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A ligation of Ru(tpy)Cl3 (tpy = 2,2':6',2"-terpyridine) with 2-(2-pyridyl)-1,8-naphthyridine) (pynp) in the presence of LiCl gave distal-[Ru(tpy)(pynp)Cl](+) (d-1Cl) selectively, whereas the ligation gave proximal-[Ru(tpy)(pynp)OH2](2+) (p-1H2O) selectively in the absence of halide ions. (The proximal/distal isomers were defined by the structural configuration between the 1,8-naphthyridine moiety and the aquo or chloro ligand.) An aquation reaction of d-1Cl quantitatively afforded distal-[Ru(tpy)(pynp)OH2](2+) (d-1H2O) in water, and d-1H2O is quantitatively photoisomerized to p-1H2O. The mechanism of the photoisomerization was investigated by transient absorption spectroscopy and quantum chemical calculations. The temperature dependence of the transient absorption spectral change suggests existence of the thermally activated process from the (3)MLCT state with the activation energy (ΔE = 49 kJ mol(-1)), which is close to that (41.7 kJ mol(-1)) of the overall photoisomerization reaction. However, quantum chemical calculations suggest another activation process involving the conformational change of the pentacoordinated distal structure to the proximal structure. Quantum chemical calculations provide redox potentials and pK(a) values for proton-coupled electron transfer reactions from Ru(II)-OH2 to Ru(IV)═O in good agreement with experiments and provide an explanation for mechanistic differences between d-1H2O and p-1H2O with respect to water oxidation. The calculations show that water nucleophilic attack (WNA) on d-[Ru(V)-O](3+) (the ruthenyl oxo species derived from d-1H2O, calculated ΔG(‡) of 87.9 kJ/mol) is favored over p-[Ru(V)-O](3+) (calculated ΔG(‡) of 104.6 kJ/mol) for O-O bond formation. Examination of the lowest unoccupied molecular orbitals in d- and p-[Ru(V)-O](3+) indicates that more orbital amplitude is concentrated on the [Ru-O] unit in the case of d-[Ru(V)-O](3+) than in the case of p-[Ru(V)-O](3+), where some of the amplitude is instead delocalized over the pynp ligand, making this isomer less electrophilic.

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.

N

A new MnIII (μ-O)2MnVI dimer, [(OH2)(Py-terpy)Mn(μ-O)2Mn(Py-terpy)(OH2)]3+ (Py-terpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) (1Py) with electron-withdrawing pyridyl (Py) groups was synthesized and characterized by UV–Vis and IR spectroscopic, X-ray crystallographic, magnetometric, and electrochemical techniques. 1Py is stable in an aqueous solution at room temperature, in contrast to the unstable Cl and Br derivatives with R-terpy (R = Cl or Br of electron-withdrawing groups). The maximum concentrations of 1Py adsorbed on saponite suggests that 1Py is adsorbed on saponite or mica as a pentavalence cation, like [1Py2H]5+ with protonation of Py groups on Py-terpy ligands. Water oxidation catalyses by 1Py were examined in homogenous solution and heterogeneous saponite or mica adsorbate systems. O2 was evolved in a reaction of 1Py with a Ce(IV) oxidant in an aqueous solution. However, the maximum turnover number (TN) of 1Py for O2 evolution was 0.63 for 4 days, showing that 1Py does not work as a catalyst for water oxidation in solution. The reactions of the 1Py/saponite or mica adsorbate with a CeIV oxidant in water catalytically produced the significant amount of O2. The maximum TNs of 1Py on saponite and mica for O2 evolution are 5.6 and 16 for 4 days, respectively. The kinetic analysis of O2 evolution suggested that the unimolecular decomposition reaction of 1Py involving O2 evolution competes with the cooperative catalysis by two equivalents of 1Py on saponite or mica. The k2 values of 1Py adsorbates were lower than those of 1 adsorbates for saponite and mica systems, in contradiction to the magnitude relationship predicted from the E1/2 values of 1Py and 1 based on our previous work (Yamazaki et al., 2012 [29] ). The lower k2 values could be explained most possibly by electrostatic repulsion between a pentavalent [1Py2H]5+ cation on saponite and mica, compared with a trivalent 1 cation.

Polychromium-oxo-deposited TiO

The construction of an artificial photosynthetic device requires detailed understanding of the catalytic aspects of photo- or photoelectro-driven water oxidation. This has been attracting much interest as one of the promising clean energy-providing systems for the future. This review mainly covers progress on electrocatalytic and photocatalytic systems for water oxidation in the last decade. It includes conventional iridium oxide colloid catalysts and the new electrodeposited cobalt-phosphate catalyst films for water oxidation.

A single-wall carbon nanotube functionalized by carboxylic groups (SWNT-CA) was found to be adsorbed on an indium tin oxide (ITO) electrode by chemical interaction between carboxylic groups and the ITO surface. The adsorption experiments indicated that the narrow pH conditions (around pH 3.0) exist for its adsorption which is restricted by preparation of stable fluid dispersion (favorable at higher pH) and by the chemical interaction (favorable at lower pH). Atomic force microscopic (AFM) measurements suggest that fragmented SWNT-CA are adsorbed, primarily lying on the surface. Electrochemical impedance analysis indicated that an electrochemical double layer capacitance of the SWNT-CA/ITO electrode is considerably higher than that for the ITO electrode, suggesting that the interfacial area between the electrode surface and the electrolyte solution is enlarged by the SWNT-CA layer. Pt particles were deposited as a catalyst on the bare ITO and SWNT-CA-coated ITO (SWNT-CA/ITO) electrodes to give respective Pt-modified electrodes (denoted as a Pt/ITO electrode and a Pt/SWNT-CA/ITO electrode, respectively). The cathodic current for the Pt/SWNT-CA/ITO electrode was 1.7 times higher than that for the Pt/ITO electrode at 0.0 V, showing that the Pt/SWNT-CA/ITO electrode works more efficiently for O2 reduction at 0.0 V due to the SWNT-CA layer. The enhancement by the SWNT-CA layer is also effective for electrocatalytic proton reduction. It could be ascribable to the enlarged interfacial area between the electrode surface and the electrolyte solution.

A plate-type alumina support was synthesized through a novel anodization technology followed by a hot water treatment, which resulted in the drastically enlargement of support BET surface area from 16.5 to 204.6 g/m2, and such BET value is even comparable to some commercial alumina supports. A high thermal stability of this kind of porous anodic alumina support was shown because as much as 63% of surface area remained after the support subjected to 700 °C air calcination for 50 h. Innovatively, an electrical heating pattern was allowed over this plate support due to the existence of Fe–Cr–Ni alloy interlayer among the support. Our work showed that the utilization of electrical heating pattern would shorten the reformer start-up time from 1 to 2 h to just a few minutes. With the porous anodic alumina support, a 17.9-wt% Ni catalyst with nickel aluminate layer was synthesized and its reforming reactivity was investigated during stationary and DSS SRM at 700 °C, under usual and electrical heating pattern. It showed excellent SRM reactivity and no deactivation was evidenced during 500 h stationary test and 100 times start–stop cycles DSS SRM test. Nevertheless, for the industrialization, some efforts should be made to alleviate the sintering of anodic supports, because after subjected to a hydrothermal treatment at 700 °C for 50 h, only 36% of surface area was kept.

A 17.9 wt.% Ni/Al 2 O 3 /alloy catalyst with porous anodic alumina support was subjected to steam reforming of methane after 700 °C steam purging and no reactivity was shown because of surface oxidation of sintered Ni particles. When 0.05 wt.% Ru doped on this catalyst, it exhibited self-activation and self-regenerative activity, resulted from the hydrogen spillover over Ru and/or Ru–Ni alloy. Moreover, a 97% CH 4 conversion was kept for 20 h over the catalyst under electrical heating pattern.

A [Ru(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine)/WO 3 hybrid (denoted as Ru-WO 3 ) film was prepared as a base layer on an indium tin oxide electrode by electrodeposition from a colloidal solution containing peroxotungstic acid, [Ru(bpy) 3 ] 2+ and poly(sodium 4-styrenesulfonate). A ruthenium purple (RP, Fe III 4 [Ru II (CN) 6 ] 3 , denoted as Fe III -Ru II ) layer was electrodeposited on a neat WO 3 film or a Ru-WO 3 film from an aqueous RP colloid solution to yield a WO 3 /RP bilayer film or a Ru-WO 3 /RP bilayer film, respectively. The spectrocyclic voltammetry measurement reveals that Fe II -Ru II is oxidized to Fe III -Ru II by a geared reaction of [Ru(bpy) 3 ] 2+/3+ and Fe III -Ru II is reduced by a geared reaction of H x WO 3 /WO 3 in the Ru-WO 3 /RP film. These geared reactions produced electrochromic hysteresis of the RP layer. However, the absorbance change in the hysteresis was smaller than that for the Ru-WO 3 /Prussian blue bilayer film reported previously, resulting from the lower electroactivities of any redox component for the Ru-WO 3 /RP film. The lower electroactivities could be explained by the specific interface between the Ru-WO 3 and RP layers. It might contribute to either an increase of the interfacial resistance between the Ru-WO 3 and RP layers, or formation of the physically precise interface between the layers to make it difficult for counter ions to be transported in the interfacial liquid phase involved in the redox reactions in the film. The specific interface at the Ru-WO 3 and RP layers could be formed possibly by the electrostatic interaction between [Ru(bpy) 3 ] 2+ and terminal [Ru(CN) 6 ] 4− moieties of RP. It could be suggested by the decreased redox potential of [Ru(bpy) 3 ] 2+ in the Ru-WO 3 layer from 1.03 to 0.61 V by formation of the RP layer.

A tungsten trioxide (WO{sub 3}) film was prepared by calcination from a precursor paste including suspended ammonium tungstate and polyethylene glycol (PEG). The ammonium tungstate suspension was yielded by an acid-base reaction of tungstic acid and an ammonium solution followed by deposition with ethanol addition. Thermogravimetric (TG) analysis showed that the TG profile of PEG is significantly influenced by deposited ammonium tungstate, suggesting that PEG is interacting strongly with deposited ammonium tungstate in the suspension paste. X-ray diffraction (XRD) data indicated that the WO{sub 3} film is crystallized by sintering over 400 deg. C. The scanning electron microscopic (SEM) measurement showed that the film is composed of the nano-structured WO{sub 3} platelets. The semiconductor properties of the film were examined by Mott-Schottky analysis to give flat band potential E{sub FB}=0.30 V vs. saturated calomel reference electrode (SCE) and donor carrier density N{sub D}=2.5x10{sup 22} cm{sup -3}, latter of which is higher than previous WO{sub 3} films by two orders of magnitude. The higher N{sub D} was explained by the large interfacial heterojunction area caused by the nano-platelet structure, which apparently increases capacitance per a unit electrode area. The WO{sub 3} film sintered at 550 deg. C produced 3.7 mA cm{supmore » -2} of a photoanodic current at 1.2 V vs. SCE under illumination with a 500 W xenon lamp due to catalytic water oxidation. This photocurrent was 4.5-12.8 times higher than those for the other control WO{sub 3} films prepared by similar but different procedures. The high catalytic activity could be explained by the nano-platelet structure. The photocurrent was generated on illumination of UV and visible light below 470 nm, and the maximum incident photon-to-current conversion efficiency (IPCE) was 47% at 320 nm at 1.2 V. Technically important procedures for preparation of nano-structured platelets were discussed. - Graphical abstract: A nano-structured WO{sub 3} platelet film was prepared by calcination from a precursor paste including suspended ammonium tungstate and polyethylene glycol. The ammonium tungstate suspension was yielded by an acid-base reaction of tungstic acid and an ammonium solution followed by deposition with ethanol addition. The photocatalytic activity of the film was 4.5-12.8 times higher than those for the other control WO{sub 3} films prepared by similar but different procedures.« less

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.

Tetraphenylporphine zinc(II) (ZnTPP) was found to be adsorbed from its CH2Cl2 solution into a Nafion (Nf) film. The characteristics of the adsorption of ZnTPP into the Nf film were studied using a visible absorption spectroscopic technique. The initial rate (v0, mol cm(-2) s(-1)) for uptake of ZnTPP was saturated with increasing ZnTPP concentration (c0, M) in the solution. This kinetic profile was analyzed in terms of a Michaelis-Menten model considering preequilibrium of ZnTPP adsorption between the solution and the outer layer of the Nf film, followed by diffusion to an inner bulk region, giving a maximum diffusion reflux of v(max) = (2.2 +/- 0.2) x 10(-13) mol cm(-2) s(-1). This is different from the kinetics for the Nf/phthalocyanine zinc(II) (ZnPc) film, which gives a linear plot of v(0) vs c(0). This can be explained by the relatively slow diffusion of ZnTPP in the film compared to that of ZnPc because of steric factors: ZnTPP contains bulky tetraphenyl moieties attached perpendicular to a porphyrin ring, whereas ZnPc has higher planarity. The isotherm for the adsorption of ZnTPP into the Nf film was analyzed using a Langmuir isotherm equation, yielding an equilibrium constant of (3.6 +/- 1.1) x 10(6) M(-1) and a saturated amount of adsorbed ZnTPP of (1.8 +/- 0.1) x 10(-9) mol cm(-2), suggesting monolayer adsorption of ZnTPP on the hydrophobic polymer network interfacial with hydrophilic transport channels without significant intermolecular overlap. This is in contrast to the multilayer adsorption mode suggested for the ZnPc adsorption. The tetraphenyl moieties could prevent the stacking of ZnTPP for multilayer adsorption.

Electrochemical reactions of Ruthenium purple, Fe 4 III [Ru II (CN) 6 ] 3 (RP; Fe III -Ru II ) were studied using a spectrocyclic voltammetry (SCV) technique. The SCV measurement for an RP film coated on an ITO electrode showed a reversible redox between RP and Ruthenium white (RW; Fe II -Ru II ) at 0.14 V vs saturated calomel reference electrode (SCE). An RP film was electrodeposited on a hybrid film of tungsten trioxide (W03)/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy) 3 ] 2+ ; bpy=2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) (denoted as WRP film) from a colloidal solution containing 0.5 mM FeCl 3 , 0.5 mM K 4 [Ru(CN) 6 ] and 40 mM KCl using a potentiodynamic multi-sweep technique. In a cyclic voltammogram (CV) of a WRP/RP film, a redox response was observed at 0.61 V in addition to essential redox responses of WRP hybrid film (a [Ru(bpy) 3 ] 2+ /Ru(bpy) 3 ] 3+ redox at 1.03 V and a H x WO 3 / WO 3 redox below 0.09 V), but a redox response of RW/RP was not observed at 0.14 V. The SCV measurement for the WRP/RP film suggested that the redox response at 0.61 V is attributed to a redox of [Ru(bpy) 3 ] 2+ /[Ru(bpy) 3 ] 3+ interacted electrostatically with RP. It also showed that RW is oxidized to RP via [Ru(bpy)3]2+/[Ru(bpy)3]3+ redox and RP is reversibly reduced to RW via H x WO 3 /WO 3 redox. This unique geared electrochemical reaction for the WRP/RP film leads to a hysteresis property of an RW/RP redox.

Phthalocyanine zinc(II) (ZnPc) was found to be adsorbed well into a Nafion (Nf) film. The kinetic analysis suggested that the adsorption of ZnPc into the Nf film is controlled by its diffusion in the Nf film with a diffusion coefficient of D = 1.9 x 10(-6) cm(2) s(-1) that is higher than those (10(-9)-10(-12) cm(2) s(-1)) of cationic redox molecules in the Nf film by 3-6 orders of magnitude. The adsorption isothermal was analyzed by a Brunauer-Emmett-Teller (BET) equation suggesting multilayer adsorption of ZnPc into the film. The BET analysis provided the amount of ZnPc for monolayer adsorption (w(m) = 1.50 x 10(-7) mol cm(-2)), from which the effective area for the ZnPc adsorption was estimated to be larger by a factor of 1.7 x 10(3) than the Nf film area (1.0 cm(2)). The absorption spectra of a Nf film adsorbing ZnPc ((Nf/ZnPc)(ads) film) exhibited two broad absorption bands at 385 and 680-750 nm without any structural features, which is significantly different from the absorption spectra of either ZnPc solution in DMF or a (Nf/ZnPc)(mix) film prepared from a DMF solution containing Nf and ZnPc by solvent evaporation. This is ascribed to the formation of a ZnPc aggregate in the (Nf/ZnPc)(ads) film. Photoluminescence data for the (Nf/ZnPc)(mix) film suggested the presence of a ZnPc monomer and dimer at equilibrium in the film with a concentration of 0.1 M and that energy transfer occurs from the monomer to the dimer in excitation of the monomer (at lambda(ex) = 609 nm) to yield emission from the dimer. By contrast, photoluminescence data for the (Nf/ZnPc)(ads) film suggested that the excited ZnPc is self-quenched significantly by the formation of the ZnPc aggregate in the film. The lesser electroactivity of ZnPc in the (Nf/ZnPc)(ads) film compared with that in the (Nf/ZnPc)(mix) film could be ascribable to more difficult diffusion of ZnPc in the former film due to the formation of the ZnPc aggregate. The adsorption of ZnPc into the Nf film was significantly regulated by simple pretreatments of the Nf film such as immersion in solvents and storage under solvent vapors. The regulation was explained by controlled physical and chemical properties of a channel for mass and ion transport that is formed by sulfonate groups, countercations, and solvent molecules in the Nf film.

Charge transport (CT) in a Nafion film incorporating [(NH3)5Ru(μ-pz)Ru(NH3)5]4+ ([RuII−RuII]4+; pz = pyrazine) was studied using a double potential-step chronoabsorptometry (DPSCA) technique. The oxidative CT by [RuII−RuII]4+/[RuII−RuIII]5+ (in a potential step from −0.2 to 0.3 V; first step) was compared with that by [RuII−RuIII]5+/[RuIII−RuIII]6+ (in a successive potential step from 0.3 to 0.7 V; second step). The predominant CTs by a physical displacement mechanism of the complexes were suggested for both of the steps. However, the rate constant of the CT for the first step was 5.2 time higher than that for the second step at 25 °C. The results on CT kinetics and dynamics revealed that the CTs in both of the steps are entropy-controlled in the activation at room temperature. The ΔH‡ (12 kJ mol-1) for the physical displacement in the second step was lower than that (24 kJ mol-1) for the first step, showing that the physical displacement for the second step is enthalpically favorable compared with that f...

Charge transport (CT) in a Nafion film incorporating [Ru(bpz)3]2+ (bpz = 2,2‘-bipyrazine) was investigated using a potential-step chronocouloabsorptometry technique. The reductive CT by [Ru(bpz)3]2+/+ was found to take place by a combination mechanism of physical displacement of the complex and charge hopping between the molecules of the complex. This is a different mechanism from that of the oxidative CT (occurring by a charge hopping mechanism) in an earlier reported Nafion/[Ru(bpy)3]2+/3+ (bpy = 2,2‘-bipyridine) system. The combination mechanism in CT was also reported in an earlier Nafion/[(NH3)5Ru−O−Ru(NH3)4−O−Ru(NH3)5]6+ (Ru-red) system. In the present [Ru(bpz)3]2+ system, the activation energy (Ea = 78 kJ·mol-1) of physical displacement is higher than that (40 kJ·mol-1) of charge hopping. In the Ru-red system, on the contrary, the Ea (13 kJ·mol-1) of physical displacement is lower than that (55 kJ·mol-1) of charge hopping. As a result, the fraction (Φc) of the contribution of charge hopping to the ...

Active catalysts for water oxidation to evolve O(2) are required for the construction of artificial photosynthetic devices that are expected to be promising energy-providing systems in the future. The citrate-stabilized IrO(2) colloid was self-assembled onto an indium tin oxide (ITO) electrode to form a monolayer of the colloidal IrO(2) particles when it was dipped in the colloid solution. The self-assembly could be achieved by a chemical interaction between carboxylate groups on the citrate stabilizer and hydroxyl groups on the ITO surface to form ester bonds. Efficient electrocatalysis for water oxidation was demonstrated using the electrode modified by the self-assembled IrO(2) colloid to yield the highest turnover frequency ((2.3-2.5) x 10(4) h(-1)) of IrO(2) in the hitherto-reported catalysts for electrochemical water oxidation.

Fructosyl amino acid oxidase (FAOD), which is active toward model compounds of the glycated proteins in blood, N epsilon-fructosyl N sigma-Z-lysine and N-fructosyl valine, was purified to homogeneity from Aspergillus terreus GP1. Though the enzyme did not use glycated proteins directly as its substrate, it used glycated human serum albumin (HSA) when HSA was treated with a protease. Linear relationships between both the concentration and the increase in absorbance and the glycation rate of glycated HSA and the increase in absorbance were observed. cDNAs coding for FAODs were cloned from cDNA libraries of A. terreus GP1 and Penicillium janthinellum AKU 3413. The coding region for both fungal FAODs consisted of 1314 bp encoding 437 amino acids. The sequence of a dinucleotide-binding motif, GXGXXG, was in the deduced N-terminal region and a similar sequence to that the active site of bacterial sarcosine oxidases was found near the C-terminal region of FAOD. The of C-terminal tripeptides SKL and AKL of FAODs from A. terreus and P. janthinellum, respectively, represent typical peroxisomal-targeting signals. Finally, FAOD protein was produced in Escherichia coli transformants in an active form, and at the same level as in the original fungi.

Visible-light-derived O(2) production was yielded by conjugating water oxidation catalysis by [(OH(2))(terpy)Mn(μ-O)(2)Mn(terpy)(OH(2))](3+) as an oxygen evolving center model and photo-sensitization of [Ru(bpy)(3)](2+) as a photoexcitation center model at an interlayer of mica.

Cores for thought! A new [Mn

Mesoporous tungsten trioxide (WO3) was prepared from tungstic acid (H2WO4) as a tungsten precursor with dodecylamine (DDA) as a template to guide porosity of the nanostructure by a solvothermal technique. The WO3 sample (denoted as WO3-DDA) prepared with DDA was moulded on an electrode to yield efficient performance for visible-light-driven photoelectrochemical (PEC) water oxidation. Powder X-ray diffraction (XRD) data of the WO3-DDA sample calcined at 400°C indicate a crystalline framework of the mesoporous structure with disordered arrangement of pores. N2 physisorption studies show a Brunauer-Emmett-Teller (BET) surface area up to 57 m2 g-1 together with type IV isotherms and uniform distribution of a nanoscale pore size in the mesopore region. Scanning electron microscopy (SEM) images exhibit well-connected tiny spherical WO3 particles with a diameter of ca. 5 to 20 nm composing the mesoporous network. The WO3-DDA electrode generated photoanodic current density of 1.1 mA cm-2 at 1.0 V versus Ag/AgCl under visible light irradiation, which is about three times higher than that of the untemplated WO3. O2 (1.49 μmol; Faraday efficiency, 65.2%) was evolved during the 1-h photoelectrolysis for the WO3-DDA electrode under the conditions employed. The mesoporous electrode turned out to work more efficiently for visible-light-driven water oxidation relative to the untemplated WO3 electrode.