Ag-doped ZnO Research Articles

Effect of Ag doping on structural, optical, and photocatalytic properties of ZnO nanoparticles

Silver-doped ZnO nanoparticles were successfully fabricated at 400°C via a simple and rapid method based on short time solid state milling and calcination of precursor powders. The effect of Ag dilute doping on the structural, optical, and photocatalytic properties of ZnO nanoparticles was investigated by X-ray diffraction (XRD), UV–vis spectrophotometer and photoluminescence (PL) spectroscopy. X-ray analysis revealed that Ag doped ZnO solidified in hexagonal wurtzite structure. The intensity of deep level emission was reduced with increasing silver doping in PL measurement. The X-ray photoelectron spectroscopy (XPS) measurement predicted that Ag was mainly in the metallic state and ZnO was in the wurtzite structure. This metallic state accompanied by unique zinc oxide properties decolorized the methyl violet, efficiently. The first-principles calculation represented Ag deep level in ZnO with an n-type behavior, while in ZnO structure with grain boundary p-type nature via shallow states is dominant same as powder samples as studied in this present work. It was suggested that these Ag-doped ZnO nanoparticles may have good applications in optoelectronics, spintronics and wastewater treatment.

Hydrothermal Growth of Ag‐Doped ZnO Nanoparticles on Electrospun Cellulose Nanofibrous Mats for Catechol Detection

AbstractWe fabricated a novel hierarchical composite mat composed of electrospun cellulose nanofibers decorated with Ag‐doped ZnO (Ag‐ZnO) nanoparticles and further demonstrated its potential application as the efficient laccase (Lac) biosensor substrate material. The cyclic voltammograms revealed that the Ag‐ZnO/cellulose nanofibrous mat provided an excellent microenvironment for Lac immobilization and benefited direct electron transfer of Lac. The fabricated Lac/Ag‐ZnO/cellulose/GCE exhibited a highly sensitive detection of catechol with a wide linear range from 0.995 to 811 µM and a low detection limit of 0.205 µM. The results indicated that Ag‐ZnO/cellulose nanofibers were the promising nanostructured materials for the construction of different biosensors.

Self-assembly and template-free synthesis of ZnO hierarchical nanostructures and their photocatalytic properties

Despite significant progress in the field of semiconductor photocatalysis has been made, it is still a great challenge to prepare low-cost photocatalysts with high activities. In our work, three dimensional (3D) flower-like ZnO hierarchical nanostructures assembled with numerous nanosheets were fabricated by a simple, template-free and one-step hydrothermal route. The products were characterized by XRD, UV–Vis, PL, SEM, TEM, HRTEM techniques. In the process, NH4F played a crucial role for the formation of ZnO hierarchical nanostructures, which was acted both as the alkali source and morphology director. Furthermore, the growth of ZnO involved a phase transformation from intermediate compound ZnF(OH) to ZnO. To further improve the photocatalytic activity, Ag-doped ZnO photocatalyst was also prepared. The photocatalytic results indicated that the Ag/ZnO exhibited higher photocatalytic activity than the pure ZnO. The great enhancement was mainly ascribed to their unique hierarchical nanostructures as well as the modification of Ag nanoparticles. Additionally, both ZnO and Ag/ZnO microspheres showed good recycling stabilities over several separation cycles in photodegradation.

Ag-doped ZnO nanoellipsoids: Potential scaffold for photocatalytic and sensing applications

Well-crystalline Ag-doped ZnO nanoellipsoids (NEs) were synthesized in large quantity and used as effective photocatalyst for the photocatalytic degradation of methyl orange (MO) and efficient electron mediator for the fabrication of highly sensitive, reliable and robust hydrazine chemical sensor. The Ag-doped NEs were synthesized by facile low-temperature (~60°C) solution process and characterized in detail using various characterization techniques. The characterizations revealed that the synthesized nanostructures are well-crystalline, possessing ellipsoidal shapes and were grown in very high density. The photocatalytic activities of these Ag-doped NEs were evaluated by measuring the rate of photodegradation reaction of hazardous methyl orange (MO) dye under UV light irradiation. By comparing the photocatalytic performance of Ag-doped ZnO NEs with those of ZnO nanoflowers, the former was found to be a much superior photocatalyst than the later. Further, Ag-doped ZnO NEs based hydrazine sensor exhibited a high sensitivity of ~9.46µA/cm2µM and detection limit of 0.07µM in a response time of <10s. Thus we find that Ag-doped ZnO nanomaterials synthesized by simple solution process holds potential as efficient photocatalysts and efficient electron mediators for the fabrication of robust and highly sensitive chemical sensors.

GGA+U study on the effects of Ag doping on the electronic structures and absorption spectra of ZnO

Nowadays, the studies on absorption spectra of Ag-doped ZnO have given two distinctly different experimental results, that is, the red shift or blue shift when the mole fraction of the impurity increases in a range from 0.0278 to 0.0417. To solve this contradiction, according to the first-principles plane-wave pseudopotential of the spin-polarized density functional theory (DFT), we set up three models for Zn1-xAgxO (x=0, 0.0278, 0.0417) to calculate the geometric structure and energy via the method of generalized gradient approximation (GGA+U). Calculated results indicate that compared with the Zn-O bond in pure ZnO system, the value of population decreases, and the bond length of Ag-O in Ag-doped ZnO system increases, this means covalent bond weakens and ionic bond strengthens. With the mole fraction of impurity increases in a range from 0.0278 to 0.0417, the orbital charges of O-2p, Zn-4s and Zn-3d keep unchanged, while the orbital charge of Ag-5s increases, and that of Ag-4d is reduced; the volume and total energy of the doped system increases, causing the system more unstable. Moreover, the formation energy of the doped system becomes lower, thereby making the doping difficult. Meanwhile, the band gap in the system narrows, and its absorption spectra exhibits a redshift. The calculated results are consistent with the experimental data, and can explain the phenomena reasonably. These results may be used in future design and preparation of new type photocatalyst from Ag-doped ZnO as a theoretical basis.

Low-intensity ultraviolet detection using a surface acoustic-wave sensor with a Ag-doped ZnO nanoparticle film

In this paper, we propose a surface acoustic wave (SAW) sensor with a Ag-doped ZnO nanoparticle film for low-intensity ultraviolet (UV) light detection. With this sensor, Ag doping is shown to effectively enhance ZnO thin film conductivity, thereby improving the SAW sensor sensitivity. Furthermore, it also enlarges the sensor’s linear response range. Prior to fabrication, the response mechanism was analyzed and the SAW device was designed. The ZnO film was characterized using scanning electron microscopy, x-ray diffraction, and atomic force microscopy. The sensor response under UV light (365 nm) irradiation was measured using a network analyzer. The characteristic improvement of the SAW UV sensor due to Ag-doping was verified by the amplitude shift of S21 from 0.31 dB to 0.97 dB under UV irradiation of 4 μW cm−2. Also, the enhanced sensitivity and lowest detection limit were evaluated as 0.2 dB/(μW cm−2) and 0.05 μW cm−2, respectively.

Some physical investigations on silver-doped ZnO sprayed thin films

The spray chemical route is used to prepare undoped and Ag-doped ZnO thin films using zinc acetate dehydrate isopropyl alcohol and silver nitrate as doping element in starting solution. XRD analysis shows that all films crystallize in a hexagonal würtzite structure with a preferential orientation along (002) direction. Similarly, the variation in peak positions of X-ray diffraction shows that the silver element is well incorporated into ZnO matrix and not remains in the interstitial sites. Surface morphology studies showed that an increase in the concentration doping causes an increase in the grain size and the mean square roughness Rq. Finally, the optical analysis via the transmittance and the reflectance measurements reveals that the bandgap energy Eg decreases from 3.29 to 3.25eV in terms of Ag content.

Comparison of Optical Properties of Ga-doped and Ag-doped ZnO Nanowire Measured at Low Temperature

Pristine ZnO, 3 wt.% Ga-doped (3GZO) and 3 wt.% Ag-doped (3SZO) ZnO nanowires (NWs) were grown using the hot- walled pulse laser deposition (HW-PLD) technique. The doping of Ga and Ag in ZnO NWs was observed by analyzing the optical and chemical properties. We optimized the synthesis conditions, including processing temperature, time, gas flow, and distance between target and substrate for the growth of pristine and doped ZnO NWs. The diameter and length of pristine and doped ZnO NWs were controlled under 200 nm and several μm, respectively. Low temperature photoluminescence (PL) was performed to observe the optical property of doped NWs. We clearly observed the shift of the near band edge (NBE) emission by using low temperature PL. In the case of 3GZO and 3SZO NWs, the center photon energy of the NBE emissions shifted to low energy direction using the Burstein Moss effect. A strong donor- bound exciton peak was found in 3 GZO NWs, while an acceptor-bound exciton peak was found in 3SZO NWs. X-ray photoelectron spectroscopy (XPS) also indicated that the shift of binding energy was mainly attributed to the interaction between the metal ion and ZnO NWs.

Two different mechanisms on UV emission enhancement in Ag-doped ZnO thin films

Ag-doped ZnO thin films were prepared by a sol–gel method. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis and photoluminescence spectra. The results show that the Ag in the ZnO thin films annealed at 500°C for 1h substitutes for Zn and exists in the form of Ag+ ion (AgZn) while the Ag in the ZnO thin films without a post-annealing mainly exists in the form of simple substance (Ag0). The incorporation of Ag indeed can improve the ultraviolet emission of ZnO thin films and suppress the visible emissions at the same time. However, the mechanisms on the ultraviolet emission enhancement in the annealed and unannealed Ag-doped ZnO thin films are very different. As for the post-annealed Ag-doped ZnO thin films, the UV emission enhancement maybe mainly results from more electron–hole pairs (excitons) due to Ag-doping while for the unannealed Ag-doped ZnO thin films; the UV emission enhancement is attributed to the resonant coupling between exciton emission in ZnO and localized surface plasmon in Ag nanoparticles.

Structural, morphological and optical studies of Ag-doped ZnO nanoparticles synthesized by simple solution combustion method

In this work, the structural, morphological and optical properties of Ag-doped ZnO nanoparticles synthesized by the simple solution combustion method are reported. The powder X-ray diffraction pattern indicates that the Ag-doped ZnO samples exhibit primary and secondary phases. The primary phase indicates the hexagonal wurtzite structure with the average crystalline size of around 30–50 nm and the secondary phase is associated with the face centered cubic structure of metallic Ag. The field emission-scanning electron microscopy and transmission electron microscopy images are coinciding with each other for aggregation of particles nature. The elemental analyses of pure and doped samples are evaluated by energy dispersive X-ray spectrometry. Raman spectra’s of the doped samples indicate that the influence of Ag-doping drastically modify the lattice vibrational characteristics in ZnO sites. Room temperature photoluminescence results show the enhanced optoelectronic properties of the Ag-doped ZnO nanoparticles.

Nano ZnO, Cu-doped ZnO, and Ag-doped ZnO assisted generation of light from imidazole

• ZnO surface enhances π electron delocalisation, lowers HOMO–LUMO energies due to adsorption. • Energy gap of MNDI-Cu–ZnO lowers compared to those of pristine ZnO and thus red shift. • Energy gap of MNDI-Ag–ZnO larger compared to that with ZnO and thus blue shift. • Shortening of decay time of MNDI indicates charge transfer from MNDI to nanocrystals. • ∆ G et −1.23 eV indicates thermodynamic feasibility of electron transfer process. A sensitive 2-(4-methoxyphenyl)-1-(naphthalene-1-yl)-4,5-diphenyl-1H-imidazole (MNDI) fluorescent sensor for nanoparticulate ZnO has been designed and synthesized. The nanocrystalline ZnO, Cu-doped ZnO, and Ag-doped ZnO have been synthesised by sol–gel method and characterized by powder X-ray diffraction, scanning electron microscopy(SEM), UV–vis diffuse reflectance, photoluminescence and life time spectral studies. All the synthesized nanoparticles display violet emission due to charge carrier-recombination. The synthesized sensor emission is enhanced by nanocrystalline pristine ZnO but is suppressed by Cu-doped ZnO and Ag-doped ZnO nanoparticles. The suppression of fluorescence is more by copper than by silver doping.

Effect of Ag doping on the microstructure and photoluminescence of ZnO nanostructures

ZnO nanostructures were obtained by metal-organic chemical vapor deposition via Ag catalyst-assisted growth in a temperature range of 200–500 °C. Growth at temperatures above 500 °C resulted in vertically aligned ZnO nanorods (NLs). Ag incorporation into ZnO up to 0.4 at.% promoted creation of basal plane stacking fault (BSF) defects and corrugation of the side facets of the NLs. The presence of BSFs give rise to an additional photoluminescence peak with a wavelength of ∼386 nm, which is slightly red-shifted compared to the commonly observed NBE emission at ∼375 nm. The observed emission was found to be specifically observed from the side facets of the NLs. It is suggested that this emission is due to a high concentration of BSFs in the ZnO as a result of an incorporation of Ag as acceptor dopant. SEM image of an Ag-doped ZnO nanorod with corrugated side facets. The observed corrugation is accompanied by a high concentration of basal plane stacking faults.

Ag-doped ZnO nanorods coated metal wire meshes as hierarchical photocatalysts with high visible-light driven photoactivity and photostability

Ag-doped ZnO nanorods were grown on stainless-steel wire meshes to fabricate the hierarchical photocatalysts with excellent visible light driven activity and anti-photocorrosion property. Effects of Ag doping and the surface structure on the surface chemistry, surface wetting properties, absorption band shift, photoelectrochemical response, and photocatalytic decolorization properties of the hierarchical photocatalysts, together with the stability of photocatalytic activity for recycled photocatalysts were investigated. Ag doping leads to red-shift in the absorption band and increased visible light absorption. Nanorods coated wire meshes hierarchical structure not only increases the surface area of photocatalysts but also makes the surface hydrophilic. The photocatalytic activity enhancement and reduced photocorrosion can be achieved because of increased surface area, enhanced hydrophilicity, and the interaction between the metal wire/ZnO and Ag/ZnO heterostructure interface which can improve the charge separation of photogenerated charge carriers.

Photocatalytic Performance of Ag Nanoparticles Modified ZnO Microplates Prepared by One-Step Method

Flower-shaped Ag-ZnO microplates were directly synthesized from an aqueous solution of zinc nitrate and silver nitrate in the presence of CTAB at 120°C. The as-synthesized products were investigated in terms of their morphological, structural, photocatalytic properties. Methylene blue (MB) and gaseous iso-propanol (IPA) are employed to evaluate the photocatalytic activity of the Ag-doped ZnO microplates. The photocurrent response experiments are also carried out. The as-formed composite shows higher efficiency of photocatalytic degradation on MB and IPA. Moreover, it also exhibits obvious photocurrent under light irradiation.

Synthesis and Characterization of One-Dimensional Ag-Doped ZnO/Ga-Doped ZnO Coaxial Nanostructure Diodes

In the pursuit of high injection current diode nanodevices, entire one-dimensional (1D) ZnO coaxial nanostructures with p-n homojunctions is one of the ideal structures. In this study, we synthesized entire 1D ZnO-based coaxial homojunction diodes with p-type Ag-doped ZnO (SZO) nanostructure shells covering n-type Ga-doped ZnO (GZO) nanopagoda (NPG) cores by a metal-organic chemical vapor deposition (MOCVD) technique. The entire 1D SZO-GZO and SZO-ZnO coaxial nanostructures exhibit better diode characteristics, such as lower threshold voltage, better rectification ratios, and better ideality factor n, than that reported for either 2D or 2D-1D p-n heterojunction and/or homojunction diodes. The binding energies of Ga and Ag were evaluated by low-temperature and temperature-dependent photoluminescence. In comparison, the SZO-GZO coaxial p-n nanostructures display better diode performance than the SZO-ZnO ones.

Microstructure and Raman scattering of Ag-doping ZnO films deposited on buffer layers

Ag-doped ZnO (ZnO:Ag) films were deposited on ZnO buffer layers by radio frequency reactive magnetron sputtering. The effect of Ag doping content on the crystallization behavior and Raman scattering of the ZnO:Ag films have been studied. The crystal structures and surface morphology of the films were systematically investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that ZnO films showed a stronger preferred orientation toward the c-axis and a more uniform grain size after appropriate Ag doping. Two additional local vibrational modes (LVMs) at 243.9 and 393.7cm−1 induced by Ag dopant in ZnO:Ag films were observed by Raman analyses at RT, corresponding to Ag atoms located at O sites (LVM of Zn–Ag) and Zn sites (LVM of Ag–O) in ZnO lattice. Meanwhile, Raman analyses showed that Ag mainly substitutes on the Zn site.

UV enhancement in polycrystalline Ag-doped ZnO films deposited by the sol–gel method

Undoped and Ag doped ZnO thin films are deposited by the sol–gel spin coating method. XRD spectra with prominent peaks along (100) (002) (101) show the polycrystalline nature of thin films. The particle size lies between 10 to 28nm as estimated by Debye‐Scherrer method and 10 to 20nm as estimated by WH plot method. Surface topology is studied by atomic force microscopy (AFM). Transmission spectra show that all the films are highly transparent (70–90%) in the visible and IR spectral region and absorption occurs near 370nm. Sharp UV emission at 393nm is observed in photoluminescence spectra of the films along with a broad green emission. Emission intensity of UV peak increases as amount of Ag incorporated into ZnO increases. It is enhanced 7 times by Ag doping in ZnO thin film. The intensity of green peak enhances at higher Ag doping percentage.

Optical and electrical properties of p-type Ag-doped ZnO nanostructures

Zn1−xAgxO nanoparticles (NPs) (x=0, 0.02, 0.04, and 0.06) were synthesized by a sol–gel method. The synthesized undoped ZnO and Zn1−xAgxO-NPs were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV–visible spectroscopy. The XRD patterns indicated that undoped and Ag-doped ZnO crystallize in a hexagonal wurtzite structure. The TEM images showed ZnO NPs with nearly spherical shapes, with particle size distributed over the nanometer range. Evidence of dopant incorporation is demonstrated in the XPS measurements of the Ag-doped ZnO NPs. The Raman measurements indicated that the undoped and Ag-doped ZnO-NPs had a high crystalline quality. From the result of UV–vis, the band-gap values of prepared undoped and Ag-doped ZnO were found to decrease with an increase in Ag concentration. The obtained undoped and Ag-doped ZnO nanoparticles were used as a source material to grow undoped and Ag-doped ZnO nanowires on n-type Si substrates, using a thermal evaporation set-up. Two probe method results indicated that the Ag-doped ZnO nanowires exhibit p-type properties.

自支撑Ag掺杂ZnO花状纳米线阵列及其光学性质

By using a simple and mild two-step water-bath method,a large area of flower-like selfsupporting Ag-doped ZnO nanoarrays were fabricated. Field emission scanning electron microscopy( FESEM),energy dispersive X-ray spectrometer( EDS),X-ray diffraction( XRD),room temperature and temperature depend photoluminescence( PL) were used to characterize the morphology, crystalline quality and optical properties of the samples. The emission related to acceptor located at 3. 360 eV and 3. 315 eV can be observed at low temperature( 85 K),and the theoretical calculated acceptor binding energy is 118 meV. In temperature depend PL spectra,the calculated values of FA emission agree well with the theoretical model.

Optimization of Photocatalytic Degradation of Phenol Using Simple Photocatalytic Reactor

The phenol photocatalytic degradation was investigated using heterogeneous catalyst Ag-doped ZnO nanowires under UV irradiation. Ag-ZnO nanowires were immobilized on borosilicate glass via a simple hydrothermal technique. Preliminary photodegradation studies were performed with Ag-ZnO nanowires at various concentrations of phenol (10 - 60 mg/L) at undiluted pH. After determination of the optimal initial concentration (30 mg/L), additional parameters including pH and light intensity were investigated to optimize photodegradation of phenol for large-scale application. The experimental results illustrate that the kinetics of degradation of phenol are pseudo-first order. Based on the relationship, experimental model and empirical correlation were generated and compared for validity. The experimental data were found to fit a cubic model (linear in UV irradiation intensity, I, and cubic in pH), over ranges of 10 - 60 W (UV lamp power) and 2.7 - 11.0 (pH) with a coefficient of determination (R2) of 0.9934. This model, of the form K(I, pH) = c00 + c10I + c01pH + c11IpH + c02pH2 + c12IpH2 + c03pH3 was found to yield a better fit than simpler (quadratic) or more complex (quartic) polynomial-based models considered. The model parameters cij and corresponding 95% confidence intervals were obtained.