Search

Abstract: Silver nanoparticles have been prepared by a non-template method. Silver nitrate can be easily decomposed into silver nanosized materials. Small nanoparticles (less than 2 nm) can be formed in aqueous solution. Larger silver particles of about 100 nm can be formed in ethanol solution. By rationally adjusting the experimental conditions we finally obtain silver particles of about 20 nm with a relatively narrow distribution in ethanol solution. Differing from the previous reports, we find that silver nanoparticles can be formed by direct decomposition of AgNO3 under UV light irradiation. No catalyst like TiO2 is needed at all. We believe that it is a further step to precede the preparation of silver nanometer sized materials. [Copyright &y& Elsevier]

Transition-metal oxides — including tungsten oxide, molybdenum oxide, titanium dioxide, vanadium pentoxide, niobium pentoxide and zinc oxide — exhibit photochromism upon bandgap excitation. These oxides constitute an important group of inorganic chromogenic materials, which is of great significance in the perspective of science and technology. During the past several decades, great progresses have been made in the microstructure, photochromic behavior and mechanism of these oxides, specifically of tungsten oxide. These studies underscore the opportunity of using these materials in photonic applications. The details will be presented in this review. [ABSTRACT FROM AUTHOR]

Oxidative stress, which involved in several inflammatory and degenerative diseases, has become interesting in most of biomedical disciplines and many types of clinical research. Antioxidants can protect biological systems from the harmful effects of oxidative stress. It can reflect the monitor effect to oxidative stress from another aspect by detecting the antioxidant capacity. Therefore, it is particularly significant to assay the antioxidant capacity of biological fluids. Herein, for the first time a fluorescence-tunable probe was developed based on polydopamine-quenched fluorescent graphitic carbon nitride (g-C 3 N 4 ) for assessing the antioxidant capacity of biological fluids. Dopamine (DA) can self-polymerize on the surface of g-C 3 N 4 to produce a polydopamine (PDA) uniform coating layer in which the fluorescence of g-C 3 N 4 is efficiently quenched by the PDA layer, showing the fluorescence “off” state. However, in the presence of antioxidants, the self-polymerized effect of DA can be effectively inhibited and leading to the fluorescence “on” state. Therefore, detecting antioxidants can be achieved by monitoring the fluorescent emission of g-C 3 N 4 . Moreover, endowed with high sensitivity and selectivity, the proposed sensing system was successfully applied to assessment antioxidant capacity in biological fluid and the results matched well with commonly used antioxidant detection method. [ABSTRACT FROM AUTHOR]

A simple graphene quantum dots (GQDs)-based fluorescence sensing system was developed for rapid, sensitive and low-cost detection of ascorbic acid (AA) in the presence of copper ions. Due to the efficient electron-transfer between GQDs and Cu 2+ ions, the fluorescence of GQDs was greatly quenched by Cu 2+ ions. Upon addition of ascorbic acid, Cu 2+ was reduced to Cu + and the interaction of Cu 2+ -GQDs was destroyed, which inhibit the quenching and thus leading to fluorescence recovery of GQDs. The detection process is ultrafast and can be completed within 5 min. The linear response range of AA was obtained from 0.3 μM to 10 μM. The detection limit was as low as 94 nM, which was comparable to or even better than other reported assays. In addition, this sensing system also showed good selectivity for detecting AA in the presence of different physiological molecules and inorganic ions. Finally, the proposed sensing system was successfully applied to assay AA in real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

The ordered array of nanovoids innanoporous networks, such ashoneycomb, Kagome, and square, provides a molecular template for theaccommodation of “guest molecules”. Compared with thecommonly studied guest molecules featuring high symmetry evenly incorporatedinto the template, guest molecules featuring lower symmetry are rareto report. Herein, we report the formation of a distinct patternedsuperlattice of guest molecules by selective trapping of guest moleculesinto the honeycomb network of trimesic acid (TMA). Two distinct surfacepatterns have been achieved by the guest inclusion induced adaptivereconstruction of a 2D molecular nanoporous network. The honeycombnetworks can synergetically tune the arrangement upon inclusion ofthe guest molecules with different core size but similar peripheralsgroups, resulting in a trihexagonal Kagome or triangular patterns. [ABSTRACT FROM AUTHOR]

Novel tungsten oxide superstructures have been constructed using two non-surfactant molecules, 1,10-diaminodecane and n-amylamine, as templates. The X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and results give detailed analysis on the microstructures. The experimental results have shown that size matching between the organic template and the inorganic framework plays a critical role in the construction of these hybrid superstructures. If the size of the template fits the pore constructed by six polytungstate anions, a superstructure is stabilized and formed. [Copyright &y& Elsevier]

A novel photochromic nanocomposite film containing polyoxotungstoeuropate K12[EuP5W30O110] entrapped in polyvinylpyrrolidone has been prepared through a spin-on coating technique. Thus-obtained amorphous nanocomposite film was characterized by IR spectra, UV–vis absorption spectra, XRD, SEM, TG-DTA, and ESR. Results show that polyoxotungstoeuropate interacts with polyvinylpyrrolidone strongly and disperses homogeneously in the matrix. The composite film exhibits good photochromic properties. When irradiated with UV light, the transparent film changes from colorless to blue. Then, bleaching occurs when the film is in contact with ambient air or O2 in the dark. The photochromism of the composite film is due to charge transfer by reduction of polyoxotungstoeuropate and oxidation of polyvinylpyrrolidone. [Copyright &y& Elsevier]

A novel photochromic gel film was prepared through entrapping 12-phosphotungstic acid (PWA) into a kind of inorganic–organic matrix co-hydrolyzed from tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES). Infrared (IR) spectra revealed that the Keggin structure characteristic of PW12O403− anions was present in the amine-functionalized silica gel skeleton and PWA interacted with R-NH3+ cations strongly. The amorphous state of the gel film was proved by X-ray diffraction (XRD) pattern. The gel film exhibited reversible photochromicity. Irradiated with ultraviolet light, the transparent film changes from colorless to blue. Then, bleaching occurs when the film is in contact with air or O2 in the dark. [Copyright &y& Elsevier]

A self-assembled layered superlattice composite film was fabricated by casting the chloroform solutions of ionic complex between dioctadecyldimethylammonium (DODA) and 18-molybdophosphate anion (P2Mo186−) onto CaF2, borosilicate glass, and quartz substrates. Infrared and UV spectra revealed that the Dawson structure characteristic of P2Mo186− was preserved in the composite film. A well-ordered superlattice structure was identified by X-ray diffraction (XRD). From XRD results and the cross-sectional area of DODA cation and P2Mo18 polyanion, a possible structural model was proposed. The P2Mo18/DODA film showed good photochromic properties. Irradiated with UV light, the transparent film changed from light yellow to blue. Then, bleaching occurred when the film was in contact with ambient air or O2 in the dark. A possible photochromic mechanism was proposed according to electron spin resonance (ESR), Fourier transform infrared (FTIR) spectra, and UV–Vis spectra. [Copyright &y& Elsevier]

Presents information on a study that examined the electronic transitions of 1, 3, 5,-triphenyl-2-pyrazoline nanocrystals using both absorption and fluorescence spectra. Methodology of the study; Results and discussion on the study.

Novel photochromic nanocomposite thin film containing phosphotungstic acid entrapped in polyacrylamide was prepared using ultrasound technique. TEM image revealed that the polyoxometalates nanoparticles with narrow size distribution were finely dispersed in polymer matrix. IR spectra showed that the Keggin geometry of polyoxometalates was still preserved inside the composite film and strong Coulombic interaction was built between heteropolyoxometalates and polyacrylamide via hydrogen bond. It was found that the thermal stability of the hybrid film was lower than that of pure polymer but the film was stable enough for photochromic application from the TG–DTA curves. The transparent film changed from colorless to blue under UV irradiation and showed reversible photochromism. The bleaching process occurred when the film was in contact with air or O2 in the dark. The photoreduced process was in accordance with radical mechanism. [Copyright &y& Elsevier]

A new photochromic film was prepared based on the Keggin type H3PW12O40 (PW12) with polyacrylamide (PAM) matrix. The microstructure, photochromic behavior and mechanism were investigated with FT-Infrared spectroscopy (FT-IR), atomic force microscopy (AFM), transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV–VIS), and electron resonance spectroscopy (ESR). FT-IR results showed that the Keggin geometry of PW12 was still preserved inside the matrix, and a charge-transfer bridge was built between PW12 and PAM via hydrogen bond. AFM images indicated that the surface topography of the polymer matrix changed after adding PW12. In the hybrid films, the PW12 particles had regular microstucture in nanoscale shown in TEM image. Under UV irradiation, the film was reduced photochemically to yield a blue species. With the increase of irradiation time, the photoreduction proceeded from one-electron to two-electron blue stage. The characteristic signals of W (V) and radical in ESR spectra indicated that the photoreduced process was in accordance with the radical mechanism. [Copyright &y& Elsevier]