Electrochemical investigation of the surface energy: Effect of the HF concentration on electroless silver deposition onto p-Si (1 1 1)

Electroless silver deposition onto p-silicon (1 1 1) from 0.005 mol l⁻¹ AgNO₃ solutions with different HF concentration was investigated by using an electrochemical direct current polarization method and open circuit potential-time (Ocp-t) technique. The fact that three-dimensional (3D) growth of silver onto silicon is favored with increasing the HF concentration was ascribed to the drop of the surface energy and approved by electrochemical direct current polarization, Ocp-t technique and atomic force microscopy (AFM). The drop slope of open-circuit potential, K_{−ΔE(OCP)/t}, was educed from the mixed-potential theory. K_{−ΔE(OCP)/t} as well as the deposition rate determined by an inductively coupled plasma atomic emission spectrometry (ICP-AES), increased with the HF concentration, yet was not a linear function. Results were explained by the stress generation and relaxation mechanisms.     

Hydrogen peroxide biosensor based on gold nanoparticles/thionine/gold nanoparticles/multi-walled carbon nanotubes-chitosans composite film-modified electrode

In this paper, an amperometric electrochemical biosensor for the detection of hydrogen peroxide (H₂O₂), based on gold nanoparticles (GNPs)/thionine (Thi)/GNPs/multi-walled carbon nanotubes (MWCNTs)-chitosans (Chits) composite film was developed. MWCNTs-Chits homogeneous composite was first dispersed in acetic acid solution and then the GNPs were in situ synthesized at the composite. The mixture was dripped on the glassy carbon electrode (GCE) and then the Thi was deposited by electropolymerization by Au-S or Au-N covalent bond effect and electrostatic adsorption effect as an electron transfer mediator. Finally, the mixture of GNPs and horseradish peroxidase (HRP) was assembled onto the modified electrode by covalent bond. The electrochemical behavior of the modified electrode was investigated by scanning electron microscope, cyclic voltammetry and chronoamperometry. This study introduces the in situ-synthesized GNPs on the other surface of the modified materials in H₂O₂ detection. The linear response range of the biosensor to H₂O₂ concentration was from 5 × 10⁻⁷ mol L⁻¹ to 1.5 × 10⁻³ mol L⁻¹ with a detection limit of 3.75 × 10⁻⁸ mol L⁻¹ (based on S/N = 3).     

The synthesis and kinetic growth of anisotropic silver particles loaded on TiO2 surface by photoelectrochemical reduction method

Silver nanorods with average diameters of 120-230 nm and aspect ratio of 1.7-5.0 were deposited on the surface of TiO₂ films by photoelectrochemical reduction of Ag⁺ to Ag under UV light. The composite films prepared on soda-lime glass substrates were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the TiO₂ film after UV irradiation in AgNO₃ solution is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. Other compounds cannot be found in the final films. The maximum deposition content of silver particles on the surface of TiO₂ film was obtained with the AgNO₃ concentration of 0.1 M. The kinetic growth rates of silver particles can be controlled by photocatalytic activity of TiO₂ films. The studies suggest that the growth rates of silver particles increase with the enhancement of photocatalytic activity of TiO₂ films. The maximum growth rate of silver particles loaded on TiO₂ films can be up to 0.353 nm min⁻¹ among samples 1#, 2# and 3#, while the corresponding apparent rate constant of TiO₂ is 1.751 × 10⁻³ min⁻¹.     

Synthesis of hollow silver spheres using poly-(styrene-methyl acrylic acid) as templates in the presence of sodium polyacrylate

Hollow silver spheres were successfully prepared by reducing AgNO₃ with ascorbic acid and using negatively charged poly-(styrene-methyl acrylic acid) (PSA) spheres as templates in the presence of sodium polyacrylate as a stabilizer. Firstly, silver cations adsorbed on the surface of PSA spheres via electrostatic attraction between the carboxyl groups and silver cations were reduced in situ by ascorbic acid. The silver nanoparticles deposited on the surface of PSA spheres served as seeds for the further growth of silver shells. After that, extra amount of AgNO₃ and ascorbic acid solutions were added to form PSA/Ag composites with thick silver shells. In order to obtain compact silver shells, the as-prepared PSA/Ag composites were heated at 150 °C for 3 h. Then hollow silver spheres were prepared by dissolving PSA templates with tetrahydrofuran.     

Dye-sensitized phototransformation of chlorophenols and their subsequent chemiluminescence reactions

A novel chemiluminescence (CL) reaction of chlorophenols (CPs), including 2-chlorophenol (2-CP), 4-CP, 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) was reported, which was based on the oxidation of the phototransformed CPs by N-bromosuccinimide (NBS). It was found that the dye-sensitized phototransformation is a prerequisite for the subsequent CL reaction, and the presence of 1.9×10^-2 mol L⁻¹ Triton X-100 or 3.7×10^-3 mol L⁻¹ CTAB can greatly enhance the CL intensity. A neutral sample solution with the presence of 2×10^-5 mol L⁻¹ fluorescein (FL) was found to be optimum for the phototransformation of 2-CP, 4-CP, 2,4-DCP and PCP, but a lower pH of 5.3 was more suitable for 2,4,6-TCP. Based on the CL reaction, detection limits of 8.6×10⁻⁸, 1.1×10⁻⁷, 1.5×10^-7, 4.6×10^-8 and 3.0×10⁻⁵ mol L⁻¹ were achieved, respectively, for 2-CP, 4-CP, 2,4-DCP, 2,4,6-TCP and PCP with the optimized conditions in the flow system. The mechanism of the phototransformation and the subsequent CL reaction were preliminarily studied and it was suggested that the singlet oxygen formed in the dye-sensitization process was responsible for the conversion of CPs into light-emitting precursors. These intermediate products were suggested to be peroxide compounds after testing by a luminal-based post-column CL detection experiment.     

Nitration of phenols in reversed micelle systems and enhanced oxidation ability of dilute nitric acid (less than 2.0 molarity) in concentrated salt solutions

In a previous paper, we have reported that dilute nitric acid in reversed micelle systems can oxidize the Br⁻ ion to Br₂ and proposed that the nitryl (or nitronium) ion NO₂⁺ should be the active species in the oxidation process. Nitration of phenol in reversed micelle systems with dilute nitric acid, CHCl₃/CTAC/H₂O (2.0 mol dm^− 3 HNO₃ in the 1.0% (v/v) H₂O phase), was performed at 35 °C to obtain 2- and 4-nitrophenols, where CTAC represents cetyltrimethylammonium chloride. In similar CTAC and AOT reversed micelle (CHCl₃ or heptane/AOT) systems, 4-methylphenol was converted to 2-nitro-4-methylphenol, where AOT stands for sodium bis(2-ethylhexyl) sulfosuccinate. In aqueous 2.0 mol dm^− 3 HNO₃ solution accompanied by 4.0 mol dm^− 3 LiCl (and a small amount of LiBr as the bromide resource), trans-1,4-dibromo-2-butene was successfully brominated to 1,2,3,4-tetrabromobutane. This result is a good evidence that the Br⁻ ion can be oxidized to Br₂ in dilute nitric acid (2.0 mol dm^− 3) provided that it contains concentrated salts. At 20-40 °C, the apparent oxidation-reaction rate constants (k/s^− 1) of Br⁻ to Br₂ were evaluated in 0.1-2.0 mol dm^− 3 HNO₃ solution accompanied by concentrated LiCl (3.5-9.0 mol dm^− 3). For chloride salts, the cation effects increased as Et₄N⁺ ? Na⁺ < Li⁺ < Ca²⁺ < Mg²⁺. Even the evolution of Cl₂ was demonstrated from < 2.0 mol dm^− 3 HNO₃ solution containing concentrated LiCl, MgCl₂, and CaCl₂ as well as AlCl₃, therefore, an indirect oxidation mechanism of the Br⁻ ion through Cl₂ was proposed as follows: 2Cl⁻ + NO₂⁺ → Cl₂ + NO₂⁻; 2Br⁻ + Cl₂ → Br₂ + 2Cl⁻.     

Investigations on Fe doped polyvinyl alcohol films with and without gamma (γ)-irradiation

This paper deals with the preparation of pure and ferric chloride (FeCl₃) doped polyvinyl alcohol (PVA) films by solution casting method. Optical and electrical properties were systematically investigated. We have found the decrease in optical band gap energy of PVA films on doping FeCl₃. The optical band gap energy values in the present work are found to be 3.10 eV for pure PVA, 2 eV for PVA:Fe³⁺ (5 mol%), 1.91 eV for PVA:Fe³⁺(15 mol%) and 1.8 eV for PVA:Fe³⁺(25 mol%). Direct current electrical conductivity (σ) of pure, FeCl₃ doped PVA films in the temperature range 70-127 °C has been studied. At 387 K dc electrical conductivity of pure PVA film is 5.5795 μ Ω⁻¹ cm⁻¹, PVA:Fe³⁺ (5 mol%) film is 10.0936 μ Ω⁻¹ cm⁻¹ and γ-Irradiated PVA:Fe³⁺ (5 mol%) film for 900 CGY/min is 22.1950 μ Ω⁻¹ cm⁻¹. The result reveals the enhancement of the electrical conductivity with γ-irradiation. FT-IR study signifies the intermolecular hydrogen bonding between Fe³⁺ ions of FeCl₃ with OH group of PVA.     

Synchronous fluorescence determination of ciprofloxacin in the pharmaceutical formulation and human serum based on the perturbed luminescence of rare-earth ions

A simple, rapid and sensitive synchronous fluorescence method was developed for the determination of ciprofloxacin (CPFX) in the pharmaceutical formulation and human serum. The results show that when Y³⁺ is added into the CPFX solution, the characteristic fluorescence of Y³⁺ is not emitted whereas the fluorescence intensity of CPFX is significantly enhanced. The synchronous fluorescence technology is employed in this method to directly determine trace amount of CPFX in human serum. A linear relationship between the fluorescence intensity and the CPFX concentration is obtained in the range of 1.0×10⁻⁹ ∼5.0×10⁻⁶ mol L⁻¹. The limit of detection (LOD) of this method attains as low as 2.0×10⁻¹⁰ mol L⁻¹ (S/N=3). The selectivity of this method is also very good. Common metal ions, rare-earth ions and some pharmaceuticals, which are usually used together with CPFX in the clinic, do not interfere with the determination of CPFX under general conditions.     

Synthesis of goethite from Fe(OH)2 precipitates: Influence of Fe(II) concentration and stirring speed

Magnetic methods are efficient tools in soil and environmental science. But in such natural environments, several magnetic minerals are generally present. So, synthetic standard samples are necessary for calibration of laboratory techniques. The aim of this study was to synthesise goethite free of magnetic impurities (concentration <∼1 μg kg⁻¹) with different crystal sizes. Goethite was prepared by oxidation of aqueous suspensions of Fe(OH)₂ precipitates. Final products were characterised by X-ray diffraction, infrared spectroscopy, scanning and transmission electron microscopy and magnetic methods. Goethite could be obtained in the absence of any trace of strong magnetic minerals using FeSO₄·7H₂O and NaOH as reactants with the following experimental conditions: temperature=45 °C, [FeSO₄·7H₂O]=0.50 mol L⁻¹, [NaOH]=0.20 mol L⁻¹, stirring speed=760 rpm. The Fe(II) concentration and the stirring speed were varied. It proved possible to modify the size of the goethite crystals by varying the Fe(II) concentration and the stirring speed, but important changes of these parameters induced the formation of other phases, lepidocrocite when the oxidation reaction was drastically accelerated and Fe₃O₄ when the reaction was slowed down. In any case, for weak magnetic fields, a low-coercivity magnetic mineral saturating at weak magnetic fields was observed. It may correspond to traces of δ-FeOOH or to domains structurally similar to δ-FeOOH inside the multidomainic crystals of δ-FeOOH.     

Rational synthesis of α-MnO2 and γ-Mn2O3 nanowires with the electrochemical characterization of α-MnO2 nanowires for supercapacitor

An acidification-hydrothermal method was developed to synthesize α-MnO₂ nanowires, which was subsequently treated with ethanol, resulting in γ-Mn₂O₃ nanowire bundles on a large scale. The electrochemical characterization was carried out by cyclic voltammetry, which indicated that the α-MnO₂ nanowires in 0.5 mol L⁻¹ Na₂SO₄ aqueous electrolyte was of an excellent electrode material for supercapacitor at the scan rate of 10 mV S⁻¹ in the range of 0.0-0.85 V.     

Luminescence enhancement effect for the determination of balofloxacin with balofloxacin-europium (III)-sodium dodecylbenzene sulfonate system

A novel method of luminescence enhancement effect for the determination of balofloxacin (BLFX) was proposed. A new system of the BLFX-Eu³⁺-SDBS (sodium dodecylbenzene sulfonate) was investigated. It was found that SDBS significantly enhanced the luminescence intensity of the BLFX-Eu³⁺ complex (about 20-fold). Under the optimized experimental conditions, the system exhibits an excellent linear relationship between the enhanced luminescence intensity and the concentration of BLFX over the range of 1.0×10⁻⁸-8.0×10⁻⁷ mol L⁻¹ with a correlation coefficient (R) of 0.9994, and the detection limit (3σ) of the method was determined as 2.0×10⁻⁹ mol L⁻¹. This method has been successfully applied for the determination of BLFX in pharmaceuticals and human urine/serum samples. Compared with most of the other methods reported, the rapid and simple procedure proposed in the text offers higher sensitivity, wider linear range, and better stability.     

Study on fluorescence properties of carbogenic nanoparticles and their application for the determination of ferrous succinate

A new type of fluorescent nanomaterial named carbogenic nanoparticles (NPs) has drawn considerable attention recently. In this study, we adopted a direct and simple synthetic method to produce the carbogenic NPs and investigated the fluorescence properties of the as-prepared carbogenic NPs in detail. It was found that the fluorescence of carbogenic NPs was stable with the variance of environmental conditions such as pH, temperature and UV irradiation. More interestingly, we found carbogenic NPs exhibited high selectivity and sensitivity towards ferric ions. Under optimum conditions, a good linear relationship could be obtained between the fluorescence intensity and concentration of ferric ions in the range of 5.0×10⁻⁵-5.0×10⁻⁴ mol L⁻¹, and the limit of detection is 11.2 μmol L⁻¹. Based on the fluorescence quenching of carbogenic NPs, a rapid and specific quantitative method was proposed for the determination of ferrous succinate. The content of ferrous succinate in commercial tablets determined by the present method was agreed with the spectrophotometric method results and the reproducibility and the recovery of the proposed method were satisfactory.     

Sensitive determination of enoxacin by its enhancement effect on the fluorescence of terbium(III)-sodium dodecylbenzene sulfonate and its luminescence mechanism

The fluorescence system of enoxacin-Tb³⁺-sodium dodecylbenzene sulfonate (SDBS) was investigated in this paper. The experiments indicated that the fluorescence intensity of Tb³⁺-SDBS was greatly enhanced by enoxacin. Accordingly, a sensitive fluorimetric method for determining enoxacin was established. The fluorescence intensity was measured by a 1-cm quartz cell with an excitation wavelength of 290 nm and an emission wavelength of 545 nm. The enhanced fluorescence intensity of the system (ΔF) showed a good linear relationship with the concentration of enoxacin in the range of 5.0×10⁻⁹ to 2.0×10⁻⁶ mol L⁻¹, its correlation coefficient was 0.9992 and the detection limit (S/N=3) was 2.8×10⁻⁹ mol L⁻¹. The presented method was used to determine enoxacin in real pharmaceutical samples. The luminescence mechanism was also discussed in detail. In the fluorescence system of enoxacin-Tb³⁺-SDBS, SDBS not only acted as the surfactant but also acted as the energy donor.     

Preparation and characterization of bifunctional, Fe3O4/ZnO nanocomposites and their use as photocatalysts

Bifunctional magnetic-optical Fe₃O₄/ZnO nanocomposites with different molar ratio were successfully synthesized by a facile two-step strategy. Compared with the other methods, it was found to be mild, inexpensive, green, convenient and efficient. Fe₃O₄ nanocrystal was used as seed for the deposit and growth of ZnO nanoparticle. A series of the characterizations manifested that the combination of Fe₃O₄ with ZnO nanoparticles was successful. Photocatalytic activity studies confirmed that as-prepared nanocomposites had excellent photodegradating behavior to Methyl Orange (MO) compared to the pure ZnO nanoparticles. The results showed that the degradation percentage of MO was about 93.6% for 1 h when the amount of catalyst was 0.51 g L⁻¹ and initial concentration of MO was 6 × 10⁻⁵ mol L⁻¹ in the pH 7 solution. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. Furthermore, the Fe₃O₄/ZnO nanocomposites could be also served as convenient recyclable photocatalysts because of their magnetic properties.     

Studies of structural and morphological characteristics of flower-like ZnO thin film and its application as photovoltaic material

In this work a new method has been employed to synthesize nanocrystalline ZnO powder under hydrothermal conditions at 80 °C using aqueous Zn(NO₃)₂·6H₂O solution and diethylamine (DEA) as the starting materials. The ZnO powder prepared by this novel method was characterized by XRD, energy dispersive X-ray spectroscopy (EDX), FTIR and UV–vis techniques. Calculation based on XRD data revealed ZnO particles to be of nanometer size (∼33 nm). The ZnO powder was subsequently used to make its thin film which exhibited flower like morphology when examined by SEM. Thin ZnO films were sensitized with N719 dye, (Bu₄N)₂[Ru(dcbpyH)₂(NCS)₂], and used as photo-anode to construct sandwich type dye-sensitized solar cell (DSSC). With such cells, V_OC = 0.680 V, J_SC = 0.61 mA cm⁻², fill factor = 0.43 and overall conversion efficiency η = 0.23% were achieved on illumination with visible light (80 mW cm⁻²).     

Removal of chloridazon by natural and ammonium kerolite samples

The adsorption of chloridazon (5-amino-4-chloro-2-phenylpyridazin-3(2H)-one) on natural and ammonium kerolite samples from aqueous solution at 10, 25 and 40 °C has been studied by using batch experiments. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (X_m) of the samples; two straight lines were obtained, which indicates that the adsorption process takes place in two different stages. Values for X_m1 (first stage) ranged from 1.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 5.1 × 10⁻² mol kg⁻¹ for ammonium kerolite at 10 °C and the values for X_m2 (second stage) ranged from 9.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 14 × 10⁻² mol kg⁻¹ for natural kerolite at 10 °C. The adsorption experiments showed on the one hand, that the ammonium kerolite is more effective than natural kerolite to adsorb chloridazon in the range of temperature studied and on the other hand, that the lower temperature, the more effective the adsorption of chloridazon on the adsorbents studied.     

Electrical and optical properties of silver doped indium oxide thin films prepared by reactive DC magnetron sputtering

Silver doped indium oxide (In_2−x Ag_x O_3−y) thin films have been prepared on glass and silicon substrates at room temperature (300 K) by reactive DC magnetron sputtering technique using an alloy target of pure indium and silver (80: 20 atomic %. The magnetron power (and hence the metal atom sputter flux) is varied in the range 40-80 W. The energy dispersive analysis of X-ray (EDAX) results show that the silver content in the film decreases with increasing magnetron power. The grain size of these films is of the order of 100 nm. The resistivity of these films is in the range 10⁻²-10⁻³ Ω cm. The work function of the silver-indium oxide films (by Kelvin Probe) are in the range: 4.64-4.55 eV. The refractive index of these films (at 632.8 nm) varies in the range: 1.141-1.195. The optical band gap of indium oxide (3.75 eV) shrinks with silver doping. Calculations of the partial ionic charge (by Sanderson's theory) show that silver doping in indium oxide thin films enhance the ionicity.     

A novel polyol method to synthesize colloidal silver nanoparticles by ultrasonic irradiation

A polyol synthesis of silver nanoparticles in the presence of ultrasonic irradiation was compared with other configurations (at ambient temperature, 120 °C, and 120 °C with injected solutions) in the absence of ultrasonic irradiation in order to obtain systematic results for morphology and size distribution. For applying ultrasonic irradiation, rather fine and uniform spherical silver particles (21 ± 3.7 nm) were obtained in a simple (at ambient temperature without mechanical stirring) and fast (within 4 min, 3.61 × 10⁻³ mol min⁻¹) manner than other cases (at ambient temperature (for 8 h, 0.03 × 10⁻³ mol min⁻¹): 86 ± 16.8 nm, 120 °C (for 12 min, 1.16 × 10⁻³ mol min⁻¹): 64 ± 14.9 nm, and 120 °C with injected solutions (during 12 min): 35 ± 6.8 nm; all other cases contained anisotropic shaped particles). Even though the temperature of polyol reaction reached only at 80 °C (<120 °C) in the presence of ultrasonic irradiation, a uniform mixing (i.e. enhanced collision between silver particle and surrounding components) by ultrasonic irradiation might induce a better formation kinetics and morphological uniformity.     

Structure and refractive index dispersive behavior of potassium niobate tantalate films prepared by pulsed laser deposition

Pure perovskite phase and crack-free KTa_0.5Nb_0.5O₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition. The structure and orientation were analyzed by X-ray diffraction. The optical properties were investigated by an ellipsometer. The relationship between the refractive index dispersive behavior and internal structure was analyzed by Sellmeier dispersion model and single electronic oscillator approximation. The parameters of room temperature monomial Sellmeier oscillator were calculated. And the refractive index dispersive parameter E₀/S₀ of KTa_0.5Nb_0.5O₃ thin films on Pt/Ti/SiO₂/Si substrates is (6.72 ± 0.04) × 10⁻¹⁴ eV m², which is consistent with those of KTN crystals and compounds with ABO₃ perovskite type structure.     

Complex and new modification techniques of thiocholine detection electrodes with carbon nanotubes

A new and complex modification technique of glassy carbon electrode (GCE) with multi-walled carbon nanotubes (MWNTs) was developed. Firstly, MWNTs were electro-deposited on GCE at 1.70 V for 2 h. Secondly, by layer-by-layer (LBL) self-assembly technique, a functional membrane of {PDDA/MWNTs}_n were fabricated by alternative immersion in 1% PDDA solution and 1 mg L⁻¹ MWNTs dispersion either. As a result, the modified membrane with five {PDDA/MWNTs} bilayers have good sensitivity, stability, anti-fouling ability and catalytic activity for thiocholine (TCh) detection, the oxidation potential on the modified GCE was decreased almost by 50% while the peak current was increased almost by 100% compared with that on bare GCE. Meanwhile, it showed a low detection limit of less than 7.500 × 10⁻⁷ mol L⁻¹ TCh.