Robustness of Ru/SiO₂ as a Hydrogen-Evolution Catalyst in a Photocatalytic System Using an Organic Photocatalyst

Effects of various metal oxide supports (SiO₂, SiO₂–Al₂O₃, TiO₂, CeO₂, and MgO) on the catalytic reactivity of ruthenium nanoparticles (RuNPs) used as a hydrogen-evolution catalyst have been evaluated in photocatalytic hydrogen evolution using 2-phenyl-4-(1-naphthyl)­quinolinium ion (QuPh⁺–NA) and dihydronicotinamide adenine dinucleotide (NADH) as a photocatalyst and an electron donor, respectively. The 3 wt % Ru/SiO₂ catalyst freshly prepared by an impregnation method exhibited the highest catalytic reactivity among RuNPs supported on various metal oxides, which was nearly the same as that of commercially available Pt nanoparticles (PtNPs) with the same metal weight. However, the initial catalytic reactivity of 3 wt % Ru/SiO₂ was lost after repetitive use, whereas the catalytic reactivity of PtNPs was maintained under the same experimental conditions. The recyclability of the 3 wt % Ru/SiO₂ was significantly improved by employing the CVD method for preparation. The initial catalytic reactivity of 0.97 wt % Ru/SiO₂ prepared by the CVD method was higher than that of 2 wt % Ru/SiO₂ prepared by the impregnation method despite the smaller Ru content. The total amount of evolved hydrogen normalized by the weight of Ru in 0.97 wt % Ru/SiO₂ was 1.7 mol g_Ru^–1, which is now close to that normalized by the weight of Pt in PtNPs (2.0 mol g_Pt^–1). Not only the preparation method but also the morphology of SiO₂ supports affected significantly the catalytic activity of Ru/SiO₂. The Ru/SiO₂ catalyst using nanosized SiO₂ with undefined shape exhibited higher catalytic activity than Ru/SiO₂ catalysts using mesoporous SiO₂ or spherical SiO₂. The kinetic study and TEM observation of the Ru/SiO₂ catalysts suggest that the microenvironment of RuNPs on SiO₂ surfaces plays an important role to exhibit the high catalytic performance in the photocatalytic hydrogen production

Efficient Photocatalytic Production of Hydrogen Peroxide from Water and Dioxygen with Bismuth Vanadate and a Cobalt(II) Chlorin Complex

Efficient photocatalytic production of H₂O₂ as a promising solar fuel from H₂O and O₂ in water has been achieved by the combination of bismuth vanadate (BiVO₄) as a durable photocatalyst with a narrow band gap for the water oxidation and a cobalt chlorin complex (Co^II(Ch)) as a selective electrocatalyst for the two-electron reduction of O₂ in a two-compartment photoelectrochemical cell separated by a Nafion membrane under simulated solar light illumination. The concentration of H₂O₂ produced in the reaction solution of the cathode cell reached as high as 61 mM, when surface-modified BiVO₄ with iron­(III) oxide­(hydroxide) (FeO­(OH)) and Co^II(Ch) were employed as a water oxidation catalyst in the photoanode and as an O₂ reduction catalyst in the cathode, respectively. The highest solar energy conversion efficiency was determined to be 6.6% under simulated solar illumination adjusted to 0.05 sun after 1 h of photocatalytic reaction (0.89% under 1 sun illumination). The conversion of chemical energy into electric energy was conducted using H₂O₂ produced by photocatalytic reaction by an H₂O₂ fuel cell, where open-circuit potential and maximum power density were recorded as 0.79 V and 2.0 mW cm^–2, respectively

Photocatalytic Hydroxylation of Benzene by Dioxygen to Phenol with a Cyano-Bridged Complex Containing Fe^II and Ru^II Incorporated in Mesoporous Silica–Alumina

Photocatalytic hydroxylation of benzene to phenol was achieved by using O₂ as an oxidant as well as an oxygen source with a cyano-bridged polynuclear metal complex containing Fe^II and Ru^II incorporated in mesoporous silica–alumina ([Fe­(H₂O)₃]₂­[Ru­(CN)₆]­@sAl-MCM-41). An apparent turnover number (TON) of phenol production per the monomer unit of [Fe­(H₂O)₃]₂[Ru­(CN)₆] was 41 for 59 h. The cyano-bridged polynuclear metal complex, [Fe­(H₂O)₃]₂­[Ru­(CN)₆], exhibited catalytic activity for thermal hydroxylation of benzene by H₂O₂ in acetonitrile (MeCN), where the apparent TON of phenol production reached 393 for 60 h. The apparent TON increased to 2500 for 114 h by incorporating [Fe­(H₂O)₃]₂­[Ru­(CN)₆] in sAl-MCM-41. Additionally, [Fe­(H₂O)₃]₂­[Ru­(CN)₆] acts as a water oxidation catalyst by using [Ru­(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) and Na₂S₂O₈ as a photosensitizer and a sacrificial electron acceptor as evidenced by ¹⁸O-isotope labeling experiments. Photoirradiation of an O₂-saturated MeCN solution containing [Fe­(H₂O)₃]₂­[Ru­(CN)₆]­@sAl-MCM-41 and scandium ion provided H₂O₂ formation, where photoexcited [Ru­(CN)₆]^4– moiety reduces O₂ as indicated by laser flash photolysis measurements. Thus, hydroxylation of benzene to phenol using molecular oxygen photocatalyzed by [Fe­(H₂O)₃]₂­[Ru­(CN)₆] occurred via a two-step route; (1) molecular oxygen was photocatalytically reduced to peroxide by using water as an electron donor, and then (2) peroxide thus formed is used as an oxidant for hydroxylation of benzene

Acetate Induced Enhancement of Photocatalytic Hydrogen Peroxide Production from Oxalic Acid and Dioxygen

The addition of acetate ion to an O₂-saturated mixed solution of acetonitrile and water containing oxalic acid as a reductant and 2-phenyl-4-(1-naphthyl)­quinolinium ion (QuPh⁺–NA) as a photocatalyst dramatically enhanced the turnover number of hydrogen peroxide (H₂O₂) production. In this photocatalytic H₂O₂ production, a base is required to facilitate deprotonation of oxalic acid forming oxalate dianion, which acts as an actual electron donor, whereas a Brønsted acid is also necessary to protonate O₂^•– for production of H₂O₂ by disproportionation. The addition of acetate ion to a reaction solution facilitates both the deprotonation of oxalic acid and the protonation of O₂^•– owing to a pH buffer effect. The quantum yield of the photocatalytic H₂O₂ production under photoirradiation (λ = 334 nm) of an O₂-saturated acetonitrile–water mixed solution containing acetate ion, oxalic acid and QuPh⁺–NA was determined to be as high as 0.34, which is more than double the quantum yield obtained by using oxalate salt as an electron donor without acetate ion (0.14). In addition, the turnover number of QuPh⁺–NA reached more than 340. The reaction mechanism and the effect of solvent composition on the photocatalytic H₂O₂ production were scrutinized by using nanosecond laser flash photolysis

Catalysis of Nickel Ferrite for Photocatalytic Water Oxidation Using [Ru(bpy)₃]²⁺ and S₂O₈^2–

Single or mixed oxides of iron and nickel have been examined as catalysts in photocatalytic water oxidation using [Ru­(bpy)₃]²⁺ as a photosensitizer and S₂O₈^2– as a sacrificial oxidant. The catalytic activity of nickel ferrite (NiFe₂O₄) is comparable to that of a catalyst containing Ir, Ru, or Co in terms of O₂ yield and O₂ evolution rate under ambient reaction conditions. NiFe₂O₄ also possesses robustness and ferromagnetic properties, which are beneficial for easy recovery from the solution after reaction. Water oxidation catalysis achieved by a composite of earth-abundant elements will contribute to a new approach to the design of catalysts for artificial photosynthesis

Protonation Equilibrium and Hydrogen Production by a Dinuclear Cobalt–Hydride Complex Reduced by Cobaltocene with Trifluoroacetic Acid

A dinuclear Co complex with bis­(pyridyl)­pyrazolato (bpp^–) and terpyridine (trpy) ligands, [Co^III₂(trpy)₂(μ-bpp)­(OH)­(OH₂)]⁴⁺ (<b>1</b>⁴⁺), undergoes three-electron reduction by cobaltocene in acetonitrile to produce <b>1</b>⁺, which is in the protonation equilibrium with the Co^IICo^III–hydride complex, and the further protonation of the hydride by trifluoroacetic acid yields hydrogen quantitatively. The kinetic study together with the detection of the Co^IICo^III-hydride complex revealed the mechanism of the hydrogen production by the reaction of <b>1</b>⁺ with trifluoroacetic acid

Water Oxidation Catalysis with Nonheme Iron Complexes under Acidic and Basic Conditions: Homogeneous or Heterogeneous?

Thermal water oxidation by cerium­(IV) ammonium nitrate (CAN) was catalyzed by nonheme iron complexes, such as Fe­(BQEN)­(OTf)₂ (<b>1</b>) and Fe­(BQCN)­(OTf)₂ (<b>2</b>) (BQEN = <i>N</i>,<i>N</i>′-dimethyl-<i>N</i>,<i>N</i>′-bis­(8-quinolyl)­ethane-1,2-diamine, BQCN = <i>N</i>,<i>N</i>′-dimethyl-<i>N</i>,<i>N</i>′-bis­(8-quinolyl)­cyclohexanediamine, OTf = CF₃SO₃^–) in a nonbuffered aqueous solution; turnover numbers of 80 ± 10 and 20 ± 5 were obtained in the O₂ evolution reaction by <b>1</b> and <b>2</b>, respectively. The ligand dissociation of the iron complexes was observed under acidic conditions, and the dissociated ligands were oxidized by CAN to yield CO₂. We also observed that <b>1</b> was converted to an iron­(IV)-oxo complex during the water oxidation in competition with the ligand oxidation. In addition, oxygen exchange between the iron­(IV)-oxo complex and H₂¹⁸O was found to occur at a much faster rate than the oxygen evolution. These results indicate that the iron complexes act as the true homogeneous catalyst for water oxidation by CAN at low pHs. In contrast, light-driven water oxidation using [Ru­(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) as a photosensitizer and S₂O₈^2– as a sacrificial electron acceptor was catalyzed by iron hydroxide nanoparticles derived from the iron complexes under basic conditions as the result of the ligand dissociation. In a buffer solution (initial pH 9.0) formation of the iron hydroxide nanoparticles with a size of around 100 nm at the end of the reaction was monitored by dynamic light scattering (DLS) in situ and characterized by X-ray photoelectron spectra (XPS) and transmission electron microscope (TEM) measurements. We thus conclude that the water oxidation by CAN was catalyzed by short-lived homogeneous iron complexes under acidic conditions, whereas iron hydroxide nanoparticles derived from iron complexes act as a heterogeneous catalyst in the light-driven water oxidation reaction under basic conditions

Mesoporous Nickel Ferrites with Spinel Structure Prepared by an Aerosol Spray Pyrolysis Method for Photocatalytic Hydrogen Evolution

Submicron-sized mesoporous nickel ferrite (NiFe₂O₄) spheres were prepared by an aerosol spray pyrolysis method using Pluronic F127 as a structure-directing agent, and their photocatalytic performance for hydrogen (H₂) evolution was examined in an aqueous MeOH solution by visible light irradiation (λ > 420 nm). The structure of the spherical mesoporous nickel ferrites was studied by transmission electron microscopy, powder X-ray diffraction, and N₂ adsorption–desorption isotherm measurements. Mesoporous NiFe₂O₄ spheres of high specific surface area (278 m² g^–1) with a highly crystalline framework were prepared by adjusting the amount of structure-directing agent and the calcining condition. High photocatalytic activity of mesoporous NiFe₂O₄ for H₂ evolution from water with methanol was achieved due to the combination of high surface area and high crystallinity of the nickel ferrites

Predictive grade of ultrasound synovitis for diagnosing rheumatoid arthritis in clinical practice and the possible difference between patients with and without seropositivity

<p><i>Objective.</i> To determine the degree of contribution and the contributing factors of ultrasound in the diagnosis of rheumatoid arthritis (RA) in daily clinical practice and the predictive differences depending on seropositivity.</p> <p><i>Methods</i>. We included 122 patients who presented with the main complaint of finger and/or wrist joint pain but for whom no definite diagnosis was reached or treatment strategy was provided. Ultrasound was performed on at least 22 joints (both wrist joints, proximal interphalangeal joint, and metacarpophalangeal joints), and patients were followed for ≥6 months. Factors contributing to RA diagnosis were determined and compared between seropositive and seronegative RA patients.</p> <p><i>Results.</i> RA was diagnosed in 52 of 122 patients, in whom the American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria (odds ratio [OR] = 4.74, <i>P</i> = 0.01) and gray scale (GS) grade of 3 (OR = 3.64, <i>P</i> = 0.04) for ≥ 1 joint were the contributing factors. In seropositive RA, the ACR/EULAR criteria (OR = 15.53, <i>P</i> < 0.001) and power Doppler (PD) ≥ 2 for ≥ 1 joint (OR = 10.48, <i>P</i> = 0.0048) were the contributing factors. In seronegative RA, PD ≥ 1 for ≥ 1 joint contributed the most (OR = 20.00, <i>P</i> = 0.0044), but the ACR/EULAR criteria did not contribute to RA diagnosis (<i>P</i> = 0.57).</p> <p><i>Conclusion.</i> Ultrasound findings contributed to RA diagnosis in clinical practice. The contributing factors are different in the presence or absence of seropositivity, and ultrasound complementation was particularly useful in seronegative RA patients.</p

The synovial grade corresponding to clinically involved joints and a feasible ultrasound-adjusted simple disease activity index for monitoring rheumatoid arthritis

<p><i>Objectives</i>: To determine which grade of ultrasound (US) synovitis corresponds to clinically involved joints in rheumatoid arthritis (RA) and develops a new US-adjusted composite measure.</p> <p><i>Methods</i>: Clinical and US examinations were performed on 137 patients with RA (28 joints). Synovial effusion, hypertrophy, and blood flow were semiquantitatively graded from 0 to 3 using gray scale (GS) and power Doppler (PD) modes. We calculated US-adjusted simple disease activity index (SDAI) and assessed feasibility, and external validity by comparing with erythrocyte sedimentation rate (ESR), and modified health assessment questionnaires (MHAQ).</p> <p><i>Results</i>: GS ≥2 and PD ≥0 corresponds to clinically swollen joints, and GS ≥2 and PD ≥1 corresponds to tender joints. The US-adjusted SDAI showed the highest correlation when US-determined swollen joints were defined as PD ≥2 with ESR, and GS ≥3 and PD ≥2 with MHAQ. A feasible US-adjusted SDAI examining only clinically involved joints still showed a higher correlation with ESR and MHAQ than SDAI.</p> <p><i>Conclusion</i>: Our composite measure complemented by US only for clinically involved joints is feasible and reliable for monitoring disease activity.</p