Xue Xi

NaGdF4:Dy3+ nanofibers and nanobelts: facile construction technique, structure and bifunctionality of luminescence and enhanced paramagnetic performances

Luminescent-magnetic bifunctional NaGdF4:Dy3+ nanofibers and nanobelts have been successfully fabricated by a combination of electrospinning followed by subsequent calcination with fluorination technology for the first time. The structure, morphologies, and luminescence and magnetic properties of the synthesized materials have been investigated by a variety of techniques. X-ray diffraction (XRD) analysis shows that as-prepared NaGdF4:Dy3+ nanostructures are pure hexagonal structures. Scanning electron microscopy (SEM) observations indicate that directly electrospinning-made PVP/[NaNO3 + Gd(NO3)3 + Dy(NO3)3] composite nanofibers and nanobelts have smooth surfaces, good dispersion and uniform size, and surfaces of NaGdF4:Dy3+ nanofibers and nanobelts become rough after calcination and fluorination processes. The mean diameters of PVP/[NaNO3 + Gd(NO3)3 + Dy(NO3)3] composite nanofibers and NaGdF4:0.5%Dy3+ nanofibers are, respectively, 402.20 ± 2.39 nm and 246.06 ± 5.84 nm at the confidence level of 95%. The mean widths and thicknesses of PVP/[NaNO3 + Gd(NO3)3 + Dy(NO3)3] composite nanobelts and NaGdF4:0.5%Dy3+ nanobelts are 4.16 ± 0.17 μm and 279 nm, and 0.83 ± 0.01 μm and 130 nm, respectively. Under the excitation of 274 nm ultraviolet light, NaGdF4:Dy3+ nanofibers and nanobelts show the predominant blue and yellow emission peaks at 478 and 570 nm corresponding to the 4F9/2 → 6HJ/2 (J = 15, 13) energy level transitions of Dy3+ ions, respectively. NaGdF4:0.5%Dy3+ nanofibers have higher photoluminescence intensity than their nanobelt counterpart. In addition, all the NaGdF4:Dy3+ nanofibers and nanobelts display superparamagnetic properties. The NaGdF4:0.5%Dy3+ nanobelts show the highest magnetization, and NaGdF4:0.5%Dy3+ nanofibers have slightly higher magnetization values than NaGdF4 nanofibers. NaGdF4:Dy3+ nanofibers and nanobelts simultaneously possess excellent luminescence and enhanced superparamagnetic properties, which make them ideally suitable for application in many fields such as solid-state lasers, lighting and displays, and magnetic resonance imaging. The design conception and construction strategy developed in this work may provide some new guidance for the synthesis of other rare earth fluoride nanostructures with various morphologies.

Flexible Janus Nanofiber to Help Achieve Simultaneous Enhanced Magnetism-Upconversion Luminescence Bifunction

Novel flexible Janus nanofibers with magnetism-upconversion luminescence bifunction have been successfully fabricated via electrospinning technology using a homemade parallel spinneret. NaYF₄:Yb³⁺, Er³⁺ and Fe₃O₄ nanoparticles (NPs) were, respectively, incorporated into polyvinyl pyrrolidone (PVP) and electrospun into Janus nanofibers with NaYF₄:Yb³⁺, Er ³⁺/PVP as one strand nanofiber of the Janus nanofiber and Fe₃O₄/PVP as the other one. The morphologies and properties of the final products were investigated in detail by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, vibrating sample magnetometry and fluorescence spectroscopy. The results reveal that Janus nanofibers simultaneously possess superior magnetic and upconversion luminescent properties due to their special nanostructure, and the upconversion luminescent characteristics and saturation magnetizations of the Janus nanofibers can be tuned by adjusting the content of NaYF₄:Yb³⁺, Er³⁺ NPs and Fe₃O₄ NPs. Compared with Fe₃O₄/NaYF₄:Yb³⁺, Er³⁺/PVP composite nanofibers, the magnetism-upconversion luminescence bifunctional Janus nanofibers provide better performances owing to isolating NaYF₄:Yb³⁺, Er³⁺ NPs from Fe₃O₄ NPs. The novel magnetism-upconversion luminescence bifunctional Janus nanofibers have potential applications in the fields of new nano-bio-label materials, drug target delivery materials and future nanodevices owing to their excellent magnetic-upconversion luminescent properties, flexibility and peculiar nanostructure. More importantly, the new strategy and construction technology are of universal significance to fabricate other bifunctional Janus nanofibers.

Tunable multicolor luminescence and white light emission realized in Eu3+ mono-activated GdF3 nanofibers with paramagnetic performance

Luminescent–magnetic bifunctional GdF3:Eu3+ nanofibers have been successfully fabricated via the combination of electrospinning followed by calcination with fluorination technique. The structure, morphologies, luminescence, and magnetic properties of the synthesized nanomaterials have been characterized by a variety of techniques. X-ray diffraction (XRD) analysis indicates that the as-obtained GdF3:Eu3+ nanofibers have a pure orthorhombic structure. Scanning electron microscope (SEM) observations show that the directly electrospinning-made PVP/[Gd(NO3)3 + Eu(NO3)3] composite nanofibers have smooth surfaces, uniform size and good dispersion, and the surfaces of GdF3:Eu3+ nanofibers become rough after calcination and fluorination process. The diameters of composite nanofibers and GdF3:Eu3+ nanofibers are respectively 333.26 ± 1.80 nm and 86.54 ± 0.55 nm under the confidence level of 95%. Under 274 nm ultraviolet light excitation, GdF3:Eu3+ nanofibers exhibit characteristic 5D3,2,1,0 → 7FJ emission of Eu3+ and the trend of their color tones changes from blue, cold white, warm white to red by adjusting the molar concentration of Eu3+. In addition, all of the samples exhibit paramagnetic features and the magnetic properties of GdF3:Eu3+ nanofibers are tunable by modulating the doping concentration of Eu3+ ions. More importantly, the tunable multicolor luminescence, white light emission and paramagnetic properties are simultaneously realized in single-phase GdF3:Eu3+ nanofibers, which are ideally suited to applications in many fields such as solid-state lasers, lighting and displays, magnetic resonance imaging. This design conception and construction strategy developed in this work may provide some new guidance for the synthesis of other rare earth fluoride nanostructures with various morphologies.

Janus nanofiber: a new strategy to achieve simultaneous enhanced magnetic-photoluminescent bifunction

Magnetic-photoluminescent bifunctional Janus nanofibers have been successfully fabricated by electrospinning technology using a homemade parallel spinneret. NaYF4:Eu3+ and Fe3O4 nanoparticles (NPs) were respectively incorporated into polyvinyl pyrrolidone (PVP) and eleactrospun into Janus nanofibers with NaYF4:Eu3+/PVP as one strand nanofiber and Fe3O4/PVP as another strand nanofiber. The morphologies, structures, magnetic and photoluminescent properties of the as-prepared samples were investigated in detail by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, vibrating sample magnetometry and fluorescence spectroscopy. The results show Janus nanofibers simultaneously possess superior magnetic and luminescent properties due to their special structure, and the luminescent characteristics and saturation magnetizations of the Janus nanofibers can be tuned by adding various amounts of NaYF4:Eu3+ NPs and Fe3O4 NPs. Compared with Fe3O4/NaYF4:Eu3+/PVP composite nanofibers, the magnetic-photoluminescent bifunctional Janus nanofibers provide better performances due to isolating NaYF4:Eu3+ NPs from Fe3O4 NPs. The novel magnetic-photoluminescent bifunctional Janus nanofibers have potential applications in the fields of new nano-bio-label materials, drug target delivery materials and future nanodevices owing to their excellent magnetic and luminescent performance. More importantly, the design conception and construction technology are of universal significance to fabricate other bifunctional Janus nanofibers.

Flexible special-structured Janus nanofiber synchronously endued with tunable trifunctionality of enhanced photoluminescence, electrical conductivity and superparamagnetism

We report a facile and highly-effective method to assemble luminescent–magnetic–electrical tri-functionalities into the special-structured Janus nanofibers. Novel and brand-new flexible special-structured [coaxial nanocable]//[nanofiber] Janus nanofibers synchronously endued with tuned and enhanced luminescent–magnetic–electrical trifunctionality have been prepared via electrospinning technology using a homemade coaxis//monoaxis spinneret for the first time. Each special-structured Janus nanofiber consists of a coaxial nanocable made of Fe3O4/PVP core and Eu(BA)3phen/PVP shell as a half side with luminescent–magnetic bifunctionality and polyaniline (PANI)/PVP nanofiber as the other half side with electrically conductive functionality. The special and novel Janus nanofiber not only can guarantee effective separation of Fe3O4 nanoparticles (NPs) and PANI from rare earth complex, but also ensure the continuity of PANI in the matrix. It is satisfactorily found that the luminescent intensity of the novel special-structured Janus nanofibers respectively reaches up to 10 and 22 times higher than those of counterpart conventional [nanofiber]//[nanofiber] Janus nanofibers and composite nanofibers owing to its peculiar nanostructure. Compared with the counterpart conventional Janus nanofibers of two independent partitions, coaxial nanocable is used as one side of the special-structured Janus nanofiber instead of nanofiber, and three independent partitions are successfully realized in the special-structured Janus nanofiber, thus the interferences among various functions are further reduced, leading to the fact that more excellent multifunctionalities can be obtained. The novel Janus nanofibers possess excellent fluorescence, superparamagnetism and electric conductivity, and further, these performances can be respectively tunable via modulating the respective Eu(BA)3phen, Fe3O4 and PANI contents. The design philosophy and the construction technique for the special-structured Janus nanofibers are of universal significance for the fabrication of other multifunctional Janus nanofiber of various performances.

Conjugate electrospinning-fabricated nanofiber yarns simultaneously endowed with bifunctionality of magnetism and enhanced fluorescence

The brand-new magnetic–fluorescent bifunctional heterogeneous nanofiber yarns have been successfully prepared by using a conjugate electrospinning method for the first time. The heterogeneous nanofiber yarns consist of [Fe3O4/polyacrylonitrile (PAN)] magnetic nanofibers and [Eu(BA)3phen/PAN] fluorescent nanofibers, which benefit for separating Fe3O4 nanoparticles (NPs) from Eu(BA)3phen complexes effectively. The morphology and properties of as-prepared samples have been studied in detail by X-ray diffractometer, scanning electron microscope, energy-dispersive spectrometer, vibrating sample magnetometer and fluorescence spectrophotometer. The results reveal that the prepared heterogeneous nanofiber yarns have large aspect ratio and uniform diameter, and the nanofibers in the yarns exhibit high orientation. The magnetism of heterogeneous nanofiber yarns can be adjusted by modulating the contents of Fe3O4 NPs. It is satisfactorily found that the fluorescence intensity of heterogeneous nanofiber yarns is much higher than that of counterpart [Fe3O4/Eu(BA)3phen/PAN] homogeneous nanofiber yarns under the same compositions and contents. The new heterogeneous nanofiber yarns have the potential applications in nanodevices, fluorescent labeling, etc., due to the superior magnetic–fluorescent bifunctional properties. Furthermore, the design idea and preparation technique also provide a simple but effective method for the preparation of other bifunctional or multifunctional nanofiber yarns.

Novel electrospun bilayered composite fibrous membrane endowed with tunable and simultaneous quadrifunctionality of electricity–magnetism at one layer and upconversion luminescence–photocatalysis at the other layer

A novel, electricity–magnetism-upconversion (UC) luminescence–photocatalysis, quadrifunctional [polyaniline (PANI)/Fe3O4/polyacrylonitrile (PAN)]/[Bi2WO6:Yb3+,Er3+/PAN] bilayered composite fibrous membrane (BLCFM) has been successfully synthesized via layer-by-layer electrospinning. PANI, Fe3O4 nanoparticles (NPs), and Bi2WO6:Yb3+,Er3+ nanofibers were incorporated into PAN and electrospun into the obtained fibrous membrane with [Bi2WO6:Yb3+,Er3+/PAN] nanofibers as one layer and [PANI/Fe3O4/PAN] nanofibers as the other layer. The composition, morphology, magnetism, UC luminescence and electrical conductivity of the composite fibrous membrane were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), vibrating sample magnetometry (VSM), photoluminescence spectroscopy (PL), and digital four-point probe tester. In addition, the degradation of rhodamine B (Rh B) was used to characterize the photocatalytic activity of the BLCFM. The results indicate that the BLCFM is simultaneously endowed with excellent UC luminescence, electrical conduction, magnetism and photocatalysis, and furthermore, UC luminescence intensity, photocatalysis, electrical conductivity and magnetic properties of BLCFM can be respectively tuned by adding various amounts of Bi2WO6:Yb3+,Er3+ nanofibers, PANI and Fe3O4 NPs. Moreover, the as-prepared, bilayered, fibrous membrane can not only achieve the order of 10−2 S cm−1 of conductivity, but also presents bright green UC luminescence under 980 nm excitation. The well-designed BLCFM demonstrates better performance than its PANI/Fe3O4/Bi2WO6:Yb3+,Er3+/PAN monolayered composite fibrous membrane (CFM) counterpart. The novel quadrifunctional BLCFM has promising applications in many areas, such as electromagnetic interference shielding, magnetic resonance imaging and environmental remediation.

Using special Janus nanobelt as constitutional unit to construct anisotropic conductive array membrane for concurrently affording color-tunable luminescence and superparamagnetism

We have used electrospinning technology to fabricate a tri-functional nanobelt array membrane exhibiting tunable anisotropic electrical conduction, superparamagnetism and color-tunable luminescence by using a lab-made co-axis//single-axis spinneret and an aluminum drum collection device. Each one-dimensional (1D) Janus nanobelt is composed of luminescent-superparamagnetic bifunctional [Fe3O4/polymethyl methacrylate (PMMA)]@[Tb(BA)3phen/Eu(BA)3phen/PMMA] coaxial nanobelt and conducting polyaniline (PANI)/PMMA nanobelt. Moreover, all Janus nanobelts are aligned in the same manner to generate a two-dimensional (2D) array film. The conductance along the length is much stronger than the conductance in the width (two perpendicular directions). Therefore, the array membrane has excellent anisotropic electrical conduction. The conduction ratio reaches 108 times between the length and width of the Janus nanobelt array membrane, which is the highest conduction ratio between the two perpendicular directions for nanobelt materials reported internationally. Furthermore, we can modulate the degree of electrically conducting anisotropy of the samples by varying the amount of PANI. In addition, the Janus nanobelt array membrane is concurrently endowed by superior and adjustable superparamagnetism and photoluminescence. Importantly, the innovative philosophy and manufacturing technique of the new Janus nanobelt array membrane provide an easy way to prepare multifunctional nano-membranes.

A novel and facile approach to obtain NiO nanowire-in-nanotube structured nanofibers with enhanced photocatalysis

NiO nanowire-in-nanotube structured nanofibers were easily and directly fabricated via one-pot uniaxial electrospinning followed by calcination process for the first time. Firstly, Ni(CH3COO)2/PVP composite nanofibers were prepared by a conventional electrospinning method, and then NiO nanowire-in-nanotube structured nanofibers were successfully synthesized by two-stage calcination procedure of Ni(CH3COO)2/PVP composite nanofibers which was determined to be the key process for preparing NiO nanowire-in-nanotube structured nanofibers. The NiO nanowire-in-nanotube structured nanofibers have pure cubic phase structure with space group of Fmm, and the outer diameter and wall thickness of nanotubes and nanowire diameter are 130 ± 0.99 nm, 30 nm and 40 nm, respectively. Preliminarily, it is satisfactorily found that NiO nanowire-in-nanotube structured nanofibers used as photocatalyst for water splitting exhibit higher H2 evolution rate of 622 μmol h−1 than counterpart NiO hollow nanofibers of 472 μmol h−1 owing to its novel nanostructure. The possible formation mechanism of NiO nanowire-in-nanotube structured nanofibers is proposed. To evaluate the universality of this novel preparative technique, taking Co3O4 as an example, it is found that Co3O4 nanowire-in-nanotube structured nanofibers are also successfully fabricated via this novel method. The special nanowire-in-nanotube structure of the one-dimensional nanomaterials makes them have promising applications in catalysis, lithium-ion battery, drug delivery, etc. This manufacturing strategy has some advantages over other methods to form nanowire-in-nanotube structured nanofibers, such as easy, highly efficient and cost effective. The design idea and synthetic technique provide a novel perspective to create other nanowire-in-nanotube structured nanomaterials.

Novel double anisotropic conductive flexible composite film endued with improved luminescence

Brand-new double anisotropic conductive flexible composite films (ACFs) were firstly put forward, devised and fabricated. The flexible array composite films were constructed via electrospinning using highly aligned Janus nanoribbons as conductive and constitutive units. The Janus nanoribbon consists of two parts, which are respectively conducting side and insulating-luminescent side. The Janus nanoribbons array composite film has two layers, and the two layers are combined tightly to form a top-to-bottom structure. In the composite film, the length direction of the Janus nanoribbons (namely conducting direction) in the two layers is perpendicular, so that a composite film with double electrically conductive anisotropy is achieved. In addition, by adjusting the content of PANI, conductive anisotropy of each layer of the composite film can be tuned, and the conductance in the conducting direction is about 108 times stronger than that in the insulating direction. The Janus nanoribbon array composite films also have tunable and improved luminescent properties, achieving bi-functionality of double anisotropically electrical conduction and luminescence. The proposed design concept and preparation technology will provide theoretical and technical support for the design and fabrication of novel multifunctional ACFs.