Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

TiO2纳米管阵列及其应用

TiO2纳米管阵列作为一种新型的纳米TiO2材料,由于具有独特的阵列结构和优异的性能,引起了人们的极大关注.本文介绍了采用阳极氧化法制备TiO2纳米管阵列的工艺条件、产物特性、形成机理,及其在氢传感器、光解水制氢、染料敏化太阳能电池与光催化降解污染物等领域的应用,分析了目前存在的问题,并提出了今后研究的对策.     

Overcoming the insolubility of carbon nanotubes through high degrees of sidewall functionalization

The use of carbon nanotubes in materials applications has been slowed due to nanotube insolubility and their incompatibility with polymers. We recently developed two protocols to overcome the insoluble nature of carbon nanotubes by affixing large amounts of addends to the nanotube sidewalls. Both processes involve reactions with aryl diazonium species. First, solvent-free functionalization techniques remove the need for any solvent during the functionalization step. This delivers functionalized carbon nanotubes with increased solubility in organic solvents and processibility in polymeric blends. Additionally, the solvent-free functionalization process can be done on large scales, thereby paving the way for use in bulk applications such as in structural materials development. The second methodology involves the functionalization of carbon nanotubes that are first dispersed as individual tubes in surfactants within aqueous media. The functionalization then ensues to afford heavily functionalized nanotubes that do not re-rope. They remain as individuals in organic solvents giving enormous increases in solubility. This protocol yields the highest degree of functionalization we have obtained thus far-up to one in nine carbon atoms on the nanotube has an organic addend. The proper characterization and solubility determinations on nanotubes are critical; therefore, this topic is discussed in detail.     

Template synthesized molecularly imprinted polymer nanotube membranes for chemical separations

In this report, we describe the synthesis of a molecularly imprinted polymer (MIP) nanotube membrane, using a porous anodic alumina oxide (AAO) membrane by surface-initiated atom transfer radical polymerization (ATRP). The use of a MIP nanotube membrane in chemical separations gives the advantage of high affinity and selectivity. Furthermore, because the molecular imprinting technique can be applied to different kinds of target molecules, ranging from small organic molecules to peptides and proteins, such MIP nanotube membranes will considerably broaden the application of nanotube membranes in chemical separations and sensors. This report also shows that the ATRP route is an efficient procedure for the preparation of molecularly imprinted polymers. Furthermore, the ATRP route works well in its formation of MIP nanotubes within a porous AAO membrane. The controllable nature of ATRP allows the growth of a MIP nanotube with uniform pores and adjustable thickness. Thus, using the same route, it is possible to tailor the synthesis of MIP nanotube membranes with either thicker MIP nanotubes for capacity improvement or thinner nanotubes for efficiency improvement.     

聚甲基丙烯酸甲酯固定化碳纳米管作为MALDI基质的研究

将聚甲基丙烯酸甲酯材料在多壁碳纳米管表面原位聚合, 利用这种修饰的碳纳米管作为基质辅助激光解析离子化(MALDI)的基质, 利用修饰后的碳纳米管可以“溶解”的特性实现了稳定的MALDI离子化, 并且消除了在低质量端的基质噪音. 此类聚合物衍生的碳纳米管具有相对较好的亲水性表面, 可“溶解”在溶剂中. 此方法适用于有机小分子、多肽、聚合物和蛋白质酶解肽段的质谱分析. 实验表明聚甲基丙烯酸甲酯固定化碳纳米管能有效地吸收和传递激光能量, 可与样品充分地分散混合, 质谱检测背景低, 重现性好, 具有较宽的可测质量范围. 此方法在小分子快速检测和蛋白质组学方面有很大的应用前景.     

Preparation of stimulus-responsive,polyfluorene-wrapped carbon nanotubes via palladium cross coupling

Decoration of carbon nanotube surfaces without damaging nanotube optoelectronic properties is an ongoing challenge. Here, we utilize Sonogashira coupling chemistry to decorate the nanotube surface without perturbing optoelectronic properties. Reactive, noncovalently functionalized polymer–nanotube complexes were prepared using a polyfluorene with aryl iodide groups in its side chains. The aryl iodides enable Pd cross coupling between polymer–nanotube complexes and small molecules or polymers derivatized with an alkyne. Modestly efficient coupling was found to occur under dilute conditions at elevated temperatures. Successful coupling between aryl iodide and alkyne partners was observed using infrared spectroscopy via the appearance of carbonyl stretches that originate from covalently linked, carbonyl-containing alkynes, and thermogravimetric analysis was used to measure reaction conversion under various conditions. Grafting of the hydrophobic polymer–nanotube complex with poly(ethylene glycol) enabled the dispersion to be transferred from organic to aqueous solution. This chemistry resulted in no damage to the nanotube sidewall, as evidenced by Raman spectroscopy. The aryl iodide-containing polyfluorene–nanotube complex was also coupled to a photoswitchable alkyne-containing spiropyran moiety and it was found that the photoswitch retained its functionality after coupling to the polymer–nanotube complex. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2723–2729     

Model of carbon nanotube growth through chemical vapor deposition

This Letter outlines a model to account for the catalyzed growth of nanotubes by chemical vapor deposition. It proposes that their formation and growth is an extension of other known processes in which graphitic structures form over metal surfaces at moderate temperatures through the decomposition of organic precursors. Importantly, the model also states that the form of carbon produced depends on the physical dimensions of the catalyzed reactions. Experimental data are presented that correlate nanotube diameters to the size of the catalyst particles. Nanotube stability as a function of nanotube type, length and diameter are also investigated through theoretical calculations.     

Monodisperse rutile microspheres with ultrasmall nanorods on surfaces: Synthesis, characterization, luminescence, and photocatalysis

This work demonstrates the process of building optoelectrically cooperative surface wetting in smart and precise way. The superhydrophobic photosensitive film is constructed with TiO(2) nanotube arrays. Compared with conventional organic dyes, CdS quantum dots (QDs) as sensitizer layer are modified on TiO(2) nanotubes surface to improve photosensitivity of the composited surface in visible light region, which offer the benefit for designing and fabricating solid state hetero-junction devices. ITO glass is introduced as top electrode to apply electrical and optical stimuli and the patterned wetting is instantly obtained with masking light through ITO. The optoelectrically cooperative wettability conversion occurred on superhydrophobic TiO(2) nanotube surface at critical voltage of 12 V, which was decreased by 18 V comparing with only using electric stimulus. This study provides potential applications for TiO(2) nanotube arrays to the associated research of liquid reprography, location-controlled microfluidic device and lab-on-chip.     

Design of highly ordered Ag-SrTiO3 nanotube arrays for photocatalytic degradation of methyl orange

Ag-SrTiO₃ nanotube arrays were successfully prepared for the degradation of methyl orange (MO) under ultraviolet irradiation. In order to form highly ordered SrTiO₃ nanotube arrays, the preparation of TiO₂ nanotube arrays by anodic oxidation of titanium foil in different electrolytes was investigated. The selected organic solvents in electrolytes include glycerol, dimethyl sulfoxide and glycol. The results indicate that the morphology of TiO₂ nanotube arrays prepared in glycol containing ammonium fluoride electrolyte is more regular. Then SrTiO₃ nanotube arrays were synthesized by a hydrothermal method using TiO₂ nanotube arrays as the precursor. In order to further improve the photocatalytic activity of SrTiO₃ nanotube arrays, Ag nanoparticles were loaded on SrTiO₃ nanotube arrays by two sets of experiments. The loaded Ag results in an enhancement of photocatalytic activity of SrTiO₃ nanotube arrays. Moreover, the effect of pH on the photocatalytic degradation of MO was also studied.     

Dispersion and phase separation of carbon nanotubes in ultrathin polymer films

The inner structure and nanoscale distribution of the stiffness was studied for polymer-single-wall carbon nanotube composites. Dispersion of nanotubes in a polystyrene and polyurethane polymer matrix was achieved by a proper choice of the organic solvent (NMP) and sonification of polymer/SWNT solutions. Ultrathin nanocomposite films were prepared through a dip-coating procedure and possessed a noticeable degree of nanotube orientation in the direction of the applied shear force. Peculiarities of the phase separation in the films were studied by atomic force microscopy (with application of force modulation mode to map the nanotube distribution within the polymer matrix) and Raman spectroscopy.     

Sidewall alkylcarboxylation of carbon nanotubes through reactions of fluoronanotubes with functional free radicals

Addition of carboxyalkyl radicals to carbon nanotube (CNT) graphene surface is a non-destructive to nanotube framework method of sidewall functionalization of CNTs with the carboxylic group terminated moieties. Fluorination activates the CNT surface towards addition reactions due to transformation of the graphene aromatic structure to a more chemically reactive polyene ??-system structure of fluoronanotubes. As a result, the sidewall addition reactions to fluoronanotubes are completed in a much shorter time spans than in the case of pristine CNTs. Carboxyalkyl CNT derivatives prepared by this method form stable suspensions in water and polar organic solvents. This enables their applications in biomedical research; for the preparation of water-based paints, inks, and coatings; and for processing and fabrication of nanocomposites.     

Electrochemical capacitance performance of polypyrrole–titania nanotube hybrid

In this study, the polypyrrole–titania nanotube hybrid has been synthesized for an electrochemical supercapacitor application. The highly ordered and independent titania nanotube array is fabricated by an electro-oxidation of titanium sheet through an electrochemical anodization process in an aqueous solution containing ammonium fluoride, phosphoric acid and ethylene glycol. The polypyrrole–titania nanotube hybrid is then prepared by electrodepositing the conducting polypyrrole into well-aligned titania nanotubes through a normal pulse voltammetry deposition process in an organic acetonitrile solution containing pyrrole monomer and lithium perchlorate. The morphology and microstructure of polypyrrole–titania nanotube hybrid are characterized by scanning electron microscopy, infrared spectroscopy and Raman spectroscopy. The electrochemical capacitance performance is determined by cyclic voltammetry and charge/discharge measurement. It indicates that the polypyrrole film can been uniformly deposited on both surfaces of titania nanotube walls, demonstrating a heterogeneous coaxial nanotube structure. The specific capacitance of polypyrrole–titania nanotube hybrid is determined to be 179?F?g^?1 based on the polypyrrole mass. The specific energy and specific power are 7.8?Wh?kg^?1 and 2.8?kW?kg^?1 at a constant charge/discharge current of 1.85?mA?cm^?2, respectively. The retained specific capacitance still keeps 85% of the initial capacity even after 200 cycle numbers. This result demonstrates the satisfying stability and durability of PPy–TiO₂ nanotube hybrid electrode in a cyclic charge/discharge process. Such a composite electrode material with highly ordered and coaxial nanotube hybrid structure can contribute high energy storage for supercapacitor applications.     

Swelling the micelle core surrounding single-walled carbon nanotubes with water-immiscible organic solvents

Solvatochromic shifts in the absorbance and fluorescence spectra are observed when surfactant-stabilized aqueous single-walled carbon nanotube (SWNT) suspensions are mixed with immiscible organic solvents. When aqueous surfactant-suspended SWNTs are mixed with o-dichlorobenzene, the spectra closely match the peaks for SWNTs dispersed in only pure o-dichlorobenzene. These spectral changes suggest that the hydrophobic region of the micelle surrounding SWNTs swells with the organic solvent when mixed. The solvatochromic shifts of the aqueous SWNT suspensions are reversible once the solvent evaporates. However, some surfactant-solvent systems show permanent changes to the fluorescence emission intensity after exposure to the organic solvent. The intensity of some large diameter SWNT (n, m) types increase by more than 175%. These differences are attributed to surfactant reorganization, which can improve nanotube coverage, resulting in decreased exposure to quenching mechanisms from the aqueous phase.     

Fabrication of semiconducting polyaniline-wrapped halloysite nanotube composite and its electrorheology

An organic/inorganic polyaniline-wrapped halloysite nanotube (PANI/HNT) composite was prepared by the in situ polymerization of aniline in the presence of a HNT dispersion. The physical properties of the resulting PANI/HNT composite were characterized by scanning electron microscopy, thermogravimetric analysis, and Fourier-transform infrared spectroscopy. This organic/inorganic composite particle was then dispersed in silicone oil as an electrorheological (ER) fluid, and its ER properties were examined using a Couette-type rotational rheometer equipped with a high-voltage generator. This novel halloysite composite-based ER fluid exhibited typical ER properties under an applied electric field.     

Noncovalent engineering of carbon nanotube surfaces by rigid,functional conjugated polymers

We report a new nonwrapping approach to noncovalent engineering of carbon nanotube surfaces by short, rigid functional conjugated polymers, poly(aryleneethynylene)s. Our technique not only enables the dissolution of various types of carbon nanotubes in organic solvents, which represents the first example of solubilization of carbon nanotubes via pi-stacking without polymer wrapping, but could also introduce numerous neutral and ionic functional groups onto the carbon nanotube surfaces.     

Double-sided anodic titania nanotube arrays: a lopsided growth process

In the past decade, the pore diameter of anodic titania nanotubes was reported to be influenced by a number of factors in organic electrolyte, for example, applied potential, working distance, water content, and temperature. All these were closely related to potential drop in the organic electrolyte. In this work, the essential role of electric field originating from the potential drop was directly revealed for the first time using a simple two-electrode anodizing method. Anodic titania nanotube arrays were grown simultaneously at both sides of a titanium foil, with tube length being longer at the front side than that at the back side. This lopsided growth was attributed to the higher ionic flux induced by electric field at the front side. Accordingly, the nanotube length was further tailored to be comparable at both sides by modulating the electric field. These results are promising to be used in parallel configuration dye-sensitized solar cells, water splitting, and gas sensors, as a result of high surface area produced by the double-sided architecture.     

Aromatic single-walled organic nanotubes self-assembled from NH-bridged azacalix[2]triptycene[2]pyridine

A novel triptycene-derived NH-bridged azacalixarene can self-assemble into an aromatic single-walled organic nanotube with large dimensions by four one-dimensional hydrogen bond chains.     

Anodic growth of highly ordered TiO2 nanotube arrays to 134 microm in length

Described is the fabrication of self-aligned highly ordered TiO(2) nanotube arrays by potentiostatic anodization of Ti foil having lengths up to 134 mum, representing well over an order of magnitude increase in length thus far reported. We have achieved the very long nanotube arrays in fluoride ion containing baths in combination with a variety of nonaqueous organic polar electrolytes including dimethyl sulfoxide, formamide, ethylene glycol, and N-methylformamide. Depending on the anodization voltage, pore diameters of the resulting nanotube arrays range from 20 to 150 nm. Our longest nanotube arrays yield a roughness factor of 4750 and length-to-width (outer diameter) aspect ratio of approximately 835. The as-prepared nanotubes are amorphous but crystallize with annealing at elevated temperatures. In initial measurements, 45 mum long nanotube-array samples, 550 degrees C annealed, under UV illumination show a remarkable water photoelectrolysis photoconversion efficiency of 16.25%.     

RGO-TiO2纳米管阵列的制备及其光电性能

采用阳极氧化的方法,通过调节阴、阳两电极间距制备不同壁厚的TiO₂纳米管阵列. 采用脉冲电还原沉积的方法将RGO负载于TiO₂纳米管阵列表面合成了RGO-TiO₂纳米管阵列. 相较于负载在薄壁TiO₂纳米管阵列上的RGO,负载于厚壁TiO₂纳米管阵列上的RGO得以充分还原,覆盖率大幅度提高,并显示出良好的光吸收性质和较低的电荷传输电阻,光电流大幅度增加.     

《高分子物理》课程中结合碳纳米管的案例教学研究

碳纳米管分子结构、性能与传统的液晶高分子材料具有非常多共性之处,是《高分子物理》课程教学中极具代表性的学科前沿教学案例。本文以碳纳米管为案例教学对象,从结构、物理和力学性能以及溶液相行为等方面,对碳纳米管与棒状刚性结构液晶高分子材料进行类比;在此基础上,将教学知识点延伸至借鉴芳纶纤维等液晶纺丝技术制备高取向度碳纳米管纤维的新方法,并对比分析碳纳米管纤维与有机纤维性能特点。通过合理设计课程主线、优选教学内容,培养学生的自主学习、学科交叉创新能力,激发学生学习的能动性,提高授课效果和教学质量。