Oxidation Of Aqueous Solutions Research Articles

Chemical and electrochemical water oxidation catalyzed by heteroleptic Ru(III) complexes of anionic 2,6 pyridine dicarboxylate ligand: Experimental and theoretical study

Herein we report two new mononuclear heteroleptic Ruthenium complexes, 1 and 2 with anionic N, O donor pyridine dicarboxylate (pdc2-) ligand along with neutral bipyridine moieties. The general formula of the complexes are [RuIII(pdc2-)(L1)Cl](1), [RuIII(pdc2-)(L2)Cl](2) (Where L1 = bipyridine, L2 = 4,4′-dimethylbipyridine). Synthesis, characterization and water oxidation catalytic properties of both complexes were investigated. A combined theoretical (DFT) and experimental study were carried out to investigate the catalytic (in presence of CAN) and electrocatalytic activity of 1 and 2 for water oxidation in aqueous solution at pH ∼ 1. During electrocatalysis, the catalytic activity wave has been detected in acetonitrile/water 1:9 (v/v) solution in the range 1.39–1.41 V vs SCE. pH based electrochemistry reveals that, water oxidation (at pH = 1) takes place via sequential proton-electron transfer process to form a RuV = O moiety, which oxidises water through I2M pathway. For water oxidation by CAN, both the molecules show appreciably high TOF values 3.47971 x10-4 s−1 and 1.183 × 10–3 s−1 for 1 and 2 respectively in comparison to similar molecules [1,2].

Microwave-Assisted Synthesis of Schiff Base Metal–Ligand Complexes with Copper and Nickel Centres for Electrochemical In Vitro Sensing of Nitric Oxide in an Aqueous Solution

Nitric oxide (NO), the smallest signalling molecule known in the human body, keeps blood vessels dilated, controls blood pressure, and has numerous other health regulatory effects. The use of Schiff base complexes incorporated onto electrodes to make electrochemical sensors has been explored as an effective method for the determination and quantification of nitric oxide in aqueous solutions. Schiff base ligands were complexed with Cu and Ni metal centres using the microwave synthesis method to produce metal–ligand complexes with enhanced capabilites for NO detection. The electrical current generated at the anode is directly proportional to NO concentrations in the solution through its oxidation to HNO3. Various characterisation techniques were implemented to verify the integrity of each step of metal–ligand synthesis as well as the final product produced, using FT-IR, UV-VIS, and TGA. The as-synthesised Schiff base complexes were electrodeposited on screen-printed carbon electrodes (SPCE) and electrochemically evaluated in a 0.1 M PBS. Furthermore, metal complexes were screened for their in vitro activity towards NO detection in an aqueous solution (PBS). The results show that the investigated sensors (SPCE/Ni-BPND and SPCE/Cu-BPND) respond positively toward NO detection. It was, therefore, identified that the two sensors also do not differ significantly in terms of precision, sensitivity, and lowest detection limit. The sensor strategies demonstrate the NO limits of detection of 0.22 µM and 0.09 µM, and they also demonstrate sensitivity values of 16.3 µA/µM and 13.1 µA/µM for SPCE/Cu-BPND and SPCE/Ni-BPND sensors, respectively.

Study on the One‐Step Synthesis of Oxides by Cationic Membrane Electrolysis of Ni and Co Chloride

AbstractThis contribution investigates whether cobalt(II) and nickel(II) chlorides can, in one step, be converted to their corresponding oxides in aqueous solutions by electrodeposition. We use the chemical precipitation method as a blank experiment, and the electrodeposition is carried out directly in a self‐made electrolytic cell with CoCl2 ⋅ 6H2O or NiCl2 ⋅ 6H2O as raw material. The crystal structure, morphology, and specific surface area of the product are characterized by X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TG), and Brunauer‐Emmett‐Teller (BET) measurements. The results show that the existence of an electric field has an obvious influence on the performance of the product. CoCl2 can realize the one‐step preparation of Co3O4 in an aqueous solution, but the product prepared with NiCl2 as the raw material is Ni(OH)2, which needs to be further calcined to obtain NiO. Therefore, it is necessary to further study the prerequisites for the one‐step preparation of oxides from metal chloride in an aqueous solution.

Adsorption Properties and Mechanism of Attapulgite to Graphene Oxide in Aqueous Solution.

In order to remove toxic graphene oxide (GO) from aqueous solution, attapulgite (ATP) was used as adsorbent to recycle it by adsorption. In this paper, the effects of different pH, adsorbent mass, GO concentration, time and temperature on the adsorption of GO by attapulgite were studied, and the adsorption performance and mechanism were further explored by XRD, AFM, XPS, FTIR, TEM and SEM tests. The results show that when T = 303 K, pH = 3, and the GO concentration is 100 mg/L in 50 mL of aqueous solution, the removal rate of GO by 40 mg of attapulgite reaches 92.83%, and the partition coefficient Kd reaches 16.31. The adsorption kinetics results showed that the adsorption equilibrium was reached at 2160 min, and the adsorption process could be described by the pseudo-second-order adsorption equation, indicating that the adsorption process was accompanied by chemical adsorption and physical adsorption. The isotherm and thermodynamic parameters show that the adsorption of GO by attapulgite is more consistent with the Langmuir isotherm model, and the reaction is a spontaneous endothermic process. The analysis shows that attapulgite is a good material for removing GO, which can provide a reference for the removal of GO in an aqueous environment.

Multilayered TNAs/SnO2/PPy/β-PbO2 anode achieving boosted electrocatalytic oxidation of As(III)

Dealing with arsenic pollution has been of great concern owing to inherent toxicity of As(III) to environments and human health. Herein, a novel multilayered SnO2/PPy/β-PbO2 structure on TiO2 nanotube arrays (TNAs/SnO2/PPy/β-PbO2) was synthesized by a multi-step electrodeposition process as an efficient electrocatalyst for As(III) oxidation in aqueous solution. Such TNAs/SnO2/PPy/β-PbO2 electrode exhibited a higher charge transfer, tolerable stability, and high oxygen evolution potential (OEP). The intriguing structure with a SnO2, PPy, and β-PbO2 active layers provided a larger electrochemical active area for electrocatalytic As(III) oxidation. The as-synthesized TNAs/SnO2/PPy/β-PbO2 anode achieved drastically enhanced As(Ⅲ) conversion efficiency of 90.72% compared to that of TNAs/β-PbO2 at circa 45.4%. The active species involved in the electrocatalytic oxidation process included superoxide radical (•O2−), sulfuric acid root radicals (•SO4−), and hydroxyl radicals (•OH). This work offers a new strategy to construct a high-efficiency electrode to meet the requirements of favorable electrocatalytic oxidation properties, good stability, and high electrocatalytic activity for As(III) transformation to As(V).

A low carbon footprint method for converting low-rank coals to oxygen-containing chemicals

Due to the urgent need to reduce CO2 emission and the shortage of petroleum, using coals especially low-rank coals as raw materials for producing chemicals has attracted much attention. Thermal extraction and oxidation in aqueous solution are efficient approaches for obtaining oxygen-containing chemicals from low-rank coals. However, yield of chemicals is limited and/or large amount of CO2 is released solely using either of the two technologies for converting low-rank coals. In this paper, a low carbon footprint method combining thermal extraction (TE) and oxy-cracking in dilute alkali aqueous solution for efficiently depolymerizing three low-rank coals, i.e., Xiaolongtan lignite (XLT), Xilinguole lignite (XLGL), and Shenfu sub-bituminous coal (SF), was proposed. The results indicate that considerable oxygen-containing compounds such as phenols, esters, and humic acids along with little CO2 emission can be obtained via the two-step depolymerization process. TE temperature significantly effects the dissolution of small molecular compounds. Comparing with XLT and XLGL, SF has lower TE and oxy-cracking activity. A good correlation between the oxy-cracking conversion of TE residues and their DTG peak temperature for the low-rank coals can be found. Therefore, the aforementioned approach is promising for high-value and low-carbon utilization of low-rank coals.

Boosting conversion efficiency of lignite to oxygen-containing chemicals by thermal extraction and subsequent oxidative depolymerization

The urgent need to reduce CO2 emission in China has stimulated renewed interest in the use of coal as raw material for chemical production. Oxidation in aqueous solution is a relatively mild method to depolymerize coal into oxygen-containing chemicals. In this paper, a novel technology combining thermal extraction (TE) of coal and the oxy-cracking of TE residue (TER), referring to the oxygen oxidation in alkaline aqueous solution under mild conditions, was proposed to obtain humic acid (HA) from Xilinguole lignite (XL). The results show that TE could not only obtain small molecular extracts, but also significantly affect the oxy-cracking performance of TER to reduce the formation of CO2. TE yield of XL reached 9.8 % at optimized temperature (300 °C). Almost no CO2 was emitted during the oxy-cracking of obtained TER at 120 °C for 1.5 h, and the oxy-cracking conversion and the HA yield were 65.03 %and 40.56 %, respectively. By the characterizations of FTIR, 13C NMR, XPS, etc, the HA mainly consists of aromatic structures and oxygen-containing groups, in which most of acidic groups are carboxyl groups. It has an extensive application in the production of industrial chemicals, such as admixtures of concrete, dispersant of coal water slurry, and so on. Therefore, the preparation technology of coal-based HA combining TE and TER oxy-cracking is a promising utilization approach of low-rank coal.

Facile synthesis of porous g-C3N4/β-SiAlON material with visible light photocatalytic activity

A porous material based on β-SiAlON ceramic matrix was synthesized by the combustion of ferrosilicon-aluminum (FSA) in nitrogen atmosphere. The material was used as a substrate for a graphitic carbon nitride (g-C3N4)-based photocatalyst. g-C3N4 was loaded on the β-SiAlON-based ceramic composite by thermal treatment of carbamide in the presence of the composite. As a result, the g-C3N4 particles were uniformly distributed in β-SiAlON composite pores. The resulting material has displayed high stability and photocatalytic activity for murexide oxidation in aqueous solution under visible-light irradiation. The results obtained have shown the approach to the preparation of g-C3N4 supported on the porous ceramic composite has potential as advanced technology to fabricate photocatalysts for the removal of organic pollutants from water.

Protein Adducts and Protein Oxidation as Molecular Mechanisms of Flavonoid Bioactivity.

There are tens of thousands of scientific papers about flavonoids and their impacts on human health. However, despite the vast amount of energy that has been put toward studying these compounds, a unified molecular mechanism that explains their bioactivity remains elusive. One contributing factor to the absence of a general mechanistic explanation of their bioactivity is the complexity of flavonoid chemistry in aqueous solutions at neutral pH. Flavonoids have acidic protons, are redox active, and frequently auto-oxidize to produce an array of degradation products including electrophilic quinones. Flavonoids are also known to interact with specificity and high affinity with a variety of proteins, and there is evidence that some of these interactions may be covalent. This review summarizes the mechanisms of flavonoid oxidation in aqueous solutions at neutral pH and proposes the formation of protein-flavonoid adducts or flavonoid-induced protein oxidation as putative mechanisms of flavonoid bioactivity in cells. Nucleophilic residues in proteins may be able to form covalent bonds with flavonoid quinones; alternatively, specific amino acid residues such as cysteine, methionine, or tyrosine in proteins could be oxidized by flavonoids. In either case, these protein-flavonoid interactions would likely occur at specific binding sites and the formation of these types of products could effectively explain how flavonoids modify proteins in cells to induce downstream biochemical and cellular changes.

Effects of Modification Degrees on the Colloidal Stability of Amphiphilic Janus Graphene Oxide in Aqueous Solution with and without Electrolytes.

Colloidal stability of modified graphene oxide (GO) is fundamental for its practical applications. Meanwhile, most of the investigations mainly focused on the nanosheets modified by a certain amount of modifiers and neglected the effects of the modification degree, which could vary the physical and chemical properties of modified GO and significantly affect its stability in solution. To the best of our knowledge, this study initially investigated the impact of modification degrees on the colloidal stability of graphene-based amphiphilic Janus nanosheets (JGO) via both experimental and theoretical approaches. The prepared JGO, asymmetrically grafted by dodecylamine, exhibited a direct relation between the modification degree and nanosheet thickness, refractive index, electrostatic properties, hydrophobicity, and the ultimate colloidal stability. In addition, the ionic strength imposed distinctive influences on the aggregation behavior of JGO. Based on the comparison between experimental results and theoretical calculation, it was revealed that the JGO should be modeled as two-dimensional (2D) nanosheets in pure water and be treated as 3D spherical particles in electrolyte solutions for the prediction with the extended Derjaguin-Landau-Verwey-Overbeek theory.

Electrochemical conversion of CO2 to CO in organic electrolyte with Cl2 and NaHCO3 produced as byproducts

A novel membrane electrolysis cell has been designed to convert CO2 into CO in organic electrolyte, with Cl2 produced on the anode from NaCl oxidation in aqueous solution. The obtained CO and Cl2 can be used as the feedstock to produce phosgene. Phosgene is a widely used acylating agent in a chemical industry, which can be used as feedstock to produce numerous high-value chemicals. Through this route, CO2 can be converted into useful chemical, with huge economic profits created in this process. Our experiment results demonstrate that CO2 can be efficiently converted into CO in our designed electrolyzer, and NaCl can be efficiently oxidized to Cl2. During long-term electrolysis process, NaHCO3 is generated and accumulated between the membrane and the cathode. This phenomenon provides clear evidence for us to better understand the mechanism of CO2 electro-reduction in organic electrolyte.

Mutual influence of cupric cations and several anions in anatase and rutile TiO2 photocatalysis.

Copper ions in aqueous solution are known to promote organic oxidation in semiconductor photocatalysis, but the counter anions seem to be important as well. In this work, the performance of Cu(ClO4)2 in presence of several anions in sodium forms (F-, Cl-, ClO4-, NO3-, and SO42-) has been examined. Phenol oxidation in aqueous solution (pH 4) under UV light was used as model reaction and TiO2 in the forms of anatase (AT) and rutile (RT) as photocatalysts. On the addition of 0.1-5mM Cu2+, the reactions on AT and RT all increased. On the addition of 1mM anions, reactions on AT increased by F-and SO42-, but reactions on RT all decreased. In presence of 3mM Cu2+, however, reactions on AT and RT all decreased by 1mM anions except NO3-. Such anion effects were also observed for H2 production on AT and RT in presence of Cu2+ and 10% methanol. A possible mechanism for the positive and negative anion effects is discussed. This work indicates that the formation of a Cu(II)/Cu(I) complex with anions weakens the positive effect of copper ions on organic oxidation in TiO2 photocatalysis.

Phenol Sulfonic Acid Oxidation in aqueous solution by UV, UV/H2O2 and Photo-Fenton Processes

In this study, advanced oxidation processes (UV, UV/H2O2, UV/H2O2/Fe(II) and UV/H2O2/Fe(III)) were investigated in lab-scale experiments for degradation of phenol sulfonic acid (PSA) in aqueous solution. The study showed that the UV/H2O2 process has removal percentage 90.9, 93.0 and 94.4 for neutral, basic and acidic conditions in 20 minutes respectively. The experimental results showed that the optimum conditions were obtained at a pH value of 3, with 4 mmol/1 H2O2, and 0.25 mmol/1 Fe(II) for the UV/H2O2/Fe(II) system and 6 mmol/l H2O2 and, 0.4 mmol/1 Fe(III) for the UV/H2O2/Fe(III) system. The reaction was influenced by the pH, the input concentration of H2O2 and the amount of the iron catalyst and the type of iron salt. As for the UV processes, UV/H2O2 showed the highest degradation rate under acidic conditions

Performance and Mechanism of Layered Double Hydroxide to Remove Graphene Oxide in Aqueous Solution

Performance and Mechanism of Layered Double Hydroxide to Remove Graphene Oxide in Aqueous Solution

Electrochemical Processing and Thermal Properties of Functional Core/Multi-Shell ZnAl/Ni/NiP Microparticles.

Electroless deposition on zinc and its alloys is challenging because of the negative standard potential of zinc, the formation of poor surface layers during oxidation in aqueous solutions, and extensive hydrogen evolution. Therefore, there are only few reports of electroless deposition on Zn and its alloys, neither of them on micro/nano powders. Here, we propose a two-step process that allows the formation of compact, uniform, and conformal Ni/NiP shell on Zn-based alloy microparticles without agglomeration. The process utilizes controlled galvanic displacement of Ni deposition in ethanol-based bath, followed by NiP autocatalytic deposition in an alkaline aqueous solution. The mechanism and effect of deposition conditions on the shell formation are discussed. Thermal stability and functional analysis of core-shell powder reveal a thermal storage capability of 98.5% with an encapsulation ratio of 66.5%. No significant morphological change of the core-shell powder and no apparent leakage of the ZnAl alloy through the Ni shell are evident following differential scanning calorimetry tests. Our two-step process paves the way to utilize electroless deposition for depositing metallic-based functional coatings on Zn-based bulk and powder materials.

Non‐competitive and competitive adsorption of Zn(II), Cu(II), and Cd(II) by a granular Fe‐Mn binary oxide in aqueous solution

AbstractThis work assessed the non‐competitive and competitive adsorption of Zn(II), Cu(II), and Cd(II) by a granular Fe‐Mn binary oxide (GFMO). Kinetic data for Zn(II), Cu(II), and Cd(II) adsorption followed with the pseudo‐second‐order model. Equilibrium data were well fitted using the Langmuir isotherm model both in single‐metal and in multi‐metal systems. The maximum adsorption capacities were determined to be 0.115, 0.124, and 0.055 mmol/g for Zn(II), Cu(II), and Cd(II) in the single‐metal solutions, respectively, while the maximum adsorption capacities were estimated to be 0.088, 0.112, and 0.041 mmol/g in multi‐metal systems. The adsorption of each metal ion was both nonspontaneous and endothermic demonstrated by thermodynamic assessments. The adsorption process was also greatly affected by pH, with the maximum adsorption at pH 6.0 for Cu(II) and 5.0 for Zn(II) and Cd(II). Metal ion adsorption was suppressed as coexisting metal ions competed for adsorption sites on the GFMO surface, suggesting an antagonistic effect. Adsorption data suggested that Cu(II) was preferentially adsorbed by GFMO in the multi‐component solutions. The adsorption of these metals by GFMO evidently proceeded on the basis of hydroxyl replacement, electrostatic attraction, and surface complexation.Novelty or SignificanceA granular Fe‐Mn binary oxide (GFMO) was synthesized in conjunction with polyvinyl alcohol to overcome the nano‐particles dispersion state of Fe‐Mn binary oxides. Because Zn(II), Cu(II), and Cd(II) with higher concentration and risk coexisted in road runoff, the performance of GFMO for Cd(II), Cu(II), and Zn(II) non‐competitive and competitive adsorption was investigated to identify their engineering application potential when GFMO applies as the filler in some green infrastructures, such as constructed wetlands, bioretentions, and rain gardens.

Lubrication by Adsorption Films of Hydrophilic Amine-based Protic Ionic Liquids: Effect of Anion Species.

In this study, we synthesize hydrophilic amine-based protic ionic liquids (PILs) with hydroxy groups in a cation and different anions. Subsequently, we evaluate the kinetic friction coefficients of iron oxide in aqueous solutions of the PILs under different sliding conditions. Ditriethanolamine malate, triethanolamine lactate, triethanolamine methoxyacetate, and triethanolamine acetate are used as PIL samples in this study. Among them, ditriethanolamine malate exhibits the lowest kinetic friction coefficient. As the number of sliding cycles increases, the excellent lubrication capability remains. Subsequently, we characterize the adsorption of the PILs on an iron oxide surface to investigate the lubrication behavior on the basis of quartz crystal microbalance with dissipation monitoring and force curve data. We expect hydrophilic PILs to be excellent water-soluble lubricants and additives for use in metal surface treatments.

Catalytic ozonation for effective degradation of aniline by sulfur-doped copper–nickel bimetallic oxide in aqueous solution

Sulfur-doped copper–nickel bimetallic oxide (S-CuNiO) was employed as the ozonation catalyst for aniline degradation. The results demonstrated that the removal efficiencies of aniline (0.1 mmol/L) significantly increased with the S-CuNiO dosage from 0 to 1.0 g/L and the ozone dose from 0 to 96.5 mg/(min L-liquid). More than 92% of aniline was decomposed within 20 min in the initial pH range of 2–11, and the removal of total organic carbon reached 71% at initial pH 6. S-CuNiO exhibited more excellent catalytic performance than CuNiO, S-CuO and S-NiO. Radical quenching experiments and electron paramagnetic resonance technique confirmed that •OH rather than O2•− played a dominant role in aniline degradation. Combined with characterization of the catalyst, the possible mechanism of catalytic ozonation was deduced. The ‒OH groups on the catalyst surface stimulated ozone to produce •OH, meanwhile ≡Cu+ and ≡Ni2+ on the surface of S-CuNiO promoted the decomposition of ozone via electron transfer to form •OH, accompanied by the production of ≡Cu2+ and ≡Ni3+. Subsequently, ≡Cu+ converted ≡Ni3+ into ≡Ni2+ and released ≡Cu2+, which was reduced to ≡Cu+ by S2− on the surface of the catalyst. Consequently, catalytic cycles were established to facilitate aniline degradation and improve its mineralization. Based on the analyses of intermediates by HPLC-TOF-MS, the possible pathways of aniline degradation were further proposed.

Influence of the morphology of Co2O3 particles on the dissolution kinetics in electrolytes

Establishment of criteria for optimizing technological processes for dissolving transition metal oxides, separating metal compounds from depleted ores, removing oxide deposits from thermotechnical equipment, and methods for cleaning compounds are of practical significance. Cobalt and its compounds are important in the production of hard and heat-resistant alloys as organic synthesis catalysts, as a component of trace elements, fertilizers and drugs. Cobalt isotopes are used as radioactive labels in medicine, as fuel in spacecraft batteries. To solve the technological issues of replenishing the deficit of cobalt by processing cobalt raw materials and its regeneration from industrial waste, it is necessary to conduct targeted research, study the regularities of its behavior during chemical processes (leaching of ores and concentrates) and during electrochemical dissolution (obtaining cobaltcontaining intermediate products for further alloy smelting). One of the important factors affecting the kinetic parameters of the dissolution of cobalt oxides is the characterization of surface properties of the solid phase. The surface structure of powdery Co2O3 oxide was studied by X-ray phase analysis and electron microscopy. The chemical dissolution of the oxide in aqueous solutions of HCl was studied. The sizes and shapes of cobalt oxide particles, the nature of their surface distribution were determined, and kinetic curves of the chemical dissolution of Co2O3 were constructed. The independence of the oxide dissolution mechanism on the acid concentration was established. The kinetic parameters of the process were calculated (specific dissolution rate, reaction order with respect to hydrogen ion). A comparative analysis of the correspondence between the obtained experimental and available literature data was carried out. The obtained experimental and calculated results are of interest in studying the regularities of the dissolution of solid oxide phases of cobalt in various electrolyte compositions.The work was carried out with funding by D. Mendeleev Chemical Technical University of Russia, Project No. X-2020-011.

Aqueous Electrochemical Partial Oxidation of Hydrocarbons By a Gas Diffusion Electrode Carrying Ru-Doped Covalent Triazine Framework

The oxidative functionalization of organic substrates to valuable chemicals has attracted global interest from both fundamental and practical viewpoints. One of the promising approaches for the C-H oxidative functionalization is an aqueous electrochemical method because it can operate under mild conditions without toxic oxidants or flammable solvents. However, there are two major challenging issues for the further dissemination of electrochemical hydrocarbon oxidation in aqueous solution. The first one is the low solubility of raw organics in aqueous media. Here, we focus on gas diffusion electrodes (GDEs) that have been originally developed for hydrogen/oxygen fuel cells in an attempt to overcome this problem. The other major issue is that highly reactive species on an electrocatalyst are required for the activation of stable C−H bonds of hydrocarbons. Although high-valency ruthenium-oxo species (RuIV=O or RuV=O) are known to catalyze O-atom insertion into stable C-H bonds, Ru-based molecular electrocatalysts generally exhibit poor robustness and also catalyze the competitive oxygen evolution reaction (OER) in aqueous solutions. Our group has recently reported that singly isolated Ru-doped covalent triazine frameworks (Ru-CTF) effectively oxidize benzyl alcohol in aqueous electrolytes without the OER[1]. Besides, Ru-CTF displayed higher stability than an organometallic complex immobilized on an electrode because of the covalently cross-linked structure of CTF. In this study, we attempt to realize the electrochemical oxidation of vaporized hydrocarbons in aqueous solutions using a GDE that supports Ru-CTFs (Ru-CTF/GDE).A mixture of 1.0 g ZnCl2, 100 mg 2,6-dicyanopyridine, and 100 mg Ketjenblack was filled into a vacuum glass tube and then heated at 400 °C for 40 hours to prepare a CTF. Ru atoms were then impregnated into the CTF using 0.91 mM RuCl3 ethanol solution for 6 h at 90 °C. A catalyst ink was prepared by dispersing 4.0 mg Ru-CTF in 38 μL 5% Nafion solution and 400 μL ethanol, which was then added dropwise onto the GDE.Ethylbenzene (EB)-saturated (1.2×103 Pa) argon gas was supplied from the backside of GDE as a model substrate. Reaction products in liquid phases after electrolysis were quantitatively analyzed using high-performance liquid chromatography. When the GDE electrode carrying Ru-CTF was applied at 1.5V vs. RHE, acetophenone was generated as the product of ethylbenzene oxidation. The amount of generated acetophenone reached up to 4.7 µmol after 6 h electrolysis. In contrast, generated acetophenone was almost negligible in the absence of ethylbenzene or for bare CTF (without Ru). These results indicated that the Ru atoms in CTF served as the active center for ethylbenzene oxidation. For comparison, electrochemical measurements of Ru-CTF/GDE with 0.2 mM EB in the electrolyte instead of gaseous EB were also conducted using the same GDE electrochemical cell. In this case, the gas chamber was filled with pure argon gas. Although the EB concentration of 0.2 mM is about one-seventh lower than the saturated concentration (solubility of EB in water: 1.4 mM), the amount of acetophenone generated from gaseous EB was over 40-fold larger than that from the electrolyte. This result demonstrates that a GDE is effective for the aqueous electrochemical oxidation of hydrophobic organic compounds. The stability of Ru-CTF on GDE was investigated by the repeated tests in which an EB oxidation reaction was performed over four consecutive cycles with the replacement of the electrolyte every 12 h. Ru-CTF on GDE had negligible deactivation for both current-time profiles and acetophenone generation with repeated use. These results indicate that Ru-CTF on GDE has good stability at 1.5 V vs. RHE.In summary, gaseous EB was successfully oxidized to acetophenone in aqueous electrolytes using a GDE that supported Ru-CTF. Singly isolated Ru-atoms coordinated with nitrogen atoms in Ru-CTF were converted to high-valency Ru=O by water oxidation, and O-atom insertion into the C-H bond of EB was facilitated. Considering that Ru-CTF is highly stable during the long-term electrolysis in aqueous solution, Ru-CTF is a novel platform as a heterogeneous electrocatalyst for partial hydrocarbon oxidation reactions. This is the first demonstration of electrochemical hydrocarbon oxidation in aqueous electrolytes using GDEs. The three-dimensional microstructures in the GDE maximized the transportation of gaseous hydrocarbons, and the oxidation reaction occurred at the triple-phase boundary. The present results clearly demonstrate that GDEs are a promising approach for the electrochemical oxidative upgrading of hydrophobic organics.Reference:[1] S. Yamaguchi et al. Chem. Commun. 2017, 53, 10437-10440.Figure. (a) Schematic illustration of GDE carrying Ru-CTF (left), Molecular structure of Ru-CTF (right), (b) The amount of acetophenone generated as a function of time with gaseous EB (Black), with 0.2 mM aqueous EB (Gray). Figure 1