Synthesis of nickel nanoparticles and carbon encapsulated nickel nanoparticles supported on carbon nanotubes

Nickel nanoparticles were prepared and uniformly supported on multi-walled carbon nanotubes (MWCNTs) by reduction route with CNTs as a reducing agent at 600 °C. As-prepared nickel nanoparticles were single crystalline with a face-center-cubic phase and a size distribution ranging from 10 to 50 nm, and they were characterized by transmission electron microscopy (TEM), high-resolution TEM and X-ray diffraction (XRD). These nickel nanoparticles would be coated with graphene layers, when they were exposed to acetylene at 600 °C. The coercivity values of nickel nanoparticles were superior to that of bulk nickel at room temperature.     

Determination of endocrine-disrupting compounds in water by carbon nanotubes solid-phase microextraction fiber coupled online with high performance liquid chromatography

The commercial solid phase microextraction (SPME) fibers are not stable enough in organic solvent and tend to swell and strip off from the silica fiber in the high performance liquid chromatography (HPLC) mobile phase, and therefore the application of SPME coupled online with HPLC is limited. In this study, an SPME fiber coated with single walled carbon nanotubes (SWCNTs), prepared by means of electrophoretic deposition, was coupled on line to HPLC for the determination of four endocrine-disrupting compounds, i.e. bisphenol A (BPA), estrone (E₁), 17α-ethynylestradiol (EE₂) and octylphenol (OP), in aqueous samples. The results showed that the SWCNTs coating on the prepared fiber did not swell and strip off from the platinum fiber throughout the experiment, thus indicating a high resistance to the HPLC mobile phase, the mixture of water and acetonitrile. The SWCNTs fiber had similar (for OP) or higher (for BPA, EE₂ and E₁) extraction efficiencies than the commonly used polyacrylate fiber, and had a lifetime of more than 120 operation times. Under the optimized conditions, the linearity of the proposed method was 1.0-30.0 μg/L for BPA and OP and 3.0-90.0 μg/L for E₁ and EE₂. The limits of detection (LODs; S/N = 3) and limits of quantification (LOQs; S/N = 10) of the method were 0.32-0.52 μg/L and 1.06-1.72 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.3-7.1% and fiber-to-fiber reproducibility (n = 3) was in the range of 1.6-8.4%. The proposed method was successfully applied for the analysis of spiked tap water and seawater samples with recoveries from 81.8 to 97.3%.     

Rapid in situ growth of oriented titanium‐nickel oxide composite nanotubes arrays coated on a nitinol wire as a solid‐phase microextraction fiber coupled to HPLC–UV

An oriented titanium‐nickel oxide composite nanotubes coating was in situ grown on a nitinol wire by direct electrochemical anodization in ethylene glycol with ammonium fluoride and water for the first time. The morphology and composition of the resulting coating showed that the anodized nitinol wire provided a titania‐rich coating. The titanium‐nickel oxide composite nanotubes coated fiber was used for solid‐phase microextraction of different aromatic compounds coupled to high‐performance liquid chromatography with UV detection. The titanium‐nickel oxide composite nanotubes coating exhibited high extraction capability, good selectivity, and rapid mass transfer for weakly polar UV filters. Thereafter the important parameters affecting extraction efficiency were investigated for solid‐phase microextraction of UV filters. Under the optimized conditions, the calibration curves were linear in the range of 0.1–300 μg/L for target UV filters with limits of detection of 0.019–0.082 μg/L. The intraday and interday precision of the proposed method with the single fiber were 5.3–7.2 and 5.9–7.9%, respectively, and the fiber‐to‐fiber reproducibility ranged from 6.3 to 8.9% for four fibers fabricated in different batches. Finally, its applicability was evaluated by the extraction and determination of target UV filters in environmental water samples.     

Carbon fibers modified with carbon nanoparticles by a facile and fast flame preparation for in-tube solid-phase microextraction

Carbon fibers (CFs) were modified with carbon nanoparticles (CNPs) by a facile and fast flame preparation method. CNPs-CFs were observed by scanning electron microscope, and the nano-scaled granular structure on the surface was found. This material was also characterized by Raman microscope and X-ray photoelectron spectroscope. It was placed into a polyetheretherketone tube to get an extraction tube, which was connected with high performance liquid chromatography for online analysis. The tube displayed the effective extraction to several polycyclic aromatic hydrocarbons (PAHs), based on the possible hydrophobic and π stacking mechanism. Under the optimized conditions (60 mL of sample volume, 2.00 mL min^?1 of sample rate, 0.5% of methanol in sample, 2.0 min of desorption time), an analytical method towards these PAH targets was established. The low limits of detection (0.001–0.005 μg L^?1), satisfactory linear ranges (0.003–5.0 μg L^?1, 0.003–10.0 μg L^?1) and efficient enrichment factors (1012–3164) were presented. The method was applied to detect trace targets in several water samples and satisfactory results were obtained. The method provided some superiorities over other analytical methods, like online test, shorter time and better sensitivity.     

Evaluation of the solid-phase microextraction fiber coated with single walled carbon nanotubes for the determination of benzene,toluene, ethylbenzene,xylenes in aqueous samples

A solid-phase microextraction (SPME) fiber coated with single walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition and treated at 500 °C in H₂ stream. In order to evaluate the characteristics of the obtained fiber, it was applied in the headspace solid-phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) from water sample and quantification by gas chromatography with flame ionization detection (GC-FID). The results indicated that the thermal treatment with H₂ enhanced the extraction of the SWCNTs fiber for BTEX significantly. Thermal stability and durability of the fiber were also investigated, showing excellent stability up to 350 °C and life time over 120 times. In the comparison with the commercial CAR–PDMS fiber, the SWCNTs fiber showed similar and higher extraction efficiencies for BTEX. Under the optimized conditions, the linearity, LODs (S/N = 3) and LOQs (S/N = 10) of the method based on the SWCNTs fiber were 0.5–50.0, 0.005–0.026 and 0.017–0.088 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.5–5.6% and fiber-to-fiber reproducibility (n = 3) was in the range of 4.2–8.3%. The proposed method was successfully applied in the analysis of BTEX compounds in seawater, tap water and wastewater from a paint plant.     

Simultaneous determination of phenyl- and sulfonyl-urea herbicides in river water at sub-parts-per-billion level by on-line preconcentration and liquid chromatography-tandem mass spectrometry

A method based on solid-phase microextraction and gas chromatography flame photometric detector for the determination of organophosphorus pesticides (OPPs) in food samples was described. Three kinds of vinyl crown ether polar fibers were prepared with sol-gel process and used for the analytes. The new coatings showed higher extraction efficiency and sensitivity for organophosphorus pesticides compared with commercial fibers—85 μm PA and 65 μm PDMS-DVB. Specifically, the benzo-15-crown-5 coating was the most effective for the target analytes. Several factors affecting the performance of SPME such as extraction temperature and time, salt addition, and dilution ratios of samples were optimized. The apparent recoveries of spiked food samples (apple juice, apple and tomato) were determined to be over 55.3% and the limits of detection (LODs) were in the range of 0.003-0.09 ng/g for the OPP studied. The method was applied to determine the concentrations of OPP in real food samples.     

Rare-Earth-compound nanowires, nanotubes, and fullerene-like nanoparticles: synthesis, characterization, and properties

Various low-dimensional nanostructures, such as nanowires, nanotubes, nanosheets, and fullerene-like nanoparticles have been selectively synthesized from rare-earth compounds (hydroxides, fluorides) based on a facile hydrothermal method. The subsequent dehydration, sulfidation, and fluoridation processes lead to the formation of rare-earth oxide, oxysulfide, and oxyhalide nanostructures, which can be functionalized further by doping with other rare-earth ions or by coating with metal nanoparticles. Owing to the interesting combination of novel nanostructures and functional compounds, these nanostructures can be expected to bring new opportunities in the vast research areas of and application in biology, catalysts, and optoelectronic devices.     

Growth of cedar-like Au nanoparticles coating on an etched stainless steel wire and its application for selective solid-phase microextraction

A novel cedar-like Au nanoparticles (AuNPs) coating was fabricated on an etched stainless steel (SS) wire by direct chemical deposition and used as an efficient and unbreakable solid phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent growth of AuNPs in chloroauric acid solution. As a result, the uniform cedar-like AuNPs coating with larger surface area was tightly attached to the etched SS wire substrate. The AuNPs coated etched SS fiber (AuNPs/SS) was examined for SPME of ultraviolet (UV) filters, phthalate esters and aromatic hydrocarbons coupled to high-performance liquid chromatography with UV detection. The fabricated fiber exclusively exhibited excellent extraction efficiency and selectivity for some aromatic hydrocarbons. Influential parameters of extraction and desorption time, temperature, stirring rate and ionic strength were investigated and optimized. The limits of detection ranged from 0.008 μg L⁻¹ to 0.037 μg L⁻¹. The single fiber repeatability varied from 3.90% to 4.50% and the fiber-to-fiber reproducibility ranged from 5.15% to 6.87%. The recovery of aromatic hydrocarbons in real water samples spiked at 2.0 μg L⁻¹ and 20 μg L⁻¹ ranged from 94.38% to 106.2% with the relative standard deviations below 6.44%. Furthermore the growth of the cedar-like AuNPs coating can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and withstands at least 200 extraction and desorption replicates.     

Ethylenediamine-anchored gold nanoparticles on multi-walled carbon nanotubes: Synthesis and characterization

Binding of gold nanoparticles (Au-NP) at amine-functionalised multi-walled carbon nanotubes (MWNTs) is proposed. The MWNTs are functionalised with acylchloride groups, which further react with ethylenediamine to form amine-functionalised MWCNTs. These amines are able to bind preformed colloidal Au-NPs. The Au/MWNT composite material facilitates electron-transfer reactions with free-diffusing redox compounds.     

High extraction efficiency for polar aromatic compounds in natural water samples using multiwalled carbon nanotubes/Nafion solid-phase microextraction coating

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes (MWCNTs)/Nafion was developed and applied for the extraction of polar aromatic compounds (PACs) in natural water samples. The characteristics and the application of this fiber were investigated. Electron microscope photographs indicated that the MWCNTs/Nafion coating with average thickness of 12.5 μm was homogeneous and porous. The MWCNTs/Nafion coated fiber exhibited higher extraction efficiency towards polar aromatic compounds compared to an 85 μm commercial PA fiber. SPME experimental conditions, such as fiber coating, extraction time, stirring rate, desorption temperature and desorption time, were optimized in order to improve the extraction efficiency. The calibration curves were linear from 0.01 to 10 μg mL⁻¹ for five PACs studied except p-nitroaniline (from 0.005 to 10 μg mL⁻¹) and m-cresol (from 0.001 to 10 μg mL⁻¹), and detection limits were within the range of 0.03–0.57 ng mL⁻¹. Single fiber and fiber-to-fiber reproducibility were less than 7.5 (n = 7) and 10.0% (n = 5), respectively. The recovery of the PACs spiked in natural water samples at 1 μg mL⁻¹ ranged from 83.3 to 106.0%.     

Carbon monolith: Preparation,characterization and application as microextraction fiber

A carbon monolith was synthesized via a polymerization–carbonization method, styrene and divinylbenzene being adopted as precursors and dodecanol as a porogen during polymerization. The resultant monolith had bimodal porous substructure, narrowly distributed nano skeleton pores and uniform textural pores or throughpores. The carbon monolith was directly used as an extracting fiber, taking place of the coated silica fibers in commercially available solid-phase microextraction device, for the extraction of phenols followed by gas chromatography–mass spectrometry. Under the studied conditions, the calibration curves were linear from 0.5 to 50 ng mL⁻¹ for phenol, o-nitrophenol, 2,4-dichlorophenol and p-chlorophenol. The limits of detection were between 0.04 and 0.43 ng mL⁻¹. The recoveries of the phenols spiked in real water samples at 10 ng mL⁻¹ were between 85% and 98% with the relative standard deviations below 10%. Compared with the commercial coated ones (e.g. PDMS, CW/DVB and DVB/CAR/PDMS), the carbon monolith-based fiber had advantages of faster extraction equilibrium and higher extraction capacity due to the superior pore connectivity and pore openness resulting from its bimodal porous substructure.     

Preparation and characterization of novel crown ether functionalized ionic liquid-based solid-phase microextraction coatings by sol-gel technology

A novel crown ether functionalized ionic liquid (IL), 1-allyl-3-(6'-oxo-benzo-15-crown-5 hexyl) imidazolium hexafluorophosphate was synthesized and used as selective stationary phase to prepare task-specific IL-based solid phase microextraction (SPME) fibers by sol-gel method and free radical cross-linking technology. The underlying mechanism of the sol-gel reaction was proposed and the successful chemical bonding of the crown ether functionalized IL to the formed hybrid organic-inorganic copolymer coating was confirmed by FT-IR spectroscopy. The performance of this in situ created crown ether functionalized IL-based SPME fibers, was investigated in detail. The coating has porous surface structure, stable performance in high temperature (to 340 °C) and in different solutions (water, organic solvent, acid and alkali), and good coating preparation reproducibility. In contrast to the sol-gel derived 1-allyl-3-methyl imidazolium hexafluorophosphate-based coating prepared in our previous work with the identical procedure, the extraction performance of this newly developed sol-gel crown ether functionalized IL-based coating was superior for alcohols, phthalate esters, phenolic environmental estrogens, fatty acids and aromatic amines due to the introduction of benzo-15-crown-5 functional group in IL structure. Moreover, it was shown to provide higher or comparable extraction efficiencies for most analytes studied than did the commercial PDMS, PDMS/DVB and PA fibers.     

碳纳米管/TiO_2复合材料的制备及表征研究

采用溶胶-凝胶法和水热合成法,制备出碳纳米管/TiO2(CNTs/TiO2)复合材料。通过X-射线衍射仪(XRD)、扫描电子显微镜(SEM),紫外-可见漫反射光谱(UV-Vis),荧光光谱(LS)检测CNTs/TiO2的晶型及形貌。结果表明:锐钛矿相TiO2纳米颗粒负载在碳纳米管的管壁上,CNTs/TiO2在紫外-可见光波长范围均有较好的吸收性能。在灭菌灯照射下,以甲基橙溶液为降解目标,CNTs/TiO2复合材料对甲基橙溶液的降解有高的光催化活性,180 min内降解率达到85%以上。     

Evaluation of carbon nanotubes as a solid-phase extraction adsorbent for the extraction of cephalosporins antibiotics, sulfonamides and phenolic compounds from aqueous solution

The adsorptive potential of carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes) for solid-phase extraction of three groups of highly polar compounds (namely cephalosporins antibiotics, sulfonamides and phenolic compounds) was tested in this article. The analytes were strongly retained by the carbon nanotubes. And acceptable recoveries were obtained with the addition of ammonium acetate into eluents. The effects of solution pH on the recoveries of the antibiotics and phenolic compounds were examined. To check the retention abilities of three groups of compounds on carbon nanotubes, fixed amount of each analyte was added to different volumes (up to 500 mL) of aqueous solution, and then extracted by the sorbents. Comparative studies showed that the carbon nanotubes were much superior to C₁₈ for the extraction of the highly polar analytes. For the cephalosporins antibiotics and sulfonamides, the carbon nanotubes showed stronger retention capability than graphitized carbon blacks, but for some of the phenolic compounds graphitized carbon blacks seemed to be more suitable, indicating different retention mechanisms of these analytes. To further assess the enrichment ability of carbon nanotubes for highly polar compounds, the solid-phase extraction method of multi-walled carbon nanotubes packed cartridge was well developed, and the sulfonamides were used as model compounds. Under the optimal procedures, the detection limits of sulfonamides were in the range of 27-38 ng L⁻¹. The spiked recoveries from several real water samples obtained for sulfathiazole and sulfadiazine ranged from 55% to 79% and 72% to 92%, respectively, while the recoveries of sulfapyridine and sulfamethazine were in the range of 85-102%.     

Synthesis and electrochemical characterization of carbon nanotubes decorated with nickel nanoparticles for use as an electrochemical capacitor

Attachment of nickel nanoparticles on multiwalled carbon nanotubes (MWCNTs) was conducted to explore the influence of Ni loading on the electrochemical capacitance of MWCNT electrodes. A chemical impregnation leaded to homogeneously disperse Ni particles onto the surface of MWCNTs, and the Ni particles were found to be an average size of 30–50 nm. The capacitive behavior of the MWCNT electrodes was investigated in 6 M KOH, by using cyclic voltammetry (CV), charge–discharge cycling, and ac electrochemical impedance spectroscopy. CV measurements showed that the Faradaic current was found to increase with the Ni coverage, indicating that the presence of Ni would enhance the pseudocapacitance through the redox process. Equivalent circuit analysis indicated that both of electrical connection and charge transfer resistances accounted for the major proportion of the overall resistance and were found to decrease with the amount of nickel. A linearity relationship between the total capacitance and the Ni population reflected that each Ni particle exhibits an identical electrochemical activity in enhancing the electrochemical capacitance. The overall electrochemical capacitance (including double layer capacitance and pseudocapacitance) of Ni-MWCNT electrode can reach a maximum of 210 F/g over 500 cycles.     

Ytterbium fluoride nanoparticles on carbon nanotubes: preparation, characterization and application for simultaneous electrochemical determination of ascorbic acid, dopamine and uric acid

A novel modified glassy carbon electrode with ytterbium fluoride nanoparticles (YFNPs)-multiwalled carbon nanotubes (MWCNTs) was fabricated and then successfully used for the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). YFNPs were successfully coated on the MWCNTs via the intermediate of noncovalent hydrophobic interactions of the MWCNTs surface with sodium dodecyl sulfate. The YFNPs and immobilization of YFNPs on MWCNTs were confirmed by transmission electron microscopy. The particle size of YFNPs was measured to be around 45 nm. The catalytic peak currents for AA, DA and UA were linearly dependent on their concentrations in the range of 2.0–600.0, 2.0–560.0 and 1.8–640.0 μM, respectively, with the corresponding detection limits of 0.77, 0.22 and 0.17 μM. The modified electrode provided good sensitivity and stability, and was successfully applied for the simultaneous determination of AA, DA and UA in human blood serum and urine samples.     

Electropolymerized multiwalled carbon nanotubes/polypyrrole fiber for solid-phase microextraction and its applications in the determination of pyrethroids

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes/polypyrrole (MWCNTs/Ppy) was prepared with an electrochemical method and used for the extraction of pyrethroids in natural water samples. The results showed that the MWCNTs/Ppy coated fiber had high organic stability, and remarkable acid and alkali resistance. In addition, the MWCNTs/Ppy coated fiber was more effective and superior to commercial PDMS and PDMS/DVD fibers in extracting pyrethroids in natural water samples. Under optimized conditions, the calibration curves were found to be linear from 0.001 to 10 μg mL⁻¹ for five of the six pyrethroids studied, the exception being fenvalerate (which was from 0.005 to 10 μg mL⁻¹), and detection limits were within the range 0.12-0.43 ng mL⁻¹. The recoveries of the pyrethroids spiked in water samples at 10 ng mL⁻¹ ranged from 83 to 112%.     

Preparation of solid-phase microextraction fiber coated with single-walled carbon nanotubes by electrophoretic deposition and its application in extracting phenols from aqueous samples

A novel solid-phase microextraction (SPME) Pt fiber coated with single-walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition (EPD) and applied to the determination of phenols in aqueous samples by direct immersion (DI)-SPME-HPLC-UV. The results revealed that EPD was a simple and reproducible technique for the preparation of SPME fibers coated with SWCNTs without the use of adhesive. The obtained SWCNT coating did not swell in organic solvents nor strip off from substrate, and possessed high mechanical strength due to the strong Van der Waals attractions between the surfaces of the SWCNTs. The prepared SPME fiber was conductive since both SWCNT coating and Pt wire were conductive. Using Pt wire as substrate, the fiber was unbreakable. Owing to the presence of oxygenated groups on SWCNTs and the high surface area of SWCNTs, the SWCNT fiber was similar to or superior to commercial PA fiber in extracting the studied phenols from aqueous sample. A durability of more than 80 analyses was achieved for one unique fiber. Under optimized conditions, the detection limits for the phenols varied between 0.9 and 3.8 ng/mL, the precisions were in the range of 0.7–3.2% (n = 3), and linear ranges were within 10 and 300 ng/mL. The method was successfully applied to the analysis of spiked seawater and tap water samples with the recoveries from 87.5 to 102.0%.     

Single-walled carbon nanotubes coated fibers for solid-phase microextraction and gas chromatography-mass spectrometric determination of pesticides in Tea samples

Using a single-walled carbon nanotubes (SWCNTs) as stationary phase of solid-phase microextraction (SPME) fibers, a simple, low cost and environmentally friendly method for extraction of 13 pesticides in Tea samples has been developed following gas chromatography-mass spectrometric determination. Potential factors affecting the extraction efficiency were investigated and optimized, including extraction and desorption time, extraction temperature, stirring rate, solution pH and ionic strength. Under optimized conditions, the linearity of the developed method was in the range of 0.125-25 ng/mL with correlation coefficients greater than 0.9928 and the limits of detections (LODs) were 0.027-0.23 ng/mL (S/N = 3). Meanwhile, the relative standard deviations (RSDs) for five successive measurements with single fiber, fiber-to-fiber, day-to-day were 2.3-13.0, 8.2-14.6 and 4.1-12.5%, respectively, indicating good reproducibility of the proposed method. The fiber had high extraction efficiency for studied pesticides in comparison with commercial poly(dimethylsiloxane) (PDMS) and polyacrylate (PA) fibers and could be used for more than 70 times without decrease of efficiency. The developed method was successfully applied for the analysis of real samples including green Tea, oolong Tea, white Tea, and flower Tea, and the recoveries of the pesticides spiked in these samples ranged from 75.1 to 118.4%. Chlorfenapyr and λ-cyhalothrin were found in the Tea samples bought randomly from local market. The results demonstrated that the developed SWCNTs-SPME method was a simple, efficient pretreatment and enrichment procedure for pesticides in complex matrices.     

Electrooxidation of ethanol on carbon nanotubes–nickel nanoparticles composites in alkaline media

In this report, the preparation of carbon nanotubes–Ni nanoparticles composites (CNT–Ni) is presented. The morphology and elemental composition of CNT–Ni composites were examined by transmission electron microscopy and X-ray diffraction. The electrochemical behaviour of carbon nanotubes–Ni nanoparticles composites in an aqueous solutions of alkali and alkaline solutions of ethanol has been studied by linear sweep voltammetry. The peak on the potentiodynamic curve for CNT–Ni composite electrode in alkaline solutions of ethanol is observed which is ascribed to the ethanol oxidation in alkaline medium. The results obtained are discussed from the point of view of employment of the CNT–Ni composites for the catalytic electrodes of fuel cells.