RESUMO
Herein we describe a successful protocol for graphite exfoliation using a biphasic liquid system (water/dichloromethane, DCM) containing ionic liquids (ILs; 1,3-dibenzylimidazolium benzoate- and 1-naphthoate). The use of (surface active) IL and sonication led to stable DCM/water (O/W) emulsion, which enhanced graphene formation, suppressed its re-aggregation and decreased shear/cavitation damage. The O/W emulsion stabilization by the ILs was studied by dynamic light scattering (DLS), whereas their interaction with the graphene sheets were described by Density Functional Theory (DFT) calculations. Moreover, a comprehensive investigation on cavitation-based exfoliation in the O/W systems was performed to assess the importance of operational parameters, including, the type of ultrasound processor, ultrasound power and insonation, and the influence of the exfoliation medium.
RESUMO
The rich plasmon resonance modes and local field enhancements of two-dimensional (2D) noble metal nanostructures have boosted their application in distinct areas like catalysis, photonics, medicine and sensing. Here, we develop a unique strategy for the controlled growth of asymmetric 2D gold nanostructures in aqueous media using graphene oxide as a template. By performing mild reduction of gold ions on the surface of Au seeds (â¼2 nm) attached to graphene oxide nanosheets, the anisotropic growth of 2D gold nanostructures can be carried out through a simple procedure with a tunable control of the final size, shape and thickness, and consequently on their optical properties, without using surfactants.
RESUMO
Anisotropic materials are characterized by a unique optical response, which is highly polarization-dependent. Of particular interest are layered materials formed by the stacking of two-dimensional (2D) crystals that are naturally anisotropic in the direction perpendicular to the 2D planes. Black phosphorus (BP) is a stack of 2D phosphorene crystals and a highly anisotropic semiconductor with a direct band gap. We show that the angular dependence of polarized Raman spectra of BP is rather unusual and can be explained only by considering complex values for the Raman tensor elements. This result can be traced back to the electron-photon and electron-phonon interactions in this material.