Conventional Hydrothermal Method Research Articles

Valorization of coal fly ash into nanozeolite by sonication-assisted hydrothermal method

The study aimed at the recycle and reuse coal fly ash (CFA) via a fast green method. Increasing dependence of coal in power sector results in increased production of CFA, the disposal of which is a major environmental issue. Sonication assisted hydrothermal (UAH) treatment has been employed to convert this CFA into versatile nanozeolite X (NZX) from CFA. The effect of CFA/NaOH, fusion temperature, fusion time and ultrasonication time were investigated. Initial precursor CFA and the synthesized NZX were characterized by XRF, XRD, FESEM, TEM, and FTIR analysis. UAH treatment produced NZX in shorter crystallization time than conventional hydrothermal (CH) method. The particle size of UAH-NZX were obtained from FESEM, BET, TEM analysis as 22–27 nm, 24.36 nm, and 2–5 nm respectively. Average crystal size of UAH-NZX was 21.58 nm as calculated using Scherrer's equation. The optimized condition for the UAH synthesis of NZX was found as CFA/NaOH ratio of 1.25, fusion temperature of 550 °C, fusion time of 1.5 h, and ultrasound time of 20 min. The characteristics of UAH-NZX zeolite was compared with CH-NZX and commercial zeolite X (CZX). The pure NZX was formed by UAH technique with 20 min ultrasound, followed by 6 h hydrothermal treatment at room temperature whereas CH technique took 96 h of hydrothermal digestion at 120 °C. The optimized CEC value of NZX, conventional hydrothermal zeolite X (CH-ZX), and CZX are 428 mmol/100 g, 242 mmol/100 g, and 293 mmol/100 g respectively. The UAH method produced NZX at shorter time with less consumption of energy than CH method with nanozeolite with higher CEC and surface area (797.53 m2/g) than both CH-NZX and CZX. The nanoscale zeolite X can be used efficiently as ion exchanger as well as adsorber.

Synthesis of high silica SSZ-13 in fluoride-free media by dry gel conversion method

Abstract Chabazite SSZ-13 has attracted wide attention due to its physiochemical properties and excellent potential as a catalyst for various application. In this study, pure phase SSZ-13 CHA zeolite with wide range of Si/Al ratio has been synthesized in a fluoride-free media by dry gel conversion method where the conversion of SSZ-13 from aluminosilicates precursor gel occurs under water vapor. The difference between products produced by conventional hydrothermal synthesis method and the new method has been investigated and characterized with XRD, SEM, XRF, and N2 adsorption. Pure SSZ-13 with wide range of Si/Al up to 182 was obtained by dry gel conversion method while pure SSZ-13 with higher Si/Al ratio than 20 with similar starting gel composition could not synthesized by hydrothermal synthesis method. Our work has demonstrated that dry gel conversion method was an effective method to synthesize pure SSZ-13 with a wide range of Si/Al ratio under fluoride media-free condition.

High mass loading of h-WO3 and α-MnO2 on flexible carbon cloth for high-energy aqueous asymmetric supercapacitor

The increasing interest in portable and consumable electronics demands efficient and low-cost energy storage devices with excellent energy storing capacity. From this point, a high mass loading of the active electrode material on three-dimensional current collectors is favorable for obtaining a higher energy storing capacity for the corresponding device. The present study demonstrates an ideal example of high-performance aqueous asymmetric supercapacitors (SCs) using α-MnO2 nanowires as the positive electrode and h-WO3 nanorods as the negative electrode, respectively. Initially, one-dimensional (1D) nanostructures composed of α-MnO2 and h-WO3 are prepared on carbon cloth by a conventional hydrothermal method. The prepared α-MnO2 and h-WO3 with a high mass loading of 4.9 mg/cm2 and 5.8 mg/cm2, respectively, show excellent electrochemical features in aqueous Na2SO4 electrolyte in the positive and negative potential regions. A high-performance asymmetric SC is developed with uniquely engineered electrodes, which exhibits the excellent electrochemical performance in an extended potential window of 1.4 V and with excellent cycling stability of ∼135% after 7500 cycles with a volumetric capacitance of 350 mF/cm3 and energy density of 0.095 mWh/cm3. This authentic scheme may offer new opportunities for developing asymmetric arrangements for energy storage devices in various portable electronic systems with a high mass loading.

Microwave-assisted preparation of hierarchical CuO@rGO nanostructures and their enhanced low-temperature H2S-sensing performance

Hierarchical CuO@rGO nanostructures, consisting of CuO nanoparticles (NPs) and reduced graphene oxide (rGO) nanosheets, were prepared with a normal-pressure microwave-assisted in-situ growth process. In the CuO@rGO composites, CuO NPs with a size range of 4–11 nm are uniformly anchored on rGO surfaces. In contrast, CuO particles of large and non-uniform distribution in the CuO-doped rGO nanosheets (CuO/rGO) were prepared by a conventional hydrothermal method. The CuO@rGO sensors show high response and selectivity to H2S (1–10 ppm) at low operating temperatures (50–150 °C). The mass ratio of copper acetate to graphene oxide during preparation (6–10) is found to highly influence the gas-sensing properties, and the 8-CuO@rGO sample shows the highest H2S-sensing performance at 100 °C. Compared with pristine CuO nanocrystals, the 8-CuO@rGO composite exhibits considerably enhanced gas-sensing performance, such as good response, high selectivity and low optimal temperature. The improved H2S-sensing performance of the CuO@rGO composites can be attributed to the synergistic effect in components and their hierarchical nanostructure.

Investigation of structural, optical and electrical properties of transition metal oxide semiconductor CdO[sbnd]ZnO nanocomposite and its effective role in the removal of water contaminants

In this technological era as the usage and development of technology is on the rise we encounter serious repercussions of pollution in both drinking and daily usage of water. Nanocomposite of Cadmium Oxide and Zinc Oxide (CdOZnO) has the property of alienating the pollutants from the water. A conventional hydrothermal method was adapted for the preparation of nanocomposite of CdOZnO from their respective metal acetate dihydrates and NaOH. Structural and morphological analysis by electron beam diffraction technique reveals the formation of unique nanorod with spherical morphology of the synthesized particle. Williamson-Hall method was used to find the crystallite size and the lattice strain. Fourier transforms infrared (FTIR) spectroscopy further confirmed the stretching and vibration of chemical bonds of the materials. The study of electronic transitions within the material was portrayed with UV–Vis absorption spectrum and the obtained energy gap is 3.99 eV. A thorough investigation of temperature dependent electrical properties of CdOZnO nanocomposite was carried out in the frequency range from 50 Hz to 5 MHz. Studies revealed that the composite material is responsible for higher photocatalytic performance under the irradiation of UV photon. The high photocatalytic activity was originated from superoxide O2− radicals due to the efficient trapping of photogenerated electrons in CdO by ZnO.

Preparation and catalytic behavior of reduced graphene oxide supported cobalt oxide hybrid nanocatalysts for CO oxidation

Abstract The reduced graphene oxide (rGO) supported cobalt oxide nanocatalysts were prepared by the conventional precipitation and hydrothermal method. The as-prepared rGO-Co3O4 was characterized by the XRD, Raman spectrum, SEM, TEM, N2-sorption, UV-Vis, XPS and H2-TPR measurements. The results show that the spinel cobalt oxide nanoparticles are highly fragmented on the rGO support and possess uniform particle size, and the as-prepared catalysts possess high specific surface area and narrow pore size distribution. The catalytic properties of the as-prepared rGO-Co3O4 catalysts for CO oxidation were evaluated through a continuous-flow fixed-bed microreactor-gas chromatograph system. The catalyst with 30% (mass fraction) reduced graphene oxide exhibits the highest activity for CO complete oxidation at 100 °C.

Evolution of defects and their effect on photoluminescence and conducting properties of green-synthesized ZnS nanoparticles

We have grown ZnS (zinc sulfide) nanoparticles (NPs) by hydrothermal and microwave (MW) heating method and a comparative study on the physical properties was carried out. Zinc acetate dihydrate (ZAD) and thioacetamide (TA) were used as Zn and S precursors, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) pattern revealed the cubic structure for ZnS and nanocrystalline nature of the samples. The careful observation of the XRD patterns of the samples grown by hydrothermal and microwave heating method indicate that microwave-synthesized ZnS (ZnS–MW) samples were strained compared to those grown by conventional hydrothermal methods. Uniform sized smaller nanoparticles were formed during microwave irradiation in a much shorter time. UV–Vis absorption spectra indicated quantum confinement effect. The emission peaks in photoluminescence spectra indicate the presence of various point defects in the samples. In the microwave synthesized sample, nucleation and growth process of the ZnS crystallites are very quick, leading to the formation of defects. The dielectric studies of both types of the samples show a typical behavior of polycrystalline semiconducting material. Under the applied A.C. fields, the conduction phenomena provide sufficient evidence for the electronic hopping between localized sites. Lower values of activation energy obtained for both dipolar relaxation and DC conductivity in the case of microwave synthesized sample indicate the applicability of such materials in various switching applications.

Fast synthesis of hierarchical CHA/AEI intergrowth zeolite with ammonium salts as mineralizing agent and its application for MTO process

Fast solvent-free synthesis of hierarchical SAPO-34/18 zeolite was realized by combining oil-bath heating and the addition of catalytic amount of ammonium salt. The obtained zeolite samples were systematically characterized by XRD, SEM, XRF, BET, NH3-TPD, and NMR. XRD and SEM results showed that high-quality SAPO-34/18 nano-crystals with plate morphology can be obtained in only 60 min. The addition of ammonium salt served as mineralizing agent which speeded up the crystallization process in solvent-free precursor. The fast heat transfer of oil-bath heating and seeding also contributed to the ultrafast synthesis. Nitrogen adsorption–desorption analysis indicated the presence of high BET surface area and micropore volume, as well as abundant mesopores and macropores. NH3-TPD and 29Si NMR results showed that the samples exhibited appropriate acid strength and concentration. The obtained SAPO catalysts showed excellent performance in MTO reaction with significantly longer catalytic lifetime and higher propylene and butylene selectivities, compared with micron-sized SAPO-34 catalyst made with the conventional hydrothermal method. The extended lifetime could be attributed to the thin-plate crystal morphology and hierarchical pore structure, which greatly alleviated the diffusion constrain and coke deposition in MTO reaction. Higher propylene and butylene selectivities could be ascribed to the larger size of the AEI cage, which allows the easy diffusion of longer alkenes. The realization of ultrafast synthesis with solvent-free precursor not only reduces the waste disposal and energy consumption, but also increases the autoclave efficiency significantly.

Template-free synthesis and photocatalytic activity of {0 0 1}-facets exposed rhombohedral NaNbO3 microcrystals

The synthesis and photocatalytic activity of rhombohedral sodium niobate powders by conventional template-free hydrothermal method from NaOH and different polymorphic types of Nb2O5 as starting materials with the presence of KOH as a mineralizer was reported in this work. The results showed that, interestingly, by using freshly-produced amorphous Nb2O5·xH2O, the rhombohedral NaNbO3 plate-like microcrystals with a high c-axis orientation and {0 0 1}-exposed basal facets can be received readily at temperature as low as 180 °C for 24 h. With commercialized monoclinic or orthorhombic Nb2O5 precursors, however, only the pure orthorhombic or a mixture of orthorhombic and rhombohedral NaNbO3 was obtained, respectively. The first-time photodegradation evaluation of methylene blue under UV irradiation for 2 h showed that this polymorphic type can be used as a novel photocatalyst with high photodegradation efficiency for both c-axis oriented, {0 0 1}-facets exposed sample (79%) and random oriented powders (66%). The enhanced photocatalytic activity of the c-axis oriented rhombohedral NaNbO3 microcrystals is ascribed to their {0 0 1}-exposed facets.

MoS2-Pt Nanoparticles Deposited on Carbon Nanostructures By a Microwave Assisted Method As Hydrogen Electrodes for H2 – Br2 Flow Batteries

The use and implementation of renewable energies has increased worldwide in recent years as a green and sustainable alternative to fossil fuels. Among the renewable energies available, wind and solar stand as the first choice to achieve this goal. Although the use of solar and wing have multiple advantages, their availability and efficient use are limited by their intermittent nature. For this reason, there has been an urgent need to design systems that store energy when is produced in excess for further use, thus, this will be always available. Redox flow batteries (RFBs) have been recognized as one of the most suitable options among the electrochemical technologies to store energy at large scale (kW - MW) and also to facilitate the integration of solar or eolic energy to the electricity grid. Over the last three decades, different RFB chemistries have been proposed and successfully demonstrated for practical applications, for instance, the all vanadium RFB. Recently, the hybrid H₂-Br₂ system has attracted attention as possible candidate for energy storage because its high power and efficiency, low reactant cost, fast kinetics and great reversibility. The redox reactions of Br₂ and H2 at the negative and positive electrode, respectively, are responsible for the energy storage with a theoretical Ecell=1.09 V. In general, the reactions of Br2 are reversible and exhibit fast kinetics on carbon felt electrodes. At the H2 electrode, the hydrogen reactions are performed at a Pt/C electrocatalyst in order to achieve low activation overpotential and fast kinetics. However, Pt electrocatalyst is poisoned by crossover of bromine and bromide species from the positive electrode to the negative electrode through the membrane during operation. Consequently, the kinetics of the H₂ reactions is affected which decreases the efficiency and energy storage capacity of the device. Some transition materials have been investigated as alternative electrocatalysts for hydrogen reactions. For example, it has been reported that MoS2 presents good catalytic activity and low overpotentials towards the hydrogen reactions. However, it is necessary to perform a fundamental study of MoS2 as electrocatalyst for the hydrogen reactions in presence of bromine and bromide species. Additionally, new synthesis methods should be explored in order to enhance the physical, chemical and electrocatalytic properties of MoS2 for its possible use in the design of H2 electrodes for the hybrid H2-Br2 RFB. In this research, MoS2 - Pt nanoparticles are synthesized directly on carbon nanostructures by a single step microwave assisted solvothermal or hydrothermal method. Carbon Nanosponge (CNS), N2 – doped Carbon Nanotubes (N2-CNT) or Multiwall Carbon Nanotubes (MWCNT) are considered in this study. The kinetics and electrocatalytic activity of the MoS2 – Pt nanoparticles are studied by cyclic voltammetry (CV), rotating disk electrode (EDR) and electrochemical impedance spectroscopy (EIS) towards the hydrogen reactions in acidic media with additions of HBr. Scanning electron microscopy (SEM) and X-Ray diffraction (XRD) are carried out to study the distribution and particle size, morphology and crystalline phases present in the MoS2-Pt/C nanomaterials. The synthesis time of the MoS2-Pt on carbon assisted by microwave is highly reduced as compared with the conventional solvothermal or hydrothermal methods, 10 min vs. 36 h. Preliminary electrochemical studies show that MoS₂-Pt based materials exhibit stability in the presence of HBr for further use as H₂ electrodes in a H₂-Br₂ RFB. Keywords: energy storage, nanomaterials, hydrothermal synthesis, RFB

All-Solid-State Supercapacitors Based on Flexible Co3O4 Nanoflowers/rGO Nanocomposites

Co3O4 nanoflowers were synthesized by a conventional hydrothermal method at 180°C for 12 h, and flexible Co3O4 nanoflowers/reduced graphene oxide (rGO) nanocomposites were prepared by mechanical mixing with rGO. The all-solid-state supercapacitors (SCs) were constructed using flexible Co3O4 nanoflowers/rGO nanocomposites as electrodes and KOH-PAAK gel as electrolyte. The results show that the obtained SCs have nearly rectangular cyclic voltammetry and linear charge/discharge curves, which indicate its fast electronic migration and response speed. The specific capacitance of the SC is as high as 190 F/g, with an excellent cycling performance (capacitance retention of 90% after 10,000 cycles). The cyclic voltammetrys of SCs are almost unchanged and can work normally when bent from 0° to 180°, exhibiting high flexibility and good reliability of the Co3O4 nanoflowers/rGO nanocomposites. In addition, a green light-emitting diode, electronic watch and electronic scale have been successfully powered by the as-fabricated SCs and can work for several minutes. All the performances have shown that the Co3O4 nanoflowers/rGO nanocomposites could have potential practical applications in the future in flexible energy storage devices.

Transformation of CO2 with glycerol to glycerol carbonate by a novel ZnWO4-ZnO catalyst

ZnWO4-ZnO catalysts with different W content were prepared by conventional hydrothermal and wet impregnation methods and applied in the direct synthesis of glycerol carbonate from CO2 and glycerol. The crystallite structure, texture property, morphology, redox and acid-base properties and the surface chemical situation of the catalysts were characterized by XRD, BET, TEM, H2-TPR, NH3/CO2-TPD and XPS. The possible activation routes of CO2 and glycerol were analyzed with DRIFTS and FTIR. ZnWO4-ZnO composite catalysts showed better catalytic performances with respect to ZnO in the carbonylation of glycerol with CO2. The improved activity of ZnWO4-ZnO catalysts was associated with the formation of ZnWO4, the interaction between ZnWO4 and ZnO, and the enhanced moderate acidic property. DIRFTS results showed that chelating bidentate carbonate species was the main adsorption pattern for CO2 on ZnO, while the introduction of W led to the bridged bidentate carbonate, which became the main adsorption pattern on ZnWO4-ZnO. As for the activation of glycerol, zinc glycerolate played an important role in the reaction process. Based on the reaction and characterization results, a plausible reaction route involved a seven-membered ring esters intermediate was suggested for the reaction of CO2 and glycerol over ZnWO4-ZnO catalysts.

Synthesis of acicular α-Bi2O3 microcrystals by microwave-assisted hydrothermal method

ABSTRACTMaterials based on bismuth(III) oxide are candidate to be used in optical and electronic devices because of their properties such as a variable band gap, photoconductivity, photoluminescence, high refractive index, and dielectric permittivity. These properties are dependent of several factors, e.g., present phases and crystal morphology. The microwave-assisted hydrothermal method (MAH) is a fast and efficient approach of synthesis to obtain semiconductor powders. However, the synthesis of monoclinic bismuth oxide (α-Bi2O3) with acicular morphology by MAH was not found in literature. In this paper, microcrystals of acicular α-Bi2O3 (monophasic) were successfully obtained by MAH using a synthesis temperature of 80°C for 0.5 h. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron, and transmission electron microscopies showed the formation of a monoclinic structure (space group P21/c) with acicular morphology that grew along the [001] direction. The temperature and time necessary to synthetize acicular microcrystals were significantly lower than those found for acicular microcrystals obtained by conventional hydrothermal method.

Effect of Surface Trap States on Photocatalytic Activity of Semiconductor Quantum Dots

Semiconductor quantum dots (QDs) are promising photocatalysts for water splitting due to the large specific area, but the influence of surface trap states on the photocatalytic activity of QDs is still not fully understood yet. To answer this question, CdSe QDs with the same morphology, diameter, crystal structure, and energy level are prepared following a hydrazine hydrate (N2H4) promoted synthesis strategy and conventional hydrothermal synthesis method. Through various characterizations and analysis, it is found that the conventional hydrothermal synthesized CdSe QDs (H-CdSe QDs) have a high concentration of Cd-involved shallow electron trap states, which seriously hinder the charge separation and transfer between CdSe and cocatalysts. In contrast, the N2H4 promoted synthesis strategy provides an energy-saving, low-cost, and facile pathway to eliminate the surface shallow electron traps, ensuring an efficient charge separation and H2 production in CdSe QDs. As a result, the N2H4-promoted synthesized CdS...

Hydrothermal synthesis and polarized micro-Raman spectroscopy of copper molybdates

Conventional and microwave-assisted hydrothermal methods were used to synthesize Cu3(MoO4)2(OH)2 ceramics. Different experimental conditions of temperature, time and precipitation rate were employed to explore the growth mechanisms, structural and morphological properties of the obtained copper molybdates. The use of microwave-assisted reactors at 150 °C/10–30 min produced a mixture of copper molybdate hydrates, while only Cu3(MoO4)2(OH)2 was obtained by using microwave processing at longer times (above 120 min) or conventional hydrothermal reactors (110–250 °C/24 h). Experiments conducted after fast and slow coprecipitation rates resulted in different crystallographic phases and morphologies. Flower-like and rod-like micrometer-sized ceramics were produced with high anisotropy and single-crystalline nature. A better understanding on the growth mechanisms, as well as on the structural and morphological characteristics of copper molybdates was attained. Based upon the relative enhancement of Raman bands in parallel or in perpendicular configuration, a symmetry assignment of 34 (17Ag + 17Bg) external modes for Cu3(MoO4)2(OH)2 ceramics (42 bands are expected) was possible. Besides, five (of six possible) internal OH-stretching modes were identified in the spectral region above 3200 cm−1.

Ultrafast synthesis of *BEA zeolite without the aid of aging pretreatment

The present study focuses on the ultrafast synthesis of *BEA zeolite, which constitutes one of the most industrially important zeolites. A pure *BEA phase was successfully synthesized within 10 min at 210 °C by carefully tuning the composition of the initial reactant mixture. To date, the ultrafast synthesis of several industrially important zeolites is achieved with the aid of aging pretreatment, followed by high temperature hydrothermal treatment. In this study, we first demonstrated the 10-min synthesis of *BEA zeolite employing organic structure-directing agents (OSDAs), without any aging process. The employment of sealed pipe reactor in conjunction with the optimization of chemical composition of starting materials are critical in obtaining pure *BEA phase in a short time. The fast-synthesized *BEA zeolite possesses properties that are similar to those synthesized by conventional hydrothermal synthesis methods in terms of crystallinity and micropore volume. A comprehensive investigation on the effects of various parameters on the seed-assisted crystallization of *BEA zeolite was also studied.

Synthesis, characterization, and application of ruthenium-doped SrTiO3 perovskite catalysts for microwave-assisted methane dry reforming

A series of ruthenium-doped strontium titanate (SrTiO3) perovskite catalysts were synthesized by conventional and microwave-assisted hydrothermal methods. The structure was analyzed by X-Ray diffraction (XRD) confirming the formation of the perovskite phase with some TiO2 anatase phase in all the catalysts. Microwave irradiation decreases the temperature and time of synthesis from 220 °C for 24 h (conventional heating) to 180 °C for 1h, without affecting the formation of perovskite. A 7 wt. % ruthenium-doped SrTiO3 catalyst showed the best dielectric properties, and thus its catalytic activity was evaluated for the methane dry reforming reaction under microwave heating in a custom fixed-bed quartz reactor. Microwave power, CH4:CO2 vol. % feed ratio and gas hourly space velocity (GHSV) were varied in order to determine the best conditions for performing dry reforming with high reactants conversions and H2/CO ratio. Stable maximum CH4 and CO2 conversions of ∼99.5% and ∼94%, respectively, at H2/CO ∼0.9 were possible to reach with the 7 wt. % ruthenium-doped SrTiO3 catalyst exposed to maximum temperatures in the vicinity of 940 °C. A comparative theoretical scale-up study shows significant improvement in H2 production capability in the case of the perovskite catalyst compared to carbon-based catalysts.

Effect of CO2 in the oxidative dehydrogenation reaction of propane over Cr/ZrO2 catalysts

Investigation was made on the effect of chromium content, and method of hydrothermal preparation of Cr/ZrO2 catalysts on their catalytic properties for CO2 oxidative dehydrogenation of propane (ODP). The catalysts were characterized by nitrogen physisorption, X-ray diffraction, Raman spectroscopy, and temperature programmed reduction and desorption of CO2 (TPD-CO2). The Cr/ZrO2 catalysts containing various chromium contents between 2.5 and 15 wt.% of Cr were prepared by conventional and microwave-assisted hydrothermal methods. Tetragonal ZrO2 was formed, with higher Cr contents, and smaller crystallite sizes obtained using the microwave-assisted method. The relationship between selectivity to propene and propane conversion suggested that independent of the preparation method, the catalytic properties could be classified in two groups, with low and high chromium contents. The TPD-CO2 results showed that a fraction of the CO2 was desorbed at temperatures higher than 500 °C, with simultaneous reduction of Cr(VI) species. The presence of CO2 in the reactants caused strong decreases of activity, selectivity, and yield towards propene. These results suggested that CO2 adsorbed strongly on the chromium oxide active sites for dehydrogenation of propane. The Cr/ZrO2 catalysts were active and selective for dehydrogenation of propane in the absence of CO2 (CDP), and became deactivated with time on stream. The activity was reestablished by thermal treatment with CO2 or O2 after deactivation in CDP catalytic cycles, with the activity always being reestablished by treatment in O2. The deactivation occurred by reduction of Cr(VI) species and by deposition of carbonaceous species produced in oligomerization reactions.

Promotional synergistic effect of Sn doping into a novel bimetallic Sn-W oxides/graphene catalyst for selective oxidation of alcohols using aqueous H2O2 without additives

A series of novel catalysts with bimetallic Sn-W oxides uniformly dispersed on reduced graphene oxide (denoted as Sn-W/RGO) were successfully prepared via a conventional one-pot hydrothermal method. Interestingly, it was found that the introduction of Sn could significantly improve the catalytic activities compared with single WO3/graphene catalyst for selective oxidation of alcohols using H2O2 without organic solvents and additives. Subsequently, the catalysts were characterized by FT-IR, XRD, Raman, FESEM, EDS, HRTEM, XPS and N2 adsorption-desorption to investigate the promotional synergistic effect of Sn among catalyst structure, surface properties and catalytic performance. The results revealed that the incorporation of Sn had induced the formation of hexagonal WO3 with dominant exposed (001) and (200) planes, meanwhile, doping Sn could dramatically increase the specific surface area, change the structural properties and enhance the interactions between Sn-W oxides and graphene, which were beneficial to the improvement of catalytic performance. Additionally, reaction parameters (temperature, time, oxidant dosage and catalyst amount) were also explored. Both aryl and alkyl alcohols exhibited high conversion and selectivity to corresponding target products over the catalyst. And delightedly, the robust catalyst could be reused for five times without significant loss in catalytic efficiency. This work demonstrates the promotional synergistic effect of Sn in a novel Sn-doped WO3/RGO catalyst and makes it a promising candidate in green oxidation of alcohols under mild reaction conditions.

Syntheses, Structure, and 2/5 Magnetization Plateau of a 2D Layered Fluorophosphate Na3Cu5(PO4)4F·4H2O

A new two-dimensional (2D) fluorophosphate compound Na3Cu5(PO4)4F·4H2O with a Cu5 cluster has been synthesized using a conventional hydrothermal method. The compound crystallizes in the orthorhombic crystal system with space group Pnma. The 2D layered structure is formed by cap-like {Cu5(PO4)4F} building units consisting of a Cu4O12F cluster plus a residual cap Cu2+ ion. Magnetic susceptibility exhibits a broad maximum at T2 = 19.2 K due to low-dimensional character followed by a long-range antiferromagnetic ordering at T1 = 11.5 K, which is further confirmed by the specific heat data. High-field magnetization measurement demonstrates a 2/5 quantum magnetization plateau above 40 T. The ESR data indicate the presence of magnetic anisotropy, in accordance with the 2D structure of the system.