MingLiang Du

When Cubic Cobalt Sulfide Meets Layered Molybdenum Disulfide: A Core–Shell System Toward Synergetic Electrocatalytic Water Splitting

A new class of Co9 S8 @MoS2 core-shell structures formed on carbon nanofibers composed of cubic Co9 S8 as cores and layered MoS2 as shells is described. The core-shell design of these nanostructures allows the advantages of MoS2 and Co9 S8 to be combined, serving as a bifunctional electrocatalyst for H2 and O2 evolution.

Structure regulation of silica nanotubes and their adsorption behaviors for heavy metal ions: pH effect, kinetics, isotherms and mechanism

Silica nanotubes (SNTs) with controlled nanotubular structure were synthesized via an electrospinning and calcination process. In this regard, SNTs were found to be ideal adsorbents for Pb(II) removal with a higher adsorption capacity, and surface modification of the SNTs by sym-diphenylcarbazide (SD-SNTs) markedly enhanced the adsorption ability due to the chelating interaction between imino groups and Pb(II). The pH effect, kinetics, isotherms and adsorption mechanism of SNTs and SD-SNTs on Pb(II) adsorption were investigated and discussed detailedly. The adsorption capacity for Pb(II) removal was found to be significantly improved with the decrease of pH value. The Langmuir adsorption model agreed well with the experimental data. As for kinetic study, the adsorption onto SNTs and SD-SNTs could be fitted to pseudo-first-order and pseudo-second-order model, respectively. In addition, the as-prepared SNTs and SD-SNTs also exhibit high adsorption ability for Cd(II) and Co(II). The experimental results demonstrate that the SNTs and SD-SNTs are potential adsorbents and can be used effectively for the treatment of heavy-metal-ions-containing wastewater.

A new strategy for the surface-free-energy-distribution induced selective growth and controlled formation of Cu2O–Au hierarchical heterostructures with a series of morphological evolutions

A strategy of surface-free-energy-distribution induced selective growth of Au nanograins (AuNGs) on specific positions of Cu2O octahedron surfaces with a series of morphological evolutions has been demonstrated. The surface energy distribution of Cu2O octahedra generally follows the order of {111} facets < crystal edges < vertices and leads to the preferential growth and evolution of the heterostructures. The morphological evolutions and crystal structures of Cu2O and Cu2O–Au hierarchical heterostructures are investigated and discussed. Meanwhile, Cu2O octahedra coated by different amounts of polyvinyl pyrrolidone (PVP) and HAuCl4 were taken as control and the results indicate that the trend in the selective growth on PVP coated Cu2O octahedra decreased significantly because of the reducing diversity of the surface-free-energy-distribution. The identity and crystal phase structures of these Cu2O, Cu2O–Au and Cu2O–PVP–Au heterostructures are manifested through X-ray diffraction (XRD) and energy-dispersive X-ray spectrometers (EDS). X-ray photoelectron spectroscopy (XPS) further probes the surface chemical compositions and chemical oxidation state of the as-prepared Cu2O and Cu2O–Au hierarchical heterostructures and test the galvanic reaction between Cu2O and AuCl4−. The growth mechanism of the surface-free-energy-distribution induced selective growth of AuNGs on Cu2O octahedra with morphological evolution is also discussed. The photocatalytic performances of the as-prepared Cu2O and Cu2O–Au hierarchical heterostructures for the degradation of methyl orange (MO) are investigated and the results suggest the substantially enhanced photocatalytic activity of these heterostructures.

WSe2 and W(SexS1−x)2 nanoflakes grown on carbon nanofibers for the electrocatalytic hydrogen evolution reaction

Transition metal dichalcogenides (TMDs) have recently attracted substantial attention due to their potential application in the catalysis of the hydrogen evolution reaction (HER). In this study, triangular WSe2 and W(SexS1−x)2 nanoflakes uniformly dispersed on the surface of electrospun carbon nanofiber mats were synthesized in a chemical vapor deposition (CVD) system. The morphology and structure of these products were systematically characterized, revealing that WSe2 nanoflakes are configured in the 2H phase with high crystallinity, and the W(SexS1−x)2 nanoflakes are configured in the alloy form without any obvious phase separation. The hybrid catalyst mats were directly used as hydrogen evolution cathodes to investigate their HER activity. Excellent HER performances, including low overpotential, high current density and long-term stability, were achieved by optimizing the content of the initial W precursor and the appropriate substitution of selenium with sulfur, which resulted from the appropriate cover density and thickness of the WSe2 nanoflakes and the defective structure of the W(SexS1−x)2 nanoflakes.

Facile fabrication of AgNPs/(PVA/PEI) nanofibers: High electrochemical efficiency and durability for biosensors

A novel, facile and green approach for the fabrication of H2O2, glutathione (GSH) and glucose detection biosensor using water-stable PVA and PVA/PEI nanofibers decorated with AgNPs by combining an in situ reduction approach and electrospinning technique has been demonstrated. Small, uniform and well-dispersed AgNPs embedded in the PVA nanofibers and immobilized on functionalized PVA/PEI nanofibers indicate the highly sensitive detection of H2O2 with a detection limit of 5 μM and exhibit a fast response, broad linear range, low detection limit and excellent stability and reusability.

A 3D dendritic WSe2 catalyst grown on carbon nanofiber mats for efficient hydrogen evolution

3D dendritic WSe2 on conductive carbon nanofiber mats (d-WSe2/CFM) was designed and synthesized by a diffusion-controlled CVD method. The d-WSe2/CFM was directly used as a cathode for the HER. The substantially improved HER performance is ascribed to the novel 3D structure with effectively exposed edge sites.

The design and construction of 3D rose-petal-shaped MoS2 hierarchical nanostructures with structure-sensitive properties

Rose-petal-shaped MoS2 hierarchical nanostructures were designed and constructed using carbonized electrospun nanofibers as a template, which exhibit highly structure-sensitive properties for the hydrogen evolution reaction (HER). We first synthesized carbon nanofiber (CNF) mats by combining the electrospinning and carbonization processes, and then the CNF mats were used as a substrate for the direct growth of MoS2 nanocrystals via the CVD method. By controlling the MoS2 morphology at the nanoscale, we constructed evolutions in the structures and preferentially exposed more catalytically active edge sites, enabling improved performance for electrochemical catalytic activity. Because of their highly exposed edges and excellent chemical and electrical coupling to the underlying CNFs, MoS2–CNF fiber mats exhibited excellent HER activity with a small overpotential of ∼0.12 V and a small Tafel slope of 45 mV per decade. Our findings provide a feasible way to design and engineer advanced nanostructures for catalysis, electronic devices, and other potential applications.

The marriage and integration of nanostructures with different dimensions for synergistic electrocatalysis

The search for new ways to make inexpensive and efficient electrocatalysts to replace precious-metal platinum catalysts for oxygen reduction and water splitting is still a great challenge. Here, we report a facile and effective strategy for the rational design and construction of three-dimensional (3D) architectures for superior electrocatalysis through the integration of one-dimensional (1D) electrospun carbon nanofibers (CNFs), 1D carbon nanotubes (CNTs) and 0D oxygen-deficient Mn3Co7–Co2Mn3O8 nanoparticles (NPs). The rationale behind the marriage and integration of nanostructures with different dimensions presented in this work is that during heat treatment, the in situ-produced CoMnO NPs are partly reduced to Co2Mn3O8 by a carbon precursor with an amount of metallic Mn3Co7 formed at the interface between the Co2Mn3O8 NPs and carbon, which can act as the catalysts for the growth of 3D CNT forests. The 3D CoMnO@CNT/CNF architectures exhibit superior electrocatalytic activity and stability for the oxygen reduction, oxygen evolution and hydrogen evolution reactions. The remarkable electrochemical properties are mainly attributed to the synergistic effects from the engineering of oxygen-deficient binary CoMn oxide NPs with exposed active sites and 3D hierarchical porous structures consisting of branched CNTs and interconnected CNFs. The present work demonstrates the first example of integrating multiple active catalytic centers onto/into 3D architectures for developing highly efficient non-precious metal nanocatalysts for electrochemical energy devices.

Probing the unexpected behavior of AuNPs migrating through nanofibers: a new strategy for the fabrication of carbon nanofiber–noble metal nanocrystal hybrid nanostructures

The intimate relationship of electrochemical sensors with high sensitivity and reliability has stimulated intensive research on developing versatile materials with excellent electrocatalytic activity. Here, we reported a novel strategy for the design of novel nanostructure-based electrochemical biosensors originating from an unexpected behavior of Au nanoparticles (AuNPs) embedded in the interior of polyacrylonitrile nanofibers (Au–PANFs), which can migrate to the external surfaces of the carbon nanofibers (Au–CNFs) during the graphitization process. Small and uniform AuNPs embedded in PANFs were synthesized via a combination of electrospinning and in situ reduction. With the conversion from the amorphous structures of PANFs to graphene layered structures of CNFs, the AuNPs can migrate from the interior of PANFs to the external surfaces of CNFs. The migration of AuNPs through the nanofiber matrix is strongly dependent on the graphitization temperature and heating rates. Three different heating rates of 2, 5, and 10 °C min−1 and graphitization temperatures of 600, 800, and 1000 °C were employed to investigate the migration and the exposed density of AuNPs on the CNFs. These novel nanomaterials were constructed as a nonenzymatic H2O2 electrochemical sensor and the sensors based on Au–CNFs with increased density of exposed AuNPs exhibit significantly promoted electrochemical activity. The Au–CNFs (1000 °C, 2 °C min−1) with high exposed density and small sizes of AuNPs possess higher specific surface area and active sites, leading to higher electrocatalytic activity. The present investigations provide a general route for the fabrication of nanostructures for novel electrochemical sensors, energy storage devices and so on.

Use of TX100-dangled epoxy as a reactive noncovalent dispersant of vapor-grown carbon nanofibers in an aqueous solution.

The dispersion of carbon nanotubes (CNTs) into individual particles or small bundles has remained a vexing problem that limits the use of the excellent properties of CNTs in composite applications. Noncovalent functionalization is an attractive option for changing the interfacial properties of nanotubes because it does not destroy the nanotube grapheme structure. In this study, a new reactive copolymer, epoxy-toluene diisocyanate-Triton X-100 (EP-TDI-TX100) was successfully synthesized, which is shown to be highly effective in dispersing vapor-grown carbon nanofibers (VGCNFs) into individual or small bundles, as evidenced by transmission electron microscopy (TEM) and UV-vis absorption spectra. The strong π-π interaction between VGCNFs and EP-TDI-TX100 was revealed by Raman spectra and the covalent reaction between curing agent was confirmed via Fourier transform infrared spectroscopy. For an effective dispersion, the optimum weight ratio of EP-TDI-TX100 to VGCNFs is 2:1. The maximum VGCNF concentration that can be homogeneously dispersed in an aqueous solution is approximately 0.64 mg/mL. The EP-TDI-TX100 molecules are adsorbed on the VGCNF surface and prevent reaggregation of VGCNFs, so that a colloidal stability of VGCNF dispersion can be maintained for 6 months.