The solventless syntheses of unique PbS nanowires of X-shaped cross sections and the cooperative effects of ethylenediamine and a second salt

Unique PbS nanowires with x-shaped cross sections, with diameters in the range of 300-800 nm with an average of 598 nm (sigma = +/-21.7% ), and lengths of up to several tens of micrometers, have been made by a solventless method. Such nanowires show high adsorptivities of the PbS nanooctahedra, which can be washed off by ultrasound. The suitable precursor is obtained from a Pb(NO3)2/octanoate/ethylenediamine/dodecanethiol molar ratio of 1:2:1:1.6, and the PbS nanowires are produced by the thermolysis of such precursors at 280 degrees C for 1 hour. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations of the products and the keys of the morphological control have been reported. For the formation of such products, two cooperative effects are found to be crucial, the roles of ethylenediamine and a second salt, lead octanonate.     

Syntheses and characterizations of bismuth nanofilms and nanorhombuses by the structure-controlling solventless method

Substrate-free bismuth nanofilms with an average thickness of 0.6 nm (sigma = +/-14.1%) and monodisperse layered Bi nanorhombuses with an average edge length of 21.5 nm (sigma = +/-14.7%) and thickness of 0.9 nm (sigma = +/-25.8%) have been successively synthesized by structure-controlling solventless thermolysis from a new layered bismuth thiolate precursor with a 31.49 A spacing. The morphologies result from self-control at an atomic level by the layered Bi(SC(12)H(25))3 crystal structure. The formation of the Bi nanofilm intermediate provides significant substantiation for this synthesis method, and detailed evidence on the conversion progress has been obtained. Both the films and the rhombuses have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), high-resolution TEM (HRTEM), and atomic force microscopy (AFM) measurements. Special UV-vis electronic absorption spectra of the nanoproducts have been studied.     

The Structure‐Controlling Solventless Synthesis and Optical Properties of Uniform Cu2S Nanodisks

Uniform Cu₂S nanodisks have been synthesized from a well‐characterized layered copper thiolate precursor by structure‐controlling solventless thermolysis at 200–220 °C under a N₂ atmosphere. The development from small Cu₂S nanoparticles (diameter ≈3 nm) to nanodisks (diameter 8.3 nm) and then to faceted nanodisks (diameter 27.5 nm, thickness 12.7 nm) is accompanied by a continuous phase transition from metastable orthorhombic to monoclinic Cu₂S, the ripening of small particles by aggregation, and finally the crystallization process. The growth of the nanoproduct is constrained by the crystal structure of the precursor and the in situ‐generated thiol molecules. Such controlled anisotropic growth leads to a nearly constant thickness of faceted nanodisks with different diameters, which has been confirmed by TEM observations and optical absorption measurements.     

Facile size-regulated synthesis of silver nanoparticles by controlled thermolysis of silver alkylcarboxylates in the presence of alkylamines with different chain lengths

Controlled thermolysis of silver alkylcarboxylates with primary alkylamines was investigated as a facile synthetic method of silver nanoparticles. A series of silver alkylcarboxylates, C(7)H(15)COOAg, C(13)H(27)COOAg, and C(17)H(35)COOAg, have been prepared and the thermolysis of those silver alkylcarboxylates in the presence of various alkylamines, C(8)H(17)NH(2), C(12)H(25)NH(2), and C(18)H(37)NH(2), with no use of solvent was conducted at 120 or 180 degrees C for 5 h, providing spherical silver nanoparticles stabilized by alkylcarboxylates and alkylamines. The size and dispersibility of nanoparticles depend on the alkyl chain length of the precursors, alkylcarboxylates and alkylamines.     

One-pot synthesis of Cu1.94S-CdS and Cu1.94S-Zn(x)Cd(1-x)S nanodisk heterostructures

Nanodisk heterostructures consisting of monoclinic Cu(1.94)S and wurtzite CdS have been colloidally synthesized for the first time. Initially, hexagonal-shaped nanodisks of Cu(1.94)S were produced upon thermolysis of a copper complex in a solvent mixture of HDA and TOA at 250 °C. Rapid addition of Cd precursor to the reaction mixture resulted in the partial conversion of Cu(1.94)S into CdS, yielding Cu(1.94)S-CdS nanoheterostructures. The original morphology of the Cu(1.94)S nanodisks was conserved during the transformation. When Zn precursor was added together with the Cd precursor, Cu(1.94)S-Zn(x)Cd(1-x)S nanodisks were generated. These two-component nanostructures are potentially useful in the fabrication of heterojunction solar cells.     

Two-photon photochemical generation of reactive enediyne

p-Quinoid cyclopropenone-containing enediyne precursor (1) has been synthesized by monocyclopropanation of one of the triple bonds in p-dimethoxy-substituted 3,4-benzocyclodeca-1,5-diyne followed by oxidative demethylation. Cyclopropenone 1 is stable up to 90 degrees C but readily produces reactive enediyne 2 upon single-photon (Phi(300)(nm) = 0.46) or two-photon (sigma(800 nm) = 0.5 GM) photolysis. The photoproduct 2 undergoes Bergman cyclization at 40 degrees C with the lifetime of 88 h.     

On the photochemistry of IONO2: absorption cross section (240-370 nm) and photolysis product yields at 248 nm

The absolute absorption cross section of IONO(2) was measured by the pulsed photolysis at 193 nm of a NO(2)/CF(3)I mixture, followed by time-resolved Fourier transform spectroscopy in the near-UV. The resulting cross section at a temperature of 296 K over the wavelength range from 240 to 370 nm is given by log(10)(sigma(IONO(2))/cm(2) molecule(-1)) = 170.4 - 3.773 lambda + 2.965 x 10(-2)lambda(2)- 1.139 x 10(-4)lambda(3) + 2.144 x 10(-7)lambda(4)- 1.587 x 10(-10)lambda(5), where lambda is in nm; the cross section, with 2sigma uncertainty, ranges from (6.5 +/- 1.9) x 10(-18) cm(2) at 240 nm to (5 +/- 3) x 10(-19) cm(2) at 350 nm, and is significantly lower than a previous measurement [J. C. M?ssinger, D. M. Rowley and R. A. Cox, Atmos. Chem. Phys., 2002, 2, 227]. The photolysis quantum yields for IO and NO(3) production at 248 nm were measured using laser induced fluorescence of IO at 445 nm, and cavity ring-down spectroscopy of NO(3) at 662 nm, yielding phi(IO) 相似文献   

Spontaneous organization of uniform CeO2 nanoflowers by 3D oriented attachment in hot surfactant solutions monitored with an in situ electrical conductance technique

Uniform CeO(2) nanoflowers were synthesized by rapid thermolysis of (NH(4))(2)Ce(NO(3))(6) in oleic acid (OA)/oleylamine (OM), by a unique 3D oriented-attachment mechanism. CeO(2) nanoflowers with controlled shape (cubic, four-petaled, and starlike) and tunable size (10-40 nm) were obtained by adjusting the reaction conditions including solvent composition, precursor concentration, reaction temperature, and reaction time. The nanoflower growth mechanism was investigated by in situ electrical conductance measurements, transmission electron microscopy, and UV/Vis spectroscopy. The CeO(2) nanoflowers are likely formed in two major steps, that is, initial formation of ceria cluster particles capped with various ligands (e.g., OA, OM, and NO(3) (-)) via hydrolysis of (NH(4))(2)Ce(NO(3))(6) at temperatures in the range 140-220 degrees C, and subsequent spontaneous organization of the primary particles into nanoflowers by 3D oriented attachment, due to a rapid decrease in surface ligand coverage caused by sudden decomposition of the precursor at temperatures above 220 degrees C in a strong redox reaction. After calcination at 400 degrees C for 4 h the 33.8 nm CeO(2) nanoflowers have a specific surface area as large as 156 m(2) g(-1) with high porosity, and they are highly active for conversion of CO to CO(2) in the low temperature range of 200-400 degrees C. The present approach has also been extended to the preparation of other transition metal oxide (CoO, NiO, and CuO(x)) nanoflowers.     

Solventless synthesis of monodisperse Cu2S nanorods, nanodisks, and nanoplatelets

Cu(2)S nanocrystals with disklike morphologies were synthesized by the solventless thermolysis of a copper alkylthiolate molecular precursor. The nanodisks ranged from circular to hexagonal prisms from 3 to 150 nm in diameter and 3 to 12 nm in thickness depending on the growth conditions. High resolution transmission electron microscopy (HRTEM) revealed the high chalcocite (hexagonal) crystal structure oriented with the c-axis ([001] direction) orthogonal to the favored growth direction. This disk morphology is thermodynamically favored as it allows the extension of the higher energy [100] and [110] surfaces with respect to the [001] planes. The hexagonal prism morphology also appears to relate to increased C-S bond cleavage of adsorbed dodecanethiol along the more energetic [100] facets relative to [001] facets. Monodisperse Cu(2)S nanodisks self-assemble into ribbons of stacked platelets. This solventless approach provides a new technique to synthesize anisotropic metal chalcogenide nanostructures with shapes that depend on both the face-sensitive thermodynamic surface energy and the surface reactivity.     

Two-photon excited fluorescence of nitrogen-vacancy centers in proton-irradiated type Ib diamond

Two-photon fluorescence spectroscopy of negatively charged nitrogen-vacancy [(N-V)-] centers in type Ib diamond single crystals have been studied with a picosecond (7.5 ps) mode-locked Nd:YVO(4) laser operating at 1064 nm. The (N-V)- centers were produced by radiation damage of diamond using a 3 MeV proton beam, followed by thermal annealing at 800 degrees C. Prior to the irradiation treatment, infrared spectroscopy of the C-N vibrational modes at 1344 cm(-1) suggested a nitrogen content of 109 +/- 10 ppm. Irradiation and annealing of the specimen led to the emergence of a new absorption band peaking at approximately 560 nm. From a measurement of the integrated absorption intensity of the sharp zero-phonon line (637 nm) at liquid nitrogen temperature, we determined a (N-V)- density of (4.5 +/- 1.1) x 10(18) centers/cm3 (or 25 +/- 6 ppm) for the substrate irradiated at a dose of 1 x 1016) H(+)/cm(2). Such a high defect density allowed us to observe two-photon excited fluorescence and measure the corresponding fluorescence decay time. No significant difference in the spectral feature and fluorescence lifetime was observed between one-photon and two-photon excitations. Assuming that the fluorescence quantum yields are the same for both processes, a two-photon absorption cross section of sigma(TPA) = (0.45 +/- 0.23) x 10(-50) cm(4).s/photon at 1064 nm was determined for the (N-V)- center based on its one-photon absorption cross section of sigma(OPA) = (3.1 +/- 0.8) x 10(-17) cm2 at 532 nm. The material is highly photostable and shows no sign of photobleaching even under continuous two-photon excitation at a peak power density of 3 GW/cm(2) for 5 min.     

Mild generation of 5-(2'-deoxyuridinyl)methyl radical from a phenyl selenide precursor

[reaction: see text] 5-(2'-Deoxyuridinyl)methyl radical (1) resulting from formal hydrogen atom abstraction from the methyl group of thymidine is produced from the respective phenyl selenide precursor (2) via 350 nm photolysis or mild thermolysis (37 degrees C in the presence of glutathione) under aerobic or anaerobic conditions. The mild thermal generation of a nucleoside radical provides an alternative to previously reported photochemical methods, which are not always compatible with nucleic acids.     

Revisiting the crystal structure and thermal properties of NaMgAl(oxalate)3 x 9 H2O/Cr(III): an extraordinary spectral hole-burning material

We have reinvestigated the crystal structure and thermal properties of NaMgAl(oxalate)(3).9H(2)O. In the thermal gravimetric analysis the steps of dehydration and decomposition/oxidation yield a mass change that is commensurate with 9 water molecules of hydration. Dehydration steps occur at 127, 171, and 201 degrees C whereas the oxalate ligand decomposes in steps at 403 and 424 degrees C with a final oxidation step at 692 degrees C. A refinement of the single crystal X-ray diffraction data taken at 200 K affirms the P3c1 space group with nine water molecules of hydration and unit cell parameters a = b = 16.7349(2) A and c = 12.6338(1) A with Z = 6. The structures can be described in terms of modulations of an idealised Z = 1 structure in P3[combining macron]lm. T-Cycle experiments of spectral holes in the R(1)-line yield a single Gaussian barrier with T(0) +/- sigma(T) of 46 +/- 21 K and three barriers with 40 +/- 12, 70 +/- 10, 107 +/- 5 K for perprotonated and partially deuterated (46%) NaMgAl(oxalate)(3).9H(2)O/Cr(iii) 0.5%, respectively.     

Absolute photoionization cross-section of the methyl radical

The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; sigma(CH3)(10.2 eV) = (5.7 +/- 0.9) x 10(-18) cm(2) and sigma(CH3)(11.0 eV) = (6.0 +/- 2.0) x 10(-18) cm(2). The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 +/- 2.0) x 10(-18) cm(2) at 10.460 eV, (5.5 +/- 2.0) x 10(-18) cm(2) at 10.466 eV, and (4.9 +/- 2.0) x 10(-18) cm(2) at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.     

Syntheses and structural characterization of luminescent platinum(II) complexes containing di-tert-butylbipyridine and new 1,1-dithiolate ligands

Three new di-tert-butylbipyridine (dbbpy) complexes of platinum(II) (1-3) containing 1,1-dithiolate ligands have been synthesized and characterized. The 1,1-dithiolates are 2,2-diacetylethylene-1,1-dithiolate (S(2)C=C(C(O)Me)2) (1), 2-cyano-2-p-bromophenylethylene-1,1-dithiolate (S(2)C=C(CN)(p-C(6)H(4)Br)) (2), and p-bromophenyl-2-cyano-3,3-dithiolatoacrylate (S(2)C=C(CN)(COO-p-C(6)H(4)Br)) (3). Complex 1 exhibits a solvatochromic charge-transfer absorption in the 430-488 nm region of the spectrum and a luminescence around 635 nm in ambient temperature CH(2)Cl(2) solution. These observations are consistent with what has been seen previously in related Pt diimine 1,1-dithiolate complexes. The nature of the emissive state is assigned as a (3)(mixed metal/dithiolate-to-diimine) charge transfer, while the solvatochromic absorption band corresponds to the singlet transition of similar orbital character. The other complexes also exhibit a low-energy solvatochromic absorption. The crystal structures of two of the complexes have been determined, representing the first time that Pt(diimine)(1,1-dithiolate) complexes have been crystallographically studied. The structures confirm the expected square planar coordination geometry with distortions in bond angles dictated by the constraints of the chelating ligands. The Pt-S and Pt-N bond lengths and S-Pt-S and N-Pt-N bond angles for the two structures are identical within experimental error (2.283(2) and 2.278(2) A; 2.053(6) and 2.050(8) A; 75.01(8) degrees and 75.40(8) degrees; 79.2(2) degrees and 79.0(2) degrees, respectively). Crystal data for 1: monoclinic, space group P2(1)/n (No. 14), with a = 7.20480(10) A, b = 20.53880(10) A, c = 19.1072(2) A, beta = 93.83 degrees, V = A(3), Z = 4, R1 = 3.34% (I > 2sigma(I)), wR2 = 9.88% (I > 2sigma(I)) for 3922 unique reflections. Crystal data for 2: monoclinic, space group P2(1)/n (No. 14), with a = 15.0940(5) A, b = 9.5182(3) A, c = 20.4772(7) A, beta = 111.151(1) degrees, V = A(3), Z = 4, R1 = 4.07% (I > 2sigma(I)), wR2 = 8.64% (I > 2sigma(I)) for 3859 unique reflections.     

High-pressure acceleration of the growth kinetics of glucose isomerase crystals

The growth and dissolution rates of glucose isomerase crystals ({1 0 1} face) were measured in situ at 0.1 and 100 MPa. From these data, we determined that the solubilities at 25 degrees C were C(e) = 3.1 +/- 0.9 and 2.6 +/- 0.5 mg mL(-1) at 0.1 and 100 MPa, respectively. At the same supersaturation of sigma = 2.5 (sigma identical with ln(C/C(e)), C = the concentration of glucose isomerase, C(e) = the solubility) and temperature (T = 25 degrees C), the growth rate under 100 MPa was 7.6 times larger than that under 0.1 MPa. This result shows, for the first time, a kinetic acceleration of the growth rates of protein crystals with increasing pressure. The growth rates vs sigma data fitted well with a two-dimensional nucleation growth model of a polynucleation type. The fitting results indicate that the acceleration is mainly due to the decrease in the molecular surface energy of the glucose isomerase crystal with pressure.     

Photochemistry of ethyl chloride caged in amorphous solid water

Caging and photo-induced decomposition of ethyl chloride molecules (EC) within a layer of amorphous solid water (ASW) on top of clean and oxygen-covered Ru(001) under ultra-high vacuum (UHV) conditions are presented. The caged molecules were estimated to reside 1.5 +/- 0.2 nm above the solid surface, based on parent molecule thermal decomposition on the clean ruthenium. Dissociative electron attachment (DEA) of the caged molecules following 193 nm laser irradiation, result in initial fragmentation to ethyl radical and chloride anion. It was found that photoreactivity on top of the clean ruthenium surface (Ru) is twenty times faster than on the oxygen-covered surface (O/Ru), with DEA cross sections: sigma(Ru) = (3.8 +/- 1) x 10(-19) cm(2) and sigma(O/Ru) = (2.1 +/- 0.3) x 10(-20) cm(2). This difference is attributed to the higher work function of oxygen-covered ruthenium, leading to smaller electron attachment probability due to mismatch of the ruthenium photo-electron energy with the adsorbed EC excited electron affinity levels. EC molecules fragmented within the cage, result in post-irradiation TPD spectra that reveal primarily C(4)H(8), C(3)H(5) and C(3)H(3), without any oxygen-containing molecules. Unique stabilization of the photoproducts has been observed with the first layer of water molecules in direct contact with the substrate, desorbing near 180 K, a significantly higher temperature than the desorption of fully caged molecules. This study may contribute for understanding stratospheric photochemistry and processes in interstellar space.     

Near-ultraviolet photodissociation of thiophenol

H(D) Rydberg atom photofragment translational spectroscopy has been used to investigate the dynamics of H(D) atom loss C6H5SH(C6H5SD) following excitation at many wavelengths lambda phot in the range of 225-290 nm. The C6H5S cofragments are formed in both their ground (X(2)B1) and first excited ((2)B2) electronic states, in a distribution of vibrational levels that spreads and shifts to higher internal energies as lambda(phot) is reduced. Excitation at lambda(phot) > 275 nm populates levels of the first (1)pi pi* state, which decay by tunnelling to the dissociative (1)pi sigma* state potential energy surface (PES). S-H torsional motion is identified as a coupling mode facilitating population transfer at the conical intersection (CI) between the diabatic (1)pi pi* and (1)pi sigma* PESs. At shorter lambda(phot), the (1)pi sigma* state is deduced to be populated either directly or by efficient vibronic coupling from higher (1)pipi* states. Flux evolving on the (1)pi sigma* PES samples a second CI, at longer R(S-H), between the diabatic (1)pi sigma* and ground ((1)pi pi) PESs, where the electronic branching between ground and excited state C6H5S fragments is determined. The C6H5S(X(2)B1) and C6H5S((2)B2) products are deduced to be formed in levels with, respectively, a' and a' vibrational symmetry-behavior that reflects both Franck-Condon effects (both in the initial photoexcitation step and in the subsequent in-plane forces acting during dissociation) and the effects of the out-of-plane coupling mode(s), nu11 and nu16a, at the (1)pi sigma*/(1)pi pi CI. The vibrational state assignments enabled by the high-energy resolution of the present data allow new and improved estimations of the bond dissociation energies, D0(C6H5S-H) < or = 28,030 +/- 100 cm(-1) and D0(C6H5S-D) < or = 28,610 +/- 100 cm(-1), and of the energy separation between the X(2)B1 and (2)B2 states of the C6H5S radical, T(00) = 2800 +/- 40 cm(-1). Similarities, and differences, between the measured energy disposals accompanying UV photoinduced X-H (X = S, O) bond fission in thiophenol and phenol are discussed.     

Universal growth of microdomains and gelation transition in agar hydrogels

Investigations were carried out on aqueous sols and gels of agar (extracted from red seaweed Gelidiella acerosa) to explore the growth of microdomains en route to gelation. Isothermal frequency sweep studies on gel samples revealed master plots showing power-law dependence of gel elastic modulus, |G*|, on oscillation frequency, omega as |G*| approximately omegan, independent of temperature, with 0.5Tg). The S(q,t) behavior close to the gel transition point (Tg approximately (38+/-3 degrees C determined from rheology) followed a stretched exponential function: S(t)=A exp(-t/ts)beta. The beta factor increased from 0.25 to 1 as the gel temperature approached 25 degrees C from Tg, and relaxation time, ts, showed a peak at T approximately 30 degrees C. The SLS data (in the sol state) suggested the scaling of scattered intensity, Is(q) approximately epsilon(-gamma) (epsilon=(T/Tg-1), T>Tg) with gamma=0.13+/-0.03, and the presence of two distinct domains characterized by a Guinier regime (low q) and a power-law regime (high q). Close to and above Tg (+2 degrees C), IS(q) scaled with q as Is(q) approximately q(-alpha) with alpha=2.2+/-0.2, which decreased to 1.4+/-1 just below Tg (-2 degrees C), implying a coil-helix transition for 0.2% (w/v) and 0.3% (w/v) samples. For a 0.01% sample, alpha=3.5+/-0.5 which indicated the presence of spherical microgels.     

Synthesis of uniform Cu2S nanowires from copper-thiolate polymer precursors by a solventless thermolytic method

Uniform hexagonal Cu2S nanowires with 2-6 nm diameters, 0.1 to several mum in length, were made by precipitation and thermolysis at 155 degrees C for 120 min from a Cu-thiolate colloid with a viscosity of 93.5 mPa/s. The morphologies of the final nanoproducts are governable through control of the coordination chemistry of Cu ions and thiols and the association of the Cu/S fragments. The evolution of nanowires, with the polymerization and heating temperature, and the parameters affecting the viscosity of the colloid precursor are reported.