农药对硫磷分子印迹聚合物合成及亲和性评价

对硫磷为模板分子,甲基丙烯酸(MAA)为功能单体,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,偶氮二异丁腈(AIBN)为引发剂,热引发沉淀聚合法合成对硫磷分子印迹聚合物(MIP)。通过计算机模拟和紫外分析阐述模板与功能单体的分子间作用;通过电镜观察和平衡吸附试验讨论引发剂用量与聚合物性质关系;通过吸附试验Scatchard分析测得最大吸附量为3.92μmol/g,平衡解离常数为91.7μmol/L,且具有较好的吸附特异性。该分子印迹聚合物性能优良,有望应用于环境中对硫磷的富集和检测。     

Chemical functionalization of carbon nanotubes for the mechanical reinforcement of polystyrene composites

An organometallic approach was used to functionalize multiwalled carbon nanotubes with n-butyllithium. This procedure was repeated two more times to achieve a higher degree of multiwalled carbon nanotube functionalization. The functionalized nanotubes have been characterized by Fourier transform infrared and Raman spectroscopy, thermogravimetrical analysis, scanning electron microscopy and sedimentation studies. It was possible to form stable suspensions of the functionalized nanotubes in tetrahydrofuran and they were used to make nanotube polymer composites. The mechanical properties of these new nanotube polymer composites were tested and they were found to show an increase of up to 25% in their Young's moduli and up to 50% in their tensile strength over pure polystyrene.     

THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

A high yield (∼32 wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800-1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

ABSTRACT

A high yield (～32?wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800–1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

Quartz crystal microbalance sensor for organic vapor detection based on molecularly imprinted polymers

Molecularly imprinted polymers on quartz crystal microbalances (QCM) are examined for their ability to detect vapors of small organic molecules with greater sensitivity and selectivity than the traditional amorphous polymer coatings. Hydroquinone and phenol serve as noncovalently bound templates that generate shape-selective cavities in a poly(acrylic) or poly(methacrylic) polymer matrix. The imprinted polymers are immobilized on the piezoelectric crystal surface via a precoated poly(isobutylene) layer. The behavior of the imprinted polymer films is characterized by the dynamic and steady-state response of the QCM frequency to pulses of organic vapors in dry air. The apparent partition coefficients are determined for imprinted and nonimprinted polymers prepared by two synthetic methods and for varying mole ratios of template to monomer. The hydroquinone-imprinted polymers and, to a lesser extent, the phenol-imprinted polymers exhibit greater sensitivity and higher selectivity than the nonimprinted polymers toward organic vapors that are structurally related to the templates. These results indicate that molecularly imprinted polymers are promising for the development of selective piezoelectric sensors for organic vapor detection.     

Synthesis and characterization of chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites for bone tissue engineering

Chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites were synthesized by a novel in situ precipitation method. The electrostatic adsorption between multiwalled carbon nanotubes and chitosan was investigated and explained by Fourier transform infrared spectroscopy analysis. Morphology studies showed that uniform distribution of hydroxyapatite particles and multiwalled carbon nanotubes in the polymer matrix was observed. In chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites, the diameters of multiwalled carbon nanotubes were about 10 nm. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The elastic modulus and compressive strength increased sharply from 509.9 to 1089.1 MPa and from 33.2 to 105.5 MPa with an increase of multiwalled carbon/chitosan weight ratios from 0 to 5 %, respectively. Finally, the cell biocompatibility of the composites was tested in vitro, which showed that they have good biocompatibility. These results suggest that the chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.     

聚丙烯腈基碳纳米管复合材料的制备及其表征

碳纳米管添加到聚合物中对其结构和性能都有深远的影响,本文通过浓硝酸对碳纳米管改性后,采用水相沉淀聚合的方法制备了聚丙烯腈/碳纳米管复合材料,同时研究了碳纳米管经过浓硝酸处理后其化学结构的变化;探讨了碳纳米管对聚丙烯腈复合材料热学和结晶性的影响。研究表明,浓硝酸常温处理不仅能除去杂质,还可以在碳纳米管表面引入羧基等含氧基团;加入碳纳米管后,聚丙烯腈的预氧化温度有一定程度的提前,放热量明显降低,同时对聚合物的结晶度也有一定程度的影响。     

Mechanical Reinforcement of Polymers Using Carbon Nanotubes

Owing to their unique mechanical properties, carbon nanotubes are considered to be ideal candidates for polymer reinforcement. However, a large amount of work must be done in order to realize their full potential. Effective processing of nanotubes and polymers to fabricate new ultra‐strong composite materials is still a great challenge. This Review explores the progress that has already been made in the area of mechanical reinforcement of polymers using carbon nanotubes. First, the mechanical properties of carbon nanotubes and the system requirements to maximize reinforcement are discussed. Then, main methods described in the literature to produce and process polymer–nanotube composites are considered and analyzed. After that, mechanical properties of various nanotube–polymer composites prepared by different techniques are critically analyzed and compared. Finally, remaining problems, the achievements so far, and the research that needs to be done in the future are discussed.     

单一结合位点分子印迹聚合物的合成及性能

采用分子自组装印迹技术在光引发条件下制备了以(S)-布洛芬为模板分子,α-甲基丙烯酸为功能单体的分子印迹聚合物。通过红外对聚合物的结构进行了表征。透射电镜结果表明,交联剂用量对印迹聚合物的形貌特征具有显著的影响。同时结合Scatchard分析研究了印迹聚合物的吸附性能及选择性识别能力,表明印迹聚合物特异性吸附容量为41μmol/g,印迹指数为2.28,对(S)-布洛芬形成单一结合位点,且表现出明显的吸附选择性。     

以预锂化多壁碳纳米管为负极的锂离子电容器性能

采用内部短路方式对多壁碳纳米管负极进行不同程度的预嵌锂处理,预嵌锂时间为5,30,60min,以预嵌锂多壁碳纳米管极片作为负极,活性炭极片作为正极,组装成锂离子电容器。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)对多壁碳纳米管及电极极片进行表征分析,采用恒流充放电(GCD)和交流阻抗谱(EIS)研究预嵌锂多壁碳纳米管负极和未预嵌锂处理多壁碳纳米管负极锂离子电容器的性能。电化学测试结果表明,多壁碳纳米管负极预嵌锂大幅提高了电容器充放电性能,对比未嵌锂多壁碳纳米管电容器,在相同的电流密度下(100mA/g),能量密度提高400%。预嵌锂60min,电流密度100mA/g时,其比容量达到57F/g。在电流密度为100～3200mA/g范围内,其最高能量密度与功率密度分别达到90Wh/kg,4130W/kg。1000次充放电循环后,容量保持率维持在85%以上,表现出良好的超级电容器性能。     

Temperature effects on resistance of aligned multiwalled carbon nanotube films

Electrical transport in vertically aligned films of multiwalled carbon nanotubes has been investigated in the -150 degrees C to 300 degrees C temperature range (all the tests were conducted in air at atmospheric pressure). In all the cases, the nanotube film exhibited a semi-conducting behavior, with the film resistance decreasing with increasing temperature. Removal of amorphous carbon contamination (via plasma etching) significantly improved the nanotube film's sensitivity to temperature changes (particularly in the 20 degrees C to 200 degrees C temperature range). All the of films tested in this study showed a consistent, repeatable behavior that was independent of the nanotube film length. The temperature sensitivity of the nanotube films was also found to be independent of the heating/cooling rates and without hysteresis. Because of the excellent repeatability and stability of the results, it is conceived that miniaturized temperature sensors could be designed using such aligned multiwalled nanotube films.     

Multiwalled carbon nanotubes embedded in sol–gel derived TiO<Subscript>2</Subscript> matrices and their use as room temperature gas sensors

Sol–gel TiO₂/Multiwall Carbon Nanotubes composites obtained by the Ti-isopropoxide route are reported as room temperature sensitive coatings. The effect of functionalizing the carbon nanotubes in strong oxidizing acids prior to the sol–gel synthesis is studied in the detection of acetone (CH₃COCH₃) and ammonia (NH₃). Although, mixed oxide phases were found in the sol–gel oxide and composites, sensing was highly reproducible in the composites, with fast adsorption/desorption cycles at room temperature. Composites based on as-received multiwalled carbon nanotubes show an increase in films resistance during acetone and ammonia adsorption, while composites based on functionalized carbon nanotubes show longer acetone desorption times and a decrease in resistance during ammonia sensing. Acetone sensing in both composites contrast with the slight decrement in resistance observed in either pure titanium oxide or carbon nanotubes, in agreement with preliminary theoretical results. In contrast, the strong dependence of NH₃ to the presence of oxygen and hydroxyl atoms on the carbon nanotube surface is not well understood.     

Novel critical point drying (CPD) based preparation and transmission electron microscopy (TEM) imaging of protein specific molecularly imprinted polymers (HydroMIPs)

We report the transmission electron microscopy (TEM) imaging of a hydrogel based molecularly imprinted polymer (HydroMIP) specific to the template molecule bovine haemoglobin (BHb). A novel critical point drying based sample preparation technique was employed to prepare the molecularly imprinted polymer (MIP) samples in a manner that would facilitate the use of TEM to image the imprinted cavities, and provide an appropriate degree of both magnification and resolution to image polymer architecture in the <10 nm range. For the first time, polymer structure has been detailed that tentatively suggests molecularly imprinted cavities, ranging from 5 to 50 nm in size, that correlate (in terms of size) with the protein molecule employed as the imprinting template. The modified critical point drying sample preparation technique used may potentially play a key role in the imaging of all molecularly imprinted polymers, particularly those prepared in the aqueous phase.     

Study of the activity of Grubbs catalyst-functionalized multiwalled carbon nanotubes in the ring opening metathesis polymerization

The synthesis of polynorbornene by ring opening metathesis polymerization (ROMP), in the presence of 1st and 2nd generation Grubbs catalyst-functionalized multiwalled carbon nanotubes (MWCNT), has been studied. MWCNTs were obtained by catalytic chemical vapour deposition (CCVD) of ethylene. A full characterization of the 1st and 2nd generation Grubbs catalyst-functionalized nanotubes was performed by FTIR and TG-DTG-MS. The amount of catalyst grafted to the nanotube surface was estimated. The activity of the catalyst-functionalized nanotubes in ROMP of 2-norbornene was found to be similar to that of bare 1st and 2nd generation Grubbs catalysts. The characterization of polynorbornene-carbon nanotube composites shows that the nanotubes are well dispersed in the polymer matrix.     

Molecularly imprinted polymer coatings for open-tubular capillary electrochromatography prepared by surface initiation

Molecularly imprinted polymer coatings were synthesized in fused-silica capillary columns by the use of a surface-coupled radical initiator. The coatings were prepared using either toluene, dichloromethane, or acetonitrile in the prepolymerization mixtures and were 0.15-2 microm thick as determined by scanning electron microscopy. Solvent-dependent differences in appearance were observed. All the molecularly imprinted polymer-based open-tubular capillary columns were able to separate the enantiomers of propranolol by means of electrochromatography. Electrochromatographic performance was found to be dependent on the type of solvent used during the synthesis.     

Self-assembly of single-walled carbon nanotubes into multiwalled carbon nanotubes in water: molecular dynamics simulations

We report discoveries from a series of molecular dynamics simulations that single-walled carbon nanotubes, with different diameters, lengths, and chiralities, can coaxially self-assemble into multiwalled carbon nanotubes in water via spontaneous insertion of smaller tubes into larger ones. The assembly process is tube-size-dependent, and the driving force is primarily the intertube van der Waals interactions. The simulations also suggest that a multiwalled carbon nanotube may be separated into single-walled carbon nanotubes under appropriate solvent conditions. This study suggests possible bottom-up self-assembly routes for the fabrication of novel nanodevices and systems.     

Adsorption of polymer coated magnetite composite particles onto carbon nanotubes and their magnetorheology

Polymer coated nano-sized magnetite (Fe₃O₄) particles with multiwalled carbon nanotube (MWNT) nanohybrid were prepared by four step procedures in this study. Initially, magnetic particles were synthesized by a co-precipitation method with ammonium hydroxide and oleic acid, and then the produced particles were coated with polyacrylamide (PAAm). Finally PAAm coated magnetite particles (Mag-PAAm) were physically adsorbed onto multiwalled carbon nanotubes (MWNT) under ultrasonication. Transmission electron microscopy (TEM) was used to investigate the formation of Mag-PAAm-MW nanohybrids nanostructure, confirming that prepared Mag-PAAM particles were well adsorbed onto the surfaces of MWNT. In addition, MR characteristics of PAAm coated magnetite particles with MWNT (Mag-PAAm-MW) nanohybrids were investigated under six different external magnetic field strengths via a rotational rheometer, exhibiting typical MR behavior of yield stress and shear stress.     

Selective adsorption and separation of dibenzothiophene by molecularly imprinted polymer on the surface of porous magnetic carbon nanospheres

A molecularly imprinted polymer was deposited on the surface of porous magnetic carbon nanosphere to obtain a sorbent for dibenzothiophene. The molecularly imprinted polymer was synthesized by using porous magnetic carbon nanosphere as the support, dibenzothiophene as the template, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linker. Field-emission scanning electron microscopy and Fourier-transformation infrared spectroscopy were used to characterize the morphology and structure of the sorbent. Adsorption results in terms of kinetics, isotherms and selective recognition adsorption indicate that the saturated adsorption amount of the sorbent towards dibenzothiophene reaches 32.00?mg g^?1 at 318 K within 40?min. The sorbent presents good selectivity for dibenzothiophene over benzothiophene with a relative selectivity coefficient of 1.70. The adsorption capacity of the sorbent towards dibenzothiophene still maintains 81.5% after five times of recycle, indicating that the obtained sorbent has excellent regeneration ability.     

Influence of functionalization of multi-walled carbon nanotubes on the properties of ethylene vinyl acetate nanocomposites

Commercially available multiwalled carbon nanotubes (MWNT) were chemically modified by amine, acid and silane and their ethylene vinyl acetate (EVA) based nanocomposites were prepared. Unmodified and modified nanotubes were characterized by thermogravimetry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Early degradation of modified nanotubes from the thermogravimetry study proved the presence of functional groups on nanotube surface. Increase in D-band to G-band ratio and a shift in radial breathing mode peaks from the Raman spectra indicated the generation of surface defects due to functionalization and variation in van der Waals force of attraction between nanotube aggregates on modification. The unmodified nanotubes improved the tensile strength by 30% with 4 weight% of filler. Amine modification imparted further increase in strength due to the presence of functional groups on the nanotube surface and the subsequent better dispersion of the nanotubes in the polymer matrix. The silane treatment imparted maximum improvement in various properties of the nanocomposites. The nanotubes provided better thermal degradation stability and also higher thermal conductivity to virgin EVA. The results were well supported by the morphological as well as swelling study of the various samples.     

Sorption capacity of carbon nanotubes prepared by mechanochemical processing of amorphous carbon

We have studied the sorption properties of nanofibrous carbon (multiwalled nanotubes) produced by milling amorphous carbon prepared through sphagnum moss pyrolysis. The results demonstrate that the sorption capacity of the carbon nanotubes depends on storage time and that their oxidation behavior depends on nanotube preparation conditions.