Photon Upconversion with a Low Threshold Excitation Intensity in Plain Water.

A triplet-triplet annihilation-based photon upconversion (TTA-UC) system with a low threshold excitation intensity (Ith) in plain water was developed. Water-soluble anionic porphyrin (PdTPPS4-) and diphenylanthracene (DCDPA2-) derivatives were used as light absorbers and emitter molecules, respectively, and no additives such as surfactants were required. The phosphorescence emission from PdTPPS4- under an excitation wavelength of 528 nm was quenched by DCDPA2-, resulting in triplet energy transfer, whereas fluorescence from DCDPA2- was observed in a short wavelength region (400-500 nm). Three independent emission studies utilizing different excitation light sources validated the TTA-UC process in a simple aqueous solution. TTA occurred after the triplet energy transfer, according to the time profiles of phosphorescence and fluorescence detected following pulse laser excitation. The Ith for TTA-UC was estimated to be lower than 6 mW cm-2, although it could not be exactly determined due to the sensitivity limit of the experimental setup. The upper limit of Ith for the aqueous solution of DCDPA2- and PdTPPS4- is the smallest value obtained to date for aqueous systems and comparable to that of high-performance TTA-UC systems in organic solutions.

Mechanism of H+ dissociation-induced O-O bond formation via intramolecular coupling of vicinal hydroxo ligands on low-valent Ru(III) centers.

The understanding of O-O bond formation is of great importance for revealing the mechanism of water oxidation in photosynthesis and for developing efficient catalysts for water oxidation in artificial photosynthesis. The chemical oxidation of the RuII2(OH)(OH2) core with the vicinal OH and OH2 ligands was spectroscopically and theoretically investigated to provide a mechanistic insight into the O-O bond formation in the core. We demonstrate O-O bond formation at the low-valent RuIII2(OH) core with the vicinal OH ligands to form the RuII2(µ-OOH) core with a µ-OOH bridge. The O-O bond formation is induced by deprotonation of one of the OH ligands of RuIII2(OH)2 via intramolecular coupling of the OH and deprotonated O- ligands, conjugated with two-electron transfer from two RuIII centers to their ligands. The intersystem crossing between singlet and triple states of RuII2(µ-OOH) is easily switched by exchange of H+ between the µ-OOH bridge and the auxiliary backbone ligand.

An Artificial Z-Scheme Constructed from Dye-Sensitized Metal Oxide Nanosheets for Visible Light-Driven Overall Water Splitting.

Sensitization of a wide-gap oxide semiconductor with a visible-light-absorbing dye has been studied for decades as a means of producing H2 from water. However, efficient overall water splitting using a dye-sensitized oxide photocatalyst has remained an unmet challenge. Here we demonstrate visible-light-driven overall water splitting into H2 and O2 using HCa2Nb3O10 nanosheets sensitized by a Ru(II) tris-diimine type photosensitizer, in combination with a WO3-based water oxidation photocatalyst and a triiodide/iodide redox couple. With the use of Pt-intercalated HCa2Nb3O10 nanosheets further modified with amorphous Al2O3 clusters as the H2 evolution component, the dye-based turnover number and frequency for H2 evolution reached 4580 and 1960 h-1, respectively. The apparent quantum yield for overall water splitting using 420 nm light was 2.4%, by far the highest among dye-sensitized overall water splitting systems reported to date. The present work clearly shows that a carefully designed dye/oxide hybrid has great potential for photocatalytic H2 production, and represents a significant leap forward in the development of solar-driven water splitting systems.

Multi-potential-step chronocoulospectrometry for electrocatalytic water oxidation by a mononuclear ruthenium aquo complex immobilized on a mesoporous ITO electrode.

A new mononuclear Ru aquo complex [Ru(C8Otpy)(H2dcbpy)(OH2)]2+ with 4,4'-dicarboxy-2,2'-bipyridine (H2dcbpy) and 4'-octyloxy-2,2':6',2''-terpyridine (C8Otpy) ligands was synthesized to investigate electrocatalytic water oxidation by the complex immobilized on a mesoporous indium-doped tin oxide (meso-ITO) electrode using a multi-potential-step chronocoulospectrometric (MPSCCS) technique. UV-visible absorption spectroscopic data indicated that [Ru(C8Otpy)(dcbpy)(OH2)] (RuOH2) is deprotonated to [Ru(C8Otpy)(dcbpy)(OH)]- (RuOH) on the meso-ITO surface even at pH 5.9 of the electrolyte solution. The cyclic voltammogram (CV) of the RuOH/meso-ITO electrode showed a pH-independent redox response at E1/2 = 0.80 V vs. Ag/AgCl in the pH range of 5-12, being assigned to a non-proton-coupled 1e- redox process of RuIIOH/RuIIIOH. The MPSCCS measurement of the RuOH/meso-ITO electrode between 0.2 and 1.5 V vs. Ag/AgCl showed that RuIV species (tentatively RuIVO) exist in a steady state of the electrocatalysis in the initial stage. This suggests that the electrochemical oxidation from RuIVO to RuVO could compete with the water nucleophilic attack for O-O bond formation involved in the rate-determining step under the employed conditions. The possibility that the water nucleophilic attack on RuIVO could also compete with the electrochemical oxidation of RuIVO to RuVO was suggested by the electrocatalytic water oxidation at a low applied potential of 1.4 V prior to the formation potential of RuVO. The MPSCCS measurement at 1.4 V for 1 h showed that RuOH is gradually transformed into an alternative catalyst (most likely RuOx nanoparticles) on the electrode. The MPSCCS technique is promising to reveal the redox reactions and catalytic aspects of molecular catalysts immobilized on an electrode for water oxidation.

Critical Hammett Electron-Donating Ability of Substituent Groups for Efficient Water Oxidation Catalysis by Mononuclear Ruthenium Aquo Complexes.

[Ru(Rtpy)(bpy)(H2O)]2+ (1R; bpy = 2,2'-bipyridine, and Rtpy = 2,2':6',2″-terpyridine derivatives) complexes with a variety of 4'-substituent groups on Rtpy were synthesized and characterized to reveal the effects of substituents on their structures, physicochemical properties, and catalytic activities for water oxidation. The geometric structures of 1R are not considerably influenced by the electron-donating ability of the 4'-substituent groups on Rtpy. Similar multistep proton-coupled electron transfer reactions were observed for 1R, and the redox potentials for each oxidation step tended to decrease with an increase in the electron-donating ability of the substituent, which is explained by the increased electron density on the Ru center by electron-donating groups, stabilizing the positive charge that builds up upon oxidation. This is consistent with the red-shift of the absorption bands around 480 nm assigned to the metal-to-ligand charge transfer transition for 1R due to the increased d orbital energy level of the Ru center. The turnover frequency (kO2) of 1R for water oxidation catalysis, however, depended greatly on the Rtpy ligands, varying from 0.05 × 10-2 to 44 × 10-2 s-1 (as the highest kO2 was observed for R = ethoxy) by a factor of 880. A critical electron-donating ability of the 4'-substituent groups with a narrow range of Hammett constants (σp = -0.27 to -0.24) found for the highest kO2 values is valuable for understanding the great difficulty in the search for efficient water oxidation catalysts. On another front, the kO2 values increased with a decrease in the redox potentials of RuIV═O/RuV═O for 1R, indicating that the potential of formation of RuV═O species for 1R is crucial for water oxidation catalysis under the employed conditions.

Visible Light-Driven Water Oxidation on an In Situ N2 -Intercalated WO3 Nanorod Photoanode Synthesized by a Dual-Functional Structure-Directing Agent.

With a view to developing a photoanode for visible light-driven water oxidation in solar water splitting cells, pure-monoclinic WO3 nanorod crystals with N2 intercalated into the lattice were synthesized by using hydrazine with a dual functional role-as an N atom source for the in situ N2 intercalation and as a structure-directing agent for the nanorod architecture-to gain higher incident photon-to-current conversion efficiency at 420 nm than with most previously reported WO3 electrodes.

Preparation of Stable Silver Nanoparticles Having Wide Red-To-Near-Infrared Extinction.

The synthesis of silver nanoparticles (AgNPs) within the interlayer space of transparent layered titania nanosheet (TNS) films is investigated. A considerable number of silver ions (≈70% against the cation exchange capacity of the TNS) are intercalated in the TNS films using methyl-viologen-containing TNSs as a precursor. The silver ion (Ag+)-containing TNS films are treated with aqueous sodium tetrahydroborate (NaBH4), resulting in a gradual color change to bright blue. Various structural analyses clearly show that crystalline AgNPs are generated within the interlayer space of the TNSs. The NaBH4-treated films show intense and characteristic near-infrared (NIR) extinction spectra up to 1800 nm. The stability of the AgNPs within the TNS against oxygen and moisture is also investigated, and 96% and 82% of the AgNPs remain after standing in air for 1 month and 1 year, respectively. The NIR extinctions of the AgNP-containing TNS films are further extended by employing different preparation procedures, for example, using sintered TNS films as starting materials and irradiating the Ag+-containing TNSs with ultraviolet (UV) light. The obtained AgNP-containing TNS films exhibit photochemical activities in the production of hydrogen from ammonia borane under visible-light irradiation and the decomposition of nitrogen monoxide under UV-light irradiation.

Superior Inorganic Ion Cofactors of Tetraborate Species Attaining Highly Efficient Heterogeneous Electrocatalysis for Water Oxidation on Cobalt Oxyhydroxide Nanoparticles.

A heterogeneous catalyst incorporating an inorganic ion cofactor for electrochemical water oxidation was exploited using a CoO(OH) nanoparticle layer-deposited electrode. The significant catalytic current for water oxidation was generated in a Na2B4O7 solution at pH 9.4 when applying 0.94 V versus Ag/AgCl in contrast to no catalytic current generation in the K2SO4 solution at the same pH. HB4O7- and B4O72- ions were indicated to act as key cofactors for the induced catalytic activity of the CoO(OH) layer. The Na2B4O7 concentration dependence of the catalytic current was analyzed based on a Michaelis-Menten-type kinetics to provide an affinity constant of cofactors to the active sites, Km = 28 ± 3.6 mM, and the maximum catalytic current density, Imax = 2.3 ± 0.13 mA cm-2. The Imax value of HB4O7- and B4O72- ions was 1.4 times higher than that (1.3 mA cm-2) for the previously reported case of CO32- ions. This could be explained by the shorter-range proton transfer from the active site to the proton-accepting cofactor because of the larger size and more flexible conformation of HB4O7- and B4O72- ions compared with that of CO32- ions.

Mechanistic Insight into Reversible Core Structural Changes of Dinuclear µ-Hydroxoruthenium(II) Complexes with a 2,8-Di-2-pyridyl-1,9,10-anthyridine Backbone Prior to Water Oxidation Catalysis.

proximal,proximal-(p,p)-[RuII2(tpy)2LXY]n+ (tpy = 2,2';6',2″-terpyridine, L = 5-phenyl-2,8-di-2-pyridyl-1,9,10-anthyridine, and X and Y = other coordination sites) yields the structurally and functionally unusual RuII(µ-OH)RuII core, which is capable of catalyzing water oxidation with key water insertion to the core (Inorg. Chem. 2015, 54, 7627). Herein, we studied a sequence of bridging-ligand substitution among p,p-[Ru2(tpy)2L(µ-Cl)]3+ (Ru2(µ-Cl)), p,p-[Ru2(tpy)2L(µ-OH)]3+ (Ru2(µ-OH)), p,p-[Ru2(tpy)2L(OH)(OH2)]3+ (Ru2(OH)(OH2)), and p,p-[Ru2(tpy)2L(OH)2]2+ (Ru2(OH)2) in aqueous solution. Ru2(µ-Cl) converted slowly (10-4 s-1) to Ru2(µ-OH), and further Ru2(µ-OH) converted very slowly (10-6 s-1) to Ru2(OH)(OH2) by the insertion of water to reach equilibrium at pH 8.5-12.3. On the basis of density functional theory (DFT) calculations, Ru2(OH)(OH2) was predicted to be thermodynamically stable by 13.3 kJ mol-1 in water compared to Ru2(µ-OH) because of the specially stabilized core structure by multiple hydrogen-bonding interactions involving aquo, hydroxo, and L backbone ligands. The observed rate from Ru2(µ-OH) to Ru2(OH)2 by the insertion of an OH- ion increased linearly with an increase in the OH- concentration from 10 to 100 mM. The water insertion to the core is very slow (∼10-6 s-1) in aqueous solution at pH 8.5-12.3, whereas the insertion of OH- ions is accelerated (10-5-10-4 s-1) above pH 13.4 by 2 orders of magnitude. The kinetic data including activation parameters suggest that the associative mechanism for the insertion of water to the RuII(µ-OH)RuII core of Ru2(µ-OH) at pH 8.5-12.3 alters the interchange mechanism for the insertion of an OH- ion to the core above pH 13.4 because of relatively stronger nucleophilic attack of OH- ions. The hypothesized p,p-[Ru2(tpy)2L(µ-OH2)]4+ and p,p-[Ru2(tpy)2L(OH2)2]4+ formed by protonation from Ru2(µ-OH) and Ru2(OH)(OH2) were predicted to be unstable by 71.3 and 112.4 kJ mol-1 compared to Ru2(µ-OH) and Ru2(OH)(OH2), respectively. The reverse reactions of Ru2(µ-OH), Ru2(OH)(OH2), and Ru2(OH)2 to Ru2(µ-Cl) below pH 5 could be caused by lowering the core charge by protonation of the µ-OH- or OH- ligand.

Morphology Control of Energy-Gap-Engineered Nb2O5 Nanowires and the Regioselective Growth of CdS for Efficient Carrier Transfer Across an Oxide-Sulphide Nanointerface.

Semiconductor nanowires with both nano- and micrometre dimensions have been used as effective materials for artificial photosynthesis; however, a single synthesis approach to provide rational control over the macroscopic morphology, which can allow for the high-throughput screening of photocatalytic performance, and carrier transfer between oxide and sulphide nanostructures has been poorly known. Our recent findings indicate that a single parameter, Nb foil thickness, in a vapor-phase synthesis method can alter the macroscopic morphology of resulting Nb2O5 nanowires. Thick Nb foil results in a free-standing Nb2O5 film, whereas a thinner foil leads to fragmentation to give a powder. During the synthesis process, a Rh dopant was provided through metal-organic chemical vapor deposition to reduce the Nb2O5 energy gap. Upon irradiation with visible light (λ > 440 nm), the free-standing nanowire film [Nb2O5:Rh-NW(F)] showed photoanodic current with a Faradaic efficiency of 99% for O2 evolution. Under identical irradiation conditions, the powdered counterpart [Nb2O5:Rh-NW(P)] showed activity for O2 evolution in the presence of an electron acceptor. The poor water-reduction ability was greatly enhanced by the Au-catalysed vapor-liquid-solid (VLS) growth of H2-evolving CdS onto the reduction sites of Nb2O5:Rh-NW(P) [Au/CdS/Nb2O5:Rh-NW(P)].

Dual-Functional Surfactant-Templated Strategy for Synthesis of an In Situ N2 -Intercalated Mesoporous WO3 Photoanode for Efficient Visible-Light-Driven Water Oxidation.

N2 -Intercalated crystalline mesoporous tungsten trioxide (WO3 ) was synthesized by a thermal decomposition technique with dodecylamine (DDA) as a surfactant template with a dual role as an N-atom source for N2 intercalation, alongside its conventional structure-directing role (by micelle formation) to induce a mesoporous structure. N2 physisorption analysis showed that the specific surface area (57.3 m2 g-1 ) of WO3 templated with DDA (WO3 -DDA) is 2.3 times higher than that of 24.5 m2 g-1 for WO3 prepared without DDA (WO3 -bulk), due to the mesoporous structure of WO3 -DDA. The Raman and X-ray photoelectron spectra of WO3 -DDA indicated intercalation of N2 into the WO3 lattice above 450 °C. The UV/Vis diffuse-reflectance spectra exhibited a significant shift of the absorption edge by 28 nm, from 459 nm (2.70 eV) to 487 nm (2.54 eV), due to N2 intercalation. This could be explained by the bandgap narrowing of WO3 -DDA by formation of a new intermediate N 2p orbital between the conduction and valance bands of WO3 . A WO3 -DDA-coated indium tin oxide (ITO) electrode calcined at 450 °C generated a photoanodic current under visible-light irradiation below 490 nm due to photoelectrochemical water oxidation, as opposed to below 470 nm for ITO/WO3 -bulk. The incident photon-to-current conversion efficiency (IPCE=24.5 %) at 420 nm and 0.5 V versus Ag/AgCl was higher than that of 2.5 % for ITO/WO3 -bulk by one order of magnitude due to N2 intercalation and the mesoporous structure of WO3 -DDA.

Light Energy Accumulation from Pyrene Derivative to Tris(bipyridine)ruthenium on Clay Surface.

A novel type of energy donor-acceptor system on a clay surface has been prepared. The energy transfer between an energy-donating cationic pyrene derivative (An-Py2+) and an energy-accepting tris(bipyridine)ruthenium complex (Ru2+) on the clay surface was investigated using absorption, emission, and lifetime measurements. An obvious energy transfer was observed, and one Ru2+ molecule quenched the emission from five molecules of An-Py2+ with an emission quenching efficiency of 85% on the clay surface. This suggests that the light energies absorbed by five of the An-Py2+ molecules were accumulated in the one Ru2+ molecule. Near-quantitative emission quenching was observed for stoichiometric amounts of An-Py2+ and Ru2+. The apparent quenching rate constant is approximately 1017 L mol-1 s-1, and thus the quenching rate constant is 107-108 times higher than the diffusion rate constant in a homogeneous solution.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

Carbonate Ions Induce Highly Efficient Electrocatalytic Water Oxidation by Cobalt Oxyhydroxide Nanoparticles.

Synthetic models of oxygen evolving complex (OEC) are used not only to gain better understanding of the mechanism and the roles of cofactors for water oxidation in photosynthesis, but also as water oxidation catalysts to realize artificial photosynthesis, which is anticipated as a promising solar fuel production system. However, although much attention has been paid to the composition and structure of active sites for development of heterogeneous OEC models, the cofactors, which are essential for water oxidation by the photosynthetic OEC, remain little studied. The high activity of CoO(OH) nanoparticles for electrocatalytic water oxidation is shown to be induced by a CO32- cofactor. The possibility of CO32- ions acting as proton acceptors for O-O bond formation based on the proton-concerted oxygen atom transfer mechanism is proposed. The O-O bond formation is supposed to be accelerated due to effective proton acceptance by adjacent CO32- ions coordinated on the CoIV center in the intermediate, which is consistent with Michaelis-Menten-type kinetics and the significant H/D isotope effect observed in electrocatalysis.

Characterization of Interfacial Charge-Transfer Photoexcitation of Polychromium-Oxo-Electrodeposited TiO2 as an Earth-Abundant Photoanode for Water Oxidation Driven by Visible Light.

Polychromium-oxo-deposited TiO2 (CrIII x Oy /TiO2 ) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth-abundant photoanodes for visible-light-driven water oxidation. The high-resolution transmission electron microscopy (HR-TEM) observation illustrated that an CrIII x Oy layer with approximately 2-3 nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the CrIII x Oy /TiO2 electrodes. However, the wavelength (below 620 nm) for photocurrent generation at CrIII x Oy /TiO2 -rutile was longer than that (below 560 nm) at CrIII x Oy /TiO2 -P25 by 60 nm, which is in agreement with the difference (0.2 eV) in the conduction band (CB) edge energy between rutile and anatase TiO2 . This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr 3d of the deposited CrIII x Oy layer to the TiO2 CB. The photocurrent generated for CrIII x Oy /TiO2 -rutile was higher than that for CrIII x Oy /TiO2 -anatase, which is ascribed to 1) more effective CrIII x Oy deposition on the rutile particles, 2) a larger electrolyte/CrIII x Oy interface for water oxidation as a result of smaller rutile particles (ca. 30-40 nm) compared with larger P25 particles (ca. 40-80 nm), and 3) more effective use of visible light owing to the low energy IFCT transition of rutile.

Intercrystal self-assembly for the design of high-quality nickel molybdate nanocrystals.

Nanowire of nickel molybdate hydrate, being recognized as an emerging supercapacitor material, was synthesized from the intercrystal self-assembly process (commonly referred to as oriented aggregation or attachment). The detailed lattice image of a NiMoO4·0.75H2O nanowire and the intermediate nanostructure before reaching the interplanar binding were successfully captured by means of high-resolution transmission and scanning electron microscopies. NiMoO4·0.75H2O possessed highly crystalline surface and internal nanostructures.

New Series of Dinuclear Ruthenium(II) Complexes Synthesized Using Photoisomerization for Efficient Water Oxidation Catalysis.

A new series of proximal,proximal-[Ru2(tpy)2(L)XY](n+) (p,p-Ru2XY, tpy = 2,2':6',2″-terpyridine, L = 5-phenyl-2,8-di(2-pyridyl)-1,9,10-anthyridine, X and Y = other coordination sites) were synthesized using photoisomerization of a mononuclear complex. The p,p-Ru2XY complexes undergo unusual reversible bridge-exchange reactions to generate p,p-Ru2(µ-Cl), p,p-Ru2(µ-OH), and p,p-Ru2(OH)(OH2) with µ-Cl, µ-OH, as well as hydroxo and aquo ligands at X and Y sites of p,p-Ru2XY, respectively. The geometric and electronic structures of these complexes were characterized based on UV-vis and (1)H NMR spectra, X-ray crystallography, and density functional theory (DFT) calculations. (1)H NMR data showed C2 symmetry of p,p-Ru2(OH)(OH2) with the distorted L chelate and nonequivalence of two tpy ligands, in contrast to the C2v symmetry of p,p-Ru2(µ-Cl) and p,p-Ru2(µ-OH). However, irrespective of the lower symmetry, p,p-Ru2(OH)(OH2) is predominantly formed in neutral and weakly basic conditions due to the specially stabilized core structure by multiple hydrogen-bond interactions among aquo, hydroxo, and backbone L ligands. The electrochemical data suggested that p,p-Ru2(OH)(OH2) (Ru(II)-OH:Ru(II)-OH2) is oxidized to the Ru(III)-OH:Ru(III)-OH state at 0.64 V vs saturated calomel electrode (SCE) and further to Ru(IV)═O:Ru(IV)-OH at 0.79 V by successive 1-proton-coupled 2-electron processes at pH 7.0. The cyclic voltammogram data exhibited that the p,p-Ru2(OH)(OH2) complex works more efficiently for electrocatalytic water oxidation, compared with a similar mononuclear complex distal-[Ru(tpy)(L)OH2](2+) (d-RuOH2) and p,p-Ru2(µ-Cl) and p,p-Ru2(µ-OH), showing that the p,p-Ru2 core structure with aquo and hydroxo ligands is important for efficient electrocatalytic water oxidation. Bulk electrolysis of the p,p-Ru2(OH)(OH2) solution corroborated the electrocatalytic cycle involving the Ru(III)-OH:Ru(III)-OH state species as a resting state. The mechanistic insight into O-O bond formation for O2 production was provided by the isotope effect on electrocatalytic water oxidation by p,p-Ru2(OH)(OH2) and d-RuOH2 in H2O and D2O media.

Open pore architecture of an ordered mesoporous IrO2 thin film for highly efficient electrocatalytic water oxidation.

We report the first accessible channel-like open pore architecture of ordered 2D hexagonal mesoporous IrO2 films and its utilization as an efficient anode for electrocatalytic water oxidation. A well-ordered mesostructure of circa 7 nm pores were obtained by a facile one-pot soft-templating strategy, employing a [Ir(OH)6](2-) precursor stabilized by a triblock copolymer "Pluronic F127" as a pore-directing template. A mesoporous IrO2 film calcined at 400 °C (∼70 nm thick) affords a high surface area of 512 m(2) cm(-3) and 2 times higher O2 evolution during the electrocatalytic water oxidation relative to an untemplated IrO2 coating film.

Sustainable synthesis of niobia thin films with open mesopore channels.

The current approaches to electrochemically synthesizing valve metal-derived nanochannel films with longitudinal nanospaces aligned at a right angle to planar substrates rely on highly toxic fluoride compounds and require severe reaction conditions. Herein, we report on a fluoride-free, room-temperature electrochemical synthesis of a genuine mesoporous niobia thin film from the parent metal. The electrochemical reaction is driven by only a 1 V bias with respect to a Pt counter electrode in an aqueous solution. The solution contained an inexpensive, less toxic potassium hydroxide, and the reaction produced favorable byproducts, namely, recyclable K8Nb6O19 and H2.

Remarkable stimulation of emission quenching on a clay surface.

Tetra-cationic pyrene derivative (Py(4+)) and tris(bipyridine)ruthenium(II) (Ru(2+)) were hybridized onto the surface of a synthesized clay. We observed the remarkable stimulation of excited Py(4+) emission quenching on the clay surface, with a very large apparent quenching rate constant (kq = 7.4 ± 0.7 × 10(15) L mol(-1) s(-1)).