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To achieve artificial photosynthesis, it is crucial to develop a catalytic system for CO2 reduction using water as the electron source. However, photochemical CO2 reduction by homogeneous molecular catalysts has predominantly been conducted in organic solvents. This study investigates the impact of water content on catalytic activity in photochemical CO2 reduction in N,N-dimethylacetamide (DMA), using [Ru(bpy)3]2+ (bpy: 2,2′-bipyridine) as a photosensitizer, 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor, and two ruthenium diimine carbonyl complexes, [Ru(bpy)2(CO)2]2+ and trans(Cl)-[Ru(Ac-5Bpy-NHMe)(CO)2Cl2] (5Bpy: 5′-amino-2,2′-bipyridine-5-carboxylic acid), as catalysts. Increasing water content significantly decreased CO and formic acid production. The similar rates of decrease for both catalysts suggest that water primarily affects the formation efficiency of free one-electron-reduced [Ru(bpy)3]2+, rather than the intrinsic catalytic activity. The reduction in cage-escape efficiency with higher water content underscores the challenges in replacing organic solvents with water in photochemical CO2 reduction. [ABSTRACT FROM AUTHOR]

Solar-driven CO2 conversion into high-value-added chemicals, powered by photovoltaics, is a promising technology for alleviating the global energy crisis and achieving carbon neutrality. However, most of these endeavors focus on CO2 electroreduction to small-molecule fuels such as CO and ethanol. In this paper, inspired by the photosynthesis of green plants and artificial photosynthesis for the electroreduction of CO2 into value-added fuel, CO2 artificial photosynthesis for the electrocarboxylation of bromobenzene (BB) with CO2 to generate the value-added carboxylation product methyl benzoate (MB) is demonstrated. Using two series-connected dye-sensitized photovoltaics and high-performance catalyst Ag electrodes, our artificial photosynthesis system achieves a 61.1% Faraday efficiency (FE) for carboxylation product MB and stability of the whole artificial photosynthesis for up to 4 h. In addition, this work provides a promising approach for the artificial photosynthesis of CO2 electrocarboxylation into high-value chemicals using renewable energy sources. [ABSTRACT FROM AUTHOR]

Inspired by the layered structure, light absorption, and charge carrier pathway of chloroplast thylakoids in natural photosynthesis, we propose a novel artificial photosynthesis platform, which is composed of layered structured vaterite as the scaffold with gold nanoparticles (AuNPs), photosensitizer eosin Y (EY), and redox enzyme L-glutamate dehydrogenase (GDH) as the functional components. The EY exhibited significantly enhanced light absorption and charge carrier generation due to the localized surface plasmon resonance (LSPR) around the AuNPs and light refraction within the layers. This artificial photosynthesis platform can regenerate reduced nicotinamide adenine dinucleotide (NADH) under visible light and promote the rapid conversion of α-ketoglutarate to L-glutamate (0.453 Mm/h). The excellent biocompatibility of layered vaterite significantly enhances the resistance of GDH to harsh conditions, including high pH (pH = 10) and elevated temperatures (37–57 °C). [ABSTRACT FROM AUTHOR]

In recent years, with the outbreak of the global energy crisis, renewable solar energy has become a focal point of research. However, the utilization efficiency of natural photosynthesis (NPS) is only about 1%. Inspired by NPS, artificial photosynthesis (APS) was developed and utilized in applications such as the regeneration of coenzymes. APS for coenzyme regeneration can overcome the problem of high energy consumption in comparison to electrocatalytic methods. Microreactors represent a promising technology. Compared with the conventional system, it has the advantages of a large specific surface area, the fast diffusion of small molecules, and high efficiency. Introducing microreactors can lead to more efficient, economical, and environmentally friendly coenzyme regeneration in artificial photosynthesis. This review begins with a brief introduction of APS and microreactors, and then summarizes research on traditional electrocatalytic coenzyme regeneration, as well as photocatalytic and photo-electrocatalysis coenzyme regeneration by APS, all based on microreactors, and compares them with the corresponding conventional system. Finally, it looks forward to the promising prospects of this technology. [ABSTRACT FROM AUTHOR]

In this study, we investigated the influence of pressure and the quantity of Co/CoO catalyst on an artificial photosynthesis process that converts CO2 and H2O into hydrocarbons (CnH2n+2, where n ≤ 18). The adsorption of CO2 and H2O on Co/CoO surfaces proved to be pivotal in this photo-catalytic reaction. Photoexcited carbon dioxide and water molecules ((CO2)* and (H2O)*) generated by illuminating the catalyst surface led to the formation of alkene hydrocarbon molecules with carbon numbers following an approximate Poisson distribution. The optimal pressure was found to be 0.40 MPa. Pressure less than 0.40 MPa resulted in low CO2 adsorption, impeding excitation for photosynthesis. At greater pressure, oil/wax accumulation on Co/CoO surfaces hindered CO2 adsorption, limiting further photosynthesis reactions. The average number of carbon atoms in the hydrocarbons and hydrocarbon yield were correlated. The amount of Co/CoO was also found to affect the hydrocarbon yield. Our study contributes to the understanding of Co/CoO-catalyzed photosynthesis and suggests that an open-flow system could potentially enhance the productivity of long-chain hydrocarbons. [ABSTRACT FROM AUTHOR]

The tetracarbonyl complexes of transition metal chalcogenides M2X2(CO)4, where M = Fe, Co, Ni, Cu and X = S, Se, are examined by density functional theory (DFT). The M2X2 core is cyclic with either planar or non-planar geometry. As a sulfide, it is present in natural enzymes and has a selective redox capacity. The reduced forms of the selenide and sulfide complexes are relevant to the hydrogen evolution reaction (HER) and they provide different positions of hydride ligand binding: (i) at a chalcogenide site, (ii) at a particular cation site and (iii) in a midway position forming equal bonds to both cation sites. The full pathway of water decomposition to molecular hydrogen and oxygen is traced by transition state theory. The iron and cobalt complexes, cobalt selenide, in particular, provide lower energy barriers in HER as compared to the nickel and copper complexes. In the oxygen evolution reaction (OER), cobalt and iron selenide tetracarbonyls provide a low energy barrier via OOH* intermediate. All of the intermediate species possess favorable excitation transitions in the visible light spectrum, as evidenced by TD-DFT calculations and they allow photoactivation. In conclusion, cobalt and iron selenide tetracarbonyl complexes emerge as promising photocatalysts in water splitting. [ABSTRACT FROM AUTHOR]

This document, titled "Catalysts in Energy Applications," explores the role of catalysis in various energy processes. It highlights the importance of catalytic reactions in traditional fossil fuel production and the transition towards sustainable energy alternatives such as biofuel production and CO2 capture. The document also discusses the significance of catalysis in hydrogen production, storage, and utilization, as well as in the development of materials and processes for artificial photosynthesis. The research papers presented in this Special Issue delve into the intricacies of catalytic processes in energy-related domains, including oxygen reduction reactions, CO2 conversion, and the electrooxidation of urea. These contributions provide valuable insights into the field of energy catalysis and offer potential advancements in more efficient and sustainable energy conversion technologies. [Extracted from the article]

Photocatalytic nitrogen fixation has attracted much attention because of its ability to synthesize ammonia under mild conditions. However, the ammonia yield is still greatly limited by the sluggish charge separation and extremely high N2 dissociation energy. Herein, two-dimensional Ti3C2 MXene ultrathin nanosheets were introduced to construct Ti3C2/TiO2 composites via electrostatic adsorption for photocatalytic nitrogen fixation. The photocatalytic activity experiments showed that after adding 0.1 wt% Ti3C2, the ammonia yield of the Ti3C2/TiO2 composite reached 67.9 μmol L−1 after 120 min of light irradiation, nearly 3 times higher than that of the monomer TiO2. XPS, DRS, LSV, and FTIR were used to explore the possible photocatalytic nitrogen fixation mechanism. Studies showed that a close interfacial contact has been formed via the bonding mode of =C-O between the Ti3C2 and TiO2 samples. The formed =C-O bond boosts an oriented photogenerated charge separation and transfer in the Ti3C2/TiO2 composite. This work provides a promising idea for constructing other efficient MXene-based composite photocatalysts for artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Plant leaf ashes were obtained via the high temperature calcination of the leaves of various plants, such as sugarcane, couchgrass, bracteata, garlic sprout, and the yellowish leek. Although the photosynthesis systems in plant leaves cannot exist after calcination, minerals in these ashes were found to exhibit photochemical activities. The samples showed solar light photocatalytic oxidation activities sufficient to degrade methylene blue dye. They were also shown to possess intrinsic dehydrogenase-like activities in reducing the colorless electron acceptor 2,3,5-triphenyltetrazolium chloride to a red formazan precipitate under solar light irradiation. The possible reasons behind these two unreported phenomena were also investigated. These ashes were characterized using a combination of physicochemical techniques. Moreover, our findings exemplify how the soluble and insoluble minerals in plant leaf ashes can be synergistically designed to yield next-generation photocatalysts. It may also lead to advances in artificial photosynthesis and photocatalytic dehydrogenase. [ABSTRACT FROM AUTHOR]

In today's society, mankind is confronted with two major problems: the energy crisis and the greenhouse effect. Artificial photosynthesis can use solar energy to convert the greenhouse gas CO2 into high-value compounds, which is an ideal solution to alleviate the energy crisis and solve the problem of global warming. The combination of ZnO and polythiophenes (PTh) can make up for each other's drawbacks, thus improving the photoresponse behavior and separation efficiency of the photogenerated carriers. The PTh layer can transfer photogenerated electrons to ZnO, thereby extending the lifetime of the photogenerated charges. The production rate of CH4 from the photoreduction of CO2 with ZnO/PTh10 is 4.3 times that of pure ZnO, and the selectivity of CH4 is increased from 70.2% to 92.2%. The conductive PTh can absorb photons to induce π–π* transition, and the photogenerated electrons can transfer from the LUMO to the conduction band (CB) of ZnO, thus more electrons are involved in the reduction of CO2. [ABSTRACT FROM AUTHOR]

Transforming solar energy into chemical bonds is a promising and viable way to store solar energy. Porphyrins are natural light-capturing antennas, and graphitic carbon nitride (g-C3N4) is an effective, artificially synthesized organic semiconductor. Their excellent complementarity has led to a growing number of research papers on porphyrin/g-C3N4 hybrids for solar energy utilization. This review highlights the recent progress in porphyrin/g-C3N4 composites, including: (1) porphyrin molecules/g-C3N4 composite photocatalysts connected via noncovalent or covalent interactions, and (2) porphyrin-based nanomaterials/g-C3N4 composite photocatalysts, such as porphyrin-based MOF/g-C3N4, porphyrin-based COF/g-C3N4, and porphyrin-based assembly/g-C3N4 heterojunction nanostructures. Additionally, the review discusses the versatile applications of these composites, including artificial photosynthesis for hydrogen evolution, CO2 reduction, and pollutant degradation. Lastly, critical summaries and perspectives on the challenges and future directions in this field are also provided. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis has rapidly developed as an actual field of research, mimicking natural photosynthesis processes in plants or bacteria to produce energy or high-value chemicals. The nanocelluloses are a family of biorenewable materials that can be engineered into nanostructures with favorable properties to serve as a host matrix for encapsulation of photoreactive moieties or cells. In this review, the production of different nanocellulose structures such as films, hydrogels, membranes, and foams together with their specific properties to function as photosynthetic devices are described. In particular, the nanocellulose's water affinity, high surface area and porosity, mechanical stability in aqueous environment, and barrier properties can be tuned by appropriate processing. From a more fundamental viewpoint, the optical properties (transparency and haze) and interaction of light with nanofibrous structures can be further optimized to enhance light harvesting, e.g., by functionalization or appropriate surface texturing. After reviewing the basic principles of natural photosynthesis and photon interactions, it is described how they can be transferred into nanocellulose structures serving as a platform for immobilization of photoreactive moieties. Using photoreactive centers, the isolated reactive protein complexes can be applied in artificial bio-hybrid nanocellulose systems through self-assembly, or metal nanoparticles, metal-organic frameworks, and quantum dots can be integrated in nanocellulose composites. Alternatively, the immobilization of algae or cyanobacteria in nanopaper coatings or a porous nanocellulose matrix allows to design photosynthetic cell factories and advanced artificial leaves. The remaining challenges in upscaling and improving photosynthesis efficiency are finally addressed in order to establish a breakthrough in utilization of nanocellulose for artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis is promising to convert solar energy and CO2 into valuable chemicals, and to alleviate the problems of the greenhouse effect and the climate change crisis. Here, we fabricated a novel photocatalyst by directly growing Bi2MoO6 nanosheets on three-dimensional (3D) N,O-doped carbon (NO-C). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the designed photocatalyst ensured the close contact between Bi2MoO6 and NO-C, and reduced the stacking of the NO-C layers to provide abundant channels for the diffusion of CO2, while NO-C can allow for fast electron transfer. The charge transfer in this composite was determined to follow a step-scheme mechanism, which not only facilitates the separation of charge carriers but also retains a strong redox capability. Benefiting from this unique 3D structure and the synergistic effect, BMO/NO-C showed excellent performance in photocatalytic CO2 reductions. The yields of the best BMO/NO-C catalysts for CH4 and CO were 9.14 and 14.49 μmol g−1 h−1, respectively. This work provides new insights into constructing step-scheme photocatalytic systems with the 3D nanostructures. [ABSTRACT FROM AUTHOR]

Cu-oxide nanophases (CuO, Cu2O, Cu0) constitute highly potent nanoplatforms for the development of efficient Artificial Photosynthesis catalysts. The highly reducing conduction band edge of the d-electrons in Cu2O dictates its efficiency towards CO2 reduction under sunlight excitation. In the present review, we discuss aspects interlinking the stability under photocorrosion of the (CuO/Cu2O/Cu0) nanophase equilibria, and performance in H2-production/CO2-reduction. Converging literature evidence shows that, because of photocorrosion, single-phase Cu-oxides would not be favorable to be used as a standalone cathodic catalyst/electrode; however, their heterojunctions and the coupling with proper partner materials is an encouraging approach. Distinction between the role of various factors is required to protect the material from photocorrosion, e.g., use of hole scavengers/electron acceptors, band-gap engineering, nano-facet engineering, and selectivity of CO2-reduction pathways, to name a few possible solutions. In this context, herein we discuss examples and synthesis efforts that aim to clarify the role of interfaces, faces, and phase stability under photocatalytic conditions. [ABSTRACT FROM AUTHOR]

Faced with the new stage of water oxidation by molecular catalysts (MCs) in artificial photosynthesis to overcome the bottle neck issue, the "Photon-flux density problem of sunlight," a two-electron oxidation process forming H2O2 in place of the conventional four-electron oxidation evolving O2 has attracted much attention. The molecular characteristics of tin(IV)-tetrapyridylporphyrin (SnTPyP), as one of the most promising MCs for the two-electron water oxidation, has been studied in detail. The protolytic equilibria among nine species of SnTPyP, with eight pKa values on the axial ligands' water molecules and peripheral pyridyl nitrogen atoms in both the ground and excited states, have been clarified through the measurements of UV-vis, fluorescence, 1H NMR, and dynamic fluorescence decay behaviour. The oxidation potentials in the Pourbaix diagram and spin densities by DFT calculation of the one-electron oxidized form of each nine species have predicted that the fully deprotonated species ([SnTPyP(O−)2]2−) and the singly deprotonated one ([SnTPyP(OH)(O−)]−) serve as the most favourable MCs for visible light-induced two-electron water oxidation when they are adsorbed on TiO2 for H2 formation or SnO2 for Z-scheme CO2 reduction in the molecular catalyst sensitized system of artificial photosynthesis. [ABSTRACT FROM AUTHOR]

(Photo-)electrocatalytic artificial photosynthesis driven by electrical and/or solar energy that converts water (H2O) and carbon dioxide (CO2) into hydrogen (H2), carbohydrates and oxygen (O2), has proven to be a promising and effective route for producing clean alternatives to fossil fuels, as well as for storing intermittent renewable energy, and thus to solve the energy crisis and climate change issues that we are facing today. Basic (photo-)electrocatalysis consists of three main processes: (1) light absorption, (2) the separation and transport of photogenerated charge carriers, and (3) the transfer of photogenerated charge carriers at the interfaces. With further research, scientists have found that these three steps are significantly affected by surface and interface properties (e.g., defect, dangling bonds, adsorption/desorption, surface recombination, electric double layer (EDL), surface dipole). Therefore, the catalytic performance, which to a great extent is determined by the physicochemical properties of surfaces and interfaces between catalyst and reactant, can be changed dramatically under working conditions. Common approaches for investigating these phenomena include X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning probe microscopy (SPM), wide angle X-ray diffraction (WAXRD), auger electron spectroscopy (AES), transmission electron microscope (TEM), etc. Generally, these techniques can only be applied under ex situ conditions and cannot fully recover the changes of catalysts in real chemical reactions. How to identify and track alterations of the catalysts, and thus provide further insight into the complex mechanisms behind them, has become a major research topic in this field. The application of in situ/operando characterization techniques enables real-time monitoring and analysis of dynamic changes. Therefore, researchers can obtain physical and/or chemical information during the reaction (e.g., morphology, chemical bonding, valence state, photocurrent distribution, surface potential variation, surface reconstruction), or even by the combination of these techniques as a suite (e.g., atomic force microscopy-based infrared spectroscopy (AFM-IR), or near-ambient-pressure STM/XPS combined system (NAP STM-XPS)) to correlate the various properties simultaneously, so as to further reveal the reaction mechanisms. In this review, we briefly describe the working principles of in situ/operando surface/interface characterization technologies (i.e., SPM and X-ray spectroscopy) and discuss the recent progress in monitoring relevant surface/interface changes during water splitting and CO2 reduction reactions (CO2RR). We hope that this review will provide our readers with some ideas and guidance about how these in situ/operando characterization techniques can help us investigate the changes in catalyst surfaces/interfaces, and further promote the development of (photo-)electrocatalytic surface and interface engineering. [ABSTRACT FROM AUTHOR]

Molecular catalysts based on coordination complexes for the generation of hydrogen via photochemical water splitting exhibit a large versatility and tunability of the catalytic properties through chemical functionalization. In the present work, we report on light-driven hydrogen production in an aqueous solution using a series of cobalt polypyridine complexes as hydrogen evolving catalysts (HECs) in combination with CuInS2@ZnS quantum dots (QDs) as sensitizers, and ascorbate as the electron donor. A peculiar trend in activity has been observed depending on the substituents present on the polypyridine ligand. This trend markedly differs from that previously recorded using [Ru(bpy)3]2+ (where bpy = 2,2'-bipyridine) as the sensitizer and can be ascribed to different kinetically limiting pathways in the photochemical reaction (viz. protonation kinetics with the ruthenium chromophore, catalyst activation via electron transfer from the QDs in the present system). Hence, this work shows how the electronic effects on light-triggered molecular catalysis are not exclusive features of the catalyst unit but depend on the whole photochemical system. [ABSTRACT FROM AUTHOR]

The syntheses of two triads are reported. Each triad is composed of two perylene-monoimides linked to a porphyrin via an ethyne unit, which bridges the perylene 9-position and a porphyrin 5- or 15-position. Each triad also contains a single tether composed of an alkynoic acid or an isophthalate unit. Each triad provides panchromatic absorption (350–700 nm) with fluorescence emission in the near-infrared region (733 or 743 nm; fluorescence quantum yield ~0.2). The syntheses rely on the preparation of trans-AB-porphyrins bearing one site for tether attachment (A), an aryl group (B), and two open meso-positions. The AB-porphyrins were prepared by the condensation of a 1,9-diformyldipyrromethane and a dipyrromethane. The installation of the two perylene-monoimide groups was achieved upon the 5,15-dibromination of the porphyrin and the subsequent copper-free Sonogashira coupling, which was accomplished before or after the attachment of the tether. The syntheses provide relatively straightforward access to a panchromatic absorber for use in bioconjugation or surface-attachment processes. [ABSTRACT FROM AUTHOR]

Photocatalysis is one of the most promising green technologies to utilize solar energy for clean energy achievement and environmental governance, such as artificial photosynthesis, water splitting, pollutants degradation, etc. Despite decades of research, the performance of photocatalysis still falls far short of the requirement of 5% solar energy conversion efficiency. Combining photocatalysis with the other physical fields has been proven to be an efficient way around this barrier which can improve the performance of photocatalysis remarkably. This review will focus on the recent advances in photocatalysis coupling by external physical fields, including Thermal-coupled photocatalysis (TCP), Mechanical-coupled photocatalysis (MCP), and Electromagnetism-coupled photocatalysis (ECP). In this paper, coupling mechanisms, materials, and applications of external physical fields are reviewed. Specifically, the promotive effect on photocatalytic activity by the external fields is highlighted. This review will provide a detailed and specific reference for photocatalysis coupling by external physical fields in a deep-going way. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis (AP) has been extensively applied in energy conversion and environment pollutants treatment. Considering the urgent demand for clean energy for human society, many researchers have endeavored to develop materials for AP. Among the materials for AP, photosensitizers play a critical role in light absorption and charge separation. Due to the fact of their excellent tunability and performance, metal-based complexes stand out from many photocatalysis photosensitizers. In this review, the evaluation parameters for photosensitizers are first summarized and then the recent developments in molecular photosensitizers based on transition metal complexes are presented. The photosensitizers in this review are divided into two categories: noble-metal-based and noble-metal-free complexes. The subcategories for each type of photosensitizer in this review are organized by element, focusing first on ruthenium, iridium, and rhenium and then on manganese, iron, and copper. Various examples of recently developed photosensitizers are also presented. [ABSTRACT FROM AUTHOR]

In this study, nanostructured ZnO arrays were synthesized by an accessible thermal oxidation (TO) methodology. The Zn films were chemically etched with nitric acid (HNO3) and then oxidized in a furnace at 500 °C for 5 h. Two different morphologies were achieved by modifying the HNO3 concentration in the etching process: (a) ZnO grass-like nanostructures and (b) rod-like nanostructures, with an etching process in HNO3 solution at 2 and 8 M concentration, respectively. The physical and chemical properties of the samples were analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Both morphologies were functionalized with hemoglobin, and a difference was found in the efficiency of functionalization, which was monitored by UV–Vis spectroscopy. The sample with the highest efficiency was the ZnO grass-like nanostructures. Afterward, the capture of carbon dioxide was evaluated by monitoring a sodium carbonate solution interacting with the as-functionalized samples. The evaluation was analyzed by UV–Vis spectroscopy and the results showed a CO2 capture of 98.3% and 54% in 180 min for the ZnO grass-like and rod-like nanostructures, respectively. [ABSTRACT FROM AUTHOR]

International guidelines have progressively addressed global warming which is caused by the greenhouse effect. The greenhouse effect originates from the atmosphere's gases which trap sunlight which, as a consequence, causes an increase in global surface temperature. Carbon dioxide is one of these greenhouse gases and is mainly produced by anthropogenic emissions. The urgency of removing atmospheric carbon dioxide from the atmosphere to reduce the greenhouse effect has initiated the development of methods to covert carbon dioxide into valuable products. One approach that was developed is the photocatalytic transformation of CO2. Photocatalysis addresses environmental issues by transferring CO2 into value added chemicals by mimicking the natural photosynthesis process. During this process, the photocatalytic system is excited by light energy. CO2 is adsorbed at the catalytic metal centers where it is subsequently reduced. To overcome several obstacles for achieving an efficient photocatalytic reduction process, the use of metal-containing polymers as photocatalysts for carbon dioxide reduction is highlighted in this review. The attention of this manuscript is directed towards recent advances in material design and mechanistic details of the process using different polymeric materials and photocatalysts. [ABSTRACT FROM AUTHOR]

The photocatalytic transformation of CO2 to valuable man-made feedstocks is a promising method for balancing the carbon cycle; however, it is often hampered by the consumption of extra hole scavengers. Here, a synergistic redox system using photogenerated electron-hole pairs was constructed by employing a porous carbon nitride with many cyanide groups as a metal-free photocatalyst. Selective CO2 reduction to CO using photogenerated electrons was achieved under mild conditions; simultaneously, various alcohols were effectively oxidized to value-added aldehydes using holes. The results showed that thermal calcination process using ammonium sulfate as porogen contributes to the construction of a porous structure. As-obtained cyanide groups can facilitate charge carrier separation and promote moderate CO2 adsorption. Electron-donating groups in alcohols could enhance the activity via a faster hydrogen-donating process. This concerted photocatalytic system that synergistically utilizes electron-hole pairs upon light excitation contributes to the construction of cost-effective and multifunctional photocatalytic systems for selective CO2 reduction and artificial photosynthesis. [ABSTRACT FROM AUTHOR]

The depletion of fossil fuels and onset of global warming dictate the achievement of efficient technologies for clean and renewable energy sources. The conversion of solar energy into chemical energy plays a vital role both in energy production and environmental protection. A photocatalytic approach for H2 production and CO2 reduction has been identified as a promising alternative for clean energy production and CO2 conversion. In this process, the most critical parameter that controls efficiency is the development of a photocatalyst. Two-dimensional nanomaterials have gained considerable attention due to the unique properties that arise from their morphology. In this paper, examples on the development of different 2D structures as photocatalysts in H2 production and CO2 reduction are discussed and a perspective on the challenges and required improvements is given. [ABSTRACT FROM AUTHOR]

The design of photocathodes for the hydrogen evolution reaction (HER), which suitably couple dye-sensitized p-type semiconductors and a hydrogen evolving catalyst (HEC), currently represents an important target in the quest for artificial photosynthesis. In the present manuscript, we report on a systematic evaluation of simple methods for the deposition of Pt metal onto dye-sensitized NiO electrodes. The standard P1 dye was taken as the chromophore of choice and two different NiO substrates were considered. Both potentiostatic and potentiodynamic procedures were evaluated either with or without the inclusion of an additional light bias. Photoelectrochemical characterization of the resulting electrodes in an aqueous solution at pH 4 showed that all the methods tested are effective to attain photocathodes for hydrogen production. The best performances (maximum photocurrent densities of −40 µA·cm−2, IPCE of 0.18%, and ~60% Faradaic yield) were achieved using appreciably fast, light-assisted deposition routes, which are associated with the growth of small Pt islands homogenously distributed on the sensitized NiO. [ABSTRACT FROM AUTHOR]

In this review, photoinduced electron transfer processes in specifically designed assembled architectures have been discussed in the light of recent results reported from our laboratories. A convenient and useful way to study these systems is described to understand the rules that drive a light-induced charge-separated states and its subsequent decay to the ground state, also with the aim of offering a tutorial for young researchers. Assembled systems of covalent or supramolecular nature have been presented, and some functional multicomponent systems for the conversion of light energy into chemical energy have been discussed. [ABSTRACT FROM AUTHOR]

Due to its thermal stability, conductivity, high exciton binding energy and high electron mobility, zinc oxide is one of the most studied semiconductors in the field of photocatalysis. However, the wide bandgap requires the use of UV photons to harness its potential. A convenient way to appease such a limitation is the doping of the lattice with foreign atoms which, in turn, introduce localized states (defects) within the bandgap. Such localized states make the material optically active in the visible range and reduce the energy required to initiate photo-driven charge separation events. In this work, we employed a green synthetic procedure to achieve a high level of doping and have demonstrated how the thermal treatment during synthesis is crucial to select specific the microscopic (molecular) nature of the defect and, ultimately, the type of chemistry (reduction versus oxidation) that the material is able to perform. We found that low-temperature treatments produce material with higher efficiency in the water photosplitting reaction. This constitutes a further step in the establishment of N-doped ZnO as a photocatalyst for artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Due to exponential industrialization and rapid population growth, the global energy crisis and environmental pollution have become two of the greatest humanitarian challenges of the 21st century [[1]]. Interestingly, the modification of photocatalysts' surface with metals has been shown in all these studies, confirming their crucial functions for various reactions, being co-catalysts, dopants, and sensitizers. The first-generation Z-scheme photocatalysts need a redox mediator dissolved in a liquid phase (traditional Z-scheme), then a solid mediator has been used (all-solid-state/second generation Z-scheme), and, finally, the direct Z-scheme photocatalysts without redox mediator have been developed [[10]]. The ternary photocatalyst, composed of titania, copper, and graphene (TiO SB 2 sb /Cu/G), was obtained by Lewandowski et al. in a fluidized bed reactor [[16]]. [Extracted from the article]

A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively. [ABSTRACT FROM AUTHOR]

In biological and life science applications, photosynthesis is an important process that involves the absorption and transformation of sunlight into chemical energy. During the photosynthesis process, the light photons are captured by the green chlorophyll pigments in their photosynthetic antennae and further funneled to the reaction center. One of the most important light harvesting complexes that are highly important in the study of photosynthesis is the membrane-attached Fenna–Matthews–Olson (FMO) complex found in the green sulfur bacteria. In this review, we discuss the mathematical formulations and computational modeling of some of the light harvesting complexes including FMO. The most recent research developments in the photosynthetic light harvesting complexes are thoroughly discussed. The theoretical background related to the spectral density, quantum coherence and density functional theory has been elaborated. Furthermore, details about the transfer and excitation of energy in different sites of the FMO complex along with other vital photosynthetic light harvesting complexes have also been provided. Finally, we conclude this review by providing the current and potential applications in environmental science, energy, health and medicine, where such mathematical and computational studies of the photosynthesis and the light harvesting complexes can be readily integrated. [ABSTRACT FROM AUTHOR]

The tetracarbonyl complexes of transition metal chalcogenides M 2 X 2 (CO) 4 , where M = Fe, Co, Ni, Cu and X = S, Se, are examined by density functional theory (DFT). The M 2 X 2 core is cyclic with either planar or non-planar geometry. As a sulfide, it is present in natural enzymes and has a selective redox capacity. The reduced forms of the selenide and sulfide complexes are relevant to the hydrogen evolution reaction (HER) and they provide different positions of hydride ligand binding: (i) at a chalcogenide site, (ii) at a particular cation site and (iii) in a midway position forming equal bonds to both cation sites. The full pathway of water decomposition to molecular hydrogen and oxygen is traced by transition state theory. The iron and cobalt complexes, cobalt selenide, in particular, provide lower energy barriers in HER as compared to the nickel and copper complexes. In the oxygen evolution reaction (OER), cobalt and iron selenide tetracarbonyls provide a low energy barrier via OOH* intermediate. All of the intermediate species possess favorable excitation transitions in the visible light spectrum, as evidenced by TD-DFT calculations and they allow photoactivation. In conclusion, cobalt and iron selenide tetracarbonyl complexes emerge as promising photocatalysts in water splitting.

The oxygen-evolving complex (OEC) is the native enzyme that catalyzes the oxidation of water in natural photosynthesis. Two new classes of manganese cluster complexes of formula Ba2Mn2L¹2(H3L¹)2(CH3OH)41 and Mn4L²6Cl2 2 were prepared (H4L¹ = N,N0-(ethane-1,2-diyl)bis (2-hydroxybenzamide); L² = methyl picolinimidate) and characterized by standard techniques including microanalysis, IR spectroscopy, ESI spectrometry, and magnetic susceptibility measurements. X-ray diffraction studies of these complexes revealed (i) a box-type structure for 1 formed by two redox-active manganese(III) ions and two barium(II) ions connected by two bridging bisamido-bisphenoxy ligand molecules; and (ii) a planar-diamond array for Mn4N6 cluster 2 where the picolinimidates act as chelating ligands through the two nitrogen atoms. The ability of 1 and 2 to split water has been studied by means of water photolysis experiments. In these experiments, the oxygen evolution was measured in aqueous media in the presence of p-benzoquinone (acting as the hydrogen acceptor), the reduction of which was followed by UV-spectroscopy. The relevant photolytic activity found for 1 is in contrast to the inactivity of 2 in the photolytic experiments. This different behavior is discussed on the basis of the structure of the biomimetic models and the proposed reaction mechanism for this process supported by DFT calculations. [ABSTRACT FROM AUTHOR]

Anatase (TiO2) and multiwalled carbon nanotubes bearing polyethylenimine (PEI) anchored on their surface were hybridized in different proportions according to a sol-gel method. The resulting nanocomposites (TiO2@PEI-MWCNTs), characterized by BET, XRD, XPS, SEM, and UV techniques, were found efficient catalysts for CO2 photoreduction into formic and acetic acids in water suspension and under visible light irradiation. PEI-grafted nanotubes co-catalysts are believed to act as CO2 activators by forming a carbamate intermediate allowing to accomplish the first example in the literature of polyamines/nanotubes/TiO2 mediated CO2 photoreduction to carboxylic acids. [ABSTRACT FROM AUTHOR]

The development of non-fullerene small molecule as electron acceptors is critical for overcoming the shortcomings of fullerene and its derivatives (such as limited absorption of light, poor morphological stability and high cost). We investigated the electronic and optical properties of the two selected promising non-fullerene acceptors (NFAs), IDIC and IDTBR, and five conjugated donor polymers using quantum-chemical method (QM). Based on the optimized structures of the studied NFAs and the polymers, the ten donor/acceptor (D/A) interfaces were constructed and investigated using QM and Marcus semi-classical model. Firstly, for the two NFAs, IDTBR displays better electron transport capability, better optical absorption ability, and much greater electron mobility than IDIC. Secondly, the configurations of D/A yield the more bathochromic-shifted and broader sunlight absorption spectra than the single moiety. Surprisingly, although IDTBR has better optical properties than IDIC, the IDIC-based interfaces possess better electron injection abilities, optical absorption properties, smaller exciton binding energies and more effective electronic separation than the IDTBR-based interfaces. Finally, all the polymer/IDIC interfaces exhibit large charge separation rate (KCS) (up to 1012-1014 s-1) and low charge recombination rate (KCR) (<106 s-1), which are more likely to result in high power conversion efficiencies (PCEs). From above analysis, it was found that the polymer/IDIC interfaces should display better performance in the utility of bulk-heterojunction solar cells (BHJ OSC) than polymer/IDTBR interfaces. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis is the imitation of natural photosynthesis, which promises an efficient way to use solar energy to synthesize organic matters, in which the key step is the coenzyme regeneration (NADH/NADPH). To achieve an efficient regeneration rate, various photocatalysts have been developed, such as g-C3N4 and mesoporous carbon nitride (mpg-C3N4). Generally, efficiency determination of different photocatalysts requires laborious experiments, high consumption of reagents, and a considerable amount of time. Here, based on the one-step artificial photosystem I method, we processed the analytical experiment in a very simple PDMS well (20 µL, a drop) to achieve a rapid screening of photocatalysts. For comparison, we used two types of graphitic carbon nitrides, few-layer g-C3N4 and mpg-C3N4. Compared with the slurry systems, firstly, the regeneration rate of mpg-C3N4 drop-reactor system is 4.3 times and 7.1 times those of the few-layer g-C3N4-slurry system and mpg-C3N4-slurry system, respectively. Secondly, this one-drop method reduces the typical verification time from 90 min to 5 min and lowers the liquid volume from 20 mL to 20 µL. Thirdly, this operation is a pump-free and soft lithography technique-free process. The miniaturization of the photocatalytic reaction in the PDMS well improves the regeneration rates, saves samples, and achieves high-throughput screening of multiple photocatalysts. [ABSTRACT FROM AUTHOR]

Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bonds using artificial photosynthesis has been under intensive investigation within the last decades. As the understanding of the underlying working principle of these complex systems continuously grows, more focus will be placed on a catalyst design for highly selective product formation. Recent reports have shown that multifunctional photocatalysts can operate with high chemoselectivity, forming different catalysis products under appropriate reaction conditions. Within this context [(bpy)Rh(Cp*)X]n+-based catalysts are highly relevant examples for a detailed understanding of product selectivity in artificial photosynthesis since the identification of a number of possible reaction intermediates has already been achieved. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting, which is a type of artificial photosynthesis, is a sustainable way of converting solar energy into chemical energy. The water oxidation half-reaction has always represented the bottleneck of this process because of the thermodynamic and kinetic challenges that are involved. Several materials have been explored and studied to address the issues pertaining to solar water oxidation. Significant advances have recently been made in the use of stable and relatively cheap metal oxides, i.e., semiconducting photocatalysts. The use of BiVO4 for this purpose can be considered advantageous because this catalyst is able to absorb a substantial portion of the solar spectrum and has favourable conduction and valence band edge positions. However, BiVO4 is also associated with poor electron mobility and slow water oxidation kinetics and these are the problems that are currently being investigated in the ongoing research in this field. This review focuses on the most recent advances in the best-performing BiVO4-based photoanodes to date. It summarizes the critical parameters that contribute to the performance of these photoanodes, and highlights so far unresolved critical features related to the scale-up of a BiVO4-based PEC water-splitting device. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid perovskite solar cells (PSCs) have emerged as a new class of optoelectronic semiconductors that revolutionized the photovoltaic research in the recent years. The perovskite solar cells present numerous advantages include unique electronic structure, bandgap tunability, superior charge transport properties, facile processing, and low cost. Perovskite solar cells have demonstrated unprecedented progress in efficiency and its architecture evolved over the period of the last 5-6 years, achieving a high power conversion efficiency of about 22% in 2016, serving as a promising candidate with the potential to replace the existing commercial PV technologies. This review discusses the progress of perovskite solar cells focusing on aspects such as superior electronic properties and unique features of halide perovskite materials compared to that of conventional light absorbing semiconductors. The review also presents a brief overview of device architectures, fabrication methods, and interface engineering of perovskite solar cells. The last part of the review elaborates on the major challenges such as hysteresis and stability issues in perovskite solar cells that serve as a bottleneck for successful commercialization of this promising PV technology. [ABSTRACT FROM AUTHOR]

Cadmium sulphide (CdS) quantum dot sensitized solar cells (QDSSCs) based on screen-printed TiO2 were assembled using a screen-printing technique. The CdS quantum dots (QDs) were grown by using the Successive Ionic Layer Adsorption and Reaction (SILAR) method. The optical properties were studied by UV-Vis absorbance spectroscopy. Photovoltaic characteristics and impedance spectroscopic measurements of CdS QDSSCs were carried out under air mass 1.5 illuminations. The experimental results of capacitance against voltage indicate a trend from positive to negative capacitance because of the injection of electrons from the Fluorine doped tin oxide (FTO) electrode into TiO2. [ABSTRACT FROM AUTHOR]

In nature, the water-splitting reaction via photosynthesis driven by sunlight in plants, algae, and cyanobacteria stores the vast solar energy and provides vital oxygen to life on earth. The recent advances in elucidating the structures and functions of natural photosynthesis has provided firm framework and solid foundation in applying the knowledge to transform the carbon-based energy to renewable solar energy into our energy systems. In this review, inspired by photosynthesis robust photo water-splitting systems using manganese-containing materials including Mn-terpy dimer/titanium oxide, Mn-oxo tetramer/Nafion, and Mn-terpy oligomer/tungsten oxide, in solar fuel production are summarized and evaluated. Potential problems and future endeavors are also discussed. [ABSTRACT FROM AUTHOR]

The hydrogen economy presents an appealing energy future but its implementation must solve numerous problems ranging from low-cost sustainable production, high-density storage, costly infrastructure, to eliminating safety concern. The use of renewable carbohydrate as a high-density hydrogen carrier and energy source for hydrogen production is possible due to emerging cell-free synthetic biology technology-cell-free synthetic pathway biotransformation (SyPaB). Assembly of numerous enzymes and co-enzymes in vitro can create complicated set of biological reactions or pathways that microorganisms or catalysts cannot complete, for example, C6H10O5 (aq) + 7 H2O (l) ?? 12 H2 (g) + 6 CO2 (g) (PLoS One 2007, 2:e456). Thanks to 100% selectivity of enzymes, modest reaction conditions, and high-purity of generated hydrogen, carbohydrate is a promising hydrogen carrier for end users. Gravimetric density of carbohydrate is 14.8 H2 mass% if water can be recycled from proton exchange membrane fuel cells or 8.33% H2 mass% without water recycling. Renewable carbohydrate can be isolated from plant biomass or would be produced from a combination of solar electricity/hydrogen and carbon dioxide fixation mediated by high-efficiency artificial photosynthesis mediated by SyPaB. The construction of this carbon-neutral carbohydrate economy would address numerous sustainability challenges, such as electricity and hydrogen storage, CO2 fixation and long-term storage, water conservation, transportation fuel production, plus feed and food production. [ABSTRACT FROM AUTHOR]

In this work, the role of In2O3 in a heterojunction with TiO2 is studied as a way of increasing the photocatalytic activity for gas-phase CO2 reduction using water as the electron donor and UV irradiation. Depending on the nature of the employed In2O3, different behaviors appear. Thus, with the high crystallite sizes of commercial In2O3, the activity is improved with respect to TiO2, with modest improvements in the selectivity to methane. On the other hand, when In2O3 obtained in the laboratory, with low crystallite size, is employed, there is a further change in selectivity toward CH4, even if the total conversion is lower than that obtained with TiO2. The selectivity improvement in the heterojunctions is attributed to an enhancement in the charge transfer and separation with the presence of In2O3, more pronounced when smaller particles are used as in the case of laboratory-made In2O3, as confirmed by time-resolved fluorescence measurements. Ternary systems formed by these heterojunctions with silver nanoparticles reflect a drastic change in selectivity toward methane, confirming the role of silver as an electron collector that favors the charge transfer to the reaction medium. [ABSTRACT FROM AUTHOR]

The photocatalytic reduction of carbon dioxide (CO2) into value-added chemicals is considered to be a green and sustainable technology, and has recently gained considerable research interest. In this work, titanium dioxide (TiO2) supported Pt, Pd, Ni, and Cu catalysts were synthesized by photodeposition. The formation of various metal species on an anatase TiO2 surface, after ultraviolet (UV) light irradiation, was investigated insightfully by the X-ray absorption near edge structure (XANES) technique. CO2 reduction under UV-light irradiation at an ambient pressure was demonstrated. To gain an insight into the charge recombination rate during reduction, the catalysts were carefully investigated by the intensity modulated photocurrent spectroscopy (IMPS) and photoluminescence spectroscopy (PL). The catalytic behaviors of the catalysts were investigated by density functional theory using the self-consistent Hubbard U-correction (DFT+U) approach. In addition, Mott–Schottky measurement was employed to study the effect of energy band alignment of metal-semiconductor on CO2 photoreduction. Heterojunction formed at Pt-, Pd-, Ni-, and Cu-TiO2 interface has crucial roles on the charge recombination and the catalytic behaviors. Furthermore, it was found that Pt-TiO2 provides the highest methanol yield of 17.85 µmol/gcat/h, and CO as a minor product. According to the IMPS data, Pt-TiO2 has the best charge transfer ability, with the mean electron transit time of 4.513 µs. We believe that this extensive study on the junction between TiO2 could provide a profound understanding of catalytic behaviors, which will pave the way for rational designs of novel catalysts with improved photocatalytic performance for CO2 reduction. [ABSTRACT FROM AUTHOR]

Sulfides are frequently used as photocatalysts, since they absorb visible light better than many oxides. They have the disadvantage of being more easily photocorroded. This occurs mostly in oxidizing conditions; therefore, they are commonly used instead in reduction processes, such as CO2 reduction to fuels or H2 production. Here a summary will be presented of a number of sulfides used in several photocatalytic processes; where appropriate, some recent reviews will be presented of their behaviour. Results obtained in recent years by our group using some octahedral sulfides will be shown, showing how to determine their wavelength-dependent photocatalytic activities, checking their mechanisms in some cases, and verifying how they can be modified to extend their wavelength range of activity. It will be shown here as well how using photocatalytic or photoelectrochemical setups, by combining some enzymes with these sulfides, allows achieving the photo-splitting of water into H2 and O2, thus constituting a scheme of artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Efficient photon to charge (PTC) transfer is considered to be the cornerstone of technological improvements in the photovoltaic (PV) industry, while it constitutes the most common process in nature. This study aims to investigate the parameters that impact efficient PV-cell photon to charge conversion in two ways: (a) providing a brief research analysis to extract the key features which affect the electrical and optical performance of PV cells' operation, and (b) investigating the dependance of these characteristics on the photon to charge mechanisms. The former direction focuses on the latest advances regarding the impacts of the microenvironment climate conditions on the PV module and its operational performance, while the latter examines the fundamental determinants of the cell's efficient operation. The electrical and optical parameters of the bulk PV cells are influenced by both the external microenvironment and the intrinsic photon to charge conversion principles. Light and energy harvesting issues need to be overcome, while nature-inspired interpretation and mimicking of photon to charge and excitation energy transfer are in an infant stage, furthering a better understanding of artificial photosynthesis. A future research orientation is proposed which focuses on scaling up development and making use of the before mentioned challenges. [ABSTRACT FROM AUTHOR]