Template‐Free Synthesis of Core–Shell TiO2 Microspheres Covered with High‐Energy {116}‐Facet‐Exposed N‐Doped Nanosheets and Enhanced Photocatalytic Activity under Visible Light

Core–shell TiO₂ microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high‐energy facets of TiO₂ also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core–shell structure is difficult to achieve and requires multiple‐steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high‐energy facet production. Therefore, it is still a significant challenge to develop low‐temperature, template‐free, shape‐controlled, and relative green self‐assembly routes for the formation of core–shell‐structured TiO₂ microspheres with high‐energy facets. Here, we report a template‐ and hydrofluoric acid free solvothermal self‐assembly approach to synthesize core–shell TiO₂ microspheres covered with high‐energy {116}‐facet‐exposed nanosheets, an approach in which 1,4‐butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high‐energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6‐tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core–shell structure, {116}‐plane‐oriented nanosheets, in situ N doping, and large surface areas has been found.     

HYDROGEN and OXYGEN PHOTOPRODUCTION BY MARINE ALGAE*

Abstract The first measurements of the simultaneous photoproduction of hydrogen and oxygen in marine green algae are reported. Eight species in the genera Chlamydomonas, Chlorella and Halochlorocococcum were tested in CO₂-free seawater. Four of the five species of Chlamydomonas were able to produce hydrogen in the light after a period of 3 - 4 h of dark anaerobic adaptation. Only one of the two Chlorella species tested was able to photoproduce hydrogen, in trace amounts. Halochlorocococcum fla–9 gave positive results and Chlamydomonas species (clone f-9) had a steady-state rate of hydrogen and oxygen production during irradiation with a stoichiometric ratio near 2:1. The integrated yields of hydrogen and oxygen produced by this species corresponds to about 450 turnovers of the photochemical reaction centers. This number exceeds (by about a factor of 20) the electron-carrying capacity of the electron transport chain linking Photosystems I and II. These data suggest that Chlamydomonas f-9 makes seawater a potential substrate for solar hydrogen and oxygen production.     

Photoelectrochemical Hydrogen Production in Alkaline Solutions Using Cu2O Coated with Earth‐Abundant Hydrogen Evolution Catalysts

The splitting of water into hydrogen and oxygen molecules using sunlight is an attractive method for solar energy storage. Until now, photoelectrochemical hydrogen evolution is mostly studied in acidic solutions, in which the hydrogen evolution is more facile than in alkaline solutions. Herein, we report photoelectrochemical hydrogen production in alkaline solutions, which are more favorable than acidic solutions for the complementary oxygen evolution half‐reaction. We show for the first time that amorphous molybdenum sulfide is a highly active hydrogen evolution catalyst in basic medium. The amorphous molybdenum sulfide catalyst and a Ni–Mo catalyst are then deposited on surface‐protected cuprous oxide photocathodes to catalyze sunlight‐driven hydrogen production in 1 M KOH. The photocathodes give photocurrents of ?6.3 mA cm^?2 at the reversible hydrogen evolution potential, the highest yet reported for a metal oxide photocathode using an earth‐abundant hydrogen evolution reaction catalyst.     

Palladium on magnetic Irish moss: A new nano‐biocatalyst for suzuki type cross‐coupling reactions

A novel heterogeneous magnetic palladium nano‐biocatalyst was designed by utilizing Irish moss, a family of sulfated polysaccharides extracted from algae, as a natural biopolymer. This magnetic Irish moss decorated with palladium (Pd–Fe₃O₄@IM) to form a biomagnetic catalytic system was synthesized and well characterized by FT–IR analysis, X‐ray powder diffraction, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. The catalyst was stable to air and moisture and displayed high catalytic activity in ligand‐free Suzuki–Miyaura cross‐coupling reactions conducted under green chemistry reaction conditions. The aromatic ketones are produced by the cross‐coupling reaction between acid chlorides and aryl boronic acid derivatives in high yields.     

解偶联剂CCCP对莱茵衣藻光照产氢过程的调控

本文研究莱茵衣藻在含硫和缺硫连续光照条件下, 不同浓度的CCCP对PSⅡ光化学效率、 光照产氢、 光合放氧以及光能的吸收和转换效率等的影响和调控规律.     

Theoretical study of salicylaldehyde conformal isomers and their intramolecular oxygen and hydrogen relations

To verify the semiempirical‐type localized hydrogen bonding analysis methods introduced by us several years ago, the intramolecular oxygen and hydrogen relations within salicylaldehyde are selected as the major topic in this theoretical study. The B3LYP/6‐31G** density functional method is chosen for both the full‐optimization and frequency‐type calculations. Four ortho‐type planar conformal isomers are proven to be local minima, and four internal rotation transition states are found by QST3‐type calculation. The special interpretations of  CHO and  OH characteristic frequencies, energy barriers, and thermal chemical results are discussed. In the semiempirical scheme, both local hydrogen bonding population analysis and localized hydrogen bond energy breaking procedures are applied to five pairs of related oxygen and hydrogen atoms in each isomer. The explanations for the strong or weak hydrogen bonds and intra‐CHO repulsion relationships are discussed. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 395–404, 1999     

Recent advances in photosynthetic energy conversion

Photosynthesis is one of the first natural processes evolved by cyanobacteria, algae and green plants to trap light and CO₂ in the form of reduced carbon compounds while simultaneously oxidizing water to oxygen. The photosynthetic energy conversion forms the basis for all the existing life today. The photosynthetic energy is being harnessed in many ways using modern technologies for the production of fuels using photosynthetic organisms, generation of direct electricity using photosystems/photosynthetic organisms in photo-bioelectrochemical cells or through photovoltaic systems. While the production of energy rich carbon fuels (ethanol, propanol) from photosynthetic organisms has already been accomplished due to advancement in understanding microbial physiology and metabolism, the photosynthetic hydrogen production as well as direct electricity generation from light is still at its infancy. Recent advances include combining photosystem complexes with hydrogenases for hydrogen production, using isolated thylakoids, photosystems on nanostructured electrodes such as gold nanoparticles, carbon nanotubes, ZnO nanoparticles for electricity generation. Many challenging optimizations on the immobilization methods, catalyst stability and isolation procedures, electron transfer strategies have acquired momentum leading to the production of more stable and higher current densities and power densities in photosynthetic devices. Further, the use of whole cell microorganisms (cyanobacteria, microalgae) rather than their isolated counterparts has produced promising results. The photosynthetic energy conversion has an enormous potential for renewable energy generation in a sustainable and environment friendly manner.     

Micromotor‐Based Energy Generation

A micromotor‐based strategy for energy generation, utilizing the conversion of liquid‐phase hydrogen to usable hydrogen gas (H₂), is described. The new motion‐based H₂‐generation concept relies on the movement of Pt‐black/Ti Janus microparticle motors in a solution of sodium borohydride (NaBH₄) fuel. This is the first report of using NaBH₄ for powering micromotors. The autonomous motion of these catalytic micromotors, as well as their bubble generation, leads to enhanced mixing and transport of NaBH₄ towards the Pt‐black catalytic surface (compared to static microparticles or films), and hence to a substantially faster rate of H₂ production. The practical utility of these micromotors is illustrated by powering a hydrogen–oxygen fuel cell car by an on‐board motion‐based hydrogen and oxygen generation. The new micromotor approach paves the way for the development of efficient on‐site energy generation for powering external devices or meeting growing demands on the energy grid.     

Layer‐by‐Layer Assemblies of Montmorillonite and Bacterial Cytochromes for Bioelectrocatalytic Devices

Clay‐based layer‐by‐layer architectures are studied in view of the development of new electrode materials for two highly attractive enzymatic reactions: metal bioremediation and hydrogen uptake. The buildup of layer‐by‐layer (LBL) assemblies of positively charged specific mediators of these enzymatic reactions and negatively charged montmorillonite nanoparticles were carried out onto gold and graphite electrodes. The structure and stability of the assemblies were examined using quartz crystal microgravimetry (QCM) and electrochemical techniques. Satisfactory catalytic efficiencies were observed through the LBL construction, either for bacterial cytochrome c₃‐mediated metal reduction, or hydrogen uptake via immobilized hydrogenase in the presence of an artificial shuttle, methylviologen. Interestingly, it is established that intercalating cytochrome c₃ layers between hydrogenase/montmorillonite layers not only protects hydrogenase from leaching, but allows H₂ uptake/evolution catalytic reaction without any additional diffusing redox mediator.     

Nitrogen,Phosphorus, and Fluorine Tri‐doped Graphene as a Multifunctional Catalyst for Self‐Powered Electrochemical Water Splitting

Electrocatalysts are required for clean energy technologies (for example, water‐splitting and metal‐air batteries). The development of a multifunctional electrocatalyst composed of nitrogen, phosphorus, and fluorine tri‐doped graphene is reported, which was obtained by thermal activation of a mixture of polyaniline‐coated graphene oxide and ammonium hexafluorophosphate (AHF). It was found that thermal decomposition of AHF provides nitrogen, phosphorus, and fluorine sources for tri‐doping with N, P, and F, and simultaneously facilitates template‐free formation of porous structures as a result of thermal gas evolution. The resultant N, P, and F tri‐doped graphene exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The trifunctional metal‐free catalyst was further used as an OER–HER bifunctional catalyst for oxygen and hydrogen gas production in an electrochemical water‐splitting unit, which was powered by an integrated Zn–air battery based on an air electrode made from the same electrocatalyst for ORR. The integrated unit, fabricated from the newly developed N, P, and F tri‐doped graphene multifunctional metal‐free catalyst, can operate in ambient air with a high gas production rate of 0.496 and 0.254 μL s⁻¹ for hydrogen and oxygen gas, respectively, showing great potential for practical applications.     

Nitrogen,Phosphorus, and Fluorine Tri‐doped Graphene as a Multifunctional Catalyst for Self‐Powered Electrochemical Water Splitting

Electrocatalysts are required for clean energy technologies (for example, water‐splitting and metal‐air batteries). The development of a multifunctional electrocatalyst composed of nitrogen, phosphorus, and fluorine tri‐doped graphene is reported, which was obtained by thermal activation of a mixture of polyaniline‐coated graphene oxide and ammonium hexafluorophosphate (AHF). It was found that thermal decomposition of AHF provides nitrogen, phosphorus, and fluorine sources for tri‐doping with N, P, and F, and simultaneously facilitates template‐free formation of porous structures as a result of thermal gas evolution. The resultant N, P, and F tri‐doped graphene exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The trifunctional metal‐free catalyst was further used as an OER–HER bifunctional catalyst for oxygen and hydrogen gas production in an electrochemical water‐splitting unit, which was powered by an integrated Zn–air battery based on an air electrode made from the same electrocatalyst for ORR. The integrated unit, fabricated from the newly developed N, P, and F tri‐doped graphene multifunctional metal‐free catalyst, can operate in ambient air with a high gas production rate of 0.496 and 0.254 μL s^?1 for hydrogen and oxygen gas, respectively, showing great potential for practical applications.     

Photoelectrochemical H2 Evolution with a Hydrogenase Immobilized on a TiO2‐Protected Silicon Electrode

The combination of enzymes with semiconductors enables the photoelectrochemical characterization of electron‐transfer processes at highly active and well‐defined catalytic sites on a light‐harvesting electrode surface. Herein, we report the integration of a hydrogenase on a TiO₂‐coated p‐Si photocathode for the photo‐reduction of protons to H₂. The immobilized hydrogenase exhibits activity on Si attributable to a bifunctional TiO₂ layer, which protects the Si electrode from oxidation and acts as a biocompatible support layer for the productive adsorption of the enzyme. The p‐Si|TiO₂|hydrogenase photocathode displays visible‐light driven production of H₂ at an energy‐storing, positive electrochemical potential and an essentially quantitative faradaic efficiency. We have thus established a widely applicable platform to wire redox enzymes in an active configuration on a p‐type semiconductor photocathode through the engineering of the enzyme–materials interface.     

[FeFe]‐Hydrogenase Mimetic Metallopolymers with Enhanced Catalytic Activity for Hydrogen Production in Water

Electrocatalytic [FeFe]‐hydrogenase mimics for the hydrogen evolution reaction (HER) generally suffer from low activity, high overpotential, aggregation, oxygen sensitivity, and low solubility in water. By using atom‐transfer radical polymerization (ATRP), a new class of [FeFe]‐metallopolymers with precise molar mass, defined composition, and low polydispersity, has been prepared. The synthetic methodology introduced here allows facile variation of polymer composition to optimize the [FeFe] solubility, activity, and long‐term chemical and aerobic stability. Water soluble functional metallopolymers facilitate electrocatalytic hydrogen production in neutral water with loadings as low as 2 ppm and operate at rates an order of magnitude faster than hydrogenases (2.5×10⁵ s^?1), and with low overpotential requirement. Furthermore, unlike the hydrogenases, these systems are insensitive to oxygen during catalysis, with turnover numbers on the order of 40 000 under both anaerobic and aerobic conditions.     

LIMITING REACTIONS IN HYDROGEN PHOTOPRODUCTION BY CHLOROPLASTS AND HYDROGENASE

Abstract— Hydrogen was photoproduced from water in a system containing isolated chloroplasts, hy-drogenase, a coupling electron carrier (ferredoxin or methyl viologen), and an oxygen scavenger. The rate and extent of hydrogen production anaerobically was much less than the rate of aerobic electron-carrier reduction by chloroplasts and was not limited by hydrogenase. The limiting reaction in the coupled system was the extent of reduction of methyl viologen anaerobically rather than its oxidation by oxygen produced during the course of the reaction. Inhibition of photosystem II by 3-(3,4dichlorophenyl)-1,1-dimethylurea and addition of a photosystem 1 electron donor did not lead to photoproduction of hydrogen or photoreduction of methyl viologen. Extensive photosystem I hydrogen evolution was obtained when thiols were also present. Platinum asbestos or palladium asbestos replaced hydrogenase in a system coupled to chloroplasts.     

Direct Bioelectrocatalysis by NADP‐Reducing Hydrogenase from Pyrococcus furiosus

The direct bioelectrocatalysis by an NAD(P)‐reducing hydrogenase is reported for the first time. In contrast to previous attempts to involve similar enzymes in bioelectrocatalysis [1–4], which were in fact unsuccessful, in our report an effective electrocatalysis by Pyrococcus furiosus hydrogenase is convincingly shown by (i) achievement of the hydrogen equilibrium potential and (ii) a high current of hydrogen oxidation (0.3 mA cm^?2 at 100 mV overpotential and at 75 °C). The latter is just a few times lower compared to enzyme electrodes based on NAD(P)‐independent hydrogenases.     

N,P‐Codoped Carbon Networks as Efficient Metal‐free Bifunctional Catalysts for Oxygen Reduction and Hydrogen Evolution Reactions

The high cost and scarcity of noble metal catalysts, such as Pt, have hindered the hydrogen production from electrochemical water splitting, the oxygen reduction in fuel cells and batteries. Herein, we developed a simple template‐free approach to three‐dimensional porous carbon networks codoped with nitrogen and phosphorus by pyrolysis of a supermolecular aggregate of self‐assembled melamine, phytic acid, and graphene oxide (MPSA/GO). The pyrolyzed MPSA/GO acted as the first metal‐free bifunctional catalyst with high activities for both oxygen reduction and hydrogen evolution. Zn–air batteries with the pyrolyzed MPSA/GO air electrode showed a high peak power density (310 W g^?1) and an excellent durability. Thus, the pyrolyzed MPSA/GO is a promising bifunctional catalyst for renewable energy technologies, particularly regenerative fuel cells.     

Self‐assembly of a cobalt(II)‐based metal–organic framework as an effective water‐splitting heterogeneous catalyst for light‐driven hydrogen production

The solar photocatalysis of water splitting represents a significant branch of enzymatic simulation by efficient chemical conversion and the generation of hydrogen as green energy provides a feasible way for the replacement of fossil fuels to solve energy and environmental issues. We report herein the self‐assembly of a Co^II‐based metal–organic framework (MOF) constructed from 4,4′,4′′,4′′′‐(ethene‐1,1,2,2‐tetrayl)tetrabenzoic acid [or tetrakis(4‐carboxyphenyl)ethylene, H₄TCPE] and 4,4′‐bipyridyl (bpy) as four‐point‐ and two‐point‐connected nodes, respectively. This material, namely, poly[(μ‐4,4′‐bipyridyl)[μ₈‐4,4′,4′′,4′′′‐(ethene‐1,1,2,2‐tetrayl)tetrabenzoato]cobalt(II)], [Co(C₃₀H₁₆O₈)(C₁₀H₈N₂)]_n, crystallized as dark‐red block‐shaped crystals with high crystallinity and was fully characterized by single‐crystal X‐ray diffraction, PXRD, IR, solid‐state UV–Vis and cyclic voltammetry (CV) measurements. The redox‐active Co^II atoms in the structure could be used as the catalytic sites for hydrogen production via water splitting. The application of this new MOF as a heterogeneous catalyst for light‐driven H₂ production has been explored in a three‐component system with fluorescein as photosensitizer and trimethylamine as the sacrificial electron donor, and the initial volume of H₂ production is about 360 µmol after 12 h irradiation.     

Control of the Transition between Ni‐C and Ni‐SIa States by the Redox State of the Proximal Fe?S Cluster in the Catalytic Cycle of [NiFe] Hydrogenase

[NiFe] hydrogenase catalyzes the reversible cleavage of H₂. The electrons produced by the H₂ cleavage pass through three Fe–S clusters in [NiFe] hydrogenase to its redox partner. It has been reported that the Ni‐SI_a, Ni‐C, and Ni‐R states of [NiFe] hydrogenase are involved in the catalytic cycle, although the mechanism and regulation of the transition between the Ni‐C and Ni‐SI_a states remain unrevealed. In this study, the FT‐IR spectra under light irradiation at 138–198 K show that the Ni‐L state of [NiFe] hydrogenase is an intermediate between the transition of the Ni‐C and Ni‐SI_a states. The transition of the Ni‐C state to the Ni‐SI_a state occurred when the proximal [Fe₄S₄]_p^2+/+ cluster was oxidized, but not when it was reduced. These results show that the catalytic cycle of [NiFe] hydrogenase is controlled by the redox state of its [Fe₄S₄]_p^2+/+ cluster, which may function as a gate for the electron flow from the NiFe active site to the redox partner.     

Effect of Temperature on Self‐Interaction of Human‐Like Collagen

Effects of temperature on self‐interaction of human‐like collagen (HLC) were investigated by hydrophobic interaction chromatography, calorimetric measurement, and sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) analysis. Results show that three types of interaction roles may exist between HLC molecules at 3–50°C, which were divided into three narrower temperature ranges. In temperature range from 3–22°C, hydrogen bonding plays a key role in the formation of a gelatinous aggregate. In the range of 22–38°C, hydrophobic bonds accompanied by hydrogen bonds are involved in the formation compact aggregates. When temperature is above 38°C the hydrophobic effect formed in the HLC monomer results in the loss of its ability to self‐interact.     

Temperature‐programmed reduction of silver(I) oxide using a titania‐supported silver catalyst under a H2 atmosphere

Reduction kinetics of silver(I) oxide using a titania‐supported silver catalyst was analyzed using temperature‐programmed reduction (TPR) with hydrogen as a reducing gas. Ag₂O reduction to Ag was observed in all samples as a single reduction step occurring at two reduction peaks. Observation of these reduction peaks indicates the existence of different lattice oxygen species, that is, surface and bulk, which are, respectively, attributed to surficial and pore‐deposited Ag₂O aggregates. The powdered samples exhibited high reducibility with average final oxidation states ranging from 0 to +0.18. The apparent activation energies for Ag₂O reduction to Ag metal were 73.35 and 81.71 kJ/mol for surficial and pore‐deposited Ag₂O aggregates, respectively. In this study, a unimolecular decay model was reported to accurately describe the reduction mechanism of Ag/TiO₂ catalysts. Hence, this would also infer that the catalyst reduction is rate‐limited by the nucleation of Ag metal instead of the topochemical reaction and the diffusion of hydrogen and oxygen molecules.