Functional and unmodified MWNTs for delivery of the water-insoluble drug Carvedilol - A drug-loading mechanism

The purpose of this study was to develop carboxyl multi-wall carbon nanotubes (MWNTs) and unmodified MWNTs loaded with a poorly water-soluble drug, intended to improve the drug loading capacity, dissolubility and study the drug-loading mechanism. MWNTs were modified with a carboxyl group through the acid treatment. MWNTs as well as the resulting functionalized MWNTs were investigated as scaffold for loading the model drug, Carvedilol (CAR), using three different methods (the fusion method, the incipient wetness impregnation method, and the solvent method). The effects of different pore size, specific surface area and physical state were systematically studied using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transformation infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), nitrogen adsorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The functional MWNTs allowed a higher drug loading than the unmodified preparations. The methods used to load the drug had a marked effect on the drug-loading, dissolution, and physical state of the drug as well as its distribution. In addition, the solubility of the drug was increased when carried by both MWNTs and functional MWNTs, and this might help to improve the bioavailability.     

Supercritical fluid-assisted synthesis of a carbon nanotubes-grafted biocompatible polymer composite

A nanocomposite consisting of multi-wall nanotubes (MWNTs) grafted with a biocompatible polymer poly(2-hydroxyethyl methacrylate) was prepared by in situ polymerization in supercritical carbon dioxide. The surface of the MWNTs was first surface modified with hydroxyl groups in the solution of KMnO₄ and a phase-transfer catalyst. MWNT-OH was then functionalized with vinyl groups using a silane coupling agent, γ-methacryloxypropyltrimethoxysilane. The silane groups can improve the dipersion of MWNTs in supercritical carbon dioxide, while the terminal vinyl groups help fabricate polymer chains on the MWNT surface. The as-synthesized products were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermo-gravimetric analysis. The SEM and TEM images showed that the nanotubes were well coated with the polymer shell. The composite had higher thermal stability than the pure polymer and dispersed well in methanol. This biocompatible polymer composite was prepared using a green method and is expected to be useful as a biomaterial composite with potential applications in the biological field.     

The effect of surface modification on heavy metal ion removal from water by carbon nanoporous adsorbent

In this work, chemically oxidized mesoporous carbon (COMC) with excellent lead adsorption performance was prepared by an acid surface modification method from mesoporous carbon (MC) by wet impregnation method. The structural order and textural properties of the mesoporous materials were studied by XRD, SEM, and nitrogen adsorption. The presence of carboxylic functional groups on the carbon surface was confirmed by FT-IR analysis. Batch adsorption experiments were conducted to study the effect of adsorbent dose, initial concentration and temperature for the removal of Pb(II) from aqueous systems. The adsorption was maximum for the initial pH in the range of 6.5-8.0. The kinetic data were best fitted to the pseudo-second order model. The adsorption of chemically oxidized mesoporous carbon to Pb(II) fits to the Langmuir model. The larger adsorption capacity of chemically oxidized mesoporous carbon for Pb(II) is mainly due to the oxygenous functional groups formed on the surface of COMC which can react with Pb(II) to form salt or complex deposited on the surface of MC.     

Comparison of Activated Carbon,Multiwalled Carbon Nanotubes,and Cadmium Hydroxide Nanowire Loaded on Activated Carbon as Adsorbents for Kinetic and Equilibrium Study of Removal of Safranine O

Activated carbon (AC), multiwalled carbon nanotube (MWCNT), and cadmium hydroxide nanowire loaded on activated carbon (Cd(OH)₂-NW-AC) have been used for the removal of safranine O (SO) from wastewater. The effects of various parameters including pH, temperature, concentration of the dye, amount of adsorbents, and contact time on the SO adsorption efficiency for all adsorbents has been investigated. Graphical correlation of fitting experimental data to various adsorption isotherm models like those of Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich for all adsorbents have been calculated. It was found that safranine O adsorption on all adsorbents was endothermic and feasible in nature. Fitting the experimental data to different kinetic models suggests that the adsorption process follows pseudo-second-order kinetics with involvement of the particle diffusion mechanism.     

Electrophoresis and orientation of multiple wall carbon nanotubes in polymer solution

This paper contains an in-depth analysis of the electrophoresis of multi-wall carbon nanotubes (MWNTs) in liquid epoxy where electrophoresis experiments under DC and AC fields were carried out for five different types of multi-wall carbon nanotubes (MWNTs). DC electrophoresis and particle image velocimetry were used to determine the electrophoretic particle mobility and zeta potential, where the MWNTs with the largest outer diameter and length led to the highest mobility values. The orientation and agglomeration of MWNTs into “striation” lines under AC electrophoresis were investigated by analysing the hue, saturation and intensity of the transmitted polarised light under microscope, following a schedule of step-wise applied voltage in the range of 0 to 100 V. Plots of hue and saturation as a function of the applied voltage were used to assess the degree of orientation and density of orientated MWNT structures, respectively, and to determine an optimum AC electric field value for the orientation of a specific MWNT type by electrophoresis.     

A facile, green, and tunable method to functionalize carbon nanotubes with water-soluble azo initiators by one-step free radical addition

Versatile functional groups were covalently attached to the surface of multiwalled carbon nanotubes (MWNTs) by one-step free radical addition of water-soluble azo initiators. The coverage density of functional groups is rationally controlled either by adjusting the feed ratio of azo initiators to MWNTs or by utilizing the starting chemicals of multifunctional groups. TEM observations in conjunction with solubility data imply that the functionalized-MWNTs have much better dispersibility and stability than pristine MWNTs in polar solvents. The attached carboxylic groups were then used as scaffolds to chelate Ag⁺ ions affording Ag/MWNTs nanohybrids in the presence of NaBH₄ reductant. This shows that the reactive groups anchored on MWNTs can be further chemically functionalized. The proposed method might open many new opportunities for the development of high-performance nanomaterials containing CNTs.     

ICP-OES研究活性炭无纺布对镉的吸附

重金属污染是一个相当严重的环境问题。镉具有很强的生物毒性和不可降解性，对生态环境和人体健康有极大威胁，被列为优先控制污染物。环境中镉的主要污染源是电镀、采矿和化学工业等部门的废水，如何简单高效去除水中的镉，有重要的社会意义和经济意义。目前，水中重金属的去除方法有化学沉淀、膜分离、离子交换、吸附、电解等，其中吸附法因简单高效而广泛应用。活性炭纤维是一种新型活性炭，孔径小且均匀，表面官能团发达，吸附性能好，逐步应用于水处理领域。以电感耦合等离子体光谱为检测手段，佐以比表面积分析，X射线衍射，元素分析和傅里叶变换红外光谱，研究比较了三种活性炭纤维(纤维炭网、活性炭无纺布、活性炭纤维毡)的结构特点及其对水中镉的吸附性能。三种活性炭纤维结构基本类似，具有较发达的孔隙结构。活性炭无纺布极性较强，表面有丰富的羟基、羧基、醛基等含氧官能团，对水中镉的吸附作用最大。因此，选择活性炭无纺布为吸附剂进行后续实验。研究了活性炭无纺布吸附镉的影响因素，如溶液pH，吸附时间等。溶液pH影响吸附剂表面电荷及水中镉的存在状态。水中镉的去除效率随溶液初始pH的增大而增大，在较低pH时，吸附剂与Cd2+间存在静电斥力，同时H+和Cd2+存在竞争吸附，pH>9时，镉的去除是吸附与沉淀协同作用的结果，选择pH为6～7。在吸附的初始阶段，活性炭无纺布对Cd2+的吸附量迅速增加，10 min时，吸附率达到72%。随着吸附位点逐渐被Cd2+所填充，吸附速率逐渐变慢，300 min时，吸附容量基本无变化，吸附趋于平衡。优化了镉的吸附条件后，进行等温吸附实验和动力学实验。结果表明，25 ℃时，吸附时间为300 min，pH 6.0条件下，当镉的平衡浓度在20.00 mg·L-1时，活性炭无纺布对镉的单位质量吸附量和单位比表面积吸附量分别是3.04 mg·g-1和0.035 mg·m-2。用Langmuir方程(R2=0.997, K_L =1.796 L·mg-1)和Freundich方程(R2=0.895, K_F=0.918 L·mg-1, n=2.12)拟合活性炭无纺布对镉的等温吸附数据，Langmuir方程计算的理论吸附量为3.07 mg·g-1，与实验值相当，并且线性系数更高，说明该体系的吸附符合Langmuir方程，主要为单分子层吸附。Langmuir分离因子介于0和1之间，表明活性炭无纺布对镉的吸附容易进行。用准一级动力学方程、准二级动力学方程、颗粒内扩散方程和Elovich方程四种动力学模型拟合吸附过程。在吸附的前5 min，镉在活性炭无纺布上的吸附符合颗粒内扩散方程(R2=0.985)，吸附主要受颗粒内扩散控制。在吸附的5～300 min，颗粒内扩散方程拟合较差。整个吸附过程符合准二级动力学方程(R2=0.999，k₂=0.367 g·mg-1·min-1)，Elovich方程(R2=0.981，a=0.271 mg·g-1, b=0.083 mg·g-1·(lg min)-1)和准一级动力学方程(R2=0.927，k₁=0.008 8 min-1)次之，颗粒内扩散方程(R2=0.785)最差。活性炭无纺布对镉的吸附过程是一种化学作用为主的吸附过程。对5.00 mg·L-1含镉水样，活性炭无纺布投放量为10 g·L-1时，吸附后水中镉的浓度小于0.10 mg·L-1，符合《污水综合排放标准》(GB 8978-1996)。活性炭无纺布可同时吸附镉，铜，铅，铬等重金属离子，选择性较差。但在电镀、采矿等实际废水中重金属种类复杂，适当提高吸附剂投放量，可同时去除多种重金属。利用活性炭无纺布吸附处理含镉水样，处理效果好、操作简单，可以作为去除水中镉的吸附剂，为含镉废水的处理提供了技术支持和理论基础。     

Simulation and fabrication of carbon nanotubes field emission pressure sensors

A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17-0.77 nA/Pa (101-550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors.     

Modification of bamboo-based activated carbon using microwave radiation and its effects on the adsorption of methylene blue

Modification of bamboo-based activated carbon was carried out in a microwave oven under N₂ atmosphere. The virgin and modified activated carbons were characterized by means of low temperature N₂ adsorption, acid-base titration, point of zero charge (pH_pzc) measurement, FTIR and XPS spectra. A gradual decrease in the surface acidic groups was observed during the modification, while the surface basicity was enhanced to some extent, which gave rise to an increase in the pH_pzc value. The species of the functional groups and relative content of various elements and groups were given further analysis using FTIR and XPS spectra. An increase in the micropores was found at the start, and the micropores were then extended into larger ones, resulting in an increase in the pore volume and average pore size. Adsorption studies showed enhanced adsorption of methylene blue on the modified activated carbons, caused mainly by the enlargement of the micropores. Adsorption isotherm fittings revealed that Langmuir and Freundlich models were applicable for the virgin and modified activated carbons, respectively. Kinetic studies exhibited faster adsorption rate of methylene blue on the modified activated carbons, and the pseudo-second-order model fitted well for all of the activated carbons.     

Preparation and characterization of biocompatible magnetic carbon nanotubes

Magnetic carbon nanotubes consisting of multi-wall carbon nanotubes (MWNTs) core and Fe₃O₄ shell were successfully prepared by in situ thermal decomposition of Fe(acac)₃ or FeCl₃ or Fe(CO)₅ in 2-pyrrolidone containing acid treated MWNTs at 240 °C with the protection of nitrogen gas. The samples were characterized by TEM, XRD, SEAD, XPS and superconducting quantum interference device. Also, their biocompatibility was compared with naked carbon nanotubes. The results showed that after coated with Fe₃O₄ nanoparticles, the obtained magnetic carbon nanotubes show superparamagnetic characteristic at room temperature, and their blocking temperature is about 80 K. The magnetic properties of the nanotubes are relevant to the content of magnetic particles, increasing content of magnetic nanoparticles leads to higher blocking temperature and saturation magnetization. The results of antimicrobial activities to bacterial cells (Escherichia coli) showed that the MWNTs have antimicrobial activity, while the magnetic nanotubes are biocompatible even with a higher concentration than that of MWNTs.