Search

CO 2 reduction as an artificial photosynthetic system is a promising technology to produce green energies and chemicals because it uses light energy to convert H 2 O and CO 2 into valuable products such as CO, HCOOH, CH 3 OH, CH 4 , and preferably higher hydrocarbons. In photocatalytic reduction, water should be used as hydrogen and electron sources for CO 2 reduction. Moreover, CH 4 formation is an attractive and challenging topic because of the eight-electron-reducing product of CO 2 . Herein, we report the development of a new Rh-Ru cocatalyst decorated on an alkaline earth-doped NaTaO 3 surface for the photocatalytic CO 2 reduction to form CH 4 using water as an electron donor. CH 4 was obtained by a photocatalytic "uphill" reaction of CO 2 reduction using Rh-Ru cocatalyst-loaded NaTaO 3 :Sr, water, and CO 2 in an aqueous suspension system. About 10% of a selectivity (electronic efficiency) was obtained for CH 4 formation under ambient conditions accompanied with O 2 evolution of the oxidation product of H 2 O.

Photocatalytic and photoelectrochemical CO 2 reduction of artificial photosynthesis is a promising chemical process to solve resource, energy, and environmental problems. An advantage of artificial photosynthesis is that solar energy is converted to chemical products using abundant water as electron and proton sources. It can be operated under ambient temperature and pressure. Especially, photocatalytic CO 2 reduction employing a powdered material would be a low-cost and scalable system for practical use because of simplicity of the total system and simple mass-production of a photocatalyst material.In this Account, single particulate photocatalysts, Z-scheme photocatalysts, and photoelectrodes are introduced for artificial photosynthetic CO 2 reduction. It is indispensable to use water as an electron donor (i.e., reasonable O 2 evolution) but not to use a sacrificial reagent of a strong electron donor, for achievement of the artificial photosynthetic CO 2 reduction accompanied by Δ G > 0. Confirmations of O 2 evolution, a ratio of reacted e - to h + estimated from obtained products, a turnover number, and a carbon source of a CO 2 reduction product are discussed as the key points for evaluation of photocatalytic and photoelectrochemical CO 2 reduction.Various metal oxide photocatalysts with wide band gaps have been developed for water splitting under UV light irradiation. However, these bare metal oxide photocatalysts without a cocatalyst do not show high photocatalytic CO 2 reduction activity in an aqueous solution. The issue comes from lack of a reaction site for CO 2 reduction and competitive reaction between water and CO 2 reduction. This raises a key issue to find a cocatalyst and optimize reaction conditions defining this research field. Loading a Ag cocatalyst as a CO 2 reduction site and NaHCO 3 addition for a smooth supply of hydrated CO 2 molecules as reactant are beneficial for efficient photocatalytic CO 2 reduction. Ag/BaLa 4 Ti 4 O 15 and Ag/NaTaO 3 :Ba reduce CO 2 to CO as a main reduction reaction using water as an electron donor even in just water and an aqueous NaHCO 3 solution. A Rh-Ru cocatalyst on NaTaO 3 :Sr gives CH 4 with 10% selectivity (Faradaic efficiency) based on the number of reacted electrons in the photocatalytic CO 2 reduction accompanied by O 2 evolution by water oxidation.Visible-light-responsive photocatalyst systems are indispensable for efficient sunlight utilization. Z-scheme systems using CuGaS 2 , (CuGa) 1- x Zn 2 x S 2 , CuGa 1- x In x S 2 , and SrTiO 3 :Rh as CO 2 -reducing photocatalyst, BiVO 4 as O 2 -evolving photocatalyst, and reduced graphene oxide (RGO) and Co-complex as electron mediator or without an electron mediator are active for CO 2 reduction using water as an electron donor under visible light irradiation. These metal sulfide photocatalysts have the potential to take part in Z-scheme systems for artificial photosynthetic CO 2 reduction, even though their ability to extract electrons from water is insufficient.A photoelectrochemical system using a photocathode is also attractive for CO 2 reduction under visible light irradiation. For example, p-type CuGaS 2 , (CuGa) 1- x Zn 2 x S 2 , Cu 1- x Ag x GaS 2 , and SrTiO 3 :Rh function as photocathodes for CO 2 reduction under visible light irradiation. Moreover, introducing a conducting polymer as a hole transporter and surface modification with Ag and ZnS improve photoelectrochemical performance.

We demonstrated photocatalytic CO 2 reduction using water as an electron donor under visible light irradiation by a Z-scheme photocatalyst and a photoelectrochemical cell using bare (CuGa) 0.5 ZnS 2 prepared by a flux method as a CO 2 -reducing photocatalyst. The Z-scheme system employing the bare (CuGa) 0.5 ZnS 2 photocatalyst and RGO-(CoO x /BiVO 4 ) as an O 2 -evolving photocatalyst produced CO of a CO 2 reduction product accompanied by H 2 and O 2 in a simple suspension system without any additives under visible light irradiation and 1 atm of CO 2 . When a basic salt (i.e., NaHCO 3 , NaOH, etc.) was added into the reactant solution (H 2 O + CO 2 ), the CO formation rate and the CO selectivity increased. The same effect of the basic salt was observed for sacrificial CO 2 reduction using SO 3 2- as an electron donor over the bare (CuGa) 0.5 ZnS 2 photocatalyst. The selectivity for the CO formation of the Z-schematic CO 2 reduction reached 10-20% in the presence of the basic salt even in an aqueous solution and without loading any cocatalysts on the (CuGa) 0.5 ZnS 2 metal sulfide photocatalyst. It is notable that CO was obtained accompanied by reasonable O 2 evolution, indicating that water was an electron donor for the CO 2 reduction. Moreover, the present Z-scheme system also showed activity for solar CO 2 reduction using water as an electron donor. The bare (CuGa) 0.5 ZnS 2 powder loaded on an FTO glass was also used as a photocathode for CO 2 reduction under visible light irradiation. CO and H 2 were obtained on the photocathode with 20% and 80% Faradaic efficiencies at 0.1 V vs RHE, respectively.

Bacteriophage (denoted as phage) infection in the bacterial fermentation industry is a major problem, leading to the loss of fermented products such as alcohol and lactic acid. Currently, the prevention of phage infection is limited to biological approaches, which are difficult to apply in an industrial setting. Herein, we report an alternative chemical approach using ground Rh-doped SrTiO 3 (denoted as g-STO:Rh) as a visible-light-driven photocatalyst. The g-STO:Rh showed selective inactivation of phage without bactericidal activity when irradiated with visible light (λ > 440 nm). After inactivation, the color of g-STO:Rh changed from gray to purple, suggesting that the Rh valence state partially changed from 3+ to 4+ induced by photocatalysis, as confirmed by diffuse reflectance spectroscopy. To study the effect of the Rh 4+ ion on phage inactivation under visible-light irradiation, the survival rate of phage for g-STO:Rh was compared to that for ground Rh,Sb-codoped SrTiO 3 (denoted as g-STO:Rh,Sb), where the change of Rh valence state from 3+ to 4+ is almost suppressed under visible-light irradiation due to charge compensation by the Sb 5+ ion. Only g-STO:Rh effectively inactivated phage, which indicated that Rh 4+ ion induced by photocatalysis particularly contributed to phage inactivation under visible-light irradiation. These results suggested that g-STO:Rh has potential as an antiphage material in bacterial fermentation.

There is increasing interest in gold nanocrystals due to their unique physical, chemical, and biocompatible properties. In order to develop a template-assisted method for the fabrication of gold nanocrystals, we demonstrate here the de novo design and synthesis of a β-sheet-forming nonapeptide (RU006: Ac-AIAKAXKIA-NH2, X = L-2-naphthylalanine) which undergoes self-assembly to form disk-like nanoarchitectures approximately 100 nm wide and 2.5 nm high. These self-assemblies tend to form a network of higher-order assemblies in ultrapure water. Using RU006 as a template molecule, we fabricated ultrathin gold nanoribbons 50-100 nm wide, 2.5 nm high, and micrometers long without external reductants. Furthermore, in order to determine the mechanism of ultrathin gold nanoribbon formation, we synthesized four different RU006 analogues. On the basis of the results obtained using RU006 and these analogues, we propose the following mechanism for the self-assembly of RU006. First, RU006 forms a network by the cooperative association of disk-like assemblies in the presence of AuCl4(-) ions that are encapsulated and concentrated within the interior cavity of the network architectures. This is followed by electron transfer from the naphthalene rings to Au(III), resulting in slow growth to form ultrathin gold nanoribbons along the template network architectures under ambient conditions. The resulting ribbons retain the dimensions of the cavity of the template architecture. Our approach will allow the construction of diverse template architectural morphologies and will find applications in the construction of a variety of metallic nanoarchitectures.

This research aims to optimize roasted green tea (Houjicha) processing by using roasting treatments to achieve acrylamide mitigation without compromising the quality. 2-Ethyl-3,5-dimethylpyrazine and 2-ethyl-3,6-dimethylpyrazine were identified as potent odorants by aroma extract dilution analysis. In preliminary sensory experiments, the desirable Houjicha flavor was produced in products roasted at 160 degrees C for 30 min and at 180 degrees C for 15 min. Under these conditions, potent odorants were formed at levels adequate for contributing to the Houjicha flavor. Acrylamide amounts in tea infusions were 2.0 and 4.0 microg/L by roasting at 160 degrees C for 30 min and at 180 degrees C for 15 min, respectively. Compared to roasting at 180 degrees C, the degradation of tea catechins was suppressed by roasting at 160 degrees C. Hence, roasting at 160 degrees C for is recommended for Houjicha processing for acrylamide mitigation, formation of potent odorants, and suppression of degradation of tea catechins.

We developed a high-performance liquid chromatography-based method for simultaneous analysis of nine catechins, gallic acid, strictinin, caffeine, and theobromine in green tea by using catechol as an internal standard. Although the high cost and instability of the catechin reference standards limit the application of this method, the addition of ascorbic acid to the standard stock solution preserved the stability of the reference standards in the solution for 1 year when stored at -30 degrees C. Furthermore, we found that the slopes of the calibration curves plotted were stable for a run time of 2000 h. Our method proved to be appropriate for quantification and yielded good correlation coefficients, detection levels, repeatability, reproducibility, and recovery rates. Quantitative data revealed that the contribution of only 200 mL of brewed tea to the total dietary catechins was approximately 220-420 mg, while that of 500 mL of bottled tea was approximately 170-900 mg.

Optimization of the solid-phase extraction cleanup procedure enabled the GC-MS analysis of acrylamide in tea samples without the interference of bromination by tea catechins. Although polyvinylpolypyrrolidone (PVPP) is available for removing tea catechins from tea extract, the peaks derived from PVPP had the same retention time as brominated acrylamide in mass chromatograms obtained by GC-MS. A considerable amount of acrylamide was formed at roasting temperatures of > or =120 degrees C; the highest acrylamide level was observed when tea samples were roasted at 180 degrees C for 10 min. Higher temperatures and longer processing times caused a decrease in the acrylamide content. Furthermore, an analysis of 82 tea samples showed that rather than the reducing sugar content, the asparagine content in tea leaves was a significant factor related to acrylamide formation in roasted products. The acrylamide level in roasted tea products was controlled by asparagine in the presence of reducing sugars.