Duanguang Yang

Sensitivity and selectivity determination of bisphenol A using SWCNT–CD conjugate modified glassy carbon electrode

In this study, we demonstrated a highly sensitive electrochemical sensor for the determination of bisphenol A (BPA) in aqueous solution by using single-walled carbon nanotubes (SWCNTs)/β-cyclodextrin (β-CD) conjugate (SWCNT-CD) modified glassy carbon electrode (GCE). The cyclic voltammetry results show that the modified GCE exhibits strong catalytic activity toward the oxidation of BPA with a well-defined cyclic voltammetric peak at 0.543 V. The response current exhibits a linear range between 10.8 nM and 18.5 μM with a high sensitivity (1256 μA mM(-1)). The detection limit of BPA is 1.0 nM (S/N=3). The enhanced performance of the fabricated sensor can be attributed to the combination of the excellent electrocatalytic properties of SWCNTs and the molecular recognition ability of β-CD. The sensor was successfully applied to determine BPA leached from real plastic samples with good recovery, ranging from 95% to 103%.

Synthesis, characterization, and electrochemical performances of core-shell Ni(SO4)0.3(OH)1.4/C and NiO/C nanobelts

In this study, Ni(SO4)0.3(OH)1.4 nanobelts have been synthesized via a simple template-free hydrothermal reaction in an aqueous solution containing nickel sulfate and sodium acetate. It is found that the molar ratio of nickel sulfate to sodium acetate plays a very important role in determining the morphology of the final product. Subsequently, core-shell Ni(SO4)0.3(OH)1.4/C composite nanobelts have been synthesized from the carbonization and polymerization of glucose under mild hydrothermal conditions in the presence of newly produced Ni(SO4)0.3(OH)1.4 nanobelts. The shell thickness of the core-shell nanobelts can be varied from 2 to 18 nm by adjusting the concentration of glucose. Additionally, the structural evolution from core-shell Ni(SO4)0.3(OH)1.4/C to NiO/C has been successfully performed through ex situ heat treatment. The belt-like morphology has still been maintained after heat treatment at 600 °C for 2 h. The as-prepared NiO/C composites were directly immobilized onto the surface of glassy carbon electrode (GCE) for nonenzymatic glucose determination. The fabricated glucose sensor has an ultrasensitive response (149.11 μA mM−1) and a low detection limit of 9.12 nM (signal/noise ratio (S/N) = 3), which are among the best values reported in the literature.

Electrochemical sensing platform for L-CySH based on nearly uniform Au nanoparticles decorated graphene nanosheets.

In this study, Au nanoparticles decorated graphene nanosheets were prepared using poly(vinylpyrrolidone) (PVP) covalently functionalized graphene oxide and chloroauric acid as template and Au precursor, respectively. Both the density and the size of Au nanoparticles deposited on the surface of graphene could be adjusted by the PVP grafting density. The graphene-Au hybrid nanosheets were then applied to fabricate a highly sensitive l-cysteine (L-CySH) electrochemical sensing platform. The cyclic voltammetry results showed that the modified glassy carbon electrode with graphene-Au hybrid nanosheets exhibited strong catalytic activity toward the electrooxidation of L-CySH. The current exhibited a widely linear response ranging from 0.1 to 24 μM with a low detection limit under the optimized conditions. The detection limit of L-CySH could reach as low as 20.5 nM (S/N=3). The enhanced electrochemical performance of the fabricated sensor was attributed to the combination of the excellent conductivity of graphene and strong catalytic property of uniform Au nanoparticles.

Water in Oil Emulsion Stabilized by Tadpole-like Single Chain Polymer Nanoparticles and Its Application in Biphase Reaction

In this study, tadpole-like single chain polymer nanoparticles (TSCPNs) were efficiently synthesized by intramolecularly cross-linking P4VP block of commercial block polymer of PMMA2250-b-P4VP286 in N,N-dimethylformamide using propargyl bromide as cross-linking agent. The intramolecular cross-linking reaction led to the production of TSCPNs with a linear tail and a cross-linked head. The as-prepared TSCPNs were then applied as emulsifier to stabilize water in chlorobenzene emulsion, and an extremely stabilized water in oil (W/O) emulsion was generated at a low TSCPNs concentration. The TSCPNs concentration was as low as 0.0075 wt % versus total weight of water and chlorobenzene for emulsion formation. The emulsifying performance of TSCPNs was better than that of low molecular surfactant, such as Span-80. The generated W/O emulsion provided an ideal medium for the reduction of oil-soluble p-nitroanisole by water-soluble sulfide to p-anisidine, an effective contact problem between the two reactants with different solubility was well solved through interfacial reaction.

Porous N-Doped Carbon Prepared from Triazine-Based Polypyrrole Network: A Highly Efficient Metal-Free Catalyst for Oxygen Reduction Reaction in Alkaline Electrolytes

Metal-free N-doped carbon (NC) materials have been regarded as one of the most promising catalysts for the oxygen reduction reaction (ORR) in alkaline media because of their outstanding ORR catalytic activity, high stability, and good methanol tolerance. Up to now, only a small minority of such catalysts have been synthesized from triazine-based polymeric networks. Herein, we report the synthesis of such NC catalyst by directly pyrolyzing a nitrogen-rich, triazine-based polypyrrole network (TPN). The TPN is fabricated by oxidative polymerization of 2,4,6-tripyrrol-1,3,5-triazine monomer using TfOH as the protonating agent and benzoyl peroxide as the oxidizing agent. The obtained NC-900 (pyrolyzed at 900 °C) catalyst exhibits excellent ORR activity in alkaline media with a high ORR onset potential (0.972 V vs RHE), a large kinetic-limiting current density (15.66 mA cm-2 at 0.60 V), and good MeOH tolerance and durability. The as-synthesized NC-900 material is a potential candidate as a highly active, stable, and low-cost ORR catalyst for alkaline fuel cells.

Formation of gradient multiwalled carbon nanotube stripe patterns by using evaporation-induced self-assembly.

Gradient stripe patterns of multiwalled carbon nanotubes (MWCNTs) with remarkable regularity over large areas were fabricated by using evaporation-induced self-assembly technique. In this method, a glass coverslip was inclinedly immersed into a suspension of MWCNTs in dichloroethane. By controlling the solvent evaporation temperature, well-defined gradient stripes were formed at the air-solvent-substrate contact line. The effects of several experimental parameters, such as the substrate tilt angle, concentration of MWCNTs, and evaporation temperature, on the regularity of stripes were discussed. A possible stripe formation process was described as a negative feedback of MWCNT concentration caused by a concavely curved shape of the meniscus. Additionally, the strips of MWCNTs on Si/SiO(2) substrate were directly used to fabricate field-effect transistor (FET) devices. The electrical properties of the MWCNT-FET devices were also investigated.

Dual responsive macroemulsion stabilized by Y-shaped amphiphilic AB2 miktoarm star copolymers

Dual responsive macroemulsions stabilized by Y-shaped amphiphilic AB2 miktoarm star polymeric emulsifiers were presented in this study. First, a amphiphilic Y-shaped AB2 miktoarm star polymer composed of poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA) and polystyrene (PS) arms was synthesized by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene monomer and atom transfer radical polymerization (ATRP) of N,N-dimethylaminoethyl methacrylate (DMAEMA) monomer. The structure and the molecular weight as well as the molecular weight distribution were carefully characterized by 1H NMR and GPC, respectively. The obtained PS–(PDMAEMA)2 miktoarm star polymers were then applied as polymer emulsifiers for both o/w and w/o macroemulsions formation, and stabilized macroemulsions could be produced at a lower emulsifier content. Meanwhile, the emulsifying performance of PS–(PDMAEMA)2 miktoarm star polymer and stimulus-response of the macroemulsion were also investigated. The PS–(PDMAEMA)2 stabilized o/w macroemulsion showed pH-induced demulsification and temperature-induced phase inversion. However, the inversion of the PS–(PDMAEMA)2 emulsifier at the oil–water interface could not be spontaneously accomplished. Furthermore, successful phase inversion was only smoothly realized for those emulsions with pH 7 water in the presence of a modulate stirring.

Massage ball-like, hollow porous Au/SiO2 microspheres templated by a Pickering emulsion derived from polymer–metal hybrid emulsifier micelles

In this study, we reported a novel, facile, Pickering emulsion-templating method to prepare massage ball-like, hollow-structured Au/SiO2 microspheres. Firstly, oil-in-water Pickering emulsions stabilized by Au@poly(ethylene oxide)-b-poly(4-vinylpyridine) (Au@PEO-b-P4VP) hybrid emulsifier micelles, which were formed by a P4VP/Au complex induced self-assembly process, were generated. Then hollow Au/SiO2 hybrid microspheres with nano-/submicro-sized protrusions on their shells, termed as massage ball-like microspheres, were successfully synthesized using the generated Pickering emulsion as template, in which the P4VP catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS) in the TEOS/n-decanol mixed oil phase occurred at the oil/water interface. As a result, a continuous SiO2 shell was formed. The uneven adsorption of polydisperse hybrid micelles at the oil/water interface as well as the volume shrinkage of the oil phase during the early hydrolysis and condensation of TEOS facilitated the formation of protrusions on the shell surface. After further removal of the polymer components embedded in the shell by calcination, hollow Au/SiO2 hybrid microspheres with micropore/mesopore bimodal porous shells were produced. The as-prepared Au/SiO2 hybrid microspheres were applied as catalysts for the reduction of p-nitrophenol with NaBH4, showing a high catalytic activity with a good recyclability owing to the large specific areas, the easily accessible Au active centres, and the enhanced mass transportation.

Well-defined poly(N-isopropylacrylamide) with a bifunctional end-group: synthesis, characterization, and thermoresponsive properties

In this study, well-defined poly(N-isopropylacrylamide) (PNIPAM) with a bisalkyne end-group was synthesized by reversible addition-fragmentation chain transfer polymerization using 2-(2-(ethylthiocarbonothioylthio)-2-methylpropanoyl-oxy)ethyl 3,5-bis(prop-2-ynyloxy) benzoate (EMEB) as the chain transfer agent. The molecular weight and polydispersity index of polymer was determined by gel permeation chromatography (GPC). The linear increase in molecular weight with conversion, unimodal, and almost symmetrical peak in GPC trace together with low polydispersity indicated the controlled polymerization process of NIPAM mediated by EMEB. Subsequently, the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition between the end-group of polymer and azide derivatives was carried out to produce PNIPAM, in which the bisfunctional end-group was modified with phenyl, octyl, amido, and hydroxyl groups. After completing the click reaction, the structure of the polymer was characterized carefully by Fourier transform infrared spectroscopy (FTIR), 1H NMR, and Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS), indicating the complete consumption of alkyne end-groups. In addition, almost no change in molecular weight as well as the polydispersity was observed by comparison with the GPC traces of polymers before and after click reaction. The cloud point temperatures (T cps) of the resulting PNIPAM derivatives in aqueous solution were investigated in detail by dynamic light scattering. The results showed that the values of T cp were ranged from 22 to 38 °C, which depended largely on end-groups as well as the polymer molecular weights.

A highly sensitive and reversible chemosensor for Hg2+ detection based on porphyrin‐thymine conjugates

In this study, we demonstrated a highly sensitive, selective, and reversible chemosensor for Hg2+ determination. This chemosensor was synthesized by direct condensation of thymin‐1‐ylacetic acid with zinc tetraaminoporphyrin, which has a porphyrin core as the fluorophore and four thymine (T) moieties as the specific interaction sites for Hg2+. The probe (4T‐ZnP) exhibited split Soret bands with a small peak at 408 nm and a strong band at 429 nm in a dimethylformamide/H2O (7/3, v/v) mixed solvent as well as a strong emission band at 614 nm. Upon the addition of Hg2+, the probe displayed strong fluorescence quenching due to the formation of T‐Hg2+‐T complexes. With the aid of the fluorescence spectrometer, the chemosensor in the dimethylformamide/H2O (7/3, v/v) mixed solvent (0.3 μM) exhibited a detection limit of 6.7 nM. Interferences from other common cations, such as Co2+, K+, Sn2+, Zn2+, Cu2+, Ni2+, Mn2+, Na+, Ca2+, Mg2+, Pb2+, and Cd2+, associated with Hg2+ analysis were effectively inhibited. Copyright