Kun Luo

Electrocatalytic activity of ligand-protected gold particles: formaldehyde oxidation

Tris(hydroxymethyl)phosphine oxide (THPO) and triphenyl phosphine oxide (PPh3O) were introduced onto the surface of colloidal gold nanoparticles (Au NPs), and the effect of capping ligands on the catalytic electrooxidation of formaldehyde was studied voltammetrically by using colloidal Au-NP-modified glassy carbon electrodes (GCEs). This was compared with polycrystalline Au and another Au-NP-modified GCE without a capping molecule. We found that PPh3O causes a larger decrease in the catalytic activity of the Au NPs in liquid than THPO does, indicating that the catalytic activity of the Au NPs is closely associated with the capping ligands. The effect of capping ligands is discussed based on the available surface ratio (ASR), which is defined as the ratio of the total surface area measured electrochemically to the calculated value based on the number and geometry of the Au NPs. These were determined to be 70.6xa0% for THPO and 0.23xa0% for PPh3O, respectively. The significant blocking of formaldehyde is probably due to the structure and hydrophobicity of the benzene rings in the PPh3O molecule, which is responsible for the decrease in catalytic activity of the Au NPs.

One-pot synthesis of ultrafine amphiphilic Janus gold nanoparticles by toluene/water emulsion reaction

Ultrafine amphiphilic Janus gold nanoparticles (Au NPs, d ≈ 2.1 nm) were synthesized in batch by the emulsion reaction between chlorotriphenylphosphine gold(I) in toluene and tetrakis(hydroxymethyl)phosphonium chloride in alkaline solution, followed with phase inversion by adding excess toluene, resulting in a yielding rate of up to 93.3%. FT-IR, Raman, TG and XPS analyses indicate that the emulsion reaction product is composed of Au NPs protected by triphenylphosphine, tris(hydroxymethyl)phosphine and their oxides. A NOESY experiment indicates that these ligands are separated into hydrophilic and lipophilic compartments on the individual Au NPs. The Janus wettability of the thin films by the static toluene/water interfacial reaction and Langmuir re-assembly of the as-dispersed emulsion reaction product suggests that spontaneous phase separation of capping ligands occurs with the formation of the Au NPs at the toluene/water interface, which can be maintained even in the colloidal state. The scalable one-pot synthesis of the amphiphilic Janus Au NPs allows further functionalization for the diagnosis and therapy of cancers and biphasic catalysis at low cost.

One-Step Synthesis of Aqueous Graphene Dispersion Stabilized by Sodium Dodecylbenzene Sulfonate

Graphite oxide (GO), prepared by modified Hummer’s method from graphite, was reduced by hydrazine hydrate in the presence of sodium dodecylbenzene sulfonate (SDBS), leading to a concentrated aqueous graphene dispersion which was stable for more than one month. The analyses of XRD, UV-vis and Raman spectroscopy indicate that the reduced graphene oxide (RGO) was formed after chemical reaction, where single or multiple graphene sheets were observed by TEM and AFM, indicating that the RGO is well-dispersed in water through the operation.

Synthesis and Catalytic Property of Au/Titania Nanocomposites on the Photolytic Degradation of Methyl Orange

Tetra-n-butyl titanate was used to synthesize a precursor titania (TiO2) gel by sol-gel method, which was successfully employed to prepare TiO2 powders by calcinating at variant temperatures. The anatase phase TiO2 was obtained at 500°C according to XRD analysis, which was selected as the support for nanogold catalysts. The reduction of HAuCl4 by tetrakis(hydroxymethyl)phosphonium chloride (THPC) was used to immobilize Au nanoparticles on the as-prepared anatase TiO2, which was compared with the normal deposition-precipitation (DP) method. SEM and UV-vis analyses indicate that the THPC-Au/TiO2 has a larger loading of Au and stronger photocatalytic activity than the DP-Au/TiO2, which offers a simple way to prepare strong Au/TiO2 photocatalysts with low Au consumption.

Preparation of Janus Ag nanoparticles by liquid/liquid interfacial reaction

Janus silver (Ag) nanoparticles have been successfully synthesized by intense agitation at the interface of toluene and water which contains Ag (PPh3)2NO3 and THPC. Contact angle of the film prepared by L-B technology is measured which indicates that the Ag nanoparticle is amphipathicity because they have hydrophobic region and hydrophilic region separately. TEM image showed the assembled morphology of Ag instead of monodispersed particles. After purification, analysis of FT-IR and XPS showed the Janus Ag nanoparticles are protected by ligands of THPC and PPh3 with a ratio of 1:1.