Polyelectrolyte nanotubes of poly(sodium 4‐styrene‐sulfonate) (PSS) with cationic poly(diallyl dimethyl ammonium chloride) (PDDA) (PSS/PDDA) were fabricated by a pressure‐filter‐template technique using microporous anodic aluminum oxide (AAO) as the template. UV‐Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and infrared spectroscopy (FT‐IR) were applied to characterize the obtained PSS/PDDA nanotubes. The results have shown that the PSS/PDDA nanotubes exhibit an amorphous structure and have the outer diameter of 200 nm and length of 25 µm respectively, which are in good agreement with the dimensions of the AAO template pores. The wall thickness of the nanotubes may be controlled by the number of the self‐assembled layers. Formation of the nanotubes follows a layer‐by‐layer (LbL) mechanism due to the electrostatic interactions, where the SO?3 groups of PSS are first adsorbed on the Lewis acid sites of AAO template pores. 相似文献
High‐quality rare‐earth fluorides, α‐NaMF4 (M=Dy, Ho, Er, Tm, Y, Yb, and Lu) nanocrystals and β‐NaMF4 (M=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y, Yb, and Lu) nanoarrays, have been synthesized by using oleic acid as a stabilizing agent through a facile hydrothermal method at 130–230 °C. The phase, shape, and size of the products are varied by careful control of synthetic conditions, including hydrothermal temperature and time, and the amounts of reactants and solvents. Tuning the hydrothermal temperature, time, and the amount of NaOH can cause the transformation from the cubic α‐NaMF4 to hexagonal phase β‐NaMF4. Upon adjustment of the amount of NaOH, NaF, M3+, and ethanol, the morphologies for the β‐NaMF4 nanoarrays can range from tube, rod, wire, and zigzagged rod, to flower‐patterned disk. Simultaneously, the size of the rare‐earth fluoride crystals is variable from 5 nm to several micrometers. A combination of “diffusion‐controlled growth” and the “organic–inorganic interface effect” is proposed to understand the formation of the nanocrystals. An ideal “1D growth” of rare‐earth fluorides is preferred at high temperatures and high ethanol contents, from which the tube‐ and rodlike nanoarrays with high aspect ratio are obtained. In contrast, the disklike β‐NaMF4 nanoarrays with low aspect ratios are produced by decreasing the ethanol content or prolonging the reaction time, an effect probably caused by “1D/2D ripening”. Multicolor up‐conversion fluorescence is also successfully realized in the Yb3+/Er3+ (green, red) and Yb3+/Tm3+ (blue) co‐doped α‐NaYF4 nanocrystals and β‐NaYF4 nanoarrays by excitation in the NIR region (980 nm). 相似文献
An ultrasensitive surface‐enhanced Raman spectroscopy (SERS) sensor based on rolling‐circle amplification (RCA)‐increased “hot‐spot” was developed for the detection of thrombin. The sensor contains a SERS gold nanoparticle@Raman label@SiO2 core‐shell nanoparticle probe in which the Raman reporter molecules are sandwiched between a gold nanoparticle core and a thin silica shell by a layer‐by‐layer method. Thrombin aptamer sequences were immobilized onto the magnetic beads (MBs) through hybridization with their complementary strand. In the presence of thrombin, the aptamer sequence was released; this allowed the remaining single‐stranded DNA (ssDNA) to act as primer and initiate in situ RCA reaction to produce long ssDNAs. Then, a large number of SERS probes were attached on the long ssDNA templates, causing thousands of SERS probes to be involved in each biomolecular recognition event. This SERS method achieved the detection of thrombin in the range from 1.0×10?12 to 1.0×10?8 M and a detection limit of 4.2×10?13 M , and showed good performance in real serum samples. 相似文献
Ag@SiO2 nanoparticles with the core-shell structure have been prepared, of which the silver core was about 50 nm and the thickness of silica shell was approximately 10 nm. In slightly alkaline aqueous solution (pH = 8), through electrostatic force between cationic polymer PDDA (i.e., poly-diallyldimethylammonium chloride) and the obtained Ag@SiO2 nanoparticles, PDDA molecules were fixed on the surface of Ag@SiO2 nanoparticles. The prepared Ag@SiO2/PDDA nanoparticles have both rich positive surface charges and rich micro-holes of silica shell. Based on micro-hole adsorption, the small molecule FITC (i.e., fluorescein isothiocyanate) marking on IgG (i.e., immunoglobulin) was adsorbed into the rich microholes of silica shell; at the same time, the negatively charge macromolecule IgG marked by FITC was firmly fixed on the rich positive charges surface of Ag@SiO2/PDDA nanoparticles by electrostatic interaction. And then, Ag@SiO2/PDDA/IgG-FITC fluorescent nanoparticles with the SPR fluorescence enhancement were prepared. The shell-type SiO2/PDDA/IgG-FITC nanoparticles were obtained by dissolving the silver core in the prepared core-shell Ag@SiO2/PDDA/IgG-FITC nanoparticles by using H2O2. Compared with the shell-type nanoparticles, the fluorescence intensity of Ag@SiO2/PDDA/IgG-FITC was enhanced 1.7 times. The prepared Ag@SiO2/PDDA/IgG-FITC nanoparticles have both SPR-based fluorescence enhancement ability and the surface distributing IgG–based obvious advantages including good biocompatibility and easy marking with other biomolecules. 相似文献
Three coordination polymers (CPs) based on the 5‐[4‐(1H‐imidazol‐1‐yl)phenyl]‐1H‐tetrazole ( HL ) ligand, namely, [Cu(μ2‐ L )(μ4‐pbda)(H2O)] ( 1 ), [Cu2(μ‐Hbtc)(H2btc)(μ3‐OH)(μ4‐ HL )] ( 2 ) and [Cu5(μ3‐ L )(μ4‐ L )(μ3‐ip)(μ3‐OH)(H2O)2] · 2H2O ( 3 ) (H2pbda = 1,4‐benzenedicarboxylic acid, H3btc = 1,3,5‐benzenetricarboxylic acid, H2ip = isophthalic acid) were hydrothermally synthesized and structurally characterized. Complex 1 represents “weave”‐type 2D layers consisting of wave‐like 1D chains and 1D straight chains, which are further connected by hydrogen bonds to form a 3D supramolecular structure. Complex 2 exhibits a uninodal (4)‐connected 2D layer with a point symbol of {44 · 62}, in which the L ligand can be described as μ5‐bridging and the H2btc– ions display multiple kinds of coordination modes to connect CuII ions into 1D “H”‐type Cu‐H2btc chains. In complex 3 , 2D Cu‐ L layers with two kinds of grids and 1D “stair”‐type Cu‐ip chains link each other to construct a 3D {412 · 63} framework, which contains the pentanuclear subunits. Deprotonated degree and coordination modes of carboxylate ligands may consequentially influence the coordination patterns of main ligands and the final structures of complexes 1 – 3 . Furthermore, electrochemical behaviors and electrocatalytic activities of the title complexes were analyzed at room temperature, suggesting practical applications in areas of electrocatalytic reduction toward nitrite and hydrogen dioxide in aqueous solutions, respectively. 相似文献
Tetranuclear, intensely blue‐coloured CuI complexes were synthesised in which two Cu2X3? units (X=Br or I) are bridged by a dicationic GFA (guanidino‐functionalised aromatic) ligand. The UV/Vis spectra show a large metal‐to‐ligand charge‐transfer (MLCT) band around 638 nm. The tetranuclear “low‐temperature” complexes are in a temperature‐dependent equilibrium with dinuclear CuI “high‐temperature” complexes, which result from the reversible elimination of two CuX groups. A massive thermochromism effect results from the extinction of the strong MLCT band upon CuX elimination with increasing temperature. For all complexes, quantum chemical calculations predict a small and method‐dependent energy difference between the possible electronic structures, namely CuI and dicationic GFA ligand (closed‐shell singlet) versus CuII and neutral GFA ligand (triplet or broken‐symmetry state). The closed‐shell singlet state is disfavoured by hybrid‐DFT functionals, which mix in exact Hartree–Fock exchange, and is favoured by larger basis sets and consideration of a polar medium. 相似文献
Using 3‐Aminopropyltriethoxysilane(APTES) as a single silica source, an amino‐rich ultrafine organosilica‐nanoparticle‐modified Au electrode was fabricated, following the formation of (3‐mercaptopropyl)‐trimethoxysilane (MPTS) monolayer on Au surface (MPTS/Au). With cetyltrimethylammonium bromide as an additive, APTES‐based gel particles on the electrode have a narrow particle size distribution of 4–7 nm and “crystal‐like” structure. AFM and electrochemical characterization confirmed the successful grafting of APTES nanoparticles on MPTS/Au. The APTES/MPTS/Au electrode is highly sensitive for the detection of copper(II) ions with a detection limit as low as 1.6×10?12 mol L?1 (S/N>3) by square wave voltammetry. The current is linear to copper(II) concentration between 1.6×10?12 and 6.25×10?10 mol L?1. 相似文献
Microporous amorphous hydrophobic silica materials with well‐defined pores were synthesized by replication of the metal–organic framework (MOF) [Cu3(1,3,5‐benzenetricarboxylate)2] (HKUST‐1). The silica replicas were obtained by using tetramethoxysilane or tetraethoxysilane as silica precursors and have a micro–meso binary pore system. The BET surface area, the micropore volume, and the mesopore volume of the silica replica, obtained by means of hydrothermal treatment at 423 K with tetraethoxysilane, are 620 m2g?1, 0.18 mL g?1, and 0.55 mL g?1, respectively. Interestingly, the silica has micropores with a pore size of 0.55 nm that corresponds to the pore‐wall thickness of the template MOF. The silica replica is hydrophobic, as confirmed by adsorption analyses, although the replica has a certain amount of silanol groups. This hydrophobicity is due to the unique condensation environment of the silica precursors in the template MOF. 相似文献
(PDDA/CdTe)n layer‐by‐layer (LBL) film immobilized with Fe(CN)63? was fabricated on the gold electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the electrochemical properties of this film. The peak current of the immobilized Fe(CN)63? increased as the number of the bilayers increased and was proportional to the scan rate. Compared with pure (PDDA/CdTe)n and (PDDA/PSS)n LBL film, Fe(CN)63? immobilized (PDDA/CdTe)n LBL film had good electron transfer ability. The immobility of Fe(CN)63? into the film was attributed to its interaction with Cd2+ on the surface of CdTe QDs. Fe(CN)63? also can interact with other metal ions, which would make Fe(CN)63? release from the film. The concentrations of metal ions will affect the CV response of Fe(CN)63? immobilized LBL film. It has provided a novel prototype of device or sensor for quantitative detection of metal ions. 相似文献
We report a one‐step convenient chemical coating method of high alumina content onto mesoporous silicas. Aluminia‐coated mesoporous silica with high surface area (?900 m2/g), tuneable pore size (2.0–3.0 nm) and high hydrothermal stability (> 60 h) is obtained. The method may also be generalized for grafting other metal oxides onto mesoporous silica in future work. 相似文献
Praseodymium (Pr3+)‐doped YF3 (core) and LaF3 ‐covered YF3 :Pr (core–shell) nanocrystals (NCs ) were prepared successfully by an ecofriendly, polyol‐based, co‐precipitation process, which were then coated with a silica shell by using a sol–gel‐based Stober method. X‐ray diffraction (XRD), transmission electron microscopy (TEM ), thermal analysis, Fourier transform infrared (FTIR) , UV /vis, energy bandgap, and photoluminescence studies were used to analyze the crystal structure, morphology, and optical properties of the nanomaterial. XRD and TEM results show that the grain size increases after sequential growth of crystalline LaF3 and the silica shell. The silica surface modification enhances the solubility and colloidal stability of the core–shell‐SiO2 NCs . The results indicate that the surface coating affects the optical properties because of the alteration in crystalline size of the materials. The emission intensity of silica‐modified NCs was significantly enhanced compared to that of core and core–shell NCs . These results are attributed to the formation of chemical bonds between core–shell and noncrystalline SiO2 shell via La–O–Si bridges, which activate the “dormant” Pr3+ ions on the surfaces of the nanoparticles. The luminescence efficiency of the as‐prepared core, core–shell, and core–shell‐SiO2 NCs are comparatively analyzed, and the observed differences are justified on the basis of the surface modification surrounding the luminescent seed core NCs . 相似文献
Silica nanoparticles (SiNPs) were chosen as a solid support material for the immobilization of a new Wilkinson’s‐type catalyst. In a first step, polymer molecules (poly(triphenylphosphine)ethylene (PTPPE); 4‐diphenylphosphine styrene as monomer) were grafted onto the silica nanoparticles by surface‐initiated photoinferter‐mediated polymerization (SI‐PIMP). The catalyst was then created by binding rhodium (Rh) to the polymer side chains, with RhCl3 ? x H2O as a precursor. The triphenylphosphine units and rhodium as RhI provide an environment to form Wilkinson’s catalyst‐like structures. Employing multinuclear (31P, 29Si, and 13C) solid‐state NMR spectroscopy (SSNMR), the structure of the catalyst bound to the polymer and the intermediates of the grafting reaction have been characterized. Finally, first applications of this catalyst in hydrogenation reactions employing para‐enriched hydrogen gas (PHIP experiments) and an assessment of its leaching properties are presented. 相似文献
Summary: Macroporous monoliths consisting of silica nanoparticles embedded in poly(methyl methacrylate) (PMMA) were synthesized in supercritical CO2. Well‐dispersed silica particles, pretreated with functional 3‐(trimethoxysilyl)propyl methacrylate (MPS), were to form colloidal PMMA nanocomposites followed by a sol‐gel transition forming interconnected structures resulting in micron‐sized pores with specific areas between 1 and 7 m2 · g−1. SEM and TEM results revealed uniform morphological characteristics of the composite materials and good dispersions of the silica nanoparticles.
SEM micrograph of PMMA/Silica nanocomposites forming interconnected macroporous monolith. The average size of the silica particles is 50 nm. 相似文献
High‐temperature, stable core–shell catalysts for ammonia decomposition have been synthesized. The highly active catalysts, which were found to be also excellent model systems for fundamental studies, are based on α‐Fe2O3 nanoparticles coated by porous silica shells. In a bottom‐up approach, hematite nanoparticles were firstly obtained from the hydrothermal reaction of ferric chlorides, L ‐lysine, and water with adjustable average sizes of 35, 47, and 75 nm. Secondly, particles of each size could be coated by a porous silica shell by means of the base‐catalyzed hydrolysis of tetraethylorthosilicate (TEOS) with cetyltetramethylammonium bromide (CTABr) as porogen. After calcination, TEM, high‐resolution scanning electron microscopy (HR‐SEM), energy‐dispersive X‐ray (EDX), XRD, and nitrogen sorption studies confirmed the successful encapsulation of hematite nanoparticles inside porous silica shells with a thickness of 20 nm, thereby leading to composites with surface areas of approximately 380 m2 g?1 and iron contents between 10.5 and 12.2 wt %. The obtained catalysts were tested in ammonia decomposition. The influence of temperature, iron oxide core size, possible diffusion limitations, and dilution effects of the reagent gas stream with noble gases were studied. The catalysts are highly stable at 750 °C with a space velocity of 120 000 cm3 gcat?1 h?1 and maintained conversions of around 80 % for the testing period time of 33 h. On the basis of the excellent stability under reaction conditions up to 800 °C, the system was investigated by in situ XRD, in which body‐centered iron was determined, in addition to FeNx, as the crystalline phase under reaction conditions above 650 °C. 相似文献