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1.
The reactions of different silver(I) reagents AgX (X ?=iodide, trifluoroacetate, triflate) with selenoethers R 2Se (R=Me, tBu) in a variety of solvents were investigated in relation with their use as precursors for Ag 2Se nanomaterials. Different reaction conditions led to different reactivities and afforded either molecular complexes or metal selenide nanoparticles. The reactions leading to in situ formation of the metal selenide nanoparticles were then extended in the presence of commercial TiO 2 (P25) to prepare silver selenide–titania nanocomposites with different Ag/Ti ratios. These nanocomposites, well characterized by elemental analysis (Ag, Se), PXRD, TEM, BET, XPS and UV/Vis studies, were investigated as photocatalysts for the degradation of formic acid (FA) solution. The xAg 2Se‐TiO 2 nanocomposites ( x=0.01, 0.13 and 0.25 mol %) exhibited a much higher catalytic activity as compared to P25, which is an established benchmark for the photocatalysis under UV light, and retained a good photocatalytic stability after recycling for several times. 相似文献
2.
Stable dispersions of surfactant-coated TiO 2–Ag based nanoparticles in apolar medium have been prepared by performing sequentially the hydrolysis of titanium(IV) isopropoxide
and the reduction of Ag + in the confined space of sodium bis(2-ethylhexyl)sulfosuccinate (NaAOT) reverse micelles. Depending on the sequence length,
this novel procedure allowed the synthesis of semiconductor–metal nanoparticles, nominally indicated as TiO 2/Ag, TiO 2/Ag/TiO 2, and TiO 2/Ag/TiO 2/Ag, stabilized by a monolayer of oriented surfactant molecules. The structural characterization of these nanoparticles has
been performed by High Resolution Transmission Electron Microscopy (HR-TEM), while optical properties were investigated by
UV–Vis absorption and fluorescence spectroscopies. TEM investigation showed the presence of globular nanoparticles with an
average diameter of about 10 nm composed by distinct amorphous TiO 2 and crystalline Ag glued domains whose structure depends on the sequence length. UV–Vis absorption measurements highlighted
the mutual metal–semiconductor influence on the TiO 2 energy band gap and on the Ag plasmon resonance. Steady-state fluorescence spectra analysis allowed to reveal the strong
inhibition of the electron–hole radiative recombination in the TiO 2 domains due to the Ag and the appearance of a new emission band centred in the 484–545 nm range. Possible attributions of
the involved electronic transition of this last emission are discussed. 相似文献
3.
TiO 2–carbon nanotube (CNT) heterojunction arrays on Ti substrate were fabricated by a two-step thermal chemical vapor deposition (CVD) method. CNT arrays were first grown on Ti substrate vertically, and then a TiO 2 layer, whose thickness could be controlled by varying the deposition time, was deposited on CNTs. Measured by electrochemical impedance spectroscopy (EIS), the thickness of the TiO 2 layer could affect the photoresponse ability significantly. About 100 nm thickness of the TiO 2 layer proved to be best for efficient charge separation among the tested samples. The optimized TiO 2–CNT heterojunction arrays displayed apparently higher photoresponse capability than that of TiO 2 nanotube arrays which was confirmed by surface photovoltage (SPV) technique based on Kelvin probe and EIS. In the photocatalytic experiments, the kinetic constants of phenol degradation with TiO 2–CNT heterojunctions and TiO 2 nanotubes were 0.75 h −1 ( R2 = 0.983) and 0.39 h −1 ( R2 = 0.995), respectively. At the same time, 53.7% of total organic carbon (TOC) was removed with TiO 2–CNT heterojunctions, while the removal of TOC was only 16.7% with TiO 2 nanotubes. These results demonstrate the super capability of the TiO 2–CNT heterojunction arrays in photocatalysis with comparison to TiO 2-only nanomaterial. 相似文献
4.
UV-photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4- d) was studied on Silver–TiO 2 semiconductors prepared by co-gelling silver acetylacetonate and titanium butoxide (TiO 2–Ag) or by incipient impregnation with silver acetylacetonate (0.5 wt% Ag) of bare TiO 2 sol–gel and TiO 2–P25 supports. The comparative study shows that only a slight modification on the specific surface area was obtained on the
TiO 2–Ag sample (60 m 2/g) as compared to the TiO 2 sol–gel bare support (65 m 2/g). XRD patterns of the samples show anatase as the crystalline phase present in the sol–gel TiO 2 preparations. By means of HRTEM and HAADF-STEM electron microscopy techniques, silver nanoparticles (<12.0 nm) were identified
which are very small to be detected by XRD. The photocatalytic oxidation of the herbicide 2,4- d used as a model of contaminant show for the kinetic parameter t 1/2 values of 45 min for the TiO 2–Ag sample, while for the impregnated Ag/TiO 2 and Ag/P25 nanomaterials t 1/2 was 124 and 66 min, respectively. The higher photoactivity of the TiO 2–Ag photocatalyst is attributed to a combined effect of the silver nanoparticles in interaction with the titania semiconductor. 相似文献
5.
Oxidation of iodide ion from an air-saturated solution under natural sunlight (900±50 W m −2) on the surfaces of TiO 2, ZnO, Fe 2O 3, MoO 3 and CeO 2 enhances by 6 to 12-fold on application of a cathodic bias of −0.2 to −0.3 V ( vs NHE) to the semiconductors; light, the semiconductor and dissolved oxygen are essential for iodine generation. The semiconductors
under an anodic bias of +0.2 to +0.3 V ( vs NHE) fail to oxidize iodide ion from air-saturated solution under sunlight. Under cathodic bias, semiconductor mixtures like
TiO 2-ZnO, TiO 2-Fe 2O 3 and ZnO-Fe 2O 3 show enhanced photocatalytic activity, indicating improved charge separation in oxide mixtures. The mechanism of photocatalysis
under cathodic bias is discussed.
相似文献
6.
Visible light-driven photocatalysis of Au 25-modified TiO 2 was investigated. It induces oxidation of phenol derivates and ferrocyanide and reduction of Ag +, Cu 2+ and dissolved oxygen. Thermodynamically uphill reactions such as oxidation of phenol accompanied by reduction of Cu 2+ are also driven. The photocatalysis, which is based on the excitation of Au 25, is observed even under 860 nm light. 相似文献
7.
Single crystals of K 2Ag 12Te 7 ( a = 11.460(2), c = 4.660(1) ?; V = 530.01 ? 3; space group: P6 3/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver and tellurium. The crystal structure is characterized by trigonal prismatic KTe 6 polyhedra, connected via two common faces to KTe 3 rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K 2Ag 12Te 6) 2 + and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit cell, distributed over two independent positions. 相似文献
8.
The activity of 0.25–5% Ag/Al 2O 3 catalysts in the selective catalytic reduction of nitrogen oxides with n-hexane under the conditions of promotion with a small amount of H 2 was studied. It was found that, upon the introduction of ∼1000 ppm of H 2 into the reaction mixture, the Ag/Al 2O 3 samples containing 1–2% Ag exhibited optimum activity and selectivity. It was established that, in the presence of 1000 ppm
of H 2, the rate of the selective catalytic reduction of NO
x
was higher by a factor of 10–13, and the onset temperature of the reaction was lower by approximately 100°C. It was found
by X-ray photoelectron spectroscopy, temperature-programmed reduction, and UV spectroscopy that the high activity of 1–2%
Ag/Al 2O 3 catalysts was due to the presence of small Ag
n
δ+ and Ag
m
0 clusters on their surface. A decrease in the concentration of Ag below the optimum value resulted in the predominance of
an inactive ionic form on the catalyst surfaces. As the concentration of Ag was increased (>2%), large particles of Ag 2O and Ag 0, which facilitate the oxidation of n-C 6H 14, were formed to lead to a decrease in selectivity and in the degree of reduction of nitrogen oxides. 相似文献
9.
TiO 2- and Ag/TiO 2-nanotubes (NTs) were synthesized by hydrothermal methods and microwave-assisted preparation, respectively. Scanning electron microscopy, high resolution transmission electron microscopy, Brunauer-Emmett-Teller particle surface area measurement and X-ray diffraction were used to characterize the nanotubes. Rutile TiO 2-NTs with Na 2Ti 5O 11 crystallinity had a length range of 200-400 nm and diameters of 10-20 nm. TiO 2- and Ag/TiO 2-NTs with a 0.4% deposition of Ag had high surface areas of 270 and 169 m 2 g −1, respectively. The evaluation of photocatalytic activity showed that Ag/TiO 2-NTs displayed higher photocatalytic activity than pure TiO 2-NTs and a 60.91% degradation of Rhodamine-B with 0.8% deposition of Ag species. Also 60% of Rhodamine-6G was physisorbed and 40% chemisorbed on the surface of TiO 2-NTs. In addition, the photocatalytic degradations of organochlorine pesticides taking α-hexachlorobenzene (BHC) and dicofol as typical examples, were compared using Ag/TiO 2-NTs, and found that their degradations rates were all higher than those obtained from commercial TiO 2. 相似文献
10.
Kinetics of oxidation of dl-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO 6) 2] 5−, has been studied in aqueous alkaline medium in the temperature range of 25–40 °C. The oxidation kinetics is first order
in the silver(III) and pipecolinate concentrations. The observed second-order rate constant, decreasing with increasing [periodate]
is virtually independent of [OH −]. α-Aminoadipate as the major oxidation product of pipecolinate has been identified by chromatographic analysis. A reaction
mechanism is proposed that involves a pre-equilibrium between [Ag(HIO 6) 2] 5− and [Ag(HIO 6)(H 2O)(OH)] 2−, a mono-periodate coordinated silver(III) complex. Both Ag(III) complexes are reduced in parallel by pipecolinate in rate-determining
steps (described by k
1 for the former Ag(III) species and k
2 for the latter). The determined rate constants and their associated activation parameters are k
1 (25 °C) = 0.40 ± 0.02 M −1 s −1, ∆ H
1≠ = 53 ± 2 kJ mol −1, ∆ S
1≠ = −74 ± 5 J K −1 mol −1 and k
2 (25 °C) = 0.64 ± 0.02 M −1 s −1, ∆ H
2≠ = 41 ± 2 kJ mol −1, ∆ S
2≠ = −110 ± 5 J K −1 mol −1. The time-resolved spectra, a positive dependence of the rate constants on ionic strength of the reaction medium, and the
consistency of pre-equilibrium constants derived from different reaction systems support the proposed reaction mechanism. 相似文献
11.
The electrical explosion of wires was used to prepare titanium dioxide nanopowders alloyed with silver nanoparticles. The
photoelectrochemical properties and electronic structure of these materials were studied. The quantum yield for the photoelectrochemical
current η and the flat band potential E
fb for TiO 2/Ag films were found to be proportional to the content of the Ag 0 phase on the electrode surface. 相似文献
12.
Coordination polymers {[Et 4N][Ag 2I 3]} n (1) and [CuBr(C 10H 8N 2S 2)] n (2) were prepared by standard Schlenk techniques. Their X-ray measurements indicate that polymer (1) crystallizes in the orthorhombic space group Pnma, and polymer (2) crystallizes in the monoclinic space group P21/n. Complex (1) has a hanging ladder-like polymeric chain which can also be described as a helical chain bridged by Ag–Ag edges. Complex
(2) exhibits a monoclinic crystal system with a slightly distorted tetrahedron. The nonlinear optical (NLO) properties of (1) and (2) were investigated by using Z-scan techniques with an 8 ns pulsed laser at 532 nm. These two coordination polymers exhibit
NLO absorption and an effective self-focusing effect. The effective α 2 and n2 values of cluster (1) are 3.04×10 −11 m W −1 and 7.6×10 −18 m 2 w −1 and the effective α 2 and n2 values of compound (2) are 1.08×10 −11 m W −1 and 3.1×10 −18 m 2 w −1 when measured in CH 2Cl 2 solution. 相似文献
13.
Na + complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m 2/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO 2 samples prepared were found to have photocatalytic activity in Cu II, Ni II and Ag I reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO 2 Degussa P25.The effects of the thermal treatment of mesoporous TiO 2 upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO 2/Ag 0 to TiO 2/Ni 0 to TiO 2/Cu 0 was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites. 相似文献
14.
Two multiple-layer heterometallic Mn II–Ag I coordination polymers, {Mn II(ampyz)(H 2O)[Ag 2I(CN) 3][Ag I(CN) 2]·ampyz}
n
( 1) and {[Mn II(benzim) 2[Ag I(CN) 2] 2][(benzim)Ag I(CN)]·H 2O}
n
( 2) where ampyz = 2-aminopyrazine and benzim = benzimidazole, have been prepared and structurally characterized. Compound 1 reveals a multiple-layer two-dimensional network with strong hexanuclear argentophilic interactions leading to an infinite
three-dimensional framework. Compound 2 has an unprecedented double-layer two-dimensional squared grid-type network with (4,4) topology through Ag I···Ag I and π–π interactions between two adjacent squared layers. These double-layer networks of 2 are linked to others by π–π interactions, leading to a three-dimensional framework. 相似文献
15.
Visible-light-driven heterostructure Ag/Bi2WO6 nanocomposites were prepared by transforming Ag+ ions into metallic Ag0 nanoparticles loaded on top of Bi2WO6 nanoplates under visible light irradiation for 1 h. XRD, XPS, SEM and TEM analyses indicated that spherical metallic Ag nanoparticles were uniformly dispersed on top of orthorhombic Bi2WO6 thin nanoplates. Rhodamine B (RhB) was used as a dye model for investigation of photocatalytic performance of Bi2WO6 nanoplates with different weight contents of Ag nanoparticles illuminated by visible radiation. In this research, 10% Ag/Bi2WO6 nanocomposites have the highest photocatalytic activity in the degradation of RhB at 94.21% within 210 min because of the rapid diffusion of electronic charge through the Schottky barrier between metallic Ag nanoparticles and Bi2WO6 thin nanoplates, good electrical conductivity of metallic Ag nanoparticles, inhibited recombination of charge carriers and enhanced photocatalytic activity of Ag/Bi2WO6 nanocomposites. Main active species of the photocatalysis and stability of the photocatalyst were also evaluated. 相似文献
16.
Silver clusters on SiO 2 support have been synthesized using 60Co gamma radiation. The irradiation of Ag + in aqueous suspension of SiO 2 in the presence of 0.2 mol dm −3 isopropanol resulted in the formation of yellow suspension. The absorption spectrum showed a band at 408 nm corresponding to typical characteristic surface plasmon resonance of Ag nanoparticles. The effect of Ag + concentration on the formation of Ag cluster indicated that the size of Ag clusters vary with Ag + concentration, which was varied from 4×10 −4 to 5×10 −3 mol dm −3. The results showed that Ag clusters are stable in the pH range of 2–9 and start agglomerating in the alkaline region at pH above 9. The effect of radiation dose rate and ratio of Ag +/SiO 2 on the formation of Ag clusters have also been investigated. The prepared clusters have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which showed the particle size of Ag clusters to be in the range of 10–20 nm. 相似文献
17.
Summary. Single crystals of K 2Ag 12Te 7 ( a = 11.460(2), c = 4.660(1) ?; V = 530.01 ? 3; space group: P6 3/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver
and tellurium. The crystal structure is characterized by trigonal prismatic KTe 6 polyhedra, connected via two common faces to KTe 3 rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four
Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K 2Ag 12Te 6) 2 + and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit
cell, distributed over two independent positions.
Received May 17, 2001. Accepted (revised) July 3, 2001 相似文献
18.
It is observed that Ag(I) catalyzes the rate of substitution of phenylhydrazine (PhNHNH 2) into hexacyanoferrate(II), producing a cherry red colored complex, [Fe(CN) 5PhNHNH 2] 3−. The reaction was monitored at 488 nm leading to the formation of the complex under the conditions: [Fe(CN) 6] 4− (5.0 × 10 −3 mol dm −3), PhNHNH 2 (2.0 × 10 −3 mol dm −3), temperature (25 ± 0.1 °C), pH (2.8 ± 0.02), and ionic strength, I (0.02 mol dm −3), (KNO 3). Under optimum conditions, absorbance at fixed times ( A
t
) is linearly related to Ag(I) in the concentration range 10.79–97.08 ng cm −3, in the presence of several diverse ions. The highest percentage error and relative standard deviations in the entire range
of Ag(I) determination are found to be 2.5% and 0.16, with a detection limit of 8.75 ng cm −3 of silver(I). The experimental accuracies expressed in terms of percentage recoveries are in the range of 97.87–102.50. The
method was successfully applied for the determination of Ag(I) in a few synthetic samples and found to be in good agreement
with those obtained from atomic absorption spectrophotometry (AAS). The validity of the proposed method has also been tested
for Ag(I) determination in spiked drinking water samples. The present catalytic kinetic method (CKM) is highly sensitive,
selective, reproducible, and inexpensive. A review of recently published catalytic spectrophotometric methods for determination
of Ag(I) has also been presented for comparison. 相似文献
19.
From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag +(aq) + 1⋅Cs +(nb) ⇆ 1⋅Ag +(nb) + Cs +(aq) taking part in the two-phase water–nitrobenzene system (where 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated to be log 10
K
ex(Ag +, 1⋅Cs +) = −1.0±0.1. Further, the stability constant of the hexaarylbenzene-based receptor⋅Ag + complex (abbreviation 1⋅Ag +) in nitrobenzene saturated with water, was calculated at a temperature of 25 °C: log 10
β
nb( 1⋅Ag +) = 5.5±0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1⋅Ag + complex species was solved. In this complex having C 3 symmetry, the cation Ag + synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene ring via cation– π interaction. 相似文献
20.
Introduction So far, considerable attention has been paid to mag-netic interaction between two different metal ions.1-3 As a potential bridging ligand, thiocyanate can coordinate to a harder metal center with N atom and softer ones with S atom at the same time, resulting in the formation of small ferromagnetic coupling.2 On the other hand, the Fe(III) atom is a good candidate as a hard acid and Ag(I) is a good candidate as a soft acid, so that the Fe(III) centers could be expected to conn… 相似文献
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