Two-step Hydrothermal Process Research Articles

Ni-Co Selenide Nanosheet/3D Graphene/Nickel Foam Binder-Free Electrode for High-Performance Supercapacitor.

Transition-metal selenide electrodes have recently attracted increasing interest in supercapacitors resulting from their superior electrochemical performance, lower-cost, and environmental friendliness. Herein, we report a novel bimetallic Ni-Co selenide nanosheet/three-dimensional (3D) graphene/nickel foam binder-free electrode (NiCo2.1Se3.3 NSs/3D G/NF) prepared via chemical vapor deposition followed by a simple two-step hydrothermal process in this paper. The NiCo2.1Se3.3 NSs array vertically on 3D G/NF with a uniform and stable structure without using any chemical binders. This novel electrode is flexible, highly conductive, and exhibits an excellent specific capacitance of ∼742.4 F g-1 at 1 mA cm-2. Furthermore, with a 10-fold increase to 10 mA cm-2, it still retains 471.78 F g-1 and a high cycling stability of ∼83.8% of the initial retention after 1000 cycles at 10 mA cm-2, demonstrating that NiCo2.1Se3.3 NSs/3D G/NF binder-free electrode has potential for energy storage application in high-performance supercapacitor fields.

Hierarchical structures of coated TiO2 nanoribbons with photodegradation and sedimentation properties

TiO2 hierarchical structure composed of H2Ti3O7 nanoribbons and TiO2 anatase nanoparticles was synthesized via a two-step hydrothermal process, including the recrystallization of TiO2 precursor into nanoribbons and the subsequent deposition of TiO2 nanoparticles on nanoribbon surface. The coated nanoribbons exhibited a good photocatalytic activity to degrade Rhodamine B (RhB) with a kinetics constant of 0.0269/min, 10 times higher than that of the as-produced nanoribbon (0.0026/min). They also possess good sedimentation properties compared to the pristine TiO2 anatase particles. The excellent photocatalytic performance together with sedimentation property makes these hybrid nanostructures effective and recyclable photocatalysts for wastewater treatment in industrial applications.

Synthesis of 1D to 3D nanostructured NiCo2S4 on nickel foam and their application in oxygen evolution reaction

Design of highly efficient, stable and low-cost water oxidation electrocatalysts continues to be a great impetus and significant challenge for renewable energy systems. In this paper, four diverse morphologies of NiCo2S4 including one-dimensional nanoneedles, two-dimensional nanosheets, three-dimensional flower-like and caterpillar-like arrays are direct grown on nickel foam via a facile two-step hydrothermal process. Influences of synthesis conditions on forming process, morphology, constitution and properties are discussed in detail. Results show that caterpillar-like NiCo2S4 catalyst displays the best electrocatalytic activity toward oxygen evolution reaction, which only needs an overpotential of 279 mV to deliver a current density of 50 mA·cm−2 and the Tafel slope is 68 mV/dec in 1 M KOH. Furthermore, caterpillar-like NiCo2S4 demonstrates excellent stability with inappreciable change of current density after 20 h of oxygen release. This work provides a wide range of possibilities for the further development of cost-effective high efficient electrocatalyst towards oxygen evolution reaction.

Coaxial-cable hierarchical tubular MnO2@Fe3O4@C heterostructures as advanced anodes for lithium-ion batteries

Nanostructured manganese oxides have been regarded as promising anodes for lithium-ion batteries (LIBs) due to their high specific capacity, environmental friendliness and low cost. However, as conversion-type electrodes, their scalable utilization is hindered by intrinsically low reaction kinetics, large volume variation and high polarization. Herein, a coaxial-cable tubular heterostructure composed of a hollow carbon skeleton, Fe3O4 nanoparticles and ultrathin MnO2 nanosheets from inside out, donated as MnO2@Fe3O4@C, is synthesized via a facile two-step hydrothermal process. The unique design integrates conductive carbon and nanostructured MnO2 and Fe3O4 into a one-dimensional (1D) hierarchically open architecture, which provides abundant electrode–electrolyte contact areas, favorable heterointerfaces and ultrafast electron/ion pathways. Benefiting from these features, the MnO2@Fe3O4@C anode exhibits a high reversible capacity of 946 mAh g−1 at 200 mA g−1 after 160 cycles, and excellent cyclability with a specific capacity of 845 mAh g−1 at 500 mA g−1 after 600 cycles. This work might provide an insightful guideline for the design of novel electrode materials.

Fabrication of core–shell CoFe2O4@HAp nanoparticles: a novel magnetic platform for biomedical applications

Biocompatible core–shell CoFe2O4@HAp magnetic nanoparticles were successfully prepared by a simple two-step hydrothermal process, and their physicochemical and magnetic properties were studied.

Synthesis of Superparamagnetic Cu0.4Zn0.6Fe2O4-Implanted Bi2S3-Capped TiO2 2D and 3D Nanostructures for Visible Light Photocatalysis.

Sharp narrow nanopetal-like and wrinkled nanoball-like cubic Cu0.4Zn0.6Fe2O4-implanted orthorhombic Bi2S3-capped anatase TiO2 heterostructures have been synthesized by a two-step hydrothermal process in acidic and basic environments. They have been characterized by high-resolution scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, selected area electron and powder X-ray diffractometries, vibrating sample magnetometry, UV–visible diffuse reflectance and photoluminescence spectroscopies, and nitrogen adsorption–desorption analysis. Both the nanostructured composites are superparamagnetic. While the nanocomposite synthesized in acidic environment absorbs in the entire visible and UV spectral regions, the absorption edge of nanocomposite obtained in basic environment narrowly misses the red end of the visible spectrum. The emission spectra of both the nanomaterials are strikingly similar, indicating similar crystal defects in anatase TiO2 lattice of both the nanocomposites. Although both the nanocomposites degrade dye under visible light, the photocatalytic activity of the sample obtained in acidic environment is superior to that prepared in basic condition. The enhanced photocatalytic activity of the nanocomposite synthesized in acidic environment is rationalized in terms of nanostructure, surface area, and optical properties.

In situ hydrothermal growth of metallic Co9S8-Ni3S2 nanoarrays on nickel foam as bifunctional electrocatalysts for hydrogen and oxygen evolution reactions

Conductivity and morphology are the two important factors affecting the performance of electrocatalysts. In this article, a facile two-step hydrothermal process was developed to grow Co9S8-Ni3S2 nanoarrays on nickel foam (Co9S8-Ni3S2 NAs/NF). The as-obtained catalyst possessed a novel morphology, in which the Co9S8 nanoneedles were surrounded by Ni3S2 ultrathin nanosheets. The resultant Co9S8-Ni3S2 nanoarrays not only permitted more exposures of active sites but also facilitated the charges and ions transport along the nanoarrays. Moreover, both Co9S8 and Ni3S2 exhibited metallic properties allowed the catalysts with conductivity (metallic conductor vs. semiconductor). Co9S8-Ni3S2 NAs/NF exhibited excellent electrocatalytic activities for both HER and OER in 1.0 M KOH solution. To reach a large current density of 100 mA cm−2, it only required overpotentials of 204 mV and 346 mV for HER and OER, respectively. After long-term electrolysis, the high activities were still preserved. This work indicates efficient electrocatalysts can be obtained by the rational design of the heterostructure, which sheds some light on the development of noble metal-free electrocatalysts.

Bi 2 O 3 quantum dots decorated TiO 2 nanobelt heterojunctions with enhanced visible‐light photoactivity

Bi2O3 quantum dots decorated TiO2 nanobelt heterojunctions were synthesised by a facile two-step hydrothermal process. The Bi2O3 quantum dots highly dispersed on the surface of TiO2 nanobelts resulted in more photosensitising sites and Bi2O3–TiO2 heterojunctions, leading to the enhanced absorbance for visible light. The strong Bi2O3–TiO2 interaction promoted the rapid transfer of photoelectrons from Bi2O3 to TiO2 and thus inhibited their recombination with holes. Meanwhile, the high-surface area facilitated the adsorption and diffusion of reactant molecules. As a result, this photocatalyst exhibited highly enhanced photoactivity in degradation of organic dyes under visible-light irradiation, which also displayed strong durability owing to the strong Bi2O3–TiO2 interaction against the leaching of Bi2O3 quantum dots.

Hollow rod-like hybrid Co2CrO4/Co1−xS for high-performance asymmetric supercapacitor

A hollow rod-like hybrid of Co2CrO4/Co1−xS is synthesized via a facile two-step hydrothermal process, and the mass ratio for Co2CrO4–Co1−xS in the hybrid is optimized. The Co2CrO4/Co1−xS electrode exhibits excellent properties with high specific capacitance of 1580 F g−1 at current density of 1 A g−1 and possesses good rate performance. An asymmetric supercapacitor of Co2CrO4/Co1−xS//AC is assembled, which can be operated within a voltage range of 0–1.6 V, demonstrating specific capacitance of 92.3 F g−1, energy density of 32.8 Wh kg−1 and highest power density of 4003.3 W kg−1. Moreover, the specific capacitance of the device remains 88% after 5000 cycles. The good characteristics of Co2CrO4/Co1−xS//AC can be ascribed to the hollow rod-like structure and the positive synergistic effects of Co2CrO4 and Co1−xS components in the hybrid. The unique structure and superior performances render Co2CrO4/Co1−xS hybrid as a promising candidate for energy storage device.

Assembly of surface-defect single-crystalline strontium titanate nanocubes acting as molecular bricks onto surface-defect single-crystalline titanium dioxide (B) nanorods for efficient visible-light-driven photocatalytic performance

Ti3+ self-doped single-crystalline SrTiO3−x nanocubes acting as molecular bricks are successfully assembled onto Ti3+ self-doping single-crystalline TiO2−x(B) nanorods through an effortless two-step hydrothermal process coupled with an in situ solid-state chemical reduction method. SrTiO3−x nanocubes act as molecular bricks, which are uniformly assembled onto the surface of TiO2−x(B) nanorods due to lattice matching. The band gap of the resultant SrTiO3−x/TiO2−x(B) sample is ∼2.97 eV, which exhibits excellent photocatalytic performance for the reduction of Cr(VI) and hydrogen production under visible light. The apparent rate constant k value for the photocatalytic reaction of SrTiO3−x/TiO2−x(B) for Cr(VI) reduction is ∼8 times higher than that of white TiO2(B). The photocatalytic hydrogen production rate for SrTiO3−x/TiO2−x(B) is ∼160.2 μmol g−1 h−1, which is ∼5 times higher than that of white TiO2(B). The enhanced photocatalytic activity can be considered to be caused by a synergetic effect of heterojunction formation and the introduction of Ti3+ self-doping, which can not only facilitate the separation of photogenerated charge carriers between TiO2−x(B) and SrTiO3−x, but also broaden the photoresponse from the UV to visible-light region.

Rational design of NiCo2S4 nanowire arrays on nickle foam as highly efficient and durable electrocatalysts toward urea electrooxidation

A 3D NiCo2S4 nanowire arrays directly grown on Ni foam electrode (NiCo2S4/NF) is prepared by two-step simple hydrothermal process. The morphology and phase composition of NiCo2S4/NF are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As expected, in the following electrocatalytic measurement, the binder-free, self-made NiCo2S4/NF electrode exhibits much higher catalytic activity, lower onset potential, better stability and greater tolerance towards urea electrooxidation compared with the Ni3S2/NF electrode synthesized under the same reaction conditions. The NiCo2S4/NF electrode delivers a current density of 720 mA cm−2 at 0.18 V (vs. Ag/AgCl) in a solution containing 5 mol L−1 KOH and 0.33 mol L−1 urea. The impressive electrocatalytic activity of the NiCo2S4/NF catalyst is largely ascribed to its distinctive structure, which exposes more electrochemical active sites at the electrode–electrolyte interface. Besides, the high intrinsic electronic conductivity also largely boosts the charge transfer rates for urea electrooxidation. The results demonstrate that the NiCo2S4/NF electrode showing a beneficial application prospect in the wastewater treatment and direct urea fuel cells.

Development of Ti bipolar plates with carbon/PTFE/TiN composites coating for PEMFCs

A highly corrosion resistant and conductive carbon/PTFE/TiN composite coating on Ti bipolar plates is prepared by a two-step hydrothermal and impregnation process. The composite coating exhibits a full coverage with uniformly distributed PTFE and TiN particles when 0.1 mol/L of glucose is used as carbon source and 10 wt % PFTE + 3 g/L TiN suspension as impregnating solution. The as-prepared composite coating film shows 0.009 μA cm−2 of corrosion current density and 13 mΩ cm2 of ICR in the simulated solution of proton exchange membrane fuel cells, respectively. Meanwhile, the potentiostatic polarization test shows that the corrosion current density of the composite coating is below 1 μA cm−2 under real PEMFC working conditions of the cathode (0.6 V) and anode (−0.1 V). Additionally, the composite coating enhances hydrophobic property with a static contact angle of 120.2°and 115.5°before and after polarization test, respectively. In summary, the Ti substrate with carbon/PTFE/TiN composite coating shows a great potential application as bipolar plates of PEMFCs.

Colorimetric determination of dopamine by exploiting the enhanced oxidase mimicking activity of hierarchical NiCo2S4-rGO composites.

A composite consisting of NiCo2S4 and reduced graphene oxide (rGO) was prepared via a hydrothermal process. Compared to individual NiCo2S4 nanomaterials or reduced graphene oxide, the composite exhibits enhanced oxidase-like activity. It is found that dopamine (DA) inhibits the ability of NiCo2S4-rGO to oxidize the substrate 3,3',5',5'-tetramethylbenzidine (TMB) to form blue colored ox-TMB. Based on these findings, a colorimetric method for determination of DA was workedout. The absorption, best measured at 652nm, increases linearly in the 0.5-100μM DA concentration range, and the limit of detection is 0.42μM. This method was successfully applied to the detection of DA in spiked human serum samples. Graphical abstract A hierarchical NiCo2S4-rGO composite was prepared through two-step hydrothermal process. It exhibits enhanced oxidase-like activity which, however, is inhibited by dopamine (DA).Hence, less blue colored ox-TMB is formed by oxidation of3,3',5,5'-tetramethylbenzidinein the presence of dopamine.

Three-Dimensional Carbon-Coated Treelike Ni3S2 Superstructures on a Nickel Foam as Binder-Free Bifunctional Electrodes

Three-dimensional (3D) nanostructures are commonly endowed with numerous active sites, large specific surface area, and good mechanical strength, which make them as an efficient candidate for energy storage and conversion. Herein, by considering the advantages of 3D nanostructures, we successfully fabricated carbon-coated nickel sulfide on a nickel foam (C@NS@NF) with a unique 3D treelike superstructure via a two-step hydrothermal process. By virtue of its hierarchical superstructures, 3D treelike architecture, and carbon shell encapsulation, the as-fabricated carbon-coated Ni3S2 can be directly served as binder-free bifunctional electrodes for supercapacitor and hydrogen evolution reaction, where high specific areal capacitance (6.086 F cm-2 at 10 mA cm-2) for supercapacitors and low overpotential (92 mV at 10 mA cm-2) for the electrocatalyst have been demonstrated. These inspiring results of this material make it as a potential candidate for energy storage and conversion.

Enhanced electrocatalytic activity of a hierarchical CeO2 @MnO2 core-shell composite for oxygen reduction reaction

A novel MnO2 nanosheet-coated CeO2 nanosphere (CeO2@MnO2) core-shell composite was successfully prepared by a simple two-step hydrothermal process as efficient catalyst for oxygen reduction reaction (ORR). XRD, XPS, SEM and TEM analysis techniques were sequentially employed to evidence this CeO2 core-MnO2 shell structure. When utilized for ORR catalyst, such hierarchical core-shell structured CeO2@MnO2 composite delivers a superior electrocatalytic activity than that of MnO2 nanoflowers and CeO2 nanospheres, which is in close proximity to that of commercial 20 wt% Pt/C in alkaline solution, and also exhibits an excellent durability. These properties make the composite potential as cathode catalyst for metal-air battery application. In addition, the enhanced mechanism arising from the synergetic effect of the MnO2 and CeO2 was preliminarily discussed.

Investigation of Various Nano-Structural Morphologies of Zinc Oxide for their Applications in Dye-Sensitized Solar Cells

In the current study, various morphologies of zinc oxide (ZnO) including nanorods, nanoflowers, nanosheets/flakes, nanospherical particles, nanohexagonal sheets, and nanoneedles have been prepared by using single step and two-step hydrothermal processes with optimized parameters such as growth temperature, growth time and compositions of both the seed and growth solutions. Fluorine doped tin oxide (FTO) coated glass was used as the substrate. The prepared morphologies were characterized with the help of scanning electron microscopy (SEM) and the purity of nanostructures was confirmed by elemental analysis (EDX). These nanostructures were used as photo-anode material to fabricate the DSSC using a dye (Rhodamine B) for enhancing the range of solar spectrum that is to be adsorbed. Finally the fabricated solar cells were characterized in terms of their efficiency, gauged by their fill factor. Among different morphologies investigated as photo anode materials; nanosheets/flakes were found to be showing maximum efficiency, with fill factor values around 0.5 due to their larger surface area, better porosity and enhanced capability of light trapping and scattering.

Graphene quantum dots-induced morphological changes in CuCo2S4 nanocomposites for supercapacitor electrodes with enhanced performance

Graphene quantum dots (GQDs) have been explored in recent years for electrochemical applications with considerable potentials. Here, we present GQD-doped CuCo2S4 nanocomposites through two-step hydrothermal process for supercapacitor electrodes. The surface of CuCo2S4 nanosheets changes from smooth to particles-accumulative shape, which assists the electrochemical cycling processes as well as the ion diffusion and charge transfer kinetics for improved supercapacitor performances. As a result, GQD/CuCo2S4 electrodes demonstrate a specific capacitance of 1725 F g−1 under a current density of 0.5 A g−1 and a cycling life of 10,000 cycles by retaining 90% of the energy storage capability. As such, this work extends the potential of GQDs in electrochemical applications by means of morphology change of CuCo2S4 nanosheets.

Fabrication of graphene-oxide/β-Bi2O3/TiO2/Bi2Ti2O7 heterojuncted nanocomposite and its sonocatalytic degradation for selected pharmaceuticals

A graphene-oxide (GO)/β-Bi2O3/TiO2/Bi2Ti2O7 heterojuncted nanocomposite, designated as GBT, was synthesized via a two-step hydrothermal process. The sonocatalytic activity of the GBT was evaluated at several frequencies (28, 580, and 970 kHz) and compared with Bi-doped GO (GB) and Ti-doped GO (GT). Transmission electron microscopy images showed heterojuncted crystal structures of Bi and Ti on GO, and X-ray diffraction patterns verified that the crystal structures consisted of β-Bi2O3, TiO2, and Bi2Ti2O7 nanocomposites. Energy-dispersive X-ray spectroscopy revealed a higher proportion of metal on GBT surfaces compared with GB and GT surfaces. The energy band gaps of GT, GB, and GBT were 3.0, 2.8, and 2.5 eV, respectively. Two pharmaceuticals (PhACs; carbamazepine [CBZ] and acetaminophen [ACE]) were selected and treated under sonolytic conditions at frequencies of 28, 580, and 970 kHz at a power level of 180 W L−1. The selected pharmaceuticals, present at initial concentrations of 20 μM, were reduced by over 99% by ultrasonic irradiation in the presence of GBT. The 580 kHz treatment achieved the most rapid organic removal among the frequencies tested. The removal kinetic of CBZ was higher than that of ACE owing to its relatively high hydrophobicity. High sonocatalytic activity of GBT was observed through measurement of H2O2 in solution. Because of its low band gaps and high surface activity, GBT exhibited higher sonolytic activity in removing selected PhACs than GT or GB.

Improved mould resistance and antibacterial activity of bamboo coated with ZnO/graphene.

Bamboo is susceptible to mould and attack by fungi because of its high content of starch and sugar. To make bamboo-based outdoor materials, a new type of bamboo timber with improved mould resistance and antibacterial activity, coated with reduced graphene oxide and nanocrystal ZnO (abbreviated as RGO@ZnOBT), was fabricated by a two-step dip-dry and hydrothermal process. A possible synthesis mechanism for RGO@ZnOBT was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscope, energy-dispersal X-ray analysis, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. According to the China standard test method, the Aspergillus niger mould resistance of RGO@ZnOBT is grade 2, whereas the Trichoderma viride and Penicillium citrinum mould resistance of RGO@ZnOBT is grade 0, both of which are better than the grade 4 of original bamboo timber. The Escherichia coli resistance test showed that the antibacterial circle of RGO@ZnOBT is 3 mm, which is significantly higher than that of original bamboo timber (0 mm). The antibacterial activity of treated bamboo is significantly improved compared with that of untreated bamboo.

Efficient hydrogen evolution and rapid degradation of organic pollutants by robust catalysts of MoS2/TNT@CNTs

Exploiting an inexpensive and high-effective composite catalyst for electrocatalytic hydrogen evolution and elimination of organic contaminant from wastewater has drawn great attentions recently. Herein, a facile two-step hydrothermal process was successfully adopted to realize the growth of MoS2 nanosheet on the surface of unique TNT@CNTs (TC). Remarkable, the optimized MoS2/TNT@CNTs (MTC) catalyst exhibited high-efficient photocatalytic activity for high concentrations (30 mg/L) of methylene blue (MB) and rhodamine B (RhB) with the photodegradation rate of 98.7% and 99.0% in 50 min, which are 2 and 6 times higher than that of pure TiO2 nanotube (TNT), respectively. Meanwhile, the novel composites also showed better hydrogen evolution reaction (HER) activity with the overpotential of 110 mV. The significant enhance in photocatalytic performance and electrocatalytic activity are attribute to formation of chemical bonds and large specific surface area, which effectively separate and transfer interfacial charges. The radical scavenging techniques confirmed that the holes (h+) and •O2− radicals played a main role in the photocatalytic process. This study suggests that the novel nanocomposite has extensive application to solve environment and energy issues due to the low-cost raw materials, simple and inexpensive synthesizing process and environmental-friendly methods.