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.

Many types of metal and semiconductor nanoparticles (NPs) are created via colloidal synthetic methods, which renders the materials hydrophobic. Such NPs are dispersed in water through surface organic cap exchange or by amphiphilic polymer encapsulation; often, water solubility is achieved via the presence of carboxylic acid functionalities on the solubilizing agents. While this renders the material water-soluble, subsequent functionalization of the systems can be very difficult. The most obvious method to derivatize carboxylic acid coated NPs is to conjugate chemical and biological moieties containing amine functionality to the NP surface using the water-soluble activator 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). However, the excess use of this reagent appears to cause complete and permanent precipitation of the NPs. We report here our method on the chemical and biological functionalization of a variety of semiconductor nanoparticle systems using novel carbodiimide reagents. These reagents do not cause precipitation even at high loading levels and can be used to efficiently functionalize carboxylic acid coated NPs.

We report here a method for synthesizing CdSe quantum dots (QDs) containing copper such that each QD is doped with four copper ions. The synthesis is a derivative of the cluster-seed method, whereby organometallic clusters act as nucleation centers for quantum dots. The method is tolerant of the chemical identity of the seed; as such, we have doped four copper ions into CdSe QDs using [Na(H2O)3]2[Cu4(SPh)6] as a cluster seed. The controlled doping allows us to monitor the photophysical properties of guest ions with X-ray spectroscopy, specifically XANES and EXAFS at the copper K-edge. These data reveal that copper can capture both electrons and holes from photoexcited CdSe QDs. When the dopant is oxidized, photoluminescence is quenched and the copper ions translocate within the CdSe matrix, which slows the return to an emissive state.

Transition metal dichalcogenides (TMDs) have attracted considerable attention in a diverse array of applications due to the breadth of possible property suites relative to other low-dimensional nanomaterials (e.g., graphene, aluminosilicates). Here, we demonstrate an alternative methodology for the exfoliation of bulk crystallites of group V-VII layered TMDs under quiescent, benchtop conditions using mild redox chemistry. Anionic polyoxometalate species generated from edge sites adsorb to the TMD surface and create Coulombic repulsion that drives layer separation without the use of shear forces. This method is generalizable (MS, MSe, and MTe) and effective in preparing high-concentration (>1 mg/mL) dispersions with narrow layer thickness distributions more rapidly and with safer reagents than alternative solution-based approaches. Finally, exfoliation of these TMDs is demonstrated in a range of solvent systems that were previously inaccessible due to large surface energy differences. These characteristics could be beneficial in the preparation of high-quality films and monoliths.

The versatile property suite of two-dimensional MXenes is driving interest in various applications, including energy storage, electromagnetic shielding, and conductive coatings. Conventionally, MXenes are synthesized by a wet-chemical etching of the parent MAX-phase in HF-containing media. The acute toxicity of HF hinders scale-up, and competing surface hydrolysis challenges control of surface composition and grafting methods. Herein, we present an efficient, room-temperature etching method that utilizes halogens (Br 2 , I 2 , ICl, IBr) in anhydrous media to synthesize MXenes from Ti 3 AlC 2 . A radicalmediated process depends strongly on the molar ratio of the halogen to MAX phase, absolute concentration of the halogen, the solvent, and temperature. This etching method provides opportunities for controlled surface chemistries to modulate MXene properties.

Rapid fabrication of large area, ordered assemblies of polymer grafted (hairy) nanoparticles (PGNs) will enable additive manufacturing of novel membrane, electronic, and photonic elements. Herein, we discuss the relationship between select processing conditions, substrate surface energy, and canopy architecture on the hierarchical structure of sub- to monolayer PGN assemblies. Varying concentrations (10, 20, and 70 nM) of polystyrene (PS) grafted (σ ∼ 1 chain/nm2) gold nanoparticles (AuNP, r 0 = 9 nm) were flow-coated onto surface-modified silicon wafers (γs ∼ 20 mN/m, hydrophobic to 80 mN/m, hydrophilic). The profile of an isolated gold–polystyrene (PS) PGN depends on substrate–canopy interface energy. At low substrate–PS interface energy (20 mN/m), the PS canopy spreads to maximize contact with the surface, whereas at high substrate–PS interface energy (80 mN/m), the chains minimize contact area resulting in a more compact, thicker PGN corona. This behavior is translated up to monolayer assemblies, where rougher, less-ordered assemblies with smaller AuNP–surface separation form on substrates with low interface energy. These films are also thinner with greater Au volume fraction, indicating that the segment density within the PS canopy depends on substrate surface energy. The impact of these processing parameters on PGN film formation parallels classic colloidal deposition even though the PS concentration is within the Landau–Levich regime for film formation from linear chains. The factors influencing local morphology, however, resemble those that affect polymer thin films. Using this understanding, we demonstrate fabrication within seconds of large area monolayer films with close-packed order.

Liquid processing of layered transition metal dichalcogenides (LTMDs) is enabling a variety of applications, ranging from catalysts and coatings, to electronics, flexible sensors, and optical filters. Current strategies, such as sonication or shear mixing, are challenged by small yields (<1%), low production rates (

The extremely large optical extinction coefficient of gold nanorods (Au-NRs) enables their use in a diverse array of technologies, rnging from plasmonic imaging, therapeutics and sensors, to large area coatings, filters, and optical attenuators. Development of the latter technologies has been hindered by the lack of cost-effective, large volume production. This is due in part to the low reactant concentration required for symmetry breaking in conventional seed-mediated synthesis. Direct scale up of laboratory procedures has limited viability because of excessive solvent volume, exhaustive postsynthesis purification processes, and the generation of large amounts of waste (e.g., hexadecyltrimethylammonium bromide(CTAB)). Following recent insights into the growth mechanism of Au-NRs and the role of seed development, we modify the classic seed-mediated synthesis via temporal control of seed and reactant concentration to demonstrate production of Au-NRs at more than 100-times the conventional concentration, while maintaining independent control and narrow distribution of nanoparticle dimensions, aspect ratio, and volume. Thus, gram scale synthesis of Au-NRs with prescribed aspect ratio and volume is feasible in a 100 mL reactor with 1/100th of organic waste relative to conventional approaches. Such scale-up techniques are crucial to cost-effectively meet the increased demand for large quantities of Au-NRs in emerging applications.