Highly Sensitive and Selective Eco-Toxic 4-Nitrophenol Chemical Sensor Based on Ag-Doped ZnO Nanoflowers Decorated with Nanosheets

Herein, we have developed a novel sensing electrode to detect the eco-toxic 4-nitrophenol (4-NP). Ag-doped-ZnO nanoflowers were synthesized by facile hydrothermal method and examined by several characterization techniques in order to understand the morphology, crystal structure, composition, and surface properties. Morphological results were confirmed by the formation of Ag-doped ZnO nanoflowers decorated with nanosheets. Ag-doped ZnO/glassy carbon electrode (GCE) electrode-material-matrix was used for electrochemical sensing of toxic 4-NP. Under optimized conditions, Ag-doped ZnO/GCE modified electrode exhibits high-sensitivity and selectivity compared to the bare GCE electrode. The Ag-doped ZnO/GCE modified electrode exhibits high electrocatalytic oxidation towards 4-NP. Anodic peak current of 4-NP is increased linearly by increasing the concentration of nitrophenol. Additionally, Ag-doped ZnO/GCE shows a wide range of sensitivity from 10 µM to 500 µM, and a linear calibration plot with a good detection limit of 3 µM (S/N = 3). The proposed Ag-doped ZnO/GCE modified electrode showed high sensing stability. In addition, the oxidation mechanism was studied. The obtained results revealed that the Ag-ZnO/GCE electrode could be the promising sensing electrode for 4-NP sensing.     

Ag掺杂AlN半导体光电性质的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势法,对Ag掺杂AlN 32原子超晶胞体系进行几何结构优化,计算并分析体系的电子结构、磁性和光学性质.结果表明:Ag掺杂后,Ag4d态电子与其近邻的N2p态电子发生杂化,引入杂质带形成受主能级,实现p型掺杂,使体系的导电能力增强,同时表现出金属性和弱磁性,其净磁矩为1.38μ_в.掺杂形成的N-Ag键电荷集居数较小,表现出强的离子键性质.掺杂后体系的介电函数虚部和光吸收谱在低能区出现新的峰值,同时复折射率函数在低能区发生变化,吸收边向低能方向延展,体系对长波吸收加强,能量损失明显减小.     

Sol–gel doped TiO<Subscript>2</Subscript> nanomaterials: a comparative study

Among the great number of sol–gel prepared nanomaterials, TiO₂ has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO₂ nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO₂ and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol–gel Ag-doped TiO₂ coatings, prepared by co-gelation and sol–gel Ag-doped TiO₂ coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.     

Simultaneous electrochemical determination of nitrate and nitrite in aqueous solution using Ag-doped zeolite-expanded graphite-epoxy electrode

In this work a new electrochemical sensor based on an Ag-doped zeolite-expanded graphite-epoxy composite electrode (AgZEGE) was evaluated as a novel alternative for the simultaneous quantitative determination of nitrate and nitrite in aqueous solutions. Cyclic voltammetry was used to characterize the electrochemical behavior of the electrode in the presence of individual or mixtures of nitrate and nitrite anions in 0.1 M Na₂SO₄ supporting electrolyte. Linear dependences of current versus nitrate and nitrite concentrations were obtained for the concentration ranges of 1-10 mM for nitrate and 0.1-1 mM for nitrite using cyclic voltammetry (CV), chronoamperometry (CA), and multiple-pulsed amperometry (MPA) procedures. The comparative assessment of the electrochemical behavior of the individual anions and mixtures of anions on this modified electrode allowed determining the working conditions for the simultaneous detection of the nitrite and nitrate anions. Applying MPA allowed enhancement of the sensitivity for direct and indirect nitrate detection and also for nitrite detection. The proposed sensor was applied in tap water samples spiked with known nitrate and nitrite concentrations and the results were in agreement with those obtained by a comparative spectrophotometric method. This work demonstrates that using multiple-pulse amperometry with the Ag-doped zeolite-expanded graphite-epoxy composite electrode provides a real opportunity for the simultaneous detection of nitrite and nitrate in aqueous solutions.     

Effect of Ag doping on the photoluminescence properties of ZnO films

ZnO:Ag films were grown on Si (1 0 0) substrates by ultrasonic spray pyrolysis at various substrate temperatures. The effect of deposition temperature on the structural and the room temperature photoluminescence (RT-PL) properties of ZnO:Ag films was studied. With the deposition temperature rising to 550 °C, the intensity of the near-band edge (NBE) emission at 378 nm decreased and a new emission peak at 399 nm was observed. On the basis of the X-ray diffraction pattern (XRD), the X-ray photoelectron (XPS) spectra of ZnO:Ag films, and the effects of annealing on the PL, we suggest that the 399 nm emission should be attributed to the electron transition from the conduction band to Ag_Zn-related complexes defects radiative centers above the valence band.     

Growth and investigation of SmBCO/Ag single grain bulk for batch production of Sm123 seed crystals

Using NdBa₂Cu₃O_y (Nd123) bulk material as a seed, we report a success in the melt-textured growth of SmBCO/Ag bulks by cold-seeding melt-growth process. Very well-textured single domain bulks of SmBCO with 5 wt% Ag₂O addition can be fabricated reproducibly under ambient atmosphere. Microstructure analysis of the obtained SmBCO/Ag bulk sample reveals that no silver particle is trapped within the mono-domain region, where the peritectic decomposition temperature goes back to the one of the Ag-free SmBCO sample. This c-axis oriented mono-domain region can be easily separated into a large amount of Sm123 seeds. Therefore, a new approach to preparation of Sm123 seed crystals in high quantity and quality can be achieved in an uncomplicated way, which exhibits significant advantage in comparison with the conventional method for Sm123 seed fabrication by MgO cold-seeding process. Experimental results show that a batch of well-textured YBCO bulks has been grown successfully by using these new Sm123 seed crystals.     

Structural,electronic properties and stability of Ag-doped GaAs nanowires: First-principles study

First-principles computations have been addressed to determine the effects of Ag substitution to the structural, electronic properties and stability of Ag-doped GaAs NW. Our results show that the substitutional Ag energetically prefers to substitute the surface Ga (E_f=−0.529 eV) under As-rich conditions and introduces a much shallow (0.19 eV above the Fermi) acceptor level, which is of typical p-type behavior. With the increase in the Ag concentration, the p-type character gradually weakens and n-type character arises. Thus, one can expect to synthesize Ag-doped GaAs NWs for p-type or n-type applications with the control of Ag concentration and its microarrangement.     

自支撑Ag掺杂ZnO花状纳米线阵列及其光学性质

利用简单、温和的二步水浴法制备一种大面积自支撑、可自由迁移的Ag掺杂ZnO花状纳米线阵列。通过场发射扫描电子显微镜(FESEM)、元素能谱(EDS)、X射线衍射谱(XRD)、室温和变温光致发光谱(PL)等一系列表征手段对所制备的自支撑Ag掺杂ZnO纳米线阵列进行了研究。研究结果显示:这种自支撑纳米材料具有良好的晶体质量和光学性质,在低温(85 K)下显示出A0X和FA为主导的受主相关发射峰,通过理论公式计算受主结合能为118 meV。在变温光致发光光谱中,FA发射峰位随温度的变化符合理论模型。     

Recycling process for 123-type bulk superconductors

Bulk (RE)-Ba-Cu-O (RE is a rare earth element or yttrium) high temperature superconductors have contained a lot of precious substances such as Ag and Pt, which led to a significant increase in production cost. However, the bulk superconductors have been thrown away once they were fractured during characterization or failed to grow in the form of single grain. The material recycling of these samples is, therefore, a great important and leads to a cost-effective production. Hence we have attempted a recycling process for Ag-doped Gd-Ba-Cu-O (GdBCO/Ag) bulk samples. The single grain GdBCO/Ag bulk sample, however, could not be grown by the cold-seeded melt-process albeit the recycled precursor powder is chemically identical to a mixture of commercial powder (reference powder). On the other hand, the hot-seeding technique enables us to fabricate readily the single grain GdBCO/Ag bulk samples even with employing the recycled precursor powder. The recycle-processed GdBCO/Ag bulk sample showed a 10% decrease in the trapped magnetic field compared with the reference bulk sample. However, most importantly this study demonstrates clearly, and for the first time, that the recycling of GdBCO/Ag bulk samples is possible, nevertheless a small degradation of superconducting properties is recognized.     

Parameters affecting carbofuran photocatalytic degradation in water using ZnO nanoparticles

Carbofuran photodegradation in water using zinc oxide nanoparticles as a catalyst was examined as well as some parameters influencing its percentage degradation rate such as zinc oxide load, initial concentration of carbofuran, the temperature of the reaction, the initial pH of the solution, and doping of zinc oxide nanoparticles with 5% (w:w) silver. Zinc oxide and Ag-doped zinc oxide nanoparticles were produced using solvothermal and photoreduction methods, respectively, and silver doping effects on the structural, optical, and photocatalytic properties of zinc oxide nanoparticles were investigated using XRD, UV-VIS spectrophotometer, TEM, SEM, SEM/EDX, and FTIR. The average diameter of the synthesized samples was 26.6, 30.55 nm for undoped zinc oxide and Ag-doped zinc oxide, respectively. Zinc oxide doping with silver did not change the shape of the zinc oxide crystal, but decreased the reflection in the visible region, as well as the energy of the bandgap, and increased the zinc oxide photocatalytic activity.