論文 - 栄長　泰明

Convection control in a flow cell on electrochemical CO<inf>2</inf> reduction using a boron-doped diamond electrode

Nihongi S., Otake A., Du J., Einaga Y.

Carbon （Carbon）  200   456 - 461 2022年11月

ISSN  00086223

　概要を見る

While it is well recognized that mass transfer is an important factor in electrochemical reactions, the influence of mass transfer, especially of the convection on the electrochemical CO2 reduction has not been investigated. In this study, we focused on the influence of convection in a flow cell system using a boron-doped diamond electrode. The results clearly showed that convection improved the product selectivity and electrode potentials in CO2 reduction. It suggested that convection controls CO2 mass transfer in a flow cell system and influences the reactivity of electrochemical CO2 reduction.

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Photophysics and electrochemistry of ruthenium complexes for electrogenerated chemiluminescence

Villani E., Sakanoue K., Einaga Y., Inagi S., Fiorani A.

Journal of Electroanalytical Chemistry （Journal of Electroanalytical Chemistry）  921 2022年09月

ISSN  15726657

　概要を見る

Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), is nowadays a powerful transduction method in electroanalysis, in particular regarding the application in clinical diagnostics. Indeed, its superior capability relies in the fruitful combination of electrochemical and photoluminescence properties. The research on efficient ECL luminophores has brought a wide range of molecules, form organic systems to inorganic complexes, however, despite this large pool of luminophores available, tris(2,2′-bipyridine)ruthenium (II) [Ru(bpy)3]2+ is still leading since the first report in 1972, in both academic research and commercially available systems. To acknowledge the outmost importance of this inorganic complex, here we report the photophysical and electrochemical properties of [Ru(bpy)3]2+ and its derivatives obtained by ligand design for application in ECL.

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A rapid and simple electrochemical detection of the free drug concentration in human serum using boron-doped diamond electrodes

Moriyama H., Ogata G., Nashimoto H., Sawamura S., Furukawa Y., Hibino H., Kusuhara H., Einaga Y.

Analyst （Analyst）  147 （ 20 ） 4442 - 4449 2022年09月

ISSN  00032654

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Monitoring drug concentration in blood and reflecting this in the dosage are crucial for safe and effective drug treatment. Most drug assays are based on total concentrations of bound and unbound proteins in the serum, although only the unbound concentration causes beneficial and adverse events. Monitoring the unbound concentration alone is expected to provide a means for further optimisation of drug treatment. However, unbound concentration monitoring has not been routinely used for drug treatment due to the long analysis time and the high cost of conventional methods. Here, we have developed a rapid electrochemical method to determine the unbound concentration in ultrafiltered human serum using boron-doped diamond (BDD) electrodes. When the anticancer drug doxorubicin was used as the test drug, the catalytic doxorubicin-mediated reduction of dissolved oxygen provided a sensitive electrochemical signal, with a detection limit of 0.14 nM. In contrast, the sensitivity of glassy carbon (GC) was inferior under the same conditions due to interference from the dissolved oxygen reduction current. The signal background ratio (S/B) of BDD and GC was 11.5 (10 nM doxorubicin) and 1.1 (50 nM), respectively. The results show that a fast measurement time within ten seconds is possible in the clinical concentration range. Additionally, in the ultrafiltered human serum, the obtained values of unbound doxorubicin concentration showed good agreement with those quantified by conventional liquid chromatography-mass spectrometry. This approach has the potential for application in clinical settings where rapid and simple analysis methods would be beneficial.

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Detection of dissolved hydrogen in water using platinum-modified boron doped diamond electrodes

Irkham , Kazama K., Einaga Y.

Journal of Electroanalytical Chemistry （Journal of Electroanalytical Chemistry）  917 2022年07月

ISSN  15726657

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The detection of molecular hydrogen in water using platinum modified boron doped diamond (Pt-BDD) was presented. A clear peak of hydrogen desorption was observed around −0.1 V in 0.1 M KCl solution. With a simple electrochemical pretreatment, the signal at Pt-BDD electrode was found to be higher and more stable compared to those using bare Pt electrode. The performance of the sensor was compared with gas chromatography method. The result shows a similar trend with either same or different concentration of H2. Lastly, the measurement was successfully conducted in the tap water even without addition of electrolyte. These result shows that Pt-BDD could be promoted as a good electrode candidate for sensing dissolved H2 in the water-based solution.

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Enzymatic Biosensors with Electrochemiluminescence Transduction

Rahmawati I., Einaga Y., Ivandini T.A., Fiorani A.

ChemElectroChem （ChemElectroChem）  9 （ 12 ）  2022年06月

　概要を見る

Sensors rely on a plurality of transduction methods, and among the available selections, electrochemical techniques offer the peculiar advantage of an easy interfacing between biological recognition elements and electronic signal transduction processes. Furthermore, electrochemical devices are qualified for decentralized point-of-care testing as they can be easily downsized and made at low cost for a wide range of potential applications, for example biomedical or environmental. Electrochemical methods of transduction differ for the technique used, as it can be voltammetry, chronoamperometry, impedance spectroscopy, or electrochemiluminescence. The latter is peculiar among electrochemical techniques since in electrochemiluminescence the analytical signal is light emission, and this offers several advantages, mainly related to background suppression and detection limit, combined with fast measurement. This review introduces the principles of enzyme biosensors coupled with electrochemiluminescence transduction, summarises the research, and finally highlights the strategies to take full advantage of this detection method.

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A New Pathway for CO<inf>2</inf>Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode

Du J., Fiorani A., Inagaki T., Otake A., Murata M., Hatanaka M., Einaga Y.

JACS Au （JACS Au）  2 （ 6 ） 1375 - 1382 2022年06月

　概要を見る

By means of an initial electrochemical carbon dioxide reduction reaction (eCO2RR), both the reaction current and Faradaic efficiency of the eCO2RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO2•-) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO2RR to take place at a low potential, that is, a low energy, where CO2•- is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO2RR. We further evaluated this effect in long-term experiments using a CO2 electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.

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Electrogenerated chemiluminescence of luminol at a boron-doped diamond electrode for the detection of hypochlorite

Rahmawati I., Saepudin E., Fiorani A., Einaga Y., Ivandini T.A.

Analyst （Analyst）  147 （ 12 ） 2696 - 2702 2022年04月

ISSN  00032654

　概要を見る

Electrogenerated chemiluminescence (ECL) of luminol at a boron-doped diamond electrode has been used for hypochlorite determination. The presence of H2O2 induces the generation of the ECL signals of luminol. In contrast, the presence of hypochlorite oxidizes luminol directly to decrease the ECL signals of luminol. Accordingly, a decrease of the ECL signals of luminol in the presence of H2O2 was used as the signal response for hypochlorite detection. A linear decrease of ECL signals with the NaClO concentration in the range from 0 to 20 μM was observed with a sensitivity of 18.56 a.u. μM−1 cm−2. An estimated detection limit of 0.88 μM was achieved, which is around one order lower than the detection limit obtained using the normal electrochemical method with the same electrode. The system also provides a good selectivity towards Cu2+ and Na+. A reproducibility of 3.40%RSD was noted for 15 repetitive measurements. The analytical performance was found to be favourable in comparison to those of other typical electrochemical and electrochemiluminescence methods, indicating that it is applicable for real sample detection.

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Boron-Doped Diamond Electrode Outperforms the State-of-the-Art Electrochemiluminescence from Microbeads Immunoassay

Sakanoue K., Fiorani A., Santo C.I., Irkham , Valenti G., Paolucci F., Einaga Y.

ACS Sensors （ACS Sensors）  7 （ 4 ） 1145 - 1155 2022年04月

　概要を見る

Electrochemiluminescence (ECL) is a powerful transduction technique where light emission from a molecular species is triggered by an electrochemical reaction. Application to biosensors has led to a wide range of electroanalytical methods with particular impact on clinical analysis for diagnostic and therapeutic monitoring. Therefore, the quest for increasing the sensitivity while maintaining reproducible and easy procedures has brought investigations and innovations in (i) electrode materials, (ii) luminophores, and (iii) reagents. Particularly, the ECL signal is strongly affected by the electrode material and its surface modification during the ECL experiments. Here, we exploit boron-doped diamond (BDD) as an electrode material in microbead-based ECL immunoassay to be compared with the approach used in commercial instrumentation. We conducted a careful characterization of ECL signals from a tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+)/tri-n-propylamine (TPrA) system, both homogeneous (i.e., free diffusing Ru(bpy)32+) and heterogeneous (i.e., Ru(bpy)32+bound on microbeads). We investigated the methods to promote TPrA oxidation, which led to the enhancement of ECL intensity, and the results revealed that the BDD surface properties greatly affect the ECL emission, so it does the addition of neutral, cationic, or anionic surfactants. Our results from homogeneous and heterogeneous microbead-based ECL show opposite outcomes, which have practical consequences in ECL optimization. In conclusion, by using Ru(bpy)32+-labeled immunoglobulins bound on microbeads, the ECL resulted in an increase of 70% and a double signal-to-noise ratio compared to platinum electrodes, which are actually used in commercial instrumentation for clinical analysis. This research infers that microbead-based ECL immunoassays with a higher sensitivity can be realized by BDD.

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Electrochemical Oxidation Behavior of Nitrogen Dioxide for Gas Detection Using Boron Doped Diamond Electrodes

Triana Y., Irkham , Einaga Y.

Electroanalysis （Electroanalysis）  34 （ 4 ） 752 - 760 2022年04月

ISSN  10400397

　概要を見る

The electrochemical oxidation reaction of nitrogen dioxide (NO2) using boron doped diamond (BDD) electrodes is presented. Cyclic voltammetry of NO2 in a 0.1 M KClO4 solution exhibits oxidation peaks at +1.1 V and +1.5 V (vs. Ag/AgCl) which are attributable to oxidation of HONO and NO2−, respectively. Moreover, the pH and scan rate dependences were investigated to study the oxidation mechanism. A linear calibration curve was observed in the concentration range of ∼1 to 5 mM (R2=0.99) with a detection limit of 11.1 ppb (S/B=3) for HONO and 58.6 ppb (S/B=3) for NO2−. In addition, the analytical performance was compared with those using glassy carbon, platinum and stainless steel as the working electrode.

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Simultaneous electrochemical detection of ozone and free chlorine with a boron-doped diamond electrode

Peng Z., Irkham N., Akai K., Murata M., Tomisaki M., Einaga Y.

Analyst （Analyst）  147 （ 8 ） 1655 - 1662 2022年03月

ISSN  00032654

　概要を見る

O3 and free chlorine play significant roles in disinfection and organic degradation. There are numerous reports about their mixed-use, yet detection of the residual concentrations is not easily accomplished, whilst the interactions between them remain unclear. Herein, we develop a detection method using a boron-doped diamond (BDD) electrode to achieve the simultaneous determination of O3 and free chlorine, which benefits from the unique property of the wide potential window of BDD electrodes. It is indicated that O3 can always be accurately determined at 0.35 V vs. Ag/AgCl in an acidic solution (pH = 4-5), whether or not free chlorine is present in the solution, whereas free chlorine can be precisely monitored at −0.78 V vs. Ag/AgCl only after the O3 is completely depleted. Furthermore, in a basic solution (pH = 9-10), the reduction peak of O3 at 0.57 V vs. Ag/AgCl promptly disappears accompanied by a decrease in the peak current of free chlorine at 1.41 V. All the phenomena observed in the acidic and basic solutions are concurrently confirmed in a quasi-neutral solution. Based on these complementary measurements, a mechanism is proposed, in which the O3 reduction results in partial oxidation of the BDD surface, hindering the reduction of free chlorine in the acidic mixture; whereas O3 reacts quickly with free chlorine in the basic solution, which causes the co-consumption of both of them. It is hoped these results will give us a guide as to how better utilize mixtures and more precisely simultaneously determine O3 and free chlorine in the mixture.

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Blood Oxygen Sensor Using a Boron-Doped Diamond Electrode

Triana Y., Ogata G., Tomisaki M., Irkham , Einaga Y.

Analytical Chemistry （Analytical Chemistry）  94 （ 9 ） 3948 - 3955 2022年03月

ISSN  00032700

　概要を見る

The electrochemical behavior of oxygen (O2) in blood was studied using boron-doped diamond (BDD) electrodes. Cyclic voltammogram of O2 in a 0.1 M phosphate buffer solution solution containing 1 × 10-6 M of bovine hemoglobin exhibits a reduction peak at -1.4 V (vs Ag/AgCl). Moreover, the scan rate dependence was investigated to study the reduction reaction mechanism, which was attributable to the reduction of O2 to H2O2 via two electrons. A linear calibration curve was observed in the concentration range of 86.88-314.63 mg L-1 (R2 = 0.99) with a detection limit of 1.0 mg L-1 (S/B = 3). The analytical performance was better than those with glassy carbon or platinum electrodes as the working electrode. In addition, an application to bovine blood was performed. The O2 concentration in the blood measured on the BDD electrodes was compared to that measured using an OxyLite Pro fiber-optic oxygen sensor device. Both methods gave similar values of the O2 concentration in the range of ∼40 to 150 mmHg. This result confirms that BDD electrodes could potentially be used to detect the O2 concentration in blood.

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Electrochemical study of CO<inf>2</inf> reduction on Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf> modified boron-doped diamond electrode

Jiwanti P.K., Alfaza A.M., Kadja G.T.M., Khalil M., Einaga Y.

Inorganic Chemistry Communications （Inorganic Chemistry Communications）  137 2022年03月

ISSN  13877003

　概要を見る

The electrochemical reduction of CO2 has been attracted researcher attention around the world. There are many researches on how to improve the value of CO2 gas by converting it to useful chemicals or feedstock. In this report, we studied electrochemical behavior of Ti3C2Tx modified on the surface of boron-doped diamond (BDD) electrode for CO2 reduction. It is shown that the presence of Ti3C2Tx could improve the catalytic effect for CO2 reduction, as the CO2 reduction peak was shifted to positive potentials. This work is expected to provide an information of potential catalyst to be applied for real CO2 reduction application.

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Core-shell copper-gold nanoparticles modified at the boron-doped diamond electrode for oxygen sensors

Gunlazuardi J., Kurniawan A.D., Jiwanti P.K., Einaga Y., Ivandini T.A.

Analytical Methods （Analytical Methods）  14 （ 7 ） 726 - 733 2022年02月

ISSN  17599660

　概要を見る

Bimetallic copper-gold (Cu@Au) nanoparticles were synthesized and utilised to modify boron-doped diamond (BDD) electrodes. Nanorod particles with a diameter size of around 10 nm and a length of around 20 nm were successfully synthesized. These nanoparticles were then attached to the BDD surface by using allylamine as the bridge. Comparison among the BDD modified with Cu@Au and individual gold nanoparticles showed that Cu@Au nanoparticles created around 3 times higher gold coverage on the BDD surface than normal gold nanoparticles. It was also found that the use of allylamine as the bridge can attach more gold than copper nanoparticles. Moreover, around two times higher current responses of oxygen reduction reaction were observed at Cu@Au-modified BDD. Good linearity in a concentration range from 2 to 9 ppm could be achieved with a sensitivity of 0.0138 mA ppm-1 and limit detection of 1.98 ppm. An application of the modified BDD for a biochemical oxygen demand (BOD) sensor using Rhodotorula mucilaginosa UICC Y-181 as the biosensing agent was also demonstrated with glucose solutions as the solution model. Sensitivity equivalent to 17.4 μA mM-1 BOD could be achieved. The system showed good stability with an RSD of 3.45% in 10 measurements. This journal is

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Electrochemical Sensor of Levofloxacin on Boron-Doped Diamond Electrode Decorated by Nickel Nanoparticles

Jiwanti P.K., Sitorus I.R., Kadja G.T.M., Wafiroh S., Einaga Y.

Indonesian Journal of Chemistry （Indonesian Journal of Chemistry）  22 （ 5 ） 1321 - 1329 2022年

ISSN  14119420

　概要を見る

Levofloxacin (LEV) was known as one of the fluoroquinolone antibiotics that widely used as an antibacterial agent. Monitoring of LEV is important due to its negative side effect on humans. The determination of LEV was studied for the first time on nickel modified on a boron-doped diamond (NiBDD) electrode using the square wave voltammetry (SWV) method to improve the catalytic and sensitivity of the sensor. The response was linear in the range of 30–100 mM LEV. LEV sensor on NiBDD was found to be selective in the presence of urea, glucose, and ascorbic acid interferences. Good reproducibility with % a relative standard deviation of 1.45% (n = 10) was achieved. Therefore, the NiBDD electrode could be potentially applied for the real detection method of LEV.

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Application of Boron-doped Diamond Electrodes: Focusing on the Electrochemical Reduction of Carbon Dioxide

Einaga Y.

Electrochemistry （Electrochemistry）  90 （ 10 ）  2022年

ISSN  13443542

　概要を見る

Boron-doped diamond (BDD) electrodes are next generation electrode materials and their electrochemical applications have been actively developed in recent years. They are expected to be useful electrode materials for improving the environment and for bio-medical applications. Here, examples of practical applications as electrochemical sensors, the development of in vivo real time measurements, and electrochemical organic synthesis using BDD electrodes are briefly introduced. In the second part, our recent work on the production of useful chemicals by means of the electrochemical reduction of CO2 using BDD electrodes is described. The work has attracted particular attention for its potential contribution to carbon neutrality and carbon recycling.

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Electro-conversion of cumene into acetophenone using boron-doped diamond electrodes

Kitano M., Saitoh T., Nishiyama S., Einaga Y., Yamamoto T.

Beilstein Journal of Organic Chemistry （Beilstein Journal of Organic Chemistry）  18   1154 - 1158 2022年

　概要を見る

A straightforward electro-conversion of cumene into acetophenone has been reported using boron-doped diamond (BDD) electrodes. This particular conversion is driven by the addition reaction of a cathodically generated hydroperoxide anion to an anodically generated cumyl cation, where the BDD's wide potential window enables the direct anodic oxidation of cumene into the cumyl cation. Since electricity is directly employed as the oxidizing and reducing reagents, the present protocol is easy to use, suitable for scale-up, and inherently safe.

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Electrochemical CO<inf>2</inf> reduction on sub-microcrystalline boron-doped diamond electrodes

Peng Z., Xu J., Kurihara K., Tomisaki M., Einaga Y.

Diamond and Related Materials （Diamond and Related Materials）  120 2021年12月

ISSN  09259635

　概要を見る

Boron-doped diamond (BDD) electrodes are being increasingly investigated for application to electrochemical CO2 reduction. Previous, studies have mainly focused on microcrystalline (MC) BDD electrodes. In our study, we present an analysis of electrochemical CO2 reduction using sub-microcrystalline (SMC) BDD electrodes with different boron doping concentrations (0.28%, 0.11% and 0.03%). Unlike the microcrystalline case, these synthetic SMC BDD films with high sp2-bonded carbon do not show a boron-concentration dependence in terms of the activity of CO2 reduction to form formic acid (HCOOH). All the electrodes enabled efficient CO2 reduction at close to the maximum Faradaic efficiency for HCOOH in the range of 70% to 80%. From our observations, it is suggested that the sp2-bonded carbon should be crucial for the CO2 reduction. The results are hoped to enable a relaxation on the restrictions on the use of BDD electrodes towards industrial CO2 reduction application.

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NickelCobalt Modified Boron-Doped Diamond as an Electrode for a Urea/H<inf>2</inf>O<inf>2</inf> Fuel Cell

Putri Y.M.T.A., Jiwanti P.K., Irkham , Gunlazuardi J., Einaga Y., Ivandini T.A.

Bulletin of the Chemical Society of Japan （Bulletin of the Chemical Society of Japan）  94 （ 12 ） 2922 - 2928 2021年12月

ISSN  00092673

　概要を見る

Among many types of fuel cells, urea/H2O2 fuel cells have garnered attention from the scientific community due to the advantages of urea. In connection to this, a nickel-cobalt-modified boron-doped diamond (NiCo-BDD) electrode was prepared via chronoamperometry. A Ni/Co ratio of 4:1 in solution was determined as the optimum ratio for the urea oxidation reaction. Results showed that the Ni and Co particles were homogeneously deposited on the BDD surface and deposited without any interaction between the particles. The prepared NiCo-BDD electrode for a urea fuel cell showed optimum performance with a 0.1M KOH and 0.50M urea solution as the anode electrolyte and a 2.0M H2O2 and 2.0M H2SO4 solution as the cathode electrolyte. An opencircuit voltage of 0.817 V with a power density of approximately 0.632 mW/sq cm at room temperature and excellent stability after 6 hr of application were achieved. NiCo-BDD significantly enhanced the catalytic activity of urea oxidation reaction compared with the Ni plate, unmodified BDD, Ni-BDD, and Co-BDD.

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Localized Graphitization on Diamond Surface as a Manifestation of Dopants

Catalan F.C.I., Anh L.T., Oh J., Kazuma E., Hayazawa N., Ikemiya N., Kamoshida N., Tateyama Y., Einaga Y., Kim Y.

Advanced Materials （Advanced Materials）  33 （ 42 ）  2021年10月

ISSN  09359648

　概要を見る

Doped diamond electrodes have attracted significant attention for decades owing to their excellent physical and electrochemical properties. However, direct experimental observation of dopant effects on the diamond surface has not been available until now. Here, low-temperature scanning tunneling microscopy is utilized to investigate the atomic-scale morphology and electronic structures of (100)- and (111)-oriented boron-doped diamond (BDD) electrodes. Graphitized domains of a few nanometers are shown to manifest the effects of boron dopants on the BDD surface. Confirmed by first-principles calculations, local density of states measurements reveal that the electronic structure of these features is characterized by in-gap states induced by boron-related lattice deformation. The dopant-related graphitization is uniquely observed in BDD (111), which explains its electrochemical superiority over the (100) facet. These experimental observations provide atomic-scale information about the role of dopants in modulating the conductivity of diamond, as well as, possibly, other functional doped materials.

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Efficient photocatalytic conversion of benzene to phenol on stabilized subnanometer WO<inf>3</inf>quantum dots

Ohno A., Watanabe H., Matsui T., Somekawa S., Tomisaki M., Einaga Y., Oaki Y., Imai H.

Catalysis Science and Technology （Catalysis Science and Technology）  11 （ 19 ） 6537 - 6542 2021年10月

ISSN  20444753

　概要を見る

Band engineering with a quantum size effect is proposed to be utilized to design photocatalytic activity for the conversion of organic compounds. Subnanometer WO3 quantum dots (QDs) are spontaneously produced with the enhancement of the photocatalytic activity in a mesoporous silica matrix by preliminary photochemical dissolution. An appropriate upshift of the conduction band of subnanometer WO3 QDs stabilized by the coverage with the surface WO bonds promotes the efficient conversion of benzene to phenol without decomposition of the product into CO2 under ultraviolet illumination.

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