共查询到20条相似文献,搜索用时 31 毫秒
1.
Daniela Aiello Rosario Aiello Flaviano Testa Tonino Martino Iolinda Aiello Massimo La Deda Mauro Ghedini 《Journal of photochemistry and photobiology. A, Chemistry》2009,201(2-3):81-86
New luminescent inorganic–organic hybrid materials incorporating the luminescent zinc(II) complex ZnL2 (λem = 457 nm and Φem = 4.4% reference values for ZnL2; HL = chelating ligand resulting from the reaction between salicylaldehyde and 3-aminopropyltriethoxysilane), covalently bonded to different types of mesoporous silica hosts (namely MCM-41, MCM-48 and SBA-15), were prepared via both the methods of grafting post-synthesis (GPS) and one-pot synthesis (OPS). The products obtained, which form the GPS [(GPS)(Zn/MCM-41), (GPS)(Zn/MCM-48), (GPS)(Zn/SBA-15)] and the OPS [(OPS)(Zn/MCM-41), (OPS)(Zn/MCM-48), (OPS)(Zn/SBA-15)] series, contain the ZnL2 guest covalently bonded to the silica framework through silicon–oxygen bonds formed when the silane group is placed at the periphery of the Zn(II) coordination sphere. GPS and OPS materials were characterized by powder X-ray diffraction, N2 adsorption/desorption, thermogravimetric analysis (TGA) and UV/vis spectroscopy. For the new mesoporous materials the emission quantum yield (EQY) was measured by means of an integrating sphere combined with a spectrofluorimeter. The ZnL2 loading (measured by the ZnL2/SiO2 ratio calculated from TGA data) for MCM-41 appears to be independent of the synthesis procedure, whereas, for both MCM-48 and SBA-15, the ZnL2/SiO2 ratio of the materials obtained via OPS is about four times higher than products obtained from GPS. The ZnL2 loaded GPS and OPS series show λem maxima at about 485 and 455 nm, respectively. Moreover, with reference to EQY (GPS)(Zn/SBA-15) and (OPS)(Zn/SBA-15), although featuring ZnL2/SiO2 ratios of 0.13 and 0.45, respectively, they showed similar EQY values: 2% and 5%. On the contrary, (GPS)(Zn/MCM-41) and (OPS)(Zn/MCM-41) which give similar ZnL2/SiO2 ratios (0.09 and 0.14) exhibit very different EQY, i.e. 2% and 22%, respectively. 相似文献
2.
Andressa H. de Morais Batista Francisco F. de Sousa Sara B. Honorato Alejandro P. Ayala Josue M. Filho Francisco W. de Sousa Antonio N. Pinheiro J.C.S. de Araujo Ronaldo F. Nascimento Antoninho Valentini Alcineia C. Oliveira 《Journal of molecular catalysis. A, Chemical》2010,315(1):86-98
Isomorphously substituted (MeDM) and impregnated metal-containing MCM-41 (MeOx/IM) catalysts, in which Me = Co, Cu, Cr, Fe or Ni, have been prepared. Structural and textural characterizations of the catalysts were performed by means of X-ray diffraction (XRD), chemical analysis, Raman spectroscopy, electron paramagnetic resonance (EPR), N2 adsorption isotherms and temperature programmed reduction (TPR). Cu2+, Co2+, and Cr4+/Cr3+ species were found over the catalysts as cations incorporated in the MCM-41 structure (MeDM) or highly dispersed oxides on the surface (MeOx/IM). The MeDM catalysts exhibited a good performance in the dehydrogenation of ethylbenzene with CO2. However, MeOx/IM catalysts had a low performance in styrene production (activity less than 15 × 10?3 mmol h?1 and selectivity for styrene less than 80%) due to the high reducibility of the metals species. However, Ni2+ or Fe3+ coordinated with the MCM-41 framework, as well as NiOx and Fe2O3 extra-framework species, is continuously oxidized by the CO2 to maintain the active sites for dehydrogenating ethylbenzene. Deactivation studies on the FeDM sample showed that Fe3+ species produced active sp2 carbon compounds, which are removed by CO2; the referred sample is catalytically selective for styrene and stable over 24 h of reaction. In contrast, highly active Ni2+ and Ni0 species produced a large amount of polyaromatic carbonaceous deposits from styrene, as identified by TPO, TG and Raman spectroscopy. An acid–base mechanism is proposed to operate to adsorb ethylbenzene and abstract the β-hydrogen. CO2 plays a role in furnishing the lattice oxygen to maintain the Fe3+ active sites in the dehydrogenation of ethylbenzene to form styrene. 相似文献
3.
The samples of dibarium magnesium orthoborate Ba2Mg(BO3)2 were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba2Mg(BO3)2 were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba2Mg(BO3)2 polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5Eu + 4A2u + 5Eg + 4A1g + 1A2g + 1A1u, of which 5Eg + 4A1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba2Mg(BO3)2 were assigned as Eg (42 cm−1), A1g (85 cm−1), Eg (156 cm−1), Eg (237 cm−1), A1g (286 cm−1), Eg (564 cm−1), A1g (761 cm−1), A1g (909 cm−1), Eg (1165 cm−1). The strongest band at 928 cm−1 in the experimental spectrum is assigned to totally symmetric stretching mode of the BO3 units. 相似文献
4.
《Comptes Rendus Chimie》2015,18(4):385-390
This work aims to reduce the prices of a wide range of nanomaterials which are unreachable in the industry by using natural sources as silicon and aluminum precursors. In a previous work, silicon and aluminum have been extracted from Volclay after applying the alkaline fusion process at 550 °C, and a water treatment of this fused clay by adopting a weight ratio (1:4, fusion mass:H2O) to synthesize Al-MCM-41 nanomaterials. In this study, the weight ratio of fusion mass:H2O was increased to 1:8 to synthesize a highly structurally ordered MCM-41 under the same reaction conditions. The Al-MCM-41 nanomaterials are investigated by inductively coupled plasma optical emission spectrometry (ICP–OES), powder X-ray diffraction (XRD), N2 adsorption–desorption measurements and scanning electron microscopy (ESEM). As a result, the increase in the weight ratio fusion mass:H2O generates more silica and aluminum, which allows the formation of well-ordered MCM-41 nanomaterials with high pore volume (0.70 cm3/g), high surface area (1044 m2/g), and uniform mesoporous diameter (3.67 nm); as a consequence, the increase in the weight ratio fusion mass:H2O leads to an increase in the mass of Al-MCM-41 (9.3 g for 1:8 compared to 5 g for 1:4), whereas the yield of production of mesoporous materials increases to 86%. 相似文献
5.
Ir–Ni oxide nanoparticles were simply prepared by stirring IrCl3 and NiCl2 precursors in aqueous base under air. The activities of a series of IrNiyOx nanoparticles with different Ir-to-Ni ratios were measured toward water oxidation in 0.1 M H2SO4. The Ir-to-Ni ratio was 1:0.125 in the most active catalyst (mass normalized > 140 A g− 1 Ir, electrochemically active surface area normalized > 203 A mmol− 1Ir). The stabilized potential for the galvanostatic oxidation (1 mA cm− 2geometric) was as low as 1.51 VRHE, corresponding to 0.28 V in overpotential. 相似文献
6.
《Comptes Rendus Chimie》2015,18(3):250-260
CuO–ZnO–Al2O3 catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al2O3 was then substituted with other supports, such as ZrO2, CeO2 and CeO2–ZrO2 in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO2 hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO2 catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO2 conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 gMeOH.kgcata−1·h−1 at 280 °C under 50 bar and a GHSV of 10,000 h−1. 相似文献
7.
We evaluated the CO2 adsorption capacity on granular and monolith carbonaceous materials, obtained by chemical activation of African palm stones with H3PO4, ZnCl2 and CaCl2 solutions at different concentrations. Textural properties of the synthesized materials were analyzed using N2 adsorption measurements at 77 K, the isotherms showed obtaining of materials microporous and moderately mesoporous, with surface areas between 161 and 1700 m2/g and pore volume between 0.09 and 0.64 cm3 g−1. Were observed different behaviors for textural parameters in each series, associated with the activating agent used in the preparation. The materials obtained have a CO2 adsorption capacity between ∼114 and 254 mg CO2/g, at atmospheric pressure and 273 K. It was established that the total amount of CO2 adsorbed under these experimental conditions is defined by the narrow micropore volume (Vn) and increased the total basicity of the materials. 相似文献
8.
《Electrochemistry communications》2007,9(10):2606-2610
Nano-sized nickel ferrite (NiFe2O4) was prepared by hydrothermal method at low temperature. The crystalline phase, morphology and specific surface area (BET) of the resultant samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and nitrogen physical adsorption, respectively. The particle sizes of the resulting NiFe2O4 samples were in the range of 5–15 nm. The electrochemical performance of NiFe2O4 nanoparticles as the anodic material in lithium ion batteries was tested. It was found that the first discharge capacity of the anode made from NiFe2O4 nanoparticles could reach a very high value of 1314 mAh g−1, while the discharge capacity decreased to 790.8 mAh g−1 and 709.0 mAh g−1 at a current density of 0.2 mA cm−2 after 2 and 3 cycles, respectively. The BET surface area is up to 111.4 m2 g−1. The reaction mechanism between lithium and nickel ferrite was also discussed based on the results of cycle voltammetry (CV) experiments. 相似文献
9.
《Spectrochimica Acta Part B: Atomic Spectroscopy》2005,60(5):699-703
The determination of chromium (VI) compounds in plants by electrothermal atomic absorption spectrometry (ET AAS) is proposed based on their leaching with 0.1 M Na2CO3. Due to the presence of relatively high amounts of Na2CO3 in the resulting samples, the temperature and time of pyrolysis and atomization stages must be optimized to minimize the influence of the matrix. A limit of detection (LOD) for determination of Cr(VI) in plants by ET AAS was found to be 0.024 μg g−1.The concentration of Cr(VI) and total chromium in plants collected in different geographical areas (South Africa and Russia), grown on soils high in chromium was determined. The concentration of Cr(VI) and total Cr in stems and leaves of plants was in the range of 0.04–0.7 μg g−1 and 0.5–10 μg g−1, respectively. The limited uptake of Cr(III) by plants, in comparison to its concentration in soil, can be explained by the very low solubility of natural Cr(III) compounds.Results for the determination of Cr(VI) were confirmed by the analysis of BCR CRM 545 (Cr(VI) in welding dust) with good agreement between certified (39.5 ± 1.3 μg mg−1) and found (38.8 ± 1.2 μg mg−1) values. The total concentration of Cr in plants has also been determined by ET AAS after dry ashing of samples at 650 °C. Results were confirmed by the analysis of BCR CRM 281 (Trace elements in Rye Grass) with good agreement between the found (2.12 ± 0.16 μg g−1) and certified value (2.14 ± 0.12 μg g−1). 相似文献
10.
《中国化学快报》2021,32(11):3501-3504
Recently, widespread attention has been devoted to the typical layered BiOCl or BiOBr because of the suitable nanostructure and band structure. However, owing to the fast carrier recombination, the photocatalytic performance of BiOX materials is not so satisfactory. Loading 1T phase WS2 nanosheets (NSs) onto Bi5O7Br NSs can improve the photocatalytic N2 fixation activity. Among these, the obtained 1T-WS2@Bi5O7Br composites with optimum 5% 1T-WS2 NSs display a significantly improved photocatalytic N2 fixation rate (8.43 mmol L−1 h−1 g−1), 2.51 times higher than pure Bi5O7Br (3.36 mmol L−1 h−1 g−1). And the outstanding stability of 1T-WS2@Bi5O7Br-5 composites is also achieved. Exactly, the photoexcited electrons from Bi5O7Br NSs are quickly transferred to conductive 1T phase WS2 as electron acceptors, which can promote the separation of carriers. In addition, 1T-WS2 NSs can provide abundant active sites on the basal and edge planes, which can promote the efficiency of photocatalytic N2 fixation. This work offers a novel solution to improve the photocatalytic performance of Bi5O7Br NSs. 相似文献
11.
Reihaneh Malakooti Zeinab Parsaee Rahele Hosseinabadi Hossein A. Oskooie Majid M. Heravi Mina Saeedi Maryam Amrollah Akram Fallah 《Comptes Rendus Chimie》2013,16(9):799-806
A novel [Cu(bpdo)2·2H2O]2+-supported SBA-15 catalyst (bpdo = 2,2′-bipyridine,1,1′-dioxide) was prepared by the impregnation method. The catalyst was characterized by XRD, TEM, and BET nitrogen adsorption–desorption method, FT-IR, UV–vis, and chemical analysis. XRD patterns and TEM analysis of [Cu(bpdo)2·2H2O]2+/SBA-15 showed highly ordered hexagonal mesoporous silica, even after immobilization. Also, nitrogen adsorption–desorption isotherms exhibited type-IV isotherms and H1 hysteresis loops according to the IUPAC classification of mesoporous materials. This green support was tested for the synthesis of benzoxanthenone and benzochromene derivatives under solvent-free conditions, with high yield of products via a simple experimental and work-up procedure. 相似文献
12.
《Electrochemistry communications》2008,10(7):1067-1070
The efficiently hydrothermal route using sucrose without any catalysts is employed to prepare the uniform carbon spheres. The monodisperse 100–150 nm carbon spheres are obtained with the activation treatment in molten KOH. The carbon spheres are characterized by transmission electron microscope, X-ray diffraction, N2 adsorption, Raman spectroscopy and electrochemical techniques. The relationships of specific capacitance and surface properties of carbon spheres are investigated. A single electrode of carbon nanosphere materials performs excellent specific capacitance (328 F g−1), area capacitance (19.2 μF cm−2) and volumetric capacitance (383 F cm−3). 相似文献
13.
We report the electrochemical performance of carbon-coated TiO2 nanobarbed fibers (TiO2@C NBFs) as anode material for lithium-ion batteries. The TiO2@C NBFs are composed of TiO2 nanorods grown on TiO2 nanofibers as a core, coated with a carbon shell. These nanostructures form a conductive network showing high capacity and C-rate performance due to fast lithium-ion diffusion and effective electron transfer. The TiO2@C NBFs show a specific reversible capacity of approximately 170 mAh g− 1 after 200 cycles at a 0.5 A g− 1 current density, and exhibit a discharge rate capability of 4 A g− 1 while retaining a capacity of about 70 mAh g− 1. The uniformly coated amorphous carbon layer plays an important role to improve the electrical conductivity during the lithiation–delithiation process. 相似文献
14.
Herein we present a strong anion receptor-assisted Mg-ion electrolyte, which is synthesized from tris(2H-hexafluoroisopropyl) borate (THFPB) and MgO in 1,2-dimethoxyethane (DME). The as-prepared borate magnesium oxide complex (BMOC) electrolyte delivers exceptional electrochemical performances, including extremely high anodic stability (up to 4.2 V vs. Mg), non-corrosivity to stainless steel and aluminium foils, and reasonable ionic conductivity of 1.74 × 10− 4 S cm− 1. In addition, by virtue of the non-nucleophilic characteristic of the BMOC electrolyte, S ||BMOC ||Mg cells have been assembled, which show a high stable discharge capacity of 1030 mAh g− 1 for 15 cycles and one well-defined voltage plateau of ≈ 1.1 V vs. Mg, yielding a desirable energy density beyond 1100 Wh kg− 1 based on the weight of sulfur in cathodes. 相似文献
15.
Vanadium dioxide (VO2) nano-sheets were directly synthesized via a continuous hydrothermal process and were investigated as electrodes in a wide potential range of 0.05–3 V vs. Li/Li+. The nano-sheets showed excellent capacity retention, with a specific capacity of 350 mAh g− 1 at an applied current of 0.1 A g− 1 and 95 mAh g− 1 at 10 A g− 1. Further electrochemical testing suggested that a significant proportion of the charge storage in the cells was due to pseudocapacitive processes. 相似文献
16.
《Chemical physics letters》1999,291(1-2):75-81
The fluorescence spectrum of all-trans-β-carotene was recorded at 170 K. The 1Bu+ → 1Ag− fluorescence exhibited clear vibrational structures constituting a mirror image with those of the 1Bu+ ← 1Ag− absorption, and the deconvolution of the entire spectrum identified the 2Ag−(0) → 1Ag−(0) transition at 14 500 cm−1. The displacements of the 1Bu+ and 2Ag− potential minima along ν1 and ν2 (the CC stretching and C–C stretching normal coordinates, respectively) were determined to be 1.2 and 0.9, and 1.6 and 1.5, respectively. Thus, much larger potential displacements in the 2Ag− state than in the 1Bu+ state have been shown. 相似文献
17.
《Journal of membrane science》2001,184(1):137-148
Ultrafiltration of either single protein solutions (lysozyme 14,300 g mol−1, pI=11; lactoferrin 80,000 g mol−1, pI=8–9) or mixed protein solution was performed with inorganic membranes (MMCO 300,000 g mol−1, pore radius 14 nm) chemically modified in order to bear either pyrophosphate (PP, anionic) or ethylenediamine (EDA, cationic) groups.The electrophoretic mobility of modified and unmodified zirconia particles fouled with proteins was similar whatever the grafted groups, meaning that the membrane surface was always made of adsorbed proteins during UF. In spite of that, for the UF of lysozyme/lactoferrin mixed solution, the maximum selectivity (S=lysozyme transmission/lactoferrin transmission=165) was observed with the EDA membrane and allowed an instantaneous purity of lysozyme in the permeate close to 100% to be achieved. Such high selectivitiy was mainly due to the negligible transmission of lactoferrin with the membrane modified with the EDA groups in the ionic strength range 0–100 mmol l−1 of NaCl at pH 7 (achieved either for mixed and single solutions). 相似文献
18.
《Electrochemistry communications》2008,10(10):1435-1437
The birnessite type manganese dioxide electrode was prepared by the electrochemical stimulation as we recently described. It showed 190 F g−1 in a Na2SO4 aqueous solution between −0.1 and 0.9 V versus Ag/AgCl at 1 A g−1. The specific capacitance of birnessite was decreased by the manganese dissolution when the reduction and oxidation were repeated. By adding small amounts of Na2HPO4 or NaHCO3 into the electrolyte, the capacitance increased to 200–230 F g−1 and the manganese dissolution was successfully suppressed. Thanks to the additives, the birnessite demonstrated the much improved cycleability over >1800 cycles. 相似文献
19.
NiCo2O4 nanosheets supported on Ni foam were synthesized by a solvothermal method. A composite of NiCo2O4 nanosheets/Ni as a carbon-free and binder-free air cathode exhibited an initial discharge capacity of 1762 mAh g− 1 with a low polarization of 0.96 V at 20 mA g− 1 for sodium–air batteries. Na2O2 nanosheets were firstly observed as the discharged product in sodium–air battery. High electrocatalytic activity of NiCo2O4 nanosheets/Ni made it a promising air electrode for rechargeable sodium–air batteries. 相似文献
20.
《Spectrochimica Acta Part B: Atomic Spectroscopy》2006,61(1):42-49
An electrothermal vaporization (ETV) system useful for the analysis of solutions and slurries has been coupled with a sector-field inductively coupled plasma mass spectrometer (ICP–MS) equipped with an array detector. The ability of this instrument to record the transient signals produced for a number of analytes in ETV–ICP–MS is demonstrated. Detection limits for Mn, Fe, Co, Ni, Cu, Zn and Ga are in the range of 4–60 pg μL− 1 for aqueous solutions and in the low μg g− 1 range for the analysis of 10 mg mL− 1 slurries of Al2O3 powders. The dynamic ranges measured for Fe, Cu and Ga spanned 3–5 orders of magnitude when the detector was operated in the low-gain mode and appear to be limited by the ETV system. Trace amounts of Fe, Cu and Ga could be directly determined in Al2O3 powders at the 2–270 μg g− 1 level without the use of thermochemical reagents. The results well agree with literature values for Fe and Cu, whereas deviations of 50% at the 90 μg g− 1 level for Ga were found. 相似文献