A highly efficient, reproducible, and scalable approach for exfoliation of MoS2 is critical for utilizing these emerging materials from coatings and composites to printable devices. Additive-free techniques, such as solvent-assisted exfoliation via sonication, are considered to be the most viable approach, where N-methyl-2-pyrrolidone (NMP) is the most effective solvent. However, understanding the mechanism of exfoliation and the key role NMP plays during the process have been elusive and challenges effective improvements in product yield and quality. Here, we report systematic experiments to understand the mechanism of solvent-assisted exfoliation by elucidating the sonolysis chemistries associated with NMP. It is confirmed that in the presence of O2(g) dissolved moisture in NMP plays a critical role during sonication. The higher the moisture content, the more efficient the exfoliation process is. Conversely, when exfoliations are carried out with dried solvents with an inert atmosphere, reaction yields decrease. This is due to redox-active species formed in situ through an autoxidation pathway that converts NMP to N-methyl succinimide by hydroperoxide intermediates. These highly reactive species appear to aid exfoliation by oxidation at reactive edge sites; the charging creates Coulombic repulsion between neighboring sheets that disrupts interlayer basal plane bonding and enables electrostatic stabilization of particles in high-dipole solvents. From these insights, exfoliation in previously reported inactive solvents (e.g., acetonitrile), as well as in the absence of probe sonication, is demonstrated. These findings illustrate that exfoliation of MoS2, and possibly TMD’s in general, can be mediated through understanding the chemistry occurring at the surface–solvent interface.

Gold nanorods (Au NRs) are the archetype of a nanoantenna, enabling the directional capture, routing, and concentration of electromagnetic fields at the nanoscale. Solution-based synthesis methods afford advantages relative to top-down fabrication but are challenged by insufficient precision of structure, presence of byproducts, limited tunability of architecture, and device integration. This is due in part to an inadequate understanding of the early stages of Au NR growth. Here, using phase transfer via ligand exchange with monothiolated polystyrene, we experimentally demonstrate the complete evolution of seed-mediated Au NR growth in hexadecyltrimethylammonium bromide (CTAB) solution. Au NR size and shape progress from slender spherocylinders at short reaction times to rods with a dumbbell profile, flattened end facets, and octagonal prismatic structures at later stages. These evolve from a single mechanism and reflect the majority of reported Au NR morphologies, albeit reflecting different stages. Additionally, the fraction of nonrod impurities in a reaction is related to the initial distribution of the structure of the seed particles. Overall, the observations of early and intermediate stage growth are consistent with the formation of a surfactant bilayer on different crystal facets at different growth stages due to a fine balance between kinetic and thermodynamic factors.

Highly dispersed and debundled carbon nanotubes were prepared in an aqueous solution of lysozyme using a combination of ultrasonication and ultracentrifugation. The product is a pH-sensitive dispersion, which remains in a highly dispersed state at pH<8 and pH>11, but in an aggregated state at pH 8-11. Photoluminescence measurements show that by changing the pH value, a reversible conversion of the highly dispersed state to the aggregated state (or vice versa) could be observed. Circular dichromism analysis confirmed that the secondary structure, as well as the majority of the tertiary structure, remains intact. Some lysozyme molecules were irreversibly bound to the nanotubes, which is possibly due to pi-pi or hydrophobic interactions. However, these interactions alone are not enough to produce fine dispersions of the nanotubes. Protonated amine interactions on the defect sites of the nanotubes play a vital role in the stabilization of the nanotubes below the isoelectric point and amine adsorption on the sidewalls of nanotubes occurs in cases where the pH value is higher than the isoelectric point.

The interactions between biological substances and carbon nanotubes (CNTs) and their effect on the nanotubes are of significant importance in this emerging era of nanobiotechnology. Consequently, highly stable dispersions of debundled CNTs in aqueous solution are an important prerequisite for their applications and for the development of nanotube-based molecular electronic and nanobiomedical devices. Here, we report that proteins can work as tools to this end if their primary structure and the pH value of the system are chosen appropriately. Proteins containing a large number of basic residues, for example, histone, are found to be the most promising protein tools for the dispersion of nanotubes. Apart from other interactions, the polarity of the protein seems to play a vital role in obtaining high yields of debundled nanotubes. In addition, an enrichment of metallic nanotubes in the products is observed, which offers a facile approach for separating nanotubes according to their electronic properties in the bulk.

Large scale biomimetic single-walled carbon nanotube (SWNT) coatings with significant antimicrobial activity, high Young's Modulus, and controlled morphology were fabricated using layer-by-layer assembly. Thickness was controlled within 1.6 nm and SWNT orientation was controlled using a directed air stream. This unique blend of multifunctionality and vertical and lateral control of a bottom-up assembly process is a significant advancement in developing macroscale assemblies with the combined attributes of SWNTs and natural materials.Concern about the spread of infections through contact with contaminated surfaces was once limited to specific groups of people including astronauts who are subject to confined living spaces and the virulence-enhancing effects of space flight 1 and people requiring surgery or implantable devices. 2 More recently, there has been growing concern about the role of contaminated surfaces in the spread of infections such as severe acute respiratory syndrome (SARS), 3,4 and Staphylococcus aureus, particularly methicillin-resistant Staphylococcus aureus (MSRA). 5 Antimicrobial surfaces are therefore desirable not only for the aerospace, defense, and medical industries but also for the consumer product and public transportation industries. We have used layer-by-layer assembly to produce coatings that combine the strength of single-walled carbon nanotubes (SWNTs) with the antimicrobial activity of lysozyme (LSZ).LSZ, a key member of ova-antimicrobials, is a powerful natural antibacterial protein. 6 It is in the class of enzymes which lyse the cell walls of Gram-positive bacteria by hydrolyzing the -1,4 linkage between N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) of gigantic polymers in the peptidoglycan (murein). 7,8 Unlike many antimicrobials, LSZ has both enzymatic and nonenzymatic activity in both its native and denatured states and is useful even in processes which require heat treatment. The potential use of LSZ as an antimicrobial agent in pharmaceuticals, food preservatives, and packaging is an active area of research, 7,8 but the effective use of LSZ requires incorporating it with a more mechanically robust material. SWNTs are well-known for exceptional combination of mechanical, electrical, thermal, and optical properties. 9-11 However, the efficient transfer of SWNTs' inherent nanoscale properties to macroscopic structures and devices has been an ongoing research challenge comprised of three main issues: SWNT dispersion, controlled assembly, and efficient load transfer. There has been growing interest in using biological materials to stabilize dispersions of pristine SWNTs. DNA enables much higher concentrations of dispersions of individual and small bundles of SWNTs 11,12 than any other known material besides superacids; 13,14 DNA-SWNT dispersions have even been used to produce liquid crystalline dispersions for solution spinning. 15 Similarly, favorable intermolecular interactions enable dispersion of individual and small bundles of SWNTs in proteins such as LSZ...