The determination of acetaminophen using a carbon nanotube:graphite-based electrode

The oxidation of acetaminophen was studied at a glassy carbon electrode modified with multi-walled carbon nanotubes and a graphite paste. Cyclic voltammety, differential pulse voltammetry and square wave voltammetry at various pH values, scan rates, and the effect of the ratio of nanotubes to graphite were investigated in order to optimize the parameters for the determination of acetaminophen. Square wave voltammetry is the most appropriate technique in giving a characteristic peak at 0.52 V at pH 5. The porous nanostructure of the electrode improves the surface area which results in an increase in the peak current. The voltammetric response is linear in the range between 75 and 2000 ng.mL^?1, with standard deviations between 0.25 and 7.8%, and a limit of detection of 25 ng.mL^?1. The method has been successfully applied to the analysis of acetaminophen in tablets and biological fluids.     

Hierarchically branched titania nanotubes with tailored diameters and branch numbers

Over the past decade, electrochemical anodization of self-organized TiO(2) nanotubes has been studied intensively with the main focus being on uniform diameters along the TiO(2) nanotube depth direction. In the present work, hierarchically branched TiO(2) nanotubes with tailored diameters and branch numbers are successfully achieved by adjusting the anodization voltage. Reducing the applied voltage by a factor of 1/√n causes a one trunk nanotube to diverge into n-branched TiO(2) nanotubes, whose diameters are 1/√n of the trunk nanotube diameter (n is an integer). Multiple layers of branched TiO(2) nanotubes are also obtained by further dividing the branched nanotubes when the applied voltage is further reduced step-by-step with a 1/√n factor. Enlargement and termination of TiO(2) nanotubes occur when the anodization voltage increases by √n times. Alternating increase and decrease in the applied voltage lead to a more sophisticated hierarchical structure of TiO(2) nanotubes. The fundamental understanding of these processes is discussed.     

还原剂对多孔阳极氧化铝纳米孔道结构的影响

多孔阳极氧化铝(PAA)和多孔阳极氧化钛纳米管(PATNT)的结构调控近年来倍受关注. 在形成机理尚不清楚的情况下, 对PAA和PATNT的结构调控很难避免盲目性. 为验证“氧气气泡模具”可以形成纳米孔道这个新观点, 本文采用化学方法对PAA的结构进行调控, 成功地引入了一种还原剂来吸收纳米孔道中的氧气气泡. 在添加还原剂的草酸溶液中得到了一种特殊的阳极氧化铝膜. 研究了还原剂的含量对磷酸溶液中形成PAA孔道结构的影响, 结果表明随着还原剂含量的增加, PAA的孔道直径逐渐减小, 有序性降低. 对比了添加还原剂前后阳极氧化过程的电压-时间曲线的差异, 结果表明, 在含有还原剂溶液中制备的阳极氧化铝膜的导电性明显提高. 在密封的条件下, 还原剂能吸收掉孔道中的氧气, 使气泡模具效应消失, 得到完全的致密型氧化膜. 这些实验事实充分证明PAA中有序孔道的形成是氧气气泡模具效应的结果.     

Fabrication of self-organized TiO2 nanotube arrays for photocatalytic reduction of CO2

The photocatalytic conversion of CO₂ and H₂O to alcohols was achieved using self-organized TiO₂ nanotube arrays (TNAs), which were prepared by electrochemical anodization of Ti foils in 1 M (NH₄)₂SO₄ electrolyte containing 0.5 wt% NH₄F. Experimental results revealed that the morphology and structure of self-organized TNAs could be strongly influenced by the applied voltage and anodization temperature, and the optimized TNAs were prepared by electrochemical anodization of Ti foils under optimal conditions (i.e., at 20 V for 2 h at 30 °C). The as-prepared TNAs were amorphous and could be transformed to anatase phase during the thermal treatment at 450 °C in air for 3 h. By using the annealed TNAs as a photocatalyst, the photocatalytic reduction of CO₂ to alcohol, predominately methanol and ethanol, was demonstrated under Xenon lamp illumination. Based on the photocatalytic measurements, the production rates of methanol and ethanol were calculated to be ～10 and ～9 nmol cm^?2 h^?1, respectively. In addition, the formation mechanism of methanol and ethanol was also tentatively proposed.     

A glassy carbon electrode modified with bismuth nanotubes in a silsesquioxane framework for sensing of trace lead and cadmium by stripping voltammetry

Single-walled bismuth nanotubes (sw-BiNTs) were self-assembled with octa(3-aminopropyl) silsesquioxane as a framework and to govern morphology. Deposited on a glassy carbon electrode (GCE), the sw-BiNTs were used for the simultaneous analysis of Pb(II) and Cd(II) by square wave stripping voltammetry. The sw-BiNTs were prepared by (a) coordination interaction between the amino groups of the silsesquioxane and the Bi(III) ions, and by (b) reduction with sodium borohydride. Transmission electron microscopy images revealed single-walled tubular structures with diameters of ~4–6 nm, and with lengths of several hundreds nanometers. GCEs modified with such sw-BiNTs perform much better than bare GCEs in stripping analysis of Pb(II) and Cd(II). The effects of adsorption quantity of sw-BiNTs, solution pH, pulse amplitude, and pulse width were optimized. The modified electrode was then used for the analysis of Pb(II) and Cd(II) in a linear response range from 0.4 to 6 μM with a sensitivity of 4.692 μA μM^?1 and 3.835 μA μM^?1, and detection limits of 1 nM and 5 nM, respectively. The method was successfully applied to the analysis of Pb(II) and Cd(II) in toy leachates, and the results were in good agreement with those obtained with atomic absorption spectrometry. Sensitivity and detection limits were compared with other voltammetric methods, and the sw-BiNTs are deemed to be an attractive alternative for practical applications. Other features of the electrode include low costs, a well reproducible nanostructure, and ease of scale-up of the fabrication process.

Thermokinetic characterisation of tin(II) chloride

Thermokinetic behaviour of SnCl₂ was investigated using differential scanning calorimetry and thermogravimetry techniques under non-isothermal conditions in air, complemented by electron microscopy and Raman spectroscopy. According to the results obtained, the oxidation of SnCl₂ at the heating rates of 5 and 100 °C min^?1 leads to the in situ formation of highly crystalline SnO₂ nanostructures in the form of nanoparticles and nanorods, respectively. The oxidation of SnCl₂ was found to be a liquid–solid (LS) phase transition at the heating rates equal or lower than 10 °C min^?1 and a gas–solid phase transition at the heating rates equal or greater than 20 °C min^?1. The activation energy of melting, vaporisation and LS oxidation of SnCl₂ was determined to be 198, 93 and 91 kJ mol^?1, respectively.     

Adsorption of 137Cs on titanate nanostructures

Various types of sodium and potassium titanate nanostructures (nanotubes, nanofibers, nanoribbons, nanwires) were synthesized and characterized by X-ray diffraction, SEM and TEM, as well BET and BJH methods. Adsorption of radiotracer ¹³⁷Cs⁺ ions from aqueous solutions on synthesized titanate nanostructures was investigated in batch technique as a function of contact time, concentration of sodium ions and pH of the solutions. It was found that among the studied nanostructures nanotubes shows the highest selectivity for ¹³⁷Cs, which is related to a zeolitic character of Cs⁺ adsorption. The efficient adsorption of ¹³⁷Cs was obtained in Na⁺ solutions with concentration below 10^?2 M, at pH 7–9 and in contact time above 2 h. Moreover, nanotubes have the higher specific surface area than other nanostructures, which results in better availability of ion exchange groups and high ion exchange capacity. These properties of nanotubes indicate that they may be used for adsorption of ¹³⁷Cs from various types of nuclear wastes.     

A Novel Electrochemical Immunosensor for Prostate-Specific Antigen Based on Noncovalent Nanocomposite of Ferrocene Monocarboxylic Acid with Graphene Oxide

A novel electrochemical immunosensor was developed for the determination of prostate-specific antigen based on immobilization of appropriate antibodies on gold nanoparticles and a poly-(2,6-pyridinediamine) modified electrode. The nanocomposite of ferrocene monocarboxylic acid hybridized graphene oxide was prepared by a π-π stacking interaction and was used as the electrochemical probe. A sandwich-type complex immunoassay was applied with polyclonal prostate-specific antigen antibodies labeled with the nanocomposite of ferrocene monocarboxylic acid hybridized graphene oxide. In order to improve the sensitivity, a potentiostatic method was used to reduce graphene oxide. Cyclic voltammetry and differential pulse voltammetry were employed to characterize the assembly process and the performance of the immunosensor. Under optimal conditions, the peak current of the immunosensor increased with concentration, showing a linear relationship between the peak current and the logarithm of the prostate-specific antigen concentrations in a wide range of 2.0 pg mL^?1 to 10.0 ng mL^?1 with a low detection limit of 0.5 pg mL^?1. The immunosensor was used for the determination of prostate-specific antigen in serum.     

Multi‐Walled Carbon Nanotubes as Sorbent for Flow Injection On‐Line Microcolumn Preconcentration Coupled with Flame Atomic Absorption Spectrometry for Determination of Cadmium and Copper

Abstract

Multi‐walled carbon nanotubes (MWNTs) were used as sorbent for flow injection (FI) on‐line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace cadmium and copper in environmental and biological samples. Effective preconcentration of trace cadmium and copper was achieved in a pH range of 4.5–6.5 and 5.0–7.5, respectively. The retained cadmium and copper were efficiently eluted with 0.5 mol L^?1 HCl for on‐line FAAS determination. The MWNTs packed microcolumn exhibited fairly fast kinetics for the adsorption of cadmium and copper, permitting the use of high sample flow rates up to at least 7.8 mL min^?1 for the FI on‐line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 60 sec at a sample loading flow rate of 4.3 mL min^?1, the enhancement factor was 24 for cadmium and 25 for copper at a sample throughput of 45 h^?1. The detection limits (3σ) were 0.30 and 0.11 µg L^?1 for Cd and Cu, respectively. The precision (RSD) for 11 replicate measurements was 2.1% at the 10‐µg L^?1 Cd level and 2.4% at the 10‐µg L^?1 Cu level. The developed method was successfully applied to the determination of trace Cd and Cu in a variety of environmental and biological samples.     

Controllable synthesis of well-ordered TiO2 nanotubes in a mixed organic electrolyte for high-efficiency photocatalysis

Well-ordered TiO 2 nanotube arrays (TNAs) were fabricated by electrochemical anodization in a mixed organic electrolyte consisting of ethylene glycol and glycerol. The morphology, structure, crystalline phase, and photocatalytic properties of TNAs were characterized by using TEM, SEM, XRD and photodegradation of methylene blue. It was found that the morphology and structure of TNAs could be significantly influenced by the anodization time and applied voltage. The obtained tube length was found to be proportional to anodization time, and the calculated growth rate of nanotubes was 0.6 m/h. The microstructure analysis demonstrated that the diameter and thickness of the nanotubes increased with the increase of anodization voltage. The growth mechanism of TNAs was also proposed according to the observed relationship between current density and time during anodization. As expected, the obtained TNAs showed a higher photocatalytic activity than the commercial TiO 2 P25 nanoparticles.     

Fabrication of AAO films with controllable nanopore size by changing electrolytes and electrolytic parameters

In this paper, we fabricate two kinds of anodic aluminum oxide (AAO) films with controllable nanopore size by changing electrolytes and electrolytic parameters. The first AAO film with a four-layer structure was fabricated by sequential anodization of aluminum in aqueous solution of H₂SO₄, H₂C₂O₄, malonic acid, and tartaric acid at different anodic oxidation voltages. The average pore diameter of the as-prepared AAO film is 25 nm in the first layer, 54 nm in the second layer, 68 nm in the third layer, and 88 nm in the fourth layer, respectively. The pore densities of each layer decrease downwards to Al substrate, which are 300?×?10⁸, 100?×?10⁸, 21?×?10⁸, and 6.9?×?10⁸ cm^?2, respectively. Furthermore, another AAO film with periodically changed pore diameter was fabricated by alternating anodization of aluminum in aqueous solution of H₃PO₄ and tartaric acid under galvanostatic mode. The anodization processes present approximately identical best ordering voltage (195 V) in H₃PO₄ and tartaric acid under galvanostatic mode. The pore diameter with periodic change can be enlarged through a pore-widening treatment. Both AAO films with special nanopore structures can be used not only as templates for preparing nano-array materials whose pore diameter presents periodic change or gradual increase, but also as nanofilters to separate materials in some special media.     

Electrochemical Characterization and Rapid Voltammetric Determination of Riluzole in Pharmaceuticals and Human Serum

The electrochemical oxidation of riluzole was investigated using cyclic and linear sweep voltammetry. Under optimized conditions, current and concentration showed linear dependence in Britton Robinson buffer at pH 3.00 for boron doped diamond and pH 3.00 phosphate buffers for glassy carbon electrodes. Differential pulse and square wave voltammetry were used for the determination of riluzole levels in serum samples and pharmaceutical formulations. The limit of detections were found as 5.25 × 10^?7 M and 8.26 × 10^?8 M for glassy carbon electrode and 1.78 × 10^?7 M and 8.42 × 10^?8 M for boron-doped diamond electrodes, in serum samples, using differential pulse and square wave methods, respectively.     

Effect of water and fluoride content on morphology and barrier layer properties of TiO2 nanotubes grown in ethylene glycol-based electrolytes

This paper studies the effect of H₂O and NH₄F content on morphology and barrier layer properties of TiO₂ nanotubes grown by potentiostatic anodization in ethylene glycol-based electrolytes. The increase in these two variables leads to an increase in the chemical attack of the formed oxide. However, each of these variables plays a different role in the formation of TiO₂ nanotubes. On the one hand, a higher percentage of H₂O in the electrolyte leads to a transition from a nanoporous to a nanotubular structure, as well as to a greater diameter of the tubes and a decrease in their length and barrier layer thickness. In contrast, a higher NH₄F concentration decreases nanotube diameter and increases their length modifying barrier layer properties due to insertion of F^? ions into the lattice. This diminishes the barrier layer resistance, but increases both the adsorption and the diffusion coefficient of F^? ions. The different roles of H₂O and NH₄F in film formation are also associated with the presence of sub-oxides detected by XPS.     

Electrochemical sensor for determination of aflatoxin B1 based on multiwalled carbon nanotubes-supported Au/Pt bimetallic nanoparticles

A sensitive and selective imprinted electrochemical sensor for the determination of aflatoxin B₁ (AFB₁) was constructed on a glassy carbon electrode by stepwise modification of functional multiwalled carbon nanotubes (MCNTs), Au/Pt bimetallic nanoparticles (Au/PtNPs), and a thin imprinted film. The fabrication of a homogeneous porous poly o-phenylenediamine (POPD)-grafted Au/Pt bimetallic multiwalled carbon nanotubes nanocomposite film was conducted by controllable electrodepositing technology. The sensitivity of the sensor was improved greatly because of the nanocomposite functional layer; the proposed sensor exhibited excellent selectivity toward AFB₁ owing to the porous molecular imprinted polymer (MIP) film. The surface morphologies of the modified electrodes were characterized using a scanning electron microscope. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. A linear relationship between the sensor response signal and the logarithm of AFB₁ concentrations ranging from 1?×?10^?10 to 1?×?10^?5 mol L^?1 was obtained with a detection limit of 0.03 nmol L^?1. It was applied to detect AFB₁ in hogwash oil successfully.     

Selective Synthesis of 2D Mesoporous CuO Agglomerates by Pulsed Spark Discharge in Water

Metal oxide nanomaterials, including copper oxide, have attracted great attention due to their unique physical and chemical properties that are dependent on particle size and morphology. In this study, we propose an alternative technique for the synthesis of 2D mesoporous CuO agglomerates that is both efficient and ecological. This technique is based on the use of pulsed spark discharges between copper electrodes immersed in deionized water. Detailed TEM analyses show that the synthesized CuO nanostructures are composed of elementary nanocrystals with sizes in the order of a few nanometers. Assessments of the effects of applied voltage (5 and 20 kV) and discharge pulse width (100 and 500 ns) demonstrate that the latter parameter influences the size and density of nanocrystals in a nanostructure. Moreover, voltage and pulse width may both be used to finely control the direct optical band gap energy of CuO nanostructures between 3.0 and 3.4 eV. The efficient and ecological technique developed in this study produces 2D mesoporous CuO agglomerates that can be readily used in other processes.

     

Online thorium determination after preconcentration in a minicolumn having XAD-4 resin impregnated with N-benzoylphenylhydroxylamine by FI-spectrophotometry

A very sensitive and selective flow injection on-line determination method of thorium (IV) after preconcentration in a minicolumn having XAD-4 resin impregnated with N-benzoylphenylhydroxylamine is described. Thorium (IV) was selectively adsorbed from aqueous solution of pH 4.5 in a minicolumn at a flow rate of 13.6 mL min^?1, eluted with 3.6 mol dm^?3 HCl (5.6 mL min^?1), mixed with arsenazo-III (0.05% in 3.6 mol dm^?3 HCl stabilized with 1% Triton X-100, 5.6 mL min^?1) at confluence point and taken to the flow through cell of spectrophotometer where its absorbance was measured at 660 nm. Peak height was used for data analyses. The preconcentration factors obtained were 32 and 162, detection limits of 0.76 and 0.150 ??g L^?1, sample throughputs of 40 and 11 h^?1 for preconcentration times of 60 and 300 s, respectively. The tolerance levels for Zr(IV) and U(VI) metal ions is increased to 50-folds higher concentration to Th(IV). The proposed method was applied on different spiked tap water, sea water and biological sample and good recovery was obtained. The method was also applied on certified reference material IAEA-SL1 (Lake Sediment) for the determination of thorium and the results were in good agreement with the reported value.     

含氯离子电解液中二氧化钛纳米管的阳极氧化形成机理及应用

采用电化学阳极氧化的方法,以氯化铵(NH₄Cl)水溶液为电解液,在纯钛表面制备了二氧化钛(TiO₂)纳米管。考察了制备电压、氧化时间、Cl^-浓度和钛基体的退火处理对阳极氧化过程的影响规律,探讨了在含氯离子电解液中纳米管的形成机理,并基于上述含氯离子电解液中纳米管形成机制,通过两步阳极氧化法得到无支撑纳米管薄膜。     

Determination of Triazine Herbicides and Metabolites by Solid Phase Extraction with HPLC Analysis

An efficient solid phase extractive preconcentration/separation method was developed for the trace determination of herbicides in aqueous samples using Amberlite XAD-4 resin as the adsorbent. The retained herbicides were eluted with methanol at a flow rate of 1.0 mL min^?1 and determined by HPLC-DAD (wavelength of 220 nm) using water (pH:4.7, phosphoric acid) and methanol (ratio 35:65) as the mobile phase with a flow rate of 1.0 mL min^?1. Quantitative recoveries of simazine, atrazine and its metabolities were achieved at optimized analysis conditions that included 0.75 g of resin; a pH of 3.0; an eluent volume of 3.0 mL; an eluent flow rate of 1.0 mL min^?1; and a sample flow rate of 4.0 mL min^?1. The limits of detection, preconcentration factor, and linear ranges for the herbicides were 0.084–0.121 µgL^?1, 1000, and 0.5–20 mg L^?1, respectively. The performance of the method was evaluated by analysis of spiked water samples. The recoveries of simazine, atrazine and their metabolities were found to be quantitative (99.6–104.8%) with RSDs of 2.2–4.8% and 2.8–4.7% for intra-day and inter-day precision, respectively. The proposed method was successfully applied for trace determination of studied analytes in waste water, apple juice, and red wine samples.     

TiO_2一维纳米材料及其纳米结构的合成

本文对合成TiO2一维纳米材料及其有序纳米阵列的阳极氧化法、模板法以及水热法进行了全面而系统的评述,着重介绍了它们的最新研究进展。阳极氧化法能制备牢固负载于基体上的TiO2纳米管阵列,这有助于构筑TiO2纳米结构及其在纳米器件上的应用;与多种制备技术如溶胶-凝胶工艺、电化学沉积以及原子层沉积等相结合,模板法可以合成出多种形貌的TiO2纳米材料如纳米管、纳米线和纳米棒,并且可以通过改变所用模板的微观尺寸来调控TiO2一维纳米材料及其有序阵列的微结构参数;水热合成法可以制备出直径小且比表面积大的TiO2纳米管粉末。从目前来看,该法还不能制备出牢固负载于基体上的有序纳米阵列。文章最后指出了TiO2一维纳米材料及其有序纳米阵列合成中存在的问题及今后发展方向。