Light-driven Oxygen Research Articles

A novel visible light-driven oxygen doped C3N4/Bi12O17Cl2/ferrate(VI) system for Bisphenol A degradation: Radical and nonradical pathways

In this study, visible light-activated photocatalyst oxygen-doped C3N4@Bi12O17Cl2 (OCN@BOC) and Fe(VI) coupling system was proposed for the efficient degradation of bisphenol A (BPA). The comprehensive characterization of the OCN@BOC photocatalyst revealed its excellent photogenerated carrier separation rate in heterogeneous structures. The OCN@BOC/Fe(VI)/Vis system exhibited a remarkable BPA removal efficiency of over 84% within 5 min. Comparatively, only 37% and 59% of BPA were degraded by single OCN@BOC and Fe(VI) in 5 min, respectively. Reactive species scavenging experiments, phenyl sulfoxide transformation experiments, and electron paramagnetic resonance experiments confirmed the involvement of superoxide radicals (⋅O2−), singlet oxygen (1O2), as well as iron(V)/iron(IV) (Fe(V)/Fe(IV)) species in the degradation process of BPA. Furthermore, density functional theoretical calculations and identification of intermediates provided insights into the potential degradation mechanism of BPA during these reactions. Additionally, simulation evaluations using an ecological structure activity relationship model demonstrated that the toxicity of BPA to the ecological environment was mitigated during its degradation process. This study presented a novel strategy for removing BPA utilizing visible light photocatalysts, highlighting promising applications for practical water environment remediation with the OCN@BOC/Fe(VI)/Vis system.

Microbial lipid synthesis based on visible light-driven oxygen doped-graphitic carbon nitride /oleaginous yeast hybrid system

The use of solar energy and heterotrophic microbes to synthesize microbial lipids is a promising strategy to solve energy crisis and reduce CO2 emissions. In this study, a photocatalyst, oxygen-doped graphitic carbon nitride (O-g-C3N4), was synthesized and combined with an oleaginous yeast strain, Cutaneotrichosporon dermatis ZZ-46, to construct a photocatalyst-microbe hybrid (PMH) system. Under illumination, the lipid yield of the PMH system reached 1.61 g/L after 96 h (87 % higher than that of control). NADPH/NADP+ ratio of ZZ-46 cells in the PMH system increased. Metabolomics results revealed that glutathione generation was increased, and the fatty acid decomposition pathway in ZZ-46 cells was inhibited in the PMH system. This study provides a new approach for the synthesis of microbial lipids based on solar energy and heterotrophic microbes.

Metal-free nitrogen-doped carbon nanodots as an artificial nanozyme for enhanced antibacterial activity

Bacterial infections have become a considerable obstacle to public health due to the emergence of antibiotic resistance. Herein, we rationally developed a novel and attractive nitrogen-doped carbon nanodots (N-CNDs) as efficient metal-free artificial nanozymes that synergistically and efficiently inhibit bacterial survival by inheriting the bacteriostatic ability of tea polyphenols and light-triggered oxidase-like catalytic activity. The excellent oxidase-mimicking activity exhibited by N-CNDs in the light was mediated by superoxide radicals (•O2−) with a high maximum reaction rate (1.59 μM⋅s−1) and a low Michaelis constant (0.421 mM). Furthermore, the constructed N-CNDs-based nanozyme was demonstrated to serve as a complex biomaterial platform for efficient sterilization by light-driven oxygen molecule generation of •O2−. Remarkably, the inherent antibacterial ability of N-CNDs can effectively inhibit both Gram-positive and Gram-negative bacteria, particularly against Gram-positive S. aureus at a minimum inhibitory concentration (MIC90) of 375 μg⋅mL−1. The inactivation rates of N-CNDs alone agsinst E. coli and S. aureus were 59.72% and 37.15%, respectively. However, the inactivation rates of E. coli and S. aureus by N-CNDs achieved by light were as high as 97.91% and 80.02%, respectively. Encouragingly, a two-way ANOVA revealed that the concentration of N-CNDs and the duration of light exposure had a synergistic effect on antibacterial behavior, which provided favorable conditions for the sustained eradication of exposed bacteria. This synergistic strategy for bacterial eradication based on a novel metal-free carbon-based nanozyme provides a powerful and feasible approach for bacterial contamination management in food safety and environmental protection.

Light-driven oxygen evolution from water oxidation with immobilised TiO2 engineered for high performance

Calcination treatments in the range of 500–900 °C of TiO2 synthesised by the sol–gel resulted in materials with variable physicochemical (i.e., optical, specific surface area, crystallite size and crystalline phase) and morphological properties. The photocatalytic performance of the prepared materials was evaluated in the oxygen evolution reaction (OER) following UV-LED irradiation of aqueous solutions containing iron ions as sacrificial electron acceptors. The highest activity for water oxidation was obtained with the photocatalyst thermally treated at 700 °C (TiO2-700). Photocatalysts with larger anatase to rutile ratio of the crystalline phases and higher surface density of oxygen vacancies (defects) displayed the best performance in OER. The oxygen defects at the photocatalyst surface have proven to be responsible for the enhanced photoactivity, acting as important active adsorption sites for water oxidation. Seeking technological application, water oxidation was accomplished by immobilising the photocatalyst with the highest OER rate measured under the established batch conditions (TiO2-700). Experiments operating under continuous mode revealed a remarkable efficiency for oxygen production, exceeding 12% of the apparent quantum efficiency (AQE) at 384 nm (UV-LED system) compared to the batch operation mode.

Anatase-Wrapped Rutile Nanorods as an Effective Electron Collector in Hybrid Photoanodes for Visible Light-Driven Oxygen Evolution.

Arrays of single crystal TiO2 rutile nanorods (RNRs) appear highly promising as electron-collecting substrates in hybrid photoanodes as the RNRs offer direct charge carriers transport pathways, contrary to the conventional electrodes prepared from TiO2 powders that suffer from the numerous charge traps at the grain boundaries. However, the specific surface area of the nanorods is highly limited by their smooth morphology, which might be detrimental in view of utilizing the RNR as a substrate for immobilizing other functional materials. In this study, we developed a novel anatase-wrapped RNR (ARNR) material fabricated by a facile seed layer-free hydrothermal method. The ARNR comprises polycrystalline anatase nanoparticles formed on the surface of RNR, resulting in a large surface area that provides more deposition sites compared to the bare nanorods. Herein, we functionalize ARNR and RNR electrodes with polymeric carbon nitride (CNx) coupled with a CoO(OH)x cocatalyst for dioxygen evolution. The anatase wrapping of the rutile nanorod scaffold is found to be crucial for effective deposition of CNx and for improved photoanode operation in visible light-driven (λ > 420 nm) oxygen evolution, yielding a significant enhancement of photocurrent (by the factor of ∼3.7 at 1.23 V vs. RHE) and faradaic efficiency of oxygen evolution (by the factor of ∼2) as compared to photoanodes without anatase interlayer. This study thus highlights the importance of careful interfacial engineering in constructing photoelectrocatalytic systems for solar energy conversion and paves the way for the use of ARNR-based electron collectors in further hybrid and composite photochemical architectures for solar fuel production.

Polymer fused GOFe: Light-driven oxygen donor and antiseptics

Phytopathogenic bacteria have been a prominent problem for the growth of plant and agricultural development. Iron-based oxygen generators will be environmental friendly materials for the treatment of phytopathogenic bacteria in hypoxia environment. To develop environmental friendly materials for bacterial treatment, a polymer fused iron(III) nano-complex (PPaba-FeEu@GO) was constructed. The PPaba-FeEu@GO was synthesized by polymerization of 4-aminobenzoic acid Fe(III) complex on the surface of 0.1 % Eu(III)-doped GO. This nano metal complex (PPaba-FeEu@GO) shows enhanced electron mobility and hole diffusion distance, hence it converts water into oxygen under LED light irradiation without adscititious cocatalyst. Moreover, PPaba-FeEu@GO can convert near-infrared light into heat. The photothermal conversion efficiency was calculated as 40.6 %. Therefore, PPaba-FeEu@GO is a light driven oxygen generator and bacterial inhibitor. Our results demonstrate that polymer fused metal-EuGO system will be kinds of reusable materials for bacterial treatment.

Designed Conducting Polymer Composites That Facilitate Long-Lived, Light-Driven Oxygen and Hydrogen Evolution from Water in a Photoelectrochemical Concentration Cell (PECC)

Light-driven water-splitting to generate hydrogen and oxygen from water is typically carried out in an electrochemical cell with an external voltage greater than 1.23 V applied between the electrodes. In this work, we examined the use of a concentration/chemical bias as a means of facilitating water-splitting under light illumination without the need for such an externally applied voltage. Such a concentration bias was created by employing a pH differential in the liquid electrolytes within the O2-generating anode half-cell and the H2-generating cathode half-cell. A novel, stretchable, highly ion-conductive polyacrylamide CsCl hydrogel was developed to connect the two half-cells. The key feature of the cell was the half-cell electrodes, which comprised thin-film conducting polymer composites that were previously designed to maximize light-driven catalysis at moderate pH. Upon being connected with the hydrogel in the presence of light irradiation (0.25 sun intensity on each electrode), the half-cells spontaneously produced hydrogen and oxygen from water, without the need for an externally applied voltage bias greater than 1.23 V. The cell operated reliably and efficiently for 14 h of continuous testing. These results demonstrate the fundamental feasibility of light-driven water-splitting in a photoelectrochemical concentration cell when employing electrodes that operate efficiently at moderate pH, even with low levels of light illumination. The designed conducting polymer composites proved ideal in that regard.

Dual metal-free polymer reactive sites for the efficient degradation of diclofenac by visible light-driven oxygen reduction to superoxide radical and hydrogen peroxide

Hydrogen peroxide (H2O2) and superoxide radical (O2˙−) play a critical role in environmental remediation technologies.

Cover Feature: Polymeric Metal Salen‐Type Complexes as Catalysts for Photoelectrocatalytic Hydrogen Peroxide Production (ChemElectroChem 21/2018)

The Cover Feature illustrates light-driven oxygen reduction to hydrogen peroxide catalyzed by polymerized Ni–salen complexes. More information can be found in the Communication by A. S. Konev et al on page 3138 in Issue 21, 2018 (DOI: 10.1002/celc.201800846).

Composition-Dependent Functionality of Copper Vanadate Photoanodes.

To understand functional roles of constituent elements in ternary metal oxide photoanodes, essential photoelectrochemical (PEC) properties are systematically analyzed on a series of copper vanadate compounds with different Cu:V elemental ratios. Homogeneous and highly continuous thin films of β-Cu2V2O7, γ-Cu3V2O8, Cu11V6O26, and Cu5V2O10 are grown via reactive co-sputtering and their performance characteristics for the light-driven oxygen evolution reaction are evaluated. All four compounds have similar bandgaps in the range of 1.83-2.03 eV, though Cu-rich phases exhibit stronger optical absorption and higher charge separation efficiencies. Transient photocurrent analysis reveals a reduction of surface catalytic activity with increasing Cu:V elemental ratio due to competitive charge recombination at Cu-related surface states. This comprehensive analysis of PEC functionalities-including photon absorption, carrier separation, and heterogeneous charge transfer-informs strategies for improving PEC activity in the copper vanadate materials system and provides insights that may aid discovery, design, and engineering of new photoelectrode materials.

Calcium, Ammonia, Redox-Active Tyrosine YZ, and Proton-Coupled Electron Transfer in the Photosynthetic Oxygen-Evolving Complex.

A redox-active tyrosine, YZ (Y161 in the D1 polypeptide), is essential in photosystem II (PSII), which conducts photosynthetic oxygen evolution. On each step of the light-driven oxygen evolving reaction, YZ radical is formed by a chlorophyll cation radical. YZ radical is then reduced by a Mn4CaO5 cluster in a proton coupled electron transfer (PCET) reaction. YZ is hydrogen bonded to His190-D1 and to water molecules in a hydrogen-bonding network, involving calcium. This network is sensitive to disruption with ammonia and to removal and replacement of calcium. Only strontium supports activity. Here, we use electron paramagnetic resonance (EPR) spectroscopy to define the influence of ammonia treatment, calcium removal, and strontium/barium substitution on YZ radical PCET at two pH values. A defined oxidation state of the metal cluster (S2) was trapped by illumination at 190 K. The net reduction and protonation of YZ radical via PCET were monitored by EPR transients collected after a 532 nm laser flash. At 190 K, YZ radical cannot oxidize the Mn4CaO5 cluster and decays on the seconds time scale by recombination with QA-. The overall decay half-time and biexponential fits were used to analyze the results. The reaction rate was independent of pH in control, calcium-reconstituted PSII (Ca-PSII). At pH 7.5, the YZ radical decay rate decreased in calcium-depleted (CD-PSII) and barium/strontium-reconstituted PSII (Ba-PSII, Sr-PSII), relative to Ca-PSII. At pH 6.0, the YZ radical decay rate was not significantly altered in CD-PSII and Sr-PSII but decreased in Ba-PSII. A two-pathway model, involving two competing proton donors with different pKa values, is proposed to explain these results. Ammonia treatment decreased the YZ decay rate in Ca-PSII, Sr-PSII, and CD-PSII, consistent with a reaction that is mediated by the hydrogen-bonding network. However, ammonia treatment did not alter the rate in Ba-PSII. This result is interpreted in terms of the large ionic radius of barium and the elevated pKa of barium-bound water, which are expected to disrupt hydrogen bonding. In addition, evidence for a functional interaction between the S2 protonated water cluster (Wn+) and the YZ proton donation pathway is presented. This interaction is proposed to increase the rate of the YZ PCET reaction.

A solid oxide photoelectrochemical cell with UV light-driven oxygen storage in mixed conducting electrodes.

A single crystalline SrTiO3 working electrode in a zirconia-based solid oxide electrochemical cell is illuminated by UV light at temperatures of 360-460 °C. In addition to photovoltaic effects, this leads to the build-up of a battery-type voltage up to more than 300 mV. After switching off UV light, this voltage only slowly decays. It is caused by UV-induced oxygen incorporation into the mixed conducting working electrode and thus by changes of the oxygen stoichiometry δ in SrTiO3-δ under UV illumination. These changes of the oxygen content could be followed in time-dependent voltage measurements and also manifest themselves in time-dependent resistance changes during and after UV illumination. Discharge currents measured after UV illumination reveal that a large fraction of the existing oxygen vacancies in SrTiO3 become filled under UV light. Additional measurements on cells with TiO2 thin film electrodes show the broader applicability of this novel approach for transforming light into chemical energy and thus the feasibility of solid oxide photoelectrochemical cells (SOPECs) in general and of a "light-charged oxygen battery" in particular.

Iron‐Based Metal–Organic Frameworks as Catalysts for Visible Light‐Driven Water Oxidation

The development of earth-abundant, active, and stable catalysts is important for solar energy conversion. Metal-organic frameworks (MOFs) have been viewed as a promising class of porous materials, which may have innovative application in photocatalysis. In this paper, three types of Fe-based MOFs and their aminofunctionalized derivatives have been fabricated and systematically studied as water oxidation catalysts (WOCs) for oxygen evolution under visible light irradiation. MIL-101(Fe) possesses a higher current density and earlier onset potential and exhibits excellent visible light-driven oxygen evolution activity than the other Fe-based catalysts. It speeds up the oxygen evolution reaction rate with the higher initial turnover frequencies value of 0.10 s(-1). Our study demonstrates that Fe-based MOFs as efficient WOCs are promising candidates for photocatalytic water oxidation process.

Analysis of photosystem II biogenesis in cyanobacteria

Photosystem II (PSII), a large multisubunit membrane protein complex found in the thylakoid membranes of cyanobacteria, algae and plants, catalyzes light-driven oxygen evolution from water and reduction of plastoquinone. Biogenesis of PSII requires coordinated assembly of at least 20 protein subunits, as well as incorporation of various organic and inorganic cofactors. The stepwise assembly process is facilitated by numerous protein factors that have been identified in recent years. Further analysis of this process requires the development or refinement of specific methods for the identification of novel assembly factors and, in particular, elucidation of the unique role of each. Here we summarize current knowledge of PSII biogenesis in cyanobacteria, focusing primarily on the impact of methodological advances and innovations. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Conrad Mullineaux.

Oxygen insertion into metal carbon bonds: formation of methylperoxo Pd(II) and Pt(II) complexes via photogenerated dinuclear intermediates.

Platinum(II) and palladium(II) complexes [M(CH3)(L)]SbF6 with substituted terpyridine ligands L undergo light-driven oxygen insertion reactions into metal methyl bonds resulting in methylperoxo complexes [M(OOCH3)(L)]SbF6. The oxygen insertion reactions occur readily for complexes with methyl ligands that are activated due to steric interaction with substituents (NH2, NHMe or CH3) at the 6,6″-positions on the terpyridine ligand. All complexes exhibit attractive intermolecular π···π or M···M interactions in the solid state and in solution, which lead to excited triplet dinuclear M-M complexes upon irradiation. A mechanism is proposed whereby a dinuclear intermediate is generated upon irradiation that has a weakened M-C bond in the excited state, resulting in the observed oxygen insertion reactions.

Energetics and kinetics of light-driven oxygen evolution at semiconductor electrodes: the example of hematite

Light-driven water-splitting (photoelectrolysis) at semiconductor electrodes continues to excite interest as a potential route to produce hydrogen as a sustainable fuel, but surprisingly little is known about the kinetics and mechanisms of the reactions involved. Here, some basic principles of semiconductor photoelectrochemistry are reviewed with particular emphasis on the effects of slow interfacial electron transfer at n-type semiconductors in the case of light-driven oxygen evolution. A simple kinetic model is outlined that considers the competition between interfacial transfer of photogenerated holes and surface recombination. The model shows that, if interfacial charge transfer is very slow, the build-up of holes at the surface will lead to substantial changes in the potential drop across the Helmholtz layer, leading to non-ideal behavior (Fermi level pinning). The kinetic model is also used to predict the response of photoanodes to chopped illumination and to periodic perturbations of illumination and potential. Recent experimental results obtained for α-Fe2O3 (hematite) photoanodes are reviewed and interpreted within the framework of the model.

Light-driven oxygen production from superoxide by Mn-binding bacterial reaction centers

One of the outstanding questions concerning the early Earth is how ancient phototrophs made the evolutionary transition from anoxygenic to oxygenic photosynthesis, which resulted in a substantial increase in the amount of oxygen in the atmosphere. We have previously demonstrated that reaction centers from anoxygenic photosynthetic bacteria can be modified to bind a redox-active Mn cofactor, thus gaining a key functional feature of photosystem II, which contains the site for water oxidation in cyanobacteria, algae, and plants [Thielges M, et al. (2005) Biochemistry 44:7389-7394]. In this paper, the Mn-binding reaction centers are shown to have a light-driven enzymatic function; namely, the ability to convert superoxide into molecular oxygen. This activity has a relatively high efficiency with a k(cat) of approximately 1 s(-1) that is significantly larger than typically observed for designed enzymes, and a K(m) of 35-40 μM that is comparable to the value of 50 μM for Mn-superoxide dismutase, which catalyzes a similar reaction. Unlike wild-type reaction centers, the highly oxidizing reaction centers are not stable in the light unless they have a bound Mn. The stability and enzymatic ability of this type of Mn-binding reaction centers would have provided primitive phototrophs with an environmental advantage before the evolution of organisms with a more complex Mn(4)Ca cluster needed to perform the multielectron reactions required to oxidize water.

Kinetics of light-driven oxygen evolution at α-Fe2O3electrodes

The kinetics of light-driven oxygen evolution at polycrystalline alpha-Fe2O3 layers prepared by aerosol-assisted chemical vapour deposition has been studied using intensity modulated photocurrent spectroscopy (IMPS). Analysis of the frequency-dependent IMPS response gives information about the competition between the 4-electron oxidation of water by photogenerated holes and losses due to electron-hole recombination via surface states. The very slow kinetics of oxygen evolution indicates the presence of a kinetic bottleneck in the overall process. Surface treatment of the alpha-Fe2O3 with dilute cobalt nitrate solution leads to a remarkable improvement in the photocurrent response, but contrary to expectation, the results of this study show that this is not due to catalysis of hole transfer but is instead the consequence of almost complete suppression of surface recombination.

Kinetics and mechanism of light-driven oxygen evolution at thin film α-Fe2O3 electrodes

Rate constants for recombination and hole transfer during oxygen evolution at illuminated α-Fe(2)O(3) electrodes were measured by intensity-modulated photocurrent spectroscopy and found to be remarkably low. Treatment of the electrode with a Co(II) solution suppressed surface recombination but did not catalyse hole transfer. Intermediates in the reaction were detected spectroscopically.

A Genetically Tagged Psb27 Protein Allows Purification of Two Consecutive Photosystem II (PSII) Assembly Intermediates in Synechocystis 6803, a Cyanobacterium

Photosystem II (PSII) is a large membrane bound molecular machine that catalyzes light-driven oxygen evolution from water. PSII constantly undergoes assembly and disassembly because of the unavoidable damage that results from its normal photochemistry. Thus, under physiological conditions, in addition to the active PSII complexes, there are always PSII subpopulations incompetent of oxygen evolution, but are in the process of undergoing elaborate biogenesis and repair. These transient complexes are difficult to characterize because of their low abundance, structural heterogeneity, and thermodynamic instability. In this study, we show that a genetically tagged Psb27 protein allows for the biochemical purification of two monomeric PSII assembly intermediates, one with an unprocessed form of D1 (His27ΔctpAPSII) and a second one with a mature form of D1 (His27PSII). Both forms were capable of light-induced charge separation, but unable to photooxidize water, largely because of the absence of a functional tetramanganese cluster. Unexpectedly, there was a significant amount of the extrinsic lumenal PsbO protein in the His27PSII, but not in the His27ΔctpAPSII complex. In contrast, two other lumenal proteins, PsbU and PsbV, were absent in both of these PSII intermediate complexes. Additionally, the only cytoplasmic extrinsic protein, Psb28 was detected in His27PSII complex. Based on these data, we have presented a refined model of PSII biogenesis, illustrating an important role of Psb27 as a gate-keeper during the complex assembly process of the oxygen-evolving centers in PSII.