The oxidative exfoliation of graphite is a promising approach to the large-scale production of graphene. Conventional oxidation of graphite essentially facilitates the exfoliation process; however, the oxidation procedure releases toxic gases and requires extensive, time-consuming steps of washing and reduction to convert exfoliated graphene oxide (GO) into reduced graphene oxide (rGO). Although toxic gases can be controlled by modifying chemical reactions, filtration, dialysis, and extensive sonication are unfavorable for large-scale production. Here, we report a complete, scalable, and green synthesis of GO, without NaNO3, followed by reduction with citric acid (CA). This approach eliminates the generation of toxic gases, simplifies the washing steps, and reduces the time required to prepare rGO. To validate the proposed method, we present spectroscopical and morphological studies, using energy-dispersive X-ray spectroscopy (EDS), UV-visible spectroscopy, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Thermal gravimetric analysis (TGA) is used to analyze the thermal properties of GO and rGO. This eco-friendly method proposes a complete guideline protocol toward large-scale production of oxidized graphene, with potential applications in supercapacitors, fuel cells, composites, batteries, and biosensors.

Recently, green-prepared oxidized graphenes have attracted huge interest in water purification and wastewater treatment. Herein, reduced graphene oxide (rGO) was prepared by a scalable and eco-friendly method, and its potential use for the removal of methylene blue (MB) from water systems, was explored. The present work includes the green protocol to produce rGO and respective spectroscopical and morphological characterizations, as well as several kinetics, isotherms, and thermodynamic analyses to successfully demonstrate the adsorption of MB. The pseudo-second-order model was appropriated to describe the adsorption kinetics of MB onto rGO, suggesting an equilibrium time of 30 min. Otherwise, the Langmuir model was more suitable to describe the adsorption isotherms, indicating a maximum adsorption capacity of 121.95 mg g−1 at 298 K. In addition, kinetics and thermodynamic analyses demonstrated that the adsorption of MB onto rGO can be treated as a mixed physisorption–chemisorption process described by H-bonding, electrostatic, and π − π interactions. These results show the potential of green-prepared rGO to remove cationic dyes from wastewater systems.

Among their amazing properties, graphene and related low-dimensional materials show quantized charge-density fluctuations-known as plasmons-when exposed to photons or electrons of suitable energies. Graphene nanoribbons offer an enhanced tunability of these resonant modes, due to their geometrically controllable band gaps. The formidable effort made over recent years in developing graphene-based technologies is however weakened by a lack of predictive modeling approaches that draw upon available ab initio methods. An example of such a framework is presented here, focusing on narrow-width graphene nanoribbons organized in periodic planar arrays. Time-dependent density-functional calculations reveal unprecedented plasmon modes of different nature at visible to infrared energies. Specifically, semimetallic (zigzag) nanoribbons display an intraband plasmon following the energy-momentum dispersion of a two-dimensional electron gas. Semiconducting (armchair) nanoribbons are instead characterized by two distinct intraband and interband plasmons, whose fascinating interplay is extremely responsive to either injection of charge carriers or increase in electronic temperature. These oscillations share some common trends with recent nanoinfrared imaging of confined edge and surface plasmon modes detected in graphene nanoribbons of 100-500 nm width. Plasmons are quantized oscillations of the valence electron density in metals, metal-dielectric interfaces and nanostructures, being usually excited by light or electronbeam radiation. Plasmon-related technologies are expected to receive a burst from nanocarbon architectures [1-10], due to one of the fascinating features of monolayer graphene (MG) [11], i.e., its extrinsic plasmon modes at terahertz (THz) frequencies [12][13][14][15][16][17][18][19][20]. These show much stronger confinement, larger tunability and lower losses [21] compared to conventional plasmonic materials, such as silver or gold. Nowadays plasmons are launched, controlled, manipulated and detected in a variety of graphene-related materials and heterostructures, which suggests that graphene-based plasmonic devices are becoming closer to reality, with the potential to operate on the "THz gap", forbidden by either classical electronics or photonics [4,22,23]. Plasmons with widely tunable frequencies have been observed in graphene nanoribbons (GNRs)-from the nano-to microrange in width [12,14,24,25]. On the theoretical side, density functional and tight-binding (TB) approaches have explored the electronic structure of zigzag and armchair GNRs, with particular attention to the band-gap values of the intrinsic systems, being a major control factor of their plasmonic properties [26][27][28][29][30]. Far fewer studies have been focused on plasmon resonances in GNRs using either a semiclassical electromagnetic picture [31] or a TB scheme [5,32,33], and specializing to THz frequencies. A comprehensive characterization of the dielectric properties of such systems is, however, lacking.Here, we provide an ab initio study o...