Long-Term Continuous Conversion of CO₂ to Formic Acid Using Boron-Doped Diamond Electrodes

The long-term durability of boron-doped diamond electrodes (BDD) used continuously in the electrochemical conversion of CO₂ to formic acid was investigated. Although the Faradaic efficiency (FE) for the production of formic acid decreased with increasing electrolysis time, the FE was easily recovered by electrochemical oxidation of the BDD electrodes in H₂SO₄, Na₂SO₄ or K₂SO₄ solutions. For practical application, the long-term production of formic acid using BDD electrodes can be successfully accomplished just by successive polarity reversal of plus and minus terminals. Furthermore, at a current density of −20 mA cm^–2, the rate of production reached 328 μmol h^–1 cm^–2, which is the highest value ever obtained using plate electrodes. Consequently, we found that BDD electrodes are ideal for industrial application of CO₂ reduction

Rewritable Superhydrophilic−Superhydrophobic Patterns on a Sintered Titanium Dioxide Substrate

This Letter describes a new fabrication process for superhydrophilic−superhydrophobic patterns on a TiO2 surface using a combination of an inkjet technique and the site-selective decomposition of a self-assembled monolayer (SAM) by a photocatalytic reaction under UV irradiation. To induce high surface wettability, we carried out simple calcination of a Ti substrate. The substrate was thus oxidized to titanium oxide and had a vortex-like rough morphology, which was suitable for the formation of wettability patterns. Furthermore, the substrate can be regenerated after elimination of the superhydrophilic−superhydrophobic patterns by the photocatalytic decomposition of TiO2 using UV irradiation, and the patterns are deposited again. The renewed surface that we created had a wettability pattern that was different from the preceding pattern. This process is based on a TiO2 surface and should offer a renewable, resource-saving, and environmentally friendly methodology for the formation of wettability patterns

In Situ Photoconductivity Kinetic Study of Nano-TiO₂ during the Photocatalytic Oxidation of Formic Acid: Effects of New Recombination and Current Doubling

In the present research, in situ photoconductivity (σ) was used to study the electron kinetics of nano-TiO₂ films during photocatalysis of formic acid under UV light irradiation. Some interesting features of the in situ σ were observed: (a) when the light was turned on, the in situ σ showed a relatively slow decrease just after a fast increase; (b) when the light was stopped, the in situ σ decayed much faster than that in pure water; (c) the in situ σ presented an abnormal increase when decaying toa dark value due to the reinjection of electrons to TiO₂ CB. We comprehensively studied the effects of formic acid amounts, UV light intensity, UV light irradiation time, and dark preadsorption time on the in situ σ, indicating the presence of the new recombination and the current-doubling effect. It was seen that the new recombination and the current-doubling effect can be weakened by soft water washing, and the presence of water also is important for the appearance of the new recombination and the current-doubling effect. Combined with the first-principles calculation, it was confirmed that the weakly adsorbed formic acid groups near the TiO₂/water interface should mainly contribute to the new recombination and the current-doubling effect. A kinetic model was proposed to simulate the time dependence of the in situ σ during the formic acid photocatalysis. The simulation shows that the inclusion of the new recombination and the current-doubling effect agrees well with the experimental results. Lastly, the effects of Au deposition on the in situ σ of TiO₂ film during the photocatalysis of formic acid were studied. The interfacial transfer of electrons from TiO₂ to Au can be identified by the in situ σ, which wakens the new recombination and the current-doubling effect

Hybrid Molecular Material Exhibiting Single-Molecule Magnet Behavior and Molecular Conductivity

Two unique materials based on Mn4 single-molecule magnet (SMM) clusters (ST = 9) and integer or non-integer average valent platinum maleonitriledithiolate (mnt2-) complexes, [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}2][Pt(mnt)2]2·2MeCN (1) and [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}4][Pt(mnt)2]2 (2), were synthesized by the material diffusion method and electrochemical oxidation, respectively (hmp- = 2-hydroxymethylpyridinate). 1 and 2 are comprised of four and six [Pt(mnt)2]n- units, respectively, in addition to a common MnII2MnIII2 double-cuboidal unit, [MnII2MnIII2(hmp)6(MeCN)2]4+ (hereinafter [Mn4]4+). Among the [Pt(mnt)2]n- units, two units in 1 and four units in 2 are coordinated with the [Mn4]4+ unit, forming a 1D chain of {−[Mn4]−[Pt(mnt)2]2−} for 1 and a discrete subunit of {[Pt(mnt)2]2−[Mn4]−[Pt(mnt)2]2} for 2. The other two [Pt(mnt)2]n- units, occupying void space of the packing, form a stacking column with the coordinating [Pt(mnt)2]n- units, finally constructing hybrid frames of aggregates consisting of [Mn4]4+ units and [Pt(mnt)2]n- units. Electronic conductivity measurements revealed that 1 is an insulator and 2 is a semiconductor with σ = 0.22 S·cm-1 at room temperature and an activation energy of 136 meV. Detailed magnetic measurements proved that the [Mn4]4+ units in 1 and 2 behave as SMMs with an ST = 9 ground state at low temperatures. There is no significant interaction between [Mn4]4+ units and [Pt(mnt)2]n- units, but interactions between localized spins of [Pt(mnt)2]n- were detected even in 2 at low temperatures where the conductivity is electronically insulated. 2 is the first example of a hybridized material exhibiting SMM behavior and electronic conductivity

Single-Chain Magnet (NEt₄)[Mn₂(5-MeOsalen)₂Fe(CN)₆] Made of Mn^III−Fe^III−Mn^III Trinuclear Single-Molecule Magnet with an <i>S</i>_T = ⁹/₂ Spin Ground State

The cyano-bridged trinuclear compound, (NEt4)[Mn2(salmen)2(MeOH)2Fe(CN)6] (1) (salmen2- = rac-N,N‘-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an ST = 9/2 spin ground state. Its relaxation time (τ) follows an Arrhenius law with τ0 = 2.5 × 10-7 s and Δeff/kB = 14 K. Moreover, below 0.3 K, τ saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt4)[Mn2 (5-MeOsalen)2Fe(CN)6] (2) (5-MeOsalen2- = N,N‘-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [MnIII(SB)−NC−FeIII−CN−MnIII(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (−NC−) and a biphenolate bridge (−(O)2−), connecting MnIII and FeIII ions and the two MnIII ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with gav = 2.03, JMn-Fe/kB = +6.5 K, and J‘/kB = +0.07 K, where J‘ is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (DT/kB = −0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (τ0 = 3.7 × 10-10 s and Δ1/kB = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects (τ‘0 = 3 × 10-8 s and Δ2/kB = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (J‘ and DT) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension

UV/Thermally Driven Rewritable Wettability Patterns on TiO₂−PDMS Composite Films

Composite films of TiO2 and polydimethylsiloxane (PDMS) are prepared by a sol−gel method, cured with UV irradiation, and then treated in hot water to crystallize the TiO2 in the film. The presence of anatase TiO2 contributes to the photoinduced superhydrophilicity of the film under UV irradiation. Contact angle studies reveal that the TiO2−PDMS composite film recovers its original hydrophobic state. Hydrophobic−superhydrophilic patterns are successfully formed on the films. The wettability patterns can be erased by UV irradiation and thermal treatment. New wettability patterns can be reconstructed, demonstrating that the film exhibits rewritable wettability without the need for organic chemicals

Hybrid Molecular Material Exhibiting Single-Molecule Magnet Behavior and Molecular Conductivity

Two unique materials based on Mn4 single-molecule magnet (SMM) clusters (ST = 9) and integer or non-integer average valent platinum maleonitriledithiolate (mnt2-) complexes, [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}2][Pt(mnt)2]2·2MeCN (1) and [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}4][Pt(mnt)2]2 (2), were synthesized by the material diffusion method and electrochemical oxidation, respectively (hmp- = 2-hydroxymethylpyridinate). 1 and 2 are comprised of four and six [Pt(mnt)2]n- units, respectively, in addition to a common MnII2MnIII2 double-cuboidal unit, [MnII2MnIII2(hmp)6(MeCN)2]4+ (hereinafter [Mn4]4+). Among the [Pt(mnt)2]n- units, two units in 1 and four units in 2 are coordinated with the [Mn4]4+ unit, forming a 1D chain of {−[Mn4]−[Pt(mnt)2]2−} for 1 and a discrete subunit of {[Pt(mnt)2]2−[Mn4]−[Pt(mnt)2]2} for 2. The other two [Pt(mnt)2]n- units, occupying void space of the packing, form a stacking column with the coordinating [Pt(mnt)2]n- units, finally constructing hybrid frames of aggregates consisting of [Mn4]4+ units and [Pt(mnt)2]n- units. Electronic conductivity measurements revealed that 1 is an insulator and 2 is a semiconductor with σ = 0.22 S·cm-1 at room temperature and an activation energy of 136 meV. Detailed magnetic measurements proved that the [Mn4]4+ units in 1 and 2 behave as SMMs with an ST = 9 ground state at low temperatures. There is no significant interaction between [Mn4]4+ units and [Pt(mnt)2]n- units, but interactions between localized spins of [Pt(mnt)2]n- were detected even in 2 at low temperatures where the conductivity is electronically insulated. 2 is the first example of a hybridized material exhibiting SMM behavior and electronic conductivity

Rod-Shaped β‑FeOOH Synthesis for Hydrogen Production under Light Irradiation

Renewable energy is spotlighted as a resource to replace fossil fuels, and among the resources, active research on hydrogen energy is ongoing. Various methods have been developed to produce hydrogen energy using photoreduction processes. In this study, we synthesized β-phase iron oxyhydroxide (β-FeOOH) using a hydrothermal method with an optimal synthesis time and investigated its photofunctional properties, including hydrogen production. The obtained samples were characterized and compared with reference data. X-ray powder diffraction results corresponded to the peaks of the reference data. A rod structure was confirmed by scanning electron microscopy, and no impurities were observed. The band-gap energy of β-FeOOH was calculated as 1.8–2.6 eV. A photoreduction process was performed based on a photo-Fenton reaction to produce hydrogen by irradiating ultraviolet (UV) on β-FeOOH. The synthesized β-FeOOH was subjected to UV irradiation for 24 h to produce hydrogen, and we confirmed that hydrogen was successfully produced. The properties of β-FeOOH were evaluated after UV irradiation

Hybrid Molecular Material Exhibiting Single-Molecule Magnet Behavior and Molecular Conductivity

Two unique materials based on Mn4 single-molecule magnet (SMM) clusters (ST = 9) and integer or non-integer average valent platinum maleonitriledithiolate (mnt2-) complexes, [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}2][Pt(mnt)2]2·2MeCN (1) and [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}4][Pt(mnt)2]2 (2), were synthesized by the material diffusion method and electrochemical oxidation, respectively (hmp- = 2-hydroxymethylpyridinate). 1 and 2 are comprised of four and six [Pt(mnt)2]n- units, respectively, in addition to a common MnII2MnIII2 double-cuboidal unit, [MnII2MnIII2(hmp)6(MeCN)2]4+ (hereinafter [Mn4]4+). Among the [Pt(mnt)2]n- units, two units in 1 and four units in 2 are coordinated with the [Mn4]4+ unit, forming a 1D chain of {−[Mn4]−[Pt(mnt)2]2−} for 1 and a discrete subunit of {[Pt(mnt)2]2−[Mn4]−[Pt(mnt)2]2} for 2. The other two [Pt(mnt)2]n- units, occupying void space of the packing, form a stacking column with the coordinating [Pt(mnt)2]n- units, finally constructing hybrid frames of aggregates consisting of [Mn4]4+ units and [Pt(mnt)2]n- units. Electronic conductivity measurements revealed that 1 is an insulator and 2 is a semiconductor with σ = 0.22 S·cm-1 at room temperature and an activation energy of 136 meV. Detailed magnetic measurements proved that the [Mn4]4+ units in 1 and 2 behave as SMMs with an ST = 9 ground state at low temperatures. There is no significant interaction between [Mn4]4+ units and [Pt(mnt)2]n- units, but interactions between localized spins of [Pt(mnt)2]n- were detected even in 2 at low temperatures where the conductivity is electronically insulated. 2 is the first example of a hybridized material exhibiting SMM behavior and electronic conductivity

Single-Chain Magnet (NEt₄)[Mn₂(5-MeOsalen)₂Fe(CN)₆] Made of Mn^III−Fe^III−Mn^III Trinuclear Single-Molecule Magnet with an <i>S</i>_T = ⁹/₂ Spin Ground State

The cyano-bridged trinuclear compound, (NEt4)[Mn2(salmen)2(MeOH)2Fe(CN)6] (1) (salmen2- = rac-N,N‘-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an ST = 9/2 spin ground state. Its relaxation time (τ) follows an Arrhenius law with τ0 = 2.5 × 10-7 s and Δeff/kB = 14 K. Moreover, below 0.3 K, τ saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt4)[Mn2 (5-MeOsalen)2Fe(CN)6] (2) (5-MeOsalen2- = N,N‘-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [MnIII(SB)−NC−FeIII−CN−MnIII(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (−NC−) and a biphenolate bridge (−(O)2−), connecting MnIII and FeIII ions and the two MnIII ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with gav = 2.03, JMn-Fe/kB = +6.5 K, and J‘/kB = +0.07 K, where J‘ is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (DT/kB = −0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (τ0 = 3.7 × 10-10 s and Δ1/kB = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects (τ‘0 = 3 × 10-8 s and Δ2/kB = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (J‘ and DT) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension