Green synthesis and characterization of Tb-Fe-O-Cu ceramic nanocomposite and its application in simultaneous electrochemical sensing of zinc,cadmium and lead

In this work, a green technique for preparing TbFeO₃/CuO was reported by employing Crataegus and Lantana Camara leaves as fuel and alkalizing agents, respectively. The new sensor based on the perovskite-type nanocomposite was employed as a sensitive and selective platform to detect Pb(II), Zn(II) and Cd(II) simultaneously. TbFeO₃/CuO/Carbon paste electrode (CPE) exhibited a large specific surface area and great electrical conductivity, which enhanced electron transport in the electrochemical process considerably. Moreover, square wave anodic stripping voltammetry (SWASV) was used for the investigation of some factors influencing the sensor sensitivity like pH, modifier concentration, as well as accumulation time and potential. Therefore, the low detection limit (LOD) and a wide linear range were obtained at optimum conditions. In this study, a linear range between 0.9 and 110 µg/L for three ions and LOD of 0.48, 0.29 and 0.12 for zinc, cadmium and lead were achieved, respectively. Moreover, TbFeO₃/CuO/CPE was employed to detect zinc, cadmium and lead ions simultaneously in the real samples so that the results have shown consistency with a standard inductively coupled plasma (ICP).     

Electrochemical sensing of H2O2 using cobalt oxide modified TiO2 nanotubes

Cobalt oxide (Co₃O₄) modified anatase titanium dioxide nanotubes (ATNTs) have been investigated for the electrochemical sensing of hydrogen peroxide (H₂O₂). ATNTs have been synthesized by a two-step anodization process. ATNTs were then modified with Co₃O₄ employing chemical bath deposition method. The structure and morphology of ATNTs and their modification with Co₃O₄ has been confirmed by X-ray diffraction by scanning electron microscopy. H₂O₂ sensing has been studied in 0.1 M PBS solution, by cyclic voltammetry and amperometry. Variation in the peak positions and current densities was observed with addition of H₂O₂ for Co₃O₄ modified ATNTs. Sensitivity and limit of detection improved with modification of ATNTs with Co₃O₄ with precursor concentration up to 0.8 M. However, at higher precursor concentrations sensitivity and limit of detection toward H₂O₂ deteriorated. Co₃O₄ Modified ATNTS using 0.8 M precursor concentration are comparatively more suitable for H₂O₂ sensing applications due to the optimum formation of Co₃O₄/ATNTs heterojunctions.     

Nickel (II) tetrapyridyl complexes as electrocatalysts and precatalysts for water oxidation

Two nickel complexes, [Ni(tpen)](ClO₄)₂.0.5CH₃COCH₃ ( 1 ) and [Ni(tpbn)](ClO₄)₂ ( 2 ), of tetrapyridyl ligands N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,2-ethanediamine (tpen) and N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiO_x composite (nickel oxide with general formula Ni_xO_yH_z) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiO_x composite active for WOR. The NiO_x composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2 . This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center.     

One‐pot synthesis of a multi‐template molecularly imprinted polymer for the extraction of six sulfonamide residues from milk before high‐performance liquid chromatography with diode array detection

A highly selective molecularly imprinted polymer sorbent was synthesized and employed for the simultaneous determination of six sulfonamide antibiotic residues (sulfanilamide, sulfacetamide, sulfadiazine, sulfathiazole, sulfamerazine, and sulfamethizole) in milk samples. Multi‐analyte imprinted particles were used as a sorbent in solid‐phase extraction. Sulfonamides were separated on a high‐performance liquid chromatography column (Merck–Lichrospher RP18e, 5 μm 250 × 4 mm) and further identified and quantified by diode array detection. Several parameters including required loading of the molecularly imprinted polymer sorbent, mass of milk, volume, and type of elution solvent, as well as time for absorption and elution were investigated to obtain optimal experimental conditions. For comparison purpose, a non‐imprinted polymer was applied under the optimum conditions. The validation study according to the European Union Decision 2002/657/EC was based on the investigation of linearity, selectivity, stability, limits of detection and quantitation, decision limit, detection capability, trueness, precision, and ruggedness according to Youden's approach. The decision limit and detection capability values in the milk were achieved from 101.9 to 113.5 μg/kg and from 114.4 to 135.4 μg/kg, respectively, depending on the target sulfonamide drug. Finally, the optimized protocol was successfully applied to commercial milk samples and human breast milk.     

Photosensitive organic-inorganic hybrid structures based on porous silicon

Abstract

In this study, the photovoltaic organic-inorganic structures were created by deposition of poly(3,4-ethylenedioxythiophene) film doped by poly(styrenesulfonate) and reduced graphene oxide on the porous silicon/silicon substrate. Formation of the hybrid structure was confirmed by means of atomic-force microscopy and Fourier transform infrared spectroscopy. The current-voltage characteristics of the obtained structures were studied. It was found the increase of electrical conductivity and photo-induced signal in organic-inorganic structures. Temporal parameters and spectral characteristics of photoresponse in the 400–1100?nm wavelength range were investigated. The widening of spectral photosensitivity in a short-wavelength range due to light absorption in various layers of the multijunction structure in comparison with single crystal silicon was revealed.     

贵金属多孔纳米结构的模板法制备及生物检测应用

贵金属多孔纳米材料是一类非常重要的新型多功能纳米材料,其具有独特的空心内部、多孔的外壁以及可调的形貌等,表现出优异的光、电、催化等特性。调制贵金属多孔纳米材料的尺寸、形状、排列和空间取向等对促进其在拉曼光谱、生物传感等方面的应用至关重要。模板法是利用与目标产物的纳米尺度特征相匹配的预制结构来指导纳米材料的合成,可以制备出其他方法难以制备的新型多孔纳米结构材料。基于模板的多样性,能够便捷的调节多孔贵金属的孔径、尺寸和组分,充分的开发贵金属纳米结构的特性。本文着重介绍了贵金属多孔纳米材料的类型和调控这些纳米结构的各种模板方法,分析了各种制备方法的优势和不足,并简要综述了贵金属多孔纳米结构在生物检测方面的一些应用进展。     

Stripped Charge of Ag Less than Deposited one Owing to Negative Capacitance Caused by Redox Reactions

Anodic stripping voltammetry was made in AgNO₃ solution, here Ag was deposited under long term potentiostatic conditions to evaluate the reduction charge, q_r, and then was stripped by linear sweep voltammetry to determine the oxidation charge, q_o. The charges were unbalanced, satisfying ca. q_o=0.7|q_r|, where other possible reduction charge such as by dioxygen and dichlorosilver were subtracted. The 30 % loss of the anodic charge can be ascribed to the negative capacitance by the potential sweep generation of Ag⁺. The generated Ag⁺ forms a dipole with a counter ion, of which orientation is the same as the direction of the externally applied electric field and opposite to the dipoles of solvent. The redox dipole decreases the conventional double layer capacitance caused by solvent dipoles, and high concentrations of Ag⁺ takes the capacitance to be negative values. The unbalanced charge, however, has no influence on quantitative determination of concentrations Ag⁺ by use of a calibration line.     

Fabrication of Nano Flower‐shaped Platinum on Glassy Carbon Electrode as a Sensitive Sensor for Lead Electrochemical Analysis

Platinum nanoflowers modified glassy carbon electrodes (PtNFs/GCE) was fabricated simply for lead determination in water samples. The modified electrodes were prepared by electrodeposition in hexachloroplatinic acid solution at constant potential. The influence of deposition time and potential on surface morphology, chemical composition, electrochemical properties of electrode were investigated. At ?0.2 V of potential and 150 s of deposition duration, platinum developed as nanoflower shape and scattered densely all over the glassy carbon surface, producing the largest electrochemically active surface areas. The highest differential pulse stripping voltammetry (DPSV) signal of lead was obtained by using the prepared electrode. Under optimized experimental condition of electrolyte, accumulation potential and time, the peak current was found to be linear proportion to lead concentration in range of 1 to 100 μg L^?1 (slope=0.371) with a limit of detection of 0.398 μg L^?1. The method has good repeatability and reproducibility with relative standard deviations of 1.47 % and 4.83 %, respectively. The modified PtNFs/GCE also demonstrated an excellent long‐term stability with only 9 % decrease in Pb peak current over 30 days. Moreover, the performance of the modified PtNFs/GCE in determination of Pb(II) in two industrial wastewaters was good agreement with data obtained by a graphite furnace atomic absorption spectrometry (GFAAS) method.     

Polystyrene-supported phosphine oxide-catalysed Beckmann rearrangement of ketoximes in 1,1,1,3,3,3-hexafluoro-2-propanol

A polystyrene-supported phosphine oxide-catalysed Beckmann rearrangement of ketoximes in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been developed. Good substrate compatibility, mild reaction conditions, good yields as well as the reusability of the catalyst/solvent made this procedure more environmentally benign.     

Preparation of stable and superior flux GO/LDH/PDA‐based nanofiltration membranes through electrostatic self‐assembly for dye purification

Graphene oxide (GO) has triggered significant attention as a new type of self‐assembly membrane material. However, the low filtration flux and unstable performance of GO membrane limit its practical application. Hence, in this work, layered double hydroxides (LDHs), as a 2D material with double‐layer channel structure and positive electricity, were self‐assembled with GO at weight ratio of 7:3 by electrostatic interaction. Then, the GO/LDH hybrids combined with polydopamine (PDA) to obtain stable and high‐flux GO‐based membranes through vacuum filtration and the structure and morphology of as‐prepared samples were characterized by FT‐IR, XRD, XPS, and SEM. Furthermore, the separation performance and surface electronegativity of membranes were tested via pure water flux, rejection efficiency, recycle experiments, and zeta potential. Results revealed that the stability and flux of composite membrane were enhanced significantly compared with neat GO‐based membrane. Further, the dye rejection rate of methylene blue (MB) is higher than Congo red (CR) and rhodamine B (Rh B) and reached to 99.8%.