MeiLing Zou

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 and green synthesis of well-dispersed Au nanoparticles in PAN nanofibers by tea polyphenols

The green natural compounds, tea polyphenols (TP), were introduced to synthesize well-dispersed Au nanoparticles (AuNPs) in polyacrylonitrile (PAN) nanofibers by combining an in situ reduction approach and electrospinning technique. The AuNPs were firstly synthesized in aqueous solution to test the reducibility of the TP. Then, the well-dispersed AuNPs in PAN nanofibers were obtained by an in situ reduction approach and electrospinning technique. Fourier transform infrared spectroscopy (FTIR) was utilized to confirm the reducibility of TP. The transmission electron microscopy (TEM) and the ultraviolet-visible spectroscopy (UV-Vis) demonstrated the formation of AuNPs and their morphology. Surprisingly, compared with the AuNPs in aqueous solution, the AuNPs in PAN nanofibers via electrospinning were much smaller and well-dispersed and it was attributed to the stabilization effect of PAN through the chelating effect between gold and cyano groups. Apart from the reducibility effect, TP also served as a stabilizer together with PAN to prevent the aggregation of AuNPs effectively, which were testified by X-ray photoelectron spectroscopy (XPS) results.

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.

Selective growth of Au nanograins on specific positions (tips, edges and facets) of Cu2O octahedrons to form Cu2O-Au hierarchical heterostructures.

This communication demonstrates a novel strategy for the selective growth of Au nanograins (AuNGs) on specific positions (tips, edges and facets) of Cu(2)O octahedrons to form Cu(2)O-Au hierarchical heterostructures. The surface energy distribution of the octahedrons generally follows the order of γ((facets)) < γ((edges)) < γ((tips)) and leads to the preferential growth and evolution of the heterostructures. These novel Cu(2)O-Au hierarchical heterostructures show fascinating degradations of methylene blue (MB), due to the suppressed electron/hole recombination phenomena and the highly efficient light harvesting.

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.

Synthesis and Immobilization of Pt Nanoparticles on Amino-Functionalized Halloysite Nanotubes toward Highly Active Catalysts

A simple and effective method for the preparation of platinum nanoparticles (Pt NPs) grown on amino-functionalized halloysite nanotubes (HNTs) was developed. The nanostructures were synthesized through the functionalization of the HNTs, followed by an in situ approach to generate Pt NPs with diameter of approximately 1.5 nm within the entire HNTs. The synthesis process, composition and morphology of the nanostructures were characterized. The results suggest PtNPs/NH2-HNTs nanostructures with ultrafine PtNPs were successfully synthesized by green chemically-reducing H2PtCl6 without the use of surfactant. The nanostructures exhibit promising catalytic properties for reducing potassium hexacyanoferrate(III) to potassium hexacyanoferrate(II). The presented experiment for novel PtNPs/NH2-HNTs nanostructures is quite simple and environmentally benign, permitting it as a potential application in the future field of catalysts.

In situ growth of Rh nanoparticles with controlled sizes and dispersions on the cross-linked PVA–PEI nanofibers and their electrocatalytic properties towards H2O2

A facile approach for the synthesis of uniform, small size and well-dispersed rhodium nanoparticles (RhNPs) on cross-linked polyvinyl alcohol–polyethyleneimine (PVA–PEI) nanofibers has been demonstrated. Various methods were firstly employed to cross-link PVA nanofibers and the cross-linked PVA–PEI nanofibers exhibited good water stability and porous structures after immersing in water for 72 h. Because of the strong chelate effects among the amine groups, hydroxyl groups and Rh3+ ions, uniform RhNPs with an average diameter of about 2.5 ± 0.2 nm can evenly and densely grow throughout the PVA–PEI nanofibers via an in situ reduction. Meanwhile, the better dispersion and smaller size of the RhNPs grown on the nanofibers in comparison with the pre-synthesized RhNPs directly deposited on the nanofibers exhibit the advantages of in situ reduction for size and dispersion control. The successful fabrication of the RhNPs/(PVA–PEI) nanofibers with various densities of well-dispersed RhNPs demonstrates that the strong chelate effects and stabilization of the PVA–PEI nanofibers also play an essential role in the size and dispersion control of RhNPs. The crystal structures, chemical bonding and interactions of the prepared nanofibers were verified using XPS and FTIR spectra and XRD patterns. These novel nanomaterials were fabricated as non-enzymatic electrochemical sensors and exhibit highly electrocatalytic activity towards H2O2.