Mixed transition-metal oxides (MTMOs) have attracted much research interest because of their promising applications in artificial enzymes. In this work, uniform hollow MnCo2O4 nanofibers have been fabricated via an electrospinning technique followed by a calcination process, which can be used as efficient oxidase mimics. In detail, the as-prepared hollow MnCo2O4 nanofibers display excellent oxidase-like activity toward the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) superior to their corresponding single-metal oxides without the addition of H2O2. Based on the high catalytic activity of hollow MnCo2O4 nanofibers and their inhibition effect by specific substances, the system of hollow MnCo2O4 nanofibers–TMB has potential to be applied in assays to detect sulfite and L-cysteine using a colorimetric approach with high sensitivity and selectivity. This work implies a broad application prospect of MTMOs in biosensors, environmental protection, food safety and medical science.

We report on the facile synthesis of magnetic CoFe2O4/Ag hybrid nanotubes, as a reliable and sensitive surface enhanced Raman scattering (SERS) substrate for sensitive detection and in situ monitoring of the catalytic degradation process of organic pollutants. This SERS substrate, based on CoFe2O4/Ag hybrid nanotubes, is achieved through an electrospinning followed by calcination process. The CoFe2O4 and Ag nanoparticles are well dispersed in the CoFe2O4/Ag hybrid nanotubes. The unique heterostructure and strong interactions between CoFe2O4 and Ag nanoparticles in the hybrid nanotubes contribute the electromagnetic field SERS enhancement. In addition, target molecules can be easily enriched on the surface of the CoFe2O4/Ag hybrid nanotubes due to their magnetic properties, further providing good SERS properties. The CoFe2O4/Ag hybrid nanotubes can be also used as a catalyst for the degradation of organic pollutants. Therefore, we have developed a facile approach by using CoFe2O4/Ag hybrid nanotubes as both catalyst and SERS substrate to determine the reaction kinetics of the catalytic degradation of organic pollutants.

A simple and green strategy was proposed for the first time to fabricate uniform polyaniline (PANi) thorn/BiOCl chip (BPB) heterostructures at a low temperature without the assistance of any surfactant. During the synthetic process, Bi2S3 nanowires acted as both the sacrificial template and the Bi source for BiOCl, affording the synchronous formation of HCl-doped PANi conductive arrays and BiOCl chips supported on residual Bi2S3 nanowires. As expected, when utilized as electrode materials for supercapacitors, the obtained BPB nanocomposite exhibited a better electrochemical performance in neutral media with enhanced specific capacitance, a more acceptable rate capability and a smaller charge-transfer resistance in comparison with the individual PANi nanofibers due to the unique hierarchical nanostructure of BPB and the synergistic effect between the ionizable BiOCl and the PANi chain.

The self-assembly of noble metal nanoparticles into new-fashioned one, two and three-dimensional structures is very important due to their superior properties in optics, electrics, catalysis, and chemical sensing compared with individual nanoparticles. Here, we first report a facile one-step approach that allows the fabrication of assembled Au nanorices induced by polyaniline (PANI). During the synthesis, a complex of HAuCl4-(3-aminopropyl)triethoxysilane (APTES) acts as both a soft template and an oxidant; then the reduction of HAuCl4 is accompanied by the oxidation of aniline, resulting in the formation of Au nanorices within a PANI matrix. The application of the prepared Au/PANI nanorices as enzyme mimics toward the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) is demonstrated. The resultant Au/PANI nanorices display an enhanced peroxidase-like catalytic activity compared with individual Au nanospheres and PANI nanofibers alone, revealing a synergistic effect between Au and PANI components in the Au/PANI nanorices. The Au/PANI nanorices are also used as efficient surface-enhanced Raman scattering (SERS) substrates for in situ monitoring of the oxidation process of TMB during the peroxidase-like catalytic reaction. On the basis of the SERS technique, a discernible detection level of H2O2 as low as 10−8 M is obtained. We envision that such a system may show more potential applications in biocatalysis, disease diagnosis and environmental monitoring.

In recent years, the fabrication of functional nanostructures with multicomponents for a variety of novel biosensors has received considerable attention due to their synergistic improved sensitivity. Herein, we report a facile approach for the preparation of Fe3O4/nitrogen-doped carbon (Fe3O4/N–C) hybrid nanofibers, and construct a sensing platform for the sensitive colorimetric detection of H2O2 and ascorbic acid (AA). During the synthetic process, a discontinuous layer of polypyrrole (PPy) is first polymerized in situ on the surface of the α-Fe2O3 nanofibers under hydrothermal reaction using α-Fe2O3 nanofibers as both a template and an oxidant. Then the prepared α-Fe2O3/PPy nanofibers are converted into Fe3O4/N–C hybrid nanofibers through pyrolysis with a thermochemical reduction process. The resulting Fe3O4/N–C hybrid nanofibers are used as a novel peroxidase mimic towards the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, with a superior catalytic activity over individual α-Fe2O3 nanofibers, α-Fe2O3/PPy nanofibers, Fe3O4/C nanofibers, and commercial Fe3O4 nanoparticles. Based on the high peroxidase-like activity of Fe3O4/N–C hybrid nanofibers, a sensing platform for the colorimetric detection of AA is developed. A good linear relationship from 0 to 50 μM and a detection limit of 0.04 μM are achieved. This work offers a new method for the preparation of Fe3O4/N–C hybrid nanofibers and presents new potential applications in biosensing, medical diagnostics and environmental monitoring.

In recent years, carbon dots (CDs) based hybrid nanomaterials have received considerable attention due to their outstanding optical and catalytic properties. Herein, CDs/Fe3O4 hybrid nanofibers are prepared via a facile electrospinning technique combined with a hydrothermal reaction and a thermochemical reduction process. During the synthetic process, α-Fe2O3 nanofibers are synthesized via electrospinning followed by a calcination process first. Then CDs modified α-Fe2O3 nanofibers can be obtained under a hydrothermal reaction. Finally, the prepared CDs modified α-Fe2O3 nanofibers are converted to CDs/Fe3O4 hybrid nanofibers through a thermochemical reduction process. The resulting CDs/Fe3O4 hybrid nanofibers show a superior peroxidase catalytic activity to individual CDs, α-Fe2O3 nanofibers, CDs/α-Fe2O3 hybrid nanofibers and commercial Fe3O4 nanoparticles. The steady-state kinetic assay exhibits an excellent affinity for TMB with a low Michaelis–Menten constant (Km) value. On the basis of the high peroxidase-like activity of CDs/Fe3O4 hybrid nanofibers, a simple approach for the colorimetric detection of H2O2 and ascorbic acid (AA) with a low detection limit of 0.917 and 0.285 μM, respectively, is developed. This work inspires researchers to develop functional hybrid nanomaterials for fabricating superior biomimetic catalysts and extends their applications in biosensors and environmental monitoring.

A simple and low cost detection of L-cysteine is essential in the fields of biosensors and medical diagnosis. In this study, we have developed a simple electrospinning, followed by calcination process to prepare FeCo nanoparticles embedded in carbon nanofibers (FeCo-CNFs) as an efficient peroxidase-like mimic for the detection of L-cysteine. FeCo nanoparticles are uniformly dispersed within CNFs, and their diameters are highly influenced by the calcination temperature. The calcination temperature also influences the peroxidase-like catalytic activity, and the maximum activity is achieved at a calcination temperature of 550 °C. Owing to the high catalytic activity of the as-prepared FeCo-CNFs, a colorimetric technique for the rapid and accurate determination of L-cysteine has been developed. The detection limit is about 0.15 μM with a wide linear range from 1 to 20 μM. In addition, a high selectivity for the detection of L-cysteine over other amino acids, glucose and common ions is achieved. This study provides a simple, rapid and sensitive sensing platform for the detection of L-cysteine, which is a promising candidate for potential applications in biosensing, medicine, environmental monitoring.

Synergistic effects play an important role in improving the catalytic activity for enzyme-like reactions. Compared to individual nanomaterials, a system consisting of multiple components usually exhibits enhanced catalytic activity as an enzyme mimic. Herein we describe the synthesis of CuFe2O4/Cu9S8/polypyrrole (PPy) ternary nanotubes as an efficient peroxidase mimic via a three-step approach involving an electrospinning process, annealing treatment and hydrothermal reaction. The remarkably enhanced catalytic activity of CuFe2O4/Cu9S8/PPy ternary nanotubes as peroxidase mimics over individual CuFe2O4 nanofibers, CuFe2O4/CuO composite nanofibers, CuFe2O4/CuS composite nanofibers, and PPy materials has been achieved, demonstrating the presence of a synergistic effect among the components. The steady-state kinetic experiment suggests a good catalytic efficiency of the CuFe2O4/Cu9S8/PPy ternary nanotubes. On the basis of high catalytic activity, a colorimetric platform for the sensitive detection of H2O2 and dopamine has been developed. This work not only offers a simple approach for the fabrication of a high performance peroxidase-like nanocatalyst, but also provides its promising potential applications in biosensors, medical diagnosis, and environmental monitoring.

Here, we report a simple one-step procedure to fabricate coaxial Te@poly(3,4-ethylenedioxythiophene) (PEDOT) nanocables via a self-assembly redox polymerization between 3,4-ethylenedioxythiophene monomer and the oxidant of sodium tellurite without the assistance of any templates and surfactants. The as-synthesized Te@PEDOT coaxial nanocables have diameters of center cores in the range of 5–10 nm, and the size of the outer shell from several nanometers to 15 nm. More interestingly, the as-prepared Te@PEDOT nanocables can be converted to Pd@PEDOT nanocables via a galvanic replacement reaction. The center core of the Pd nanowire exhibits a high crystallinity. The application of the synthesized Pd@PEDOT nanocables as peroxidase-like catalysts for the colorimetric detection of H2O2 is reported. The synergistic effect between the Pd nanowire and electrically conducting PEDOT enhances the catalytic activity toward the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine in the presence of H2O2. A detection limit toward H2O2 is as low as 4.83 μM, and a linear range from 10 to 100 μM has been achieved. This work offers a potential versatile route for the fabrication of cable-like nanocomposites with conducting polymers and other active components, which display great promise in applications such as catalysis, nanoelectronic devices, and energy storage and conversion.Keywords: colorimetric detection; nanocables; palladium; peroxidase-like activity; poly(3,4-ethylenedioxythiophene)

A novel composite nanostructure of C–CoOx–C with CoOx nanoparticles embedded in N-containing porous graphite carbon nanofibers (CNF) is successfully prepared via sintering the electrospun polyacrylonitrile–cobalt acetate tetrahydrate nanofibers covered by a polypyrrole (PPy) sheath that were attained from the chemical vapor-phase polymerization of pyrrole monomers using concentrated nitric acid as both the dopant and oxidant for the first time. The unique configuration with a well-defined morphology possesses a large specific surface area and prominent conductivity contributed to by the catalysis of metallic Co and the external PPy-derived carbon envelope, which could facilitate effective electron transfer and rapid ion penetration in C–CoOx–C, thus improving its electrochemical performance. As expected, when employed as an electrode active material for supercapacitors, the resultant C–CoOx–C showed a more acceptable specific capacitance, better rate capability and higher cycling stability than individual CNF and CoOx nanoparticle-decorated CNF without the coating of a N-doped carbon layer from PPy (C–CoOx).

Herein, we report a simple procedure to decorate small palladium nanoparticles (Pd NPs) on the surface of CoFe2O4 nanotubes; the decorated nanotubes possess intrinsic peroxidase-like activity for the sensitive detection of H2O2. The CoFe2O4 nanotubes are prepared via an electrospinning technique, followed by a calcination process in air. The functionalization of Pd NPs on the surface of CoFe2O4 nanotubes was achieved through an in situ reduction process using ascorbic acid (AA) as a reducing agent. The synthesized Pd nanoparticles, which are small in size, are evenly dispersed on the surface of the CoFe2O4 nanotubes. The hollow structure of the CoFe2O4 nanotubes and the uniform distribution of the Pd nanoparticles enhance peroxidase-like activity toward the catalytic oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. The peroxidase-like property of the Pd/CoFe2O4 composite nanotubes provides a facile approach for the colorimetric detection of H2O2 with a low detection limit. This work provides great potential for Pd/CoFe2O4 nanotubes as enzyme-like nanocatalysts to sensitively detect H2O2 in biological systems.

In this work, we demonstrate the fabrication of polypyrrole (PPy) decorated TiO2/Fe2O3 (TiO2/Fe2O3/PPy) composite nanofibers with a core–shell structure as an artificial enzyme system with a high peroxidase-like activity. The TiO2/Fe2O3 nanofibers with a diameter in the range of 40–150 nm and a relatively narrow distribution of diameter size are prepared via an electrospinning technique and followed by a calcination process. Then we are able to in situ polymerize a layer of PPy on the surface of the TiO2/Fe2O3 nanofibers by using Fe2O3 on the surface of nanofibers as an oxidant. The resulting ternary TiO2/Fe2O3/PPy composite nanofibers exhibit an enhanced peroxidase-like activity toward the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 over independent TiO2, Fe2O3 and TiO2/Fe2O3 composite nanofibers due to the synergistic effect. On the basis of the high peroxidase-like activity, a simple approach for the colorimetric detection of H2O2 with a detection limit of 2.4 μM and a linear detection range from 2 to 50 μM has been proposed. This work offers a new way for manipulating the enzyme-like performance of electrospun nanofibers for a wide range of potential applications in biosensing and environmental monitoring.

We have described a soft-template method that allows the one-pot fabrication of ring-like conducting polymer/noble metal nanocomposites. An insoluble complex of (CTA)2PdBr4 was used as a template and the composite nanorings were synthesized via the redox reaction between PdBr42− and the monomer.

•Bi2S3 nanorods-reduced graphene oxide nanosheet (BGNS) composites were prepared.•A simple and facile one-pot hydrothermal reaction was developed.•The synthetic procedure could accomplish the controlled fabrication of BGNS hybrids.•The novel BGNS composites exhibited enhanced supercapacitor performance.Bi2S3 nanorods-reduced graphene oxide nanosheet (BGNS) composites with uniform morphology have been successfully prepared via a facile one-pot hydrothermal reaction using thioacetamide (TAA) as both the sulfur source and reducing agent. The simple and versatile synthetic procedure could accomplish the controlled fabrication of BGNS hybrids with tunable size and composition through adjusting the additive amount of GO. When employed as active materials for supercapacitor electrodes, in comparison with pristine rGO and X-Bi2S3 that obtained in the absence of GO, the BGNS composites displayed enhanced electrochemical performance by combining desired functions of individual components and introducing extra synergistic effects into the system. It is believed that the novel BGNS composites with multifarious advantages including nontoxicity, abundant resource and low cost are promising for practical application in supercapacitors.

Herein, we report the fabrication of polyacrylonitrile (PAN) nanofibers supported Pd–Pt alloy nanoparticles (PAN/Pd–Pt) through a simple and reliable approach by combining an electrospinning technique and in situ reduction process. The resulting PAN/Pd–Pt membranes are composed of a well-defined fiber-like structure with uniform sizes. Pd–Pt alloy nanoparticles are well dispersed on the surface of PAN nanofibers and the composition of alloy nanoparticles can be regulated through adjusting the feed molar ratio of Na2PdCl4 and K2PtCl4. The obtained products are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. The as-prepared PAN/Pd–Pt composite exhibits a remarkable catalytic performance towards the hydrogen generation from the hydrolysis of ammonia borane (NH3BH3, AB). By tuning the composition of the alloy nanoparticles of the nanocatalyst, a turnover frequency (TOF) of 51.9 mol H2 min−1 (mol Pd–Pt alloy)−1 was achieved, much higher than Pd and Pt-based nanocatalysts. In addition, the as-prepared PAN/Pd–Pt composite nanofibers show good recycling stability, as the catalyst can be easily separated from the suspension system. The electrospun nanofiber membrane supported noble metal nanoalloy catalysts shows high potential to find applications for the development of hydrogen generation for clean energy.

V2O5-doped α-Fe2O3 composite nanotubes have been successfully fabricated via a simple one-step electrospinning technique followed by calcination treatment. For the first time, we found that the magnetic properties of the as-prepared samples were significantly dependent on the contents of the dopant. In comparison with pristine α-Fe2O3, perfect reversibility, more excellent capacitance and better cycling stability were simultaneously observed for the hybrid metal oxide with an appropriate mass ratio of V2O5 (VFNT1) when it was utilized for supercapacitor electrodes, indicating that the doped α-Fe2O3 tubular nanostructures are fairly promising for practical applications not only in magnetic recording but also in the energy storage field.

In this report, a palladium/polypyrrole/polyacrylonitrile (Pd/PPy/PAN) composite nanofiber membranes was synthesized by a one-pot redox polymerization process between pyrrole monomers and Na2PdCl4 in the presence of electrospun PAN nanofibers, without the introduction of any other surfactants or reductants. The as-prepared Pd/PPy/PAN nanofiber membrane exhibited good catalytic performance towards hydrogen generation from the hydrolysis of ammonia borane (AB). The apparent activation energy (Ea) was calculated to be about 33.5 kJ mol−1. In addition, the Pd nanoparticles (Pd NPs) were encapsulated in PPy layers on the surface of the PAN nanofibers, enabling the catalyst to be stable against poisoning and easily separated from the suspension system. The catalytic activity does not weaken after five cycles. This study indicated that the obtained Pd/PPy/PAN composite nanofiber membrane could be applied as an alternative in exploring new catalysts for hydrogen generation, as hydrogen is an important fuel as a clean power source.

•The electrospun nanofibers were firstly used for the hydrogen generation.•Ag/Pd NPs were uniformly distributed on the surface of the PAN nanofibers.•The PAN/Ag/Pd composite nanofibers exhibited excellent catalytic activity.•Good recycle stability and easy separation from the reacted system was achieved.A high-performance hydrogen generation system based on the electrospun polyacrylonitrile (PAN)/Ag/Pd composite nanofibers, which were prepared by microwave reducing the electrospun PAN/AgNO3 nanofibers and followed by a replacement reaction has been demonstrated. The morphology of the as-prepared PAN/Ag/Pd composite nanofibers and the metal nanoparticles on the fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. It has been demonstrated that the obtained PAN/Ag/Pd composite nanofibers possess fine morphology and high catalytic activities for H2 generation from aqueous solution of ammonia borane (NH3BH3, AB). The H2 generation test exhibited that the catalyst had excellent catalytic activity (with turnover frequency (TOF) of 377.2 mol H2 h−1 (mol Pd)−1), good recycle stability and easy-separation from the reaction system. This new kind of nanofibers possesses great potential application for the new clean energy development.

•GO nanosheets decorated with ultrafine Pd nanoparticles have been fabricated.•The Pd/GO nanocomposites show remarkable catalytic activity and good stability.•The catalytic activity is much higher than the conventional Pd/C catalysts.In this report, graphene oxide (GO) nanosheets decorated with ultrafine Pd nanoparticles (Pd NPs) have been successfully fabricated through a reaction between [Pd2(μ-CO)2Cl4]2− and water in the presence of GO nanosheets without any surfactant or other reductant. The as-synthesized small Pd NPs with average diameter of about 4.4 nm were well-dispersed on the surface of GO nanosheets. The Pd/GO nanocomposites show remarkable catalytic activity toward the hydrogenation of p-nitrophenol at room temperature. The kinetic apparent rate constant (kapp) could reach about 34.3 × 10−3 s−1. Furthermore, the as-prepared Pd/GO nanocomposites could also be used as an efficient and stable catalyst for hydrogen production from hydrolytic dehydrogenation of ammonia borane (AB). The catalytic activity is much higher than the conventional Pd/C catalysts.

An electrochemical method for the detection of dopamine based on a glass carbon electrode modified with electrospun CeO2/Au composite nanofibers was investigated in this article. The CeO2/Au composite nanofibers were prepared by the electrospinning technique and then annealed in air. The CeO2/Au composite nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. Cyclic voltammetry (CV) showed that the electrospun CeO2/Au composite nanofibers modified carbon glass electrode exhibited an excellent electrocatalytic response to the dopamine (DA). The detection limit (S/N = 3) was as low as 0.056 μM and the sensitivity could reach 127 μA mM−1 cm−2. All these demonstrated that the electrospun CeO2/Au composite nanofibers were good electrocatalyst for the oxidation of dopamine.

Pure Pd hollow nanocubes assembled with uniform nanoparticles were successfully fabricated via a one-step redox reaction by using Cu2O nanocubes as both sacrificial templates and the reducing agents. Almost no residual Cu2O cores remained in the final Pd cubic nanoshells which were composed of nanograins with an average diameter of approximately 6.5 nm. A wide liner range (0.1–24.0 mM), a relatively high sensitivity (287.7 mA M−1 cm−2) and a comparable detection limit (7.4 μM, S/N = 3) were observed in the electrochemical experiments, indicating that the obtained Pd hollow nanocubes as enzyme-free catalysts possessed excellent electrocatalytic activity to the reduction of H2O2.

CuS-graphene nanosheet (GNS) composites with well-defined morphology have been successfully fabricated via a simple one-pot hydrothermal route by using thioacetamide (TAA) as both the sulfur source and reducing agent. The as-prepared CuS-GNS composites with an appropriate content of graphene exhibited an even higher peroxidase-like catalytic activity than pristine CuS nanoparticles in acetate buffer solution (pH = 4.0), which provided a facile method for the colorimetric detection of hydrogen peroxide (H2O2). It was calculated that H2O2 could be detected as low as 1.2 μM (S/N = 3) with a wide linear range from 2.0 to 20.0 μM (R2 = 0.992), indicating that the as-prepared catalyst as an artificial peroxidase is promising for application in biosensors and environmental monitoring.

MnO2/graphene oxide (GO) composite nanosheets have been successfully fabricated by a simple wet-chemical synthetic route. The composition and structure of the resulting MnO2/GO composites were characterized by transmission electron microscopy (TEM), energy dispersive X-ray diffraction (EDX), Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) patterns. The MnO2/GO composite nanosheets exhibited good electrocatalytic behavior in detecting hydrazine at an applied potential of +0.6 V. The sensor showed a good linear dependence on hydrazine concentration in the range of 3 × 10−6 to 1.12 × 10−3 with a sensitivity of 1007 μA mM−1 cm−2. The detection limit is 0.16 μM at the signal-to-noise ratio of 3. Furthermore, the MnO2/GO modified electrode exhibits freedom from interference by other co-existing electroactive species. These results demonstrate that MnO2/GO composites have great potential in the application of hydrazine detection.

In this article, Prussian blue (PB) covered multiwalled carbon nanotubes (MWCNTs)/polypyrrole (PPy) ternary composite nanofibers with good dispersibility in water and ethanol have been prepared by directly mixing ferric-(III) chloride and potassium ferricyanide in the presence of MWCNT/PPy coaxial nanofibers under ambient conditions. Transmission electron microscopy shows that the as-synthesized PB nanoparticles covered on the surface of MWCNT/PPy nanofibers. Fourier-transform infrared spectroscopy, UV–Visible spectroscopy, and X-ray diffraction patterns have been used to characterize the obtained MWCNT/PPy/PB ternary composite nanofibers. The MWCNT/PPy/PB ternary composite nanofibers exhibit good electrocatalytic response to detection of H2O2 and provide a new material to modify electrode for amperometric biosensors.

CNT/PPy/KxMnO2, a novel ternary core–shell nanowires, was successfully prepared by a two-step self-assembly method and utilized as an electrocatalyst for the oxidation of hydrogen peroxide. The as-synthesized products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and Fourier-transform infrared spectra (FTIR) measurements. The results exhibited that the KxMnO2 nanosheets were grown on the surface of CNT/PPy core–shell nanotubes. The planes of the KxMnO2 nanosheets were more or less perpendicular to the CNT/PPy nanotubes. Cyclic voltammetry (CV) results demonstrated that the CNT/PPy/KxMnO2 composite nanowires, as a nonenzyme catalyst, performed well with regards to the oxidation of hydrogen peroxide in 0.1 M phosphate buffer solution (pH 7.0). The composite had a fast response with a linear range of 5.0 μM to 9.7 mM and a relatively low detection limit of 2.4 μM (S/N = 3). The sensitivity of the sensor for H2O2 was 114.6 μA mM−1 cm−2. These excellent properties might be due to the large surface area of the composite nanowires and the quick electron transfer promoted by the combination of CNT and PPy.Highlights► Novel ternary core–shell CNT/PPy/KxMnO2 nanowires are prepared by a two-step self-assembly method. ► KxMnO2 nanosheets are grown more or less perpendicular to the CNT/PPy nanotubes. ► The CNT/PPy/KxMnO2 nanowires exhibit good performance as electrocatalysts towards the oxidation of H2O2.

A facile and aqueous-phase method based on the electron transfer reduction process for fabricating core-sheath structured polyaniline (PANI)/SnO2 composite nanorods supported Pd nanocatalyst has been demonstrated. The Pd nanoparticles synthesized by this strategy have a small size of smaller than 3.0 nm. The well dispersed Pd nanoparticles with small sizes supported on core-sheath PANI/SnO2 composite nanorods exhibited an ultrahigh catalytic activity during the catalytic reduction of p-nitrophenol into p-aminophenol by NaBH4 in aqueous solution. The kinetic apparent rate constant (kapp) reach to be about 26.9 × 10−3 s−1. It is believed that this method could be extended to cover many kinds of other functional composite nanomaterials where the active component is expected to bring in new features and applications.

Fe3O4 microsphere is a good candidate as support for catalyst because of its unique magnetic property and large surface area. Coating Fe3O4 microspheres with other materials can protect them from being dissolved in acid solution or add functional groups on their surface to adsorb catalyst. In this paper, a carbon layer was coated onto Fe3O4 microspheres by hydrothermal treatment using polyethylene glycol as the connecting agents between glucose and Fe3O4 spheres. Through tuning the added amounts of reactants, the thickness of the carbon layer could be well-controlled. Because of the abundant reductive groups on the surface of carbon layer, noble metal ions could be easily adsorbed and in situ reduced to nanoparticles (6−12 nm). The prepared catalyst not only had unique antiacid and magnetic properties, but also exhibited a higher catalytic activity toward the reduction of methyl orange than commercially used Pd/C catalyst.Keywords: coating; environmental degradation; functional composites; magnetic properties; nanocomposites

Tetragonal starlike microstructures of polyaniline (PANI) doped with aspartic acid (AA) have been synthesized under hydrothermal conditions for the first time. It was found that the morphologies of the obtained samples were much sensitive to the concentration of the doping amino acid. Hydrothermal synthesis by monitoring the reaction time provided a platform for understanding the process of the polymerization. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), Fourier transmission infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). Furthermore, the tetragonal starlike PANI modified glassy carbon electrode (GCE) exhibited high electrocatalytic activity for sensing dopamine.

A novel and simple method for the fabrication of polypyrrole (PPy) capsules and nanotubes via a chemical oxidation polymerization in the presence of Rhodamine B (RB) at room temperature is described.

In this work, graphene/prussian blue (PB) composite nanosheets with good dispersibility in aqueous solutions have been synthesized by mixing ferric-(III) chloride and potassium ferricyanide in the presence of graphene under ambient conditions. Transmission electron microscopy (TEM) shows that the average size of the as-synthesized PB nanoparticles on the surface of graphene nanosheets is about 20 nm. Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) patterns have been used to characterize the chemical composition of the obtained graphene/PB composite nanosheets. The graphene/PB composite nanosheets exhibit good electrocatalytic behavior to detection of H2O2 at an applied potential of −0.05 V. The sensor shows a good linear dependence on H2O2 concentration in the range of 0.02–0.2 mM with a sensitivity of 196.6 μA mM−1 cm−2. The detection limit is 1.9 μM at the signal-to-noise ratio of 3. Furthermore, the graphene/PB modified electrode exhibits freedom of interference from other co-existing electroactive species. This work provides a new kind of composite modified electrode for amperometric biosensors.

A simple one-step method to fabricate hierarchically porous TiO2/Pd composite hollow spheres without any template was developed by using solvothermal treatment. Pd nanoparticles (2–5 nm) were well dispersed in the mesopores of the TiO2 hollow spheres via in-situ reduction. In our experiment, polyvinylpyrrolidone played an important role in the synthetic process as the reducing agent and the connective material between TiO2 and Pd nanoparticles. HF species generated from solvothermal reaction leaded to the formation of TiO2 hollow spheres and Ostwald ripening was another main factor that affected the size and structure of the hollow spheres. The as-prepared TiO2/Pd composite hollow spheres exhibited high electrocatalytic activity towards the reduction of H2O2. The sensitivity was about 226.72 μA mM−1 cm−2 with a detection limit of 3.81 μM at a signal-to-noise ratio of 3. These results made the hierarchically porous TiO2/Pd composite a promising platform for fabricating new nonenzymic biosensors.Graphical AbstractA new one-step solvothermal method was developed to prepare Pd nanoparticles embedded hierarchically porous TiO2 hollow spheres. Due to its unique nanostructure, the prepared TiO2/Pd modified GC electrode exhibit a high sensitivity (226.72 μA mM−1 cm−2), a relatively low reduction potential (−0.2 V), a fast response time (<3 s) and a relatively low detection limit of 3.81 μM (S/N=3) towards H2O2.

Pt/polypyrrole (PPy) hybrid hollow microspheres were successfully prepared by wet chemical method via Fe3O4 template and evaluated as electrocatalysts for the reduction of hydrogen peroxide. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), inductive coupled plasma emission spectrum (ICP) and Fourier-transform infrared spectra (FTIR) measurements. The results exhibited that ultra-high-density Pt nanoparticles (NPs) were well deposited on the PPy shell with the mean diameters of around 4.1 nm. Cyclic voltammetry (CV) results demonstrated that Pt/PPy hybrid hollow microspheres, as enzyme-less catalysts, exhibited good electrocatalytic activity towards the reduction of hydrogen peroxide in 0.1 M phosphate buffer solution (pH = 7.0). The composite had a fast response of less than 2 s with linear range of 1.0–8.0 mM and a relatively low detection limit of 1.2 μM (S/N = 3). The sensitivity of the sensor for H2O2 was 80.4 mA M−1 cm−2.

With an accurate control of the dispersity and size of the palladium nanoparticles (Pd NPs), carbon spheres/Pd NPs composite was prepared without any extra reducing agents. In order to fully understand the formation mechanism and find out the best condition for the fabrication of carbon/Pd composite spheres, the effects of temperature, reaction time, pH value, and the weight ratio of PdCl2 to carbon spheres on the morphology of the final products were investigated. A superior product with small (d = 7.66 nm, σ = 1.94 nm), homogeneously distributed Pd crystals was obtained at pH 7 and a reaction temperature of 70 °C in ethanol. The Pd NPs decorated carbon sphere was used as support for electroactive polyaniline (PANI) in our work because it could enhance their sensing properties which were afforded by catalytic Pd NPs and hydrophilic carbon spheres. The sensor based on carbon/Pd/PANI exhibited a high sensitivity of 656.0693 mA M−1 cm−2 and a detection limit of 5.48 μM toward the reduction of H2O2. In addition, the carbon/Pd/PANI sensor also showed good selectivity between H2O2 and ascorbic acid.

•Hierarchical α-Fe2O3 nanotube@MnO2 nanosheet core-shell networks were prepared.•The mass ratio of MnO2 to α-Fe2O3 can be easily controlled.•The α-Fe2O3@MnO2 heterostructures exhibited improved supercapacitive property.The incompetency of conventional single-phase electrode materials remains a stumbling block for making further breakthroughs in high-performance supercapacitors. In this work, α-Fe2O3 nanotube@MnO2 nanosheet hierarchical networks with tunable mass ratio of MnO2 to α-Fe2O3 are prepared via a simple two-step method for supercapacitor electrodes. The α-Fe2O3@MnO2 core-shell heterostructures, especially the FM10020 containing 60.1 wt% of MnO2, exhibit a larger specific capacitance of 289.9 F g−1 at 1.0 A g−1, a better rate capability of 40.8% at 5.0 A g−1 and a higher cycling stability of 85.3% after 1200 cycles than the pure MnO2, highlighting the advantages of such unique configuration accompanied by the synergistic effect. It is believed that these intriguing results will provide an alternative way for the construction of metal oxide-based composite nanostructures with improved electrochemical performance.Hierarchical α-Fe2O3 nanotube@MnO2 nanosheet networks with tunable mass ratio between MnO2 and α-Fe2O3 are prepared via a simple two-step method for high-performance supercapacitor electrodes.

In recent years, the fabrication of functional nanostructures with multicomponents for a variety of novel biosensors has received considerable attention due to their synergistic improved sensitivity. Herein, we report a facile approach for the preparation of Fe3O4/nitrogen-doped carbon (Fe3O4/N–C) hybrid nanofibers, and construct a sensing platform for the sensitive colorimetric detection of H2O2 and ascorbic acid (AA). During the synthetic process, a discontinuous layer of polypyrrole (PPy) is first polymerized in situ on the surface of the α-Fe2O3 nanofibers under hydrothermal reaction using α-Fe2O3 nanofibers as both a template and an oxidant. Then the prepared α-Fe2O3/PPy nanofibers are converted into Fe3O4/N–C hybrid nanofibers through pyrolysis with a thermochemical reduction process. The resulting Fe3O4/N–C hybrid nanofibers are used as a novel peroxidase mimic towards the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, with a superior catalytic activity over individual α-Fe2O3 nanofibers, α-Fe2O3/PPy nanofibers, Fe3O4/C nanofibers, and commercial Fe3O4 nanoparticles. Based on the high peroxidase-like activity of Fe3O4/N–C hybrid nanofibers, a sensing platform for the colorimetric detection of AA is developed. A good linear relationship from 0 to 50 μM and a detection limit of 0.04 μM are achieved. This work offers a new method for the preparation of Fe3O4/N–C hybrid nanofibers and presents new potential applications in biosensing, medical diagnostics and environmental monitoring.

Tetragonal starlike microstructures of polyaniline (PANI) doped with aspartic acid (AA) have been synthesized under hydrothermal conditions for the first time. It was found that the morphologies of the obtained samples were much sensitive to the concentration of the doping amino acid. Hydrothermal synthesis by monitoring the reaction time provided a platform for understanding the process of the polymerization. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), Fourier transmission infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). Furthermore, the tetragonal starlike PANI modified glassy carbon electrode (GCE) exhibited high electrocatalytic activity for sensing dopamine.

V2O5-doped α-Fe2O3 composite nanotubes have been successfully fabricated via a simple one-step electrospinning technique followed by calcination treatment. For the first time, we found that the magnetic properties of the as-prepared samples were significantly dependent on the contents of the dopant. In comparison with pristine α-Fe2O3, perfect reversibility, more excellent capacitance and better cycling stability were simultaneously observed for the hybrid metal oxide with an appropriate mass ratio of V2O5 (VFNT1) when it was utilized for supercapacitor electrodes, indicating that the doped α-Fe2O3 tubular nanostructures are fairly promising for practical applications not only in magnetic recording but also in the energy storage field.

In this report, a palladium/polypyrrole/polyacrylonitrile (Pd/PPy/PAN) composite nanofiber membranes was synthesized by a one-pot redox polymerization process between pyrrole monomers and Na2PdCl4 in the presence of electrospun PAN nanofibers, without the introduction of any other surfactants or reductants. The as-prepared Pd/PPy/PAN nanofiber membrane exhibited good catalytic performance towards hydrogen generation from the hydrolysis of ammonia borane (AB). The apparent activation energy (Ea) was calculated to be about 33.5 kJ mol−1. In addition, the Pd nanoparticles (Pd NPs) were encapsulated in PPy layers on the surface of the PAN nanofibers, enabling the catalyst to be stable against poisoning and easily separated from the suspension system. The catalytic activity does not weaken after five cycles. This study indicated that the obtained Pd/PPy/PAN composite nanofiber membrane could be applied as an alternative in exploring new catalysts for hydrogen generation, as hydrogen is an important fuel as a clean power source.

We have described a soft-template method that allows the one-pot fabrication of ring-like conducting polymer/noble metal nanocomposites. An insoluble complex of (CTA)2PdBr4 was used as a template and the composite nanorings were synthesized via the redox reaction between PdBr42− and the monomer.

CuS-graphene nanosheet (GNS) composites with well-defined morphology have been successfully fabricated via a simple one-pot hydrothermal route by using thioacetamide (TAA) as both the sulfur source and reducing agent. The as-prepared CuS-GNS composites with an appropriate content of graphene exhibited an even higher peroxidase-like catalytic activity than pristine CuS nanoparticles in acetate buffer solution (pH = 4.0), which provided a facile method for the colorimetric detection of hydrogen peroxide (H2O2). It was calculated that H2O2 could be detected as low as 1.2 μM (S/N = 3) with a wide linear range from 2.0 to 20.0 μM (R2 = 0.992), indicating that the as-prepared catalyst as an artificial peroxidase is promising for application in biosensors and environmental monitoring.

A simple and green strategy was proposed for the first time to fabricate uniform polyaniline (PANi) thorn/BiOCl chip (BPB) heterostructures at a low temperature without the assistance of any surfactant. During the synthetic process, Bi2S3 nanowires acted as both the sacrificial template and the Bi source for BiOCl, affording the synchronous formation of HCl-doped PANi conductive arrays and BiOCl chips supported on residual Bi2S3 nanowires. As expected, when utilized as electrode materials for supercapacitors, the obtained BPB nanocomposite exhibited a better electrochemical performance in neutral media with enhanced specific capacitance, a more acceptable rate capability and a smaller charge-transfer resistance in comparison with the individual PANi nanofibers due to the unique hierarchical nanostructure of BPB and the synergistic effect between the ionizable BiOCl and the PANi chain.

A simple and low cost detection of L-cysteine is essential in the fields of biosensors and medical diagnosis. In this study, we have developed a simple electrospinning, followed by calcination process to prepare FeCo nanoparticles embedded in carbon nanofibers (FeCo-CNFs) as an efficient peroxidase-like mimic for the detection of L-cysteine. FeCo nanoparticles are uniformly dispersed within CNFs, and their diameters are highly influenced by the calcination temperature. The calcination temperature also influences the peroxidase-like catalytic activity, and the maximum activity is achieved at a calcination temperature of 550 °C. Owing to the high catalytic activity of the as-prepared FeCo-CNFs, a colorimetric technique for the rapid and accurate determination of L-cysteine has been developed. The detection limit is about 0.15 μM with a wide linear range from 1 to 20 μM. In addition, a high selectivity for the detection of L-cysteine over other amino acids, glucose and common ions is achieved. This study provides a simple, rapid and sensitive sensing platform for the detection of L-cysteine, which is a promising candidate for potential applications in biosensing, medicine, environmental monitoring.