A facile synthesis of homogeneous Ag nanostructures on modified polypyrrole (PPy) films through direct chemical deposition has been demonstrated. The as-prepared Ag nanostructures are highly sensitive and reproducible in the SERS detection of the target analyte, methylene blue (MB).

Anatase TiO2 nanosheets supported on reduced graphene oxide (RGO) were synthesized via a one-step, solvothermal method. During the solvothermal step, graphene oxide (GO) was reduced to RGO, and, subsequently, anatase TiO2 with 73.7% exposed {001} facets was grown in situ on the surfaces of the RGO nanosheets. Compared with pure TiO2, the RGO/TiO2 hybrid nanocomposite had improved photoactivity as a result of effective photoinduced electron transfer from TiO2 to the RGO acceptor through interfacial interactions. Trapping tests showed that the oxidation of dye molecules proceeded for about 22% through the reaction with •OH radicals, and the remaining 78% occurred via direct interactions with holes. The holes left in TiO2 crystals were the main reason for the enhanced photocatalytic properties of the RGO/TiO2 composite. This paper not only reports the fabrication of highly active photocatalysts but also gives deeper insight into the photocatalytic mechanism of carbon/TiO2 composites.Keywords: photocatalytic mechanism; RGO/TiO2 hybrid nanocomposites; TiO2 {001} facets;

The precursor-directed method has been firstly used for the preparation of M-type barium ferrite (BaFe12O19) particles in this article, where Fe3O4 microspheres were selected as the precursor. During the preparation process, it can be found that the volume ratio of water to ethanol plays an important role in determining the crystalline phase, and a high-purity magnetoplumbite structure can be achieved under the optimized conditions. Thanks to the morphology and dispersion of Fe3O4 microspheres, the obtained product presents a quasi-spherical shape, good dispersion, and relatively uniform particle size even after high-temperature heat treatment. Especially, the as-prepared barium ferrite exhibits excellent magnetic properties with both high intrinsic coercivity (5342 Oe) and large saturation magnetization (68.3 emu g−1), which are better than most results from some unconventional techniques. A series of Co–Ti substituted barium ferrite particles [Ba(CoTi)xFe12−2xO19, 0.25 ≤ x ≤ 1.0] are also prepared through the same technique by using Co–Ti substituted Fe3O4 microspheres as precursors, and they also display high-purity crystalline phase, quasi-spherical shape, and good dispersion, indicating that this route can be versatile for barium ferrite with different chemical compositions. However, with an increasing heteroatom content, the intrinsic coercivity and saturation magnetization drastically decrease because of the selective substitution of Fe3+ sites by Co2+ and Ti4+ in the magnetoplumbite structure.

A series of polyaniline (PANI) materials have been prepared by a reverse dropping method with the assistance of polyvinylpyrrolidone (PVP). It can be found that PVP and the dropping rate play critical roles in determining the morphology evolution of PANI, and the restriction of PVP is highly dependent on the dropping rate. Well dispersed PANI nanoparticles can only be obtained under moderate conditions. Thanks to the unique preparative process, these samples show significant changes in the length and oxidation state of conjugated chains, as proved by the results of UV/vis absorption spectra and FT-IR spectra, which result in their distinguishable conductivity and microwave absorption. Very interestingly, PANI nanoparticles exhibit substantially enhanced microwave absorption properties. In particular the optimum one, PANI-NP2, presents very strong reflection loss (−40.5 dB at 5.8 GHz) and wide response bandwidth (3.2–18 GHz over −10 dB), which are indeed comparable to those composites of PANI with various magnetic particles, implying promising applications as a kind of light-weight and highly effective microwave absorber. By systematically investigating the electromagnetic parameters, it can be concluded that suitable complex permittivity, improved characteristic impedance and multiple relaxation processes in PANI nanoparticles should be responsible for their good microwave absorption.

We demonstrate the use of amino acids as directing agents to synthesize hierarchical silver microspheres assembled by nanosheets with well-defined morphologies, in the absence of any other surfactants or capping agents. This fabrication method avoids the absorption of macromolecules and enables clean surface on the Ag microspheres. The chemical nature of the amino acids plays a vital role in the hierarchical structure of the Ag microspheres. As found, amino acids with simple structures and 2–3 carbon atoms like alanine and glycine lead to more loosely packed Ag microspheres, and those with more complicated structures and more carbon atoms, e.g. glycine, glutamine, and asparagine, result in close-packed Ag particles assembled by thinner nanosheets. By adjusting the concentration of AgNO3 solution, size as well as the surface roughness of the Ag microspheres can be well controlled. Individual particles of the constructed hierarchical Ag microspheres with highly roughened surface can act as sensitive SERS platforms. Detection of chemical molecules and monitoring of the plasmon-driven chemical reactions have been carried out through a single particle SERS technique.

Here, we demonstrate a facile synthesis of homogeneous Ag nanostructures fully covering the polyaniline (PANI) membrane surface simply by introducing organic acid in the AgNO3 reaction solution, as an improved technique to fabricate well-defined Ag nanostructures on PANI substrates through a direct chemical deposition method [Langmuir2010, 26, 8882]. It is found that the chemical nature of the acid is crucial to create a homogeneous nucleation environment for Ag growth, where, in this case, homogeneous Ag nanostructures that are assembled by Ag nanosheets are produced with the assistance of succinic acid and lactic acid, but only scattered Ag particles with camphorsulfonic acid. Improved surface wettability of PANI membranes after acid doping may also account for the higher surface coverage of Ag nanostructures. The Ag nanostructures fully covering the PANI surface are extremely sensitive in the detection of a target analyte, 4-mercaptobenzoic acid (4-MBA), using surface-enhanced Raman spectroscopy (SERS), with a detection limit of 10–12 M. We believe the facilely fabricated SERS-active substrates based on conducting polymer-mediated growth of Ag nanostructures can be promising in the trace detection of chemical and biological molecules.Keywords: membrane; nanostructure; polyaniline; silver; surface-enhanced Raman spectroscopy;

Nano-sized anatase TiO2 with exposed {001} facets was synthesized from lamellar protonated titanate precursor. Owing to small size (ca. 11 nm) and high surface area (155 m2 g−1), the crystals with 26.1% {001} facets exhibited markedly superior photoactivity to reference ca. 76 nm anatase TiO2 nanosheets with 88.4% {001} facets.

Herein we obtain a novel incorporating style of polyaniline (PANI)/TiO2 composites (Ns) via a designed two-step route. In comparison with conventional incorporating style (Cs), one-dimensional (1D) PANI is introduced in the step of TiO2 crystal growth instead of after crystallization. During the hydrothermal process, 1D PANI can act as an effective template to stabilize TiO2 particles at nanoscale through interfacial chemical bonds. In this way, the transition of some newly formed anatase crystals to rutile phase is partly suppressed. Also, the as-prepared composites show obvious light response in a wide range of 230–900 nm due to the sensitizing effect of PANI. Ns exhibit the improved visible photocatalytic property with scarce decrease of UV photoactivity. Overall, this work would provide new insights into the fabrication of conducting polymer/semiconductor composites with desired nanostructure as high performance photocatalysts and would facilitate their applications in environmental purification and solar energy conversion.Graphical abstractHighlights► New strategy for synthesis of polyaniline/TiO2 composites with desired structure. ► Polyaniline acts as an effective template in TiO2 system besides sensitizer. ► Composites possess high visible activity and similar UV activity compared to TiO2.

Mixed surfactant solution, containing cetyltrimethyl ammonium bromide (CTAB) and sodium dodecylbenzyl sulfonate (SDBS), is used to prepare polyaniline (PANI) with soft 1D structure and high electrical conductivity. The mixed surfactants in the reaction play double roles of soft templates and dispersion reagents. The influence of CTAB–SDBS ratio on the morphology and conductive property of PANI is investigated. Through varying the proportion of surfactants, uniformly branched nanofibers with higher aspect ratio and good dispersion are obtained, which possess the highest conductivity (0.102 S·cm−1). Moreover, FT-IR spectra are measured to explain the change of structure and conductivity under assistance of mixed surfactants. As a result, the mixed surfactants have significant effect on the electron density of whole structure as well as the PANI molecular orientation.The novel method for synthesis of PANI nanofiber is proposed via a synergism of anionic surfactant (SDBS) and cationic surfactant (CTAB). The proportion of mixed surfactants has significant effect on the morphology and electrical conductivity. Uniform PANI nanofibers with the highest conductivity are obtained as 2:1 of CTAB/SDBS ratio.Highlights► Novel method for synthesis of PANI nanofibers with high conductivity is proposed. ► SDBS–CTAB mixed systems play double roles of soft template and dispersion reagent. ► Morphology and conductivity can be optimized by varying CTAB/SDBS ratio.

A series of carbon materials [CF-x (where x denotes carbonization temperature)] have been prepared by pyrolysis of an anion-exchange resin at different temperatures (500–700 °C). X-ray diffraction and Raman spectroscopy suggest the presence of tiny crystalline domains in these materials, whose content is strongly determined by carbonization temperature. The microwave absorption of these materials is examined in the frequency range of 2–18 GHz, and it is found that the reflection loss characteristics are highly sensitive to the carbonization temperature. At a thickness of 2 mm, CF-600 exhibits the best microwave absorbing ability with a maximum reflection loss of −20.6 dB at 16 GHz, and a bandwidth exceeding −10 dB in the range 13.5–18 GHz. It is concluded that dielectric loss in cooperation with better matched characteristic impedance results in the excellent microwave absorption of CF-600. Furthermore, a reflection loss exceeding −10 dB can be obtained in the range of 7–18 GHz by manipulating the thickness from 2 to 3.5 mm, and the maximum can reach −37.0 dB at 10.8 GHz with a thickness of 2.8 mm. These materials may be used as light-weight and highly effective microwave absorbers over a wide frequency range.

We report a facile synthesis of large-area homogeneous three-dimensional (3D) Ag nanostructures on Au-supported polyaniline (PANI) membranes through a direct chemical reduction of metal ions by PANI. The citric acid absorbed on the Au nuclei that are prefabricated on PANI membranes directs Ag nanoaprticles (AgNPs) to self-assemble into 3D Ag nanosheet structures. The fabricated hybrid metal nanostructures display uniform surface-enhanced Raman scattering (SERS) responses throughout the whole surface area, with an average enhancement factor of 106−107. The nanocavities formed by the stereotypical stacking of these Ag nanosheets and the junctions and gaps between two neighboring AgNPs are believed to be responsible for the strong SERS response upon plasmon absorption. These homogeneous metal nanostructure decorated PANI membranes can be used as highly efficient SERS substrates for sensitive detection of chemical and biological analytes.

Nickel nanomaterials with a wide range of morphologies and sizes, such as superfine nanoparticles, urchinlike chains, smooth chains, rings, and hexagonal Ni/Ni(OH)2 heterogeneous structure plates, are synthesized in a single reaction system by simply adjusting the reaction conditions. The morphology transformation mechanism is systematically investigated. Magnetic measurement of urchinlike chains, smooth chains, and rings shows that the saturation magnetization (Ms) decreases with reduced sample size, and remanent magnetization (Mr) decreases with increasing reaction temperature. Additionally, coercivity (Hc) of urchinlike chains which is apparently larger than that of bulk nickel depends more on size than on shape anisotropy according to spherical chain reversal magnetization model. Enhanced microwave absorption of Ni/Ni(OH)2 hexagonal plates compared with smooth chains and rings is due to the synergistic effect of magnetic loss and dielectric loss. Particularly, the urchinlike nickel chains exhibit a best absorption property in contrast with other as-synthesized samples and other reported nickel structures, which can be attributed to the geometrical effect, high initial permeability, point discharge effect, and multiple absorption. The prepared nickel nanomaterials can be applied as promising absorbing materials.

Hierarchical cobalt assemblies such as spheres, flowers with dendritic petals, and flowers with sharp petals are successfully synthesized via a facile liquid-phase reduction method by simply adjusting the reaction conditions. The morphology evolution process and transformation mechanism from spheres to dendrites and finally to flowers have been systematically investigated. It is determined that coercivity Hc depends more on sample size than on shape anisotropy, while saturation magnetization Ms is greatly affected by pinned surface magnetic moment. Even at a thinner thickness, as-synthesized cobalt samples exhibit stronger microwave absorbing ability compared with reported cobalt in the same frequency band. Especially, the cobalt flowers with dendritic petals exhibit the strongest absorption in middle frequency because incident wave and reflected wave are totally canceled at matching thickness. The architectural design of material morphologies is critical for improving properties toward future application.

Barium ferrite (BaFe12O19) nanoparticles have been successfully synthesized from solvothermal route with the assistance of surfactant P123 (EO20PO70EO20), which has been proven to be a better method for barium-ferrite synthesis as compared to conventional hydrothermal technique, and the resultant product shows high-purity crystalline phase, small particle size, excellent magnetic properties, and characteristic of single magnetic domains. A series of Co−Ti-doped barium-ferrite nanoparticles [Ba(CoTi)xFe12−2xO19, 0.25 ≤ x ≤ 1.0] were also prepared by this method, indicating that this route is versatile for barium-ferrite nanoparticles with different chemical compositions. With increasing heteroatoms content, saturation magnetization and coercivity drastically decreased because of the selective substitution of Fe3+ sites by Co2+ and Ti4+ in the magnetoplumbite structure. By supplying these inorganic nanoparticles as nucleation sites, polyaniline/ferrite composites were prepared through in situ polymerization technique. Compared with pure polyaniline, these composites exhibited essentially enhanced reflection loss properties because of the synergetic behavior between organic and inorganic materials, and proper heteroatom substitution can even improve the reflection loss. More importantly, well reflection loss over a wide frequency range can be simply achieved by manipulating the absorber thickness, suggesting these composites may be used as lightweight and highly effective microwave absorbers.

Copolymers of aniline (An) and pyrrole (Py), poly(aniline-co-pyrrole), have been prepared by a conventional chemical oxidative polymerization from monomer mixtures of various compositions, with ammonium persulfate (APS) as the oxidant and hydrochloric acid as the dopant, and the morphologies and physico-electrochemical properties of the poly(aniline-co-pyrrole) have been investigated. Poly(aniline-co-pyrrole) prepared with more polyaniline (PANI) or polypyrrole (PPy) component have similar morphologies, structures, thermal and electrochemical performances, and the relative dosage (molar ratio) of An and Py monomers during the polymerization is crucial to the properties of the resulting poly(aniline-co-pyrrole). More monomer applied in the polymerization of An and Py mixtures would result in products with similar properties to the individual homopolymer of that monomer, while poly(aniline-co-pyrrole) prepared from equimolar An and Py monomer displays unique properties. The conductivity is a non-linear function of chemical composition, and this chemical heterogeneity might lead to the broad DSC curves and various morphologies of the poly(aniline-co-pyrrole) copolymers.

A ferromagnetic γ-Fe2O3–MWCNT composite was prepared by a reverse microemulsion technique, and was transformed to a Fe/Fe3C–MWCNT composite by further heat-treatment in H2 atmosphere at 950 °C. TEM result suggests that MWCNTs are both surface decorated and filled with γ-Fe2O3 or Fe/Fe3C nanoparticles. The saturation magnetization and anisotropy field are particularly strong for Fe/Fe3C–MWCNT. The reflection loss of Fe/Fe3C–MWCNT is better than that of γ-Fe2O3–MWCNT at all frequencies between 2 and 18 GHz, resulting from enhanced magnetic loss and better matched characteristic impedance, rather than electric loss, as shown by the complex relative permeability μr=μ′r−jμ″rμr=μ′r−jμ″r and permittivity εr=ε′r−jε″rεr=ε′r−jε″r. The microwave absorbing properties can be modulated simply by manipulating the thickness of the prepared Fe/Fe3C–MWCNT composite for application in different frequency bands.

Structure parameters and field-dependent magnetic properties of BaFe12O19 nanoparticles synthesized from different Fe/Ba ratios by reverse micelle technique were investigated. Pure barium ferrite phase and best magnetic properties could be obtained for the sample prepared from Fe/Ba ratio of 11, with grain size in the range of 20–30 nm as shown by TEM. The existence of α-Fe2O3 in other materials obviously decreases the magnetization properties, but coercivities of the materials from Fe/Ba ratio of 9.5 and 10 are abnormally even higher than the prepared pure BaFe12O19. The abnormal high coercivities of some prepared materials were explained from anisotropy mechanisms of nanoparticles.

Nanometer β-Ni(OH)2, showed by XRD, was prepared by our supersonic coordination–precipitation method, with an average grain size of about 50 nm by TEM. Proton diffusion coefficient of nanometer Ni(OH)2 and spherical Ni(OH)2 were 1.93 × 10−11, and 5.50 × 10−13 cm2/s, respectively, with combination of chronocoulometry and cyclic voltammetry. Charge–discharge test of simulated batteries at 0.2 °C showed that addition of 8 mass% of our prepared nanometer Ni(OH)2 in nickel hydroxide electrodes led to increases in cathode discharge specific capacity (CDSC) by nearly 10% and the chargeability of the electrode by about 50 mAh/g, and a decrease in polarization. Cycle life test of AA-type MH-Ni batteries discovered that effect of nanometer Ni(OH)2 in increasing CDSC was more apparent for the first 100 cycles and not much difference was found after 350 cycles. XAS demonstrated a higher oxidation state of Ni in fully charged nanometer Ni(OH)2 composite electrode (Nano-E) and a lower one in discharged Nano-E, compared with micrometer Ni(OH)2 spherical electrodes (Micro-E). A larger structure distortion was found in Nano-E, offering more vacancies for proton diffusion. Thus conversion between Ni2+ and Ni3+ was promoted during the charge–discharge process, which was assumed to be one explanation of increasing CDSC with the addition of nanometer Ni(OH)2.

Nano-sized anatase TiO2 with exposed {001} facets was synthesized from lamellar protonated titanate precursor. Owing to small size (ca. 11 nm) and high surface area (155 m2 g−1), the crystals with 26.1% {001} facets exhibited markedly superior photoactivity to reference ca. 76 nm anatase TiO2 nanosheets with 88.4% {001} facets.