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The synthesis of spiropyran dyes exhibiting solvent-driven isomerization even in the dark condition is an important subject for the design of optical materials. A conventional synthesis strategy involves the conjugation of indoline moieties with electron-deficient aromatic moieties. Herein, we report that a spiropyran conjugated with a hydroxynaphthalene moiety (1) is a new member exhibiting solvent-driven isomerization, even bearing an electron-donating −OH moiety. The dye exists as a colorless spirocyclic (SP) form in nonpolar media. It, however, shows a blue color in polar media, especially in aqueous media, due to the formation of ring-opened merocyanine (MC) forms, where the isomerization terminates in 10 s even at room temperature. The spontaneous SP → MC isomerization originates from the MC forms stabilized by the highly delocalized π-electrons on the hydroxynaphthalene moiety. The solvation in polar media and the hydrogen bonding interaction with water molecules decrease the ground-state energy of the MC forms, triggering spontaneous isomerization. The dye exhibits two MC absorption bands assigned to the trans–trans–cis (TTC) and cis–trans–cis (CTC) isomers. The absorbance of the CTC band increases more significantly with an increase in the water content, and the increase exhibits a linear relationship with a hydrogen-bond donor acidity of solvents. The phenolate oxygen of the CTC form has larger hydrogen-bond acceptor basicity, resulting in stronger stabilization by the water molecule.

The generation of hydrogen peroxide (H2O2) from water and dioxygen by sunlight-driven heterogeneous photocatalysis is a promising method for the artificial photosynthesis of a liquid solar fuel. We previously found that resorcinol-formaldehyde (RF) resin powders prepared by high-temperature hydrothermal synthesis act as highly active semiconductor photocatalysts for H2O2 generation. Herein, we report that RF resin powders doped with poly(3-hexylthiophene-2,5-diyl) (RF/P3HT) exhibit enhanced photocatalytic activities. The highly dispersed P3HT within the resin particles created charge transfer complexes with the conduction band of the resin via electron donation, facilitating efficient transfer of the photogenerated conduction band electrons through P3HT. This enhanced charge separation promoted efficient water oxidation and O2 reduction. The solar-to-chemical conversion efficiency for H2O2 generation on the RF/P3HT resin in water under simulated sunlight irradiation with atmospheric pressure of O2 was ∼1.0%, which is the highest efficiency reported for powder catalysts in artificial photosynthesis.

Hydrogen peroxide (H2O2) has received increasing attention as an energy carrier. To achieve a sustainable energy society, photocatalytic H2O2 splitting (H2O2 (l) → H2 (g) + O2 (g); ΔG° = + 131 kJ mol−1) is a desirable reaction for on-site H2 generation. However, this reaction has not been reported because conventional photocatalysis decomposes H2O2 by disproportionation (H2O2 (l) → H2O (l) + 1/2O2 (g); ΔG° = −117 kJ mol−1) and by promoting H2O2 reduction instead of H+ reduction. Here we report the successful example of H2O2 splitting. Visible light irradiation of a graphitic carbon nitride loaded with graphene quantum dots as co-catalysts (GQDs/g-C3N4) in a H2O2 solution containing phosphoric acid (H3PO4) produces H2. H3PO4 associates with H2O2 via hydrogen bonding, and this stabilization of H2O2 suppresses its reduction, thus promoting H+ reduction. The all-organic photosystem with H3PO4 as a stabilizer may provide a basis of photocatalytic H2O2 splitting., While H2 can serve as a renewable fuel, its large scale production, storage, and transport are challenging. Here, authors show H2O2 to serve as a potential energy carrier via the photocatalytic production of H2 from stabilized H2O2 solutions and metal-free catalysts.

Ammonia is an indispensable chemical. Photocatalytic NH3 production via dinitrogen fixation using water by sunlight illumination under ambient conditions is a promising strategy, although previousl...

Photocatalytic splitting of aqueous NH3 into H2 and N2 on semiconductor powders is an important reaction toward on-site production of H2 from NH3, a promising hydrogen carrier for sustainable energ...

Ternary polymer blends of polyamide 6 (PA6), polycarbonate (PC), and phenol novolac (PN) were prepared by a melt mixing process. PN catalyzes the exchange reaction between PA6 and PC and promotes the generation of a copolymer, which improves the compatibility. Herein, the catalytic effect of PN was experimentally supported by an increase in torque during melt mixing and mass signals from copolymer fragments detected by mass spectroscopy. The characteristic behavior of the exchange reaction changed significantly with increasing PN amount. The promotion of in situ copolymer generation led to the formation of ternary blends, which show homogeneous morphologies and superior mechanical properties, such as high stiffness and good elongation, compared with those of the binary blends without PN. Using excess PN causes some drawbacks like brittleness due to the decomposition of the PC component. A loading amount of 1–3 wt % PN was suitable for achieving a ternary blend with improved properties.

Ternary polymer blends comprising miscible and immiscible components are examined to improve the mechanical properties of polyamide 6 (PA6) under humid and high-temperature conditions. Miscible polymers increase the glass transition temperature (Tg), owing to their strong inter-molecular interactions, while phase-separated immiscible polymers reinforce the physical properties of PA6 as filler materials. Ternary blends exhibit these combined miscible and immiscible component contributions. Thus, in this study, ternary blends comprising PA6, polyethylene terephthalate (PET, immiscible component), and phenol novolac (PN, miscible component) are prepared by melt mixing. The PA6 stiffness in the water-absorbed state is reinforced by PET. Moreover, the proposed PA6/PET/PN ternary blends exhibit higher Tg values and lower water absorption rates than those of the PA6/PET binary blend, owing to the PN contribution. The PET and PN contributions are achieved independently and can be controlled via the composition ratios of the component polymers. Multifaceted property tailoring is thus demonstrated.

Au nanoparticles loaded on semiconductor TiO2 absorb visible light due to their surface plasmon resonance (SPR) and inject the photogenerated hot electrons (ehot-) into the conduction band of TiO2. The separated charges promote oxidation and reduction reactions. The step that determines the rate of the plasmonic photocatalysis on the Au/TiO2 system is the ehot- injection through the Schottky barrier created at the Au-TiO2 interface. In the present work, niobium (Nb5+) oxide species were doped at the Au-TiO2 interface by loading Nb5+ onto the TiO2 surface followed by deposition of Au particles (2 wt % of TiO2). Visible light irradiation of the Au/Nb5+/TiO2 catalysts promotes aerobic oxidation of alcohols with much higher efficiency than that of undoped Au/TiO2. Lewis acidity of the Nb5+ species located at the interface cancels the negative charges of Au and creates a barrier with a narrower depletion layer, promoting tunneling ehot- injection. Efficiency of the ehot- injection depends on the amount of Nb5+ doped. Loading small amounts of Nb5+ (∼0.1 wt % of TiO2) creates mononuclear NbO4 species and shows large activity enhancement. In contrast, loading larger amounts of Nb5+ creates aggregated polynuclear Nb2O5 species. They decrease the electron density of Au particles and weaken their SPR absorption. This suppresses the ehot- generation on the Au particles and decreases the activity of plasmonic photocatalysis.

The photocatalytic generation of hydrogen peroxide from water and dioxygen (H2O + 1/2O2 → H2O2, ΔG° = +117 kJ mol–1) under sunlight is a promising strategy for the artificial photosynthesis of a liquid fuel. We had previously found that resorcinol–formaldehyde (RF) resin powders prepared by the base-catalysed high-temperature hydrothermal method act as semiconductor photocatalysts for H2O2 generation. Herein, we report that RF resins prepared by the acid-catalysed high-temperature hydrothermal method (~523 K) using common acids at pH < 4 exhibit enhanced photocatalytic activity. The base- and acid-catalysed methods both produce methylene- and methine-bridged resins consisting of π-conjugated and π-stacked benzenoid–quinoid donor–acceptor resorcinol units. The acidic conditions result in the resins with a lower bandgap (1.7 eV) and higher conductivity because the lower-degree of crosslinking creates a strongly π-stacked architecture. The irradiation of the RF-acid resins with simulated sunlight in water with atmospheric-pressure O2 generates H2O2 at a solar-to-chemical conversion efficiency of 0.7%, which is the highest efficiency ever reported for powder catalysts used in artificial photosynthesis. Low-bandgap polymers hold great potential for photocatalytic generation of hydrogen peroxide, but increasing catalytic activity remains challenging. Here, a solar-to-chemical conversion efficiency of 0.7 % is reached for a resorcinol-formaldehyde resin powder prepared via acid-catalyzed high-temperature hydrothermal synthesis.

Electrospinning is a widely used production method for nanoscale fine polymer fiber fabrics. An ultrafine fiber made of polymers such as polyvinylpyrrolidone (PVP) polyacrylic acid (PAA) has immense potential for applications in air filters, batteries, and biosensors. However, producing fabrics with long uniformly distributed ultrafine fibers of a mean diameter below ~ 200 nm is still a challenge, because such elongated-ultrafine fibers tend to break into beads before they reach the collector. Here, we exploits the thixotropy of the solution given by the addition of 2,2,6,6-tetramethylpiperidin-1-oxyl-oxidized cellulose nanofibers to recover the solution viscosity for stabilizing the electrostatically elongated nanofibers, whereby the solution is smooth in the syringe needle owing to the shear force but regain its original viscosity after being freed from electrostatic force. Using this method, we successfully fabricated a non-woven ultrafine-long nanofiber made of PVP and PAA with a mean diameter as low as ~ 90 nm with a negligible number of beads.

Ammonia (NH3), which is an indispensable chemical, is produced by the Haber–Bosch process using H2 and N2 under severe reaction conditions. Although photocatalytic N2 fixation with water under ambient conditions is ideal, all previously reported catalysts show low efficiency. Here, we report that a metal-free organic semiconductor could provide a new basis for photocatalytic N2 fixation. We show that phosphorus-doped carbon nitride containing surface nitrogen vacancies (PCN-V), prepared by simple thermal condensation of the precursors under H2, produces NH3 from N2 with water under visible light irradiation. The doped P atoms promote water oxidation by the photoformed valence-band holes, and the N vacancies promote N2 reduction by the conduction-band electrons. These phenomena facilitate efficient N2 fixation with a solar-to-chemical conversion (SCC) efficiency of 0.1%, which is comparable to the average solar-to-biomass conversion efficiency of natural photosynthesis by typical plants. Thus, this metal-f...

Polymer blends of polyamide 6 (PA6) and phenol novolac (PN) were prepared by melt mixing. Up to 30 wt% of high molecular weight PN (HPN) or low molecular weight PN (LPN) was blended with PA6, and the physical and mechanical properties were examined. The water absorption of PA6 is inhibited by PN, and this effect is independent of the molecular weight of PN. PA6 and PN are miscible, and their blends show a single glass transition temperature ( T g) that is higher than that of PA6. HPN can enhance the T g of PA6 more efficiently than LPN because of its high T g. PA6 and the PA6/LPN blend after immersion in water had lower-than-room-temperature T gs transitioning to rubbery states. In contrast, the PA6/HPN blend after immersion in water had a higher-than-room-temperature T g. The PA6/HPN blend in water has excellent mechanical properties in its glassy state compared to those of PA6 in the dry state. Thus, the PA6/HPN blend can be used to broaden the applications of PA6, especially in humid conditions.

Visible-light irradiation (λ < 600 nm) of commercially-available CdS in alcohol successfully promotes hydrogenation of azobenzene to hydrazobenzene with more than 95% selectivity. This is promoted by strong adsorption of azobenzene to the photoformed zerovalent Cd species adjacent to the surface S vacancies on CdS; this leads to efficient reduction to hydrazobenzene.

Transparent glass fiber composites were prepared with a refractive-index-adjustable thermoplastic blend. The opacity of a polymer blend is affected by the phase separation and crystallization properties. Polyamide 6 (PA6)/poly (m-xylene adipamide) (MXD6) blends are intrinsically miscible and transparent in the molten state; further, crystallization is suppressed by polymer chain disordering induced by in-situ transamidation. Thus, the transparency of the molten state was maintained after a sufficient period of melt-mixing. The refractive index was adjusted to that of the glass fiber reinforcement by altering the PA6/MXD6 blend ratio. Injection-molded glass fiber composites of PA6/MXD6 had good transparency and mechanical properties.

Generating hydrogen peroxide (H2O2) from water and dioxygen (O2) by photocatalysis is one ideal artificial photosynthesis for solar fuel production. Several early reported powdered photocatalysts, however, produce small amounts of H2O2 ( 420 nm) in pure water with O2, successfully produces millimolar levels of H2O2 via water oxidation by valence band holes and selective two-electron reduction of O2 by conduction band electrons. The incorporation of triply branched MTI units creates a condensed melem layer. This facilitates efficient intra- and interlayer transfer of photogenerated charge carriers and shows high electrical conductivity. The solar-to-chemical conversion efficiency for H2O2 production on the catalyst is 0.18%, which is higher than that of natural photosynthesis (∼0.1%) ...

Ammonia (NH3) is an essential chemical in modern society, currently manufactured via the Haber–Bosch process with H2 and N2 under extremely high pressure (>200 bar) and high-temperature conditions (>673 K). Toxic nitrate anion (NO3–) contained in wastewater is one potential nitrogen source. Selective NO3–-to-NH3 transformation via eight-electron reduction, if promoted at atmospheric pressure and room temperature, may become a powerful recycling process for NH3 production. Several photocatalytic systems have been proposed, but many of them produce nitrogen gas (N2) via five-electron reduction of NO3–. Here, we report that unmodified TiO2, when photoexcited by ultraviolet (UV) light (λ > 300 nm) with formic acid (HCOOH) as an electron donor, promotes selective NO3–-to-NH3 reduction with 97% selectivity. Surface defects and Lewis acid sites of TiO2 behave as reduction sites for NO3–. The surface defect selectively promotes eight-electron reduction (NH3 formation), while the Lewis acid site promotes nonselect...

Photocatalytic N2 reduction with water by sunlight irradiation is a challenging issue toward sustainable energy society, but previously reported photocatalysts had suffered from low stability and l...

The hypochlorite anion (OCl−), a reactive oxygen species (ROS), is an important microbicidal agent in the immune system. Accurate and selective detection of OCl− in environmental and biological samples by a fluorescent molecular sensor is an important subject. All previously reported sensors, however, have suffered from tedious multi-step synthesis for the sensors and the use of large amounts of organic solvents for the analysis. Herein, we report that a coumarin–dihydroperimidine dye prepared by facile condensation behaves as a fluorescent sensor for OCl− in 99% water. The sensor exhibits weak fluorescence, but OCl−-selective dehydrogenation of its dihydroperimidine unit creates a strong blue fluorescence. This turn-on fluorescence response facilitates selective and sensitive detection of OCl− in the physiological pH range. Ab initio calculation revealed that the fluorescence enhancement by OCl− is triggered by intramolecular proton transfer from the coumarin –OH to the imine nitrogen of the formed perimidine moiety.

Carbon fiber reinforced thermoplastics (CFRTPs) with superior mechanical properties and hygrothermal resistance were fabricated using a strategically designed ternary polymer blend of polyamide 6 (PA6), polyethylene terephthalate (PET), and phenol novolac (PN). The polymer blend was designed to improve the hygrothermal stability of PA6 while retaining good adhesivity to carbon fiber. The miscible and immiscible components in the blend (PN and PET, respectively) have different contributions that act cooperatively to improve the hygrothermal resistance of PA6. The interfacial strength between the ternary polymer blend and carbon fiber is as high as that for PA6 because all components in the polymer matrix include polar functional groups. CFRTPs having the ternary blend as the polymer matrix exhibit superior stiffness under hygrothermal conditions than a conventional PA6-matrix CFRTP.

Colloidal suspensions of gold nanoparticles (AuNPs) in water can be prepared by heating water containing HAuCl4 with citric acid as reductant and surface stabilizing reagent. This thermal reduction method, however, promotes aggregation of the formed AuNPs, resulting in bimodal distribution of AuNPs. Here we report that UV (254 nm) irradiation of water containing HAuCl4 with citric acid at room temperature successfully reduces HAuCl4 and produces monodispersed AuNPs, while suppressing aggregation of the formed AuNPs. Changing the intensity of UV light or the amount of citric acid added successfully produces AuNPs with tunable sizes and narrow size distributions.

Tafenoquine (TQ), a fluorescent antimalarial drug, was used as a receptor for the fluorometric detection of hypochlorite (OCl−). TQ itself exhibits a strong fluorescence at 476 nm, but OCl−-selective cyclization of its pentan-1,4-diamine moiety creates a blue-shifted fluorescence at 361 nm. This ratiometric response facilitates rapid, selective, and sensitive detection of OCl− in aqueous media with physiological pH. This response is also applicable to a simple test kit analysis and allows fluorometric OCl− imaging in living cells.

Quantitative determination of toxic cyanide anions (CN−) in biological samples is an important subject. We synthesized a naphthalimide–coumarin conjugate with a simple imine linker (1), which behaves as a fluorescent receptor for ratiometric quantification of CN−. It exhibits green naphthalimide fluorescence at 533 nm, originating from the excited-state intramolecular charge transfer (ESICT) from coumarin to naphthalimide fluorophores. Selective CN− addition to the imine linker affords an α-amino nitrile product. This suppresses ESICT and creates coumarin fluorescence at 444 nm and naphthalimide fluorescence at 533 nm originating from direct photoexcitation of the respective fluorophores. The emission intensity at 533 nm is maintained upon CN− addition and can be used as an internal standard for analysis. This ratiometric response enables self-calibrating CN− quantification based on the intensities of two emissions in solution and in cells. This facilitates rapid (within 3 min), selective, and sensitive ratiometric detection of very low levels of CN− (>1.8 μM).

Partial oxidation of cyclohexane (CHA) to cyclohexanone (CHA-one) with molecular oxygen (O2) is one of the most important reactions. Photocatalytic oxidation has been studied extensively with TiO2-based catalysts. Their CHA-one selectivities are, however, insufficient because the formed CHA-one is subsequently decomposed by photocatalysis involving the reaction with superoxide anion (O2●–) produced by one-electron reduction of O2 on TiO2. Here we report that TiO2, when hybridized with reduced graphene oxide (rGO), catalyzes photooxidation of CHA to CHA-one with enhanced activity and selectivity under UV light (λ > 300 nm). The TiO2/rGO hybrids produce CHA-one with twice the amount formed on bare TiO2 with much higher selectivity (>80%) than that on bare TiO2 (ca. 60%). The conduction band electrons photoformed on TiO2 are transferred to rGO, promoting efficient charge separation and enhanced photocatalytic cycles. The trapped electrons on rGO selectively promote two-electron reduction of O2 and suppress o...

The design of a safe and sustainable process for the synthesis of hydrogen peroxide (H2O2) is a very important subject from the viewpoint of green chemistry. Photocatalytic H2O2 production with earth-abundant water and molecular oxygen (O2) as resources is an ideal process. A successful system based on an organic semiconductor has been proposed; however, it suffers from poor photostability. Here we report an inorganic photocatalyst for H2O2 synthesis. Visible light irradiation (λ >420 nm) of the semiconductor BiVO4 loaded with Au nanoparticles (Au/BiVO4) in pure water with O2 successfully produces H2O2. The bottom of the BiVO4 conduction band (0.02 V vs NHE, pH 0) is more positive than the one-electron reduction potential of O2 (−0.13 V) while more negative than the two-electron reduction potential of O2 (0.68 V). This thus suppresses one-electron reduction of O2 and selectively promotes two-electron reduction of O2, resulting in efficient H2O2 formation.

A naphthalimide–dicyanoisophorone conjugate (1) was synthesized and used as a chemodosimeter for fluorometric and colorimetric detection of hypochlorous acid (HClO) and hypochlorite (OCl–) in aqueous media. This molecule shows a strong reddish-purple color and a weak fluorescence, but HClO/OCl–-selective oxidative decomposition of the dicyanoisophorone moiety promotes a color fading and a fluorescence enhancement. Ab initio calculation revealed that these responses to HClO/OCl– originate from the suppression of intramolecular electron transfer from the photoexcited naphthalimide moiety by the decomposition of the dicyanoisophorone moiety. These colorimetric and fluorometric responses facilitate relatively rapid (∼5 min), selective, and sensitive detection of HClO/OCl– as low as ∼1.3 μM under physiological conditions.

Hypochlorite anion (ClO&minus, ) is a widely-used disinfectant and a microbicidal agent in the immune system. Accurate detection of ClO&minus, in environmental and biological samples by simply prepared chemosensors/chemodosimeters is important. Herein, we report that a naphthalimide&ndash, sulfonylhydrazine conjugate with an imine (C=N) linker, prepared via simple condensation, acts as an effective fluorescent chemodosimeter for ClO&minus, The molecule exhibits a weak emission, but ClO&minus, selective cleavage of its C = N bond creates a strong green emission. Ab initio calculation showed that the emission enhancement by ClO&minus, originates from the suppression of intramolecular electron transfer from the photoexcited naphthalimide through the C = N linker. This response enables selective and sensitive detection of ClO&minus, at physiological pH range (7&ndash, 9) and allows fluorometric ClO&minus, imaging in the presence of cells.

Artificial photosynthesis is a critical challenge in moving towards a sustainable energy future. Photocatalytic generation of hydrogen peroxide from water and dioxygen (H2O + $$\frac{1}{2}$$ O2 → H2O2, ΔG° = 117 kJ mol–1) by sunlight is a promising strategy for artificial photosynthesis because H2O2 is a storable and transportable fuel that can be used directly for electricity generation. All previously reported powder photocatalysts, however, have suffered from low efficiency in H2O2 generation. Here we report that resorcinol–formaldehyde resins, widely used inexpensive polymers, act as efficient semiconductor photocatalysts to provide a new basis for H2O2 generation. Simple high-temperature hydrothermal synthesis (~523 K) produces low-bandgap resorcinol–formaldehyde resins comprising π-conjugated and π-stacked benzenoid–quinoid donor–acceptor resorcinol couples. The resins absorb broad-wavelength light up to 700 nm and catalyse water oxidation and O2 reduction by the photogenerated charges. Simulated sunlight irradiation of the resins stably generates H2O2 with more than 0.5% solar-to-chemical conversion efficiency. Therefore, this metal-free system shows significant potential as a new artificial photosynthesis system. Generation of hydrogen peroxide from water and dioxygen is promising for artificial photosynthesis but photocatalysts suffer from low efficiency. Resorcinol–formaldehyde resins exhibit stable H2O2 generation with more than 0.5% solar-to-chemical conversion efficiency.

We synthesized a pyrylium–coumarin dyad (1) and used it for colorimetric detection of cyanide anions (CN−) in aqueous media. The receptor itself exhibits a long-wavelength absorption band at 643 nm due to the strong intramolecular charge transfer (ICT) from the diethylaminocoumarin to the pyrylium moiety. Selective nucleophilic addition of CN− to the pyrylium ring triggers the ring cleavage rapidly (within 8 min). This suppresses the ICT and decreases the intensity of the 643 nm band, along with an appearance of a new shorter-wavelength band at 472 nm assigned to the π,π* transition of the diethylaminocoumarin moiety. This drastic absorption change (643 nm → 472 nm) facilitates ratiometric detection of CN− based on the intensities of these two absorption bands in the visible region and successfully detects CN− as low as 8 μM.

We synthesized an indanedione–coumarin dyad (1) and used it as an off–on type fluorescent receptor for rapid, selective, and sensitive detection of CN− in an aqueous mixture. The receptor itself shows very weak fluorescence from the coumarin moiety due to the photoinduced electron transfer (PET) from the photoexcited coumarin to the indanedione moiety. Selective nucleophilic addition of CN− to the β-carbon of the receptor suppresses the PET and results in strong fluorescence enhancement. The reaction mechanism was fully confirmed by 1H, 13C NMR, Job's plot, and FAB-MS analysis. The receptor successfully detects CN− as low as 25 μM within 20 min.

Photocatalytic production of hydrogen peroxide (H2O2) from ethanol (EtOH) and molecular oxygen (O2) was carried out by visible light irradiation (λ > 420 nm) of mesoporous graphitic carbon nitride (GCN) catalysts with different surface areas prepared by silica-templated thermal polymerization of cyanamide. On these catalysts, the photoformed positive hole oxidize EtOH and the conduction band electrons localized at the 1,4-positions of the melem unit promote two-electron reduction of O2 (H2O2 formation). The GCN catalysts with 56 and 160 m2 g–1 surface areas exhibit higher activity for H2O2 production than the catalyst prepared without silica template (surface area: 10 m2 g–1), but a further increase in the surface area (228 m2 g–1) decreases the activity. In addition, the selectivity for H2O2 formation significantly decreases with an increase in the surface area. The mesoporous GCN with larger surface areas inherently contain a larger number of primary amine moieties at the surface of mesopores. These def...

A coumarin–imine–quinoxaline linkage designed based on the Strecker reaction selectively exhibits blue fluorescence on the addition of CN− to an imine moiety at neutral pH. The receptor facilitates rapid (within 5 min), selective, and sensitive (detection limit: 1.4 µM) detection of CN−.

Photoirradiation (λ > 300 nm) of TiO2 loaded with Pd nanoparticles (ca. 2 wt%, 5 nm diameter) in water containing alcohols and azobenzene derivatives at room temperature successfully produces the corresponding secondary amines with high yields. This is facilitated via consecutive photocatalytic and catalytic reactions: (i) photocatalytic oxidation of alcohols (aldehyde formation) and reduction of azobenzenes (aniline formation); (ii) catalytic condensation of the formed aldehydes with anilines on the TiO2 surface (imine formation); and (iii) photocatalytic hydrogenation of the formed imines (secondary amine formation). This catalytic system successfully produces several kinds of secondary amines with >80% yields.

We synthesized an indolium–coumarin dyad (1) and its derivatives with –Cl (2), –N(CH3)2 (3), or –NO2 (4) substituent, and used them for fluorometric detection of cyanide anions (CN(-)) in aqueous media. All of the dyads exhibit fluorescence enhancement by CN(-) via a nucleophilic interaction of CN(-) with the indolium carbon atoms. Their fluorescence response and selectivity to CN(-), however, depend strongly on the substituents. Ab initio calculation and kinetic analysis were performed to verify the behaviors. Substitution of electron-withdrawing groups (2 and 4) increases the electrophilicity of the indolium carbon. This decreases the activation enthalpy for the nucleophilic interaction with CN(-) and facilitates rapid CN(-) sensing. Compound 4 with very high electrophilicity, however, also promotes nucleophilic interaction with OH(-) in the solution, resulting in decreased CN(-) selectivity. As a result of this, the –Cl-substituted compound 2 containing the indolium carbon with appropriate electrophilicity facilitates rapid (within 1 min) and selective CN(-) detection.

Photoreductive synthesis of colloidal gold nanoparticles (AuNPs) from Au3+ is one important process for nanoprocessing. Several methods have been proposed; however, there is no report of a method capable of producing AuNPs with inexpensive reagents acting as both reductant and surface stabilizer, promoted solely under photoirradiation. We found that UV irradiation of water with Au3+ and benzoic acid successfully produces monodispersed AuNPs, where thermal reduction does not occur in the dark condition even at elevated temperatures. Photoexcitation of a benzoate–Au3+ complex reduces Au3+ while oxidizing benzoic acid. The benzoic acid molecules are adsorbed on the AuNPs and act as surface stabilizers. Change in light intensity and benzoic acid amount successfully creates AuNPs with controllable sizes. The obtained AuNPs can easily be redispersed in an organic solvent or loaded onto a solid support by simple treatments.

Ammonia (NH3) is an essential chemical in modern society. It is currently manufactured by the Haber–Bosch process using H2 and N2 under extremely high-pressure (>200 bar) and high-temperature (>673 K) conditions. Photocatalytic NH3 production from water and N2 at atmospheric pressure and room temperature is ideal. Several semiconductor photocatalysts have been proposed, but all suffer from low efficiency. Here we report that a commercially available TiO2 with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N2, successfully produces NH3. The active sites for N2 reduction are the Ti3+ species on the oxygen vacancies. These species act as adsorption sites for N2 and trapping sites for the photoformed conduction band electrons. These properties therefore promote efficient reduction of N2 to NH3. The solar-to-chemical energy conversion efficiency is 0.02%, which is the highest efficiency among the early reported photocatalytic systems. This noble-metal-free TiO2 ...

Platinum (Pt) nanoparticles with4 nm diameter loaded on graphitic carbon nitride (g-C3N4) by reduction at 673 K behave as efficient co-catalysts for photocatalytic hydrogen evolution under visible light (λ420 nm). This is achieved by strong Pt-support interaction due to the high temperature treatment, which facilitates efficient transfer of photoformed conduction band electrons on g-C3N4 to Pt particles.

Cyanine dyes with indolium-coumarin linkages exhibit selective fluorescence enhancement for cyanide anions (CN(-)) via the nucleophilic interaction of CN(-) with their indolium carbon atoms. This facilitates rapid (detection time: 1 min) and sensitive (detection limit: 0.4 μM) sensing of CN(-) in aqueous media.

Visible light irradiation (λ > 450 nm) of Pt nanoparticles supported on Degussa P25 TiO2 (Pt/P25 catalyst) promotes efficient and selective aerobic oxidation of aniline to nitrosobenzene. This is facilicated via the interband excitation of Pt atoms by visible light followed by the transfer of activated electrons to the TiO2 conduction band. The positive charges formed on the Pt surface oxidize substrates, and the conduction band electrons reduce O2, promoting photocatalytic cycles. The high activity of Pt/P25 is due to the high electron density of Pt particles. They behave as Lewis base sites for reductive deprotonation of aniline, thus promoting efficient aniline oxidation. The Pt/P25 catalyst, when photoirradiated at a low temperature (∼283 K), suppresses subsequent condensation of aniline and the formed nitrosobenzene, successfully producing nitrosobenzene with a very high selectivity (90%).

UV or visible light irradiation of gold nanoparticles (AuNPs) modified with a thiol-terminated spiropyran dye promotes reversible aggregation or dispersion of AuNPs. This is facilitated by the electrostatic repulsion/attraction between the AuNPs controlled by the ring-opening/closing photoisomerization of the surface dyes. This photochemical method successfully produces aggregates of AuNPs with tunable sizes (20–340 nm) and narrow size distributions (standard deviation

Catalytic deoxygenation of epoxides into the corresponding alkenes is a very important reaction in organic synthesis. Early reported systems, however, require noble metals, high reaction temperatures (>373 K), or toxic reducing agents. Here, we report a noble-metal-free heterogeneous catalytic system driven with alcohol as a reducing agent at room temperature. Photoirradiation (λ

Fully bio-based polyamide 11 (PA11) and poly(vinylcatechol) (PVCa) blends prepared by melt mixing demonstrate thermodynamic miscibility and excellent engineering properties. The glass transition temperature (Tg) of PA11 increases upon blending with PVCa; an 85/15 wt% PA11/PVCa blend exhibits a Tg 23–26 °C higher than that of PA11 devoid of additives. Morphological observations revealed that the PA11/PVCa blends do not phase-separate, confirming the homogeneity of PA11 and PVCa. Good chemical resistance of the PA11/PVCa blends was confirmed, with the blends resisting morphological changes even after immersion in methanol, which is a good solvent for PVCa. Tensile testing revealed that the PA11/PVCa blends have higher moduli and strengths than PA11. A PA11/nonpolar polystyrene blend was also examined by the same experimental procedure, which revealed that strong hydrogen bonding between PA11 and PVCa is the primary reason for the miscibility and excellent performance of PA11/PVCa blends.

Visible light irradiation (λ450 nm) of Pt-Cu bimetallic alloy nanoparticles (~3-5 nm) supported on anatase TiO2 efficiently promotes aerobic oxidation. This is facilicated via the interband excitation of Pt atoms by visible light followed by the transfer of activated electrons to the anatase conduction band. The positive charges formed on the nanoparticles oxidize substrates, and the conduction band electrons reduce molecular oxygen, promoting photocatalytic cycles. The apparent quantum yield for the reaction on the Pt-Cu alloy catalyst is ~17% under irradiation of 550 nm monochromatic light, which is much higher than that obtained on the monometallic Pt catalyst (~7%). Cu alloying with Pt decreases the work function of nanoparticles and decreases the height of the Schottky barrier created at the nanoparticle/anatase heterojunction. This promotes efficient electron transfer from the photoactivated nanoparticles to anatase, resulting in enhanced photocatalytic activity. The Pt-Cu alloy catalyst is successfully activated by sunlight and enables efficient and selective aerobic oxidation of alcohols at ambient temperature.

We report that the rutile crystallites, isolated from Degussa (Evonik) P25 TiO2 by a hydrofluoric acid treatment, behave as a highly efficient photocatalyst for hydrogenation of nitroaromatics. Photoirradiation (λ >300 nm) of the isolated rutile particles with alcohol as a hydrogen source successfully promotes chemoselective hydrogenation of nitroaromatics to anilines, with an activity higher than that of commercially available rutile TiO2. The high activity of the isolated rutile particles is due to the specific distribution of structural defects (oxygen vacancy sites) on the particles. These particles contain a relatively small number of inner defects behaving as recombination centers for photoformed electron (e–) and positive hole (h+) pairs, and a relatively large number of surface defects behaving as reduction sites for nitroaromatics. Photoexcitation of the isolated particles therefore promotes efficient charge separation between e– and h+, and facilitates rapid reduction of nitroaromatics adsorbed ...

Photocatalytic production of hydrogen peroxide (H2O2) on semiconductor catalysts with alcohol as a hydrogen source and molecular oxygen (O2) as an oxygen source has attracted much attention as a potential method for safe H2O2 synthesis, because the reaction can be carried out without the use of explosive H2/O2 mixed gases. Early reported photocatalytic systems with aliphatic alcohol as a hydrogen source, however, produce only a few millimolar levels of H2O2. We found that benzylic alcohols, when used as a hydrogen source for photoreaction in water with titanium dioxide (TiO2) photocatalyst, produce a very high concentration of H2O2 (ca. 40 mM). Raman spectroscopy and electron spin resonance analysis revealed that the enhanced H2O2 formation is due to the efficient formation of side-on coordinated peroxo species on the photoactivated TiO2 surface, via the reaction of benzylic alcohol and O2. The peroxo species is readily transformed to H2O2, thus facilitating highly efficient H2O2 production.

A spiropyran derivative containing a simple NO bidentate ligand (2) was synthesized. The ligand acts as a colorimetric chemodosimeter for selective Cu(2+) detection in aqueous media. The ligand, even when treated at elevated temperature (60 °C), exists as a spirocyclic form and shows almost no absorption in the visible region. This is because the electron donation by an amine substituent suppresses spirocycle-opening. Treatment of the solution with Cu(2+) at 60 °C, however, creates a strong absorption at 450-650 nm, whereas other metal cations do not promote spectral change. IR, NMR, and ab initio calculation revealed that Cu(2+) is coordinated with two 2 ligands and produces 1:2 Cu(2+)-amine complex intermediately. This is converted to the 1:2 Cu(+)-imine complex via oxidative dehydrogenation of amine moieties, along with the reduction of Cu(2+). The formation of the imine complex decreases the electron density of nitrogen atoms and weakens the electron donation ability. This thus promotes thermal spirocycle opening and facilitates coloration of the solution.

TiO2 loaded with Pd particles (Pd/TiO2), when photoirradiated at λ > 300 nm in alcohol containing primary amine, efficiently promotes N-monoalkylation of amine with alcohol, producing the corresponding secondary amine with almost quantitative yields. This occurs via tandem photocatalytic and catalytic reactions: (i) Pd-assisted alcohol oxidation on the photoactivated TiO2, (ii) condensation of the formed aldehyde with amine on the TiO2 surface, and (iii) hydrogenation of the formed imine by the surface H atoms on the Pd particles. The rate-determining step is the imine hydrogenation, and the reaction depends strongly on the size of the Pd particles. The catalyst with 0.3 wt % Pd, containing 2–2.5 nm Pd particles, shows the highest activity for imine hydrogenation, and smaller or larger Pd particles are inefficient. Calculations of the number of surface Pd atoms based on the cuboctahedron particle model revealed that the Pd atoms on the triangle site of Pd particles are the active site for hydrogenation. L...

Solar-to-chemical energy conversion is a challenging subject for renewable energy storage. In the past 40 years, overall water splitting into H2 and O2 by semiconductor photocatalysis has been studied extensively; however, they need noble metals and extreme care to avoid explosion of the mixed gases. Here we report that generating hydrogen peroxide (H2O2) from water and O2 by organic semiconductor photocatalysts could provide a new basis for clean energy storage without metal and explosion risk. We found that carbon nitride-aromatic diimide-graphene nanohybrids prepared by simple hydrothermal-calcination procedure produce H2O2 from pure water and O2 under visible light (λ420 nm). Photoexcitation of the semiconducting carbon nitride-aromatic diimide moiety transfers their conduction band electrons to graphene and enhances charge separation. The valence band holes on the semiconducting moiety oxidize water, while the electrons on the graphene moiety promote selective two-electron reduction of O2. This metal-free system produces H2O2 with solar-to-chemical energy conversion efficiency 0.20%, comparable to the highest levels achieved by powdered water-splitting photocatalysts.

We synthesized a coumarin-spiropyran dyad with a hydrogenated pyran moiety (2), behaving as an off-on type fluorescent receptor for rapid, selective, and sensitive detection of cyanide anion (CN(-)) in aqueous media. The receptor itself shows almost no fluorescence with a quantum yield0.01, due to the delocalization of π-electrons over the molecule. Selective nucleophilic addition of CN(-) to the spirocarbon of the molecule rapidly promotes spirocycle opening within only 3 min. This leads to localization of π-electrons on the coumarin moiety and exhibits strong light-blue fluorescence at 459 nm with very high quantum yield (0.52). As a result of this, the receptor facilitates rapid, selective, and sensitive fluorometric detection of CN(-) as low as 1.0 μM.