atoms are used as the reactive sites to promote the combination of electron and sacrificial agent in the system. This work may provide insights into the research of new carbon cocatalyst materials.

Enhancing photocatalytic nitrogen fixation performance of Co-doped bismuth molybdate through band engineering tuning

Energy band engineering strategy by doping has been extensively proved to have great influence on photocatalytic properties of semiconductors. Herein, a novel Co-doped Bi2MoO6 (Co-BMO) photocatalyst was developed for photocatalytic nitrogen fixation. Co-BMO with microsphere structure was synthesized by a one-step solvothermal method. The NH3 yield of 0.3 % Co-BMO (130.07 μmol·h−1·gcat−1) was about 3.9 times higher than that of pure BMO without scavengers and visible light irradiation. The band gap of 0.3 % Co-BMO was reduced and the average PL lifetime was improved due to the successful doping of Co2+, which directly led to higher separation efficiency of photogenerated carriers and improved photocatalyst activity. In addition, gas chromatography (GC) tests showed that 0.3 % Co-BMO had a higher photocatalytic oxygen production capacity, which meant that more protons would be involved in the nitrogen reduction reaction. Their synergistic effect greatly enhanced the photocatalytic nitrogen fixation ability of 0.3 % Co-BMO. This novel photocatalyst may be a promising candidate for photocatalytic nitrogen fixation.

Visible-light photocatalytic oxygen production on a high-entropy oxide by multiple-heterojunction introduction

High-entropy oxides (HEOs), as multi-component ceramics with high configurational entropy, have been of recent interest due to their attractive properties including photocatalytic activity for H2 production and CO2 conversion. However, the photocatalytic activity of HEOs is still limited to ultraviolet light. In this study, to achieve visible-light-driven photocatalysis, 10 different heterojunctions were simultaneously introduced in the Ti-Zr-Nb-Ta-W-O system. The oxide, which was synthesized by a high-pressure torsion method and oxidation, successfully produced oxygen from water under visible light without co-catalyst addition. The photocatalytic performance was attributed to high visible-light absorption, low bandgap, appropriate band structure, presence of multiple heterojunctions and accordingly easy electron-hole separation and slow recombination. These results not only show the potential of high-entropy oxides as new visible-light-active photocatalysts, but also introduce the multiple-heterojunction introduction as a strategy to achieve photocatalysis under visible light.

Constructing 0D/1D Ag3PO4/TiO2 S-scheme heterojunction for efficient photodegradation and oxygen evolution

An S-scheme heterojunction photocatalyst is capable of boosting photogenerated carrier separation and transfer, thus maintaining high photooxidation and photoredox ability. Herein, a 0D Ag3PO4 nanoparticles (NPs)/1D TiO2 nanofibers (NFs) S-scheme heterojunction with intimate interfacial contact was designed via the the hydro-thermal method. Benefiting from the abundant hydroxyl groups and size confinement effect of TiO2 NFs, the average diameter of the Ag3PO4 nanoparticles decreased from 100 to 22 nm, which favored the construction of a 0D/1D geometry heterojunction. The multifunctional Ag3PO4/TiO2 sample exhibited excellent photocatalytic activity and stability in photocatalytic oxygen production (726 µmol/g/h) and photocatalytic degradation of various organic contaminants such as rhodamine B (100%), phenol (60%) and tetracycline hydrochloride (100%). The significant improvements in the photocatalytic performance and stability can be attributed to the intimate interfacial contacts and rich active sites of 0D/1D geometry, fast charge carrier migration, and outstanding photoredox properties induced by the S-scheme charge-transfer route. This work offers a promising strategy for constructing 0D/1D S-scheme heterojunction photocatalysts for improved photocatalytic performance.

Inside Back Cover: Boosting Photocatalytic Water Oxidation Over Bifunctional Rh0‐Rh3+ Sites (Angew. Chem. Int. Ed. 42/2021)

Bifunctional Rh0–Rh3+ sites anchored on Mo-doped BiVO4 show a high visible-light photocatalytic oxygen production activity, as reported by Peng Fei Liu, Zheng Jiang, Hua Gui Yang, and co-workers in their Research Article on page 22761. Operando XAFS results and DFT calculations illustrate the bifunctional OER mechanism on the Rh0–Rh3+ sites: the oxygen intermediate attacks the Rh3+ sites, facilitating a hydrogen atom transfer to the adjacent Rh0 sites, which synergistically optimizes the OER energetics.

Boosting Photocatalytic Water Oxidation Over Bifunctional Rh0 -Rh3+ Sites.

Photocatalytic water splitting provides an economically feasible way for converting solar energy into hydrogen. Great efforts have been devoted to developing efficient photocatalysts; however, the surface catalytic reactions, especially for the sluggish oxygen evolution reaction (OER), still remain a challenge, which limits the overall photocatalytic energy efficiency. Herein, we design a Rhn cluster cocatalyst, with Rh0 -Rh3+ sites anchoring the Mo-doped BiVO4 model photocatalytic system. The resultant photocatalyst enables a high visible-light photocatalytic oxygen production activity of 7.11 mmol g-1 h-1 and an apparent quantum efficiency of 29.37 % at 420 nm. The turnover frequency (TOF) achieves 416.73 h-1 , which is 378 times higher than that of the photocatalyst only with Rh3+ species. Operando X-ray absorption characterization shows the OER process on the Rh0 -Rh3+ sites. The DFT calculations further illustrate a bifunctional OER mechanism over the Rh0 -Rh3+ sites, in which the oxygen intermediate attacks the Rh3+ sites with assistance of a hydrogen atom transfer to the Rh0 sites, thus breaking the scaling relationship of various oxygen intermediates.

Boosting Photocatalytic Water Oxidation Over Bifunctional Rh0‐Rh3+ Sites

AbstractPhotocatalytic water splitting provides an economically feasible way for converting solar energy into hydrogen. Great efforts have been devoted to developing efficient photocatalysts; however, the surface catalytic reactions, especially for the sluggish oxygen evolution reaction (OER), still remain a challenge, which limits the overall photocatalytic energy efficiency. Herein, we design a Rhn cluster cocatalyst, with Rh0‐Rh3+ sites anchoring the Mo‐doped BiVO4 model photocatalytic system. The resultant photocatalyst enables a high visible‐light photocatalytic oxygen production activity of 7.11 mmol g−1 h−1 and an apparent quantum efficiency of 29.37 % at 420 nm. The turnover frequency (TOF) achieves 416.73 h−1, which is 378 times higher than that of the photocatalyst only with Rh3+ species. Operando X‐ray absorption characterization shows the OER process on the Rh0‐Rh3+ sites. The DFT calculations further illustrate a bifunctional OER mechanism over the Rh0‐Rh3+ sites, in which the oxygen intermediate attacks the Rh3+ sites with assistance of a hydrogen atom transfer to the Rh0 sites, thus breaking the scaling relationship of various oxygen intermediates.

Pentagonal transition-metal (group X) chalcogenide monolayers: Intrinsic semiconductors for photocatalysis

Two-dimensional (2D) materials attract enormous attention and show promising applications in many fields of science and technologies (nanodevices, energy storage/harvest and catalytic processes, etc.). Pentagonal compounds emerge as a new family in 2D materials along with classic trigonal transition metal dichalcogenides and MXenes, which have been intensively investigated to date. Encouraged by the successful synthesis of pentagonal PdSe2 using CVD method, we explore nine pentagonal monolayers, MX2 (M = Ni, Pd & Pt, and X = S, Se & Te), based on the first-principles calculations. We find that all MX2 are dynamically and thermodynamically stable, and intrinsic semiconductors. Our results show that PdTe2 exhibits excellent potential application in solar water splitting due to optimal band gap and suitable band-edge positions matching with both the water reduction and oxidation potentials (0 and 1.23 V vs. NHE). We further find that the majority of MX2 monolayers (except NiTe2) are applicable in photocatalytic oxygen production. Our findings are expected to shed light on the possible synthesis of pentagonal MX2 and their application in photocatalytic water splitting.

Cobalt monoxide/tungsten trioxide p-n heterojunction boosting charge separation for efficient visible-light-driven gaseous toluene degradation

A novel cobalt monoxide/tungsten trioxide p-n heterojunction was fabricated via a two-step hydrothermal method for improving the photocatalytic activity for gaseous pollutant degradation and oxygen evolution. The TEM characterization results indicated that the CoO nanoparticles with diameter of 30 nm were uniformly distributed on the surface of WO3 nanoplates, which not only increased the light absorption efficiency but also promoted charge separation efficiency owing to a formed internal electric field in p-n junction hybridized system. In all samples, 15 wt% CoO/WO3 displayed the highest photocatalytic activity, where the degradation conversion of toluene achieved to 85.4% in 4 h, which were 2.0- and 20.3-folds higher than that of WO3 and CoO, respectively. Besides, the as-prepared CoO/WO3 composite also exhibited significantly increased photocatalytic oxygen production under visible light irradiation. Moreover, by in-situ infrared spectra, the main intermediate products, including benzyl alcohol, benzaldehyde, benzoic acid and formate or acetate were clearly clarified at the interface over the catalysts. Combined with the ESR, VB-XPS and UPS, a possible mechanism for the photocatalytic process over the CoO/WO3p-n heterojunctions were proposed and discussed.

Solar-driven photocatalytic water oxidation of Ag3PO4/CNTs@MoSe2 ternary composite photocatalyst

Photocatalytic water splitting is a promising and effective way to simultaneously tackle energy requirement and environmental pollution. The fabrication of a novel and efficient non-metallic co-catalyst is increasingly essential for the improvement of photocatalytic oxygen production. Herein, a novel ternary composite based photocatalyst with high oxygen evolution activity was synthesized and fully characterized. The composite introduced here consists of CNTs and MoSe2 as a new cocatalyst in order to accelerate the activity of Ag3PO4 photocatalysis. The optimal oxygen generation rate of 102.3 μmol L−1 g−1 h−1 for the ternary Ag3PO4/CNTs@MoSe2 photocatalyst was achieved under the visible-light irradiation, which is higher than pure Ag3PO4 (2.88 times), Ag3PO4/CNTs (1.91 times) and Ag3PO4/MoSe2 (1.31 times) samples. The superior oxygen evolution is mainly attributed to CNTs@MoSe2 as binary co-catalysts which can bing about the effective separation and transportation of the photoexcited charge carriers and good electrical conductivity. The present work will set the foundations of designing high-performance Ag3PO4-based photocatalysts for energy and environmental applications.

Rational design of cocatalyst system for improving the photocatalytic hydrogen evolution activity of graphite carbon nitride

CoS-Co(OH)2 heterostructure with conductive polypyrrole (PPy) as charger transfer mediator were rationally designed and embedded onto the g-C3N4 photocatalyst as the dual noble-metal-free cocatalyst for the first time, for improving the transport, separation and utilization efficiency of the photo-generated charge carriers. Notably, CoS, acting as photocatalytic hydrogen production cocatalyst, not only facilitated the utilization of charge carriers, but also accelerated the charge separation owing to its lower flat band potential. Furthermore, Co(OH)2 photocatalytic oxygen production cocatalyst exhibited a synergistic effect with CoS for further improving the charge carriers utilization efficiency. Consequently, g-C3N4-PPy, ternary g-C3N4-PPy-CoS and quaternary g-C3N4-PPy-CoS-Co(OH)2 heterostructures exhibited the photocatalytic hydrogen production activities of 2.49, 23.27 and 46.67 μmol/h, which were 17, 155 and 311-fold in comparison with that of pristine g-C3N4, respectively. This work provided a hopeful insight for the design of high performance cocatalyst for improving the transport, separation and utilization of photo-exited charge carriers.

Surface-defect-rich mesoporous NH2-MIL-125 (Ti)@Bi2MoO6 core-shell heterojunction with improved charge separation and enhanced visible-light-driven photocatalytic performance

Mesoporous NH2-MIL-125(Ti)@Bi2MoO6 core-shell heterojunctions with surface defects were fabricated through a facile solvothermal method. The mesoporous core-shell structure with a large relative surface area of 87.7 m2 g−1 and narrow pore size of 8.2 nm extends the photoresponse to the range of visible light due to the narrow band gap of ∼1.89 eV. The visible-light-driven photocatalytic degradation efficiency of highly toxic dichlorophen and trichlorophenol were 93.28 and 92.19%, respectively, and the corresponding rate constants were approximately 8 and 17 times higher than the rates achieved by pristine NH2-MIL-125(Ti). The photocatalytic oxygen production rate was increased to 171.3 µmol g−1. Recycling for several cycles indicates high stability, which is favorable for practical applications. The excellent photocatalytic performance can be ascribed to the formation of the core-shell heterojunctions and to the surface defects that favor charge separation and visible light absorption; the mesoporous structure offers an adequate number of surface active sites and mass transfer. This novel mesoporous core-shell photocatalyst will have potential applications in the environment, and this strategy offers a new insight into fabrication of other high-performance core-shell structure photocatalysts.

Bi plasmon-enhanced mesoporous Bi2MoO6/Ti3+ self-doped TiO2 microsphere heterojunctions as efficient visible-light-driven photocatalysts

Bi plasmon-enhanced mesoporous Bi2MoO6/Ti3+ self-doped TiO2 microsphere heterojunctions (Bi-BMO/TiO2-x) have been synthesized by a mild hydrothermal method combined with an in situ solid-state chemical reduction process, and subsequently annealed at 400 °C in N2 atmosphere. The prepared Bi-BMO/TiO2-x photocatalysts are characterized by X-ray diffraction, N2 adsorption, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results reveal that Ti3+ self-doped TiO2 is loaded on surface of mesoporous Bi2MoO6 microsphere efficiently and metallic Bi is produced for surface plasmon resonance (SPR). Under visible-light irradiation, the heterojunctions photocatalyst shows excellent photodegradation and photoelectrochemical properties of ∼95% for phenol removal rate and 20 μA/cm2 for photocurrent density, respectively, which is several times higher than that of single component. Moreover, it also has high photocatalytic oxygen production with a rate of 134 μmol h-1 g-1. The enhanced photocatalytic activities are mainly attributed to the existence of Ti3+ self-doping and heterojunction structure, which narrow the band gap to extend photoresponse to visible light region. Another reason is the influence of SPR of metallic Bi. They all promote the spatial separation and transfer of photogenerated charge carriers.

Efficient photocatalytic oxygen production over Ca-modified LaTiO2N

LaTiO2N has been considered a promising candidate for efficient photocatalytic water splitting. However, its photocatalytic activity is often hampered by the presence of structural defects and poor charge mobility. In this work, we introduced Ca into the crystal structure of LaTiO2N via a simple co-precipitation method and investigated the photocatalytic and photoelectrochemical properties for the full range solid solution La1−xCaxTiO2+yN1−y (0⩽x, y⩽1). Our results show that incorporating Ca into LaTiO2N induces a strong structural shrinkage as well as a space group change from I mma to P nma around a middle doping point (x=0.5). The presence of Ca effectively boosts the photocatalytic oxygen production and aids photocurrent extraction for LaTiO2N. The best photocatalytic activity was achieved for sample La0.3Ca0.7TiO2.7N0.3 with oxygen production rate ∼66.96μmol/h under visible light illumination (λ⩾420nm), corresponding to apparent quantum efficiency ∼3.13%. XPS analysis revealed a substantial reduction in surface Ti3+ species and a removal of A-site cation segregation for samples containing Ca. Further photoelectrochemical analysis highlights the critical role of Ca in enhancing the charge mobility of LaTiO2N. The better photocatalytic performance of Ca-modified LaTiO2N can be understood as a result of defect removal, high charge mobility, and improved surface charge migration pathways that considerably prolong the lifetimes of photogenerated charges.

Zr-Doped Mesoporous Ta3N5 Microspheres for Efficient Photocatalytic Water Oxidation.

Tantalum nitride (Ta3N5) has been considered as a promising candidate for photocatalytic water splitting because of its strong visible-light absorbance as far as 600 nm. However, its catalytic activity is often hampered by various intrinsic/extrinsic defects. Here, we prepared a series of Zr-doped mesoporous tantalum nitride (Ta3N5) via a template-free method and carried out a detailed investigation of the role of Zr doping upon the photocatalytic performance. Various physicochemical properties including crystal structure, optical absorption, and so on were systematically explored. Our results show that doping Zr into Ta3N5 induces an enhancement of oxygen content and a suppression of absorption band around 720 nm, indicating an increase of ON• defects and a decrease of VN••• defects in the structure. Introduction of Zr significantly boosts the photocatalytic oxygen production of Ta3N5. The optimized photocatalytic oxygen production rate approaches 105 μmol h-1 under visible light illumination (λ ≥ 420 nm), corresponding to an apparent quantum efficiency as high as 3.2%. Photoelectrochemical analysis and DFT calculation reveal that the superior photocatalytic activity of Zr-doped Ta3N5 originates from a high level of ON• defects' concentration, which contributes to a high electron mobility, and a low level of VN••• defects' concentration, which often act as charge recombination centers.

Efficient Photocatalytic Oxygen Production over Nitrogen‐Doped Sr4Nb2O9 under Visible‐Light Irradiation

AbstractPhotocatalytic water splitting is an appealing process for solar energy conversions yet it is often limited by the slow oxidation of water to oxygen half‐reaction. Here we performed an investigation on N‐doped Sr4Nb2O9 as a water oxidation photocatalyst. Our results show that N doping is an effective approach to improve the visible‐light response of Sr4Nb2O9. Efficient photocatalytic oxygen production was observed after N doping, and the highest production rate of ∼27 μmol h−1 under visible‐light irradiation corresponds to an apparent quantum efficiency of ∼0.31 %. Clear anodic photocurrent can be generated under visible‐light illumination, and the flat‐band potential was determined to be ∼−1.25 V vs. Ag/AgCl at pH 7. Theoretical calculations reveal that N doping introduces additional valence bands and is responsible for the visible‐light response. Variations in light absorption and photo‐oxidation performance can be controlled by modifying these valence band positions using different nitridation temperatures.

Ag3PO4 Microcrystals Synthesized by Room-Temperature Solid State Reaction: Enhanced Photocatalytic Activity and Photoelectronchemistry Performance**Supported by the Beijing Higher Education Young Elite Teacher Project under Grant No YETP1297, the Fundamental Research Funds for the Central Universities under Grant No 2014MDLXYZY05, the Undergraduate Innovative Test Program of China under Grant Nos GCCX2015110009 and BEIJ2015110024, and the National Natural Science Foundation of China

Ag3PO4 microcrystals with highly enhanced visible light photocatalytic activity are prepared by a facile and simple solid state reaction at room temperature. The composition, morphology and optical properties of the as-prepared Ag3PO4 microcrystals are characterized by x-ray diffraction, scanning electron microscopy and UV-vis diffuse reflectance spectra. The photocatalytic properties of Ag3PO4 are investigated by the degradation of both methylene blue and methyl orange dyes under visible light irradiation. The as-prepared Ag3PO4 microcrystals possess high photocatalytic oxygen production with the rate of 673 μmolh−1 g−1. Moreover, the as-prepared Ag3PO4 microcrystals show an enhanced photoelectrochemistry performance under irradiation of visible light.