Removal of sodium dodecyl sulfate surfactant from aqueous dispersions of single-wall carbon nanotubes

Iterative Strategy for Sorting Single-Chirality Single-Walled Carbon Nanotubes from Aqueous to Organic Systems

Significant advancements in electronic devices and integrated circuits have been facilitated by semiconducting single-walled carbon nanotubes (SWCNTs) sorted by conjugated polymers (CPs). However, the variety of CPs with single-chirality selectivity is limited, and the sorting results are strongly dependent on the chiral distribution of the starting materials. To address this, we develop an iterative strategy to achieve single-chirality SWCNT separation from aqueous to organic systems, based on a multistep tandem extraction technique that allows a gentle and nondestructive separation of surfactants from SWCNTs, ensuring an efficient system transfer. In parallel, we refined the iterative sorting process between CPs. Employing two starting materials with narrow diameter distributions, using three CPs, we successfully sorted out five single-chirality SWCNTs of the (9,5), (8,6), (10,5), (8,7), and (11,3) species in organic systems. This strategy bridges the gap between aqueous and organic separation systems, achieving efficient complementarity between them.

Stochastic Formation of Quantum Defects in Carbon Nanotubes

Small perturbations in the structure of materials significantly affect their properties. One example is single wall carbon nanotubes (SWCNTs), which exhibit chirality-dependent near-infrared (NIR) fluorescence. They can be modified with quantum defects through the reaction with diazonium salts, and the number or distribution of these defects determines their photophysics. However, the presence of multiple chiralities in typical SWCNT samples complicates the identification of defect-related emission features. Here, we show that quantum defects do not affect aqueous two-phase extraction (ATPE) of different SWCNT chiralities into different phases, which suggests low numbers of defects. For bulk samples, the bandgap emission (E11) of monochiral (6,5)-SWCNTs decreases, and the defect-related emission feature (E11*) increases with diazonium salt concentration and represents a proxy for the defect number. The high purity of monochiral samples from ATPE allows us to image NIR fluorescence contributions (E11 = 986 nm and E11* = 1140 nm) on the single SWCNT level. Interestingly, we observe a stochastic (Poisson) distribution of quantum defects. SWCNTs have most likely one to three defects (for low to high (bulk) quantum defect densities). Additionally, we verify this number by following single reaction events that appear as discrete steps in the temporal fluorescence traces. We thereby count single reactions via NIR imaging and demonstrate that stochasticity plays a crucial role in the optical properties of SWCNTs. These results show that there can be a large discrepancy between ensemble and single particle experiments/properties of nanomaterials.

Single-chirality of single-walled carbon nanotubes (SWCNTs) through chromatography and its potential biological applications

Gel chromatography is used to separate single-chirality and selective-diameter SWCNTs. We also explore the use of photothermal therapy and biosensor applications based on single-chirality, selected-diameter, and unique geometric shape.

Nanotube Functionalization: Investigation, Methods and Demonstrated Applications

This review presents an update on nanotube functionalization, including an investigation of their methods and applications. The review starts with the discussion of microscopy and spectroscopy investigations of functionalized carbon nanotubes (CNTs). The results of transmission electron microscopy and scanning tunnelling microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy and resistivity measurements are summarized. The update on the methods of the functionalization of CNTs, such as covalent and non-covalent modification or the substitution of carbon atoms, is presented. The demonstrated applications of functionalized CNTs in nanoelectronics, composites, electrochemical energy storage, electrode materials, sensors and biomedicine are discussed.

Destructing surfactant network in nanoemulsions by positively charged magnetic nanorods to enhance oil-water separation

The separation of ultrafine oil droplets from wasted nanoemulsions stabilized with high concentration of surfactants is precondition for oil reuse and the safe discharge of effluent. However, the double barriers of the interfacial film and network structures formed by surfactants in nanoemulsions significantly impede the oil-water separation. To destroy these surfactant protective layers, we proposed a newly-developed polyethyleneimine micelle template approach to achieve simultaneous surface charge manipulation and morphology transformation of magnetic nanospheres to magnetic nanorods. The results revealed that positively charged magnetic nanospheres exhibited limited separation performance of nanoemulsions, with a maximum chemical oxygen demand (COD) removal of 50%, whereas magnetic nanorods achieved more than 95% COD removal in less than 30 s. The magnetic nanorods were also applicable to wasted nanoemulsions from different sources and exhibited excellent resistance to wide pH changes. Owing to their unique one-dimensional structure, the interfacial dispersion of magnetic nanorods was significantly promoted, leading to the efficient capture of surfactants and widespread destruction of both the interfacial film and network structure, which facilitated droplet merging into the oil phase. The easy-to-prepare and easy-to-tune strategy in this study paves a feasible avenue to simultaneously tailor surface charge and morphology of magnetic nanoparticles, and reveals the huge potential of morphology manipulation for producing high-performance nanomaterials to be applied in complex interfacial interaction process. We believe that the newly-developed magnetic-nanorods significantly contribute to hazardous oily waste remediation and advances technology evolution toward problematic oil-pollution control.

Gel Chromatography for Separation of Single-Walled Carbon Nanotubes

Carbon nanotubes (CNTs), having either metallic or semiconducting properties depending on their chirality, are advanced materials that can be used for different devices and materials (e.g., fuel cells, transistors, solar cells, reinforced materials, and medical materials) due to their excellent electrical conductivity, mechanical strength, and thermal conductivity. Single-walled CNTs (SWNTs) have received special attention due to their outstanding electrical and optical properties; however, the inability to selectively synthesize specific types of CNTs has been a major obstacle for their commercialization. Therefore, researchers have studied different methods for the separation of SWNTs based on their electrical and optical properties. Gel chromatography methods enable the large-scale separation of metallic/semiconducting (m/s) SWNTs and single-chirality SWNTs with specific bandgaps. The core principle of gel chromatography-based SWNT separation is the interaction between the SWNTs and gels, which depends on the unique electrical properties of the former. Controlled pore glass, silica gel, agarose-based gel, and allyl dextran-based gel have been exploited as mediums for gel chromatography. In this paper, the interaction between SWNTs and gels and the different gel chromatography-based SWNT separation technologies are introduced. This paper can serve as a reference for researchers who plan to separate SWNTs with gel chromatography.

Using a Novel Approach to Estimate Packing Density and Related Electrical Resistance in Multiwall Carbon Nanotube Networks

In this work, we use contrast image processing to estimate the concentration of multi-wall carbon nanotubes (MWCNT) in a given network. The fractal dimension factor (D) of the CNT network that provides an estimate of its geometrical complexity, is determined and correlated to network resistance. Six fabricated devices with different CNT concentrations exhibit D factors ranging from 1.82 to 1.98. The lower D-factor was associated with the highly complex network with a large number of CNTs in it. The less complex network, having the lower density of CNTs had the highest D factor of approximately 2, which is the characteristic value for a two-dimensional network. The electrical resistance of the thin MWCNT network was found to scale with the areal mass density of MWCNTs by a power law, with a percolation exponent of 1.42 and a percolation threshold of 0.12 μg/cm2. The sheet resistance of the films with a high concentration of MWCNTs was about six orders of magnitude lower than that of less dense networks; an effect attributed to an increase in the number of CNT-CNT contacts, enabling more efficient electron transfer. The dependence of the resistance on the areal density of CNTs in the network and on CNT network complexity was analyzed to validate a two-dimension percolation behavior.

Transparent Conductive Flexible Trilayer Films for a Deicing Window and Self-Recover Bending Sensor Based on a Single-Walled Carbon Nanotube/Polyvinyl Butyral Interlayer

A flexible transparent conductive film (TCF) is an important component in many modern smart devices. Recent TCF is always fabricated based on indium tin oxide (ITO). However, the drawbacks of ITO (e.g., brittle nature, high cost, and resource scarcity) and the complex preparation process of TCF limit the massive production and further application of TCF. Herein, a facile and low-cost method is proposed to prepare flexible TCF. Rolls of single-walled carbon nanotubes (SWCNTs)/polyvinyl butyral (PVB) interlayer film were first fabricated by the roll-to-roll (R2R) spraying method. Then, the interlayer film was laminated between polycarbonate (PC) films (0.1 mm in thickness) to fabricate a transparent (80% optical transmittance) but flexible trilayer film. Such a prepared trilayer film shows multifunctional applications. For example, on the one hand, high conductivity and uniform distribution of resistance ensure that it can work as a deicing window with good performance at a low voltage. On the other hand, its flexibility, rapid self-recovery, and stable response enable it to be used as a bending sensor, which shows remarkable stability, repeatability, and durability. This study provides a facile method to fabricate TCF based on commercial but low-cost materials, which is suitable for industrial production and wide practical applications.

The enhanced removal and phytodegradation of sodium dodecyl sulfate (SDS) in wastewater using controllable water hyacinth

Surfactant is an emerging and popular pollutant in both rural and urban areas and its treatment efficacy by phytoremediation is rarely reported. Water hyacinth was utilized to clean anionic surfactant sodium dodecyl sulfate (SDS) in water and its growth and physiological activities were regulated with Chromolaena odorata L. extract. SDS was effectively removed from the water and then transferred to both root and aerial part of water hyacinth. Part of SDS was converted into low-molecular weight degradation intermediates by the hydrogen abstraction reactions in water hyacinth. The removal efficiency and the degradation of SDS were evidently strengthened accompanying with enhanced root activity and ascorbate peroxidase (APX) activity in the presence of Chromolaena odorata L. extract. Meanwhile, the growth of water hyacinth was effectively controlled, exhibiting low-growth rate (≤0.036 g.day^-1). Furthermore, the root was considered as the major organ to degrade SDS, which was correlated to the remarkable increase in APX activity and a slight increase in root activity under both SDS and extract stress. In conclusion, water hyacinth managed with Chromolaena odorata L. extract should be proposed as an eco-friendly biotechnical treatment for the surfactant.

Removal of ciprofloxacin from aqueous solutions by ionic surfactant-modified carbon nanotubes

Ionic surfactants may impact removal efficiency of organic contaminants from aqueous solution, but research regarding the adsorption mechanisms on surfactant-modified carbon nanotubes (CNTs) was limited. In this study, three multi-walled and one single-walled CNTs were used as adsorbents to investigate the adsorption behavior and mechanisms of ciprofloxacin (CIP) on CNTs modified by ionic surfactants (cationic CTAB (Cetyltrimethylamnonium bromide) or anionic SDS (Sodium dodecyl sulfate)). More than 80% (82-88%) of the total removed CIP on CTAB-modified CNTs occurred within the first 6 h, much higher than that on SDS-modified CNTs (57-78%). Modeling adsorption kinetics demonstrated that CIP adsorption on surfactant-modified CNTs was controlled by multiple and faster processes, and both external mass transfer and intraparticle diffusion are limiting factors. Relative to SDS, CTAB was significantly (P < 0.001) concentration-dependent in suppressing CIP removal. Besides, the increase in 1/n values of Freundlich model with increasing CTAB concentration suggested that CTAB could be a stronger competitor for CIP adsorption. Hydrophobic interactions predominated zwitterionic CIP adsorption on all CNTs tested, while electrostatic interactions could help control ionizable CIP adsorption on surfactant-modified CNTs depending upon pH. CIP adsorption on modified SWCNTs significantly declined with increasing ionic strength from 1 mM to 100 mM relative to those multi-walled CNTs because the more favorable aggregation of SWCNTs reduced the CIP adsorption, irrespective of which surfactant was added. Significant desorption hysteresis of adsorbed CIP released by SDS and water was observed, but not by CTAB, by which 32.6-54.4% of adsorbed CIP were removed. For SDS-modified CNTs, the mean release ratio (RR) followed an order of MWCNTs (0.075) > MHCNTs (0.058) > SWCNTs (0.057) > MCCNTs (0.049), significantly (P < 0.001) lower than CTAB-CNTs (0.37-0.56). It can be predicted that the tested surfactants co-existing with CNTs depress removal efficiency of diverse contaminants similar to CIP in aqueous systems.

Effect of anion co-existence on ionic organic pollutants removal over Ca based layered double hydroxide

The effects of co-existing anions (NO₃^- or SO₄^2-) on the removal of sodium dodecylsulfate (SDS), representing anionic organic pollutants, by Ca-based layered double hydroxide (CaAl-LDH-Cl) are investigated to provide fundamental insights on the ionic surfactant removal in the presence of co-existing anions, and facilitate the establishment of a practical and advanced water treatment for environmental remediation. The SO₄^2- system shows higher adsorption capacity (4.43 mmol·g^-1) and larger d-spacing of adsorption resultant (3.4 nm) than the control system with no co-existing anion (3.64 mmol·g^-1, 3.25 nm) and the NO₃^- system (3.82 mmol·g^-1, 3.27 nm). The macroscopic and microscopic analyses reveal that, NO₃^- had a little influence on the SDS removal due to strong electrolysis, while SO₄^2- could significantly promote the SDS removal. Moreover, the reaction mechanism varies under different molar ratios of DS^-/SO₄^2-.