The differences in surfactant adsorption on carbon nanotubes and their bundles

Upgrading Waste Activated Carbon by Equipping Micro-/Mesopore-Dominant Microstructures from the Perspective of Circular Economy

Equipping wastes with interesting properties in response to the circular economy could release environmental burdens by reducing resource exploitation and material manufacturing. In this study, we demonstrated that the waste regenerated activated carbon (RAC) could become micro-/mesopore-dominant through a simple surfactant/gel modification. This was achieved by associating carbon precursors, such as commercially available low-cost surfactants/methyl cellulose thickening reagents, with the pores of RAC. Following heat treatment, associated carbon precursors were carbonized, hence modifying the microstructure of RAC to be micro-/mesopore-dominant. The surfactant modification gave rise to a micropore-dominant RAC by increasing the micropore volume (PVmicro) together with significantly decreasing the mesopore volume (PVmeso) and macropore volume (PVmacro). In contrast, gel modification led to mesopore-rich RAC by blocking micropores with carbonized methyl cellulose and a surfactant matrix. Interestingly, both surfactant/gel modifications were insensitive to the properties of the surfactant applied, which provided a new alternative for waste/low-grade surfactant mixture disposal. Our results provide an important demonstration that waste could be effectively upgraded with a rational design by exhibiting new properties in response to the circular economy.

Non-covalent Methods of Engineering Optical Sensors Based on Single-Walled Carbon Nanotubes

Optical sensors based on single-walled carbon nanotubes (SWCNTs) demonstrate tradeoffs that limit their use in in vivo and in vitro environments. Sensor characteristics are primarily governed by the non-covalent wrapping used to suspend the hydrophobic SWCNTs in aqueous solutions, and we herein review the advantages and disadvantages of several of these different wrappings. Sensors based on surfactant wrappings can show enhanced quantum efficiency, high stability, scalability, and diminished selectivity. Conversely, sensors based on synthetic and bio-polymer wrappings tend to show lower quantum efficiency, stability, and scalability, while demonstrating improved selectivity. Major efforts have focused on optimizing sensors based on DNA wrappings, which have intermediate properties that can be improved through synthetic modifications. Although SWCNT sensors have, to date, been mainly engineered using empirical approaches, herein we highlight alternative techniques based on iterative screening that offer a more guided approach to tuning sensor properties. These more rational techniques can yield new combinations that incorporate the advantages of the diverse nanotube wrappings available to create high performance optical sensors.

Hyperspectral Imaging Microscopy of Acetaminophen Adsorbed on Multiwalled Carbon Nanotubes

In this study, enhanced dark-field hyperspectral imaging (ED-HSI) was employed to directly observe acetaminophen (AAP), a model pharmaceutical and personal care product (PPCP), adsorbed on multiwalled carbon nanotubes with large diameters (L-MWCNT) and small diameters (S-MWCNT) under equilibrium conditions. The ED-HSI results revealed that (1) AAP molecules primarily adsorbed onto the external surfaces, rather than the internal surfaces of L- and S-MWCNT aggregates, (2) or on sidewall of the dispersed tubes, but not at their end caps. Besides, ED-HSI images showed that the surface coverage ratio of AAP/S-MWCNT is smaller than that of AAP/L-MWCNT (1.1 vs 3.4), indicating that there are more available adsorption sites on S-MWCNT than L-MWCNT when the adsorption reached equilibrium. This finding was consistent with the adsorption capacities of S-MWCNT and L-MWCNT (252.7 vs 54.6 mg g^-1). Direct visualization of sorption sites for PPCP molecules provides new insights into the heterogeneous structures and surface properties of MWCNT and helps elucidate the adsorption mechanisms that are fundamental to the design of functional adsorbents for PPCP contaminants.

Surfactant Assemblies on Selected Nanostructured Surfaces: Evidence, Driving Forces, and Applications

Surfactant adsorption at solid-liquid interfaces is critical for a number of applications of vast industrial interest and can also be used to seed surface-modification processes. Many of the surfaces of interest are nanostructured, as they might present surface roughness at the molecular scale, chemical heterogeneity, as well as a combination of both surface roughness and chemical heterogeneity. These effects provide lateral confinement on the surfactant aggregates. It is of interest to quantify how much surfactant adsorbs on such nanostructured surfaces and how the surfactant aggregates vary as the degree of lateral confinement changes. This review focuses on experimental evidence on selected substrates, including gold- and carbon-based substrates, suggesting that lateral confinement can have pronounced effects both on the amount adsorbed and on the morphology of the aggregates as well as on a systematic study, via diverse simulation approaches, on the effect of lateral confinement on the structure of the surfactant aggregates. Atomistic and coarse-grained simulations conducted for surfactants on graphene sheets and carbon nanotubes are reviewed, as well as coarse-grained simulations for surfactant adsorption on nanostructured surfaces. Finally, we suggest a few possible extensions of these studies that could positively impact a few practical applications. In particular, the simultaneous effect of lateral confinement and of the coadsorption of molecular compounds within the surface aggregates is expected to yield interesting fundamental results with long-lasting consequences in applications ranging from drug delivery to the design of advanced materials.

2D equation-of-state model for corona phase molecular recognition on single-walled carbon nanotube and graphene surfaces

Corona phase molecular recognition (CoPhMoRe) has been recently introduced as a means of generating synthetic molecular recognition sites on nanoparticle surfaces. A synthetic heteropolymer is adsorbed and confined to the surface of a nanoparticle, forming a corona phase capable of highly selective molecular recognition due to the conformational imposition of the particle surface on the polymer. In this work, we develop a computationally predictive model for analytes adsorbing onto one type of polymer corona phase composed of hydrophobic anchors on hydrophilic loops around a single-walled carbon nanotube (SWCNT) surface using a 2D equation of state that takes into consideration the analyte-polymer, analyte-nanoparticle, and polymer-nanoparticle interactions using parameters determined independently from molecular simulation. The SWCNT curvature is found to contribute weakly to the overall interaction energy, exhibiting no correlation for three of the corona phases considered, and differences of less than 5% and 20% over a larger curvature range for two other corona phases, respectively. Overall, the resulting model for this anchor-loop CoPhMoRe is able to correctly predict 83% of an experimental 374 analyte-polymer library, generating experimental fluorescence responses within 20% error of the experimental values. The modeling framework presented here represents an important step forward in the design of suitable polymers to target specific analytes.

Interactions between nanofibers in fiber-surfactant suspensions: theory of corresponding distances

We present the theory of corresponding distances for interactions mediated by soft nanostructures in fibrous materials. Based on the fundamental understanding of the mechanism that determines the internal structure of the soft component, our theory allows us to predict the entire force field mediated by the soft component for any angle and distance between the fibers from a single simulation or a single experiment. This replaces hundreds of simulations by just one which enables the routine computation of complete fiber-soft-fiber force fields by high-level methods, such as atomistic simulations, and thereby amounts to a true step advancement for soft nanotechnology.

Surfactant-based dispersant for multiwall carbon nanotubes to prepare ceramic composites by a sol-gel method

A dispersant for multiwall carbon nanotubes (MWCNTs) is proposed that fulfils the requirements of creating a uniform dispersion in the matrix and obtaining a good interface between CNTs and the matrix, and is soluble in generic nonpolar solvents. This dispersant is based on a long chain surfactant, called in this work dabcosil stearate, containing a stearate-based 18-carbon alkyl chain as an anion, and a silsesquioxane containing a bridged, positively charged 1,4-diazoniabicyclo[2.2.2]octane group. It provides not only a very good dispersion medium for the MWCNTs, but also a very good interface between MWCNTs and ceramic matrices, such as alumina and zirconia, prepared by the sol-gel method.