Search

The rational designs of particle size, morphology and surface states of the Au nanoparticles(AuNPs) are crucial for Au nanocatalyst. We herein report a method to synthesize the silica microspheres supported AuNPs(ca. 1 nm) and their application in controlling the reaction conversion and selectivity in styrene epoxidation. Surfactant-free AuNPs deposited on silica microspheres were in situ fabricated with aid of the Ag nanoparticles (AgNPs) as sacrificial template by galvanic replacement reaction, leading to AuNPs/SiO2 catalyst directly without any post-treatment to expose crystal facets. A high conversion of 46.7% and selectivity of 91.7% to styrene oxide was achieved with H2O2 as oxidant in ethanol. The solid catalyst could be reused at least 10 reaction cycles without significant decrease in activity and selectivity. This study not only supplies an active, recoverable catalyst for styrene oxidation with green oxidant and solvent, but also demonstrates that the silica microspheres functionalized with thiol groups have a superior ability in stabilizing noble metal nanoparticles even without any surfactant.

The synthesis of Ag nanoparticles (AgNPs) frequently requires the participation of organic ligands. However, how the organic ligands attached on their surfaces would affect the antibacterial activity of the AgNPs remains to be explored. Based on a novel in situ synthesis approach, silica supported AgNPs with bare surfaces were fabricated and further functionalized with different organic ligands (–OH, –Ph, –SH, and –COOH) and the antibacterial activities of the bare AgNPs and AgNPs with different ligands were investigated. Though all specimens exhibited different antibacterial capabilities against Escherichia coli (E. coli), the minimal inhibitory concentration (MIC) of AgNPs functionalized with –COOH was the smallest and as low as 8–16 μg ml−1, indicating the best antibacterial performance among the 4 ligands. In addition, the cytotoxicity test of the bare AgNPs and AgNPs with ligands indicated that all the AgNPs caused no significant damage to human cells, suggesting their good potential for antibacterial applications in daily life.

The authors describe an electrochemical sensor for hydrogen peroxide (H2O2). It was constructed by consecutive, selective modification of a glassy carbon electrode (GCE) with Prussian Blue (PB), layered molybdenum disulfide (MoS2), and reduced graphene oxide (rGO). The properties of the modified GCE were characterized via high-resolution transmission electron microscopy, UV-vis spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide in comparison to GCEs modified with MoS2-rGO or PB only. Response is linear in the 0.3 μM to 1.15 mM H2O2 concentration range at a working analytical voltage of 0.1 V, with a 0.14 μM detection limit. The electrochemical sensitivity is 2883.5 μA·μM−1·cm−2, and response is fast (

An effective method of concurrent extraction and purification for polysaccharides from Gentiana scabra Bunge stems was developed by microwave-assisted aqueous two-phase extraction (MA-ATPE). Ethanol/sodium dihydrogen phosphate was employed to form aqueous two-phase system (ATPS) by evaluating the extraction properties of five combinations of ethanol/salt systems. The important factors, namely, the composition of ATPS, extraction temperature, solvent-to-material ratio, extraction time and the particle size were investigated by single factor experiment and response surface methodology (RSM) combined with Box–Behnken Design (BBD). The final extraction conditions were concluded as follows: ethanol concentration 21.73% (w/w) and NaH 2 PO 4 concentration 23.27% (w/w) for the ATPS, extraction temperature 95 °C, extraction time 5.8 min, solvent-to-material ratio 21:1 (mL/g) and particle size 80 mesh. Under the optimum conditions, the extraction yield of polysaccharides were 15.97 ± 0.32% for the top phase, 0.58 ± 0.26% for the bottom phase and 16.55 ± 0.13% for total polysaccharides, and the purity of water-soluble polysaccharides was 78.19 ± 0.42%. Compared with smashing tissue extraction (STE), microwave assisted-extraction (MAE), ultrasonic-assisted extraction (UAE) and heat reflux extraction (HRE), microwave-assisted aqueous two-phase extraction not only improved the yield and purity of water-soluble polysaccharides, but also obtained a variety of polysaccharides. In addition, the chemical characterization of polysaccahrides from both the two phases were carried out by Fourier transforms infrared spectrum (FT-IR) and High performance liquid chromatography derivatization with 1-phenyl-3-methy-5-pyrazolone (HPLC-PMP). The extraction mechanism was also discussed by scanning electron microscope (SEM). Therefore, as an efficient and promising technique, microwave-assisted aqueous two-phase extraction may be a viable option for the simultaneous extraction and purification of polysaccharides from plants.

A facile one-step sol-gel method was used to prepare CdTe nanocrystals(NCs) doped silica microspheres with luxuriant thiol group on their surface using 3-mercaptopropyl trimethoxysilane(MPTMS) as organosilane in the aqueous solution. As the ligand and organosilane, MPTMS ensured the doping efficiency of CdTe NCs by ligand exchange and a large thiol group exposed to the solution to activate the surface of silica microspheres. The remodeled sol-gel process was performed at a lower temperature, which protected the thiol groups from degradation. Meanwhile, the particle size and size distribution can be controlled by varying synthesis conditions, such as the stirring rate and the reaction temperature. This user-friendly method provides a platform for immobilization of chemical groups such as carboxyl for combination of bioactive and diagnostic molecules at the surface of CdTe NCs doped silica microspheres through thiol-ene chemistry for high-throughput microarrays.

A potential method called microwave-assisted aqueous two-phase extraction (MA-ATPE) was developed for concurrent extraction and purification of gentiopicroside from Gentiana scabra Bunge. Formation characteristics of aqueous two-phase system (ATPS) composed of ethanol and 25 kinds of salts were investigated; K2HPO4 (w/w, 21.71%) and ethanol (w/w, 40.72%) were determined to be the optimal compositions of ATPS. Response surface methodology based on Box–Behnken design was used to investigate the extraction conditions, the optimal parameters were summarized as follows: 80°C of extraction temperature, 31 s of extraction time, 11:1 (mL/g) of liquid-to-solid ratio, 100 meshes of particle size and 806 W of microwave power. Under these conditions, the extraction yield of gentiopicroside was 65.32 ± 0.24 mg/g with a recovery of 96.51%. Compared with other four methods, the purity of gentiopicroside in the crude extracts reached 17.16 ± 0.25%, which was significantly higher than that of smashing tissue extraction, microwave assisted-extraction, ultrasonic-assisted extraction and heat reflux extraction, respectively. In addition, the phase-forming salt can be recyclable. Therefore, MA-ATPE was an excellent and alternative technique to the conventional extraction approaches of gentiopicroside.

A simple aqueous two-phase systems (ATPS) was proposed for the purification of lignans from Schisandra chinensis Baill (S. chinensis) extracts. Taking Schisandrol A (S), Schisantherin A (ST), Deoxyschisandrin (DS), Schisandrin B (SB) and Schisandrin C (SC) as indicative mark, the partition behaviors of lignans compounds analyzed by High performance chromatography were investigated first, ATPS composed of 21% (w/w) ammonium sulfate [(NH4)2SO4] and 22% (w/w) ethanol with a K of 50.81 was chosen. Response surface methodology (RSM) based on Box-Behnken Design was further used to study the effect of temperature, pH and concentration of lignans on purification of lignans. The optimized ATPS conditions were found at pH 2.7, temperature 32.56 °C and total concentration of five lignans 259.24 μg/mL. Under these optimal conditions, the remove ratio of polysaccharide and protein reached 95.12% and 90.43%, respectively, especially the purity of the five lignans increased 5-fold from 0.98% to 4.49% with the recovery rate of 97.07%, which was well matched with the value predicted by the model. Compared with other liquid-liquid extractions, the ethanol/salt system proposed in this study was much simpler, lower in cost because of the high recovery of phase-forming components, which will provide a potential approach for large-scale production of bioactive ingredients in plants.

Hierarchical NiO nanospheres composed of porous nanosheets are prepared by a facile trisodium citrate assisted precipitation route followed by a calcination process. Effects of the trisodium citrate on the microstructure and electrochemical performances of NiO nanospheres are systematically investigated. The XRD, SEM, TEM, BET, and TG analyses show that the key point of the successful realization is that the citrate positioned in the precursor α-Ni(OH)2 layer, which can prevent the restacking of α-Ni(OH)2 sheets, yielding better crystallinity, high surface area (182 m2 g−1) as well as pore volume (0.15 cm3 g−1) and hierarchical porous ball-like morphology of NiO nanospheres by the calcination of the precursor. Electrochemical results show that the hierarchically porous NiO obtained with trisodium citrate assisted route exhibits high rate charge–discharge performance (463 F g−1 at 4.5 A g−1), longer cyclic stability (95% capacitance remained after 1000 charge–discharge cycles at 0.5 A g−1) as compared to the NiO prepared in the absence of sodium citrate (182 F g−1 at 4.5 A g−1; 70% capacitance retention after 1000 charge–discharge cycles at 0.5 A g−1). Further, due to facile mass transfer in the perfectly porous nanosheet, the citrate-assisted NiO show lower equivalent series resistance as revealed from the impedance studies.

A green and simple approach has been developed to synthesize un-coated Ag nanoparticles (AgNPs) in situ on the surface of thiol-group-functionalized silica dioxide microspheres (TSMs) in the aqueous solution. As soon as the Ag+ ions attach onto the surface of TSMs, nucleation and growth of AgNPs can spontaneously complete within one minute without other reducing agents or capping agents. The main reason is that the self-assembled silane-layer formed by mercaptosilane molecules could reduce the Ag0 formation energy, transport electrons efficiently, improve the nucleation density, and protect AgNPs against oxidation. Thus, the supported AgNPs show excellent chemical/photochemical stability in air and solution. Meanwhile, the size of as-prepared AgNPs could be controlled by tuning the concentration of Ag+ ions. This process provides a general route to generate bare AgNPs on the surface of silica dioxide in situ, which might be extended to other materials and is promising in developing novel methodologies for making supported noble metal NPs with desired structure and properties.

One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530–660 nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.

Under microwave radiation, Ag(+)-doped CdS semiconductor nanocrystals with high photoluminescence quantum yield (approximately 58%) and a surprisingly large optical window (480 to 630 nm) are formed controllably using a center-doping strategy and are optimized through a green approach in pure water solution.