Electrocatalytic Oxidation of Catechol at Multi‐Walled Carbon Nanotubes Modified Electrode

In 0.05 mol/L phosphate buffer solution (pH 7.0), carbon nanotubes modified electrode exhibits rapid response, strong catalytic activity with high stability toward the electrochemical oxidation of catechol. The electrochemical behavior of catechol on both the multi‐walled and single‐walled carbon nanotubes modified electrode was investigated. The experimental conditions, such as pH of the solution and scan rate were optimized. The currents (measured by constant potential amperometry) increase linearly with the concentrations of catechol in the range of 2.0×10^?5–1.2×10^?3 mol/L. Moreover, at the multi‐walled carbon nanotubes modified electrode the electrochemical responses of catechol and ascorbic acid can be separated clearly.     

Polymeric Nanocomposites of Polyurethane Block Copolymers and Functionalized Multi‐Walled Carbon Nanotubes as Crosslinkers

Summary: We report on a new route to synthesize polymeric carbon nanotube‐polyurethane (PU) nanocomposites. Multi‐walled carbon nanotubes (MWNTs) functionalized by chemical modification were incorporated as a crosslinker in prepolymer, which was prepared from a reaction of 4,4′‐methylene bis(phenylisocyanate) and poly(ε‐caprolactone)diol. The reinforcing effect of carbon nanotubes in crosslinked MWNT‐PU nanocomposites was more pronounced as compared to that in conventional MWNT‐PU nanocomposites. The optimum content of chemically modified MWNTs for crosslinking with polyurethane was determined to be approximately 4 wt.‐% in our samples, based on observation of a NCO peak in FT‐IR spectroscopy. MWNT‐crosslinked polyurethane containing 4 wt.‐% modified MWNTs showed the highest modulus and tensile strength among the composites and pure PU. The presence of functionalized MWNTs in the polymeric nanocomposite yielded enhancement in the thermal stability due to crosslinking of the MWNTs with PU.

Possible configuration for MWNT‐PU nanocomposite molecules and FT‐IR spectra of samples obtained during reaction of prepolymer with functionalized MWNTs (second step).     

Facile Synthesis and Enhanced Nonlinear Optical Properties of Porphyrin‐Functionalized Multi‐Walled Carbon Nanotubes

Two multi‐walled carbon nanotube (MWCNT)‐based nanohybrids, MWCNT–ZnTPP and MWCNT–TPP (TPP=5‐[4‐{2‐(4‐formylphenoxy)‐ ethyloxy}phenyl]‐10,15,20‐triphenylporphyrin, ZnTPP=5‐[4‐{(4‐formylphenyl)ethynyl}phenyl]‐10,15,20‐triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3‐dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X‐ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT–porphyrin composite materials. Z‐scan studies reveal that these MWCNT–porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT–porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs.     

DFT Studies of Ag‐Loading Intrinsic and Functionalized Single‐Walled Carbon Nanotubes

The first principles study was performed on the stability of Ag adsorbed on the internal walls of single‐walled carbon nanotube (SWCNT) and loaded on acid modified SWCNT. The calculation results show that Ag can be adsorbed stably on the internal walls of SWCNT. With the increase of SWCNT diameter, the adsorption energy increases in a certain range. Ag can also be loaded on the modified SWCNT surface in the form of COOAg and OAg groups, and COOAg group is more stable than OAg group. For either the adsorption on the inner SWCNT or the load on the modified SWCNT surface, only a small proportion of the Ag ions can be stably bonded to the walls of SWCNT.     

氢键诱导的聚吡咯/苯磺酸功能化多壁碳纳米管的制备及其电化学行为

采用原位芳基重氮化反应对碳纳米管进行苯磺酸功能化, 进而制备了聚吡咯/苯磺酸化碳纳米管复合材料(PPy/f-MWCNTs), 通过透射电镜(TEM)及扫描电镜(SEM)测试发现, 氢键诱导使聚吡咯成功地包覆在碳纳米管表面. 循环伏安和恒流充放电测试结果表明, 复合材料具有良好的电化学电容性能, 当聚吡咯与苯磺酸化碳纳米管质量比为1:1时, 复合材料在1.0 A·g-1的电流密度下的比容量达266 F·g-1, 而且聚吡咯利用率比未功能化聚吡咯/碳纳米管(PPy/p-MWCNTs)和纯聚吡咯(PPy)提高了1倍以上.     

Electrocatalytic Reduction of Oxygen at Multi‐Walled Carbon Nanotubes and Cobalt Porphyrin Modified Glassy Carbon Electrode

The multi‐walled carbon nanotubes (MWNTs) modified glassy carbon electrode exhibited electrocatalytic activity to the reduction of oxygen in 0.1 M HAc‐NaAc (pH 3.8) buffer solution. Further modification with cobalt porphyrin film on the MWNTs by adsorption, the resulted modified electrode showed more efficient catalytic activity to O₂ reduction. The reduction peak potential of O₂ is shifted much more positively to 0.12 V (vs. Ag/AgCl), and the peak current is increased greatly. Cyclic voltammetry (CV), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), were used to characterize the material and the modified film on electrode surface. Electrochemical experiments gave the total number of electron transfer for oxygen reduction as about 3, which indicated a co‐exist process of 2 electrons and 4 electrons for reduction of oxygen at this modified electrode. Meanwhile, the catalytic activities of the multilayer film (MWNTs/CoTMPyP)_n prepared by layer‐by‐layer method were investigated, and the results showed that the peak current of O₂ reduction increased and the peak potential shifted to a positive direction with the increase of layer numbers.     

Selective and Scalable Chemical Removal of Thin Single‐Walled Carbon Nanotubes from their Mixtures with Double‐Walled Carbon Nanotubes

Double‐walled carbon nanotubes (DWCNTs) are materials in high demand due to their superior properties. However, it is very challenging to prepare DWCNTs samples of high purity. In particular, the removal of single‐walled carbon nanotubes (SWCNTs) contaminants is a major problem. Here, a procedure for a selective removal of thin‐diameter SWCNTs from their mixtures with DWCNTs by lithium vapor treatment is investigated. The results are evaluated by Raman spectroscopy and in situ Raman spectroelectrochemistry. It is shown that the amount of SWCNTs was reduced by about 35 % after lithium vapor treatment of the studied SWCNTs–DWCNTs mixture.     

Simultaneous Voltammetric Determination of Uric Acid and Ascorbic Acid Using a Carbon‐Paste Electrode Modified with Multi‐Walled Carbon Nanotubes/Nafion and Cobalt(II)nitrosalophen

A composition of multiwalled carbon nanotube (MWCNT), Nafion and cobalt(II)‐5‐nitrosalophen (CoNSal) is applied for the modification of carbon‐paste electrode (CPE). The pretreated MWCNT is well dispersed in the alcoholic solution of Nafion under the ultrasonic agitation, and the resulted suspension is used as modifier (with 10% w/w) in the matrix of the paste electrode. The prepared electrode further modified by addition of 3 wt% of CoNSal. The resulted modified electrode is used as a sensitive voltammetric sensor for simultaneous determination of uric acid (UA) and ascorbic acid (AA). The electrode showed efficient electrocatalytic activity in lowering the anodic overpotentials and enhancement of the anodic currents. This electrode is able to completely resolve the voltammetric response of UA and AA. The effects of potential sweep rate and pH of the buffer solution on the response of the electrode, toward UA and AA, and the peak resolution is thoroughly investigated by cyclic and differential pulse voltammetry (CV and DPV). The best peak resolution for these compounds using the modified electrode is obtained in solutions with pH 4. The ΔE_p for UA and AA in these methods is about 315 mV, which is considerably better than previous reports for these compounds. A linear dynamic range of 1×10^?7 to 1×10^?4 M with a detection limit of 6×10^?8 M is resulted for UA in buffered solutions with pH 4.0. The voltammetric response characteristics for AA are obtained as, the linear range of 5×10^?7 to 1×10^?4 M with the detection limit of 1×10^?7 M. The voltammetric detection system was very stable and the reproducibility of the electrode response, based on the six measurements during one month, was less than 3.5% for the slope of the calibration curves of UA and AA. The prepared modified electrode is successfully applied for the determination of AA and UA in mixture samples and reasonable accuracies are resulted.     

Fabrication and Characterization of Carbon Nanotube‐Hydroxyapatite Nanocomposite: Application to Anodic Stripping Voltammetric Determination of Cadmium

A novel chemically modified electrode for stripping determination of cadmium is presented in this paper, based on carbon nanotube‐hydroxyapatite (CNT‐HAP) nanocomposite, which can be prepared by an easy and effective one‐step sonication. The newly synthesized nanocomposite was characterized with FTIR, TEM, and electrochemical methods. Due to the combination of the strong absorption ability of HAP and excellent electroanalytical properties of CNTs, the GC/CNT‐HAP electrode has been successfully used for determination of Cd²⁺ by anodic stripping voltammetry with a linear range of 20 nM–3 μM. The sensitivity and detection limit are 25.6 μA/μM and 4 nM, respectively. The practical application of the proposed electrode has been carried out for the determination of trace levels of Cd²⁺ in real water samples.     

NH2‐Functionalized Multi Walled Carbon Nanotubes Decorated with ZnO Nanoparticles and Graphene Quantum Dots for Sensitive Assay of Pimozide

In this study, a novel and sensitive electrochemical nanosensor for the determination of antipsychotic drug Pimozide (PZ) is proposed using NH₂ functionalized multi walled carbon nanotubes (NH₂fMWCNT) decorated with and ZnO nanoparticles (ZnONPs) co‐catalyzed by graphene quantum dots (GQDs). Prior to electrochemical analyses of PZ, the designed nanosensor was well characterized in terms of surface morphology by scanning electron microscopy (SEM) and SEM armed with EDX analysis. Electrochemical impedance spectroscopy (EIS) employed to investigate the electron transfer capability and cyclic voltammetry (CV) technique was used to successfully compare the redox response of PZ on the surface of modified and unmodified electrode. The designed nanosensor response was linear between 6.25×10^?11–1.20×10^?7 M concentration range of PZ with a limit of detection value as 1.02×10^?11 M. The influence of interfering agents was further studied to examine the selectivity of the designed sensor. A rapid screening of PZ as is required in pharmaceutical and biological samples underscores the paramount importance of nano based electrochemical sensor for its sensitive and selective detection.     

On the Adsorption of Some Catechol Derivatives from Aqueous Solutions onto Activated Carbon Cloth: Equilibrium and Kinetic Studies

The removal of some of pollutants including catechol, 3-methylcatechol, 3-methoxycatechol, and 2,3-dihydroxybenzoic acid by adsorption onto activated carbon cloth (ACC) at 35.0 ± 0.1°C was investigated. The equilibrium experimental data were fitted to Langmuir, Freundlich, Temkin, Langmuir-Freundlich, and Redlich-Peterson isotherms. Also the kinetic experimental data were fitted to the pseudo-first-order and pseudo-second-order kinetic models. It was found that the pseudo-second-order model describes the kinetic of adsorption better than the other one. By comparing the obtained results with the previously reported data, it can be concluded that ACC is a high efficient adsorbent for removal of phenolic compounds from aqueous solutions.     

A Comparison between Different Agro-wastes and Carbon Nanotubes for Removal of Sarafloxacin from Wastewater: Kinetics and Equilibrium Studies

In the current study, eco-structured and efficient removal of the veterinary fluoroquinolone antibiotic sarafloxacin (SARA) from wastewater has been explored. The adsorptive power of four agro-wastes (AWs) derived from pistachio nutshells (PNS) and Aloe vera leaves (AV) as well as the multi-walled carbon nanotubes (MWCNTs) has been assessed. Adsorbent derived from raw pistachio nutshells (RPNS) was the most efficient among the four tested AWs (%removal ‘%R’ = 82.39%), while MWCNTs showed the best adsorptive power amongst the five adsorbents (%R = 96.20%). Plackett-Burman design (PBD) was used to optimize the adsorption process. Two responses (‘%R’ and adsorption capacity ‘q_e’) were optimized as a function of four variables (pH, adsorbent dose ‘AD’ (dose of RPNS and MWCNTs), adsorbate concentration [SARA] and contact time ‘CT’). The effect of pH was similar for both RPNS and MWCNTs. Morphological and textural characterization of the tested adsorbents was carried out using FT-IR spectroscopy, SEM and BET analyses. Conversion of waste-derived materials into carbonaceous material was investigated by Raman spectroscopy. Equilibrium studies showed that Freundlich isotherm is the most suitable isotherm to describe the adsorption of SARA onto RPNS. Kinetics’ investigation shows that the adsorption of SARA onto RPNS follows a pseudo-second order (PSO) model.     

Selective Synthesis of Single‐ and Multi‐Walled Supramolecular Nanotubes by Using Solvophobic/Solvophilic Controls: Stepwise Radial Growth via “Coil‐on‐Tube” Intermediates

Novel hexa‐peri‐hexabenzocoronene (HBC) derivatives, ^FHBC and ^FHBC*, which carry perfluoroalkyl segments on one side of the HBC core and long alkyl tails on the other, were synthesized. Their perfluoroalkyl segments are highly solvated in C₆F₆ (solvophilic effect) and do not assemble, whereas in CH₂Cl₂, they are excluded (solvophobic effect) and assemble together consequently. For example, the use of C₆F₆ and CH₂Cl₂ as assembling media for ^FHBC leads to the selective formation of single‐ and multi‐walled nanotubes, respectively. When a higher monomer concentration is applied in CH₂Cl₂, multi‐walled nanotubes with a larger number of walls result. ^FHBC in CH₂Cl₂ self‐assembles rather slowly, thereby allowing for the observation of coil‐on‐tube structures, which are possible intermediates for the stepwise radial growth of the nanotubular wall. Casting of the multi‐walled nanotubes onto a quartz plate yields a superhydrophobic thin film with a water contact angle of 161±2°.     

Multi‐Wall Carbon Nanotube Paste Electrode for Adsorptive Stripping Determination of Quercetin: A Comparison with Graphite Paste Electrode via Voltammetry and Chronopotentiometry

Adsorptive‐stripping voltammetry and chronopotentiometry were used to study the adsorption and oxidation of quercetin at both graphite‐nujol paste electrode (GPE) and carbon nanotubes‐nujol paste electrode (CNTPE) for the potential application of carbon nanotube to flavonoids determination. As compared with GPE, CNTPE showed very great power to adsorb quercetin and resulted in a considerable signals enhancement. The adsorption isotherm of quercetin on CNTPE was of Langmuir type, and the stripping of quercetin adsorbed on CNTs showed a quasi‐reversible oxidation reaction involving two‐electron and two‐proton. The high adsorbtive activity of CNTPE was contributed to the high specific surface area and the special surface characteristics of carbon nanotubes. The peak current response of differential pulse voltammetry depended linearly on quercetin concentration. A linear equation I_p(μA)=0.987c(μmol L^?1)+0.023 with a correlation coefficient of 0.994 was obtained over the concentration range 0.1–1.0 μmol L^?1.     

Adsorptive Removal of Thorium(IV) from Aqueous Solutions Using Synthesized Polyamidoxime Chelating Resin: Equilibrium,Kinetic, and Thermodynamic Studies

In this study, an amidoximated chelating ion exchange resin was prepared by poly-acrylonitrile (PAN) grafted potato starch. The adsorbent characterizations such as specific surface area, pore volume, average pore radius, and Fourier transform infrared (FTIR) spectrum of the resin were measured. The effects of pH, adsorbent dosage, contact time, initial concentration of thorium ion, and temperature on adsorption of thorium ion from aqueous solutions were investigated. Four isotherm models including Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin were applied to analyze the equilibrium isotherm data. The results showed that Langmuir and Temkin models had a good agreement with experimental data. The maximum capacity of the adsorbent using the Langmuir isotherm model was 227.27 mg · g^?1. The kinetic models like pseudo-first-order, pseudo-second-order, Elovich, and intraparticle were examined to describe the adsorption process. The kinetics of the adsorption process was found to follow the pseudo-second-order kinetic model. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were also calculated using equilibrium constant values at various temperatures (25, 35, 45, 55°C) and the positive value for ΔH° showed an endothermic adsorption process. The study suggests that the prepared adsorbent has promising potential for the removal of thorium from wastewaters.      

Adsorption of Heavy Metal Ions from Aqueous Solutions by Zeolite Based on Oil Shale Ash: Kinetic and Equilibrium Studies

Na-A zeolite was successfully synthesized via the alkaline fusion method with oil shale ash as the raw material. The adsorption capacity of it was tested by removing Cu²⁺, Ni²⁺, Pb²⁺ and Cd²⁺ from aqueous solutions. The results reveal the maximum adsorption capacity of adsorbent for Pb²⁺, Cu²⁺, Cd²⁺ and Ni²⁺ were 224.72, 156.74, 118.34 and 53.02 mg/g, respectively. The effects of contact time and pH value of solutions on the adsorption efficiency of the zeolite were evaluated. Besides, The equilibrium adsorption data and the batch kinetic data were correlated with Langmuir and Freundlich models and the pseudo-first-order and pseudo-second-order models separately. The results show that the Langmuir isotherm and the pseudo-second-order equation were more suitable for the adsorption of Na-A zeolite for the metal ions. In addition, Thermodynamic parameters of the adsorption(the Gibbs free energy, entropy, and enthalpy) were also evaluated and discussed. The results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions and the synthesized zeolite was an effective adsorbent for the removal of metal ions from aqueous solution.     

Dechlorination of carbon tetrachloride by Nanoscale Nickeled Zero‐Valent Iron @ Multi‐Walled Carbon Nanotubes: Impact of reaction conditions,kinetics and mechanism

The nanoscale nickeled zero‐valent iron @ multi‐walled carbon nanotubes (NF@MWCNTs) were synthesized, characterized and used to dispose carbon tetrachloride (CT) in aqueous solution. Scanning electron microscopy (SEM), X‐ray energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) gas sorptometry measurements were conducted to characterize the microstructure of the NF@MWCNTs. And batch experiments under different operation parameters were conducted to investigated the activity of NF@MWCNTs on degrading CT, including the content of NF@MWCNTs composites, temperature, catalyst dosage, initial pH and different anions. The experimental results showed that 4% nickel content of Ni/Fe bimetal and 2:1 doping ratio of Fe/MWCNTs were the wise choices in this study, which provided excellent degradation efficiency of CT when compared with nanoscale zero‐valent iron (nZVI) (97.44% and 55.28%, respectively). That was benefited from the fact that MWCNTs as an excellent support material could reduce the activation energy of 7.952 kJ/mol, and the nickel metal further reduced the reaction activation energy of 11.022 kJ/mol as presented in the conceptual model. Beyond that, NF@MWCNTs showed good reusability after five times consecutive reaction. Based on these, the reaction mechanism and degradation pathway also had been discussed.