Oxidation of Molybdenum-Based Single-Metallic/bimetallic Carbide MXenes in Aqueous Suspensions: Mechanistic Insights.

Molybdenum carbide MXenes have garnered considerable attention in electronics, energy storage, and catalysis. However, they are prone to oxidative degradation, but the associated mechanisms have not been systematically explored. Therefore, the oxidation mechanisms of Mo-based single-metallic/bimetallic carbide MXenes including MoCT, MoTiCT, and MoTiCT in aqueous suspensions were investigated for the first time in this study.

Biocompatible and Oxidation-Resistant Ti C T MXene with Halogen-Free Surface Terminations.

Surface chemistry influences not only physicochemical properties but also safety and applications of MXene nanomaterials. Fluorinated Ti C T MXene, synthesized using conventional HF-based etchants, raises concerns regarding harmful effects on electronics and toxicity to living organisms. In this study, well-delaminated halogen-free Ti C T flakes are synthesized using NaOH-based etching solution.

Universal Ligands for Dispersion of Two-Dimensional MXene in Organic Solvents.

Ligands can control the surface chemistry, physicochemical properties, processing, and applications of nanomaterials. MXenes are the fastest growing family of two-dimensional (2D) nanomaterials, showing promise for energy, electronic, and environmental applications. However, complex oxidation states, surface terminal groups, and interaction with the environment have hindered the development of organic ligands suitable for MXenes.

Tunable TiCT MXene-Derived TiO Nanocrystals at Controlled pH and Temperature.

While two-dimensional (2D) TiCT MXene in aqueous dispersions spontaneously oxidizes into titanium dioxide (TiO) nanocrystals, the crystallization mechanism has not been comprehensively understood and the resultant crystal structures are not controlled among three representative polymorphs: anatase, rutile, and brookite. In this study, such control on the lattice structures and domain sizes of the MXene-derived TiO crystallites is demonstrated by means of the oxidation conditions, pH, and temperature (3.0-11.

Fast and High-Yield Anhydrous Synthesis of Ti C T MXene with High Electrical Conductivity and Exceptional Mechanical Strength.

2D transition metal carbides or nitrides (MXenes) have attracted considerable attention from materials scientists and engineers owing to their physicochemical properties. Currently, MXenes are synthesized from MAX-phase precursors using aqueous HF. Here, in order to enhance the production of MXenes, an anhydrous etching solution is proposed, consisting of dimethylsulfoxide as solvent with its high boiling point, NH HF as an etchant, CH SO H as an acid, and NH PF as an intercalant.

Mechanism and Kinetics of Oxidation Reaction of Aqueous TiCT Suspensions at Different pHs and Temperatures.

Understanding the oxidation reaction of aqueous TiCT MXene suspensions is very important for fostering fundamental academic studies as well as widespread industrial applications. Herein, we investigated the mechanism and kinetics of the oxidation reaction of aqueous TiCT suspensions at various pH and temperature conditions. Through comprehensive analysis, the mechanism of the chemical oxidative degradation of aqueous TiCT colloids was established.

DNA- and Field-Mediated Assembly of Magnetic Nanoparticles into High-Aspect Ratio Crystals.

Under an applied magnetic field, superparamagnetic Fe O nanoparticles with complementary DNA strands assemble into crystalline, pseudo-1D elongated superlattice structures. The assembly process is driven through a combination of DNA hybridization and particle dipolar coupling, a property dependent on particle composition, size, and interparticle distance. The DNA controls interparticle distance and crystal symmetry, while the magnetic field leads to anisotropic crystal growth.

Stabilization of Colloidal Crystals Engineered with DNA.

A postsynthetic method for stabilizing colloidal crystals programmed from DNA is developed. The method relies on Ag ions to stabilize the particle-connecting DNA duplexes within the crystal lattice, essentially transforming them from loosely bound structures to ones with very strong interparticle links. Such crystals do not dissociate as a function of temperature like normal DNA or DNA-interconnected superlattices, and they can be moved from water to organic media or the solid state, and stay intact.

Density-Gradient Control over Nanoparticle Supercrystal Formation.

With the advent of DNA-directed methods to form "single crystal" nanoparticle superlattices, new opportunities for studying the properties of such structures across many length scales now exist. These structure-property relationships rely on the ability of one to deliberately use DNA to control crystal symmetry, lattice parameter, and microscale crystal habit. Although DNA-programmed colloidal crystals consistently form thermodynamically favored crystal habits with a well-defined symmetry and lattice parameter based upon well-established design rules, the sizes of such crystals often vary substantially.

Direct Observation of Plasmon-Induced Interfacial Charge Separation in Metal/Semiconductor Hybrid Nanostructures by Measuring Surface Potentials.

Plasmon-induced interfacial charge separation (PICS) is one of the key processes responsible for the improved conversion efficiencies of energy-harvesting devices that incorporate metal nanostructures. In this Letter, we reveal a mechanism of PICS by visualizing (with nanometer-scale resolution) and characterizing plasmon-exciton coupling between p-type poly(pyrrole) (PPy) nanowires (NWs) and Ag nanoparticles (NPs) using light-irradiated Kelvin probe force microscopy (KPFM). Under blue-light irradiation, the Ag NPs are expected to donate electrons to the PPy NWs via a hot electron injection process.

Orthogonal Chemical Modification of Template-Synthesized Nanostructures with DNA.

Very few chemical strategies for the selective functionalization of nanostructures have been developed despite their potential for controlling high-order assembly processes. We report a novel approach for the selective chemical functionalization and localized assembly of one-dimensional nanostructures (rods), based upon the systematic activation (DNA functionalization) and passivation (self-assembled monolayers) of specific surface sites through the use of orthogonal chemical reactions on electrochemically grown metal nanorod arrays in porous anodic aluminum oxide templates. The ability to orthogonally functionalize the ends or the side of a nanorod, as well as the gaps between two rods, with different DNA strands allows one to synthesize nanostructure assemblies that would be difficult to realize any other way and that could ultimately be utilized for making a wide variety of device architectures.