•Amorphous PtNiP ternary nanocomposite was synthesized by hypophospite-assisted reduction.•Nickel salt played a key role in the formation of amorphous structure for PtNiP.•PtNiP showed excellent electrocatalytic activity and long-term stability for MOR in alkaline.•XPS was used to analyze the superior electrochemical performance of PtNiP.Amorphous PtNiP ternary nanoparticles were successfully synthesized via a hypophospite-assisted reduction process for methanol electro-oxidation. Due to the difficulty of P doping into pure Pt, it was found that improving the reaction temperature led to the phase transformation of Pt-P binary alloys from amorphous to crystalline by the same hypophospite-assisted reduction method. Adding a small quantity of nickel salt in the Pt-P synthetic solution could promote the P content by the formation of NiP matrixes, leading to the PtNiP ternary nanoparticles with amorphous structure. Notably, amorphous PtNiP ternary nanoparticles showed high electrochemical activity and long-term stability for methanol oxidation, which was explained by XPS analysis.Download high-res image (284KB)Download full-size image

•PolyDOPA/RGO served as a versatile platform for in situ growth of Fe3O4 and Pd NPs.•The synthetic process was green, without any toxic reductant or surfactant.•The sensors displayed wide linear range and low LOD for nitrite detection due to synergistic effect.•The content of nitrite in cured food was effectively detected and monitored.A green and effective route was used to synthesize Pd/Fe3O4/polyDOPA/RGO for in situ nucleation and growth of Fe3O4 and Pd on reduced graphene oxide (RGO), based on the polyDOPA (3,4-Dihydroxy-l-phenylalanine, DOPA) coating as a versatile platform. The Pd/Fe3O4/polyDOPA/RGO composite showed superior electrocatalytic activity toward nitrite oxidation due to electronic effect. The amperometric response results demonstrated that Pd/Fe3O4/polyDOPA/RGO modified glassy carbon electrode was further employed to determine nitrite with a wide linear range of 2.5–6470 μM and a low detection limit of 0.5 μM. With good anti-interference toward various anions and cations and good stability, the proposed sensor was successfully applied for the determination of nitrite in Yellow River water and sausage extract with satisfactory results. Moreover, this sensor could be used to effectively monitor the change of nitrite content during the rapid corruption of Chinese cabbage. It was found that the content of nitrite reached at the maximum level within one day and then decreased to a low level after three day-corruption, which was agreed with the tendency measured by ionic chromatography.Download high-res image (203KB)Download full-size image

Palladium–cobalt alloy nanoparticles were synthesized and dispersed on carbon black support, aiming to have a less expensive catalyst. Catalytic behaviors of PdCo/C catalyst for the oxidation of hydroquinone (HQ) with H2O2 in aqueous solution were evaluated using high-performance liquid chromatography (HPLC). The results revealed that PdCo/C catalyst had better catalytic activity than an equal amount of commercial Pd/C and Co/C catalysts because of the d-band hybridization between Pd and Co. The effects of pH value, solvent, and various interferents including inorganic and organic compounds on the efficiency of HQ oxidation were further investigated. Furthermore, on the basis of mixed potential theory, comprehensive electrochemical measurements such as the open-circuit potential-time (OCP-t) technique and Tafel plot were efficient to assess the catalytic activity of the catalyst, and the results obtained were consistent with those of HPLC measurements. The efficient HQ oxidation was closely associated with the catalytic activity of PdCo nanoparticles because they accelerated the electron-transfer process and facilitated the generation of OH radicals.Keywords: free radicals; interferences; mixed potential measurement; oxidation of hydroquinone; PdCo alloy nanoparticles

The authors describe a colorimetric method for the determination of Hg(II) ions by exploiting the peroxidase-lile activity of few-layered MoS2 nanosheets (MoS2-NSs). These were prepared by sonication-induced exfoliation of bulk MoS2 crystals in aqueous surfactant solution. The MoS2-NSs were found to acts as a peroxidase mimic that is capable of oxidizing the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to give a blue product with an absorption maximum at 652 nm. The addition of Hg(II) strongly accelerates the kinetics of this reaction. It is shown that the enzyme mimic possesses a high affinity for TMB and a lower pseudo-Michaelis-Menten constant. The stimulating effect of Hg(II) is seriously influenced by the change of surface charge. The use of nanosheets covered with (negatively charged) polystyrene sulfonate results in a decrease in the formation of blue dye, while those covered with (cationic) poly(diallyldimethyl ammonium) ions cause a small increase. Under optimal conditions, the peroxidase-like activity of MoS2-NSs is affected by Hg(II) in the 2.0 to 200 μM concentration range. The method has a detection limit (LOD) of 0.5 μM which is much below the allowed level in cosmetics (1 ppm; ca. 5 μM). The method display excellent sensitivity, selectivity and stability. It was applied to the determination of total mercury in cosmetic samples, and results compared well with results obtained by ICP-AES.

•Pt flowerlike nanocrystals on PDA/RGO are prepared via chemical reduction.•Heating and PDA modification are necessary to synthesize Pt flowerlike crystals.•Pt(F)-PDA/RGO exhibits excellent catalytic activity for methanol electro-oxidation.•Pt(F)-PDA/RGO is easily activated and keeps good catalytic stability.A simple and effective approach was demonstrated to synthesize flowerlike Pt nanocrystals on polydopamine (PDA) functionalized reduced oxide graphene (RGO). Inspired by mussels, the PDA/RGO composites were obtained via the reduction of GO nanosheets by dopamine, followed by simultaneous capping by PDA. Then, the synthesis of Pt flowerlike nanocrystals assembled with small elongated nanoparticles on PDA/RGO (Pt(F)-PDA/RGO) was carried out by mixing H2PtCl6 with PDA/RGO in the presence of ascorbic acid under boiling. PDA as a surface-adherent and multifunctional biopolymer played a dual role: dispersing stable RGO into aqueous solution and providing functional groups to bind metal ions and metal nanoparticles. The as-prepared Pt(F)-PDA/RGO catalyst showed considerably improved catalytic activity and stability toward methanol electrooxidation, compared with Pt nanoclusters on PDA/RGO (Pt(C)-PDA/RGO) and Pt nanoparticles on pristine graphene sheets (Pt/RGO). The kinetic characterization of Pt(F)-PDA/RGO was further discussed by cyclic voltammetry. This simple and green approach could be applicable to other metallic nanocrystals as a novel platform in catalysis, fuel cells and biosensors.Figure optionsDownload full-size imageDownload as PowerPoint slide

Although Al has a lower redox potential [Al3+/Al, −1.67 V vs. SHE] than most metallic ions, metal galvanic replacement reactions on pure aluminum foil can be hardly observed because of the existence of the thin layer of aluminum oxide, In this work, we develop a facile, economical and general approach to achieve large-scale production of silver and gold dendrites as well as other metal hierarchical micro/nanostructures (Cu, Pt, Pd, Ni, Co and Zn) on commercial aluminum foil in the presence of NaF or NH4F. Studies of the galvanic replacement reaction by open circuit potential–time (OCP–t) measurements demonstrate that fluoride plays an important role in etching the alumina layer and thus induces the continuous proceeding of the galvanic replacement reaction. The synthesis process is carried out at room temperature and without any templates, surfactants, or special reagents. The obtained silver and gold dendrites show significantly enhanced SERS signals of a self-assembled monolayer of 2-naphthalenethiol and 4-mercaptobenzoic acid, and also could effectively catalyze the reduction reaction of 4-nitrophenol and 2-nitrophenol at room temperature.

Au–Pt alloy particles with cauliflower-like microstructures of varying Pt/Au ratios were electrodeposited on indium tin oxide (ITO) substrates by constant potential electrolysis at E = −0.25 V. The results of X-ray diffraction and X-ray photoelectron spectroscopy confirm that the bimetallic alloys can be obtained for different Pt/Au ratios including 4/1, 1/1 and 1/4. The formation of alloyed cauliflower-like microstructures may be the result of the fast formation of gold seeds as the core and subsequent simultaneous deposition of Au and Pt from cyclic voltammetric study. The effect of surface composition of Au–Pt alloy particles on electrocatalytic methanol oxidation were investigated in H2SO4 solution. The electrocatalytic abilities including electrochemical surface area, peak current density and the turnover number of methanol oxidation follow the order of Pt4Au1 > Pt > Pt1Au1. The results can be ascribed to that electronic effect may be prominent while bifunctional effect is insignificant for Au–Pt alloy systems because the electrocatalytic activity of Au is negligible in acidic media. Additionally, the Pt4Au1 electrode has superior kinetics of methanol electro-oxidation than monometallic Pt electrode by calculating the electron transfer coefficient (α).Highlights► Au–Pt cauliflower-like alloys of varying Pt/Au ratios have been electrodeposited. ► The electrocatalytic efficiency follows the order of Pt4Au1 > Pt > Pt1Au1. ► Alloyed Pt with Au promotes the catalytic activity mainly through electronic effect. ► Pt4Au1 has enhanced kinetics of methanol electro-oxidation than monometallic Pt.