Yunxing Li

Starch nanocrystals as particle stabilisers of oil‐in‐water emulsions

BACKGROUND As an environmentally benign particle emulsifier, starch nanocrystal (SNC) has attracted considerable attention. By submitting waxy maize starch to acid below the gelatinisation temperature of starch, nanoscale crystalline residues, which are SNCs, were separated from starch granules by hydrolysing amorphous regions. The SNC could be used as a particle emulsifier to stabilise emulsions. RESULTS The SNC could adsorb at the oil-water interface to stabilise oil-in-water emulsions with high stability to coalescence. The creaming of emulsions occurred after homogenisation but decreased with increasing SNC content, which was mainly due to the formation of an inter-particle network in the emulsions. Because of the amount of sulfuric groups at the surface, the SNC was negatively charged. Therefore, at low pH values or high salt content the electrostatic repulsion of the SNC was reduced, which further caused droplet aggregation and an increase in size of the particles in the emulsions stabilised by the SNC. CONCLUSION The SNC was an efficient particle emulsifier for preparing Pickering emulsions. The size of emulsions stabilised by the SNC could be tailored by changing the pH value or salt concentration.

A facile method to fabricate polystyrene/silver composite particles and their catalytic properties

Herein a facile method is developed for fabrication of polystyrene/silver (PS/Ag) composite particles based on colloid thermodynamics. In our system, once the silver nanoparticles are formed in the presence of PS microspheres, they will play the role of steric stabilizer and attach spontaneously onto the surface of PS microspheres to reduce the Gibbs free energy of the colloidal system. The resultant PS/Ag composite particles have been characterized extensively by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. The results indicate that the structure and morphology of the PS/Ag composite particles could be controlled easily by changing the molar ratio of sodium borohydride and silver nitrate. More significantly, the PS/Ag composite particles exhibit good catalytic activity and reusability at low catalyst concentration during the reduction of p-nitrophenol by sodium borohydride. Hence, it is expected that the as-prepared PS/Ag composite particles show promise and great potential for practical application in catalysis.

Colloid Thermodynamic Effect as the Universal Driving Force for Fabricating Various Functional Composite Particles

The design and fabrication of functional nanocomposites is an active area of research because composite particles have significantly improved physical and chemical properties over those of their single-component counterparts. Traditionally, chemical pretreatments of the components were used to enhance their physicochemical or chemical interactions. Here, we propose a novel approach to taking advantage of the beauty of thermodynamics. A series of functional materials, including graphene nanosheets, carbon nanotubes, noble metals, magnetic materials, conducting polymers, attapulgite, and etc. were incorporated with polystyrene particles by a thermodynamic driving force. This unique approach is facile and versatile and shows the considerable significance of developments in both scientific methodology and particle engineering.

Highly facile and efficient assembly of palladium nanoparticles on polystyrene microspheres and their application in catalysis

Catalytic applications of supported palladium nanoparticles (PdNPs) in the liquid phase reactions are of considerable importance. Herein the polystyrene/palladium (PS/Pd) composite particles composed of PS microspheres decorated with PdNPs with different sizes are prepared facilely and effectively based on a thermodynamic effect. Compared with the reported synthetic methods, surface functionalizations or modifications of PS microspheres and PdNPs are not necessary at all. The formation of PS/Pd composite particles has been demonstrated by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-optical emission spectroscopy (ICP-OES). Finally, the catalytic performance of as-prepared PS/Pd composite particles is investigated during the reduction of p-nitrophenol by sodium borohydride, and noticeably, they have shown a high catalytic activity and a good stability.

Facile and controllable synthesis of polystyrene/palladium nanoparticle@polypyrrole nanocomposite particles

Herein is reported a facile and controllable route for coating polystyrene (PS) particles with palladium nanoparticle@polypyrrole (PdNP@PPy) nanocomposites based on the “Swelling–Diffusion–Interfacial-Polymerization Method” (SDIPM). The formation of PdNP@PPy nanocomposites was achieved by using palladium chloride as the oxidant for pyrrole. The synthesized PS/PdNP@PPy nanocomposite particles were characterized extensively by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, and C, H, and N elemental microanalyses. Significantly, it is clearly found that highly dispersed PdNPs with small size are well embedded in the PPy shell. Moreover, the resultant PS/PdNP@PPy nanocomposite particles have a well-defined core/shell structure, and then the mass loading of PdNP@PPy nanocomposites on the surface of PS particles can be controlled simply by changing the weight ratio of pyrrole/PS. The synthesized PS/PdNP@PPy nanocomposite particles also show good catalytic activity and reusability in the reduction of p-nitrophenol by NaBH4.

One-step synthesis of silica hollow particles in a W/O inverse emulsion

Porous silica hollow particles have been fabricated by a one-step approach in water in oil (W/O) inverse emulsion. Ammonia water droplets stabilized by alkyl-phenol polyoxyethylene ether (TX-4) in tetraethoxysilane (TEOS)/cyclohexane solution act as soft templates for constructing the silica hollow particles. The formation mechanism is discussed in detail from the equilibrium between the diffusion and reactions of TEOS and its products (hydrolysates and polycondensates) on the W/O interface. The structure and morphology of the resultant silica hollow particles are well controlled by changing the parameters involving the concentration of TX-4, TEOS, and ammonia. The synthesized products have been characterized using transmission electron microscopy, scanning electron microscopy, solid state NMR, and nitrogen adsorption–desorption measurements.

Facile synthesis of polystyrene/gold composite particles as a highly active and reusable catalyst for aerobic oxidation of benzyl alcohol in water

PS/Au composite particles have been synthesized facilely based on a thermodynamic effect. More significantly, the PS/Au composite particles can catalyze the aerobic oxidation of benzyl alcohol remarkably under mild conditions (1 atm, air as oxidant, K2CO3, 30 °C, in water) and be reused several times without significant loss of activity.

Functional polyaniline-assisted decoration of polystyrene microspheres with noble metal nanoparticles and their enhanced catalytic properties

The use of polystyrene (PS) microsphere modified by polyaniline (PANi) as a functional support for Au nanoparticles (NPs) is described herein. Specifically, a simple strategy, involving swelling followed by diffusion and interfacial polymerization of aniline monomer, was applied to fabricate the PS/PANi composite particles, independent of any surface treatments of the PS seed microspheres. At mildly acidic pH, the surface of PANi was enriched with positive charge, hence enabling the negatively charged Au NPs (stabilized by trisodium citrate) to be uniformly attached onto the PS/PANi composite particles via a simple electrostatic self-assembly approach. The prepared PS/PANi-Au composite particles exhibit high catalytic activity and superior reusability in the reduction of p-nitrophenol using NaBH4. Notably, this type of self-assembly could not only effectively control the density of the supported Au NPs with different sizes but could also easily immobilize other noble metal (Ag, Pt, and Pd) NPs onto the surface of the PS/PANi composite particles. More significantly, in addition to providing anchoring sites for immobilizing noble metal NPs, the PANi coating also contributes to the higher catalytic activity of PS/PANi-Au composite particles due to the synergistic effect of PANi and Au NPs.

In Situ Growth of Clean Pd Nanoparticles on Polystyrene Microspheres Assisted by Functional Reduced Graphene Oxide and Their Excellent Catalytic Properties

Herein an in situ growth of clean palladium nanoparticles (Pd NPs) on functional reduced graphene oxide (RGO)-coated polystyrene (PS) microspheres is achieved by a simple two-step process. On the basis of the hydrophobic interaction and π-electron interaction, the PS/RGO composite particles are first prepared by the reduction of graphene oxide in the presence of PS microspheres. Second, without using any additional reducing agent or stabilizer, the clean Pd NPs grow in situ on the surface of PS/RGO composite particles in water through a spontaneous redox reaction between Pd2+ and RGO. Significantly, owing to the stabilizer-free surface of Pd NPs and the synergistic effect of RGO and Pd NPs, the resultant PS/RGO@Pd composite particles feature pronounced catalytic activity toward the reduction of p-nitrophenol and Suzuki coupling reactions. Moreover, the catalyst particles can be easily recovered by centrifugation because of the large size of support microspheres and recycled consecutively.

Facile and Controllable Assembly of Multiwalled Carbon Nanotubes on Polystyrene Microspheres

Herein a facile and controllable heterocoagulation between polystyrene (PS) microspheres and multiwalled carbon nanotubes (MWCNTs) is introduced based on colloid thermodynamics. The MWCNTs play the role of steric stabilizer for stabilizing the metastable PS microspheres and thus immobilize spontaneously on the surface of PS microspheres. The synthesized MWCNTs-coated PS composite particles have been extensively characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetry and Raman spectroscopy. The results indicate that the structure and morphology of the resultant MWCNTs-coated PS composite particles are significantly affected by the weight ratio of PS and MWNCTs and the amount of poly(vinylpyrrolidone) that is injected into PS dispersion before they are mixed with MWCNTs. Therefore, these composite particles have the potential to produce MWCNTs-based composite materials with controllable mass loading and dispersity of MWCNTs.