Artificial Photosynthetic Systems Research Articles

Accelerating Small Electron Polaron Dissociation and Hole Transfer at Solid-Liquid Interface for Enhanced Heterogeneous Photoreaction.

In a photocatalysis process, quick charge recombination induced by small electron polarons in a photocatalyst and sluggish kinetics of hole transfer at the solid-liquid interface have greatly limited photocatalytic efficiency. Herein, we demonstrate hydrated transition metal ions as mediators that can simultaneously accelerate small electron polaron dissociation (via metal ion reduction) and hole transfer (through high-valence metal production) at the solid-liquid interface for improved photocatalytic pollutant degradation. Fe3+, by virtue of its excellent redox ability as a homogeneous mediator, enables the BiVO4 photocatalyst to achieve drastically increased photocatalytic degradation performance, up to 684 times that without Fe3+. The enhanced performance results from Fe(IV) species production (via Fe3+ oxidation) induced by dissociation of small electron polarons (via Fe3+ reduction), featuring an extremely low kinetic barrier (5.4 kJ mol-1) for oxygen atom transfer thanks to the donor-acceptor orbital interaction between Fe(IV) and organic pollutants. This work constructs a high-efficiency artificial photosynthetic system through synergistically eliminating electron localization and breaking hole transfer limitation at the solid-liquid interface for constructing high-efficiency artificial photosynthetic systems.

A cluster-nanozyme-coenzyme system mimicking natural photosynthesis for CO2 reduction under intermittent light irradiation

Natural photosynthesis utilizes solar energy to convert water and atmospheric CO2 into carbohydrates through all-weather light/dark reactions based on molecule-based enzymes and coenzymes, inspiring extensive development of artificial photosynthesis. However, development of efficient artificial photosynthetic systems free of noble metals, as well as rational integration of functional units into a single system at the molecular level, remain challenging. Here we report an artificial system, the assembly system of Cu6 cluster and cobalt terpyridine complex, that mimics natural photosynthesis through precise integration of nanozyme complexes and ubiquinone (coenzyme Q) on Cu6 clusters. This biomimetic system efficiently reduces CO2 to CO in light reaction, achieving a production rate of 740.7 μmol·g−1·h−1 with high durability for at least 188 hours. Notably, our system realizes the decoupling of light and dark reactions, utilizing the phenol-evolutive coenzyme Q acting as an electron reservoir. By regulating the stabilizer of coenzyme Q, the dark reaction time can be extended up to 8.5 hours, which fully meets the natural day/night cycle requirements. Our findings advance the molecular design of artificial systems that replicate the comprehensive functions of natural photosynthesis.

Artificial photosynthetic system for diluted CO2 reduction in gas-solid phase

Rational design of robust photocatalytic systems to direct capture and in-situ convert diluted CO2 from flue gas is a promising but challenging way to achieve carbon neutrality. Here, we report a new type of host-guest photocatalysts by integrating CO2-enriching ionic liquids and photoactive metal-organic frameworks PCN-250-Fe2M (M = Fe, Co, Ni, Zn, Mn) for artificial photosynthetic diluted CO2 reduction in gas-solid phase. As a result, [Emim]BF4(39.3 wt%)@PCN-250-Fe2Co exhibits a record high CO2-to-CO reduction rate of 313.34 μmol g−1 h−1 under pure CO2 atmosphere and 153.42 μmol g−1 h−1 under diluted CO2 (15%) with about 100% selectivity. In scaled-up experiments with 1.0 g catalyst and natural sunlight irradiation, the concentration of pure and diluted CO2 (15%) could be significantly decreased to below 85% and 10%, respectively, indicating its industrial application potential. Further experiments and theoretical calculations reveal that ionic liquids not only benefit CO2 enrichment, but also form synergistic effect with Co2+ sites in PCN-250-Fe2Co, resulting in a significant reduction in Gibbs energy barrier during the rate-determining step of CO2-to-CO conversion.

Photosynthetic biohybrid systems for solar fuels catalysis.

Photosynthetic reaction center (RC) proteins are finely tuned molecular systems optimized for solar energy conversion. RCs effectively capture and convert sunlight with near unity quantum efficiency utilizing light-induced directional electron transfer through a series of molecular cofactors embedded within the protein core to generate a long-lived charge separated state with a useable electrochemical potential. Of current interest are new strategies that couple RC chemistry to the direct synthesis of energy-rich compounds. This Feature Article highlights recent work from our lab on RC and RC-inspired hybrid systems that capture the Sun's energy and convert it to chemical energy in the form of H2, a carbon-neutral energy source derived from water. Biohybrids made from the Photosystem I (PSI) RC are among the best photocatalytic H2-producing protein hybrids to date. Targeted self-assembly strategies that couple abiotic catalysts to PSI translate to catalyst incorporation at intrinsic PSI sites within thylakoid membranes to achieve complete solar water-splitting systems. RC-inspired biohybrids interface synthetic photosensitizers and molecular catalysts with small proteins to create photocatalytic systems and enable the spectroscopic discernment of the structural features and electron transfer processes that underpin solar-driven proton reduction. In total, these studies showcase the incredible scientific opportunities photosynthetic biohybrid research provides for harnessing the optimal qualities of both artificial and natural photosynthetic systems and developing materials that capture, convert, and store solar energy as a fuel.

Strategies and Applications for Supramolecular Protein Self-Assembly.

Supramolecular chemistry achieves higher-order molecular self-assembly through non-covalent interactions. Utilizing supramolecular methods to explore the polymorphism of proteins, the building blocks of life, from a "bottom-up" perspective is essential for constructing diverse and functional biomaterials. In recent years, significant progress has been achieved in the design strategies and functional applications of supramolecular protein self-assembly, becoming a focal point for researchers. This paper reviews classical supramolecular strategies driving protein self-assembly, including electrostatic interactions, metal coordination, hydrogen bonding, hydrophobic interactions, host-guest interactions, and other mechanisms. We discuss how these supramolecular interactions regulate protein assembly processes and highlight protein supramolecular assemblies' unique structural and functional advantages in constructing artificial photosynthetic systems, protein hydrogels, bio-delivery systems, and other functional materials. The enormous potential and significance of supramolecular protein materials are elucidated. Finally, the challenges in preparing and applying protein supramolecular assemblies are summarized, and future development directions are projected.

Anisotropic Dual S‐Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response

AbstractThe design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S‐scheme heterojunction artificial photosynthetic system composed of Bi2O3−BiOBr−AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55‐fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag‐based materials, this dual S‐scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Anisotropic Dual S-Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response.

The design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S-scheme heterojunction artificial photosynthetic system composed of Bi2O3-BiOBr-AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55-fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag-based materials, this dual S-scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Iso‐Elemental ZnIn2S4/Zn3In2S6 Heterojunction with Low Contact Energy Barrier Boosts Artificial Photosynthesis of Hydrogen Peroxide

AbstractArtificial photosynthesis emerges as a strategic pathway to produce hydrogen peroxide (H2O2), an environmentally benign oxidant and a clean energy carrier. Nonetheless, in many heterojunction‐based artificial photosynthetic systems, the H2O2 productivity is significantly hindered by poor carrier transport, narrow spectral light absorption, and a lack of adequate active sites for the two‐electron oxygen reduction reaction. Herein, a catalyst architecture with an iso‐elemental heterojunction formed by interfacing Zn3In2S6 nano‐flowers and ZnIn2S4 nanosheets is proposed. This catalyst exhibits a H2O2 production rate as high as 23.47 µmol g−1 min−1 under UV–vis light irradiation, which is attributed to the minimized contact energy barrier and enhanced lattice match at the ZnIn2S4/Zn3In2S6 interface thanks to the iso‐elemental catalyst architecture which aids in enhanced efficient separation and transfer of photogenerated carriers. Theoretical simulations alongside comprehensive in‐situ and ex‐situ characterizations confirm the photo‐redox sites for H2O2 generation and effective carrier dynamics across the catalyst surface. Moreover, substituting one reduction‐type catalyst ZnIn2S4 with other non‐iso‐elemental catalysts like CdIn2S4, TiO2, and CdS further confirms the feasibility and superiority of the proposed iso‐elemental configuration. This work offers a new perspective on designing heterojunction catalysts for artificial photosynthesis of H2O2.

Achieving a solar-to-chemical efficiency of 3.6% in ambient conditions by inhibiting interlayer charges transport

Efficiently converting solar energy into chemical energy remains a formidable challenge in artificial photosynthetic systems. To date, rarely has an artificial photosynthetic system operating in the open air surpassed the highest solar-to-biomass conversion efficiency (1%) observed in plants. In this study, we present a three-dimension polymeric photocatalyst achieving a solar-to-H2O2 conversion efficiency of 3.6% under ambient conditions, including real water, open air, and room temperature. The impressive performance is attributed to the efficient storage of electrons inside materials via expeditious intramolecular charge transfer, and the fast extraction of the stored electrons by O2 that can diffuse into the internal pores of the self-supporting three-dimensional material. This construction strategy suppresses the interlayer transfer of excitons, polarizers and carriers, effectively increases the utilization of internal excitons to 82%. This breakthrough provides a perspective to substantially enhance photocatalytic performance and bear substantial implications for sustainable energy generation and environmental remediation.

An S-scheme artificial photosynthetic system with H-TiO2/g-C3N4 heterojunction coupled with MXene boosts solar H2 evolution

Solar hydrogen production via water splitting is pivotal for solar energy harnessing, addressing key challenges in energy and environmental sustainability. However, two critical issues persist with single-component photocatalysts: suboptimal carrier transport and inadequate light absorption. While heterojunction-based artificial photosynthetic systems like Z-scheme photocatalysts have been explored, their charge recombination and light harvesting efficiency are still unsatisfactory. S-scheme heterojunctions have gained attention in photocatalysis, owing to their pronounced built-in electric field and superior redox capabilities. In this study, we introduce a MXene-based S-scheme H-TiO2/g-C3N4/Ti3C2 heterojunction (TCMX), synthesized through electrostatic self-assembly. The as-prepared TCMX exhibited an excellent photocatalytic hydrogen evolution rate of 53.67 mmol g−1 h−1 surpassing the performance of commercial Rutile TiO2, H-TiO2, g-C3N4, and HTCN. The effectiveness of TCMX is largely due to the built-in electric field in the S-scheme heterojunction and the cocatalytic activity of MXene promoting rapid separation of photogenerated charges and resulting in well-separated electron and hole enriched sites. This study offers a new approach to enhance photocatalytic hydrogen evolution efficiency and paves the way for the future design of S-scheme heterojunctions.

De novo design of proteins housing excitonically coupled chlorophyll special pairs

Natural photosystems couple light harvesting to charge separation using a ‘special pair’ of chlorophyll molecules that accepts excitation energy from the antenna and initiates an electron-transfer cascade. To investigate the photophysics of special pairs independently of the complexities of native photosynthetic proteins, and as a first step toward creating synthetic photosystems for new energy conversion technologies, we designed C2-symmetric proteins that hold two chlorophyll molecules in closely juxtaposed arrangements. X-ray crystallography confirmed that one designed protein binds two chlorophylls in the same orientation as native special pairs, whereas a second designed protein positions them in a previously unseen geometry. Spectroscopy revealed that the chlorophylls are excitonically coupled, and fluorescence lifetime imaging demonstrated energy transfer. The cryo-electron microscopy structure of a designed 24-chlorophyll octahedral nanocage with a special pair on each edge closely matched the design model. The results suggest that the de novo design of artificial photosynthetic systems is within reach of current computational methods.

Efficient Intra‐Supramolecular Electron Transfer in Zinc Porphyrin‐Coumarin Dyads

AbstractWe report herein the electron transfer process of a novel supramolecular dyads composed of zinc tetraphenylporphyrin (ZnTPP) and zinc 5,15‐dinonyl‐10,20‐diphenylporphyrin (ZnDPP), as electron donors, and ethyl(4‐pyridyl) coumarin‐3‐carboxylate (EPCC), as an electron acceptor, through metal‐ligand coordination bond in dichloromethane. The optical absorption studies revealed the formation of the moderate stable supramolecular donor‐acceptor dyads. The fluorescence measurements showed a significant fluorescence quenching of the singlet‐excited state of the singlet‐excited states of ZnTPP and ZnDPP upon addition of different amounts of EPCC. Such quenching behavior could be attributed to the electron transfer from the singlet‐excited state of porphyrin to EPCC. The bimolecular quenching rates were determined to be 1.98×1012 and 7.59×1012 L mol−1 s−1 for ZnTPP‐EPCC and ZnDPP‐EPCC, respectively, respectively. The fluorescence lifetime measurements suggest fast and efficient intra‐supramolecular electron transfer from the singlet states of porphyrin derivatives to EPCC. Furthermore, the formation of the supramolecular dyads was confirmed by the Raman technique and computational studies. The finding that the examined zinc porphyrin ‐ coumarin supramolecular dyads absorb light in a wide range of UV‐visible spectrum, fast and efficient electron transfer render the examined supramolecular dyad as simple models for the reaction centers of the artificial photosynthetic systems.

Light-driven CO2 utilization for chemical production in bacterium biohybrids

Artificial photosynthetic systems provide an alternative approach for the sustainable, efficient, and versatile production of biofuels and biochemicals. However, improving the efficiency of electron transfer between semiconductor materials and microbial cells remains a challenge. In this study, an inorganic-biological photosynthetic biohybrid system (IBPHS) consisting of photocatalytic and biocatalytic modules was developed by integrating cadmium telluride quantum dots (CdTe QDs) with Escherichia coli cells. A photocatalytic module was constructed by biosynthesizing CdTe QDs to capture light and generate electrons. The biocatalytic module was built by converting photo-induced electrons to enhance NADH regeneration; thus, the NADH content in E. coli under blue light increased by 5.1-fold compared to that in darkness. Finally, IBPHS was utilized to drive CO2 reduction pathways for versatile bioproduction such as formate and pyruvate, with CO2 utilization rates up to 51.98 and 21.92 mg/gDCW/h, respectively, exceeding that of cyanobacteria. This study offers a promising platform for the rational design of biohybrids for efficient biomanufacturing processes with high complexity and functionality.

Deciphering Photoinduced Catalytic Reaction Mechanisms in Natural and Artificial Photosynthetic Systems on Multiple Temporal and Spatial Scales Using X-ray Probes.

Utilization of renewable energies for catalytically generating value-added chemicals is highly desirable in this era of rising energy demands and climate change impacts. Artificial photosynthetic systems or photocatalysts utilize light to convert abundant CO2, H2O, and O2 to fuels, such as carbohydrates and hydrogen, thus converting light energy to storable chemical resources. The emergence of intense X-ray pulses from synchrotrons, ultrafast X-ray pulses from X-ray free electron lasers, and table-top laser-driven sources over the past decades opens new frontiers in deciphering photoinduced catalytic reaction mechanisms on the multiple temporal and spatial scales. Operando X-ray spectroscopic methods offer a new set of electronic transitions in probing the oxidation states, coordinating geometry, and spin states of the metal catalytic center and photosensitizers with unprecedented energy and time resolution. Operando X-ray scattering methods enable previously elusive reaction steps to be characterized on different length scales and time scales. The methodological progress and their application examples collected in this review will offer a glimpse into the accomplishments and current state in deciphering reaction mechanisms for both natural and synthetic systems. Looking forward, there are still many challenges and opportunities at the frontier of catalytic research that will require further advancement of the characterization techniques.

Integrating CO2 reduction, H2O oxidation and H2 evolution catalysts into a dual S-scheme artificial photosynthetic system for tunable syngas production

It remains a challenge to achieve overall photocatalytic conversion of CO2 with H2O into tunable syngas and O2. Herein, by inserting BiVO4 into the heterointerface of hollow core-shell CdS@T-COF S-scheme photocatalyst, an innovative CdS/BiVO4@T-COF dual S-scheme heterojunction is developed, which gives an almost stoichiometric evolution of syngas (453.6 μmol gcat−1 h−1) and O2 (230.5 μmol gcat−1 h−1). Moreover, the CO output and selectivity only decline by around 20% when pure CO2 is replaced by diluted CO2 (15%) atmosphere. The BiVO4 embedding not only augments the internal electric field and band bending, upgrading the separation efficiency of active carriers, but also alters the roles of the components involved, separating the occurrence of CO, O2 and H2 evolution on T-COF, BiVO4 and CdS in lower energy barriers. Besides, varying the T-COF thickness can modulate the availability of CO2, H2O and photon to different sites, thereby adjusting the CO/H2 ratio in a wide window. This work opens an avenue for customizing three-in-one artificial photosynthetic systems for coupling three half reactions.

Dual electron transfer routes in core-shell double Z-scheme artificial photosynthetic system for improved photoredox activity

Developing artificial photosynthetic system with high activity is significant for long-term solar light conversion. Inspired by the natural Z-scheme photosystem, a ternary core-shell ZnIn2S4/MoO3/MoS2 (ZOS) composite with double Z-scheme junction was prepared by in-situ vulcanization of MoO3 nanosheets. Such in-situ formed intimate interfaces can overcome the high interfacial charge transfer barrier between different composites thus boosting the charge separation efficiency. The dual Z-scheme heterojunction provided dual electron transfer routes and favored the charge transfer. In addition, the ternary core-shell structure offered more spatially separated active sites which also increased the photocatalytic activity. Profiting from these strategies, the optimized ZOS-1 sample afforded 3.71 mmol·g−1·h−1 hydrogen evolution rate at 420 nm, which was 18.5 and 2.5 times higher than that of MoO3 and ZnIn2S4, respectively. In addition, 88% tetracycline can be eliminated in the solution within 70 min in the presence of ZOS-1 sample. This study provides an effective strategy for designing high-efficiency artificial photosynthetic systems under Z-scheme charge transfer routes in photocatalytic reactions.

Hypoxic environment of wounds and photosynthesis-based oxygen therapy.

The hypoxic environment is among the most important factors that complicates the healing of chronic wounds, such as venous leg ulcers, pressure injuries and diabetic foot ulcers, which seriously affects the quality of life of patients. Various oxygen supply treatments are used in clinical practice to improve the hypoxic environment at the wound site. However, problems still occur, such as insufficient oxygen supply, short oxygen infusion time and potential biosafety risks. In recent years, artificial photosynthetic systems have become a research hotspot in the fields of materials and energy. Photosynthesis is expected to improve the oxygen level at wound sites and promote wound healing because the method provides a continuous oxygen supply and has good biosafety. In this paper, oxygen treatment methods for wounds are reviewed, and the oxygen supply principle and construction of artificial photosynthesis systems are described. Finally, research progress on the photosynthetic oxygen production system to promote wound healing is summarized.

Artificial Photosynthetic System with Spatial Dual Reduction Site Enabling Enhanced Solar Hydrogen Production.

Although S-scheme artificial photosynthesis shows promise for photocatalytic hydrogen production, traditional methods often overly concentrate on a single reduction site. This limitation results in inadequate redox capability and inefficient charge separation, which hampers the efficiency of the photocatalytic hydrogen evolution reaction. To overcome this limitation, a double S-scheme system is proposed that leverages dual reduction sites, thereby preserving energetic photo-electrons and holes to enhance apparent quantum efficiency. The design features a double S-scheme junction consisting of CdS nanospheres decorated with anatase TiO2 nanoparticles coupled with graphitic C3 N4 . The as-prepared catalyst exhibits a hydrogen evolution rate of 26.84mmolg-1 h-1 and an apparent quantum efficiency of 40.2% at 365 nm. This enhanced photocatalytic hydrogen evolution is ascribed to the efficient charge separation and transport induced by the double S-scheme. Both theoretical calculations and comprehensive spectroscopy tests (both insitu and exsitu) affirm the efficient charge transport across the catalyst interface. Moreover, substituting the reduction-type catalyst CdS with other similar sulfides like ZnIn2 S4 , ZnS, MoS2 and In2 S3 further confirms the feasibility of the proposed double S-scheme configuration. The findings provide a pathway to designing more effective double S-scheme artificial photosynthetic systems, opening up fresh perspectives in enhancing photocatalytic hydrogen evolution performance.

Hydroxypyridinate-bridged paddlewheel-type dirhodium complex as a catalyst for photochemical and electrochemical hydrogen evolution.

Electrochemical and photochemical hydrogen (H2) evolution activities of a 6-fluoro-2-hydroxypyridinate (fhp-)-bridged paddlewheel-type dirhodium (Rh2) complex, [Rh2(fhp)4], were investigated through experimental and theoretical approaches. In DMF, the [Rh2(fhp)4] underwent a one-electron reduction (assigned to Rh24+/3+) at -1.31V vs SCE in the cathodic region. Adding trifluoroacetic acid as a proton source to the electrochemical cell containing [Rh2(fhp)4], the significant catalytic current, i.e., electrochemical H2 evolution, was observed; the turnover frequency and overpotential of electrochemical H2 evolution were 18 244s-1 and 732 mV, respectively. The reaction mechanism of electrochemical H2 evolution catalyzed by [Rh2(fhp)4] in DMF was examined in detail by theoretically predicting the redox potentials and pKa values of the reaction intermediates using density functional theory calculations. The calculations revealed that (i) the formation of a one-electron reduced species, [Rh2(fhp)4]-, triggered for H2 evolution and (ii) the protonation and reduction processes of [Rh2(fhp)4]- to further reduced hydride intermediates proceeded directly via a concerted proton-electron transfer mechanism. Moreover, [Rh2(fhp)4] was shown to be a highly efficient H2 evolution catalyst (HEC) for photochemical proton reduction reactions when combined with an artificial photosynthetic (AP) system containing [Ir(ppy)2(dtbbpy)]PF6 and triethylamine, which served as a photosensitizer and a sacrificial electron donor, respectively. Under visible light irradiation, the total amount of H2 evolved and its turnover number (per Rh ion) were 1361.0 µmol and 13 610, respectively, which are superior to those of previously reported AP systems with rhodium complexes as HEC.

Boosting the Oxygen Evolution Activity of FeNi Oxides/Hydroxides by Molecular and Atomic Engineering.

FeNi oxides/hydroxides are the best performing catalysts for oxidizing water at basic pH. Consequently, their improvement is the cornerstone to develop more efficient artificial photosynthetic systems. During the last 5 years different reports have demonstrated an enhancement of their activity by engineering their structures via: (1) modulation of the number of oxygen, iron and nickel vacancies; (2) single atoms (SAs) doping with metals such as Au, Ir, Ru and Pt; and (3) modification of their surface using organic ligands. All these strategies have led to more active and stable electrocatalysts for oxygen evolution rection (OER). In this Concept, we critically analyze these strategies using the most relevant examples.