Duration Of Hydrothermal Treatment Research Articles

Micro/Meso‐Porous Double‐Shell Hollow Carbon Spheres through Spatially Confined Pyrolysis for Supercapacitors and Zinc‐Ion Capacitor

AbstractEnergy storage in supercapacitors and hybrid zinc ion capacitors (ZIC) using porous carbon materials offers a promising alternative method for clean energy solutions. The unique combination of hierarchical porous structure and nitrogen doping in these materials has demonstrated significant capacity for energy storage. Nevertheless, the full potential of these materials, particularly the relationship between pore structure configuration and performance, remains underexplored. Herein, a confined pyrolysis strategy based on the polymerization characteristics of polydopamine (PDA) was developed to construction of hollow carbon spheres with microporous/mesoporous dual shell structure. The depth of micropores and cavity can be controlled by adjusting the duration of heat treatment and hydrothermal treatment, in accordance with the decomposition and polymerization characteristics of PDA. Due to the elasticity of this structure, the relationship between the micro/mesoporous depth of the prepared carbon spheres and the energy storage performance in supercapacitors and ZIC is established. Through optimizing the ion transport capacity of carbon spheres and considering the influence of its internal cavity structure on energy storage, the resulting carbon spheres exhibit high specific capacitance of 389 F g−1 in supercapacitor and specific capacitance of 260 F g−1 and excellent stability with 99.3 % retention after 30000 chare/discharge cycles in ZIC.

Micro/Meso-Porous Double-Shell Hollow Carbon Spheres through Spatially Confined Pyrolysis for Supercapacitors and Zinc-Ion Capacitor.

Energy storage in supercapacitors and hybrid zinc ion capacitors (ZIC) using porous carbon materials offers a promising alternative method for clean energy solutions. The unique combination of hierarchical porous structure and nitrogen doping in these materials has demonstrated significant capacity for energy storage. Nevertheless, the full potential of these materials, particularly the relationship between pore structure configuration and performance, remains underexplored. Herein, a confined pyrolysis strategy based on the polymerization characteristics of polydopamine (PDA) was developed to construction of hollow carbon spheres with microporous/mesoporous dual shell structure. The depth of micropores and cavity can be controlled by adjusting the duration of heat treatment and hydrothermal treatment, in accordance with the decomposition and polymerization characteristics of PDA. Due to the elasticity of this structure, the relationship between the micro/mesoporous depth of the prepared carbon spheres and the energy storage performance in supercapacitors and ZIC is established. Through optimizing the ion transport capacity of carbon spheres and considering the influence of its internal cavity structure on energy storage, the resulting carbon spheres exhibit high specific capacitance of 389 F g-1 in supercapacitor and specific capacitance of 260 F g-1 and excellent stability with 99.3 % retention after 30000 chare/discharge cycles in ZIC.

Enhancing Bioactivity and Mechanical Properties of Nano-Hydroxyapatite Derived from Oyster Shells through Hydrothermal Synthesis.

Nano-hydroxyapatite (nHA) demonstrates favorable biological activity, cell adhesion, cell proliferation, and osteoconductivity, making it highly valuable in biomedicine. It is extensively used as a bone substitute and in bone transplantation within the dental and orthopedic fields. This study employed oyster shells as a calcium source to synthesize nHA at 150 °C with various hydrothermal reaction durations (10 min, 1 h, 6 h, and 12 h). As a control, HA synthesized via a wet precipitation method for 1 h at room temperature was utilized. Subsequent material analyses, including XRD, FE-SEM, FTIR, and ICP-MS, were conducted, followed by comprehensive evaluations of the bioactivity, cell attachment, cell proliferation, and sintering properties of the synthesized nHA. The results indicated that nHA synthesized through the hydrothermal reaction produced nanoscale crystals, with the aspect ratio of nHA particles increasing with the duration of hydrothermal treatment. Notably, rod-like nHA particles became prominent with hydrothermal durations exceeding 6 h. nHA particles derived from oyster shells contained carbonate and trace elements (Na, Mg, K, and Sr), similar to constituents found in human hard tissue such as bone and teeth. The immersion of nHA synthesized at 150 °C for 1 h (HT2) in simulated body fluid (SBF) for 28 d led to the formation of a bone-like apatite layer on the surface, indicating the excellent bioactivity of the synthesized nHA. The cell culture results revealed superior cell attachment and proliferation for nHA (HT2). Following the sequential formation and sintering at 1200 °C for 4 h, HT2 ceramics exhibited enhanced microhardness (5.65 GPa) and fracture toughness (1.23 MPa·m0.5), surpassing those of human tooth enamel.

CuMn2O4 spinel electrodes: effect of the hydrothermal treatment duration on electrochemical performance

CuMn2O4 (CMO) thin films are produced using a simple hydrothermal method. The influence of reaction duration on the electrodes’ electrochemical performance is investigated. XRD data shows improved crystal structure after 24-h reaction time, with a crystallite size of 12.17 nm. Distinct vibrational peaks associated with Cu–O and Mn–O are observed in the ATR-FTIR spectra, corroborating the spinel formation after 24 h. XPS analysis shows a compositional shift over time, starting with copper hydroxide at 12 h, evolving into a mix of copper and manganese oxides, hydroxides, and oxyhydroxides by 18 h, and achieving the desired spinel composition by 24 h. Microscopic analysis reveals CMO is arranged as small sheet structures, with 4.95 ± 2.92 µm in length after 24-h reaction. The CMO24h electrode displays a maximum specific capacitance of 1187.50 Fg−1 at a scan rate of 1 mVs−1 in 1 M Na2SO4 electrolyte. The electrochemical performance of the synthesized CMO electrodes reveals a high potential for energy storage applications.

Enhanced photocatalytic reduction of p-nitrophenol by polyvinylpyrrolidone-modified MOF/porous MgO composite heterostructures

Catalysts derived from Metal-Organic Frameworks (MOF) present a compelling blend of cost-effectiveness and superior performance in reduction reactions. In this study, polymer-decorated MOF-Cobalt (MOF-Co) was deposited onto porous magnesium oxide (MgO) layers, acquired through surface modification of AZ31 Mg alloy via plasma-assisted oxidation, with the aim of fabricating novel catalysts for reduction reactions. Herein, this synthesis involved the utilization of Cobalt-benzene dicarboxylic acid (Co-BDC), where cobalt ions served as metal nodes and 1,4-benzene dicarboxylic acid (H2BDC) functioned as an organic linker, with and without the presence of polyvinylpyrrolidone (PVP) as an active site enhancer. The morphology of the prepared catalysts was affected by several factors such as pH, hydrothermal treatment duration, PVP content, and the presence of a MgO layer. The optimal catalyst, designated as metal-organic frameworks-cobalt at 80 °C temperature and 1 h of hydrothermal treatment at pH 4 (MOF-Co 1.4), was synthesized on the MgO layer using a solution containing 1.7 g of PVP, H2BDC, and Co(NO₃)₂.6H₂O. The paper-like morphology of the MOF-Co 1.4 catalyst facilitated exceptional performance, efficiently degrading p-nitrophenol (p-NP) under visible light irradiation with an impressive 99.74 % efficiency within just 5 min of exposure, while also demonstrating stability over five successive cycles. ·O2− species was found to drive the reduction reaction to p-aminophenol, with harmless compounds as byproducts, while GC-MS analysis identified intermediates in the reduction of p-NP. Density functional theory (DFT) calculations suggested that H2BDC and PVP jointly provided multi-active sites, enabling effective contact with reactants and rapid electron transfer, thus playing a synergistic role in the catalytic reduction process. This study pioneers a novel method for designing efficient bulk catalysts, achieving high efficiency and stability in pollutant degradation with fast, low-energy fabrication.

Enhanced Photoelectrochemical Property of TiO2 Nanotube Array Photoanode Deposited with Al,Cr-Codoped SrTiO3 Nanocubes.

There is a demand for the effective utilization of solar energy with highly functional photoelectrodes for photoelectrochemical (PEC) applications, such as water splitting and CO2 reduction. TiO2 nanotube arrays (TNTA) with a large surface area have been studied as potential photoelectrodes mainly due to their strong oxidation potential. However, it has disadvantages of fast charge recombination and little responsivity to visible light. In this study, we prepared TNTA by anodizing a Ti plate and decorated the TNTA with Al,Cr-codoped SrTiO3 (STO) nanocubes through a hydrothermal treatment to enhance the PEC properties. We also prepared pristine and undoped STO-decorated TNTA for comparison. The hydrothermal treatment duration was optimized for the TNTA-STO:Al,Cr sample to achieve the best PEC performance. Finally, the possible PEC reaction mechanism was proposed based on the obtained experimental results.

Formation and growth of anatase TiO2 nanocrystals under hydrothermal conditions

This work is devoted to the study of the processes of formation and growth of TiO2 nanoparticles under hydrothermal conditions. TiO2 nanocrystals were obtained during the dehydration of hydrated titanium dioxide by varying the temperature and duration of hydrothermal treatment, as well as the method of precipitation of the synthesis precursor. The study of various characteristics of the synthesized TiO2 nanoparticles by PXRD, SEM, TEM, and low-temperature nitrogen sorption made it possible to propose mechanisms for the formation of crystalline titanium dioxide from an X-ray amorphous precursor and the growth of titanium dioxide nanocrystals with an anatase structure under hydrothermal conditions. Within the scope of the chosen model of oriented attachment, the dependence of the sizes of TiO2 crystallites on the parameters of hydrothermal synthesis is mathematically described. It was concluded that the direct precipitation of the synthesis precursor from titanium tetrachloride is superior to the reverse. It is shown that the temperature of hydrothermal treatment largely determines the size and morphology of the formed crystallites and TiO2 nanoparticles, the rate of the crystallization process, and the preferred mechanisms of nanocrystal growth, while the duration of synthesis affects the agglomeration processes and the specific surface area of titanium dioxide powders.

The influence of hydrothermal treatment on TiO2 nanostructure films transformed from titanates and their photoelectrochemical water splitting properties

Anatase non-stoichiometric TiO2 nanostructure films transformed from titanates were fabricated using the alkaline hydrothermal method at different treatment durations. The field emission scanning electron microscopy (FESEM) images demonstrated the morphological change of TiO2 from nanosheets to nanowires. The X-ray diffraction (XRD) patterns confirmed the anatase phase for TiO2 nanostructures. The UV–vis-NIR measurement indicated the decline in visible light absorption with increasing treatment duration. For the photoelectrochemical (PEC) measurement, four hours hydrothermal synthesis TiO2 annealed in air at 500 °C for 90 min showed the optimal photocurrent response with the maximum photocurrent density of 149.1µA/cm2 at 0.8 V vs. Ag/AgCl, which is attributed to the narrow bandgap (3.22 eV), improved carrier density (4.806×1018 cm−3) and longest lifetime of carriers (3.2 ms). Thus, nanosheet morphology was found to be more superior than nanowire morphology and a relatively short hydrothermal treatment duration was beneficial to PEC water splitting properties. In addition, for superior PEC performance, appropriate nanosheet density and surface area are necessary. The results demonstrated that TiO2 nanostructures transformed from titanates could be used for PEC application and the PEC characteristics could be tuned and modified for better water splitting performance.

Hydrothermal conversion of mixed uranium(IV)-cerium(III) oxalates into U1-xCexO2+δ·nH2O solid solutions.

Uranium-cerium oxide solid solutions, U1-xCexO2+δ·nH2O, were prepared through hydrothermal conversion of mixed U(IV)-Ce(III) oxalate precursors, cerium being used as a surrogate for plutonium. Whatever the starting pH, the fluorite-type structure of AnO2 was obtained after heating at 250 °C for 24 h. The initial pH of the reaction media appeared to affect significantly the oxide morphology: for pH ≤ 2, the powder was found to be composed of microspheres, whereas for more alkaline pH values, agglomerates of nanocrystallites were found. Furthermore, a study of the hydrothermal treatment duration (T = 250 °C, pH = 8, t = 1-48 h) showed that fluorite-type mixed dioxides started to form after only 1 h, and then became single phase after 3 h. SEM and TEM/EDS analyses revealed that the cationic distribution narrowed with time to finally form highly homogeneous mixed oxides. Such a preparation route was then applied to various cerium incorporation rates and it was found that the formation of U1-xCexO2+δ·nH2O mixed oxides was possible for 0.1 ≤ x ≤ 0.75. In all the systems investigated, the speciation of uranium and cerium was questioned in both the solid and liquid phases. Thermodynamic calculations and evaluation of the O/M ratio in the final oxides led us to understand the complex redox behaviour of uranium and cerium in solution during hydrothermal processes and to propose a conversion mechanism.

Crystal Design and Photoactivity of TiO2 Nanorod Template Decorated with Nanostructured Bi2S3 Visible Light Sensitizer.

In this study, TiO2-Bi2S3 composites with various morphologies were synthesized through hydrothermal vulcanization with sputtering deposited Bi2O3 sacrificial layer method on the TiO2 nanorod templates. The morphologies of decorated Bi2S3 nanostructures on the TiO2 nanorod templates are controlled by the duration of hydrothermal vulcanization treatment. The Bi2S3 crystals in lumpy filament, nanowire, and nanorod feature were decorated on the TiO2 nanorod template after 1, 3, and 5 h hydrothermal vulcanization, respectively. Comparatively, TiO2-Bi2S3 composites with Bi2S3 nanowires exhibit the best photocurrent density, the lowest interfacial resistance value and the highest photodegradation efficiency towards Rhodamine B solution. The possible Z-scheme photoinduced charge separation mechanism and suitable morphology of Bi2S3 nanowires might account for the high photoactivity of TiO2 nanorod-Bi2S3 nanowire composites.

Features of the synthesis of highly dispersed alumophosphates AlPO4·nH2O

Aluminum orthophosphate of the composition AlPO4·2H2O with a monoclinic structure identical to the structure of the natural mineral metavariscite was obtained by condensation method during hydrothermal treatment of alumophosphate solutions with a concentration (g/l) of Al2O3 90 – 115, P2O5 340 – 440 in the temperature range 95–99 °C. For the first time, the role of aging of the alumophosphate system in shortening of the induction period, simultaneous nucleation of primary particles in the entire volume of the solution and the formation of a pasty product with a predominant particle size of 1–10 μm, in contrast to 30–50 μm, characteristic of a fine-crystalline product obtained without aging of the solution, is established. It is shown that pasty AlPO4·2H2O, in comparison with fine-crystalline, is hardly soluble in HCl even under prolonged heating. The influence of P2O5 content in the alumophosphate solution, the conditions of its aging and the duration of hydrothermal treatment on the particle size distribution for synthesized aluminum orthophosphates have been established. Anhydrous alumophosphate obtained by dehydration of pasty AlPO4·2H2O in the temperature range of 150–200 °C with subsequent heat treatment at 900 °C is readily soluble in acids, and the predominant particle size is 5–13 μm.

A Novel Strategy to Produce a Soluble and Bioactive Wheat Bran Ingredient Rich in Ferulic Acid.

Wheat bran (WB) is a byproduct from the milling industry that contains bioactive compounds beneficial to human health. The aim of this work was on the one hand, increasing extractability of antioxidant and anti-inflammatory compounds (specifically ferulic acid, FA), through enzymatic hydrolysis combined with hydrothermal treatment (HT) and high hydrostatic pressure (HHP). On the other hand, enhancing the stability of final ingredient applying spray-drying (SPD) and microencapsulation (MEC). The use of HT increased FA, total phenolics (TP), and antioxidant capacity (AC) in WB hydrolysates, regardless the HT duration. However, the HT tested (30 min, HT30) produced a loss in anti-inflammatory activity (AIA). The combination of HT (15 min, HT15) with HHP increased AIA of the WB. SPD enhanced the TP yield in WB with no significant effect of inlet temperature (up to 140 °C) on phenolic profile mainly composed of trans-FA and smaller amounts of cis-FA and apigenin diglucosides. SPD caused a temperature-dependent increase in AC (160 °C > 140 °C > 130 °C). SPD inlet temperatures affected total solids yield (from 22 to 36%), with the highest values at 140 °C. The use of HHP in combination with HT resulted in >2-fold increase in total solids yield.

Studies on the synthesis of ZSM-5 by interzeolite transformation from zeolite Y without using organic structure directing agents

Abstract In this work, a study of the interzeolite transformation from a parent zeolite Y (FAU topology) into zeolite ZSM-5 (MFI topology) was carried out, without using organic structure directing agents, by addition of SiO2 to adjust the composition of the starting gel. Depending on the SiO2/Al2O3 molar ratio, zeolite Y can be present in amounts equivalent to those of seed-assisted syntheses. Zeolite Y was successfully transformed in ZSM-5, but a rigorous control of OH−/SiO2 and Na+/SiO2 molar ratios is necessary to avoid incomplete transformation and/or contamination by layered silicates, such as magadiite and kenyaite. For hydrothermal treatment duration lesser than 12 h, the phase dissolution of the Y zeolite is observed, resulting in amorphous phase after 24 h. From 48 h, nucleation and growth of ZSM-5 crystals, with increasing crystallinity up to 120 h, is observed. During the interzeolite transformation, FTIR spectra show the disappearance of the band at 568 cm−1 and the appearance of a band at 545 cm−1, assigned to the 5-membered double rings of ZSM-5. Scanning electron microscopy images suggest that the crystallites of zeolite Y condense and absorb silicate species from solution to form larger aggregates of ZSM-5 zeolite. These structural and morphological changes are accompanied by textural changes detected in nitrogen adsorption isotherms. These results suggested that a combined solution mediated and solid-state transformation mechanism is probably occurring. Since these zeolites do not possess any other structural features in common, RBU approach seems to be more adequate to describe this specific interzeolite transformation.

Improving the process of hydrothermal treatment and dehulling of different triticale grain fractions in the production of groats

The influence of hydrothermal treatment (grain moistening) and dehulling duration on the yield and quality of groats from different fractions of triticale grain was studied. Comparative analysis of groats yield and its culinary quality at different grain moisture, depending on its fractions, was performed. The degree of the influence of the studied factors on the yield and quality of triticale groats was determined. The influence of dehulling duration, the size of a triticale caryopsis and grain moisture content is reliable. These factors significantly influenced the groats yield and quality. In addition, the influence of the duration of grain dehulling was the highest. The highest groats yield was obtained at the dehulling duration of 20 s, the lowest – at dehulling for 180 s. The social survey was conducted and the main priorities for buyers of cereal products were established. It was proved that while choosing food, consumers pay the most attention to culinary characteristics of the finished product. It was established that it is optimal to dehull triticale grain for 100 s. The application of such parameters of treatment makes it possible to obtain the yield of whole groats of 88.8 % with the culinary quality of 6.7 points. The groats quality meets the requirements of DSTU 76992015 Wheat Groats. Technical specifications. Based on the research, it was established that the separation of the triticale grain into fractions that differ in their geometric properties, in particular, thickness, is effective. The peculiarities of groats yield, depending on the triticale grain fraction, were determined. Application of hydrothermal treatment of triticale grain (moistening up to 14.0 %) makes it possible to increase the groats yield up to 88.7 %. The treatment of the fractions with grain thickness less than 2.4 mm ensures the groats yield up to 87.8 %. The groats yield during dehulling the grain, which has a thickness of more than 2.4 mm, is from 88.8 to 89.1 %. To produce the groats from triticale grain, it is advisable to use the grains that have a thickness of 2.8 mm or more. The optimum duration of dehulling is 100 s. To increase the overall culinary assessment by 1 point, it is recommended to increase the duration of dehulling a large grain up to 140 s. This method differs from the classical one by the fact that it uses a large grain fraction with the lower moisture content. The developed recommendations can be used by grain processing enterprises during processing triticale with the view to intensifying the production.

Influence of hydrothermal treatment parameters on the phase composition of zeolites

Analcime was prepared by hydrothermal transformation of metakaolin-based geopolymer activated by means of sodium water glass. Gradual transformation of geopolymer through primary and unstable zeolitic phases up to final analcime was studied as a function of hydrothermal treatment duration (6–48 h) and access of water vapour under the selected conditions (165 °C, 0.5 MPa). Composition, microstructure, and thermal stability of the prepared samples were assessed using simultaneous thermogravimetry and differential scanning calorimetry, X-ray diffraction and high-temperature XRD analyses, and scanning electron microscopy. In the case of shorter autoclaving and access of water vapour, the mix of different zeolitic phases was formed: analcime, zeolite P2 gmelinite-Na, and chabazite-Na. From the time of 24 h and autoclaving in the closed moulds, pure cubic analcime was detected. Uniform microstructure of these samples comprised of trapezoid particles with the diameter between 50 and 60 µm. Prolongation of autoclaving time did not lead to the significant change of particle size and their composition. Dehydration of detected zeolites took place through the formation of defect or unknown zeolitic structures before the structural collapse happened.

Short-Time Hydrothermal Synthesis of CuBi2O4 Nanocolumn Arrays for Efficient Visible-Light Photocatalysis.

In this article, a short-time hydrothermal method is developed to prepare CuBi2O4 nanocolumn arrays. By using Bi(NO3)3·5H2O in acetic acid and Cu(NO3)2·3H2O in ethanol as precursor solutions, tetragonal CuBi2O4 with good visible light absorption can be fabricated within 0.5 h at 120 °C. Tetragonal structured CuBi2O4 can be formed after 15 min hydrothermal treatment, however it possesses poor visible light absorption and low photocatalytic activity. Extending the hydrothermal treatment duration to 0.5 h results in a significant improvement invisible light absorption of the tetragonal CuBi2O4. The CuBi2O4 obtained through 0.5 h hydrothermal synthesis shows a band gap of 1.75 eV and exhibits the highest photocatalytic performance among the CuBi2O4 prepared with various hydrothermal time. The removal rate of methylene blue by the 0.5 h CuBi2O4 reaches 91% under visible light irradiation for 0.5 h. This study proposes a novel strategy to prepare photoactive CuBi2O4 nanocolumn arrays within 0.5 h at a moderate temperature of 120 °C. The hydrothermal method provides a facile strategy for the fast synthesis of metal-oxide-based photocatalysts at mild reaction conditions.

Hydrothermal Preparation of Fe2O3 Nanoparticles for Fe-Air Battery Anodes

Fe2O3 nanoparticles were synthesized from iron nitrate [Fe(NO3)3·9H2O] by hydrothermal method for Fe-air battery anodes. The crystal structure and morphology of the obtained Fe2O3 powder were studied by x-ray diffraction and scanning electron microscopy. Fe2O3/acetylene black (AB) composite electrodes were fabricated by mixing the synthesized Fe2O3 nanoparticles with AB carbon and were then subjected to electrochemical measurements. Results indicated that the duration of hydrothermal treatment significantly influences the morphology and size of synthesized Fe2O3. The morphology and particle size of Fe2O3 also affect the electrochemical properties of Fe2O3/AB composite electrodes, viz., smaller particles provide greater capacity than larger ones. The resistance of electrodes gradually increases during cycling, thereby causing a decrease in the capacity of Fe2O3/AB electrodes.

Improvement of the process of hydrothermal treatment and peeling of spelt wheat grain during cereal production

The influence of hydrothermal treatment (grain moistening, steeping) and peeling duration on the yield and quality of spelt wheat cereal was studied. The mechanism of the influence of the studied factors on the formation of cereal and culinary quality of the product was established. A comparative analysis of the yield and quality of cereals after hydrothermal treatment at actual humidity content from 13.0 to 14.0 % was performed. Due to the hydrothermal treatment, the properties of the endosperm and shells change significantly. This leads to an increase in the strength of endosperm and formation of higher yield of the finished product. The influence of peeling duration and hydration gradient on the yield of cereal and middling is reliable. The influence of duration of spelt wheat steeping on this process was insignificant. Application of grain damping (humidity content of 15.0–16.0 %) makes it possible to increase the yield of cereal from 88.6 % to 91.7 %. Culinary quality does not change in this case. The obtained mathematical models of the influence of damping steeping, peeling of grain on the yield and quality of cereals are linear. Their accuracy is proved by the high determination coefficients ( R 2 =0.97‒0.98) and by the absence of autocorrelation of residues. In the technology of production of cereals from spelt wheat the recommended method of hydrothermal treatment implies its damping up to 15.0 % of moisture content, which makes it possible to increase the yield of cereals by 3.1 %. The difference from the classical method is the absence of the grain steeping phase before peeling. Damping of spelt wheat grain up to 15.0 % with peeling duration of 160 s is optimum. The proposed way of treatment allows getting 86.5 % of cereals with culinary quality of 8–9 points. The developed recommendations may be used by food industry enterprises during conducting marketing activities or production intensification.

Optimization By Experimental Design of the Synthesis of RuxIr1-XO2 Electrocatalysts for the Oxygen Evolution Reaction in a PEM-URFC

IntroductionThe Oxygen Evolution Reaction (OER) is a crucial bottleneck for developing water electrolysis cells, such as Proton Exchange Membrane Electrolysis Cells (PEMEC) and/or Unitized Regenerative Fuel Cells (URFC), since the cell voltage is mainly limited by the slow kinetics of the oxygen electrode leading to relatively high energy consumption (5 kWh/Nm3 of H2). Many transition metal oxide electrocatalysts of the OER have been developed for many years [1-3], most of them based on ruthenium iridium mixed oxides RuxIr1-xO2 [2-5]. The electrocatalytic activity and the OER mechanism depend greatly on the crystalline size and structure of the catalytic materials which are determined by the synthesis method, such as the polyol method [6], the instant method [7] or the Pechini-Adams method [8]. In this communication we will present a new method, i.e. the hydrothermal synthesis [9], which allows to control the morphology of metal oxide nanoparticles, particularly to obtain crystalline nanoparticles of small size (~ 6 nm). This method, which requires an autoclave reactor to control the pressure up to 5 bars and the temperature up to 200°C, was mostly used until now for the preparation of ruthenium oxides for super capacitors [10]. The crystallographic structure and the average size of the nanoparticles obtained depend on 4 factors: pH of the synthesis medium (pH)Temperature of the hydrothermal treatment (TH)Duration of the hydrothermal treatment (DH)Temperature of the subsequent annealing treatment under air (AT) which have been varied in 4 levels leading to 44 = 256 experiments for a complete experimental design. Using a fractional experimental design of the hydrothermal synthesis of ruthenium oxides reduces this number to 16 experiments and allows optimizing the electrocatalytic properties of the nanoparticles obtained. In particular 2 catalysts, e.g. one with an optimized structure leading to an OER high current density (135 mA cm-2 at 1.8 V vs. RHE), and the other one with an optimized particle size of 10 nm, led to experimental responses close to those predicted by the experimental design [11]. Mixed RuxIr1-xO2 electrocatalysts with a larger particle size are more convenient to use as an electronic conducting support, particularly stable at the high electrode potential encountered in the OER, and allowing the deposition of supported Pt nanoparticles for the Oxygen Reduction Reaction (ORR). ExperimentalFour electrocatalysts (RuO2, Ru0.75Ir0.25O2, Ru0.5Ir0.5O2, Ru0.25Ir0.75O2) for the OER were synthesized by the optimized hydrothermal method, and characterized by physicochemical methods (XRD, TEM, TGA) and electrochemical methods (CV, LSV). A bi-functional electrocatalyst (Pt/IrRuO2) was prepared by deposition of Pt nanoparticles on a Ru0.75Ir0.25O2 catalyst acting as a conducting support. Their electrocatalytic properties were investigated in a 3-electrode electrochemical cell thermostated at 25°C by recording the polarization curves, j(E), at a very slow sweep rate (1 mV s-1) from 1.2 V to 1.9 V vs. RHE for the OER and from 1.05 V to 0.45 V vs. RHE for the ORR in an Unitized Regenerative PEM FC (PEM-URFC). Some conclusions A bi-functional electrocatalyst (Pt/IrRuO2) is able to activate both the OER and the ORR.However the electrode stability is questionable since platinum can be oxidized at high potential so that the reduction of oxygen needs higher overvoltages.The potential of the positive electrode can be decreased by oxidizing, instead of water, another hydrogen-containing compound, such as methanol, in the presence of water, allowing a better durability of electrode materials and a decrease of the electric energy consumption. [1] S. Trasatti, Electrochim. Acta 29 (1984) 1503. [2] S. Park, Y.Y. Shao, J. Liu, Y. Wang, Energy Environ. Sci. 5 (2012) 9331-9344. [3] T. Reier, H.N. Nong, D. Teschner, R Schlogl, P. Strasser, Advan. Energy Mat, 7 (2017). [4] J.B. Cheng, H.M. Zhang, G.B. Chen, Y.N. Zhang, Electrochim. Acta 54 (2009) 6250-6256. [5] S. Siracusano, N. Van Dijk, E. Payne-Johnson, V. Baglio, A.S. Aricò, Appl. Catal. B: Environ. 111–112 (2012) 376–380. [6] T. Audichon, B. Guenot, S. Baranton, M. Cretin, C. Lamy, C. Coutanceau, Appl. Catal. B: Environ. 200 (2017) 493-502. [7] A. Devadas, S. Baranton, T.W. Napporn, C. Coutanceau, J. Power Sources 196 (2011) 4044-4053. [8] J. Ribeiro, M. S. Moats, A.R. Andrade, J. Appl. Electrochem. 38 (2008) 767-775. [9] K.H. Chang, C.C. Hu, C.Y. Chou, Chem. Mat. 19 (2007) 2112-2119. [10] K.H. Chang, C.C. Hu, Electrochem. Solid-State Lett. 7 (2004) A466-A469. [11] B. Guenot, PhD Thesis, May 2017, University of Montpellier, France

Synthesis and Study of New Luminescent Carbon Particles with High Emission Quantum Yield

Luminescent carbon nanoparticles (CNPs) having a high mass yield of carbon material and emission quantum yield are synthesized from lentil grain flour via thermal carbonization, followed by treatment in nitric acid, and by the hydrothermal method. The luminescent and optical properties, solubility, and stability of solutions of various CNPs during interaction between particles and electromagnetic radiation are studied and analyzed by photoluminescence and optical absorption methods. When carbonization temperatures are 400 and 500°C, the mass yields of carbon materials are 34.6 and 29.7%, respectively. The amount of CNPs whose sizes are less than 50 nm is 7.2–12.5%, whereas the proportion of particles soluble in pure water is no more than 0.8% of the weight of a carbon material. New particles having a mass yield of 81–104% and high solubility of CNPs in water are formed as a result of special treatment of carbon material powders in HNO3. The solubility of CNP powders is strongly dependent on temperature and pH of a solvent; some samples achieve 30.3 g/L at 96.9°C. The energy of the direct band gap of CNPs is 3.325–3.445 eV, and the carbon nuclei of the particles contain structural defects and various surface groups of high concentration. Some absorption bands, including those at 271 (NH1) and 370 nm (NH2), appear in the optical absorption spectra after hydrothermal treatment of all CNPs in the presence of ammonia or urea. The structural features of the NH1 and NH2 bands, the photoluminescence spectra, and the magnitudes and the stability of quantum yields of different CNPs are thoroughly studied depending on temperature and duration of hydrothermal treatment. The maximum quantum yield of the best CNP samples during excitation with 406 nm laser radiation is 39.3%, which is a promising indicator for practical use.