Self-powered photodetectors (SPPDs) are promising candidates for high-sensitivity and high-speed applications because they do not require batteries as an external power source. It is a challenge to fabricate visible-light photodetectors. Herein, vertically aligned two-dimensional (2D) Sn3O4 nanoflakes on carbon fiber paper were prepared by a modified hydrothermal approach and used as a self-powered photoelectrochemical cell-type visible-light detector. The detector exhibits reproducible and flexible properties as well as an enhanced photosensitive performance. The improved photoresponse was attributed to the synergistic effects of the vertically grown Sn3O4 nanoflakes and carbon fiber paper substrate; the former provided efficient active sites, as it exposed more catalytic sites to the electrolyte and absorbed more light scattered among the nanoflakes, and the latter benefited charge transport. The photocatalytic activity of the three-dimensional (3D) Sn3O4 hierarchal structure on rhodamine B under visible-light irradiation was investigated and shown to have a degradation rate constant of 3.2 × 10–2 min–1. The advantage over ordinal materials for use in an SPPD device is that this material is flexible and easily recoverable as a photocatalyst.

Metal oxide nanostructure detectors must adsorb both oxygen molecules and incident light to achieve ultrahigh photogain. However, the oxygen adsorption and desorption process can prolong the photoresponse time of the photogain. Therefore, it is a challenge to fabricate such metal oxide nanostructures that have the ability to adsorb both oxygen molecules and incident light simultaneously to generate large amounts of carriers under light illumination, using a simple preparation method. In this work, self-connected core–shell SnO2 microspheres were prepared and used as a photodetector. The interconnected SnO2 device exhibited improved photoresponse properties with photocurrent of 15.4 μA at room temperature, representing a nearly 43-fold enhancement compared with traditional photodetectors. The underlying mechanism for this process was revealed by Hall mobility versus temperature and photocurrent versus power intensity characteristics. We found that conducting channels among the tightly interconnected microspheres are mainly responsible for the improved photocurrent response, providing effective paths for electron transport as well as available sites for charge carrier accumulation.

Undoped ZnS microspheres with a size of 4–5 μm were produced using a hydrothermal method with different ratios of Zn and S precursors. Structural and morphological measurements show that the sphalerite ZnS microspheres have a cavity surface self-assembled with nanoplates with a thickness of 20–30 nm. Experimentally measured magnetic hysteresis curves for the undoped ZnS microspheres clearly indicate ferromagnetic behavior at room temperature with a saturation magnetization Ms = 3.66 and 1.566 memu g−1 for an atomic ratio of Zn to S equal to 0.966 and 1.32, respectively. The calculations based on density functional theory within the generalized gradient approximation + Hubbard U (GGA + U) approach demonstrated that the ZnS (111) surface with Zn vacancies produces a ferromagnetic state with a magnetic moment per unit cell of 2.0 μB; the defective ZnS (111) surface with mixed Zn and S vacancies has a reduced magnetic moment of 1.12 μB because of the structural reconstruction, while the defective ZnS (111) surface with only S vacancies is non-magnetic. The observed weak ferromagnetism for the ZnS microspheres can be ascribed to the Zn vacancies and the cavity surface; the latter results in a large number of unsaturated bonds for the S and Zn atoms at the interfacial and surface regions. These studies will be helpful for understanding the d0 ferromagnetism.

A facile and high-throughput strategy is presented to fabricate three-dimensional hierarchically porous Au films with good flexibility and transferability via displacement reaction of a Ag-coated electrospun nanofiber template. The films are constructed by mesoporous Au nanotubes, homogeneous in the macroscale but rough and porous in the nanoscale. Each nanotube-block is micro/nanostructured with evenly distributed mesopores on the tubewalls. Further experiments have revealed that the Ag sputtering time and displacement reaction conditions are the key influential factors determining the film architecture. Such structured film has exhibited significant surface-enhanced Raman scattering activity with good stability and reproducibility and shown the possibility of molecule-level detection. Additionally, the strategy is general for fabricating other hierarchically porous Au films, such as mesoporous Au hollow sphere arrays.

•A facile route was employed to engineer the sulfur vacancies and impurities in NiCo2S4.•Effects of sulfur vacancies and impurities on the nanomaterial supercapacitive properties were clearly identified.•An optimal supercapacitive performance integrating high specific capacitance, favorable rate capability and long-term cyclic stability was achieved.High efficiency supercapacitors require the electrode materials which integrate high specific capacitance, favorable rate capability and long-term cyclic stability. These features are often associated with vacancies and impurities in the electrodes. Understanding the mechanism behind the related process provides a deep insight into improved supercapacitive performance. Here we present the synthesis of spinel structured nickel cobalt sulfide (NiCo2S4) nanomaterials with tunable sulfur vacancy concentrations and impurities by controlling the sulfurization process. The effects of these defects on the nanomaterial supercapacitive properties were then clearly identified. Interestingly, on one hand, the sulfur vacancies were found to increase the specific capacitance by improving electrical conductivity, while, on the other hand, they hindered the rate capability and cyclic stability due to the increased crystal structure disordering. An optimal supercapacitive performance was achieved, namely, high specific capacitance, favorable rate capability and long-term cyclic stability were documented for both three-electrode system and solid-state asymmetric supercapacitor device. These results have significant implications for the design and optimization of pseudocapacitive properties of transition metal compounds.

A simple and green strategy is presented to decorate graphene with nanoparticles, based on laser ablation of targets in graphene auqeous solution. Ag and graphene oxide (GO) are chosen as model materials. The surface of GO sheets is strongly anchored with spherical Ag nanoparticles. The density and size of the Ag nanoparticles can be easily tuned by laser ablation conditions. Further, the GO sheets can be decorated with other nanoparticles from simple metals or semiconductors to multicomponent hybrids. Additionally, the Ag nanoparticle/GO sheet colloids can be utilized as blocks to build three-dimensional structures, such as sandwich membranes by evaporation-induced self-assembly. These graphene-based composite materials could be very useful in catalysis, sensors, and nanodevices. Particularly, the Ag nanoparticle/GO sheet sandwich composite membranes exhibit excellent surface-enhanced Raman scattering performance and possess the huge potential in trace-detecting persistent organic pollutants in the environment.

A simple and green strategy is presented to fabricate Ag-decorated ZnO nanorod arrays based on electrophoretic deposition in a Ag colloidal solution prepared by laser ablation in water. The edges or corners of each nanorod's upper surface feature dendritic aggregates consisting of nanoparticles, and the other surfaces exhibit irregular particles of less than 200 nm in size. Overall, the created Ag nanostructure/ZnO nanorod is hierarchically micro/nanostructured and very rough at the nanoscale. The inter-particle spacings in the decoration layer are nanometers to tens of nanometers in scale. Further experiments have revealed that suitable electrophoretic potential and sufficient growth duration are crucial for obtaining complete coverage on every nanorod. The site-specific deposition of Ag nanoparticles on ZnO nanorods can be explained by the different distributions of the electric field and the colloidal concentration during electrophoresis. Such heterogeneous nanorod arrays are functionalized and exhibit excellent surface-enhanced Raman scattering performance. This study provides a new method for creating decorated nanorod arrays with novel nanostructures by using unstable colloidal nanoparticles as building blocks and deepens the understanding of the physical mechanisms of electrophoretic deposition.

A facile one-pot hydrothermal method was developed to synthesize a CoMoO4/Co3O4 hybrid nanostructure where CoMoO4 nanosheets were supported by a hierarchical framework assembled by Co3O4 nanorods. The morphology and structure of this three dimensional nanocomposite were characterized in detail and a rational growth mechanism was proposed based on them. The unique structural features of our CoMoO4/Co3O4 hierarchical nanohybrid allow for high specific surface and multiple faradaic redox reactions for electrode materials of supercapacitors. Consequently, a high specific capacitance (1062.5 F g−1 at the current density of 1 A g−1) and an excellent cyclic performance (90.38% of the initial capacitance retained after 2000 cycles at a current density of 20 A g−1) were obtained. In addition, an asymmetric supercapacitor with high energy density of 31.64 W h kg−1 was achieved at a power density of 7270 W kg−1. This work thus provides an excellent candidate for high-performance supercapacitor fabrication.

Hierarchical porous ZnO microspheres decorated with gold nanoparticles (AuNPs) were successfully synthesized by a facile solvothermal route. The hierarchical ZnO superstructure was constructed of interconnected nanoplates with numerous voids. Photoluminescence, X-ray photoelectron spectroscopy, and electron paramagnetic resonance measurements demonstrated that the main defects were oxygen vacancies (VO•) with minor interstitial oxygen (Oi–) in the hierarchical ZnO hollow microspheres. The as-prepared hierarchical ZnO hollow microspheres and the AuNPs used to decorate them were examined for their photocatalytic degradation ability and as gas sensors. The photodegradation results demonstrated that the degradation rate constant on rhodamine B for undecorated ZnO microspheres was 0.43 min–1, which increased to 1.76 min–1 for AuNP-decorated ZnO microspheres. The AuNP-functionalized ZnO microspheres displayed superior sensing properties, with a 3-fold enhancement in their gas response to 1 ppb of dibutyl phthalate.Keywords: hollow microspheres; photocatalytic; sensing properties; ZnS;

Spontaneous structure transition is an important process in the formation of normal crystals, which determines the structure and properties of the final products. However, it is difficult to study this process in an atom system experimentally. As an alternative, a detailed experimental study of this process in a nanoparticle system is reported here.

A simple and green strategy is presented to fabricate CuO quantum dot-assembled nanospheres based on laser ablation of Cu metal targets in water. The colloidal nanospheres are mesoporous, with an average size of approximately 200 nm. Furthermore, the quantum dots, as a building block, can be easily tuned in size by changing the laser power. Importantly, such mesoporous nanospheres exhibit good photocatalytic activity due to their unique structure.

Typical morphology substrates can improve the efficiency of surface-enhanced Raman scattering; the need for SERS substrates of controlled morphology requires an extensive study. In this paper, one-dimensional ZnS:Al nanostructures with the width of approximately 300 nm and the length of tens um, and micro-scale structures with the width of several um and the length of tens um were synthesized via thermal evaporation on Au-coated silicon substrates and were used to study their size effects on Raman scattering and photoluminescent spectra. The photoluminescence spectra reveal the strongest green emission at a 5 at% Al source, which originates from the Al-dopant emission. The Raman spectra reveal that the size and morphology of the ZnS:Al nanowires greatly influences the Raman scattering, whereas the Al-dopant concentration has a lesser effect on the Raman scattering. The observed Raman scattering intensity of the saw-like ZnS:Al nanowires with the width of tens nm was eight times larger than that of the bulk sample. The enhanced Raman scattering can be regarded as multiple scattering and weak exciton—phonon coupling. The branched one-dimensional nanostructure can be used as an ideal substrate to enhance Raman scattering.

Silicon nanowires with vertical, slanting and zigzag architectures have been fabricated by metal-assisted chemical etching of silicon wafers (n-Si(100), n-Si(111) and n-Si(110)). Two types of zigzag SiNWs with various turning angles (125° and 150°) were obtained via metal-assisted chemical etching using non-Si(100) wafers. The observations reveal that the etching direction of non-Si(100) wafers depends on the shape of the deposited metal catalyst. A proposed mechanism, considering longitudinal and lateral etching, has been developed to explain the etching behaviors.

Flower-like hollow microspheres were synthesized on a large scale using a one-step hydrothermal route. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy. The results showed that the shells of the hollow microspheres were composed of numerous type II SnO/Sn3O4 heterostructures. A 500 °C annealing treatment changed the type II SnO/Sn3O4 heterostructures into type I SnO2/Sn3O4 heterostructures; at 700 °C, the products were pure SnO2 semiconductors. A photocatalytic degradation test showed that the highest efficiency degradation of rhodamine B (RhB) was obtained using type II SnO/Sn3O4 heterostructure semiconductors with a degradation rate constant of 2.3 × 10−3 min−1. This highly efficient activity was induced by enhanced charge separation in type II SnO/Sn3O4 heterostructure semiconductors.

•ZnS:Mn films were deposited on GaN substrates by the pulsed laser deposition method.•The blue (465 nm) and orange (600 nm) dual color emissions can be tuned by deposition temperature and annealing temperature.•The broad orange emission (600 nm) consists of two emission bands centered at 590 and 615 nm.•The peak emission at 600 nm shows a blue shift from 5 to 70 K, then a red shift up to 300 K.ZnS:Mn thin films have been grown on GaN substrates by pulsed laser deposition, and their structures and optical properties have been investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and electron paramagnetic resonance. The ZnS:Mn thin films have a cubic structure that is oriented mainly along the (1 1 1) plane. The crystal quality was optimized by varying the deposition conditions. Room temperature PL measurements with a 325 nm excitation source show that there are three emission bands located at 434 nm, 465 nm and ~600 nm. The intensity ratio of the blue emission bands (434 nm, 465 nm) to the orange (600 nm) was determined by the deposition conditions. The broad orange emission consisted of two emission bands centered at 590 and 615 nm, and it exhibited a red shift for measurement temperatures between 5 and 70 K, followed by a blue shift at temperatures up to 300 K. The tunable blue and orange dual color emissions make this material a candidate for use as a warm white lighting emitting device.

Nanoparticle clusters are usually referred to as colloidal molecules due to their composition, configuration and gap dependent properties. Here, we report a general strategy for high yielding fabrication of homo- and hetero-nanoparticle clusters on a substrate with controlled configuration and gap through a self-assembly process mediated by electrostatic interaction.

ZnS ceramics were successfully synthesized by the solid-state reaction method under different conditions. The structural transformation of ZnS ceramics from zinc-blende to hexagonal wurtzite was observed with the help of X-ray diffraction (XRD). The hexagonal wurtzite ZnS ceramics with much better quality were obtained at a sintering temperature of 1100 °C and for 100 min sintering time, meanwhile the relative density reaches 94%. Room temperature photoluminescence measurements with 325 nm excitation showed four emission bands, that is, the near band edge (NBE) emission band at ∼342 nm, the emission band of ∼407 nm from the sulfur vacancies, the emission peak at 488 nm which was explained as the radioactive transition from the conduction band to the energy level of zinc vacancies, and the green emission band at 525 nm which was attributed to the recombination of electrons from the energy level of sulfur vacancies with the holes from the line or surface defects. The observed green PL emission of the wurtzite-type ZnS ceramics could provide an interesting application in the development of novel luminescent devices.Highlights► ZnS ceramics were successfully synthesized by the solid-state reaction method in argon atmosphere under different conditions. ► The structural transformation of ZnS ceramics from zinc-blende to hexagonal wurtzite was observed. ► Blue and green emissions were observed from the room temperature photoluminescence (PL) measurements of ZnS ceramics.

In this paper, microsaws and microtowers have been prepared by vapor–liquid–solid (VLS) and vapor–solid (VS) methods, respectively, which are based on thermal evaporation. The role of Au catalyst in defining the morphology of the ZnS microstructures has been found. The microsaws were synthesized onto the sapphire substrate in the presence of Au catalyst, and the microtowers were produced onto Au-uncoated sapphire substrate. The microstructural changes were studied through a scanning electron microscope. The structural characterization of the microstructures was indicated by X-ray diffraction and a high-resolution transmission electron microscope. Room temperature photoluminescence measurements with 325 nm excitation showed four emission bands located at ∼400 nm, ∼480 nm, ∼520 nm and ∼580 nm.Graphical abstractHighlights► Microsaws and microtowers were synthesized onto Au-coated and Au-uncoated sapphire substrate, respectively, as shown in Fig. 1(a, b). ► Without Au catalysts, the high intensity of diffraction peaks reveals the growth direction along the [001] direction, as shown in Fig. 1c. ► New yellow emission band at 580 nm was observed for both the ZnS microtowers and microsaws.

Different sizes of CdS nanobelts were synthesized at 800, 850, and 900 °C by the thermal evaporation of CdS powders on Au-coated silicon substrates and were used to study the size effects of Raman scattering and photoluminescent spectra. The Raman spectra of CdS nanobelts clearly exhibit first- and second-order longitudinal optical (LO) Raman peaks, surface phonon peaks, and multiphonon processes when excited using a wavelength of 532 nm. The mechanism of exciton–phonon coupling was observed to be mainly associated with the Fröhlich interaction, and the coupling strength of the exciton–phonon increases with increasing lateral size. Compared with a larger CdS nanobelt, a narrower nanobelt exhibits a larger tensile strain. Recombination of free excitons (FX), excitons bound to neutral impurities (A0X), and donor–acceptor pairs (DAP) were identified from a low-temperature PL spectrum. At temperatures below ∼123 K, a red shift of the FX energy occurs with decreasing lateral size due to a larger uniaxial tensile strain; at temperatures above ∼123 K, a red shift of the FX energy occurs with increasing lateral size because of the reabsorption of the emitted light inside the thicker belt, indicating that the FX energy is affected by both the tensile strain and the surface-depletion-induced quantum confinement (the reabsorption of the emitted light) in the nanobelt.

In this paper, we report the first successful growth of (3C-ZnS)n/(2H-ZnS)m superlattice structures in Mn-doped ZnS nanoribbons prepared on Au-coated Si substrates by a chemical vapor transport method. The lattice-resolved HRTEM image presents the self-assembled (3C-ZnS)(111)/(2H-ZnS)(100) superlattices, where both the (3C-ZnS) ZnS atom layer and the (2H-ZnS) atom layer are alternately arrayed in the plane of nanoribbons along the axis growth direction. The individual Mn-doped ZnS nanoribbons, with uniform widths ranging from 100 to 800 nm and lengths ranging from tens to one hundred micrometers, are composed of the hexagonal wurtzite atom layers growing along the [100] axis direction and [001] vertical direction and the zinc-blende atom layers growing along the ⟨111⟩ direction. An identical strong photoluminescence transition peak at 580 nm was observed for all ZnS:Mn samples, and the peak intensity reaches a maximum with a Mn content of 0.68 atom % from the EDX analysis in 2 atom % Mn-doped ZnS samples.

A facile one-pot hydrothermal method was developed to synthesize a CoMoO4/Co3O4 hybrid nanostructure where CoMoO4 nanosheets were supported by a hierarchical framework assembled by Co3O4 nanorods. The morphology and structure of this three dimensional nanocomposite were characterized in detail and a rational growth mechanism was proposed based on them. The unique structural features of our CoMoO4/Co3O4 hierarchical nanohybrid allow for high specific surface and multiple faradaic redox reactions for electrode materials of supercapacitors. Consequently, a high specific capacitance (1062.5 F g−1 at the current density of 1 A g−1) and an excellent cyclic performance (90.38% of the initial capacitance retained after 2000 cycles at a current density of 20 A g−1) were obtained. In addition, an asymmetric supercapacitor with high energy density of 31.64 W h kg−1 was achieved at a power density of 7270 W kg−1. This work thus provides an excellent candidate for high-performance supercapacitor fabrication.

A simple and green strategy is presented to fabricate Ag-decorated ZnO nanorod arrays based on electrophoretic deposition in a Ag colloidal solution prepared by laser ablation in water. The edges or corners of each nanorod's upper surface feature dendritic aggregates consisting of nanoparticles, and the other surfaces exhibit irregular particles of less than 200 nm in size. Overall, the created Ag nanostructure/ZnO nanorod is hierarchically micro/nanostructured and very rough at the nanoscale. The inter-particle spacings in the decoration layer are nanometers to tens of nanometers in scale. Further experiments have revealed that suitable electrophoretic potential and sufficient growth duration are crucial for obtaining complete coverage on every nanorod. The site-specific deposition of Ag nanoparticles on ZnO nanorods can be explained by the different distributions of the electric field and the colloidal concentration during electrophoresis. Such heterogeneous nanorod arrays are functionalized and exhibit excellent surface-enhanced Raman scattering performance. This study provides a new method for creating decorated nanorod arrays with novel nanostructures by using unstable colloidal nanoparticles as building blocks and deepens the understanding of the physical mechanisms of electrophoretic deposition.