Thorough removal of inorganic and organic mercury from aqueous solutions by adsorption on Lemna minor powder

The adsorption ability of duckweed (Lemna minor) powders for removing inorganic and organic mercury (methyl and ethyl mercury) has been studied using cold vapour atomic absorption spectrometry. The optimal adsorption conditions were: (a) the pH value of the solution 7.0 for inorganic and ethyl mercury, 9.0 for methyl mercury, and (b) equilibrium adsorption time 10, 20, and 40 min for inorganic mercury, methyl mercury, and ethyl mercury, respectively. After adsorption by L. minor powder for 40 min, when the initial concentrations of inorganic and organic mercury were under 12.0 μg L⁻¹ and 50.0 μg L⁻¹, respectively, the residual concentrations of mercury could meet the criterion of drinking water (1.0 μg L⁻¹) and the permitted discharge limit of wastewater (10.0 μg L⁻¹) set by China and USEPA, respectively. Thorough removal of both inorganic and organic mercury from aqueous solutions was reported for the first time. The significant adsorption sites were C–O–P and phosphate groups by the surface electrostatic interactions with aqueous inorganic and organic mercury cations, and then the selective adsorption was resulted from the strong chelating interaction between amine groups and mercury on the surface of L. minor cells.     

Optimal exponential feeding strategy for dual-substrate biostimulation of phenol degradation using Cupriavidus taiwanensis

The exponential feeding strategy (EFS) of dual substrates (i.e., phenol and glycerol) was applied to optimize the overall performance of phenol degradation by Cupriavidus taiwanensis R186. Addition of a second substrate (e.g., glycerol) could stimulate the phenol biodegradation efficiency of strain R186. Hence, a feasible EFS was developed for fed-batch phenol biodegradation using the dual-substrate biostimulation technique. The phenol degradation kinetics was well characterized with proposed model and response surface analysis. Our findings quantitatively revealed that glycerol could effectively enhance the phenol degradation performance, as the highest phenol degradation efficiency occurred with the supplementation of 0.8–1.2 g L⁻¹ of glycerol. The optimal dual-substrate EFS was identified via contour analysis and kinetic modeling. With the optimal dual-substrate EFS (i.e., a feeding rate constant (α₁ and α₂) of 0.5 and 0.3, respectively), the shortest time (ca. 13.80 h) for phenol degradation was achieved with a specific growth rate of ca. 0.281 h⁻¹.     

Effect of metal ions on reactive dye decolorization by laccase from Ganoderma lucidum

In this work, the influence of different metal ions on laccase activity and laccase-catalyzed dye decolorization was investigated under in vitro conditions using crude laccase obtained from a white rot fungus Ganoderma lucidum. Laccase activity was enhanced by metal ions such as Ca²⁺, Co²⁺, Cu²⁺ and Zn²⁺ at low concentrations (1 mM). Increasing the concentration of metal ions except that of Cu²⁺ and Zn²⁺ up to 5 mM and above decreased the enzyme activity. Among several heavy metals, Fe²⁺ highly inhibited the enzyme activity. Effect of metal ions was tested on decolorization of two reactive dyes, namely Remazol black-B (RB-5) and Remazol brilliant blue R (RBBR) at a concentration of 50 mg l⁻¹. The presence of heavy metals generally did not exert much influence on the decolorization except Fe²⁺. Cu²⁺ and Cr⁶⁺ enhanced the decolorization of both dyes. In the presence of 1 mM Cu²⁺, 94% of RB-5 and 35.5% of RBBR were decolorized during 1 h incubation. G. lucidum laccase was able to tolerate mixture of several metal ions. Treatment of simulated reactive dye effluent by laccase showed that the redox mediator system is necessary for effluent decolorization. Syringaldehyde, a natural redox mediator, was very effective than the synthetic mediator 1-hydroxybenzotriazole (HBT). The initial rate of effluent decolorization in presence of syringaldehyde (0.0831 h⁻¹) was 5.6 times higher than HBT (0.0152 h⁻¹). Although the rate of decolorization was markedly decreased in the effluent containing mixed metal ions, presence of syringaldehyde showed effective decolorization. This study indicates that G. lucidum laccase and natural redox mediator system could be a potential candidate for color removal from reactive dye effluent.     

Single and binary chromium(VI) and Remazol Black B biosorption properties of Phormidium sp.

Wastewaters of textile and leather dying industries may contain significant quantities of chromium(VI) ions besides anionic and water-soluble dyes. Moreover the temperature of these wastewaters may be a controlling parameter affecting the biosorption efficiency. In this study biosorption of chromium(VI) and Remazol Black B reactive dye by dried Phormidium sp., a thermophilic cyanobacterium, was studied as a function of initial chromium(VI) concentration and temperature in no dye and 100 mg l⁻¹ dye-containing media at an initial pH value of 2.0 at which the biomass exhibited the maximum chromium(VI) and dye uptakes. The decrease of both metal and dye uptakes with temperature indicated that the uptakes were exothermic in nature. Equilibrium uptake of chromium(VI) enhanced considerably with both chromium(VI) and 100 mg l⁻¹ dye concentrations. Moreover the presence of chromium(VI) also increased the uptake of dye. At 25 °C, 22.8 mg g⁻¹ chromium(VI) and 91.3 mg g⁻¹ dye were sorbed by the biomass in binary 100 mg l⁻¹ chromium(VI) and 100 mg l⁻¹ dye-containing medium. The Langmuir was the best suitable adsorption model for describing the biosorption of chromium(VI) individually and in dye-containing medium. The pseudo-second-order kinetic model described both the chromium(VI) and dye biosorptions kinetics accurately.     

Characterization of electron irradiated GaN n-p diode

Electron-beam irradiated GaN n⁺-p diodes were characterized by deep level transient spectroscopy (DLTS) and optical responsivity measurements. The GaN n⁺-p diode structures were grown by metal organic chemical vapor deposition technique, and the electron irradiation was done by the energies of 1 MeV and 2 MeV with dose of 1 × 10¹⁶ cm^− 2. In DLTS measurement, the defect states of E_c − 0.36 eV and E_c − 0.44 eV in the electron irradiated diodes appeared newly. The optical responsivity of GaN n⁺-p diode was characterized in ultra-violet region, and then the maximum optical responsivity at 350 nm was decreased after electron-beam irradiation.     

Deep level transient spectroscopy on charge traps in high-k ZrO2

The deep trap properties of high-dielectric-constant (k) ZrO₂ thin films were examined by deep level transient spectroscopy (DLTS). The hole traps of a ZrO₂ dielectric deposited by sputtering were investigated in a MOS structure over the temperature range, 375 K-525 K. The potential depth, cross section and concentration of hole traps were estimated to be ∼ 2.5 eV, ∼ 1.8 × 10^− 16 cm² and ∼ 1.0 × 10¹⁶ cm^− 3, respectively. DLTS of ZrO₂ dielectrics can be used to examine the threshold voltage shift (?V_th) during the operation of SONOS-type flash memory devices, which employ high-k materials.     

Direct electrochemical behavior of cytochrome c on sodium dodecyl sulfate modified electrode and its application to nitric oxide biosensor

Polyacrylamide (PAM), sodium dodecyl sulfate (SDS) and cytochrome c (Cyt c) were immobilized on the surface of a glass carbon electrode (GCE), respectively, to form a Cyt c /SDS/PAM/GCE. The modified electrode was characterized with the electrochemical impedance. The direct electrochemical behaviors of Cyt c on SDS/PAM/GCE were obtained by using cyclic voltammetry. A pair of well-defined and reversible redox peaks could be observed in a 0.10 M pH 7.0 phosphate buffer solution. The anodic and cathodic peak potentials of Cyt c were at 0.051 V and − 0.003 V (vs. Ag/AgCl), respectively. The Cyt c on SDS/PAM/GCE exhibited well electrocatalytic activity to reduction of nitric oxide. The relative electrochemical parameters were obtained. The resulted electrode displayed a rapid amperometric response to the reduction of nitric oxide. The catalytic current is linear to the nitric oxide concentration in the range of 8.0 × 10^− 7 M to 9.5 × 10^− 5 M and the detection limit was 1.0 × 10^− 7 M (Signal/Noise = 3). The proposed biosensor could be used to detect quantitatively nitric oxide.     

Electrochemical studies of cystine modified self-assembled monolayer for Escherichia coli detection

An electrochemical DNA biosensor based on cystine modified self-assembled monolayer (cys-SAM) onto gold electrode (AuE) has been fabricated for Escherichia coli (E. coli) detection. This biosensing electrode has been characterized using scanning electron microscopy (SEM), FT-IR spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under the optimum conditions, this DNA biosensor can be used to detect complementary target DNA concentration in the range of 1 × 10^− 6 M to 1 × 10^− 20 M within 60 s of hybridization time at 25 °C and has been found to be stable for about four months when stored at 4 °C.     

Composition dependent thermoelectric properties of sintered Mg2Si1−xGex (x = 0 to 1) initiated from a melt-grown polycrystalline source

Fabrication of Mg₂Si_1−xGe_x (x = 0-1.0) was carried out using a spark plasma sintering technique initiated from melt-grown polycrystalline Mg₂Si_1−xGe_x powder. The thermoelectric properties were evaluated from RT to 873 K. The power factor of Mg₂Si_1−xGe_x with higher Ge content (x = 0.6-1.0) tends to decrease at higher temperatures, and the maximum value of about 2.2 × 10^− 5 Wcm^− 1K^− 2 was observed at 420 K for Mg₂Si and Mg₂Si_0.6Ge_0.4. The coexistence of Si and Ge gave rise to a decrease in the thermal conductivity in the Mg₂Si_1−xGe_x. The values close to 0.02 Wcm^− 1K^− 1 were obtained for Mg₂Si_1−xGe_x (x = 0.4-0.6) over the temperature range from 573 to 773 K, with the minimum value being about 0.018 Wcm^− 1K^− 1 at 773 K for Mg₂Si_0.4Ge_0.6. The maximum dimensionless figure of merit was estimated to be 0.67 at 750 K for samples of Mg₂Si_0.6Ge_0.4.     

Chemical bath deposition of PbS nanocrystals: Effect of substrate

Nanocrystalline PbS layers have been deposited chemically on Si, Ge and GaAs substrates from alkaline solutions containing 0.05 mol l^− 1 of Pb(NO₃)₂, 0.04 mol l^− 1 of thiourea, 0.05 mol l^− 1 of triethanolamine, and 0.15 mol l^− 1 of NaOH. Rutherford backscattering spectroscopy, transmission electron and atomic force microscopy reveal that the chemical nature of the substrate has a profound influence on the structure and thickness of the deposited layers. It is found that a large lattice mismatch between the substrate and PbS results in formation of coarse-grained layers with a small effective thickness (e.g. PbS on Si). On the other hand, close matching of lattice constants leads to deposition of thicker layers with smaller grain size (e.g. PbS on Ge, GaAs).     

Aqueous two-phase systems: a new approach for the determination of p-aminophenol

A new method has been developed for the spectrophotometric determination of p-aminophenol (PAP) in water, paracetamol formulations and human urine samples with a recovery rate between 94.9 and 101%. This method exploits an aqueous two-phase system (ATPS) liquid-liquid extraction technique with the reaction of PAP, sodium nitroprusside and hydroxylamine hydrochloride in pH 12.0, which produces the [Fe₂(CN)₁₀]¹⁰⁻ anion complex that spontaneously concentrates in the top phase of the ATPS (K[Fe₂(CN)₁₀]¹⁰⁻=97.7). The ATPS does not require an organic solvent, which is a safer and cleaner liquid-liquid extraction technique for the determination of PAP. The linear range of detection was from 5.00 to 500 μg kg⁻¹ (R ≥ 0.9990; n = 8) with a coefficient of variation of 2.11% (n = 5). The method exhibited a detection limit of 2.40 μg kg⁻¹ and a quantification limit of 8.00 μg kg⁻¹. The ATPS method showed a recovery that ranged between 96.4 and 103% for the determination of PAP in natural water and wastewater samples, which was in excellent agreement with the results of the standard 4-aminoantipyrine method that was performed on the same samples.     

Structure and negative thermal expansion of Pb1 −xBixTiO3

Pb_1-xBi_xTiO₃ (x = 0.0-0.1) compounds were prepared to study the unique dopant effect of bismuth in PbTiO₃. Their thermal expansions and structures were investigated by high-temperature X-ray diffraction and X-ray Rietveld method. The results indicated that Bismuth substitution evidently weakened the tetragonality of PbTiO₃ solid solution, but increased the spontaneous polarization. Both the enhanced spontaneous polarization and the decreased tetragonality led to small volume shrinkage with temperature rising, where the average volumetric thermal expansion coefficient changed from − 1.99 × 10^− 5/°C for pure PbTiO₃ to − 0.56 × 10^− 5/°C for Pb_0.90Bi_0.10TiO₃. The Curie point of Pb_1 − xBi_xTiO₃ was slightly raised compared to PbTiO₃ and permitted one to use it in a wide temperature range.     

Enhanced thermoelectric properties of NaCo2O4 by adding ZnO

The primary phase present in the as-sintered Na(Co_1 − xZn_x)₂O₄ (0 ≤ x ≤ 0.1) bodies was the solid solution of the constituent oxides with a bronze-type layered structure. The electrical conductivity of the Na(Co_1 − xZn_x)₂O₄ samples significantly increased with an increase in ZnO content. The sign of the Seebeck coefficient for all samples was positive over the whole temperature range (723-1073 K), i.e., p-type conduction. The power factor of Na(Co_0.95Zn_0.05)₂O₄ showed an outstanding power factor (1.7 × 10^− 3Wm^− 1 K^− 2) at 1073 K. The power factor was above four times superior to that of ZnO-free NaCo₂O₄ (0.4 × 10^− 3Wm^− 1 K^− 2). This originates from an unusually large Seebeck coefficient (415 μVK^− 1) accompanied with high conductivity (127Ω^− 1 cm^− 1) at 1073 K.     

Optical and electrical properties of vapour phase grown Zn1 − xCrxTe crystals

The optical and electrical properties of vapour phase grown crystals of diluted magnetic semiconductor Zn_1 − xCr_xTe were investigated for 0 ≤ x ≤ 0.005. The diffuse reflectance spectra exhibited an increase in the fundamental absorption edge (E₀) with composition x and were also dominated by a broad absorption band around 5200 cm^− 1 arising from ⁵T₂ → ⁵E transition. The ⁵T₂ and ⁵E levels originate from the crystal field splitting of the ⁵D free ion in the ground state. The electrical resistivity measurements revealed semiconducting behaviour of the samples with p-type conductivity in the temperature range of 200-450 K.     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by Substituting Mg for Co

The microwave dielectric properties of La(Mg_0.5−xCo_xSn_0.5)O₃ ceramics were examined with a view to exploiting them for mobile communication. The La(Mg_0.5−xCo_xSn_0.5)O₃ ceramics were prepared using the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Co_0.1Sn_0.5)O₃ ceramics revealed that La(Mg_0.4Co_0.1Sn_0.5)O₃ is the main crystalline phase, which is accompanied by small extent of La₂Sn₂O₇ as the second phase. Formation of this Sn-rich second phase was attributed to the loss of MgO upon ignition. Increasing the sintering temperatures seemed to promote the formation of La₂Sn₂O₇. An apparent density of 6.67 g cm⁻³, a dielectric constant (?_r) of 20.3, a quality factor (Q.F.) of 70,500 GHz, and a temperature coefficient of resonant frequency (τ_f) of −77 ppm °C⁻¹ were obtained for La(Mg_0.4Co_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Influence of electron irradiation on characteristics of Si1−xGex p-n-structures

Electrically active defects induced by irradiation with 4 MeV electrons and their influence on dynamic and static parameters of p-n-structures with bases on boron doped Si_1−xGe_x alloys (0<x?0.06) have been investigated. It has been found that after irradiation with the electron fluence Φ=2×10¹⁴ cm⁻² lifetime of minority charge carriers decreases more than 12 times and forward voltage increases twice. Deep level transient spectroscopy (DLTS) studies have shown that interstitial carbon atoms are dominant electrically active defects induced by the irradiation. These defects are transformed into the complexes “interstitial carbon—interstitial oxygen” upon annealing of irradiated samples in the temperature range 50-100 °C.     

Fabrication of Neisseria gonorrhoeae biosensor based on chitosan-MWCNT platform

We report results of studies relating to preparation and characterization of DNA electrodes based on the chitosan-MWCNT/ITO nanobiocomposite platform for electrochemical detection of gonorrhoea, the most common bacterial sexually transmitted disease. (STD). This biosensing electrode has been characterized using FT-IR, SEM, cyclic voltammetry and differential pulse voltammetry, etc. The sensing characteristics have been investigated in phosphate buffer saline using methylene blue as the hybridization indicator. This DNA biosensor has a response time of 60 s and is found to be stable for about 4 months when stored at 4 °C. The results of DPV studies reveal that this bioelectrode can detect complementary DNA concentration in a wide range of 1 × 10^− 6 M to 1 × 10^− 17 M with a detection limit of 1 × 10^− 16 M.     

Preparation and characterization of CuIn1 − xGaxSe2 − ySy thin film solar cells by rapid thermal processing

This paper describes the synthesis and characterization of CuIn_1 − xGa_xSe_2 − yS_y (CIGSeS) thin-film solar cells prepared by rapid thermal processing (RTP). An efficiency of 12.78% has been achieved on ~ 2 µm thick absorber. Materials characterization of these films was done by SEM, EDS, XRD, and AES. J-V curves were obtained at different temperatures. It was found that the open circuit voltage increases as temperature decreases while the short circuit current stays constant. Dependence of the open circuit voltage and fill factor on temperature has been estimated. Bandgap value calculated from the intercept of the linear extrapolation was 1.1-1.2 eV. Capacitance-voltage analysis gave a carrier density of 4.0 × 10¹⁵ cm^− 3.     

Structure and thermal conductivity of Gd2(TixZr1 − x)2O7 ceramics

The Gd₂(Ti_xZr_1 − x)₂O₇ (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd₂(Ti_xZr_1 − x)₂O₇ were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd₂(Ti_xZr_1 − x)₂O₇ from room temperature to 1400 °C was measured by a laser-flash method. The Gd₂Zr₂O₇ has a defect fluorite-type structure; however, Gd₂(Ti_xZr_1 − x)₂O₇ (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd₂Zr₂O₇ and Gd₂Ti₂O₇ are infinitely soluable. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ is within the range of 1.33 to 2.86 W m^− 1 K^− 1 from room temperature to 1400 °C.