Effects of solution chemistry on the adsorption of ibuprofen and triclosan onto carbon nanotubes

Single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and oxidized MWCNTs (O-MWCNTs) were studied for the adsorption of ibuprofen (IBU) and triclosan (TCS) as representative types of pharmaceutical and personal care products (PPCPs) under different chemical solution conditions. A good fitting of sorption isotherms was obtained using a Polanyi-Manes model (PMM). IBU and TCS sorption was stronger for SWCNTs than for MWCNTs due to higher specific surface area. The high oxygen content of O-MWCNT further depressed PPCP sorption. The sorption capacity of PPCPs was found to be pH-dependent, and more adsorption was observed at pHs below their pK(a) values. Ionic strength was also found to substantially affect TCS adsorption, with higher adsorption capacity observed for TCS at lower ionic strength. In the presence of a reference aquatic fulvic acid (FA), sorption of IBU and TCS was reduced due to the competitive sorption of FA on carbon nanotubes (CNTs). Sorption isotherm results with SWCNTs, MWCNTs and O-MWCNTs confirmed that the surface chemistry of CNTs, the chemical properties of PPCPs, and aqueous solution chemistry (pH, ionic strength, fulvic acid) all play an important role in PPCP adsorption onto CNTs.     

Carbon nanotubes as sorbents for the gas phase preconcentration of semivolatile organics in a microtrap

In this paper we present the application of carbon nanotubes as unique sorbents for the fabrication of microtraps for the nanoscale adsorption/desorption of relatively large semivolatile organic molecules. The microtrap application requires high adsorption capacity as well as easy desorbability; the latter being critical for semivolatile compounds. The sorbent characteristics of single and multiwalled carbon nanotubes for gas phase adsorption/desorption of several compounds has been studied. The nonporous nature of carbon nanotubes (CNTs) eliminates the mass transfer resistance related to diffusion into pore structures, thus allowing easy desorbability. At the same time, their high aspects ratios lead to large breakthrough volumes. As compared to a commercial sorbent Carbopack, the breakthrough volume was as much as an order of magnitude higher in the CNTs, while the rate of desorption measured as the peak width at half height of the desorption band was eight times lower. The trapping and desorption characteristics of single and multi walled nanotubes were found to be comparable. We also found that the presence of disordered carbon impurities, which could be removed by controlled oxidative annealing could greatly degrade the performance of CNTs.     

Effective photocatalytic degradation of atrazine over titania-coated carbon nanotubes (CNTs) coupled with microwave energy

Microwave-assisted photocatalytic (MAPC) degradation of atrazine over nanotitania coated multiwalled carbon nanotubes (TiO(2)/MWCNTs) was investigated in this study. As a result, degradation efficiency of atrazine over TiO(2)/CNTs prepared by hydrothermal method was about 30% and 20% higher than that of titania P25 and anatase prepared hydrothermally in given time. The TiO(2)/CNTs composite samples were characterized by TGA-DSC, TEM, UV-vis DRS, XRD and BET, to explain the reason for efficient degradation and adsorption process of atrazine. Microwave thermal effect in this process was also investigated. Intermediates of degradation both in MAPC process and microwave-assisted photodegradation (MAPD) process were identified by LC/MS. It suggests that MWCNTs have special effects on atrazine degradation during MAPC process, like strong microwave absorption capability.     

Microtrapping characteristics of single and multi-walled carbon nanotubes

Carbon nanotubes (CNTs) possess some highly desirable sorbent characteristics, which make them attractive for a variety of applications including micro-scale preconcentration. The main advantage of CNTs is that they are non-porous, thus eliminating the mass transfer resistance related to diffusion into pore structures. Their high aspects ratio leads to large specific capacity, consequently they have the potential to be the next generation high performance sorbent. In this paper we present the microtrapping. The objective of this paper was to study the sorption of select organic compounds on single and multi-walled nanotubes either packed or self-assembled onto a micro-sorbent trap. The data show that the CNTs show highly favorable adsorption as well as desorption. The former is characterized by relatively large breakthrough volumes and isosteric heats of adsorption (DeltaH(s), close to 64 kJ/mol). Similarly, rapid desorption from CNTs was demonstrated by narrow desorption bandwidth. The elimination of non-tubular carbons (NTC) from the CNT surface is important, as they reduce the performance of these sorbents.     

中分子毒素在碳纳米管上的吸附

研究了两种不同形态的碳纳米管(随机生长多壁碳纳米管(MWCNTs)及定向生长多壁碳纳米管(ACNTs))对典型中分子毒素的吸附性能. 并与两种现有商用血液灌流吸附材料(活性炭(AC)及大孔吸附树脂(MR))进行了对比. 结果显示, 碳纳米管(CNTs)具有优异的中分子吸附能力, 其中MWCNTs对典型中分子毒素的吸附量可达47.18 mg·g-1, 为活性炭的10.8倍, 为大孔吸附树脂的5.5倍. 此外, 碳纳米管的吸附非常迅速, 中分子毒素在MWCNTs及ACNTs达到吸附平衡的时间仅为10 min和15 min, 而活性炭及大孔吸附树脂则分别需要60 min及120 min. 碳纳米管优异的吸附性能得益于其独特的微观结构所形成的发达的中孔. 因此, 碳纳米管可望成为高效的吸附材料, 应用于血液灌流中.     

Critical Evaluation of Adsorption–Desorption Hysteresis of Heavy Metal Ions from Carbon Nanotubes: Influence of Wall Number and Surface Functionalization

Single‐, double‐, and multi‐walled carbon nanotubes (SWCNTs, DWCNTs, and MWCNTs), and two oxidized MWCNTs with different oxygen contents (2.51 wt % and 3.5 wt %) were used to study the effect of the wall number and surface functionalization of CNTs on their adsorption capacity and adsorption–desorption hysteresis for heavy metal ions (Ni^II, Cd^II, and Pb^II). Metal ions adsorbed on CNTs could be desorbed by lowering the solution pH. Adsoprtion of heavy metal ions was not completely reversible when the supernatant was replaced with metal ion‐free electrolyte solution. With increasing wall number and amount of surface functional groups, CNTs had more surface defects and exhibited higher adsorption capacity and higher adsorption–desorption hysteresis index (HI) values. The coverage of heavy metal ions on the surface of CNTs, solution pH, and temperature affect the metal ion adsorption–desorption hysteresis. A possible shift in the adsorption mechanism from mainly irreversible to largely reversible processes may take place, as the amount of metal ions adsorbed on CNTs increases. Heavy metal ions may be irreversibly adsorbed on defect sites.     

Fabrication of carbon nanotube sheets and their bilirubin adsorption capacity

Bilirubin adsorption on carbon nanotube surfaces has been studied to develop a new adsorbent in the plasma apheresis. Powder-like carbon nanotubes were first examined under various adsorption conditions such as temperatures and initial concentrations of bilirubin solutions. The adsorption capacity was measured from the residual concentrations of bilirubin in the solution after the adsorption process using a visible absorption spectroscopy. We found that multi-walled carbon nanotubes (MWCNTs) exhibit greater adsorption capacity for bilirubin molecules than that of single-walled carbon nanotubes (SWCNTs). To guarantee the safety of the adsorbents, we fabricated carbon nanotube sheets in which leakage of CNTs to the plasma is suppressed. Since SWCNTs are more suitable for robust sheets, a complex sheet consisting of SWCNTs as the scaffolds and MWCNTs as the efficient adsorbents. CNT/polyaniline complex sheets were also fabricated. Bilirubin adsorption capacity of CNTs has been found to be much larger than that of the conventional materials because of their large surface areas and large adsorption capability for polycyclic compound molecules due to their surface structure similar to graphite.     

碳纳米管/活性炭复合微球的制备及其对VB12的吸附应用

采用反相乳液法制备碳纳米管/壳聚糖复合微球(CNTs/CTS), 并对其进一步炭化、活化制得碳纳米管/活性炭复合微球(CNTs/AC). 以此复合微球为吸附材料, 探索了其对中分子代表物质VB12的吸附. 研究结果表明, 碳纳米管含量70%(w)的复合微球经水蒸气适当活化后球形度好、吸附性能优异, 其对VB12的吸附量达23.59 mg·g-1, 分别是活性炭和大孔吸附树脂的5.4和2.7倍. 分析表明这是由于碳纳米管/活性炭复合微球具有发达的中孔结构.     

Influence of pH and surface oxygen-containing groups on multiwalled carbon nanotubes on the transformation and adsorption of 1-naphthol

The pH-dependent behavior, including the transformation of 1-naphthol by oxidative polymerization to form precipitates in solution and the adsorption of 1-naphthol onto carbon nanotubes (CNTs), was examined. Neglecting the precipitate loss of 1-naphthol and possibly of similar chemicals may result in the overestimation of their adsorption and inadequate interpretation of the underlying adsorption mechanisms. Surface oxygen-containing groups on CNTs and the dissociated species of these groups can interact with the dissociated and neutral species of 1-naphthol in a way similar to polymerization, thus promoting the adsorption of 1-naphthol onto CNTs. Adsorption onto CNTs may reduce the polymeric precipitates of 1-naphthol in solution by possibly decreasing aqueous 1-naphthol concentrations. These observations and the underlying mechanisms are important for predicting the fate and risks of naphthalene and carbaryl in the environment because 1-naphthol is a primary metabolite of naphthalene and carbaryl. In addition, it is possible to enhance the removal of 1-naphthol and similar chemicals by controlling the pH and designing specific surface functional groups for CNTs.     

High-sensitivity matrix-assisted laser desorption/ionization Fourier transform mass spectrometry analyses of small carbohydrates and amino acids using oxidized carbon nanotubes prepared by chemical vapor deposition as matrix

In matrix-assisted laser desorption/ionization (MALDI) Fourier transform mass spectrometry (FTMS) analyses of small oligosaccharides and amino acids, high sensitivities for oligosaccharides (10 fmol) were obtained by introducing oxidized carbon nanotubes (CNTs) with short and open-end structure as valuable matrix. The CNTs were deposited in porous anodic alumina (PAA) templates by chemical vapor deposition. Transmission electron microscopy (TEM) images show that those CNTs include low levels of amorphous carbon. Thus, the background interference signals generally caused by amorphous carbon powder in CNTs can be reduced effectively. Experiments also confirmed that the FTMS signal intensity of CNTs prepared in PAA template is much lower than that of commercial multi-wall carbon nanotubes (MCNTs). Moreover, the purified process for CNTs with mixed acid (H₂SO₄ and HNO₃) also contributed to the minimization of background. Intense signals corresponding to alkali cation adduct of neutral carbohydrates and amino acids have been acquired. In addition, reliable quantitative analyses for urine and corn root were also achieved successfully. The present work will open a new way to the application of oxidized CNTs as an effective matrix in MALDI MS research.     

Comparison of the Enrichment Efficiency of Multiwalled Carbon Nanotubes, C18 Silica, and Activated Carbon as the Adsorbents for the Solid Phase Extraction of Atrazine and Simazine in Water Samples

Multiwalled carbon nanotubes with exceptional merits as SPE adsorbents for enrichment of environmental pollutants have absorbed much attention. The goal of this paper was to make a comparison with it and regular adsorbents such as C18 silica and activated carbon in the extraction capacity of atrazine and simazine. The results indicated that multiwalled carbon nanotubes were very suitable for determination of atrazine and simazine because of an enrichment performance similar to that of C18 silica. In contrast, the spiked recovery of simazine was higher than that of atrazine using multiwalled carbon nanotubes as packing material for SPE. However, reverse results were obtained when the extraction was performed with packing of C18 silica. Moreover, as the extraction of simazine was concerned, multiwalled carbon nanotubes were much better than C18 silica. As for the enrichment of atrazine, C18 silica achieved greater extraction factor than multiwalled carbon nanotubes. Activated carbon did not give the expected extraction efficiency because of its large size and blank volume and less active sites for adsorption. All these experimental results indicated that multiwalled carbon nanotubes could be used as a valuable alternative adsorbent for SPE of atrazine and simazine in many real water samples.     

Antibacterial effects of carbon nanotubes: size does matter!

We provide the first evidence that the size (diameter) of carbon nanotubes (CNTs) is a key factor governing their antibacterial effects and that the likely main CNT-cytotoxicity mechanism is cell membrane damage by direct contact with CNTs. Experiments with well-characterized single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) demonstrate that SWNTs are much more toxic to bacteria than MWNTs. Gene expression data show that in the presence of both MWNTs and SWNTs, Escherichia coli expresses high levels of stress-related gene products, with the quantity and magnitude of expression being much higher in the presence of SWNTs.     

Adsorption of fluoride from water by amorphous alumina supported on carbon nanotubes

A new candidate for fluoride adsorption from water, amorphous Al₂O₃ supported on carbon nanotubes (Al₂O₃/CNTs), is reported in this Letter. The adsorption isotherms show that the best fluoride adsorption of Al₂O₃/CNTs occurs at a pH range of 5.0–9.0. The adsorption capacity for Al₂O₃/CNTs is about 13.5 times higher than that of AC-300 carbon, 4 times higher than that of γ-Al₂O₃ at equilibrium fluoride concentration of 12 mg/l. The broad range of the pH values and high adsorption capacity of Al₂O₃/CNTs make it very suitable for potential applications in fluoride removal from water.     

Affinity-based elimination of aromatic VOCs by highly crystalline multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are capable of adsorbing pollutant chemicals. Their adsorptive capacities and adsorbing mechanisms, however, are not fully understood. As-grown CNTs often contain both crystalline and amorphous carbon, and the ratio of carbon types can affect adsorption. In this study, highly crystalline multi-walled carbon nanotubes (HC-MWCNTs) were used as the adsorbent for volatile organic compounds (VOCs) in contaminated air samples. Air containing 23 added VOCs (1,1-dichloroethylene, dichloromethane, trans-1,2-dichloroethylene, cis-1,2-dichloroethylene, chloroform, 1,1,1-trichloroethane, carbon tetrachloride, 1,2-dichloroethane, benzene, trichloroethylene, 1,2-dichloropropane, bromodichloromethane, cis-1,3-dichloropropene, toluene, trans-1,3-dichloropropene, 1,1,2-trichloroethane, tetrachloroethylene, dibromochloromethane, m-xylene, p-xylene, o-xylene, bromoform, and p-dichlorobenzene) was used for model samples. Adsorptive experiments were carried out by passing the air samples through a cartridge packed with HC-MWCNTs. Initial results showing high selectivity and high affinity for adsorbing aromatic VOCs (benzene, toluene, m-xylene, p-xylene, o-xylene, and p-dichlorobenzene) have provided new insight into the adsorption mechanisms. Data suggest that the HC-MWCNTs, unlike conventional carbon materials, adsorb aromatic compounds according to Fukui's frontier theory, which is based on the interactions between the HOMO and LUMO of the aromatic VOCs and those of the HC-MWCNTs.     

Reactivity of silicon and germanium doped CNTs toward aromatic sulfur compounds: A theoretical approach

Adsorption processes of thiophene and benzothiophene on pristine carbon nanotubes (CNTs), and on CNTs doped with Si or Ge, have been modeled with Density Functional. This is the first study on the chemical reactivity of such doped tubes. The calculated data suggest that the presence of silicon or germanium atoms in CNTs increases their reactivity toward thiophene, and benzothiophene. The adsorption of these species on pristine CNTs seems very unlikely to occur, while the addition products involving doped CNTs were found to be very stable, with respect to the isolated reactants, in terms of Gibbs free energy. Several of these adsorption processes were found to be significantly exergonic (ΔG < 0) in non-polar liquid phase. The results reported in this work suggest that Si and Ge defects on CNTs increase their reactivity toward unsaturated species, and could make them useful in the removal processes of aromatic sulfur compounds from oil-hydrocarbons. However, according to our results, CNTs doped with Si atoms are expected to be more efficient as aromatic sulfur compounds scavengers than those doped with Ge. These results also suggest that the presence of silicon and germanium atoms in the CNTs structures enhances their reactivity toward nucleophilic molecules, compared to pristine carbon nanotubes.     

一维纳米炭/竹炭的制备及其对Pb~(2+)的吸附

以二甲苯为炭源、二茂铁为催化剂,采用CVD法在竹炭上催化气相生长了一维纳米炭,采用扫描电镜、透射电镜及氮吸附仪等对一维纳米炭/竹炭的形貌、微结构及比表面积进行了表征,并研究了一维纳米炭/竹炭复合材料对重金属离子Pb2+的吸附性能.结果表明,采用CVD法可以在竹炭上生长一维纳米炭,且随着气相生长时间的延长,竹炭上的一维纳米炭变得更加浓密而均匀.竹炭上生长一维纳米炭后,对Pb2+的吸附能力增强,硝酸氧化处理可以进一步提高一维纳米炭/竹炭对Pb2+的吸附能力.     

Light-Assisted Ullmann Coupling of Phenols and Aryl Halides: The Synergetic Effect Between Plasmonic Copper Nanoparticles and Carbon Nanotubes from Various Sources

Utilizing light and plastic wastes as resources to turn the wasted phenols and hazardous aryl halides into value added chemicals seems to be an attractive idea for alleviating the energy crisis and environmental problems. In this work, plasmonic copper nanoparticles (Cu NPs) were loaded onto carbon nanotubes (CNTs) from various sources including commercial CNTs and those derived from plastic wastes. Under visible-light irradiation, the catalyst could efficiently convert phenols and aryl halides to diaryl ethers. Similar with commercial CNTs, excellent activity is also achieved when utilizing CNTs derived from different kinds of plastic wastes as support for the system. Further investigation shows that the visible-light irradiation and light-excited plasmonic Cu NPs are necessary to inhibit the phenol degradation on CNTs and in turn promote the cross-coupling of phenol and aryl halides. Compared with metal oxides and other carbon materials, the excellent capability of CNTs to absorb light, to convert light to heat, and to adsorb both two reactants simultaneously are critical to enhance the activity of Cu NPs, achieving high yields of diaryl ethers. This study could provide a novel strategy for catalyst design and generate a more economically sustainable process.     

改性碳纳米管常温下吸附分离低浓度CO2

采用浸渍法将四乙烯五胺(TEPA)和三乙烯四胺(TETA)负载至碳纳米管(CNTs)上,得到一种固态胺吸附剂CNTs-TEPA和CNTs-TETA,用以吸附低浓度下的CO2.利用扫描电镜(SEM)、透射电镜(TEM)、傅里叶红外(FTIR)光谱、N2物理吸附脱附、元素分析和热重分析(TGA)等方法表征样品.结果表明:CNTs-TEPA和CNTs-TETA形态并未发生变化,仍保留CNTs规整有序的孔道结构,但样品的比表面积和孔容都显著减小.在常温条件下,CNTs-TEPA和CNTs-TETA的CO2吸附量与CNTs相比有显著提高,同时,在胺浸渍质量相同的情况下,改性后的CNTs-TEPA效果优于CNTs-TETA.温度从20℃升至30℃,CNTs-TEPA和CNTs-TETA的CO2吸附量分别从126.7、101.2mg·g-1升至139.3、110.4mg·g-1.CNTs的吸附量随着温度的增加变化不明显.最后,采用Suyadal和Yasyerli两种模型对CO2的动态吸附穿透曲线进行拟合,结果说明Yasyerli模型对CNTs、CNTs-TEPA和CNTs-TETA的CO2吸附过程的拟合程度更高.     

碳纳米管对结晶紫的吸附研究

研究了碳纳米管对溶液中结晶紫的吸附性能,考察了溶液浓度、溶液p H、吸附时间和吸附温度等因素对吸附行为的影响,初步探讨了碳纳米管对结晶紫的吸附机理。结果表明,碳纳米管对结晶紫的吸附量随着溶液初始浓度的增大而升高;酸性条件有利于吸附的进行,最佳p H等于5;对结晶紫的吸附在3h达到平衡,吸附速率常数为779.76h-1;温度的变化对结晶紫的吸附量影响不大。通过Langmuir方程和Freundlich方程对吸附进行拟合,平衡吸附量Qe与平衡质量浓度Ce之间的关系符合Freundlich等温吸附方程所描述的规律,说明吸附过程以物理吸附为主。