Doped ZnO Nanofibers Research Articles

Ultraselective, ultrasensitive, point-of-care electrochemical sensor for detection of Hg(II) ions with electrospun-InZnO nanofibers

Mercury is one of the top three most hazardous substances (Agency for Toxic Substances and Disease Registry). It is among one of the highly toxic water pollutants causing damage to the brain, lungs, nervous system, and many other vital human organs. Hence, detecting Hg(II) at the lowest concentration (picomolar-femtomolar) is highly desirable to avoid adverse health effects. This article outlines an insightful electrochemical sensor platform for ultraselective sensing of Hg(II) with Self Assembled Monolayers (SAM) of mercaptosuccinic acid (MSA) cross-linked pyridinedicarboxylic acid (PDCA) on top of indium doped ZnO nanofibers (InZnO-NF). The sensor achieves a limit of detection (LOD) 3.13 fM. To improve charge transport properties, indium-doping is used. The MSA-PDCA combination with multifunctional strategy has excellent selectivity towards targeted Hg(II) ions because of its highest stability constant and strong coordinate covalent bond of carboxyl groups (–COOH) with Hg(II). The interaction of Hg(II) ions with InZnO/MSA-PDCA is observed in terms of a change of charge transfer resistance (Rct), which is used as a primary sensing parameter and directly proportional to the mass of targeted Hg(II) ions. The proposed portable electrochemical sensor is the first of its kind capable of ultrasensitive detection of Hg(II) ions in the femtomolar range and useful as a Point-of-care testing platform.

Samarium doped ZnO nanofibers for designing orange - red light emitting fabrics

Abstract In this paper, we report the orange - red luminescence from samarium doped ZnO nanofibers fabricated by Electrospinning. The as-prepared samarium doped ZnO nanofibers was examined by XRD, SEM-EDX, UV-VIS and FTIR characterizations. XRD revealed the presence of sharp peaks of ZnO in agreement with hexagonal wurtzite ZnO peaks. SEM explored the formation of ultralong smooth nanofibers. EDX revealed the presence of Zn, O and Sm peaks confirms the formation of samarium doped ZnO nanofibers. The band gap energy of samarium doped ZnO nanofibers was found to be increasing from 3.7 eV to 3.8 eV with increase in concentration of dopant as computed by UV-Vis spectroscopy. An eminent stretching bond of Zn-O was observed in prepared nanofibers by FTIR spectroscopy. A very bright orange-red luminescence was observed upon excitation at 394nm in photoluminescence study of samarium doped ZnO nanofibers. The resulting luminescence is result of two prominent peaks due to magnetically allowed transition 4G5/2 → 6H7/2 and electrically forced transition 4G5/2 → 6H9/2. These are the distinctive peaks of dopant Sm3+ ions. It is interesting to see the luminescence is from dopant while the host’s defect luminescence is latent. This disguised the operative energy transfer from host ZnO to dopant Sm3+ ion. From the colour parameters calculated by CIE analysis, the prepared samarium doped ZnO nanofibers is suitable for designing the orange-red light emitting fabrics.

Synergistic effect of N-decorated and Mn(2+) doped ZnO nanofibers with enhanced photocatalytic activity.

Here we report a high efficiency photocatalyst, i.e., Mn2+-doped and N-decorated ZnO nanofibers (NFs) enriched with vacancy defects, fabricated via electrospinning and a subsequent controlled annealing process. This nanocatalyst exhibits excellent visible-light photocatalytic activity and an apparent quantum efficiency up to 12.77%, which is 50 times higher than that of pure ZnO. It also demonstrates good stability and durability in repeated photocatalytic degradation experiments. A comprehensive structural analysis shows that high density of oxygen vacancies and nitrogen are introduced into the nanofibers surface. Hence, the significant enhanced visible photocatalytic properties for Mn-ZnO NFs are due to the synergetic effects of both Mn2+ doping and N decorated. Further investigations exhibit that the Mn2+-doping facilitates the formation of N-decorated and surface defects when annealing in N2 atmosphere. N doping induce the huge band gap decrease and thus significantly enhance the absorption of ZnO nanofibers in the range of visible-light. Overall, this paper provides a new approach to fabricate visible-light nanocatalysts using both doping and annealing under anoxic ambient.

Fe Doped-ZnO Nanofibers Synthesized by Electrospinning

Fe Doped-ZnO Nanofibers Synthesized by Electrospinning

Excellent acetone sensor of La-doped ZnO nanofibers with unique bead-like structures

In this work, Lanthanum (La) doped ZnO nanofibers with bead-like structures were facilely produced by electrospinning technique. The obtained La-doped ZnO products were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show that La doping changes the structures of ZnO nanofibers markedly. La-doped ZnO nanofibers have unique bead-like nanostructures, in which two phases of hexagonal La2O3 and wurtzite ZnO coexist along with partially incorporation of La into ZnO lattice. The gas sensing performances of the La-doped ZnO nanostructures to acetone were investigated via static gas sensor testing system. The sensing test results indicate that an appropriate amount of La doping greatly improves the gas sensing properties of ZnO nanofibers. The 1.0wt% La-doped ZnO sensor has the highest selectivity and response (64, to 200ppm acetone at 340°C), in addition to its short response time and recovery time. The unique bead-like structure and the gas sensing mechanism of La-doped ZnO nanofibers are discussed. The La-doped ZnO nanostructures we have produced can be used as a promising material for acetone sensors.

Preparation, characterization and gas sensing properties of pure and Ce doped ZnO hollow nanofibers

Pure and Ce doped ZnO hollow nanofibers have been synthesized via facile single capillary electrospinning, and characterized by XRD, XPS and SEM analysis. XRD studies indicate that the as-prepared samples are well crystallized and can be indexed to hexagonal wurtzite ZnO. XPS spectra show that the samples consist of Zn, O and Ce elements. Compared with pure sample, Ce doped ZnO nanofibers exhibit improved sensing performance to acetone at 260°C. Especially, the sensor can detect acetone down to 5ppm with obvious response (11.49). These results demonstrate that Ce doped ZnO hollow nanofibers can be used as the sensing material for fabricating high performance acetone sensors. The acetone sensing mechanism of Ce doped ZnO nanofibers is discussed too.

Optical properties of Ti/TiO2 caped Tb3+-doped ZnO nanofibers

ZnO:Tb nanofibers are fabricated by electrospinning method. X-ray diffraction and Raman results show that the sample is of hexagonal phase. The positions of doped diffraction peaks shift toward the small angle and the shift does not change with Tb content. Photoluminescence (PL) spectra of Tb-doped ZnO nanofibers show a strong defect-related emission and indicate that the doping affects the crystallinity of ZnO. It is found that Ti-capped can enhance the ultraviolet emission of ZnO nanofiber, while the defect-related emission is depressed. The enhancement in ultraviolet emission is mostly attributed to the surface plasmon coupling effect at the interface. The PL results indicate that the ZnO is not a proper matrix for Tb3+ ion.

Electrospun La<sup>3+</sup>-Doped ZnO Nanofibers with High Photocatalytic Activity for Rhodamine B Degradation

Grape-like structure La3+-doped ZnO nanofibers with different doping concentrations were prepared by electrospinning-calcination technology. The resultant nanofibers were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), photoluminescence spectrum (PL) and X-ray photoelectron spectrum (XPS) respectively. The photocatalytic activities of the nanofibers for the degradation of Rhodamine B (RhB) in aqueous solution were studied. Results show that the doping concentration of La3+ has an significant influence on the photocatalytic performance of the nanofibers, and 2 mol.% La3+ is the optimal doping concentration.

Structural studies of magnetic Fe doped ZnO nanofibers

This work reports structural properties of room temperature ferromagnetic Fe doped ZnO nanofibers (NFs). The NFs were obtained by electrospinning and calcination in air. The input atomic ratio of Fe to Zn ions was about 0.1. The structural characterization was performed by X-ray (XRD) examination, using the synchrotron radiation, and Energy-Filtered Transmission Electron Microscopy (EFTEM) analysis. Incorporating Fe ions into ZnO does not affect the crystal structure of the wurtzite host. No clear evidence of the second phase (Fe, FeO, Fe2O3 or ZnFe2O4) was detected. Diameters of crystals responsible for the magnetic properties ranged from 3 to 10nm. We did not observe any precipitates of the different phase with diameters equal or larger than 1.5nm. It implies that the magnetic signal comes from Fe ions built-in ZnO crystals. No other crystals (besides ZnO crystals) were observed in this range of sizes. We propose that the low activation energy for the nanocrystals growth in NFs allows a large amount of doped ions to be built-in the ZnO crystals.

Visible light photocatalytic activity of novel MWCNT-doped ZnO electrospun nanofibers

Multi wall carbon nanotube (MWCNT) doped ZnO nanofibers were fabricated by electrospinning for the first time. We have successfully demonstrated the photocatalytic activity of doped nanofibers under visible light. Scanning electron microscopy showed that the diameter of MWCNT-doped ZnO nanofibers varied from 120 to 300nm without agglomeration of MWCNT. Fourier transform infrared spectroscopy and X-ray diffraction studies proved the formation of ZnO bond and wurtzite structure with smaller crystal size in doped nanofibers. Raman spectra demonstrated slight shift in bond position after nanofiber doping, indicating the chemical bond between MWCNT and ZnO. X-ray photoelectron spectroscopy showed that ZnOC bond were formed in the nanofibers and the energy band gaps were 3.11 and 2.94eV for pure and doped ZnO nanofibers, respectively. Thermal gravimetric analysis revealed a total weight loss of 55% with no variation in mass reduction at temperature above 460°C. In comparison with ZnO nanofibers, a 7-fold enhancement in photocatalytic activity was observed under UV light as a result of delaying electron–hole recombination as verified by photoluminescence spectroscopy. The improvement in the visible light photocatalytic performance was assigned to the role of MWCNT as photosensitizer and the synergistic effect between MWCNT and ZnO.

The role of Al and Mg in the hydrogen storage of electrospun ZnO nanofibers

Pure and doped ZnO nanofibers with Al and Mg were successfully synthesized via an electrospinning method using a sol–gel containing Polyvinylpyrrolidone as a spinning aid and a zinc nitrate precursor. Calcination of the doped and undoped electrospun nanofibers was conducted at 500 °C in air, and the resultant structures were analyzed by X-ray diffraction (XRD) and Raman spectroscopy. The diameter of the doped nanofibers decreased with increasing viscosity and conductivity, as measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) showed that Mg and Al are present in ZnO nanofibers. The pressure composition isotherm (PCI) demonstrated that the capacity of hydrogen storage in pure zinc oxide nanofibers is a factor of two greater than that of zinc oxide nanoparticles. However, Al-doped ZnO nanofibers have the highest capacity of hydrogen storage (2.81 wt%) at room temperature.

Characterization of Mg doped ZnO nanocrystallites prepared via electrospinning

Undoped and Mg doped ZnO nanofibers with different doping concentrations were successfully synthesized using the electrospinning technique. The nanofiber structures were calcined at 300°C, 400°C, 500°C, and 600°C respectively. It was observed that the nanofibers turned into a nanoparticular structure at the calcining temperature of 400°C. The nanoceramic mats were characterized by the Fourier transform infrared-attenuated total reflectance spectroscopy and by the scanning electron microscopy. The electronic band transitions of as-deposited and calcined films were identified by the evaluation of the photoluminescence measurements at room temperature. It was observed that the exitonic transition energy of the ZnO nanostructure blue-shifted to a high energy value with an increasing Mg doping ratio. In order to estimate the decomposition temperature of the nanofibers turning into a nanoparticular structure, the nanofiber structure was calcined at temperatures between 300°C and 400°C, the temperature ramp being 20°C. The evaluation of the emission spectra of the calcined structures show that the decomposition of electrospun nanofibers started at 320°C. In addition, band gap energies of the samples were determined by the transmittance measurement of the samples and by the UV–VIS spectrophotometer at the room temperature.

Magnetic Fe doped ZnO nanofibers obtained by electrospinning

We demonstrate structural and room temperature magnetic properties of Fe doped ZnO nanofibers (NFs) obtained by electrospinning followed by calcination. The observed NFs, formed from crystalographically oriented, approximately 4.5 nm particles conglomerates, were approximately 200 nm in diameter. The reported synthesis of room temperature ferromagnetic Fe doped ZnO NFs is both facile and economical, and is therefore suggested as a generic method of fabricating biocompatible magnetic materials. The major substrates selected for the NFs synthesis (Zn, Fe) comprised of relatively low toxicity materials. Incorporating 10% Fe into ZnO does not modify the wurtzite crystal structure of the host material. No evidence of impurity phase was detected by either X-ray or electron diffraction. Magnetometry studies and Magnetic Force Microscopy imaging reveal a local ferromagnetic order that persists up to room temperature. We suggest that the observed phenomenon is either due to a mechanism mediated by presence of oxygen vacancies and/or is related to iron-rich precipitates.