Single walled carbon nanotube reactivity and cytotoxicity following extended aqueous exposure

Globally carbon nanoparticles are increasingly utilized, yet it is not known if these nanoparticles pose a threat to the environment or human health. This investigation examined ‘as-prepared’, and acid cleaned carbon nanoparticle physicochemical characteristics (by FTIR, TEM, FESEM, UV-VIS and X-ray microanalysis), and whether these characteristics changed following 2.5-7 yr exposure to pH neutral saline or fresh water. To determine if these aqueous aged nanotubes were cytotoxic, these nanotubes were incubated with human epithelial monolayers and analyzed for cell viability (vital staining) and ultrastructural nanoparticle binding/localization (TEM, FESEM). The presence of Ni and Y catalyst, was less damaging to cells than CNT lattice surface oxidation. Extended fresh water storage of oxidized CNTs did not reduce surface reactive groups, nor lessen cell membrane destruction or cell death. However storing oxidized CNTs in saline or NOM significantly reduced CNT-induced cell membrane damage and increased cell survival to control levels.     

Photocatalytic degradation of gaseous toluene over Ag-doping TiO₂ nanotube powder prepared by anodization coupled with impregnation method

In this work, Ag-doping TiO₂ nanotubes were prepared and employed as the photocatalyst for the degradation of toluene. The TiO₂ nanotube powder was produced by the rapid-breakdown potentiostatic anodization of Ti foil in chloride-containing electrolytes, and then doped with Ag through an incipient wetness impregnation method. The samples were characterized by scanning electron microscope, high-resolution transmission electron microscopy, X-ray diffraction, surface photovoltage measurements, X-ray photoelectron spectroscopy and N₂ adsorption. The nanotubular TiO₂ photocatalysts showed an outer diameter of approximately 40 nm, fine mesoporous structure and high specific surface area. The photocatalytic activity of Ag-doping TiO₂ nanotube powder was evaluated through photooxidation of gaseous toluene. The results indicated that the degradation efficiency of toluene could get 98% after 4 h reaction using the Ag-doping TiO₂ nanotubes as the photocatalyst under UV light illumination, which was higher than that of the pure TiO₂ nanotubes, Ag-doping P25 or P25. Benzaldehyde species could be observed during the photocatalytic oxidation monitored by in situ FTIR, and the formed benzaldehyde intermediate during reaction would be partially oxidized into CO₂ and H₂O.     

Fractal structures of single-walled carbon nanotubes in biologically relevant conditions: Role of chirality vs. media conditions

Aggregate structure of covalently functionalized chiral specific semiconducting single-walled carbon nanotubes (SWNTs) was systematically studied employing static light scattering (SLS). Fractal dimensions (D_f) of two specific chirality SWNTs—SG65 and SG76 with (6, 5) and (7, 6) chiral enrichments—were measured under four biological exposure media conditions, namely: Dulbecco’s Modified Eagle Medium (DMEM), Minimum Essential Medium (MEM), Roswell Park Memorial Institute (RPMI) 1640 medium, and 0.9% saline solution. The SWNTs exhibited chiral dependence on D_f with SG65 showing more fractal or loosely bound aggregate structures, i.e., lower D_f values (range of 2.24 ± 0.03 to 2.64 ± 0.05), compared to the SG76 sample (range of 2.58 ± 0.13 to 2.90 ± 0.08). All the D_f values reported are highly reproducible, measured from multiple SLS runs and estimated with ‘random block-effects’ statistical analysis that yielded all p values to be <0.001. The key mechanism for such difference in D_f between the SWNT samples was identified as the difference in van der Waals (VDW) interaction energies of these samples, where higher VDW of SG76 resulted in tighter packing density. Effect of medium type showed lower sensitivity; however, presence of di-valent cations (Ca²⁺) in DMEM and MEM media resulted in relatively loose or more fractal aggregates. Moreover, presence of fetal bovine serum (FBS) and bovine serum albumin (BSA), used to mimic the in vitro cell culture condition, reduced the D_f values, i.e., created more fractal structures. Steric hindrance to aggregation was identified as the key mechanism for creating the fractal structures. Also, increase in FBS concentration from 1% to 10% resulted in increasingly lower D_f values.     

Enhanced sorption of perfluorooctane sulfonate (PFOS) on carbon nanotube-filled electrospun nanofibrous membranes

Multi-walled carbon nanotube-filled electrospun nanofibrous membranes (MWCNT-ENFMs) were prepared by electrospinning. The addition of MWCNTs (0.5 wt.% vs. ENFMs) doubled the specific surface area and tensile strength of the ENFMs. The MWCNT-ENFMs were used to adsorb perfluorooctane sulfonate (PFOS) in aqueous solutions. The sorption kinetics results showed that the sorption rate of PFOS onto the MWCNT-ENFMs was much higher than the sorption rate of PFOS onto the pure ENFMs control, and the pseudo-second-order model (PSOM) described the sorption kinetics well. The sorption isotherms indicated that the sorption capacity of the MWCNT-ENFMs for PFOS (16.29 ± 0.26 μmol g⁻¹) increased approximately 18 times, compared with the pure ENFMs (0.92 ± 0.06 μmol g⁻¹). Moreover, the solution pH significantly affected the sorption efficiency and sorption mechanism. The MWCNT-ENFMs were negatively charged from pH 2.0–10.0, but the electrostatic repulsion between the MWCNT-ENFMs and PFOS was overcome by the hydrophobic interactions between PFOS and the MWCNTs or nanofibers. The strong hydrophobic interactions between PFOS and the MWCNTs played a dominant role in the sorption process. For the pure ENFMs, the electrostatic repulsion was conquered by the hydrophobic interactions between PFOS and the nanofibers at pH > 3.1. In addition to the hydrophobic interactions, an electrostatic attraction between PFOS and the pure ENFMs was involved in the sorption process at pH < 3.1.     

MWNTs及MWNTs/TiO_2对水中1,2,3-三氯苯的吸附特性研究

采用批量平衡实验,对比研究了多壁碳纳米管（MWNTs）及多壁碳纳米管/二氧化钛复合材料（MWNTs/TiO2）对水中1,2,3-三氯苯的吸附特性。结果表明,在相同条件下,MWNTs及MWNTs/TiO2对1,2,3-三氯苯（1,2,3-TCB）的最大吸附量分别为71.8 mg/g和3.05 mg/g,pH值在2~11之间变化时,两者的吸附均不受pH值变化的影响。2种吸附剂的吸附过程均符合拟二级动力学方程,但MWNTs/TiO2对1,2,3-TCB的吸附速率常数为0.4159 g/（mg.m in）,约为MWNTs的50倍左右,说明MWNTs/TiO2具有更强的吸附驱动力。1,2,3-TCB在2种吸附剂上的吸附过程均可用Freund lich吸附等温线来描述,其热力学参数吉布斯自由能△G0均为负、标准焓变△H0与熵变△S0均为正表明,MWNTs及MWNTs/TiO2吸附1,2,3-TCB过程为自发吸热反应。与MWNTs相比,MWNTs/TiO2具有可光催化再生的优点,能用于被污染水体的原位修复。     

Effects of ionic strength and temperature on the aggregation and deposition of multi-walled carbon nanotubes

The aggregation and deposition of carbon nanotubes(CNTs) determines their transport and fate in natural waters.Therefore,the aggregation kinetics of humic-acid treated multi-walled carbon nanotubes(HA-MWCNTs) was investigated by time-resolved dynamic light scattering in NaCl and CaCl_2 electrolyte solutions.Increased ionic strength induced HA-MWCNT aggregation due to the less negative zeta potential and the reduced electrostatic repulsion.The critical coagulation concentration(CCC) values of HA-MWCNTs were 80 mmol/L in NaCl and 1.3 mmol/L in CaCl_2 electrolyte,showing that Ca~(2+) causes more serious aggregation than Na~+.The aggregation behavior of HA-MWCNTs was consistent with Derjaguin-Landau-Verwey-Overbeek theory.The deposition kinetics of HA-MWCNTs was measured by the optical absorbance at 800 ran.The critical deposition concentrations for HA-MWCNT in NaCl and CaCl_2 solutions were close to the CCC values,therefore the rate of deposition cannot be increased by changing the ionic strength in the diffusion-limited aggregation regime.The deposition process was correlated to the aggregation since larger aggregates increased gravitational deposition and decreased random Brownian diffusion.HA-MWCNTs hydrodynamic diameters were evaluated at 5,15 and 25℃.Higher temperature caused faster aggregation due to the reduced electrostatic repulsion and increased random Brownian motion and collision frequency.HA-MWCNTs aggregate faster at higher temperature in either NaCl or CaCl_2electrolyte due to the decreased electrostatic repulsion and increased random Brownian motion.Our results suggest that CNT aggregation and deposition are two correlated processes governed by the electrolyte,and CNT transport is favored at low ionic strength and low temperature.     

碳纳米管电极电还原降解水中头孢他啶

通过SEM、FITR、CV、Tafel等表征,以头孢他啶为目标污染物,研究了自制多壁碳纳米管电极电还原难降解有机物等的特性,并用高效液相色谱检测反应后目标污染物的质量浓度.结果表明,该电极性能稳定,可耐受一定程度的腐蚀,具有较好的性能.循环伏安结果表明,在800 mV左右获得较大的氧化峰,峰值达到-0.2 mA,头孢他啶在该电极上的降解是不可逆的.碳纳米管电极电还原降解头孢他啶的适宜工艺条件为:电极间距1 cm,电压15 V,初始质量浓度1 mg·L-1,离子强度1 g·L-1,pH=6.0.此条件下,反应60 min,头孢他啶的去除效率可达90%以上,该降解过程为二级反应.     

负载多壁碳纳米管的多孔Ti/SnO2-Sb-Ni电极电催化氧化双酚A

为发展废水中双酚A（BPA）的处理技术和保护水环境安全,采用“电沉积-热分解”法制备负载多壁碳纳米管（MWCNTs）的多孔Ti/SnO₂-Sb-Ni电极,研究了电极对BPA的去除能力、动力学特征和矿化效率,初步分析了BPA的降解途径.结果表明,当浸渍液中n（Sn）∶n（Sb）∶n（Ni）为100∶10∶1、ρ（MWCNTs）为0.8g·L^-1时,制备的电极对BPA的去除效果最好;负载MWCNTs使得电极表面的晶体尺寸更小,可增大电极的比表面积,为电催化反应提供更多的活性位点,进而提高电极的电催化效率.当c（Na₂SO₄）为10mmol·L^-1、反应液初始pH为5和电流密度为50 mA·cm^-2时,对50 mg·L^-1的BPA降解60 min时去除效率达到99.76%;去除过程符合一级反应动力学方程,速率常数为0.096 min^-1;电解120 min时,TOC去除率达到67.01%.采用液相色谱-串联质谱分析法（...     

MWCNTs预涂覆及预吸附处理缓解低压膜腐殖酸污染的机制研究

以腐殖酸(Humic Acid,HA)为研究对象,采用多壁碳纳米管(Multiwalled Carbon Nanotubes,MWCNTs)对聚偏氟乙烯(Polyvinylidene Fluoride,PVDF)平板超滤膜进行预涂覆改性处理,并与等量MWCNTs分散状态时吸附处理HA对膜污染的缓解效果进行了对比,考察了MWCNTs在处理HA过程中缓解膜污染的机制.同时,分析了MWCNTs投量和溶液离子变化对MWCNTs吸附及截留作用缓解膜污染的影响.结果表明,MWCNTs预涂覆与吸附相比,能够更有效地缓解膜污染,其中,分散剂为乙醇的MWCNTs预涂覆层对膜污染的缓解效果最好.增加MWCNTs投量不能无限地提高其对HA的吸附及截留效果;添加Na~+会造成MWCNTs对HA的吸附及截留效果变差;添加Ca~(2+)能够提高MWCNTs对HA的吸附及截留效果.膜表面污染照片及膜电镜观测结果表明,乙醇分散MWCNTs在超滤膜(UF)表面形成的预涂覆层呈均匀的层状结构,HA被拦截在MWCNTs层的多孔结构内,不易进入PVDF膜膜孔,反洗时易脱附,可逆性高;纯水分散MWCNTs在超滤膜表面形成的预涂覆层易于团聚,HA容易透过MWCNTs涂覆层进而堵塞PVDF膜膜孔,可逆性低;MWCNTs预吸附处理后形成MWCNTs和HA的包裹体,不经微滤膜滤除,会在PVDF膜表面产生复合污染.     

Degradation of carbamazepine by MWCNTs-promoted generation of high-valent iron-oxo species in a mild system with O-bridged iron perfluorophthalocyanine dimers

Metal phthalocyanine has been extensively studied as a catalyst for degradation of carbamazepine (CBZ). However, metal phthalocyanine tends to undergo their own dimerization or polymerization, thereby reducing their activity points and affecting their catalytic properties. In this study, a catalytic system consisting of O-bridged iron perfluorophthalocyanine dimers (FePcF₁₆-O-FePcF₁₆), multi-walled carbon nanotubes (MWCNTs) and H₂O₂ was proposed. The results showed MWCNTs loaded with FePcF₁₆-O-FePcF₁₆ can achieve excellent degradation of CBZ with smaller dosages of FePcF₁₆-O-FePcF₁₆ and H₂O₂, and milder reaction temperatures. In addition, the results of experiments revealed the reaction mechanism of non-hydroxyl radicals. The highly oxidized high-valent iron-oxo (Fe(IV)=O) species was the main reactive species in the FePcF₁₆-O-FePcF₁₆/MWCNTs/H₂O₂ system. It is noteworthy that MWCNTs can improve the dispersion of FePcF₁₆-O-FePcF₁₆, contributing to the production of highly oxidized Fe(IV)=O. Then, the pathway of CBZ oxidative degradation was speculated, and the study results also provide new ideas for metal phthalocyanine-loaded carbon materials to degrade emerging pollutants.