Dongxiang Li

Facile synthesis of concentrated gold nanoparticles with low size-distribution in water: temperature and pH controls

The citrate reduction method for the synthesis of gold nanoparticles (GNPs) has known advantages but usually provides the products with low nanoparticle concentration and limits its application. Herein, we report a facile method to synthesize GNPs from concentrated chloroauric acid (2.5 mM) via adding sodium hydroxide and controlling the temperature. It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations. The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition. Moreover, this modified synthesis method can save more than 90% energy in the heating step. Such environmental-friendly synthesis method for gold nanoparticles may have a great potential in large-scale manufacturing for commercial and industrial demand.

Surfactant-free microemulsion composed of oleic acid, n-propanol, and H2O.

Generally, a microemulsion consists of oil, water, surfactant, and sometimes cosurfactant. Herein, we report a surfactant-free microemulsion (denoted as SFME), consisting of oleic acid (oil phase), water, and n-propanol without the amphiphilic molecular structure of a traditional surfactant. The phase behavior of the ternary system was investigated, showing that there were a single-phase microemulsion region and a multiphase region in the ternary phase diagram. The electrical conductivity measurement was employed to investigate the microregions of the single-phase microemulsion region, and three different microregions, that is, water-in-oleic acid (W/O), a bicontinuous (B.C.) region, and oleic acid-in-water (O/W), were identified, which were further confirmed by freeze-fracture and cryogenic transmission electron microscopy (FF-TEM and Cryo-TEM) observations. The polarity and the salt solubility of water domains in the W/O SFME were investigated by UV-visible spectroscopy using methyl orange and potassium ferricyanide as probes, respectively. Experimental results showed that the water domains in the W/O microemulsion had a lower polarity than bulk water and a normal solubility for salt species, indicating that the SFMEs have much significance in the preparation of various nanomaterials.

Synthesis of Mg2Al-Cl layered double hydroxide nanosheets in a surfactant-free reverse microemulsion

The synthesis of Mg2Al-Cl layered double hydroxide (LDH) nanosheets in a surfactant-free reverse microemulsion is described. The microemulsion was composed of toluene, isopropanol, and an aqueous solution as the dispersed phase. An aqueous LDH nanosheet dispersion was obtained by a double-microemulsion technique. LDH nanosheets were characterized by X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and thermogravimetric and elemental analyses. The LDH nanosheets consisted of a single brucite layer without any loading of organic molecules. To the best of our knowledge, this is the first report of a naked LDH monolayer aqueous dispersion being directly obtained. The LDH monolayers can be used as building blocks for LDH-based functional materials.

Hierarchical ZnO Nanostructures Derived from Zn-Al Layered Double Hydroxides and their Photocatalytic Activity

Hierarchical ZnO Nanostructures Derived from Zn-Al Layered Double Hydroxides and their Photocatalytic Activity In this work, Zn-Al layered double hydroxide (LDH) nanocrystals were used as a single precursor to fabricate ZnO/Zn-Al LDH nanocomposite based on the dissolution of aluminium hydroxide in NaOH. The newly formed ZnO nanorods vertically align on two sides of thinned LDH nanosheet to form “sandwich-like” nanostructure. The following calcination of these ZnO/Zn-Al LDH nanostructures at moderate temperature provided ZnO-Al2O3 mixed metal oxide nanocomposites. Both of ZnO/Zn-Al LDH and ZnO-Al2O3 samples were investigated as photocatalysts and showed selective activity for the photolysis of different dyes under low-Watt UV irradiation. Such photocatalytic mixed metal hydroxide/oxide nanocomposites should facilitate the decontamination of industrial wastewater and be helpful to environmental remediation.

Dendritic amphiphiles of carbosilane dendrimers with peripheral PEG for drug encapsulation

Amphiphilic dendritic macromolecules are suitable for the noncovalent encapsulation of guest molecules and could potentially be applied in drug-delivery systems. In this work, amphiphilic carbosilane dendrimers with peripheral poly(ethylene glycol) (PEG) units were synthesized using a hydrosilylation reaction, and their encapsulation properties were studied by fluorescence spectroscopy, using pyrene as the probe molecule. The results showed that the encapsulating capacity of the dendrimers increased as the number of PEG units increased, and that it also depended to some degree on the dendrimer generation.

Zn-Ga/Zn-In Layered Double Hydroxides:Synthesis, Characterization and Adsorption to Methyl Orange

Zn-Ga/Zn-In Layered Double Hydroxides:Synthesis, Characterization and Adsorption to Methyl Orange Zn-Ga and Zn-In layered double hydroxides (LDHs) were synthesized by coprecipitation method and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), FTIR and BET analysis. The particles of Zn-Ga/Zn-In LDHs are typical hexagonal layered nanodisks or soft nanoflakes with different size and thickness as changing Zn/Ga (In) molar ratio in the preparation. Zn-Ga LDHs have high adsorption ability to methyl orange in water, while calcined Zn-Ga LDHs can adsorb methyl orange via a slow reconstruction process. Zn-In LDHs have not adsorption capability to methyl orange, but calcined Zn-In LDHs show weak adsorption to methyl orange through reconstruction.