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。     

Synthesis and characterisation of potassium polytitanate for photocatalytic degradation of crystal violet

Potassium titanate nanostructures were synthesised by hydrothermal treatment of TiO2 （P25） in KOH and H2O2. As-produced powders were characterised by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption methods. Longitudinally-oriented-wire-like structures with a length up to several micrometres and diameters ranging from 10 to 30 nm were obtained. Larger size fibrous nanowires resulting from the hydrotherrnal treatment showed high affinity in adsorbing crystal violet （CV）, which was mainly due to their high surface area. The photocatalytic bleaching of CV solution revealed that the wires are photoactive under ultraviolet light irradiation. Macroporous nanowires are considered as effective adsorbents of CV, capable of photocatalvtic degradation, and they can be easily separated from the solution by settling.     

合成时间对钛酸盐纳米材料的影响及其吸附水中铅的性能研究

以Ti O2(ST-01)和Na OH为原料,采用碱性水热法通过调节反应时间合成不同形貌的钛酸盐纳米材料(TNs),利用XRD、SEM、BET对材料的形貌、结构、比表面积和化学组成等物化性能进行表征,并通过其对水中Pb(Ⅱ)的静态吸附实验,考察材料对Pb(Ⅱ)的吸附性能和吸附规律.结果表明,12~72 h合成的TNs均为纯净的单斜相钛酸盐,比表面积为243.05~286.20 m2·g-1;12~36 h合成的TNs主要为片状结构,48 h以上的TNs为线状结构.TNs-12、TNs-24、TNs-36、TNs-48、TNs-60和TNs-72对Pb(Ⅱ)的吸附量分别为479.40、504.12、482.00、388.10、364.60和399.00 mg·g-1,片状的TNs对Pb(Ⅱ)具有比线状更高的吸附能力,其中以TNs-24对Pb(Ⅱ)的吸附量最高.TNs-24对Pb(Ⅱ)的吸附结果符合准二级动力学模型和Langmuir模型,吸附平衡时间为120 min;TNs对Pb(Ⅱ)的吸附为放热过程,低温或室温便有较高的吸附量;最佳吸附p H为5.0;当p H为1.0时,TNs-24的解析率可达到99.00%;再生的TNs对Pb(Ⅱ)循环吸附6次的去除率仍可达到97%以上,可见TNs可很好地去除水中重金属Pb(Ⅱ).因此,最佳合成时间可控制在12~24 h;当溶液中存在共存Cd(Ⅱ)或Ni(Ⅱ)时,TNs-24对Pb(Ⅱ)的平衡吸附量及去除率均有所下降;吸附机制主要是Pb(Ⅱ)与TNs层间的H+和Na+发生离子交换作用.     

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.     

钛酸钡压电臭氧化降解水中的硝基苯

将臭氧（O₃）体系与压电（PE）体系相结合提出了压电臭氧化（PE-O₃）体系,探究了该体系对难降解有机污染物硝基苯（NB）的降解效果,考察了转速、O₃浓度、钛酸钡（BT）投加量和初始pH值对NB去除的影响.此外,探讨了PE-O₃体系降解NB过程中存在的活性物质,并分析了反应机理.结果表明：PE-O₃体系对NB的降解体现出明显的协同效应（协同系数高达5.04）,在15min内对NB的去除率高达85.37%,反应符合一级反应动力学规律,k为0.1256min^-1.此外,PE-O₃体系在120min内对NB实现了74.06%的矿化.随着磁力转子转速的增加,体系反应速率提升,当转速提高到1500r/min时,反应速率常数可达到0.1446min^-1.反应速率随体系中BT浓度和O₃浓度的增加而增加,但一定程度后,增长趋势变缓.NB降解速率随pH值的增加而增大,当pH值为9.0时,在15min后体系中的NB降解率达85.69%.反应过程中产生的是降解NB的主要活性物质.