Biostabilised icosahedral gold nanoparticles: synthesis,cyclic voltammetric studies and catalytic activity towards 4-nitrophenol reduction

A green and cost-effective biosynthetic approach for the preparation of icosahedral gold nanoparticles (AuNPs) using an aqueous leaf extract of Polygonum minus as reducing and stabilising factor is described. The reduction of Au³⁺ ions to elemental Au rapidly occurred and is completed within 20 minutes at room temperature. The size of the nanoparticles is highly sensitive to the AuCl₄^?/leaf extract concentration ratio and pH. Transmission electron microscopy and X-ray diffraction data indicated that the nanoparticles were in a crystalline shape (face-centred cubic), mostly icosahedral and nearly monodispersed with an average size of 23 nm. Cyclic voltammetric studies suggested that flavonoids, such as quercetin and myricetin present in the leaf extract had a tendency to donate electrons to Au³⁺ ions and the formation of elemental Au was possible due to the transfer of electrons from these flavonoids to Au³⁺ ions. Infrared absorption of the AuNPs and the leaf extract revealed that the oxidised (quinone) form of quercetin and myricetin were presumably the main stabilising agents in the formation of stable nanoparticles. The present biosynthesis of AuNPs was simple, rapid, cost-effective and environmentally friendly. The newly prepared biostabilised icosahedral AuNPs show good catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP).     

Catalytic activity of hybrid platinum nanoparticle-[C60]fullerene nanowhisker composites for 4-nitrophenol reduction

Abstract

Composites comprising platinum nanoparticles loaded on [C₆₀]fullerene nanowhiskers were prepared by a liquid-liquid interfacial precipitation method. The synthesized platinum nanoparticle-[C₆₀]fullerene nanowhisker composites were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The catalytic activity of the platinum nanoparticle-[C₆₀]fullerene nanowhisker composites was confirmed for the reduction of 4-nitrophenol by UV–vis spectroscopy. The reduction of 4-nitrophenol catalyzed by the platinum nanoparticle-[C₆₀]fullerene nanowhisker composites followed the pseudo-first-order reaction rate law.     

Vacuum-assisted synthesis of tiny Au nanoparticles entrapped into mesoporous carbon matrix with superior catalytic activity for 4-nitrophenol reduction

In this work, we report a vacuum-assisted approach to synthesize tiny Au nanopartciles (Au NPs) entrapped into mesoporous carbon matrix (denoted as Au@MC). The tiny Au NPs are stably entrapped within the mesoporous structure and possess a small particle size (～2.64?nm). The composite also exhibits a high specific surface area (～421?m² g^?1), which may provide convenient transportation and diffusion for substrate molecules. Thus, Au@MC exhibits superior catalytic activity and reusability for 4-nitropheno (4-NP) reduction. The vacuum-assisted synthesis with unique nanostructure is expected to be applied in the preparation of other catalysts.     

Anchoring gold nanoparticles on graphene nanosheets functionalized with cationic polyelectrolyte: a novel catalyst for 4-nitrophenol reduction

In this paper, a stable aqueous dispersion of graphene nanosheets (GNs) has been prepared by chemical reduction of graphene oxide (GO) with hydrazine hydrate in the presence of poly [(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11). Taking advantages of the fact that PQ11 is a positively charged polymer exhibiting reducing ability, we further demonstrated the subsequent decoration of GN with gold nanoparticals (AuNPs) by in-situ chemical reduction of HAuCl4. It was found that such nanocomposites exhibit good catalytic activity toward 4-nitrophenol (4-NP) reduction and the GN supports also enhance the catalytic activity via a synergistic effect.     

Maghemite/ZnO nanocomposites: A highly efficient,reusable and non-noble metal catalyst for reduction of 4-nitrophenol

Maghemite/ZnO nanocomposites synthesized by a two step process were used for catalytic reduction of p-nitrophenol. Maghemite nanoparticles were synthesized by hydrothermal technique followed by deposition of ZnO on it via co-precipitation process. X-ray diffraction analysis suggested formation of Maghemite and ZnO with tetragonal and hexagonal close packed structure respectively whereas electron microscopy images indicated the formation of near spherical nanocomposites with a size range of 30–50 nm. Maghemite/ZnO calcined at 300 °C is investigated as heterogeneous catalyst for reduction of p-nitrophenol and its catalytic activity is compared with that of Maghemite and ZnO nanoparticles. The parameters responsible for reduction of p-nitrophenol over Maghemite/ZnO were scrutinized using Response Surface Methodologyand the predicted values of reduction efficiency were found to be in a good agreement with the experimental findings (R² > 0.9). The highest achievable percentage of reduction of target molecular species was noted to be of 98.6%. Optimization study showed that maximum reduction efficiency was observed at optimum conditions: p-NP concentration = 0.2 mM, Maghemite/ZnO loading = 200 ppm, reaction time = 6 min. Maghemite/ZnO has shown noticeably higher catalytic activity than pure oxides which remained almost unaltered for five consecutive cycling suggesting possible commercial potential of the developed material.     

Synthesis of well-dispersed Ag nanoparticles on eggshell membrane for catalytic reduction of 4-nitrophenol

A novel functional bio-nanocomposite was prepared by deposition of Ag nanoparticles onto the surface of natural eggshell membrane fibers. Practically, the functional groups exposed on the fiber surface can provide locations to anchor Ag ions when immersed into metal precursor solution. The synthesized small-sized Ag nanoparticles with uniform distribution is well decorated on the surface of interwoven fibers of eggshell membrane. The effectiveness of the as-prepared AgNPs/ESM composites as a solid phase heterogeneous catalyst has been evaluated, for the first time, on the well-known 4-nitrophenol reduction to 4-aminophenol in the presence of excess borohydride. Moreover, the kinetics of the reduction reaction was investigated at different temperatures to determine the activation energy. This work provides an important example in the introduction of natural membranes for the fabrication of functional hybrid nanocomposites which could be very useful in varying fields.     

Synthesis of bipyramidal gold nanoparticle-[C60]fullerene nanowhisker composites and catalytic reduction of 4-nitrophenol

The seed solution was prepared by dissolving hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O), trisodium citrate dihydrate (C₆H₅Na₃O₇·2H₂O), and sodium borohydride (NaBH₄) in distilled water. The resulting reddish-purple seed solution was stirred for 3 h at room temperature. The growth solution was prepared by mixing hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O), cetyltrimethylammonium bromide (CTAB, (C₁₆H₃₃)N(CH₃)₃Br), silver nitrate (AgNO₃), hydrochloric acid (HCl), and ascorbic acid (C₆H₈O₆) in distilled water. Subsequently, 100 μL of this seed solution was transferred into 10 mL of the growth solution. The mixed solution was maintained at 30 °C for 3 h to obtain a solution of bipyramidal gold nanoparticles. The bipyramidal gold nanoparticle-[C₆₀] fullerene nanowhisker composites were synthesized by applying the liquid-liquid interfacial precipitation (LLIP) method to a saturated solution of C₆₀ in toluene, the solution of bipyramidal gold nanoparticles, and isopropyl alcohol. The prepared bipyramidal gold nanoparticle-[C₆₀] fullerene nanowhisker composites were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The catalytic activity of these composites was confirmed in the reduction of 4-nitrophenol by UV-Vis spectroscopy.     

The effect of support on the structure and photocatalytic activity of ternary ZnO-ZnFe2O4/palygorskite composite photocatalysts

The ternary ZnO-ZnFe₂O₄/palygorskite composite photocatalysts were fabricated via a solvothermal method followed by thermal treatment. The structure, morphology and photoelectric performances of samples were characterized, and the results indicated that ZnO/ZnFe₂O₄ nanoparticles with size of 25–30 nm were adequately anchored on the palygorskite fibers surface. Compared with ZnO, ZnFe₂O₄, ZnO/ZnFe₂O₄ and ZnO/palygorskite, the ZnO-ZnFe₂O₄/palygorskite composite photocatalysts exhibited significantly improved photocatalytic activity in degradation of methylene blue (MB). Especially, the optimal photocatalyst (ZF1.5) displayed the highest photocatalytic activity, achieving 99.68% and 99.48% degradation efficiency after 90 min of UV–vis (350 ≤ λ ≤ 780 nm) and 100 min of visible-light (λ ≥ 420 nm) irradiation, respectively. The photocatalysis degradation process matched well with the Langmuir-Hinshelwood kinetics. The obtained improvement of photocatalytic activity was ascribed to the synergetic effect of superior visible-light utilization; effective charge carrier separation and palygorskite support effect (optimize nanoparticles dispersibility, developed mesoporous structure, enlarge specific surface area and increase adsorption capacity).     

Synthesis of cuprous oxide nanoparticles on graphitic carbon nitride and reduced graphene oxide and their catalytic performance toward the reduction of 4-nitrophenol

In this work, a desired Cu₂O catalyst supported on graphitic carbon nitride and reduced graphene oxide hybrid (Cu₂O/g-C₃N₄–rGO) with excellent catalytic performance in the reduction of 4-nitrophenol (4-NP) by NaBH₄ has been fabricated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), N₂ adsorption/desorption and Fourier-transform infrared (FTIR) techniques as well as catalytic test using the reduction of 4-NP by NaBH₄ as probe reaction have been used to investigate the structure–properties relationship of the as-prepared Cu₂O/g-C₃N₄–rGO composites. The results demonstrate that ultrafine Cu₂O nanoparticles can be stably anchored on g-C₃N₄–rGO hybrid by tuning the initial ratio of rGO (reduced graphene oxide) to g-C₃N₄, where homogeneous dispersion of g-C₃N₄ on sheet-like rGO plays a very important role in confining the ultrafine Cu₂O nanoparticles and excellent catalytic performance is noticed on Cu₂O/g-C₃N₄–rGO composite for the reduction of 4-NP by NaBH₄ with an activity parameter up to 6330 s^-1g^-1.

Graphical abstract

     

Voltammetric determination of 4-nitrophenol using a modified carbon paste electrode based on a new synthetic crown ether/silver nanoparticles

A novel modified carbon-paste electrode (CPE) with a new synthetic ligand: 6,7,9,10,17,18,19, 20,21, 22-decahydrodibenzo[h,r][1,4,7,11,15]trioxadiazacyclonanodecine-16,23dione(DTD)/Ag nanoparticles (AgNP) was employed for 4-nitrophenol measurement in natural water. Various parameters such as pH, modifier, accumulation time and scan rate were optimized. The proposed electrode showed a good response towards 4-nitrophenol determination. Under the optimized conditions the reduction peak current, showed a good linear relationship with the nitrophenol concentration in the range comprised between 1 × 10^− 6 mol L^− 1 and 1 × 10^− 4 mol L^− 1. The developed electrode was successfully applied for the determination of 4-nitrophenol in water samples.     

Facile synthesis of Au nanoparticles supported on polyphosphazene functionalized carbon nanotubes for catalytic reduction of 4-nitrophenol

Carbon nanotubes (CNTs) functionalized with cyclotriphosphazene-containing polyphosphazenes (PZS) were found to cause the facile immobilization of Au nanoparticles on the surface. The PZS functional layers not only improved the dispersion of CNTs in aqueous solution but also used as a platform for subsequent immobilization of Au nanoparticles. The functionalized CNTs and the Au@PZS@CNTs nanohybrids were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, X-ray diffraction, thermogravimetric analysis, Atomic absorption spectrum, and X-ray photoelectron spectroscopy. The results showed that the PZS layers with thickness of about 25 nm were formed uniformly on CNT surfaces by polycondensation between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol, and that high density of homogeneously dispersed spherical Au nanoparticles with average size of 6 nm was immobilized on their outer surface. Meanwhile, the catalytic activity and reusability of the Au@PZS@CNTs nanohybrids were investigated by employing the reduction of 4-nitrophenol into 4-aminophenol by NaBH₄ as a model reaction.     

Functionalized graphene oxide and multi-walled carbon nanotubes in hexadecyl trimethyl ammonium bromide and chitosan matrix as metal-free catalyst for enhanced oxygen reduction reaction

The development of new catalysts for high-performance and cost-effective oxygen reduction is crucial in the commercialization of fuel cells. Herein, we demonstrate the use of a novel metal-free catalyst, hexadecyl trimethyl ammonium bromide (CTAB)-functionalized graphene oxide (GO) and multi-walled carbon nanotubes (MWCNT) in CTAB and chitosan matrix (CTAB/GO/MCWNT/CS), which exhibits a significant synergistic catalytic effect on oxygen reduction reaction. Compared with commercially available Pt/C catalysts, enhanced electrocatalytic activity, improved long-term operational stability, and excellent tolerance to methanol in alkaline fuel cells were observed for the novel composite catalyst.     

石墨烯负载四硫化三钴复合物氧还原催化剂的制备与性能

选取二氯化钴和硫脲为钴源和硫源,以自制的还原氧化石墨烯(rGO)为载体,采用回流法在乙二醇溶剂中一步合成出Co₃S₄/rGO复合物。利用X射线衍射、扫描电镜和拉曼光谱(Raman)等手段对催化剂进行结构与形貌表征。结果表明:Co₃S₄/rGO样品中生成了具有立方结构的Co₃S₄细小晶粒,生长在rGO上的Co₃S₄晶粒发生聚集,具有较好的分散性。Co₃S₄/rGO的拉曼谱图的峰强比(I_D/I_G)为0.92,Co₃S₄对石墨烯结构无明显影响,石墨烯起到载体作用。在0.5mol/L H₂SO_4电解液中,线扫伏安测试表明,Co₃S₄/rGO催化剂具有良好的氧还原催化性能,氧还原起始电位为0.75V(vs.RHE),在动力学电位区,Tafel斜率和传递系数分别为119.5mV和0.49,氧分子在Co₃S₄/rGO催化剂上按四电子机理直接还原成水。     

The growth of carbon nanotubes on large areas of silicon substrate using commercial iron oxide nanoparticles as a catalyst

A new approach to chemical vapour deposition (CVD) growth of carbon nanotubes (CNTs) using commercial magnetite nanoparticles, avoiding its in situ synthesis, is reported. Commercial magnetite nanoparticles were used as catalyst material to growth multiwalled carbon nanotubes by chemical vapour deposition onto a silicon substrate of several square centimeters in area. It is shown that the application of an alternating electric field during the deposition of catalytical nanoparticles is an effective technique to avoid their agglomeration allowing nanotube growth. Scanning electron microscopy showed that the nanotubes grow perpendicularly to the substrate and formed an aligned nanotubes array. The array density can be controlled by modifying the deposited nanoparticle concentration.     

Effect of oxidation on Li-ion secondary battery with non-stoichiometric silicon oxide (SiOx) nanoparticles generated in cold plasma

In order to study the effect of oxidation on anode material for Li-ion secondary battery, non-stoichiometric silicon oxide nanoparticles are synthesized using inductively coupled plasma (13.56 MHz). The chemical compositions and size distribution of the generated nanoparticles are measured with EDS and SMPS (Scanning Mobility Particle Sizer). The chemical composition of the nanoparticles was very similar with that of a non-stoichiometric silicon oxide film. For Li-ion secondary battery, it is recommended that the oxygen concentration should be reduced below 18 at.%. It is also revealed that pitch coating was a good method for preventing the natural oxidation and improving capacity.     

Ultrathin Co3O4 nanosheets highly dispersed on reduced graphene oxide: An efficient bi-functional catalyst for Li-O2 battery

Ultrathin Co₃O₄ nanosheets grown on the reduced graphene oxide (Co₃O₄/rGO) was synthesized by a simple hydrothermal method and was investigated as a cathode in a Li-O₂ battery. Benefited from the synergistic effect between Co₃O₄ and rGO, the hybrid exhibits a high initial capacity of 10,528 mAh g^?1 along with a high coulombic efficiency (84.4%) at 100 mA g^?1. In addition, the batteries show an enhanced cycling stability and after 113 cycles, the cut-off discharge voltage remains above 2.5 V. The outstanding performance is intimately related to the high surface area of rGO, which not only provide carbon skeleton for the uniform distribution of Co₃O₄ nanosheets but also facilitate the reversible formation and decomposition of insoluble Li₂O₂. The results of electrochemical tests confirm that the Co₃O₄/rGO hybrid is a promising candidate for the Li-O₂ batteries.     

Facile synthesis of porous hollow iron oxide nanoparticles supported on carbon nanotubes

Porous hollow iron oxide nanoparticles (PHNPs) supported on carbon nanotubes (CNTs) were facilely synthesized by etching Fe@Fe_xO_y/CNT with dilute nitric acid aqueous solution at ambient temperature without the assistance of any surfactants and ligands. The mean diameter of hollow iron oxide nanoparticles was about 17 nm, with a wall thickness of about 4 nm. The formation mechanism of PHNPs is discussed based on the characterization results from TEM, XRD and H₂-TPR. The combination of nanoscale Kirkendall effect and selective acid etching is proposed to be responsible for the formation of CNT supported PHNPs, through a transformation from core/void/shell structures to hollow nanoparticles.     

Shape-controlled synthesis of porous AuPt nanoparticles and their superior electrocatalytic activity for oxygen reduction reaction

Control of structure and morphology of Pt-based nanomaterials is of great importance for electrochemical energy conversions. In this work, we report an efficient one-step synthesis of bimetallic porous AuPt nanoparticles (PAuPt NPs) in an aqueous solution. The proposed synthesis is performed by a simple stirring treatment of an aqueous reactive mixture including K₂PtCl₄, HAuCl₄, Pluronic F127 and ascorbic acid at a pH value of 1 without organic solvent or high temperature. Due to their porous structure and bimetallic composition, as-made PAuPt NPs exhibit excellent electrocatalytic activity for oxygen reduction reaction.