A feasibility study of a new photosynthesis bioreactor design using TiO2 particles combined with enzymes

A new photo-bioreactorsystemin which a photocatalysis in a light stage is separated from a biocatalysis in a dark stage is proposed for an artificial photosynthesis system with a high selectivity of products through the use of light energy without denaturation of enzyme due to light irradiation. To realize the concept, an electron transfer system applicable to the mentioned photo-bioreactor was studied. In this study, TiO₂ particles and formate dehydrogenase (FDH) were used as a photocatalyst and a catalyst of the CO₂ fixation, respectively. Methyl viologen, NAD⁺ and diaphorase (DAH) were used to mediate electron transfer from TiO₂ to FDH. From pH activity profiles of the enzymes, both FDH and DAH were most active around pH 7, and coupling of these reactions was capable at that pH value. In the coupled reaction examined by using a electrode system instead of TiO₂ particles, the concentration of DAH affected the rate of CO₂ fixation and the rate had a maximum against the concentration, whilst the concentration of FDH had little effect. The proposed electron transfer system performed successfully in a batch operation. The results were so encouraging that a feasibility of the photo-bioreactor system proposed in this study was indicated.     

Ultrathin and Small‐Size Graphene Oxide as an Electron Mediator for Perovskite‐Based Z‐Scheme System to Significantly Enhance Photocatalytic CO2 Reduction

The judicious design of efficient electron mediators to accelerate the interfacial charge transfer in a Z‐scheme system is one of the viable strategies to improve the performance of photocatalysts for artificial photosynthesis. Herein, ultrathin and small‐size graphene oxide (USGO) nanosheets are constructed and employed as the electron mediator to elaborately exploit an efficient CsPbBr₃‐based all‐solid‐state Z‐scheme system in combination with α‐Fe₂O₃ for visible‐light‐driven CO₂ reduction with water as the electron source. CsPbBr₃ and α‐Fe₂O₃ can be closely anchored on USGO nanosheets, owing to the existence of interfacial strong chemical bonding behaviors, which can significantly accelerate the photogenerated carrier transfer between CsPbBr₃ and α‐Fe₂O₃. The resultant improved charge separation efficiency endows the Z‐scheme system exhibiting a record‐high electron consumption rate of 147.6 µmol g^?1 h^?1 for photocatalytic CO₂‐to‐CO conversion concomitant with stoichiometric O₂ from water oxidation, which is over 19 and 12 times higher than that of pristine CsPbBr₃ nanocrystals and the mixture of CsPbBr₃ and α‐Fe₂O₃, respectively. This work provides a novel and effective strategy for improving the catalytic activity of halide‐perovskite‐based photocatalysts, promoting their practical applications in the field of artificial photosynthesis.     

Guest-Induced Multilevel Charge Transport Strategy for Developing Metal-Organic Frameworks to Boost Photocatalytic CO2 Reduction

Encapsulating photogenerated charge-hopping nodes and space transport bridges within metal–organic frameworks (MOFs) is a promising method of boosting the photocatalytic performance. Herein, this work embeds electron transfer media (9,10-bis(4-pyridyl)anthracene (BPAN)) in MOF cavities to build multi-level electron transfer paths. The MOF cavities are accurately regulated to investigate the significance of the multi-level electron transfer paths in the process of CO₂ photoreduction by evaluating the difference in the number of guest media. The prepared MOFs, {[Co(BPAN)(1,4-dicarboxybenzene)(H₂O)₂]·BPAN·2H₂O} and {[Co(BPAN)₂(4,4′-biphenyldicarboxylic acid)₂(H₂O)₂]·2BPAN·2H₂O} (denoted as BPAN-Co-1 and BPAN-Co-2), exhibit efficient visible-light-driven CO₂ conversion properties. The CO photoreduction efficacy of BPAN-Co-2 (5598 µmol g⁻¹ h⁻¹) is superior to that of most reported MOF-based catalysts. In addition, the enhanced CO₂ photoreduction ability is supported by density functional theory (DFT). This work illustrates the feasibility of realizing charge separation characteristics in MOF catalysts at the molecular level, and provides new insight for designing high-performance MOFs for artificial photosynthesis.     

Pyridinic Nitrogen Doped Carbon Dots Supply Electrons to Improve Photosynthesis and Extracellular Electron Transfer of Chlorella pyrenoidosa

Optimizing photosynthesis is imperative for providing energy and organics for all life on the earth. Here, carbon dots doped with pyridinic nitrogen (named lev-CDs) are synthesized by the one-pot hydrothermal method, and the structure–function relationship between functional groups on lev-CDs and photosynthesis of Chlorella pyrenoidosa (C. pyrenoidosa) is proposed. Pyridinic nitrogen plays a key role in the positive effect on photosynthesis caused by lev-CDs. In detail, lev-CDs act as electron donors to supply photo-induced electrons to P680⁺ and QA⁺, causing electron transfer from lev-CDs to the photosynthetic electron transport chain in the photosystems. In return, the recombination efficiency of electron–hole pairs on lev-CDs decreases. As a result, the electron transfer rate in the electron transport chain, the activity of photosystem II, and the Calvin cycle are enhanced. Moreover, the electron transfer rate between C. pyrenoidosa and external circumstances enhanced by lev-CDs is about 50%, and electrons exported from C. pyrenoidosa can be used to reduce iron(III). This study is of great significance for engineering nanomaterials to improve photosynthesis.     

Polymeric photovoltaic materials

Recent developments in conjugated polymer-based photovoltaic elements have been reviewed. The photophysics of such photoactive devices is based on the photoinduced electron transfer from donor-type semiconducting conjugated polymers onto acceptor-type conjugated polymers or acceptor molecules such as Buckminsterfullerene, C₆₀. Photoinduced electron transfer in solid composite films of fullerenes embedded into conjugated polymers is reversible, ultrafast (within 300 fs) with a quantum efficiency approaching unity, and metastable. Similar to the first step in natural photosynthesis, this photoinduced electron transfer leads to a number of potentially interesting applications, which include sensitization of the photoconductivity and photovoltaic phenomena. Furthermore, using the conjugated polymer donors in polymer blends with another conjugated polymer acceptor, similar photovoltaic elements have been realized. Examples of photovoltaic architectures are discussed with their potential in terrestrial solar energy conversion.     

Effect of interfacial segregation of magnesium on high carbon (18%Cr) cast steel

Abstract

The effect of Mg on the microstructure and properties of a high carbon cast steel (nominal composition, wt-%: 18Cr–2Ni–0·75Mo–Mn–Si–Fe_bal.) is investigated. It is shown that the microaddition of Mg refines the primary carbide (Cr_0·51Fe_0·49)₇C₃ and promotes an equiaxial dendritic structure, and the resulting structure refinement improves significantly the impact toughness of the alloy. Using Auger electron spectroscopy and electron probe microanalysis, it is shown that there is an unusually high Mg segregation (~70 at.-%) at the carbide interface region. It is proposed that the Mg enrichment at the carbide interface is primarily a result of the liquid phase separation that occurs in liquid Fe–Mg alloys when the Mg level attains a minimum value (~1–2 at.-%), and that this initial enrichment is a result of a combination of Mg rejection by the carbide and uphill diffusion of Mg to the carbide interface region. A thermodynamic analysis is presented to show the degree of component (Cr, Ni) segregation required for uphill diffusion of Mg to occur, which is in qualitative agreement with that observed.

MST/1046     

Ni‐Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction

One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO₂ molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni‐nanocluster loaded black TiO₂ (Ni/TiO_2[Vo]) with built‐in dual active sites for selective photocatalytic CO₂ conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO₂ binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO_2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO₂ (P‐25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.     

Intrinsic defects in biomass-derived carbons facilitate electroreduction of CO2

Developing efficient carbon-based metal-free electrocatalysts can bridge the gap between laboratory studies and practical applications of CO₂ reduction. However, along with the ambiguous understanding of the active sites in carbon-based electrocatalysts, carbon-based electrocatalysts with high selectivity and satisfactory stability for electroreduction of CO₂ remain rare. Here, using the nitrogen rich silk cocoon as a precursor, carbon-based electrocatalysts with intrinsic defects can be prepared for efficient and long-term electroreduction of CO₂ by a simple two-step carbonization. The obtained electrocatalyst can catalyze CO₂ reduction to CO with a Faradaic efficiency of ~ 89% and maintain good selectivity for about 10 days. Particularly, our experimental studies suggest that in-plane defects are the main active sites on which the rate-determining step for CO₂ reduction should be the direct electron transfer to CO₂ but not the proton-coupled electron transfer. Further theoretical calculations consistently demonstrate that the intrinsic defects in carbon matrix, particularly the pentagon-containing defects, act as main active sites to accelerate the direct electron transfer for CO₂ reduction. In addition, our synthetic approach can convert egg white into efficient catalysts for CO₂ electroreduction. These findings, providing new insights into the biomass-derived catalysts, should pave the way for fabricating efficient and stable carbon-based electrocatalysts with catalytically active defects by using naturally abundant precursors.

     

Nanoscale Janus Z-Scheme Heterojunction for Boosting Artificial Photosynthesis

Artificial photosynthesis for CO₂ reduction coupled with water oxidation currently suffers from low efficiency due to inadequate interfacial charge separation of conventional Z-scheme heterojunctions. Herein, an unprecedented nanoscale Janus Z-scheme heterojunction of CsPbBr₃/TiO_x is constructed for photocatalytic CO₂ reduction. Benefitting from the short carrier transport distance and direct contact interface, CsPbBr₃/TiO_x exhibits significantly accelerated interfacial charge transfer between CsPbBr₃ and TiO_x (8.90 × 10⁸ s⁻¹) compared with CsPbBr₃:TiO_x counterpart (4.87 × 10⁷ s−¹) prepared by traditional electrostatic self-assembling. The electron consumption rate of cobalt doped CsPbBr₃/TiO_x can reach as high as 405.2 ± 5.6 µmol g⁻¹ h⁻¹ for photocatalytic CO₂ reduction to CO coupled with H₂O oxidation to O₂ under AM1.5 sunlight (100 mW cm⁻²), over 11-fold higher than that of CsPbBr₃:TiO_x, and surpassing the reported halide-perovskite-based photocatalysts under similar conditions. This work provides a novel strategy to boost charge transfer of photocatalysts for enhancing the performance of artificial photosynthesis.     

Plasmon-enhanced fluorescence in heterochlorophyllous peridinin-chlorophyll-protein photosynthetic complex

We study the fluorescence properties of peridinin-chlorophyll-protein light-harvesting complex reconstituted with both chlorophyll a and chlorophyll b coupled to spherical gold nanoparticles. Since there is a bidirectional energy transfer between the chlorophylls, the impact of plasmon excitations upon the energy transfer dynamics can be studied in such a hybrid nanostructure. The results show that the emission of both chlorophyll a and chlorophyll b in a reconstituted PCP is strongly enhanced when the light-harvesting complexes are separated from the metallic nanoparticles by a 12-nm-thick SiO₂ layer, the average enhancement reaches a factor of 8. The analysis of fluorescence decay curves indicates that the energy transfer between chlorophyll a and chlorophyll b is also influenced by plasmon excitations in gold nanoparticles.     

Functionalising nanocrystalline TiO2 films: dye sensitised solar cells and optical biosensors

Abstract

The fabrication of porous, nanocrystalline titanium dioxide (TiO₂) films is considered first, and their application as dye sensitised photovoltaic devices is summarised. The electron transfer and transport dynamics within such devices is then discussed in more detail, focusing on electron transfer between the TiO₂ and the molecular dyes, and the role of intra band trap states in the TiO₂. The authors conclude by introducing a new potential application of such nanocrystalline TiO₂ films, as a substrate for enzyme immobilisation in bioanalytical devices.     

Chlorophylls derivatives: Photophysical properties,assemblies, nanostructures and biomedical applications

Chlorophylls are one of the most abundant organic pigments on the earth, which play an important role in the photosynthesis of plants, algae and bacteria. With the development of chromatography and chemical synthesis technology, many new chlorophylls from nature have been identified, and similar typical heterocyclic macrocyclic chlorophyll derivatives have also been designed and synthesized. Their chemical structures have significantly affected the absorption of light, energy transfer efficiency, excited-state lifetime, etc. Inspired by the chlorophylls interactions in chloroplasts for light-harvesting, we realized that intramolecular assembly and the resultant nanostructures played a more prominent role in their photophysical and photochemical properties, even in further biomedical applications, such as photodynamic and photothermal therapy, photocatalytic diagnosis, as well as optical, photoacoustic, magnetic resonance and nuclear medical imaging. In this review, we discuss the photo-properties of chlorophylls, overview the driving forces of assembly, and summarize biomedical-relevant advantages incorporated supramolecular nanostructures. In particular, the dynamic assembly under physiological condition provides unpredictable and interesting biological effects, such as aggregation/assembly induced drug retention in disease areas, optimized biodistribution and optimized the pharmacokinetics. The labeling on the assembly also provides a useful tool for us to observe the self-assembled nanostructures in vivo in a non-invasive way. Through the elaboration of different examples of chlorophylls, we hope to provide some inspiration for the biomedical application design of chlorophylls derivatives.     

Synthesis and enhanced photocatalytic activity of tin oxide nanoparticles coated on multi-walled carbon nanotube

A nanocomposite of SnO₂ nanoparticles coated on multi-walled carbon nanotube (MWNT@SnO₂) was synthesized and characterized by thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, nitrogen physisorption measurements, photoluminescence. The results show that the SnO₂ nanoparticles with a narrow size of 4 nm are uniformly deposited on MWNT. The photocatalytic activity of the nanocomposite was studied using methyl orange as a model organic pollutant. MWNT@SnO₂ exhibits much higher photocatalytic activity than that of commercial TiO₂ (P-25). The promotion is mainly contributed from electron transfer between SnO₂ and MWNT.     

IR‐Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2 Generation

The ultrafast transfer of plasmon‐induced hot electrons is considered an effective kinetics process to enhance the photoconversion efficiencies of semiconductors through strong localized surface plasmon resonance (LSPR) of plasmonic nanostructures. Although this classical sensitization approach is widely used in noble‐metal–semiconductor systems, it remains unclear in nonmetallic plasmonic heterostructures. Here, by combining ultrafast transient absorption spectroscopy with theoretical simulations, IR‐driven transfer of plasmon‐induced hot electron in a nonmetallic branched heterostructure is demonstrated, which is fabricated through solvothermal growth of plasmonic W₁₈O₄₉ nanowires (as branches) onto TiO₂ electrospun nanofibers (as backbones). The ultrafast transfer of hot electron from the W₁₈O₄₉ branches to the TiO₂ backbones occurs within a timeframe on the order of 200 fs with very large rate constants ranging from 3.8 × 10¹² to 5.5 × 10¹² s^?1. Upon LSPR excitation by low‐energy IR photons, the W₁₈O₄₉/TiO₂ branched heterostructure exhibits obviously enhanced catalytic H₂ generation from ammonia borane compared with that of W₁₈O₄₉ nanowires. Further investigations by finely controlling experimental conditions unambiguously confirm that this plasmon‐enhanced catalytic activity arises from the transfer of hot electron rather than from the photothermal effect.     

Investigations on structural, optical and electrochemical properties of blue luminescence SnO2 nanoparticles

A simple solution approach has been developed to synthesis SnO₂ nanoparticles using polyethylene glycol as stabilizer. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), UV–Vis absorption spectroscopy, photoluminescence (PL) emission spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the nanoparticles. XRD, HR-TEM and AFM indicate that the SnO₂ nanoparticles correspond to tetragonal crystal structure with size ranges below Bohr’s exciton radius. UV–Vis absorption spectrum showed band gap exhibiting a 1.3 eV shift from that of bulk SnO₂ structures. The blue emission owing to transition of an electron from conduction band to deeply trapped hole in SnO₂ nanoparticles was analyzed using PL spectroscopy. The charge transfer capability had been investigated using CV and EIS in different electrolytes. A detailed exploration on confinement effect that occurred in SnO₂ nanoparticles, mechanism behind visible emission and electron transfer mechanism in different electrolyte was discussed.     

Electron transfer processes in double lanthanide activated YPO4

This work reviews electron transfer processes in double lanthanide doped YPO₄ studied using a diversity of optical techniques. The aim is to identify those transfer processes and to relate them with the location of lanthanide electron donor and lanthanide electron acceptor states within the bandgap of YPO₄. Electron transfer from the valence band to a trivalent lanthanide impurity or to the conduction band was studied by traditional single photon excitation on single lanthanide doped YPO₄. This work reports on YPO₄ doped with the electron donor Ce³⁺ and co-doped with an electron acceptor Pr³⁺, Er³⁺, Nd³⁺, Ho³⁺, Dy³⁺, Tm³⁺, or Sm³⁺ studied by means of thermoluminescence and optical stimulated luminescence techniques. The same samples were studied by pump and probe two photon spectroscopy utilizing synchrotron photons to transfer electrons from Ce³⁺ to Ln³⁺ defects and 445 nm laser diode to probe the concentration of created Ln²⁺.     

Broadband emission from Ce3+/Mn2+/Yb3+ tri-doped oxyfluoride glasses for glass greenhouse

In this work, a kind of oxyfluoride glasses tri-doped with Ce³⁺/Mn²⁺/Yb³⁺ ions was prepared by a simple and fast high temperature melting method. Under excitation with 300 nm light, two meaningful broad band emissions (ranged from 340 to 500 nm and 510–700 nm) were obtained, which matched well with the absorption of the chlorophylls. Under near-infrared (980 nm) excitation, an abnormal up-conversion luminescence was demonstrated in the oxyfluoride glasses by the energy transfer from Yb³⁺ to Mn²⁺. In addition, the up-conversion emission has a red shift along with the increase of the doping concentration of Mn²⁺, which would contribute to match the action spectrum of photosynthesis better. Our materials will be favored to extend the utilization of solar energy in glass greenhouse for plant cultivation.     

HOMO–HOMO Electron Transfer: An Elegant Strategy for p-Type Doping of Polymer Semiconductors toward Thermoelectric Applications

Unlike the conventional p-doping of organic semiconductors (OSCs) using acceptors, here, an efficient doping concept for diketopyrrolopyrrole-based polymer PDPP[T]₂-EDOT (OSC-1) is presented using an oxidized p-type semiconductor, Spiro-OMeTAD(TFSI)₂ (OSC-2), exploiting electron transfer from HOMO_OSC-1 to HOMO_OSC-2. A shift of work function toward the HOMO_OSC-1 upon doping is confirmed by ultraviolet photoelectron spectroscopy (UPS). Detailed X-ray photoelectron spectroscopy (XPS) and UV–vis–NIR absorption studies confirm HOMO_OSC-1 to HOMO_OSC-2 electron transfer. The reduction products of Spiro-OMeTAD(TFSI)₂ to Spiro-OMeTAD(TFSI) and Spiro-OMeTAD is also confirmed and their relative amounts in doped samples is determined. Mott–Schottky analysis shows two orders of magnitude increase in free charge carrier density and one order of magnitude increase in the charge carrier mobility. The conductivity increases considerably by four orders of magnitude to a maximum of 10 S m⁻¹ for a very low doping ratio of 8 mol%. The doped polymer films exhibit high thermal and ambient stability resulting in a maximum power factor of 0.07  µ W m⁻¹ K⁻² at a Seebeck coefficient of 140 µ V K⁻¹ for a very low doping ratio of 4 mol%. Also, the concept of HOMO_OSC-1 to HOMO_OSC-2 electron transfer is a highly efficient, stable and generic way to p-dope other conjugated polymers.     

Determination of first-order molecular hyperpolarizability of EAADCy and EDMAADCy using steady-state spectroscopic data and quantum-chemical calculations

Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) and ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate (EDMAADCy) organic molecules containing separate electron donor and electron acceptor groups belong to biphenyl derivatives in which a large dipole moment change between ground (S₀) and the first intramolecular charge transfer excited (S₁) states, as well as a large transition moment have been noted. The existence of electronically excited states with a strong intermolecular charge transfer (ICT) character is an essential prerequisite for large non-linear optical properties. Therefore, in this paper, we present a scrupulous analysis of the first-order hyperpolarizabilities of the studied molecules using an equivalent internal field model of an organic molecule. The calculated (using semiempirical calculations, CAChe WS 5.04) additive part of the first-order hyperpolarizability, β_add, values are discussed in relationship to the experimental data of the charge transfer hyperpolarizability, β_CT, obtained from steady-state spectroscopic measurements.     

Donor-Linked Fullerenes: Photoinduced electron transfer and its potential application

Redox-active fullerenes can be covalently bound to a variety of donors, their photophysical properties have been investigated. Their photochemical processes. Including electron transfer and energy transfer, are varied, depending on the donor, linkage between the donor and C₆₀, and solvent. Regardless of the solvent and linkage, the charge-separated state is produced efficiently in zinc porphyrin-C₆₀ systems, showing that C_6o is a good electron acceptor. The most intriguing characteristic of C₆₀ in electron transfer is that C₆₀ accelerates photoinduced charge separation and retards charge recombination in the dark. The long-lived charge-transfer state: of the C₆₀–porphyrin dyad was successfully converted to photocurrent using a self-assembled monolayer technique. These findings will provide a new strategy for the design and synthesis of artificial photosynthetic systems and photoactive materials using C₆₀ as a building block.