Cd-doped ZnO Research Articles

镉掺杂氧化锌纳米花的制备及其光催化活性

The flower-like Cd-doped ZnO nanostructures were synthesized by hydrothermal method using zinc chloride( ZnCl 2),cadmium chloride( CdCl 2),sodium hydroxide( NaOH) as reactants. Then,the photocatalytic activities of as-grown samples were investigated by photo-degradation of rhodamine B( RhB). The samples were characterized by X-ray diffraction( XRD),scanning electron microscopy( SEM),energy-dispersive X-ray analysis( EDS),photoluminescence( PL) spectroscopy,UV-visible spectroscopy. Experimental results show that with the Cd doping,the morphologies of ZnO changed greatly,and the size of ZnO became smaller. In addition,compared with the undoped ZnO,the absorption edge and the UV emission peak of the Cd-doped ZnO nanoflowers made a red shift clearly. The band gap decreased from 3. 24 eV to 3. 16 eV. Finally,in the photocatalytic experiment,the photocatalytic activity of Cd-doped ZnO was enhanced,and the degradation of rhodamine B( RhB) was up to 98% after the irradiation for 3 h. So the photocatalytic activities of Cd-doped ZnO nanoflowers were higher than that of the undoped ZnO.

Microstructure and photoluminescence of ZnO：Cd nanorods synthesized by hydrothermal method

High-quality ZnO and Cd-doped ZnO nanorods with different Cd-doping concentrations are synthesized by using the hydrothermal method. Microstructures and photoluminescence of the samples are systematically investigated by SEM, X-ray diffraction (XRD), Raman scattering spectrum and photoluminescence (PL) spectrum. Results of XRD analysis indicate that ZnO and ZnO:Cd crystallites exhibit a hexagonal wurtzite structure. SEM shows that the nanorods become smaller due to Cd doping. There is an internal tension which induces the decrease of optical band gap in Cd-doped nanorods. Cd-doping increases the intensity of violet emission peak near 2.90 eV and the blue emission peak located at 2.67 eV appears when the doping concentration is up to 2%. This study can be used for developing blue-violet-emitting devices.

Gas sensing properties of Cd-doped ZnO nanofibers synthesized by the electrospinning method

The response of ZnO nanofibers is significantly enhanced via Cd doping, which can be attributed to the change of defects in ZnO and has been confirmed by PL and XPS analysis.

Cd-doped ZnO quantum dots-based immunoassay for the quantitative determination of bisphenol A

Bisphenol A (BPA) is a ubiquitous environmental contaminant in food products and aquatic ecosystems. Its endocrine and developmental toxicity presents a serious concern to human health and an effective high-throughput method for its detection is desirable. In this paper, water-soluble quantum dots (QDs) have been conjugated covalently with BPA antibodies and the conjugate has been utilized in a competitive fluorescence-linked immunoassay (FLISA). Cd-doped ZnO QDs were functionalized with poly(amidoamine) (PAMAM) dendrimers, as evidenced by ultraviolet absorption spectrum and fluorescence emission spectra analyses, and this led to their successful transfer into aqueous solution. Biological mass spectrometry demonstrated that the bisphenol A antibodies were successfully coupled to the water-soluble QDs, and the structures of these conjugates kept intact. The FLISA method allowed for BPA determination in a linear working range of 20.8–330.3ngmL−1 with the limit of detection (LOD) of 13.1ngmL−1. The recoveries of BPA from water samples were from 85.92% to 109.62%. In conclusion, a rapid and sensitive FLISA was developed by utilizing novel QD coupling method and validated for use in aqueous samples.

Fabrication of porous Cd-doped ZnO nanorods with enhanced photocatalytic activity and stability

Porous Cd-doped ZnO nanorods have been successfully synthesized on a large scale by a precursor thermal decomposition route. Rod-like Zn1−xCdxC2O4 precursors with 1 μm in average length were firstly fabricated via a solvothermal process. After calcining the Zn1−xCdxC2O4 precursors, the porous Cd-doped ZnO nanorods were obtained. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared Cd-doped ZnO nanorods for degradation of organic compounds and the printing and dyeing sewage under the 365 nm of UV light illumination were investigated. The results show that Cd-doped ZnO nanorods have a higher photocatalytic activity than pure ZnO and P25. This enhanced photocatalytic activity is attributed to the Cd doping, which increases the defects in the ZnO nanoparticles and reduces the bandgap width of ZnO. Furthermore, the photodegradation rate does not show an obvious decrease during ten successive cycles, indicating that our Cd-doped ZnO nanorods are very stable.

Synthesis and Characterizations of Cd-Doped ZnO Multipods for Environmental Remediation Application

Well-crystalline Cd-doped ZnO multipods were synthesized by simple and facile hydrothermal process by using zinc chloride, cadmium chloride, hexamethylenetetramine and ammonium hydroxide at low-temperature. The synthesized materials were characterized in terms of their morphological, structural, compositional and optical properties. The morphological investigations done by field emission scanning electron microscopy (FESEM) reveal that the synthesized products are multipods shaped and grown in high density. The structural and compositional properties, observed by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) attached with FESEM and Fourier transform infrared (FTIR) spectroscopy exhibit that the synthesized multipods are well-crystalline and possessing wurtzite hexagonal phase pure Cd-doped ZnO. The as-synthesized Cd-doped ZnO multipods exhibited good optical properties as was confirmed by UV-vis. spectroscopy. Finally, the as-synthesized Cd-doped ZnO multipods were used environmental remediation application. For this, the synthesized multipods were used as an effective photocatalyst for the photocatalytic degradation of acridine orange (AO) which exhibit -92.4% degradation within 90 min. This work demonstrates that doped ZnO materials could be used as efficient photocatalyst for the photocatalytic degradation of various organic dyes and chemicals.

A study of photoluminescence properties and performance improvement of Cd-doped ZnO quantum dots prepared by the sol–gel method

In the present work, ZnO quantum dots (QDs) have been prepared by the sol–gel method, and the performance of the QDs has been improved. The effect of Cd concentration on the structural and luminescent properties of the QDs, as well as the effect of the mass ratio of trioctylphosphine oxide (TOPO)/octadecylamine (ODA), has been investigated. The ZnO and Cd-doped ZnO QDs have hexagonal wurtzite structures and are 3 to 6 nm in diameter. When the Cd content was increased, the QD particle size was reduced; this effect was confirmed in the corresponding ultraviolet–visible spectra. The fluorescence intensity was simultaneously enhanced significantly. Both the UV and fluorescence spectra were blue-shifted. The luminous intensity was further enhanced when the QDs were modified with TOPO/ODA. Fourier transform infrared and X-ray diffraction techniques proved that the polymer successfully coated the surfaces of the QDs. A TOPO/ODA mass ratio of 1:2 was determined to result in the best optical performance among the different ratios examined. The results showed that the described synthetic method is appropriate for the preparation of doped QDs with high-fluorescence quantum efficiency.

Influences of Cd-Substitution and Intrinsic Vacancies on the Electronic Structures and Optical Properties of ZnO Nanotubes

The electronic structures and optical properties of the defect-free armchair and zigzag ZnO nanotubes (NTs) as well as ZnO NTs containing defects have been investigated using the first-principles projector augmented wave potential within density functional theory framework. Simultaneously, the relevant properties for the corresponding ZnO sheets are also exhibited for comparison. Attributing to the influence of curvature, the band gaps of the defect-free, Cd substitutional, and O deficient ZnO NTs are decreased, as compared with the corresponding sheets. Moreover, for both ZnO sheets and ZnO NTs, the band gap of the substitutional Cd case is smaller than that of the defect-free case, by contraries, O vacancy case is larger. In particular, the Zn vacancy could introduce magnetism in both ZnO sheet and ZnO NTs. Curvature-induced drifting of the conduction bands towards the Femi level allows the electronic excitations from the valence band to conduction band at Γ-point through optical absorption in the visible region. The near-band-edge emission of the Cd-doped ZnO NTs shows a slight red shift, while the presence of the O vacancy contributes strongly to optical absorption in the visible region. This finding is useful for the design of new generation of materials with improved solar radiation absorption.

First-principles calculations of Cd-doped ZnO thin films deposited by pulse laser deposition

Zn1−xCdxO thin films are deposited on quartz substrate by pulse laser deposition. Their band structure and optical properties are experimentally and theoretically investigated. By varying Cd concentration, the band gap of Zn1−xCdxO films can be adjusted in a wide range from 3.219 eV for ZnO to 2.197 eV for Zn0.5Cd0.5O, which produces different emissions from ultraviolet to Kelly light in their photoluminescence spectra. Simultaneity, the electronic structure and band gap of Zn1−xCdxO are investigated by the density functional theory (DFT) with a combined generalized gradient approximation (GGA) plus Hubbard U approach, which precisely predicts the band-gaps of ZnO and Zn1−xCdxO alloys. Both the experimental results and theoretical simulation reveal that with increasing Cd concentration in Zn1−xCdxO alloys, their absorption coefficients in visible light range are evidently enhanced. The adjustable photoluminescence emission and enhanced visible light absorption endow Zn1−xCdxO alloys potential applications in optoelectronic and photocatalytic fields.

Synthesis, characterization and photoluminescence of ZnO:Cd rosette-like nanostructures using solution process

Well crystalline undoped and Cd-doped ZnO rosette-like structures were successfully synthesized at low temperature (80°C) via solution process technique during 30min. Zinc nitrate, cadmium nitrate, sodium hydroxide and hexamine were used as starting materials. The morphology and microstructure were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. X-ray diffraction indicated that the structure has a single phase with wurtzite structure. FESEM indicated that rosette like structures have been formed. This rosette consists of nanorods with length 210 and 460nm and diameter 50 and 74nm for undoped and Cd doped ZnO, respectively. HRTEM showed a decrease in the lattice parameter after the Cd doping. EDX showed that the amount of Cd incorporated into ZnO is 6.4wt.%. Photoluminescence measurements taken on both doped and undoped samples showed that, in the Cd-doped ZnO nanostructures, the band-edge UV emission is blue shifted and the broad green emission intensity decreased.

Photocatalytic and bactericidal activities of hydrothermally synthesized nanocrystalline Cd-doped ZnO

Nanocrystalline Cd-doped ZnO has been obtained by hydrothermal synthesis and characterized by powder X-ray diffraction, energy dispersive X-ray spectrum, high resolution scanning electron micrographs and UV–visible diffuse reflectance, photoluminescence and electrochemical impedance spectra. Cd-doping by hydrothermal method decreases the grain size and destroys the microstructure. Although doping does not modify the band gap it suppresses the deep level emission, decreases the charge-transfer resistance and increases the capacitance. Cd-doping enhances the photocatalytic and bactericidal activities.

The Effects of Transverse Magnetic Field on Pulsed Laser Deposition of Cd-doped ZnO Films

The Effects of Transverse Magnetic Field on Pulsed Laser Deposition of Cd-doped ZnO Films

Optical investigation on cadmium-doped zinc oxide nanoparticles synthesized by using a sonochemical method

Cadmium-doped zinc oxide CdxZn1−xO (x = 0, 0.05, 0.15 and 0.40) nanoparticles were synthesized by using a sonochemical method. The X-ray diffraction (XRD) patterns show that CdxZn1−xO nanoparticles keep a wurtzite structure up to x = 0.40. However, the lattice parameters a, c, and internal parameter u gradually increase with increasing x. The Raman scattering investigation indicates that the Raman mode shows a significant softening in Cd-doped ZnO nanoparticles with increasing x, which suggests an expansion of the Zn–O bond. We also observe a significant red-shift of the band gap for CdxZn1−xO nanoparticles as x increases, i.e., the gap energy Eg ∼ 3.21 eV for x = 0 shifts to 2.92 eV for x = 0.40. In addition, the Urbach band tail gradually increases with x-value, which indicates an enhancement of the defect states in samples with Cd incorporation. In CdxZn1−xO nanoparticles, we further find that the near band-edge (NBE) emission band shows a red-shift with increase in x-value. A broad photoluminescence (PL) band is also observed at around 590 nm, which enhances from x = 0 to 0.15. With further increases in the x-value to 0.40, a weak PL band appears around 450 nm while the broad band around 590 nm is suppressed. The variation of PL intensity is ascribed to the change of the Cd-doping induced defect states and the nonradiative energy transfers.

Enhancement of the Ultraviolet Luminescence Intensity from Cd-Doped ZnO Films Caused by Exciton Binding

ZnO films doped with the cadmium (0.4–0.6%) were grown on crystalline sapphire c-Al2O3 substrates applying radiofrequency magnetron sputtering at the temperature of 400 ◦C in Ar–O2 atmosphere. The as-grown films were investigated in detail using X-ray diffraction, X-ray photoelectron spectroscopy, and cathodoluminescence spectra. The X-ray diffraction analysis revealed that the films possess a hexagonal wurtzite-type structure with the dominant crystallite orientation along the c axis. It was found that the small concentration of the cadmium significantly enhances the ultraviolet emission associated with excitonic transitions. We suggest that this enhancement effect mainly results from appearance of the cadmium isoelectronic traps, which may bind an exciton, thereby increasing the probability of radiation recombination. The effect of Cd isoelectronic impurity on structural and luminescent properties of ZnO films is discussed.

Visible light-activated cadmium-doped ZnO nanostructured photocatalyst for the treatment of methylene blue dye

An attempt was made to prepare Cd-doped ZnO photocatalyst for visible light assisted degradation of a textile dye (methylene blue, MB) in aqueous solutions by a traditional sol–gel process. The as-prepared nanoparticles were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, and photoluminescence spectra techniques. The results showed that the Cd-doped ZnO possess the single-phase hexagonal wurtzite structure. The photocatalytic activity of the nanoparticles under visible light was investigated by measuring the photodegradation of MB in aqueous dispersion. The effects of key operation parameters such as initial dye concentration, catalyst loading as well as initial pH value on the decolorization extents were investigated. The results indicate that the decolorization of the organic molecule followed a pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Under the optimum operation conditions, approximately 85.0% dye removal was achieved within 3.5 h.

First-principles study on the electronic structures and structural stability of Cd-doped ZnO

The VASP (Vienna Ab-initio Simulation Package) based on the density-functional theory (DFT) method combined with projector augmented wave (PAW) method is used to calculate the lattice parameters, band gap, density of states (DOS), and formation enthalpy of ZnCdO alloy by considering all the doping configurations. The calculation results indicate that the average parameters of wurtzite (wz) Zn1-xCdxO alloy, a and c, increase linearly, but the ratio of c/a does not change obviously with the increase of Cd content. With increasing Cd content, the band gap is reduced and the variation of band gap can be fitted by Eg(x)=3.28-5.04x+4.60x2, which is consistent with the experimental results. At a given Cd content, different doping configurations result in different Eg values, being one of the reasons of widening of the photoluminescence spectra of ZnCdO alloy. The DOS of wz-ZnCdO alloy in conduction band is shifted towards the lower energy side after Cd doping, causing the reduction of band gap. The reduction of band gap can be attributed to the contribution of 5s states of Cd. By comparing the formation enthalpy of wz-ZnCdO with those of zinc blende and rocksalt ZnCdO alloys, we find that the wurtzite phase of ZnCdO can coexist with zinc blende phase in the range of Cd content from 0.25 to 0.75 and will transit to the rocksalt phase at the Cd content of about 0.80.

Study on interactions between Cadmium and defects in Cd-doped ZnO by first-principle calculations

An ab initio calculation based on density functional theory is applied to study the formation energy and transition energy level of defects and complexes in Cd-dopped ZnO. The calculation shows that the incorporation of Cd into ZnO leads to the increase of the O vacancies (V O). V O exists in the form of Cd Zn–V O complex, which can balance the strain caused by Cd Zn and V O. Due to high formation energy of the Zn interstitials (Zn i ) and deep transition energy level of V O, Zn i and V O cannot serve singly as the source of the n-type carriers in Cd-dopped ZnO. It is also found that the Zn i -Cd Zn-V O complex is a shallow donor like Zn i , but has lower formation energy. Thus, the source of n-type carriers is believed to be a complex with Zn i -Cd Zn-V O structures in Cd-doped ZnO.

The influence of temperature on the structure of Cd-doped ZnO nanopowders

A new and facile method has been used for preparation of CdZnO nanopowder. The prepared nanopowder was in the form of binary mixture of CdO and ZnO until annealing temperature 400 °C. When the annealing temperature increased above 400 °C the structure of the nanopowder was changed from binary mixture to a single hexagonal phase. Thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to follow the change in the microstructure and morphology of the prepared nanopowders at different temperatures. The effect of calcination temperature on the growth dynamics of CdZnO nanopowder showed that the dynamic growth index was 1.13 below 400 °C and 0.5 above it. This indicates that the rate of the grain growth was very fast especially at calcination temperature range 400-750 °C.

Electrical and Hydrogen-Sensing Characteristics of Field Effect Transistors Based on Nanorods of ZnO and WO2.72

Top-gated field effect transistors (FETs) using Au-gap (5 microm) electrodes on glass substrate and SiO2/Si as gate have been fabricated with undoped and doped nanorods of ZnO as well as with WO2.72 nanorods as active semiconductor elements. The I-V characteristics at different gate voltages show that the nanorods are n-type semiconductors and the derived transfer characteristics show that the FET devices function in the depletion mode. Al-doping (3 at%) enhances the carrier mobility of ZnO nanorods to 128.6 cm2/V x s as against to 0.009 cm2/V x s estimated in the case of the undoped nanorods. Doping with Cd and Mg (3 at%) as well as N (approximately 1 at%) similarly increases the mobility although to a smaller extent. The Cd-doped ZnO nanorods exhibit the high sensitivity (defined as the ratio of the resistance in air to that in the hydrogen) (20) for 1000 ppm of hydrogen. Application of gate voltage decreases the recovery times of the nanorod sensors. FETs based on WO2.72 nanorods also show the depletion mode type characteristics and a carrier mobility of 8.38 cm2/V x s is obtained. The WO2.72 based FETs exhibit good sensitivity (approximately 10) for 1000 ppm hydrogen.

Synthesis, characterization and charge transport mechanism of CdZnO nanorods

ZnO and Cd-doped ZnO nanostructures were prepared by new facile method at 80 °C. XRD measurement indicated that both samples had typical hexagonal wurtzite structures. Transmission electron microscopy (TEM) measurement shows that rod-like crystals have been formed. EDX measurement confirms the incorporation of the cadmium ion into the crystalline lattice of ZnO and indicated that cadmium ions uniformly distributed on the surface of the rods. The doping with cadmium ions has a great influence on the optical properties of the ZnO. The electrical measurements of Cd-doped ZnO nanorod were measured. The current–voltage ( I– V) characteristic curve revealed that the charge transport above 4 V is mainly non-linear due to grain boundary contribution. The complex impedance spectroscopy was confirmed that the grain boundary effect controls the charge transport mechanism through CdZnO ceramic material.