Multiwall Carbon Nanotubes and Nanofibers in Gallionella

This is a report of microbial formation of multiwall carbon nanotubes (MWCNT) and nanofibers at normal pressure and temperature. Our results demonstrate a single cell organism's ability to form complicated material of high industrial interest. The microorganism, Gallionella, is classified as autotrophic and dysoxic. It uses CO₂ for its carbon source and grows in environments with low concentrations of free oxygen. The organisms were taken from a deep bedrock tunnel where water leaking from cracks in the rock formed a precipitate of iron as a bacterial slime on the rock wall. Detailed investigations of the samples by transmission electron microscopy (TEM) revealed several types of MWCNT. The stalk single MWCNT was observed with a diameter of about 10 nm and with an inner diameter of 1.35 nm. The wall of the nanotube is built by graphite layers. The 10 to 20 sheets are used to form the tubes. The measured spacing between the lines is 0.34 nm, which is an average value of interlayer spacing, close to the graphitic distance (0.335 nm). HRTEM images reveal a two-dimensional lattice with a spacing of 0.24 nm, indicating the presence of graphene.     

Encapsulation of Pt-labelled DNA Molecules inside Carbon Nanotubes

Experiments on encapsulating Pt--labelled DNA molecules inside multiwalled carbon nanotubes (MWCNT) were performed under temperature and pressure conditions of 400K and 3 Bar. The DNA-CNT hybrids were purified via agarose gel electrophoresis and analyzed via high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the Pt-labelled DNA molecules attached to the outside walls of CNTs could be removed by electrophoresis. The HR-TEM and EDX results demonstrated that 2-3% of the Pt-labelled DNA molecules were successfully encapsulated inside the MWCNTs. The experimental study complements our previous molecular dynamics simulations on encapsulation of single stranded DNA oligonucleotides inside single wall carbon nanotubes under similar conditions in water. The van der Waals interaction between CNT and Pt-labelled DNA is believed to be the main driving force for this phenomenon. The DNA-CNT molecular complex could be further explored for potential applications in bio-nanotechnology.     

Adsorption of Cu(II) on Oxidized Multi-Walled Carbon Nanotubes in the Presence of Hydroxylated and Carboxylated Fullerenes

The adsorption of Cu(II) on oxidized multi-walled carbon nanotubes (oMWCNTs) as a function of contact time, pH, ionic strength, temperature, and hydroxylated fullerene (C₆₀(OH)_n) and carboxylated fullerene (C₆₀(C(COOH)₂)_n) were studied under ambient conditions using batch techniques. The results showed that the adsorption of Cu(II) had rapidly reached equilibrium and the kinetic process was well described by a pseudo-second-order rate model. Cu(II) adsorption on oMWCNTs was dependent on pH but independent of ionic strength. Compared with the Freundlich model, the Langmuir model was more suitable for analyzing the adsorption isotherms. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Cu(II) adsorption on oMWCNTs was spontaneous and endothermic. The effect of C₆₀(OH)_n on Cu(II) adsorption of oMWCNTs was not significant at low C₆₀(OH)_n concentration, whereas a negative effect was observed at higher concentration. The adsorption of Cu(II) on oMWCNTs was enhanced with increasing pH values at pH < 5, but decreased at pH ≥ 5. The presence of C₆₀(C(COOH)₂)_n inhibited the adsorption of Cu(II) onto oMWCNTs at pH 4–6. The double sorption site model was applied to simulate the adsorption isotherms of Cu(II) in the presence of C₆₀(OH)_n and fitted the experimental data well.     

Adsorption of DDT from Contaminated Soil using Carbon Nanotubes

This paper presents results of an investigation into the use of carbon nanotubes (CNTs) for the adsorption of DDT in soil and solution. DDT is a known endocrine-disrupting chemical with observed persistence, harm to the environment, and a human health concern. Thus, it is important to clean it up from the environment. In this study, CNT is selected because it has high surface area for adsorption. Adsorption experiments were conducted using the batch equilibrium technique with a fixed soil:solution ratio. Adsorption of DDT onto the CNTs was characterized by an initial rapid adsorption, which eventually became constant within 22 hours, perhaps due to limited surface area of the CNTs available for DDT adsorption. Results of the study demonstrated the relative adsorption increase with increasing solution concentration. The results obtained indicate the importance of CNTs in the adsorption of DDT and show that they have a great potential application for remediation of DDT from contaminated soil.     

Transport of Surface-modified Carbon Nanotubes through a Soil Column

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.     

Restrictions on the Production of Multi-Wall Carbon Nanotubes and Nanofibers by Gallionella sp.

The enzymatic oxidization of dissolved Fe(II) to Fe(III) by neutrophilic Fe-oxidizing bacteria plays a significant role in biological cycling of iron by inducing the precipitation of Fe(III) oxyhydroxide in aqueous environments. Among the diverse neutrophilic Fe-oxidizing bacteria, the genus Gallionella has received wide attention for its production of unique twisted extracellular stalks. Hallberg and Tai (2014 Hallberg R, Tai CW. 2014. Multi-wall carbon nanotubes and nanofibers in Gallionella. Geomicrobiol J 31(9):764–768.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) recently reported the detection of multi-wall carbon nanotubes on the twisted-stalks, and they viewed those carbon nanotubes as being biologically produced by Gallionella. We scrutinized Gallionella-produced biofilms collected from natural environments by scanning electron microscopy and high-resolution transmission electron microscopy. Ferrihydrite and lepidocrocite were the only nano-scaled minerals observed on the stalk, while there were nanometer-sized sheet-like graphitic contaminants on the grid in the vicinity of the sample which showed the same morphology as Hallberg and Tai (2014 Hallberg R, Tai CW. 2014. Multi-wall carbon nanotubes and nanofibers in Gallionella. Geomicrobiol J 31(9):764–768.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) observed. Moreover, similar materials on an empty grid and a grid loaded with randomly selected synthesized materials were also observed. Based on the current knowledge of carbon nanotube syntheses, none of the three known synthesizing methods including root-growth, rolling-up and bottom-up could be biochemically produced by any life because of the significant kinetic and energy obstacles. The carbon nanomaterials reported by Hallberg and Tai (2014 Hallberg R, Tai CW. 2014. Multi-wall carbon nanotubes and nanofibers in Gallionella. Geomicrobiol J 31(9):764–768.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) were clearly contaminations from amorphous carbon film on the grids for holding samples for transmission electron microscopic observations.     

Coupled Surface Plasmon-Polariton Modes of Metallic Single-Walled Carbon Nanotubes

The propagation of the coupled surface plasmon-polariton modes in the metallic single-walled carbon nanotubes are investigated, taking into account the retardation effects. A simple model based on the classical electrodynamics and the two-fluid hydrodynamic theory is proposed. The dispersion relation of the surface polariton modes is obtained in order to survey the effects of the two-fluid model and the insulating dielectric media.     

Atomistic Simulations of Uniaxial Tensile Behaviors of Single-walled Carbon Nanotubes

Atomistic simulations, using the second-generation reactive empirical bond order (REBO) potential, are performed to investigate the uniaxial tensile behaviors of single-walled carbon nanotubes (SWCNTs). It is found that the effect of the nanotube diameters on the elastic modulus, the tensile strength and the stress vs. strain relation of SWCNTs is small yet noticeable. However, the effect of the degree of helicity is significant.     

碳纳米管固定化纤维素酶的最佳工艺研究

纤维素酶在环保、医药、食品等领域都具有广泛的应用前景,但由于纤维素酶的生产成本较高,生物活性较低,使得纤维素酶的应用受到了限制。为了寻找一种固定化纤维素酶的方法,使酶可以重复多次使用,首次以多壁碳纳米管为载体固定化纤维素酶,研究功能化的多壁碳纳米管固定化纤维素酶的固定化条件,采用正交试验对酶固定化中的主要条件进行优化,并通过傅里叶变换红外光谱仪对多壁碳纳米管（multiwalled carbon nanotube,MWCNTs）、纤维素酶及固定化纤维素酶的结构进行表征。结果表明,固定化纤维素酶的最佳工艺条件为：酶浓度5 mg·mL-1,温度40 ℃,pH 5.0,固定化时间3 h;通过傅里叶变换红外光谱证实纤维素酶成功固定到多壁碳纳米管上。     

PEGylated Single-Walled Carbon Nanotubes as Nanocarriers for Cyclosporin A Delivery

Single-walled carbon nanotubes (SWCNTs) have attracted the attention of many researchers due to their remarkable physicochemical features and have been found to be a new family of nanovectors for the delivery of therapeutic molecules. The ability of these nanostructures to load large amounts of drug molecules on their outer surface has been considered as the main advantage by many investigators. Here, we report the development of a PEGylated SWCNT-mediated delivery system for cyclosporin A (CsA) as a potent immunosuppressive agent. The available OH group in the CsA structure was first linked to a bi-functional linker (i.e., succinic anhydride) in order to provide a COOH terminal group. CsA succinylation process was optimized by using the modified simplex method. The resulting compound, CsA–CO–(CH₂)₂–COOH, was then grafted onto the exterior surface of SWCNTs, previously PEGylated with phospholipid–PEG₅₀₀₀–NH₂ conjugates, through the formation of an amide bond with the free amine group of PEGylated SWCNTs. Drug loading, stability of the PEGylated SWCNT–CsA complex, and in vitro release of the drug were evaluated. Loading efficiencies of almost 72% and 68% were achieved by UV spectrophotometry and elemental analysis methods, respectively. It was observed that 57.3% of cyclosporine was released from CsA–Pl–PEG₅₀₀₀–SWCNTs after 3 days. In this investigation, we conjugated CsA to an amine-terminated phospholipid–polyethylene glycol chain attached on SWCNTs via a cleavable ester bond and demonstrated the possible potential of PEGylated SWCNT-based systems for CsA delivery.     

碳纤维/碳纳米管增强磷酸钙生物复合材料的血液相容性研究

目的：探讨以碳长纤维模拟骨组织中的胶原纤维束,碳纳米管弥散分布在骨水泥基质中所制备的仿生复合材料的血液相容性。方法：采用血小板静态浸渍黏附、聚集实验法,通过扫描电镜（SEM）观察复合材料表面、粗糙断面及气孔内的血栓形成情况,对其血液相容性进行研究。结果：以两种碳材料为增强相制备的复合材料与血液接触后,在材料光滑的表面、粗糙的断面及气孔内、以及碳纤维与碳纳米管的表面,由于纤维蛋白原的吸附量较少使血小板难以黏附、聚集,因此,在材料表面未能形成白血栓。结论：以碳纤维和碳纳米管为增强相制备的骨水泥生物复合材料具有良好的血液相容性。     

Glucose Biosensor Based on a Glassy Carbon Electrode Modified with Polythionine and Multiwalled Carbon Nanotubes

A novel glucose biosensor was fabricated. The first layer of the biosensor was polythionine, which was formed by the electrochemical polymerisation of the thionine monomer on a glassy carbon electrode. The remaining layers were coated with chitosan-MWCNTs, GOx, and the chitosan-PTFE film in sequence. The MWCNTs embedded in FAD were like “conductive wires” connecting FAD with electrode, reduced the distance between them and were propitious to fast direct electron transfer. Combining with good electrical conductivity of PTH and MWCNTs, the current response was enlarged. The sensor was a parallel multi-component reaction system (PMRS) and excellent electrocatalytic performance for glucose could be obtained without a mediator. The glucose sensor had a working voltage of −0.42 V, an optimum working temperature of 25°C, an optimum working pH of 7.0, and the best percentage of polytetrafluoroethylene emulsion (PTFE) in the outer composite film was 2%. Under the optimised conditions, the biosensor displayed a high sensitivity of 2.80 µA mM⁻¹ cm⁻² and a low detection limit of 5 µM (S/N = 3), with a response time of less than 15 s and a linear range of 0.04 mM to 2.5 mM. Furthermore, the fabricated biosensor had a good selectivity, reproducibility, and long-term stability, indicating that the novel CTS+PTFE/GOx/MWCNTs/PTH composite is a promising material for immobilization of biomolecules and fabrication of third generation biosensors.