Efficient Photocatalytic Oxygen Research Articles

Designing delafossite CuAl1-xTMxO2 solid solutions: the role of 3d transition metal spin states in photo(electro)catalytic performance

This study delves into the effects of 3d transition metal (TM) spin states on the structural and electronic properties of CuAl1-xTMxO2 solid solutions, focusing on their implications for photo(electro)catalytic performance. The research reveals that the Jahn–Teller distortion, associated with TM3+, is a critical factor in determining the lattice parameters and photo(electro)catalytic performances. Solid solutions without Jahn–Teller distortion adhere to Vegard's law, whereas those with strong distortion exhibit deviations, indicating the influence of TMO6 octahedral distortion on solubility and lattice parameters. The electronic structure of solid solutions with weak Jahn–Teller distortion is governed by the O–Cu–O and TMO6 crystal fields, which leads to a narrowed bandgap and reduced conduction band minimum (CBM), impacting the hydrogen evolution potential. In particular, the CuAl0.5Cr0.5O2 shows a significant enhancement in photocurrent density and hydrogen production rate due to its balanced light absorption and effective charge carrier separation. In contrast, the weak Jahn–Teller distortion in CuAl1-xFexO2 results in localized electronic states at CBM, leading to diminished carrier mobility. Solid solutions with strong Jahn–Teller distortion, such as CuAl1-xTMxO2 (TM = Mn and Ni), display a range of electronic properties from semiconductor to semimetallic, with the semimetallic CuAl0.9Mn0.1O2 capable of infrared light absorption and efficient photocatalytic hydrogen and oxygen production.

Cs-Doped WO3 with Enhanced Conduction Band for Efficient Photocatalytic Oxygen Evolution Reaction Driven by Long-Wavelength Visible Light.

Cesium doped WO3 (Cs-WO3) photocatalyst with high and stable oxidation activity was successfully synthesized by a one-step hydrothermal method using Cs2CO3 as the doped metal ion source and tungstic acid (H2WO4) as the tungsten source. A series of analytical characterization tools and oxygen precipitation activity tests were used to compare the effects of different additions of Cs2CO3 on the crystal structure and microscopic morphologies. The UV-visible diffuse reflectance spectra (DRS) of Cs-doped material exhibited a significant red shift in the absorption edge with new shoulders appearing at 440-520 nm. The formation of an oxygen vacancy was confirmed in Cs-WO3 by the EPR signal, which can effectively regulate the electronic structure of the catalyst surface and contribute to improving the activity of the oxygen evolution reaction (OER). The photocatalytic OER results showed that the Cs-WO3-0.1 exhibited the optimal oxygen precipitation activity, reaching 58.28 µmol at 6 h, which was greater than six times higher than that of WO3-0 (9.76 μmol). It can be attributed to the synergistic effect of the increase in the conduction band position of Cs-WO3-0.1 (0.11 V) and oxygen vacancies compared to WO3-0, which accelerate the electron conduction rate and slow down the rapid compounding of photogenerated electrons-holes, improving the water-catalytic oxygen precipitation activity of WO3.

Efficient photocatalytic molecular oxygen activation by TTF-based heterojunction for water purification

Tetrathiafulvalene (TTF), one of the well-known organic photoelectric materials, was served as active sites to accelerate the activation of molecular oxygen to degrade organic pollutants. Herein, a kind of Z-scheme heterojunction photocatalysis was constructed based on g-C3N4 and TTF. According to the experimental results, the mechanism of Z-scheme heterojunction was supported, in which photogenerated electrons transferred from g-C3N4 to TTF. More importantly, TTF on the catalyst surface could serve not only as electron donor, but also as the terminal active site to transfer photoexcited electrons to adsorbed oxygen molecules, producing mass of ⋅O2–. Meanwhile, the activation rate constant of TCN-5 for RhB was 0.0624 min−1, which was 10 and 5 times of g-C3N4 and TTF, respectively. In addition, the results of EPR spectra, rotating disk electrode measurement and molecular oxygen activation measurement also demonstrated that this catalyst was energetically favorable to generate ⋅O2– through the single-electron reduction pathway of molecular oxygen. Finally, four possible photodegradation routes for RhB were proposed based on the results of HPLC-MS. This work provides a new insight on the application of organic photoelectric materials in the purification of wastewater by the molecular oxygen activation.

Photocatalytic manipulation of Ca2+ signaling for regulating cellular and animal behaviors via MOF-enabled H2O2 generation.

The in situ generation of H2O2 in cells in response to external stimulation has exceptional advantages in modulating intracellular Ca2+ dynamics, including high controllability and biological safety, but has been rarely explored. Here, we develop photocatalyst-based metal-organic frameworks (DCSA-MOFs) to modulate Ca2+ responses in cells, multicellular spheroids, and organs. By virtue of the efficient photocatalytic oxygen reduction to H2O2 without sacrificial agents, photoexcited DCSA-MOFs can rapidly trigger Ca2+ outflow from the endoplasmic reticulum with single-cell precision in a repeatable and controllable manner, enabling the propagation of intercellular Ca2+ waves (ICW) over long distances in two-dimensional and three-dimensional cell cultures. After photoexcitation, ICWs induced by DCSA-MOFs can activate neural activities in the optical tectum of tadpoles and thighs of spinal frogs, eliciting the corresponding motor behaviors. Our study offers a versatile optical nongenetic modulation technique that enables remote, repeatable, and controlled manipulation of cellular and animal behaviors.

An Efficient Photocatalytic Oxygen Evolution System with the Coupling of Polyoxometalates with Bismuth Vanadate

In this work, a coupling system consisting of bismuth vanadate (BiVO4) and cobalt-based polyoxometalates (Co-POMs) was developed to enhance the oxygen evolution reaction. Crystallization-driven self-assembly and the wet chemical synthesis method were deployed in synthesizing Co-POMs and monoclinic–tetragonal mixed–phase BiVO4, respectively. The introduction of Co-POMs into a BiVO4-containing mixture significantly enhanced the water oxidation reaction, with a more than twofold increment in the total amount of oxygen evolved. For instance, 461.2 µmol of oxygen was evolved from the system containing 20 mg of Co-POMs compared to 195 µmol of oxygen produced from a pristine BiVO4 system. This extraordinary improvement in the oxygen evolution reaction indicates the existence of a positive synergic effect between BiVO4 and Co-POMs, in which Co-POMs could act as effective cocatalysts to extract photogenerated charge carriers generated by BiVO4 and improve the charge transfer process. However, the amount of oxygen produced was slightly reduced to 440.7 µmol with an increase in AgNO3 loading from 30 mg to 60 mg. This unforeseen phenomenon could be elucidated by the shielding effect of silver particles, in which a higher AgNO3 loading led to a more prominent shielding effect. The presence of silver nanoparticles on post-reaction BiVO4 was confirmed by TEM and XPS analysis. This newly established process scheme provides an insight into the development of an efficient photocatalytic oxygen evolution system in realizing future commercial applications toward green energy production.

Anchoring single Co sites on bipyridine-based covalent triazine framework for efficient photocatalytic oxygen evolution

The photocatalytic oxygen evolution reaction (OER) is a half-reaction of water splitting for oxygen evolution, faces the drawback of sluggish kinetics. Developing highly efficient photocatalysts for OER represents a significant challenge in the field of water splitting advancement. Herein we report the bipyridine-based covalent triazine framework (CTF-Bpy) with the periodic metal coordination sites and suitable band gap position for efficient photocatalytic oxygen evolution. Single Co sites are introduced into CTF-Bpy as cocatalyst through a facile immersion treatment. The obtained CTF-Bpy-Co exhibited remarkable photocatalytic oxygen evolution performance, achieving an initial rate of up to 3359 μmol g–1 h–1 within the first hour and an average rate of 1503 μmol g–1 h–1 over 5 h under visible light irradiation (λ ≥ 420 nm), which exceeds most of the reported porous organic polymers. Moreover, CTF-Bpy-Co can achieve continuous oxygen evolution for a duration of 40 h and the total oxygen production amount of up to 180 μmol. Charge density difference using density functional theory calculations confirm that the Co single site is the reaction site that drives the photooxidation of water to generate oxygen.

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.

Unification of hot spots and catalytic sites on isolated boron centers in porous carbon nitride nanosheets for efficient photocatalytic oxygen evolution

The quest for maximum photocatalysis necessitates the unification of hot spots and catalytic sites on photocatalysts. Herein, boron atoms were successfully incorporated into the tri-s-triazine unit of C3N4 (PCN-B-X), in the form of isolated B-N coordination. In-situ experimental and simulation analyses collectively demonstrated that the resulting atomic B centers and cyano groups functioned as hot spots to amplify charge dynamics and localized charge density. Concurrently, B-N coordination served as catalytic sites, reducing the activation energy for oxygen evolution reaction. Whereas, excessive B precursor led to partial B-B bonding, adversely affecting optical absorption and charge separation. Consequently, the optimal photocatalytic activity was achieved at an oxygen evolution rate of 248.9 µmol h−1 g−1 (λ > 420 nm), when the hot spots and catalytic sites were harmoniously aligned on isolated B coordination in PCN-B-20, surpassing that of C3N4 by 5.2 times. This study provides insights into photocatalytic mechanism and suggests approaches to develop robust metal-free photocatalysts for solar fuel production.

Realizing Photocatalytic Overall Water Splitting by Modulating the Thickness-Induced Reaction Energy Barrier of Fluorenone-Based Covalent Organic Frameworks.

Direct photocatalytic hydrogen and oxygen evolution from water splitting is an attractive approach for producing chemical fuels. In this work, a novel fluorenone-based covalent organic framework (COF-SCAU-2) is successfully exfoliated into ultrathin three-layer nanosheets (UCOF-SCAU-2) for photocatalytic overall water splitting (OWS) under visible light. The ultrathin structures of UCOF-SCAU-2 greatly enhance carrier separation, utilization efficiency, and the exposure of active surface sites. Surprisingly, UCOF-SCAU-2 exhibits efficient photocatalytic OWS performance, with hydrogen and oxygen evolution rates reaching 0.046 and 0.021 mmol h-1 g-1 , respectively,under visible-light irradiation, whereas bulk COF-SCAU-2 shows no activity for photocatalytic OWS. Charge-carrier kinetic analysis and DFT calculations confirm that reducing the thickness of the COF nanosheets increasesthe number ofaccessible active sites, reduces the distance for charge migration, prolongs the lifetimes of photogenerated carriers, and decreases the Gibbs free energy of the rate-limiting step compared to nonexfoliated COFs. This work offers new insights into the effect of the layer thickness of COFs on photocatalytic OWS.

An ultrafast H* migration channel and oxidation activity driven by multifunctional Co atoms on twin Co0.01Mn0.29Cd0.7S homojunction surface for photocatalytic overall water splitting

Low kinetics of water dissociation, unfavorable hydrogen adsorption, and high water-oxidation barriers restrict the photocatalytic overall water splitting (OWS) efficiency over sulfides. Herein, multifunctional Co atoms are doped on the twin Mn0.3Cd0.7S homojunction surface for efficient photocatalytic hydrogen (H2) and oxygen (O2) evolution. An ultrafast hydrogen atom (H*) migration channel bridging the water dissociation/H2 evolution step is established between cubic-S and hexagonal-S sites by introducing Co atoms, facilitating the HER kinetics. Specifically, Co atoms regulate the electron properties of neighboring S atoms and weaken their charge accumulation, which promotes cubic-S sites to capture sufficient H* from the water dissociation zone and accelerates hexagonal-S sites to release H2 through the H* migration channel. Meanwhile, unsaturated Co atoms on the cubic phase as oxygen evolution reaction (OER) sites promote water deprotonation and optimize the kinetics of the rate-determining step to form OOH* intermediate, enhancing water oxidation activity. Co atoms strengthen the internal electric field of the homojunction and local polarized electric field by increasing the work function difference between the two phases and introducing the high spin polarization, inhibiting the bulk and surface recombination of photogenerated carriers. The Co0.01Mn0.29Cd0.7S exhibits visible-light-driven H2 and O2 evolution rates of 443.12 and 219.67 μmol g−1 h−1, about 50 times that of the Mn0.3Cd0.7S. This work provides some guidance for the design of homojunction photocatalysts with efficient OWS performance.

Engineering the Near-Surface Structure of WO3 by an Amorphous Layer with Trivalent Ni and Self-Adapting Oxygen Vacancies for Efficient Photocatalytic and Photoelectrochemical Acidic Oxygen Evolution Reaction.

Exploiting an effective strategy to tailor the construction, composition, and local electronic structure of the photocatalyst surface is pivotal to photocatalytic activity, but remains challenging. Transition metal elements can boost the oxygen evolution reaction activity especially one like Ni in high oxidation states, whereas it is uneasy to prepare Ni3+ under mild conditions or play to their strengths in acidic conditions. In this article, we report a facile "etch and dope" synthesis of Ni3+-doped WO3 nanosheets with oxygen vacancies. Through detailed experimental and theoretical studies, it is established that the abundant oxygen vacancies and the doped Ni3+ ions in the near-surface amorphous layer can synergistically optimize the surface electronic structure of WO3 and the adsorption and desorption of intermediates. Impressively, the etched WO3 nanosheets coupled with Ni3+ offer a greatly promoted photocatalytic performance of 1.78 mmol g-1 h-1, and the photoanode achieves a photocurrent density of 2.11 mA cm-2 at 1.23 V versus reversible hydrogen electrode (VRHE). This work provides a new inspiration for rational manufacture of defects and high-valence metal ions in catalysts for photocatalytic and photoelectrochemical reactions.

Efficient Photocatalytic Hydrogen and Oxygen Evolution by Side-Group Engineered Benzodiimidazole Oligomers with Strong Built-in Electric Fields and Short-Range Crystallinity.

The insufficient charge separation and sluggish exciton transport severely limit the utilization of polymeric photocatalysts. To resolve the above issues, we incorporate bountiful carboxyl substituents within a novel benzodiimidazole oligomer and assemble it into a crystalline semiconductor. The photocatalyst is polar, hydrophilic, short-range crystalline, and capable of both hydrogen and oxygen evolution. The introduction of carboxyl side-groups adds asymmetry to the local structure and increases the built-in electric field. Further, accelerated carrier transfer is enabled via the short-range crystallinity. The superior hydrogen and oxygen production rates of 18.63 and 2.87 mmol g-1 h-1 represent one of the best performances ever reported among dual-functional polymeric photocatalysts. Our work initiates studies on high-performance oligomer photocatalysts, opening a new frontier to produce solar fuel.

Efficient Photocatalytic Hydrogen and Oxygen Evolution by Side‐Group Engineered Benzodiimidazole Oligomers with Strong Built‐in Electric Fields and Short‐Range Crystallinity

AbstractThe insufficient charge separation and sluggish exciton transport severely limit the utilization of polymeric photocatalysts. To resolve the above issues, we incorporate bountiful carboxyl substituents within a novel benzodiimidazole oligomer and assemble it into a crystalline semiconductor. The photocatalyst is polar, hydrophilic, short‐range crystalline, and capable of both hydrogen and oxygen evolution. The introduction of carboxyl side‐groups adds asymmetry to the local structure and increases the built‐in electric field. Further, accelerated carrier transfer is enabled via the short‐range crystallinity. The superior hydrogen and oxygen production rates of 18.63 and 2.87 mmol g−1 h−1 represent one of the best performances ever reported among dual‐functional polymeric photocatalysts. Our work initiates studies on high‐performance oligomer photocatalysts, opening a new frontier to produce solar fuel.

Facile synthesis of ZnCd-MOF/Ag3PO4 heterojunction for highly efficient photocatalytic oxygen evolution

Facile synthesis of ZnCd-MOF/Ag3PO4 heterojunction for highly efficient photocatalytic oxygen evolution

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Synergetic excitonic and defective effects in confined SnO2/α-Fe2O3 nanoheterojunctions for efficient photocatalytic molecular oxygen activation

The research with respect to the excitonic effect now predominantly focuses on the organic semiconductors, while the case taking place in the inorganic semiconductors is rarely discussed. Here, cone and hyacinthus orientalis-like SnO2/α-Fe2O3 nanoheterojunctions were obtained via a simplistic hydrothermal synthesis followed by a annealing process, which respectively showed unique spherical hollow structure and 2D hierarchical nanosheets on their surface. Abundant oxygen vacancies confined in lattice of nanoheterojunctions were introduced, which facilitated the exchange of ambiance oxygen and lattice oxygen. Systematic examinations revealed that the optimized nanoheterojunctions and rich oxygen vacancies led to superior visible-light photocatalytic activity in the activation of active molecular oxygen, including H2O2 production. This work brightens excitonic and defective aspects for the chemical interface design in bulk heterojunction materials to produce reactive oxygen species with high photocatalytic activity, and provide guidance for the construction of efficient heterostructures and extend their potentials to other fields.

Efficient photocatalytic oxygen activation by oxygen-vacancy-rich CeO2-based heterojunctions: Synergistic effect of photoexcited electrons transfer and oxygen chemisorption

Photocatalytic molecular O2 activation has a broad prospect for generation of reactive oxygen species, but many of these conversions are unsatisfactory due to the poor oxygen adsorption capacity and low carrier utilization. To solve these problems, oxygen-vacancy-rich CeO2-based heterojunctions were constructed to improve oxygen chemisorption and photoexcited electrons transfer. The results of X-ray photoelectron spectroscopy, Raman and electron paramagnetic resonance tests suggested that there were abundant oxygen vacancies on the surface of the CeO2, which can act as oxygen adsorption sites to accelerate the chemisorption of O2. Density functional theory (DFT) calculations, electrochemical and photochemical analyses proved that photogenerated electrons transferred from AgI to CeO2 on the AgI/CeO2 heterojunction interface, which inhibited the recombination of charge carriers and thus generated more electrons to facilitate the activation of O2. Profiting from the excellent photocatalytic oxygen activation performance, the pseudo-first-order degradation kinetics constant of tetracycline by the AgI(5%)/CeO2 was about 3 times and 47 times higher than that of CeO2 and AgI, respectively. And AgI(5%)/CeO2 can completely inactivate Escherichia coli (E. coli) within 8 min under visible light irradiation. Moreover, we also explored the degradation pathway of tetracycline and the inactivation mechanism of E. coli. This work is expected to inspire more wonderful research on improving the molecular O2 activation efficiency from different aspects.

Synthesis of Z-scheme cobalt porphyrin/nitrogen-doped graphene quantum dot heterojunctions for efficient molecule-based photocatalytic oxygen evolution

CoP nanowires are transformed to 0D Z-scheme CoP/NGQDs heterojunctions in the present of NGQDs, which exhibit the currently highest POE rate on the molecule (350 μmol g−1 h−1) due to the generation of a new excited state of (CoP+·NGQDs−)*.

A novel Cl- modification approach to develop highly efficient photocatalytic oxygen evolution over BiVO4 with AQE of 34.6%

Abstract Water oxidation with multielectron transfer is regarded as the crucial step in photocatalytic water splitting. However, a facile but efficient method to promote its slow kinetics is still highly demanding. This work demonstrates that Cl- surface modification drastically enhances photocatalytic water oxidation over BiVO4 as well as WO3. The optimal modified BiVO4 achieves a photocatalytic activity of 4.2 orders enhancement relative to the pristine BiVO4, giving up to an excellent apparent quantum efficiency of 34.6% at 420 nm. Cl--modified 30-facet BiVO4 with 2.6 times enhancement confirms that the surface reaction involved with photogenerated holes can be dramatically accelerated by Cl- modification in addition to enhanced charge carrier separation. Our results highlight the impact of Cl- modification on the reaction kinetics and pathway during the photocatalytic water oxidation process, which has been mostly overlooked. Systematic studies (DFT simulations, kinetic experiments) reveal that Cl- modification remarkably reduces the photocatalytic water oxidation energy barrier and alters reaction pathway, which is also manifested in facilitated H2O molecule activation in synchronous illumination XPS (SI-XPS) study. The EXAFS and angle-resolved XPS (AR-XPS) results show that Cl bonds to Bi and mainly concentrates on the surface of modified BiVO4. Our findings provide an effective and facile approach to exploring efficient O2 evolution semiconductors for photocatalytic water splitting.

Co3O4 Nanocrystals with an Oxygen Vacancy-Rich and Highly Reactive (222) Facet on Carbon Nitride Scaffolds for Efficient Photocatalytic Oxygen Evolution.

Oxygen evolution reaction (OER) with sluggish kinetics is the rate-determining step of water splitting, which dominates the solar-to-hydrogen fuel conversion efficiency. Herein, we constructed an oxygen vacancy-rich and highly reactive (222) facet in Co3O4 nanocrystals anchored on carbon nitride nanofiber (CNF) by a solvothermal reduction method. The resulting Co3O4 nanocrystals/CNF (COCNF) demonstrated a dramatically enhanced OER with a rate of 24.9 μmol/h under visible light, which is 124 times higher than that of CNF. This excellent catalytic activity of COCNF is based on a synergistic effect between its binary components for charge separation, oxygen vacancies for enhanced conductivity, and facet (222) exposure of Co3O4 nanocrystals for improved heterogeneous kinetics. Density functional theory (DFT) calculations revealed the water oxidation mechanism at different facets and found that the formed oxygen vacancies lead to a reduction of the materials' bandgap. The correlation between Co3O4 crystal facets and the inherent OER catalytic activities under acidic solution was in the order of (222) > (220) > (311).