Synthesis of flower-like gold nanoparticles and their electrocatalytic activity towards the oxidation of methanol and the reduction of oxygen

This article describes the synthesis of branched flower-like gold (Au) nanocrystals and their electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Gold nanoflowers (GNFs) were obtained by a one-pot synthesis using N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid (HEPES) as a reducing/stabilizing agent. The GNFs have been characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical measurements. The UV-visible spectra show two bands corresponding to the transverse and longitudinal surface plasmon (SP) absorption at 532 and 720 nm, respectively, for the colloidal GNFs. The GNFs were self-assembled on a sol-gel-derived silicate network, which was preassembled on a polycrystalline Au electrode and used for electrocatalytic applications. The GNFs retain their morphology on the silicate network; the UV-visible diffuse reflectance spectra (DRS) of GNFs on the silicate network show longitudinal and transverse bands as in the case of colloidal GNFs. The GNFs show excellent electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Oxidation of methanol in alkaline solution was observed at approximately 0.245 V, which is much less positive than that on an unmodified polycrystalline gold electrode. Reduction of oxygen to H2O2 and the further reduction of H2O2 to water in neutral pH were observed at less negative potentials on the GNFs electrode. The electrocatalytic activity of GNFs is significantly higher than that of the spherically shaped citrate-stabilized Au nanoparticles (SGNs).     

TiO2/activated carbon fibers photocatalyst: Effects of coating procedures on the microstructure, adhesion property, and photocatalytic ability

In order to more easily separate TiO₂ photocatalyst from the treated wastewater, TiO₂ film was immobilized on the surface of activated carbon fibers (ACFs) by employing two kinds of coating procedures, dip-coating, and hydrothermal treatment. The effects of coating procedures on microstructure of TiO₂-coated ACFs (TiO₂/ACFs), such as morphology, porous property, crystal structure, and light absorption characteristics were investigated in detail. The adhesion property between TiO₂ film and ACFs was evaluated by ultrasonic vibration, and the photocatalytic activity of TiO₂/ACFs was tested by the photocatalytic decoloration of methylene blue solution. The results show that hydrothermal treatment presented many advantages to obtain high-performance TiO₂/ACFs photocatalyst in comparison with dip-coating. Hydrothermal treatment could improve the binding property between TiO₂ films and ACFs, which endowed the as-obtained TiO₂/ACFs photocatalyst with improved reusable performance, and TiO₂/ACFs synthesized by hydrothermal treatment presented higher photocatalytic activity.     

Influence of atmospheric plasma on physicochemical properties of vapor-grown graphite nanofibers

Vapor-grown graphite nanofibers (GNFs) were modified by plasma treatments using low-pressure plasmas with different gases (Ar gas only and/or Ar/O2 gases), flow rates, pressures, and powers. Surface characterizations and morphologies of the GNFs after plasma treatment were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, titration, and transmission electron microscopy (TEM) measurements. Also, the investigation of thermomechanical behavior and impact strengths of the GNFs/epoxy composites was performed by dynamic-mechanical thermal analysis (DMTA) and Izod impact testing, respectively. The plasma treatment of the fibers changed the surface morphologies by forming a layer with a thickness on the order of 1 nm, mainly consisting of oxygen functional groups such as hydroxyl, carbonyl, and carboxyl groups. After functionalization of the complete surfaces, further plasma treatment did not enhance the superficial oxygen content but slightly changed the portions of the functional groups. Also, the composites with plasma-treated GNFs showed an increase in T(g) and impact strength compared to the composites containing the same amount of plasma-untreated GNFs.     

Adsorption properties of iodine-doped activated carbon fiber

Iodine-doped activated carbon fibers (ACFs) were prepared by the iodine immersion method on pitch-based ACF. Then iodine-doped ACFs were heated in argon at 523 K for 4 h and at 673 K for 2 h. The iodine structure of the resultant iodine-doped ACFs was examined using X-ray photoelectron spectroscopy. The micropore structures were determined by N(2) adsorption at 77 K. The surface area and micropore volume of iodine-doped ACFs are less than those of pristine ACFs. However, the pore width does not change with the iodine doping. The effects of iodine doping on adsorption properties of ACFs for H(2)O and NO at 303 K were examined. The iodine doping affected remarkably the adsorptivities of ACFs for H(2)O and NO. In particular, iodine-doped ACFs treated at 673 K show enhanced adsorptivities for H(2)O and NO. This result suggests that iodine molecules doped on the micropores should be charged by heat treatment at 673 K.     

金纳米花介导的近红外热疗对人喉癌Hep-2细胞增殖的抑制作用

采用弱配体柠檬酸钠修饰的金纳米花为介导材料,考察了其对人喉癌Hep-2细胞的NIR热疗作用,结果表明,这种金纳米花材料具有良好的NIR光热转换性能,可有效抑制Hep-2细胞增殖.     

Studies on pore structures and surface functional groups of pitch-based activated carbon fibers

The present study concerns the physical activation and chemical oxidation of pitch-based activated carbon fibers (ACFs) as ways to improve the adsorption properties. The surface oxides of the ACFs studied were determined by Boehm's titration and the pore structures were studied by the BET method with N(2)/77 K adsorption. Also, the adsorption properties of the ACFs were investigated with chromium ion adsorption by different adsorption models. As a result, it was observed that carboxyl groups were largely created after nitric acid treatment on ACFs. The affinity for chromium ions increases with increasing specific surface area, micropore volume, and surface functionalities of ACFs as the activation time increases.     

Ammonia removal of activated carbon fibers produced by oxyfluorination

In this study, activated carbon fibers (ACFs) were produced by an oxyfluorination treatment to enhance the capacity of ammonia gas removal. The introduction of polar groups, such as CF, CO, and COOH, on the ACFs was confirmed by a XPS analysis, and N2/77 K adsorption isotherm characteristics including specific surface area and total and micropore volumes were studied by the BET and t-plot methods. The ammonia-removal efficiency was confirmed by a gas-detecting tube technique. As a result, the specific surface area and micropore volume of ACFs were slightly destroyed as the surface treatment time was increased. However, the oxyfluorinated ACFs led to an increase of fluorine and oxygen-containing polar functional groups in ACF surfaces, resulting in an increase in the ammonia-removal efficiency of the ACFs produced.     

Preparation and electrochemical behaviors of platinum nanoparticles impregnated on binary carbon supports as catalyst electrodes of direct methanol fuel cells

Binary carbon-supported platinum (Pt) nanoparticles were prepared by a chemical reduction method of Pt precursor on two types of carbon materials such as carbon blacks (CBs) and graphite nanofibers (GNFs). Average sizes and loading levels of Pt metal particles were dependent on a mixing ratio of two carbon materials. The highest electroactivity for methanol oxidation was obtained by preparing the binary carbon supports consisting of GNFs and CBs with a weight ratio of 30:70. Furthermore, with an increase of GNFs content from 0% to 30%, a charge-transfer resistance changed from 19 Ohm cm² to 11 Ohm cm². The change of electroactivity or the resistance of catalyst electrodes was attributed to the changes of specific surface area and morphological changes of carbon-supported catalyst electrodes by controlling the mixing ratio of GNFs and CBs.     

NO removal of Ni-electroplated activated carbon fibers

In this study, activated carbon fibers (ACFs) were treated by a Ni-electroplating technique in order to remove nitric oxide (NO). The surface properties of the ACFs were investigated by XPS measurement. N2/77 K adsorption isotherm characteristics were determined by the BET equation. Also, NO-removal efficiency was confirmed by gas chromatography. For experimental results, Ni2p was introduced on ACFs during the Ni-electroplating technique. The nickel deposited on ACFs appeared to increase the NO removal despite the decrease in the BET specific surface areas and micropore volumes compared to nontreated ACFs. Consequently, it was found that NO conversion of ACFs was significantly improved due to the catalytic reaction of nickel deposited on ACFs.     

Start-up of Completely Autotrophic Nitrogen Removal Over Nitrite Enhanced by Hydrophilic-Modified Carbon Fiber

In order to assess the effects of the surface hydrophilicity of supports on the biofilm formation and evaluate the performance of completely autotrophic nitrogen removal over nitrite (CANON) process in a sequencing batch biofilm reactor (SBBR), unmodified activity carbon fibers (ACFs) and ACFs hydrophilic modified by heat treatment were used as supports. CANON process was initiated in a SBBR from conventional activated sludge. An operation temperature of 32 ± 2 °C, dissolved oxygen (DO) level at 1.5 mg L⁻¹ and free ammonia (FA) concentration with 3.98–15.93 mg L⁻¹ were maintained in the SBBR. Fourier transform infrared (FT-IR) spectra and Boehm’s neutralizing titration exhibited that modified ACFs had more oxygen-containing groups than unmodified ACFs. Larger biofilm growth on the modified surfaces examined by scanning electron microscopy and biofilm’s total dry weight, and the biofilm on the modified surfaces were more active, compared with those on the unmodified surfaces. This study demonstrates the hydrophilic-modified ACFs have better biological affinity than unmodified ACFs. Maximal total nitrogen removal rate of 0.088 k g N m⁻³ day⁻¹ was achieved for the CANON process on day 80, indicating the CANON process was successfully started up. Apart from supports, the strategies of DO supplying and controlling FA concentration were also keys in starting up the CANON process within a shorter period.     

Adsorption of lead(II) from aqueous solution onto several types of activated carbon fibers

In this work, the adsorption of Pb(II) from aqueous solution was investigated on various types of activated carbon fibers (ACFs) manufactured from polyacrylonitrile and phenolic resin. The textural and physicochemical properties of the ACFs were determined by the N₂-BET method and acid-base titration. The experimental adsorption equilibrium data of Pb(II) on the ACFs were obtained in a batch adsorber, and the Langmuir isotherm model better fitted the experimental data. The effects of the type of ACF and precursor of ACF, solution pH and temperature upon the adsorption of Pb(II) on the ACFs were examined in detail. The adsorption capacity was highly dependent upon the precursor of ACF. The Pb(II) adsorption capacity of the ACFs augmented when the solution pH and temperature were increased from 2 to 4 and from 288 to 308 K, respectively. The effect of the pH was attributed to the interactions between the surface of the ACF and Pb²⁺ ions present in the water solution. The Pb(II) adsorption capacity of the ACFs was enhanced by oxidation with HNO₃ solution and the enhancement factor was between 1.1 and 1.4. The reversibility of the adsorption of Pb(II) was investigated by first adsorbing Pb(II) on an ACF and then desorbing the Pb(II). It was noticed that Pb(II) was substantially desorbed from ACF while reducing the solution pH to 2. It was concluded that the Pb(II) was mainly adsorbed on the ACFs by chemisorption, electrostatic interactions and ion exchange.     

Quantum sieving effect of modified activated carbon fibers on H2 and D2 adsorption at 20 K

Quantum sieving of activated carbon fibers (ACFs) and their fluorides was observed for H(2) and D(2) adsorption at 20 K. Fluorination reduced the slit-shaped pore width of ACFs by 0.2 nm. The activated carbon fibers can act as highly efficient quantum sieves for H(2) and D(2), because the effective size of an H(2) molecule is larger than that of a D(2) molecule due to the uncertainty principle and the molecular size difference between H(2) and D(2) is significant in the micropore space. The D(2)/H(2) selectivity of ACFs evaluated by ideal adsorption solution theory was larger than that of the fluorinated ACFs.     

Effect of activated graphite nanofibers on electrochemical activities of Pt–Ru nanoparticles for fuel cells

In this work, graphite nanofibers (GNFs) were chemically activated for high specific surface area, small pore diameter, and high oxygen-containing groups with different KOH/GNFs ratios and used as carbon supports of Pt–Ru nanoparticles for fuel cells. As a result, the oxygen functional groups and specific surface area of carbon supports were increased with increasing the ratios of KOH/GNFs up to 4:1, while the average of Pt–Ru nanoparticle size was decreased owing to the improvement of dispersibility of the Pt–Ru/K–GNFs catalysts. The electrochemical activity of the Pt–Ru/K–GNFs catalysts was improved by the larger available active surface area due to the increase of oxygen functional groups and specific surface area. Therefore, it was found that chemical activation using KOH could influence the surface characteristic of carbon supports, resulting in enhanced electrochemical activity of the Pt–Ru/K–GNFs catalysts of fuel cells.     

Influence of oxygen plasma treatment on hydrogen chloride removal of activated carbon fibers

The oxygen plasma treatment of activated carbon fibers (ACFs) was carried out to introduce oxygen-containing groups onto carbon surfaces. Surface properties of the ACFs were determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). N2/77 K adsorption isotherms were investigated by BET and D-R plot methods to characterize specific surface area, pore volume, and pore size distribution. The efficiency of hydrochloride removal was confirmed by two kinds of methods; one is detecting tubes (range: 1-40 ppm), and the other is a gas chromatography technique. As experimental results, the hydrochloride removal efficiency of the ACFs was increased with the number of plasma treatment times up to around 300%, resulting from newly formed oxygen-containing functional groups (especially phenolic and carboxylic) on carbon surfaces, in the decreased specific surface areas or pore volumes. These results indicate that the plasma treatment leads to the increase of hydrochloride removal due to the improvement of surface functional groups containing oxygen on the carbon surfaces.     

Room-Temperature Synthesis of Germanium Oxide Nanofilaments and Their Potential Use as Luminescent Self-Cleaning Surfaces

Germanium oxide nanofilaments (GNFs) have been synthesized under ambient conditions from the gas phase using germanium tetrachloride as a precursor. Non-crystalline GNFs synthesized by this procedure are 1–10 μm in length and 80–110 nm in diameter applying Droplet Assisted Growth and Shaping (DAGS) Chemistry. The relative humidity has been adjusted at various values in order to demonstrate the crucial role of humidity in the gas phase for the nanofilament synthesis. The novel GNFs show a strong luminescence emission in the ultra-violet and light blue region. In addition, a self-cleaning and superhydrophobic properties could be introduced in the luminescent GNF nanofilaments by simple treatment with silane molecules.     

Platinum Nanoparticles Supported on Graphite Nanofibers Prepared by Microwave Irradiation and Its Electrocatalytic Activity

Platinum nanoparticles supported on graphite nanofibers (GNFs) were prepared by microwave assistant heating polyol process. TEM images showed that microwave prepared Pt nanoparticles supported on GNFs were small and uniform, and the average diameter was about 3.4 nm. Cyclic voltammetric test showed that Pt/GNFs exhibited very high electrocatalytic activity for methanol oxidation.     

Influence of anodic treatment on heavy metal ion removal by activated carbon fibers

In this work, the effect of electrochemical oxidation treatment on activated carbon fibers (ACFs) was studied in the context of Cr(VI), Cu(II), and Ni(II) adsorption behavior. Ten weight percent phosphoric acid (A-ACFs) and ammonia (B-ACFs) were used for acidic and basic electrolytes, respectively. Surface properties of ACFs were determined by X-ray photoelectron spectroscopy (XPS). The specific surface area and the pore structure were evaluated from nitrogen adsorption data at 77 K. As a result, the electrochemical oxidation treatment led to an increase in the amount of oxygen-containing functional groups. Also, the adsorption capacity of the electrochemically oxidized ACFs was improved in the order B-ACFs > A-ACFs > untreated-ACFs, in spite of a decrease in specific surface area which resulted from pore blocking by functional groups and pore destruction by acidic electrolyte. It was clearly found that the heavy metal ions were largely influenced by the functional groups on the ACF surfaces.     

Influence of copper content on NO removal of the activated carbon fibers produced by electroplating

In this study, the activated carbon fibers (ACFs) on which copper metal was deposited by electroplating were used to remove nitric oxide (NO). N(2)/77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by BET and T-plot methods. NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper content supported on ACFs led to an increase in the NO conversion, in spite of the decrease of the specific surface area or the micropore volume of ACFs. Consequently, the presence of Cu on ACFs played an important role in improving the NO reduction into O(2) and N(2), which was mainly attributed to the catalytic reactions of Cz-NO-Cu.     

Glycosyl-nucleoside fluorinated amphiphiles as components of nanostructured hydrogels

The synthesis of two novel glycosyl-nucleoside fluorinated amphiphiles (GNFs) derived from the 2H,2H,3H,3H-perfluoro-undecanoyl hydrophobic chain is described. The GNF amphiphiles, which feature either β-d-glucopyranosyl or β-d-lactopyranosyl moieties linked to a thymine base via a 1,2,3 triazole linker, were prepared using a ‘double click’ chemistry route. Surface tension measurements, gelation properties, and TEM studies show that GNFs spontaneously assemble into supramolecular structures. Similarly to their hydrocarbon analogues (GNLs), the GNFs have unique gelation properties in water. A minimum hydrogelation concentration of 0.1% (w/w), was determined in the case of the β-d-glucopyranosyl derivative. Cell viability studies indicate that fluorocarbon GNF 5 was not toxic for human cells (Huh7), whereas hydrocarbon analogue GNL is toxic above 100 μm.     

Low Temperature Catalytic Hydrolysis of Carbon Disulfide on Activated Carbon Fibers Modified by Non-thermal Plasma

In order to improve the carbon disulfide (CS₂) catalytic hydrolysis efficiency of activated carbon fibers (ACFs), ACFs surface was modified by non-thermal plasma (NTP). In particular, the effects of modification conditions on the catalyst properties were studied, including the reactor structure, modification atmosphere, modification time, output voltage and discharge gap. The catalytic activity study showed that ACFs with NTP modification enhanced CS₂ catalytic hydrolysis. The optimal reactor structure, modification atmosphere, modification time, output voltage and discharge gap was a coaxial cylinder, an N₂ atmosphere, 5 min, 7 kV and 7.5 mm, respectively. The effect of the NTP modification on the micro-structural properties of the ACFs was characterized using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS) methods. The results showed that NTP modification improved the dispersion of functional groups and increased the number of oxygen-containing and nitrogen-containing functional groups, thus the catalytic activity could be enhanced. The present results indicated that NTP modification was an effective way to manipulate ACFs surface properties for the CS₂ catalytic hydrolysis reaction.