Academic literature on the topic 'Hydrogen, Dyes, Photocatalysis, Artificial Photosynthesis'

Production of green energy is important considering the depletion of fossil fuels and increase in greenhouse gases. Light harvesting T-metal complexes with earth abundant T-metal photocatalysts show promising ways of producing green energy.

Wastewater from the textile industry has a substantial impact on water quality. Synthetic dyes used in the textile production process are often discharged into water bodies as residues. Highly colored wastewater causes various of problems for the aquatic environment such as: reducing light penetration, inhibiting photosynthesis and being toxic to certain organisms. Since most dyes are resistant to biodegradation and are not completely removed by conventional methods (adsorption, coagulation-flocculation, activated sludge, membrane filtration) they persist in the environment. Advanced oxidation processes (AOPs) based on hydrogen peroxide (H2O2) have been proven to decolorize only some of the dyes from wastewater by photocatalysis. In this article, we compared two very different photocatalytic systems (UV/peroxydisulfate and UV/H2O2). Photocatalyzed activation of peroxydisulfate (PDS) generated sulfate radicals (SO4•−), which reacted with the selected anthraquinone dye of concern, Acid Blue 129 (AB129). Various conditions, such as pH and concentration of PDS were applied, in order to obtain an effective decolorization effect, which was significantly better than in the case of hydroxyl radicals. The kinetics of the reaction followed a pseudo-first order model. The main reaction pathway was also proposed based on quantum chemical analysis. Moreover, the toxicity of the solution after treatment was evaluated using Daphnia magna and Lemna minor, and was found to be significantly lower compared to the toxicity of the initial dye.

AbstractIn recent years, excellent research has revealed that light-harvesting systems (LHSs) are composed of beautifully aligned chlorophyll molecules; the regulated alignment of chlorophylls is responsible for the efficient and selective light-harvesting energy transfer processes in purple bacteria. This finding led to the construction of a regularly arranged assembly of functional dyes as a step toward fabricating artificial LHSs. While most approaches toward the construction of dye assemblies have depended on molecular interactions such as covalent, coordination, and hydrogen bonds, my approach involves guest–host interactions using an inorganic nanosheet as the host material. This short review presents the construction of a 2D dye assembly and its effective utilization in artificial light-harvesting applications. Owing to the highly stable and uniform 2D alignment of functional dyes on inorganic nanosheets, nearly 100 % singlet–singlet energy transfer and efficient light-harvesting were achieved. I believe that the results presented herein will contribute to the construction of efficient photochemical reaction systems in supramolecular host–guest assemblies, which may facilitate the realization of artificial photosynthesis.

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.

The increasing interest and applications of photocatalysis, namely hydrogen production, artificial photosynthesis, and water remediation and disinfection, still face several drawbacks that prevent this technology from being fully implemented at the industrial level. The need to improve the performance of photocatalytic processes and extend their potential working under visible light has boosted the synthesis of new and more efficient semiconductor materials. Thus far, semiconductor–semiconductor heterojunction is the most remarkable alternative. Not only are the characteristics of the new materials relevant to the process performance, but also a deep understanding of the charge transfer mechanisms and the relationship with the process variables and nature of the semiconductors. However, there are several different charge transfer mechanisms responsible for the activity of the composites regardless the synthesis materials. In fact, different mechanisms can be carried out for the same junction. Focusing primarily on the photocatalytic generation of hydrogen, the objective of this review is to unravel the charge transfer mechanisms after the in-depth analyses of already reported literature and establish the guidelines for future research.

Abstract Artificial photosynthesis of solar fuels is deemed as one of the Holy grails of renewable energy technology for simultaneously solving energy and environmental issues. At the present, it is one of the most involved programs in the international Mission Innovation Challenge for Accelerating the Clean Energy Revolution. Solar-driven water splitting and CO2 conversion are the main research application of artificial photosynthesis. However, these reactions are extremely challenging due to energetically uphill (G>0) and non-spontaneous multi-electron transfer processes, which are difficult to be understood by traditional knowledge of catalysis. An efficient solar energy conversion system must simultaneously deal well with light absorption, charge separation and transfer, surface redox reactions. Particularly, efficient charge separation and transfer by retarding back electron transfer, are often regarded as the key determining steps for overall solar energy conversion. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions—type-II and Z-scheme heterojunctions have been widely acknowledged [1]. Recently, lead halide perovskites (LHPs) with the chemical formula of ABX3, where A is an organic or inorganic cation (A= Cs+, MA+, FA+), B is Pb2+, and X is a halogen anion (Br-, Cl-, I-), such as CH3NH3PbI3,FAPbI3, and CsPbBr3 have been widely investigated as auspicious semiconductor photocatalysts for photocatalytic H2 production and photocatalytic CO2 reduction owing to their impressive photoelectrochemical properties, facile to synthesize, high carrier mobility, low exciton binding energy, and long carrier lifetime [2]. However, the high toxicity and notorious instability upon exposure to light, moisture, and high temperature are the major obstacles to their practical use.Therefore, developing alternative lead-free semiconductor photocatalysts with similar optoelectronic properties to the LHPs is highly needed. Inorganic halide double-perovskites and analogous oxide double-perovskites with the chemical formula of A2B'B"X6 and A2B'B"O6, respectively, are layered 3D materials, which have been considered as a novel ecofriendly visible light responsive semiconductor photocatalysts to replace the toxic lead-halide perovskite. The main feature of the halide and oxide double-perovskites is that their structures can be accommodated with different transition metal combinations on B' and B" site cations to tune their intrinsic properties such as light absorption, carrier mobilities, chemical diversity, and so on. Theoretically, an auspicious photocatalytic activity can be realized from them owing to their impressive photophysical properties. However, poor charge separation and severe charge recombination have restricted their practical photocatalytic application. Recently, several halides and oxides double perovskites have been demonstrated as visible light-responsive photocatalysts for photocatalytic CO2 reduction and photocatalytic half-reaction (oxygen and hydrogen evolution reactions) such as Cs2AgBrBr6, Cs2AgSbBr6, Sr2CoTaO6, Sr2CoWO6, etc. [3-5]. However, for oxide double perovskites even though they have shown bifunctional photocatalytic oxygen and hydrogen two half-reactions with visible light but their potential as photocatalytic CO2 reduction and one-step overall water splitting have not been achieved so far. Therefore, further improvement of the material design and synthesis by assembling heterostructure based on two eco-friendly halide and oxide double perovskites may play a key role in achieving high efficient photocatalytic performance under visible-light-irradiation. Thought is a challenging task, but holds great potential in advancing science and technology in photocatalysis. References Liao, C. Li, S.-Y. Liu, B. Fang, H. Yang, Emerging frontiers of Z-scheme photocatalytic systems, Trends in Chemistry. 4 (2022) 111–127. -C. Wang, N. Li, A.M. Idris, J. Wang, X. Du, Z. Pan, Z. Li, Surface Defect Engineering of CsPbBr3 Nanocrystals for High Efficient Photocatalytic CO2 Reduction, Solar RRL. 5 (2021) 2100154. Idris, A. M.; Liu, T.; Shah, J. H.; Zhang, X.; Ma, C.; Malik, A. S.; Jin, A. Solar RRL 2020, 4 (3), 1900456. Idris, A. M.; Liu, T.; Hussain Shah, J.; Han, H.; Li, C. ACS Sustainable Chemistry&Engineering 2020, 8 (37), 14190-14197. Wang, H. Huang, Z. Zhang, C. Wang, Y. Yang, Q. Li, D. Xu, Lead-free perovskite Cs2AgBiBr6@g-C3N4 Z-scheme system for improving CH4 production in photocatalytic CO2 reduction, Applied Catalysis B: Environmental. 282 (2021).

Abstract Nanoscale objects feature very large surface-area-to-volume ratios and are now understood as powerful tools for catalysis, but their nature as nanomaterials brings challenges including toxicity and nanomaterial pollution. Immobilization is considered a feasible strategy for addressing these limitations. Here, as a proof-of-concept for the immobilization of nanoscale catalysts in the extracellular matrix of bacterial biofilms, we genetically engineered amyloid monomers of the Escherichia coli curli nanofiber system that are secreted and can self-assemble and anchor nano-objects in a spatially precise manner. We demonstrated three scalable, tunable and reusable catalysis systems: biofilm-anchored gold nanoparticles to reduce nitro aromatic compounds such as the pollutant p-nitrophenol, biofilm-anchored hybrid Cd0.9Zn0.1S quantum dots and gold nanoparticles to degrade organic dyes and biofilm-anchored CdSeS@ZnS quantum dots in a semi-artificial photosynthesis system for hydrogen production. Our work demonstrates how the ability of biofilms to grow in scalable and complex spatial arrangements can be exploited for catalytic applications and clearly illustrates the design utility of segregating high-energy nano-objects from injury-prone cellular components by engineering anchoring points in an extracellular matrix.

Energy and environment are the key global challenges in the 21st century. Solar energy is considered the most promising clean and sustainable energy resource due to its university, inexhaustible and environmental friendliness. One of the most viable means of solar energy conversion and utilization is artificially converting solar energy into chemical energy as natural photosynthesis does. H2 produced from water splitting and CO2 reduction, are the major research topics of artificial photosynthesis. However, the effective conversion of solar energy into chemical energy by cost-effective artificial means on a large scale remains elusive. Metal oxide-based photocatalysts are the most studied materials for photocatalytic water splitting and CO2 reduction. Particularly, perovskite oxides with the chemical formula of ABO3 have been intensively studied as semiconductor photocatalysts. However, overwhelmingly of the perovskite oxides are only active under UV-light-irradiation, which limited their potential in solar energy application. Therefore, breakthrough technology and step-change materials, particularly, visible-light-responsive photocatalysts are highly desirable for the development of photocatalytic systems. In recent years, copious progress has been made in designing materials that function under visible-light-irradiation. So far, the most successful strategy is anion doping of oxide semiconductors, such as nitrogen or sulfur dope to form oxynitrides and oxysulfides, respectively. For example, nitrogen-doped oxynitrides such as (Ga1-xZnx)(N1-xOx) and ANbO2N (A=Sr, Ba, and La)1, and sulfur-doped oxysulfides such as Sm2Ti2S2O5 2 showed efficient photocatalytic overall water splitting activities under visible-light-irradiation. Particularly, oxynitrides (Ga1-xZnx)(N1-xOx) based photocatalyst sheet, showed remarkable photocatalytic overall water splitting activity with AQE of more than 30% at l»420 nm3. However, these oxynitrides and oxysulfides suffer stability problems due to photocorrosion, hindering their potential practical application in photocatalytic applications. Recently, it has been theorized that double perovskite oxides (DPOs) with the chemical formula of A2BʹB"O6 can function as efficient and stable visible-light-responsive photocatalysts for photocatalytic water splitting and CO2 reduction. However, DPOs have been rarely studied for photocatalytic water splitting and CO2 reduction due to the difficulty of obtaining pure phase materials and the paucity of exposed active sites. Thus, developing efficient and stable visible-light-responsive DPOs photocatalysts for photocatalytic water splitting and CO2 reduction becomes important. In this regard, recently, we have demonstrated a series of efficient and stable visible-light-responsive DPOs photocatalysts for photocatalytic water splitting. For instance, Sr2CoWO6 and Sr2CoTaO6 can serve as an efficient and stable bifunctional photocatalyst for both photocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction(HER)4, 5, and Sr2NiWO6 can efficiently drive the photocatalytic OER6. Even though these DPOs have been demonstrated as visible-light-responsive photocatalysts with suitable CB and VB positions that straddle the theoretical potentials for overall water splitting, however, one-step overall water splitting has not been achieved so far, and their potential for photocatalytic CO2 reduction has not been studied yet. Overall water splitting under visible-light-irradiation based on particulate photocatalysts is a challenging reaction, which is regarded as one of the “Holy Grail” of sciences. And oxide semiconductors showing both photocatalytic OER and HER activities are rare. Nevertheless, bifunctional photocatalytic OER and HER were successfully demonstrated based on Sr2CoWO6 and Sr2CoTaO6. Further improvement of the material designs and developing appropriate cocatalysts may play a key role in achieving one-step overall water splitting under visible-light-irradiation based on DPOs photocatalysts. This work is mainly to explore the possibility of utilizing DPOs materials as visible-light-responsive photocatalysts for photocatalytic water splitting and CO2 reduction reaction, which is challenging work but has great potential value in advancing science and technology in photocatalysis. We anticipated that this work will provide a novel and rational strategy for improving the light absorption, charge separation and charge utilization in DPOs photocatalysts. References Maeda, K.; Teramura, K.; Masuda, H.; Takata, T.; Saito, N.; Inoue, Y.; Domen, K. The Journal of Physical Chemistry B 2006, 110 (26), 13107-13112. Ma, G.; Kuang, Y.; Murthy, D. H.; Hisatomi, T.; Seo, J.; Chen, S.; Matsuzaki, H.; Suzuki, Y.; Katayama, M.; Minegishi, T. The Journal of Physical Chemistry C 2018, 122 (25), 13492-13499. Kato, H.; Asakura, K.; Kudo, A. Journal of the American Chemical Society 2003, 125 (10), 3082-3089. Idris, A. M.; Liu, T.; Shah, J. H.; Zhang, X.; Ma, C.; Malik, A. S.; Jin, A. Solar RRL 2020, 4 (3), 1900456. Idris, A. M.; Liu, T.; Hussain Shah, J.; Han, H.; Li, C. ACS Sustainable Chemistry&Engineering 2020, 8 (37), 14190-14197. Idris, A. M.; Liu, T.; Hussain Shah, J.; Malik, A. S.; Zhao, D.; Han, H.; Li, C. ACS Applied Materials&Interfaces 2020, 12 (23), 25938-25948.

AbstractDevelopment of a versatile, sustainable and efficient photosynthesis system that integrates intricate catalytic networks and energy modules at the same location is of considerable future value to energy transformation. In the present study, we develop a coenzyme-mediated supramolecular host-guest semibiological system that combines artificial and enzymatic catalysis for photocatalytic hydrogen evolution from alcohol dehydrogenation. This approach involves modification of the microenvironment of a dithiolene-embedded metal-organic cage to trap an organic dye and NADH molecule simultaneously, serving as a hydrogenase analogue to induce effective proton reduction inside the artificial host. This abiotic photocatalytic system is further embedded into the pocket of the alcohol dehydrogenase to couple enzymatic alcohol dehydrogenation. This host-guest approach allows in situ regeneration of NAD+/NADH couple to transfer protons and electrons between the two catalytic cycles, thereby paving a unique avenue for a synergic combination of abiotic and biotic synthetic sequences for photocatalytic fuel and chemical transformation.

The humankind today needs to face an epochal transition from a fossil fuel to a renewable source-based economy. Renewable sources are our chance to build a clean world with unlimited and widespread energy. Nowadays renewable energies could be properly harvested to produce electricity, while the development of a future clean fuel is less advanced. Since our energetic consumption is made essentially of fuels we need to build devices to transform renewable energy, such as solar radiation, into chemical energy of bonds. A promising future fuel is hydrogen since its carbon footprint is zero and it can be obtained from an abundant source such as water. Nature, through the photosynthesis, could inspire us to build our feed in the form of fuels. In this research project DSSC (dye-sensitized solar cells) have been modified to produce chemical energy instead of electricity. Attention has been focused on hydrogen production semi-reaction, thus the use of a sacrificial electron donor has been adopted. Such system is composed of TiO2 nanoparticles covered by a reduction catalyst and a metal-free organic sensitizer to harvest the visible spectrum of solar radiation. The aim of this research has been the development of molecular approaches to provide efficient light harvesting systems and reduction catalysts. Molecular design allowed a fine tuning of materials properties and a deep understanding of structure/performances relationships. The first part of the project has focused on designing push-pull structures to harvest visible light portion of solar spectrum. Fine molecular tuning of metal-free dyes afforded enhanced performances depending on the kind of modification. We modified a known phenothiazine dye in the donor, spacer and acceptor units in order to derive structure/performances relationships. Enhanced light harvesting properties and photo-stability have been afforded through π-spacer modification with various mono- and polycyclic simple and fused thiophene derivatives, while decoration of the donor core with glycolic or sugar chains gave better hydrophilicity and surface wettability. Lastly hydroxamic acids have been introduced as alternative anchoring groups to give stronger ester bonds on TiO2 surface and prevent hydrolysis in aqueous media. The second part of the research has concerned the study of cobaloximes as alternative noble metal free reduction catalysts. Starting from a mini-library of cobaloximes bearing various equatorial bridges, axial ligands, and starting oxidation numbers, molecular structure/efficiency studies have been done, while UV/Vis spectroscopy has been used to investigate the nature of the eventual Co(I) species transiently formed. For cobaloximes a Co(I) species is hypothesized but not confirmed in photocatalytic experiments and optimization of efficiency and stability of new catalysts need a deep understanding of the catalytic cycle in order to intervene in the critical intermediates.

In light of its rapidly growing energy demand, human society has an urgent need to become much more strongly reliant on renewable and sustainable energy carriers. Molecular hydrogen made from water with solar energy could provide an ideal case. The development of inexpensive, robust and rare element free catalysts is crucial for this technology to succeed. Enzymes in nature can give us ideas about what such catalysts could look like, but for the directed adjustment of any natural or synthetic catalyst to the requirements of large scale catalysis, its capabilities and limitations need to be understood on the level of individual reaction steps. This thesis deals with kinetic and mechanistic investigations of photo- and electrocatalytic hydrogen production with natural and synthetic molecular catalysts. Photochemical hydrogen production can be achieved with both E. coli Hyd-2 [NiFe] hydrogenase and a synthetic dinuclear [FeFe] hydrogenase active site model by ruthenium polypyridyl photosensitization. The overall quantum yields are on the order of several percent. Transient UV-Vis absorption experiments reveal that these yields are strongly controlled by the competition of charge recombination reactions with catalysis. With the hydrogenase major electron losses occur at the stage of enzyme reduction by the reduced photosensitizer. In contrast, catalyst reduction is very efficient in case of the synthetic dinuclear active site model. Here, losses presumably occur at the stage of reduced catalyst intermediates. Moreover, the synthetic catalyst is prone to structural changes induced by competing ligands such as secondary amines or DMF, which lead to catalytically active, potentially mononuclear, species. Investigations of electrocatalytic hydrogen production with a mononuclear catalyst by cyclic voltammetry provide detailed kinetic and mechanistic information on the catalyst itself. By extension of existing theory, it is possible to distinguish between alternative catalytic pathways and to extract rate constants for individual steps of catalysis. The equilibrium constant for catalyst protonation can be determined, and limits can be set on both the protonation and deprotonation rate constant. Hydrogen bond formation likely involves two catalyst molecules, and even the second order rate constant characterizing hydrogen bond formation and/or release can be determined.