•Laminar-like CuS/RGO/CuS nanocomposite in-situ grown on Cu foam through a one-step hydrothermal process•CuS/RGO/CuS/Cu electrochemical sensor with ultrahigh-sensitivity and low detection limit•Glucose in blood was determined.A novel ultrasensitive nonenzymatic sensor was prepared by in-situ growing layered CuS/RGO/CuS (reduced graphene oxide, RGO) nanostructure on the Cu foam surface through a hydrotherm-assisted process. The CuS/RGO/CuS nanocomposite was characterized with X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectrometer (XPS) and field emission scanning electron microscopy (FESEM). This CuS/RGO/CuS/Cu was directly used as electrochemical sensor of glucose, and its performance was evaluated by cyclic voltammetry and amperometry techniques. The nonenzymatic biosensor exhibited ultrahigh linear sensitivities of 22.67 and 10.54 mA mM− 1 cm− 2 in the concentration ranges of 1–655 μM and 0.655–1.055 mM, respectively. The detection limit was determined to be 0.5 μM with the signal-to-noise of three. Furthermore the sensor showed good long-term stability and good performance in human blood analysis. The present work gives a new insight into facile preparation of metal sulfides/RGO/metal sulfides nanocomposite on its metal substrate and its potential application in nonenzymatic glucose sensor.CuS/RGO/CuS nanocomposite of lamellar structure was in-situ-grown on Cu foam through a one-pot hydrothermal approach. As-prepared CuS/RGO/CuS/Cu was directly served as a nonenzymatic glucose sensor with an ultrahigh sensitivity.

A nanocomposite consisting of CuO, reduced graphene oxide (rGO) and Cu2O nanoparticles was hydrothermally and in-situ deposited on a copper foil. The composite contains 3 kinds of interfaces, namely CuO/rGO, rGO/Cu2O and Cu2O/Cu. This facilitates redox reactions to occur between graphene oxide and the copper foil, and also leads to electrostatic attraction between the positively charged copper ions and negatively charged rGO. This, in turn, leads to improved electron and ion transfer. The modified foil is shown to directly act as a sensor for amperometric detection of both glucose (at 0.65 V vs SCE) and hydrogen peroxide (at −0.3 V). Figures of merit for sensing glucose (in 0.1 M NaOH) include (a) an ultrahigh sensitivity of 3401 µA·mM-1·cm-2, (b) a limit of detection as low as 0.10 μM, (c) a linear detection range extends from 0.5 μM to 8.3 mM, and (d) a response time of <0.5 s. As for sensing hydrogen peroxide (at pH 7), the sensitivity is 366.2 µA·mM-1·cm-2, the limit of detection is 0.05 μM, the linear range extends from 0.5 μM to 9.7 mM, and the response time is 0.8 s.

•RGO/FeS in-situ grown on Fe foil via facile one-pot hydrothermal method.•Fe foil served as the iron source of FeS, reductant of GO and current collector.•A porous structure with the interconnection of FeS nanosheets.•A bind-free supercapacitor electrode with excellent performance.RGO/FeS composites on Fe foil were successfully prepared via a facile one-pot hydrothermal method, in which Fe foil acted as Fe source of FeS, reductant of GO and subsequent current collector. As-prepared RGO/FeS was directly served as the electrode of supercapacitor which exhibited a high specific capacitance of 900 mF cm−2 (300 F g−1) and a superior cyclability of 97.5% maximum capacity retention after 2000 cycles. Furthermore, an asymmetric supercapacitor (ASC) was assembled using Ni(OH)2 as the positive electrode and RGO/FeS as the negative electrode. This ASC delivered a high power density of 20930.4 W kg−1 with an energy density of 11.63 Wh kg−1, or a high energy density of 27.91 Wh kg−1 at the power density of 2093.18 W kg−1, indicating RGO/FeS is a promising negative electrode of supercapacitor.A porous RGO/FeS composite was in-situ grown on Fe foil surface. This RGO/FeS was directly used as supercapacitor electrode, which exhibited excellent electrochemical performance: 900 mF cm−2 (300 F g−1) and 97.5% maximum capacity retention after 2000 cycles.Download high-res image (272KB)Download full-size image

Rational architectural design is the key to improve specific capacitance. Herein, we present a facile one-step hydrothermal process for the fabrication of a TiO2/RGO/MoO2 composite with an unprecedented 3D walnut-shaped hierarchical nanostructure, in which amorphous TiO2 is decorated on the RGO (reduced graphene oxide)/MoO2 surface via a Mo-involved in situ growth route on Mo net (TiO2/RGO/MoO2@Mo). This 3D structure coated with ultrafine arched nanorods is a great breakthrough in electrochemical performances of TiO2– or MoO2-based electrodes as it exhibits an extraordinary areal capacitance of 3927 mF cm−2 at 3 mA cm−2 (i.e. 1636 F g−1 at 1.25 A g−1) with only 3.5% capacitance loss after 5000 cycles. Such an excellent performance is benefitted from the following factors: (i) amorphous TiO2 sculptured MoO2 blocky particles supply more active-site accessibility and facilitate the accommodation of volume expansion. (ii) Arched MoO2 nanorods as well as the walnut-shaped spheres of the composite provide electron transfer paths. (iii) RGO is a soft scaffold, which relieves the volume expansion during the charge/discharge processes.

A roe-shaped ternary nanocomposite, Ni3(PO4)2/RGO/Co3(PO4)2 (NRC), was grown in situ on cobalt foam (CoF). The synthesis and loading of NRC on the CoF was completed through a one-step hydrothermal process by immersing the CoF in an aqueous solution of GO and Ni2+ in the presence of H2PO4−, in which the CoF served as the support, reductant and Co source. Three interfaces of Co3(PO4)2/CoF, RGO/Co3(PO4)2, and Ni3(PO4)2/RGO with strong interactions were constructed based on an in situ conversion reaction of Co to Co3(PO4)2, a redox reaction between GO and the CoF, and the electrostatic attraction force of Ni2+ and GO, respectively. The as-synthesized NRC@CoF had a hierarchically porous structure, and directly acted as a supercapacitor electrode and delivered excellent electrochemical performances: a specific capacitance of 10 237.5 mF cm−2 (1137.5 F g−1) at 5 mA cm−2 (0.56 A g−1) with a capacity retention of 117.8% after 14 000 cycles. Furthermore, NRC@CoF-based asymmetric supercapacitors (ASCs) exhibited a specific capacitance of 4845.9 mF cm−2 (115.4 F g−1) at 5 mA cm−2 (0.12 A g−1), and a high energy density of 44.82 W h kg−1 at a power density of 428.6 W kg−1, as well as good cyclic stability (91.9% after 18 000 cycles).

A Fe2O3/reduced graphene oxide (RGO)/Fe3O4 nanocomposite in situ grown on Fe foil was synthesized via a simple one-step hydrothermal growth process, where the iron foil served as support, reductant of graphene oxide, Fe source of Fe3O4, and also the current collector of the electrode. When it directly acted as the electrode of a supercapacitor, as-synthesized Fe2O3/RGO/Fe3O4@Fe exhibited excellent electrochemical performance with a high capability of 337.5 mF/cm2 at 20 mA/cm2 and a superior cyclability with 2.3% capacity loss from the 600th to the 2000th cycle.Keywords: Fe foil; Fe2O3/RGO/Fe3O4; graphene oxide; hydrothermal process; supercapacitor

Ti3C2Tx, a 2D titanium carbide in the MXenes family, is obtained from Ti3AlC2 through selective etching of the Al layer. Due to its good conductivity and high volumetric capacitance, Ti3C2Tx is regarded as a promising candidate for supercapacitors. In this paper, the fabrication of Ti3C2Tx/RGO composites with different proportions of Ti3C2Tx and RGO is reported, in which RGO acts as a conductive “bridge” to connect different Ti3C2Tx blocks and a matrix to alleviate the volume change during charge/discharge process. In addition, RGO nanosheets can serve as a second nanoscale current collector and support as well for the electrode. The electrochemical performance of the as-fabricated Ti3C2Tx/RGO electrodes, characterized by CV, GCD, and EIS, are also reported. A highest specific capacitance (Cs) of 154.3 F/g at 2 A/g is obtained at the Ti3C2Tx: RGO weight ratio of 7:1 combined with an outstanding capacity retention (124.7 F/g) after 6000 cycles at 4 A/g.

•A series of NF-based composites were synthesized in situ on nickel foam.•The composites were directly used as binder-free electrodes for Li-ion batteries.•The composite electrodes were first designed and fabricated for Li-ion batteries.•The composite electrodes were prepared by a simple one-step hydrothermal process.•The NRNN composite electrode exhibited a high reversible capacity.A series of nickel foam (NF)-based composites of MxOy/RGO/Ni(OH)2 [MxOy = Co3O4, MnO2, and Ni(OH)2] with diverse multilayer nano-architectures were designed and grown in situ on NF through a one-pot hydrothermal process. Based on the redox reaction between the active NF substrate and graphene oxide (GO), along with electrostatic forces between the Mn+ ions and GO in the solution, strong interactions take place at the interfaces of MxOy/RGO, RGO/Ni(OH)2, and Ni(OH)2/Ni, and thus, there is good contact for electron transfer. These MxOy/RGO/Ni(OH)2 samples were directly used as conductive-agent- and binder-free anodes for lithium ion batteries (LIBs), and the Ni(OH)2/RGO/Ni(OH)2/NF composite electrode showed a high specific capacity, good rate capability, and excellent cycling stability, especially, it had a high reversible capacity of about 1330 mAh g−1 even after 200 cycles at 100 mA g−1. This general strategy presents a promising route for the design and synthesis of various multilayer nano-architectural transition metal oxides (hydroxide)/RGO composites on NF as energy storage materials.A series of NF-based composites of MxOy/RGO/Ni(OH)2 [MxOy = Co3O4, MnO2, and Ni(OH)2] with diverse multilayer nano-architectures were designed and grown in-situ on nickel foam (NF) through a facile one-pot hydrothermal approach. These composites were directly used as conductive-agent- and binder-free anodes for LIBs, and the Ni(OH)2/RGO/Ni(OH)2/NF composite electrode exhibited a particularly high reversible capacity of about 1330 mAh g−1, even after 200 cycles at 100 mA g−1

A unique MoS2/RGO/MoS2 (MRMS) nanostructured composite is prepared on Mo net surface through an in-situ hydrothermal synthesis. During the synthesis process, Mo net serves as not only a support but also Mo source for the lower MoS2 layer and reductant of GO. MRMS samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM). As-synthesized MoS2/RGO/MoS2@Modirectlyactedassupercapacitorelectrodewhichexhibitedexcellentelectrochemicalperformance(*): A high capacity of 1138.5 mF cm−2 at 20 mA cm−2 (455.3 F g−1), and a capacity retention of 98.8% after 4000 running times. A symmetric supercapacitor device consisting of two MRMS electrodes was assembled, which exhibited an energy density of 6.22 Wh kg−1 and power density of 1.87 kW kg−1.

A facile one-step hydrothermal process is employed to synthesize a TiO2/RGO/Ni(OH)2 (reduced graphene oxide, RGO) composite on nickel foam (NF) by means of an in-situ growth route. In this case, NF acts as support, nickel source of Ni(OH)2, and supplement reductant of GO. For comparison, RGO nanosheets serve as nano-sized flexible support for connecting TiO2 and Ni(OH)2 blocks, which improves the electron transfer and alleviates the volume changes during the repeated charge/discharge process thanks to its high conductivity and mechanical properties. Besides, P25 (commercial TiO2 consisting of 80% anatase and 20% rutile) serves as TiO2 source, at different GO/P25 ratio of 1%, 2%, 5%, 10% and 20%. Electrochemical performances of TiO2/RGO/Ni(OH)2/NF electrode were evaluated by using cyclic voltammetry (CV), galvanostatic charge/discharge tests (GCD) and electrochemical impedance spectroscopy (EIS) in 1 M KOH electrolyte. The TiO2/RGO/Ni(OH)2/NF electrode exhibited significantly enhanced capacitive performance when the weight ratio of GO/P25 was 10%. It delivered high capability of 4342 mF cm−2 at a current density of 5 mA cm−2 (374.3 F g−1 at 0.43 A g−1), and excellent charge-discharge cycling stability with 93.75% capacitance retention after 2000 cycles. An asymmetric supercapacitor (ASC) device consisting of this TiO2/RGO/Ni(OH)2/NF and an AC negative electrode was assembled.

MoS2/RGO/Ni3S2 nanocomposite with a unique nanosheet-on-nanosheet structure was prepared through a hydrothermal process by depositing a MoS2 layer on the upper surface side of reduced graphene oxide (RGO) nanosheets and Ni3S2 layer on the lower surface sides. Furthermore, this, MoS2/RGO/Ni3S2 nanocomposite was simultaneously loaded on a Ni foam (NF) substrate. During the synthesis process, nickel foam serves not only as a support but also as the Ni source for the composite and a reductant of GO. When used as an electrochemical electrode, as-prepared MoS2/RGO/Ni3S2@NF, it exhibited excellent electrochemical performance with a high capacity of 8.841 F cm−2 at 50 mA cm−2, and excellent cyclability, exhibiting capacity retention of 98.4% after 11,000 charge-discharge cycles at the current density of 80 mA cm−2.A unique MoS2/RGO/Ni3S2 nanosheet-on-nanosheet composite was designed and constructed on Ni foam substrate. As prepared MoS2/RGO/Ni3S2 composite was directly utilized as supercapcacitor electrode, which performed superior electrochemical performance: a capacitance up to 8.841 F cm−2 at 50 mA cm−2 (1235.3 F g−1 at 7 A g−1), and retention 98.4% even after 11,000 cycles at high rate of 80 mA cm−2.

A three-layer nanostructure of a CuS/reduced graphene oxide (RGO)/Ni3S2 composite was in situ grown on nickel foam (NF) through a one-step hydrothermal-assisted process. During this process, the bottom Ni3S2 layer and middle RGO layer were simultaneously formed through the redox reaction of the Ni element on the foam surface of NF with GO and subsequent vulcanization. The upper CuS layer, consisting of sphere and fiber-like blocks, was converted from Cu2+ adsorbed by electrostatic forces and then well anchored on the RGO surface. The binder-free CuS/RGO/Ni3S2 electrode delivered high specific capacitance (10494.5 mF cm−2 at a current density of 40 mA cm−2, i.e., 1692.7 F g−1 at 6.5 A g−1). It also exhibited an excellent cycling stability with ca. 91.5% of the initial capacitance retention after 4000 charge–discharge cycles at a current density of 100 mA cm−2. The good electrochemical performance and simple accessibility prove that this CuS/RGO/Ni3S2 composite is a promising material for supercapacitor applications.

A unique structure consisting of two kinds of Ni(OH)2 layers on the top and the bottom, respectively, of the same reduced graphene oxide (RGO) layer has been designed and synthesized through a facile hydrothermal process. The lower layer of Ni(OH)2, covered with a thin RGO film, is transformed in situ from the surface of a Ni foam substrate through the redox reaction of elemental Ni and graphene oxide (GO), while the upper layer of Ni(OH)2 nanoflakes from Ni ions in the solution is vertically assembled on the top surface of the RGO of the lower RGO/Ni(OH)2 layer. This composite can be regarded as combining RGO with a “pseudocomposite” of Ni(OH)2 material because the upper and lower Ni(OH)2 layers are different in morphology, particle size, and Ni2+ source. The bottom layer mainly acts as a rough support, while the upper Ni(OH)2 is suitable to act as the main active material for supercapacitor electrodes. The lower layer of Ni(OH)2/RGO, however, plays key roles in forming the aligned structure and in the subsequent cycling stability. The composite film has a high areal mass loading of 4.7 mg cm−2, and superior supercapacitor performance. It features a specific capacitance of up to 15.65 F cm−2 (i.e., 3328.7 F g−1) at a current density of 7 mA cm−2 (1.5 A g−1) and a capacity retention of 90.6%, even after 5000 cycles at the high rate of 20 mA cm−2 (4.3 A g−1), indicating that it has a promising application as an efficient electrode for high-performance supercapacitors.

Co9S8, Ni3S2, and reduced graphene oxide (RGO) were combined to construct a graphene composite with two mixed metal sulfide components. Co9S8/RGO/Ni3S2 composite films were hydrothermal-assisted synthesized on nickel foam (NF) by using a modified “active metal substrate” route in which nickel foam acted as both a substrate and Ni source for composite films. It is found that the Co9S8/RGO/Ni3S2/NF electrode exhibits superior capacitive performance with high capability (13.53 F cm–2 at 20 mA cm–2, i.e., 2611.9 F g–1 at 3.9 A g–1), excellent rate capability, and enhanced electrochemical stability, with 91.7% retention after 1000 continuous charge–discharge cycles even at a high current density of 80 mA cm–2.Keywords: chemical redox; Co9S8/RGO/Ni3S2 composites; hydrothermal method; Ni foam; supercapacitor

A nanocomposite for supercapacitor electrode materials was designed and developed by integrating partially disabled Cu2O (low specific capacity, but high cycling ability) and Ni(OH)2 (low cyclability and high specific capacity) in the presence of reduced graphene oxide (RGO) nanosheets. Nanocomposite of Cu2O/RGO/Ni(OH)2 was directly grown on nickel foam (NF) through a facile one-pot hydrothermal process without any other reductant or oxidant, in which nickel foam acted as both a reductant of GO and Ni source, and a substrate for nanocomposite. The resultant Cu2O/RGO/Ni(OH)2 nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectrometer (XPS), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The electrochemical performance of the as-synthesized Cu2O/RGO/Ni(OH)2/NF electrodes were evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectrometry (EIS) in 6 mol L−1 KOH aqueous solution. This Cu2O/RGO/Ni(OH)2 nanocomposite exhibits superior capacitive performance: high capability (3969.3 mF cm−2 at 30 mA cm−2, i.e., 923.1 F g−1 at 7.0 A g−1), excellent cycling stability (92.4% retention even after 4,000 cycles, for RGO/Ni(OH)2/NF, 92.3% after 1,000 cycles), and good rate capacitance (50.3% capacity remaining at 200 mA cm−2).

A reduced graphene oxide (RGO)-based nanocomposite of redox counterpart of the oxides of Cu(I)-Cu(II) pair for Faradaic reaction, Cu2O/CuO/RGO, was controllably synthesized through a facile, eco-friendly one-step hydrothermal-assisted redox reaction of elemental Cu and graphene oxide (GO) without the addition of any other reagents. The resultant Cu2O/CuO/RGO nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, Thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). It is found that, when dealloyed nanoporous Cu was used as a Cu source, the uniform spherical Cu2O/CuO nanoparticles with double size scales (∼25 nm and ∼5 nm) were anchored on RGO sheets. This Cu2O/CuO/RGO nanocomposite redox counterpart exhibits improved rate capability and excellent cycling stability, i.e., only ca. 21.4% of the capacity was lost when the discharge current density increases from 1 A g−1 (173.4 F g−1) to 10 A g−1 (136.3 F g−1). Especially, the capacity remains almost unchanged (98.2%) after 100,000 cycles at 10 A g−1. The good electrochemical performance and simple accessibility prove that this Cu2O/CuO/RGO composite consisting of a pair of redox counterparts is a promising material for supercapacitor applications.

A unique sandwich structure of Ni3S2/RGO/Ni3S2 consisting of Ni3S2 nanosheets was designed and constructed on nickel foam (NF) by a one-step hydrothermal process. The lower Ni3S2 layer was converted in situ from the Ni foam substrate, while the upper Ni3S2 layer with vertical nanosheets resulted from Ni2+ ions in the solution. This Ni3S2/RGO/Ni3S2/NF nanocomposite was directly utilized as a supercapacitor electrode, which possessed a high areal mass loading of 5.2 mg cm−2, and superior performance: a specific capacitance of up to 16.82 F cm−2 (i.e., 3234.62 F g−1) at a current density of 20 mA cm−2 (3.85 A g−1) and 90% retention of the initial capacitance after 1000 cycles at the high rate of 100 mA cm−2 (19.23 A g−1).

•The in situ synthesis of RGO/ZnO on Zn foil through a one-step hydrothermal process.•No other reagent was needed apart from Zn foil and GO.•Good sensing performance of xanthine.A novel nonenzymatic xanthine (Xa) sensor was developed based on reduced graphene oxide (RGO)/zinc oxide (ZnO)/Zn foil. RGO/ZnO nanocomposites were grown directly on the surface of zinc foil through a hydrothermo-assisted redox reaction between graphene oxide (GO) and Zn foil. The as-synthesized RGO/ZnO/Zn foils were characterized through X-ray diffraction (XRD), Raman spectroscopy, and a field emission scanning electron microscope (FESEM), and the results confirmed that ZnO nanoparticles were dispersed highly inside RGO sheets. The RGO/ZnO/Zn foil was used directly as a xanthine electrochemical sensor, and its performance was evaluated through cyclic voltammetry and differential pulse voltammetry in a pH 7.0 phosphate buffer solution. This nonenzymatic biosensor showed a linear response to xanthine in concentrations ranging from 5 to 400 μM, with a sensitivity of 2.10 μA μM−1 cm−2 and a detection limit of 1.67 μM (S/N = 3). The present work supplies a new insight into the one-step preparation of graphene/metal oxide composite film on the conductive metal substrate and its application as an electrochemical sensor.Based on redox between graphene oxide and Zn foil, in situ-grown, reduced graphene oxide and zinc oxide on zinc foil were prepared by applying a simple one-pot hydrothermal approach. As-prepared RGO/ZnO/Zn foil was fabricated directly for a xanthine nonenzymatic biosensor.

Graphene/metal oxide composites have attracted considerable attention for various applications, such as energy storage, catalysts, and electronics, however, the lack of effective and environmentally friendly fabrication methods for obtaining uniform graphene/metal oxide nanocomposites on a large scale has been one of the main technical barriers to real applications. We have developed a simple, efficient, and environmentally benign approach to the synthesis of reduced graphene oxide (RGO)/metal oxide composites via hydrothermal reaction of graphene oxide and metal powder under mild reaction conditions. For iron oxide as an example, by controlling the ratio of graphene oxide to Fe powder (mGO/mFe), the hydrothermal temperature, and the addition of a mild oxidizing/reducing agent, the valence of Fe in the iron oxide products can be well tuned, i.e., various iron oxide/RGO composites, including RGO/Fe3O4, RGO/Fe3O4/Fe2O3, and RGO/Fe2O3, could be synthesized. RGO/FexOy composites in this study deliver a Li-ion storage capacity of 988.5 mA h g−1 at a current density of 100 mA g−1. After cycling at 500 mA g−1 for 300 cycles, a capacity of 868.4 mA h g−1 can still be maintained (with no capacity decay). When the current density is 2000 mA g−1, the capacity of 657.0 mA h g−1 is still retained, showing superior rate capability. The work described here provides a promising pathway to construct various graphene-based metal oxides as electrode materials for Li-ion batteries.

•A uniform 3D nest-like nanostructure of RGO/Ni3S2 nanocomposite on Ni foam, in-situ synthesized using a simple, green one-pot hydrothermal approach, exhibits superior capacitive performance (7440 mF cm−2 at 10 mA cm−2, i.e., 2188.8 F g−1 at 2.9 A g−1 and 1016 F g−1 at 29.0 A g−1).Highlights.•RGO/Ni3S2/NF composite was in-situ synthesized through a one-step hydrothermal process.•No other reagent except Ni foam, GO and S powder was added.•RGO/Ni3S2, RGO/Ni(OH)2, and RGO/Ni3S2/Ni(OH)2 can be controllably synthesized.•As-prepared RGO/Ni3S2/NF nanocomposite exhibits high capability and cyclability.A facile one-step solution-phase route to RGO/Ni3S2 on nickel foam (RGO/Ni3S2/NF) was presented. The RGO/Ni3S2/NF (RNS) nanocomposites were hydrothermal-assisted synthesized, in which nickel foam acted as an auxiliary reductant of GO and S, a Ni source of Ni3S2, and a substrate for composite film. RGO/Ni3S2/NF composites were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscope (FESEM), and transmission electron microscopy (TEM). The electrochemical performances of the supercapacitor with as-synthesized RGO/Ni3S2/NF (RNS) electrodes are evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectrometry (EIS) in 2 M KOH aqueous solution. It is found that the RGO/Ni3S2/NF electrode exhibits superior supercapacitor performance (7440 mF cm−2 at 10 mA cm−2, i.e., 2188.8 F g−1 at 2.9 A g−1), compared with the Ni3S2/NF electrode (4360 mF cm−2 at 10 mA cm−2) and the RGO/Ni(OH)2/NF electrode (3400 mF cm−2 at 10 mA cm−2) prepared under identical conditions. Both the temperature and sulfur content play important roles in the controlled synthesis of RNS and its electrochemical performance.

Reduced graphene oxide (RGO) on nickel hydroxide (Ni(OH)2) film was synthesized via a green and facile hydrothermal approach. In this process, graphene oxide (GO) was reduced by nickel foam (NF) while the nickel metal was oxidized to Ni(OH)2 film simultaneously, which resulted in RGO on Ni(OH)2 structure. The RGO/Ni(OH)2 composite film was characterized using by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscope (FESEM). The electrochemical performances of the supercapacitor with the as-synthesized RGO/Ni(OH)2 composite films as electrodes were evaluated using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectrometry (EIS) in 1 M KOH aqueous solution. Results indicated that the RGO/Ni(OH)2/NF composite electrodes exhibited superior capacitive performance with high capability (2500 mF cm−2 at a current density of 5 mA cm−2, or 1667 F g−1 at 3.3 A g−1), compared with pure Ni(OH)2/NF (450 mF cm−2 at 5 mA cm−2, 409 F g−1 at 3.3 A g−1) prepared under the identical conditions. Our study highlights the importance of anchoring RGO films on Ni(OH)2 surface for maximizing the optimized utilization of electrochemically active Ni(OH)2 and graphene for energy storage application in supercapacitors.

Novel visible light-driven phtotocatalysts composed by silver halides and graphitic carbon nitride (i.e. AgX@g-C3N4, X = Cl, Br, I) were synthesized by in situ precipitation of AgX nanoparticles on the surface of sheet-like g-C3N4. The resultant AgX@g-C3N4 nanocomposites were characterized with state-of-the-art instruments, showing significant enhancement in photocatalytic degradation of methyl orange under the irradiation of visible light. Their excellent photocatalytic performance is attributed to the efficient separation of photogenerated electron–hole pairs and their higher photostability in comparison with pure AgX.Graphical abstractHighlights► Novel AgX@g-C3N4 (X = Cl, Br and I) photocatalysts were prepared by in situ deposition. ► Excellent photo-activity and stability in degradation of organic dye. ► Efficient separation of photogenerated electrons and holes in nanocomposites. ► Synergetic effects of AgX and g-C3N4.

Ag/PPy (polypyrrole) composite colloids were prepared through the reaction of silver nitrate with pyrrole solution in DMF either in the dark, or under the irradiation of femtosecond laser (fs) pulse or UV lamp. The UV–vis spectra of the nanocomposite colloid display an intense absorption band around 620 nm, accompanied by a weak one around 470 nm. The colors and optical absorption spectra of as-synthesized colloids can be reversibly tuned between blue and red, corresponding to absorption band of 620 nm and 526 nm, within few seconds by adding base and acid solutions or gases in turn into the composite colloid suspension. In addition, excess of H+ solution enhanced the absorption band around 470 nm and, at the same time, depressed that around 620 nm. The possible mechanism for the formation and optical absorption properties of the Ag/PPy composite colloid was proposed.

Black phosphorus (BP) nanostructures such as nanosheets and nanoparticles have attracted considerable attention in recent years due to their unique properties and great potential in various physical, chemical, and biological fields. In this article, water-soluble and biocompatible PEGylated BP nanoparticles with a high yield were prepared by one-pot solventless high energy mechanical milling technique. The resultant BP nanoparticles can efficiently convert near infrared (NIR) light into heat, and exhibit excellent photostability, which makes them suitable as a novel nanotheranostic agent for photoacoustic (PA) imaging and photothermal therapy of cancer. The in-vitro results demonstrate the excellent biocompatibility of PEGylated BP nanoparticles, which can be used for photothermal ablation of cancer cells under irradiation with NIR light. The in-vivo PA images demonstrate that these BP nanoparticles can be efficiently accumulated in tumors through the enhanced permeability retention effect. The resultant BP nanoparticles can be further utilized for photothermal ablation of tumors by irradiation with NIR light. The tumor-bearing mice were completely recovered after photothermal treatment with BP nanoparticles, in comparison with mice from control groups. Our research highlights the great potential of PEGylated BP nanoparticles in detection and treatment of cancer.

Graphene/metal oxide composites have attracted considerable attention for various applications, such as energy storage, catalysts, and electronics, however, the lack of effective and environmentally friendly fabrication methods for obtaining uniform graphene/metal oxide nanocomposites on a large scale has been one of the main technical barriers to real applications. We have developed a simple, efficient, and environmentally benign approach to the synthesis of reduced graphene oxide (RGO)/metal oxide composites via hydrothermal reaction of graphene oxide and metal powder under mild reaction conditions. For iron oxide as an example, by controlling the ratio of graphene oxide to Fe powder (mGO/mFe), the hydrothermal temperature, and the addition of a mild oxidizing/reducing agent, the valence of Fe in the iron oxide products can be well tuned, i.e., various iron oxide/RGO composites, including RGO/Fe3O4, RGO/Fe3O4/Fe2O3, and RGO/Fe2O3, could be synthesized. RGO/FexOy composites in this study deliver a Li-ion storage capacity of 988.5 mA h g−1 at a current density of 100 mA g−1. After cycling at 500 mA g−1 for 300 cycles, a capacity of 868.4 mA h g−1 can still be maintained (with no capacity decay). When the current density is 2000 mA g−1, the capacity of 657.0 mA h g−1 is still retained, showing superior rate capability. The work described here provides a promising pathway to construct various graphene-based metal oxides as electrode materials for Li-ion batteries.

A unique structure consisting of two kinds of Ni(OH)2 layers on the top and the bottom, respectively, of the same reduced graphene oxide (RGO) layer has been designed and synthesized through a facile hydrothermal process. The lower layer of Ni(OH)2, covered with a thin RGO film, is transformed in situ from the surface of a Ni foam substrate through the redox reaction of elemental Ni and graphene oxide (GO), while the upper layer of Ni(OH)2 nanoflakes from Ni ions in the solution is vertically assembled on the top surface of the RGO of the lower RGO/Ni(OH)2 layer. This composite can be regarded as combining RGO with a “pseudocomposite” of Ni(OH)2 material because the upper and lower Ni(OH)2 layers are different in morphology, particle size, and Ni2+ source. The bottom layer mainly acts as a rough support, while the upper Ni(OH)2 is suitable to act as the main active material for supercapacitor electrodes. The lower layer of Ni(OH)2/RGO, however, plays key roles in forming the aligned structure and in the subsequent cycling stability. The composite film has a high areal mass loading of 4.7 mg cm−2, and superior supercapacitor performance. It features a specific capacitance of up to 15.65 F cm−2 (i.e., 3328.7 F g−1) at a current density of 7 mA cm−2 (1.5 A g−1) and a capacity retention of 90.6%, even after 5000 cycles at the high rate of 20 mA cm−2 (4.3 A g−1), indicating that it has a promising application as an efficient electrode for high-performance supercapacitors.