Structural and Electronic Properties of Graphene Oxide for Different Degree of Oxidation1

In the last year, the investigation of two-dimensional materials as graphene oxide is a fundamental goal to produce innovative devices with wide range of applications in many areas. In the present work, we report a systematic study of structural and electronic properties of graphene oxide for different oxidations levels (25%, 50%, 75%, 100%) using density functional calculations for electronic ground state and a statistical approach on carbon-carbon bond length obtained after the geometric optimization of graphene covered with epoxide and hydroxyl functional groups. The theoretical models proposed and studied here are accord with the well-known experimental data. Our statistical results of the carbon-carbon bond length shown that hydroxyl groups disturbs the structure of graphene more than epoxide groups, however, both hydroxyl and epoxide groups are responsible of the change of hybridization sp2 to sp3, while the degree of oxidation increase. In addition, our electronic structure calculations confirm that with low degree of oxidation, the graphene oxide is semiconductor, and with full degree of oxidation graphene oxide is an insulating material. The minimum of total energy is found when the graphene oxide has full coverage. This work can contribute to understand the plasticity and ductility properties of graphene oxide recently reported

Modeling Plasmonics and Electronics in Semiconducting Graphene Nanostrips

In recent decades, both academia and industry have shown noteworthy interest in investigating the semiconducting properties of graphene. Nevertheless, the lack of a suitable bandgap in graphene has restricted its practical applications in the current semiconductor industry. To overcome this limitation, graphene micro/nano-strips have been actively explored. The focus of the present study centers on modeling the electronic and plasmonic characteristics of graphene strips with varying widths: 2.7, 100, 135 nm, and 4 m. This analysis is conducted at ultralow energies (0.3 eV, or ~73 THz). We employ conventional density functional computations to estimate the Fermi velocity of graphene, refining the results via the GW approximation. Utilizing the accurate Fermi velocity, we employ a semi-analytical model to explore the ground state and plasmon properties (frequency and dispersion) of these graphene strips. Notably, this approach effectively replicates the density of states observed in narrow experimental graphene nano-strips (2.7 nm) grown on Ge(001) and, similarly, reproduces the plasmon spectrum found in synthesized graphene microstrips (4 μm) on Si/SiO2. Interestingly, our study also offers insights into the potential application of this approach in comprehending the plasmon frequency and plasmon dispersion of graphene nano-strips (~135 nm) acquired through liquid-phase exfoliation. The outcomes of this investigation present compelling evidence that the properties of graphene-based strips can be customized to fulfill specific requirements and applications. These findings hold significant promise for advancing graphene-based technologies, bridging the gap between fundamental research and tangible applications. Doi: 10.28991/ESJ-2023-07-05-01 Full Text: PD

Adsorption Kinetics of Hg(II) on Eco-Friendly Prepared Oxidized Graphenes

Extra-functionalized oxidized graphenes are widely preferred for the removal of different pollutants, however, removal with pristine oxidized graphenes, i.e., graphene oxide (GO) and reduced graphene oxide (rGO) is vaguely explored. Herein, we report a comparative adsorption kinetics study of the removal of mercury(II) (Hg(II)) from water using eco-friendly prepared GO and rGO. This work consists of the synthesis protocol and the corresponding morphological and spectroscopical characterization of the obtained pristine adsorbents as well as the adsorption mechanism in terms of initial concentration, removal percentage, pseudo-first and pseudo-second-order models, intraparticle diffusion study, and pH analysis. In particular, scanning electron microscope (SEM) and transmission electron microscope (TEM) images evidence the presence of thin sheets with some defects on the GO structure, these defects substantially disappear in rGO, after reduction. Raman spectrum of rGO shows a less intense D* peak which is attributed to the diamond-like carbon phase. Most importantly, the equilibrium adsorption time in GO is 10 min with a removal percentage of ~28% while in rGO it is 20 min with a removal percentage of ~75%. The adsorption process of Hg(II) either in GO or rGO is more in line with the pseudo-second-order model, suggesting that the adsorption kinetics could be controlled by chemisorption. Our results evidence the interesting adsorbing properties of pristine oxidized graphenes and are expected to be useful for the proposal and study of non-extra functionalized graphene-based materials for water treatment

Proving Surface Plasmons in Graphene Nanoribbons Organized as 2D Periodic Arrays and Potential Applications in Biosensors

Surface-plasmon-based biosensors have become excellent platforms for detecting biomolecular interactions. While there are several methods to exciting surface plasmons, the major challenge is improving their sensitivity. In relation to this, graphene-based nanomaterials have been theoretically and experimentally proven to increase the sensitivity of surface plasmons. Notably, graphene nanoribbons display more versatile electronic and optical properties due to their controllable bandgaps in comparison to those of zero-gap graphene. In this work, we use a semi-analytical approach to investigate the plasmonic character of two-dimensional graphene nanoribbon arrays, considering free-standing models, i.e., models in which contact with the supporting substrate does not affect their electronic properties. Our findings provide evidence that the plasmon frequency and plasmon dispersion are highly sensitive to geometrical factors or the experimental setup within the terahertz regime. More importantly, possible applications in the molecular detection of lactose, α-thrombin, chlorpyrifos-methyl, glucose, and malaria are discussed. These predictions can be used in future experiments, which, according to what is reported here, can be correctly fitted to the input parameters of possible biosensors based on graphene nanoribbon arrays

Analysis of covid-19 outbreak in Ecuador using the logistic model

At the end of 2019, the COVID-19 disease emerged in the city of Wuhan, China, and caused an outbreak of unusual viral pneumonia. Being highly transmissible, this novel coronavirus disease has spread fast all over the world. COVID-19 continues to challenge most developed countries in the search for an effective strategy to either prevent infection or to avoid the spreading of the disease. While several developed countries have managed to contain COVID-19, several countries in Latin America continue to report an increase in the daily number of infected people. Ecuador, particularly, became the epicenter of the COVID-19 outbreak in the region during March and April 2020. In this context, the present study shows a simple mathematical approach to understand the effect of the COVID-19 outbreak in Ecuador (and some Latin American countries such as Brazil, Peru, and Colombia). The proposed method is based on the exponential model, discrete logistic equation, and differential logistic model using one-year data from March 1, 2020, to February 28, 2021. This study presents the estimated growth rate coefficient (λ), the total number of cases (N), and the midpoint of maximum infection (t_0) as well as the variability of the λ coefficient as a function of total cases and time. The exponential model shows a high value of λ=0.185 which decreases to λ=0.014 and λ=0.056 according to the discrete and differential logistic models, respectively. An accurate value of the total number of cases of infected people was found by analyzing the number of daily cases as a function of the total of cases whose value (N~409 K) agrees with the data reported at the end of May 2021, validating the proposed approach. How to use the current mathematical approach for long-term prediction is also discussed here. Most importantly, the proposed method has two important characteristics: (i) the mathematical model is as simple as possible compared to other time-consuming approaches, and (ii) it can be used to study the effect of COVID-19 and predicts its consequences in other countries, allowing revenue new decisions against the COVID-19 diseas

Environmental Radon Measurements using a closed chamber for building materials and water and a feasible program for Ecuador

Scuola di Dottorato in Scienze, Comunicazione e Tecnologie ""Archimede" Ciclo XXVIII, a.a. 2015-2016Università della Calabri

Modeling 2D Arrangements of Graphene Nanoribbons

In the last two decades, interest in graphene has grown extensively due to its extraordinary properties and potential for various applications such as sensing and communication. However, graphene is intrinsically a semimetal with a zero bandgap, which considerably delays its use where a suitable bandgap is required. In this context, quasi-one-dimensional counterparts known as graphene nanoribbons (GNRs) have demonstrated sizeable bandgaps and versatile electronic properties, which make them promising candidates for photonic and plasmonic applications. While progress has recently been made toward the synthesis of GNRs, theoretical models to envisage their electronic and optical properties have been restricted to ab initio approaches, which are not feasible for wide systems because of the large number of atoms tangled. Here, we use a semi-analytical model based on Dirac cone approximation to show the adjustable electronic and plasmonic characteristics of wide and experimental GNRs, both freestanding and non-freestanding. This approach utilizes the group velocity of graphene, which is calculated using density functional computations (vF=0.829×106 m s−1), as the primary input. Importantly, our research reveals that at the terahertz level, the plasmon-momentum dispersion is highly responsive to changes by varying the ribbon width or charge carrier concentrations, the other involved parameters can be manipulated by setting values from experiments or more sophisticated predictions. In particular, this model can replicate the electronic properties of GNRs on Ge(001) and GNRs on Au(111). From the plasmonic side, the plasmon spectrum of graphene microribbon arrays of 4 μm wide on Si/SiO2 and GNR arrays on Si are found in good agreement with experiments. The potential use of GNRs in sensing molecules such as chlorpyrifos-methyl is also discussed. Chlorpyrifos-methyl is chosen as the test molecule because it is a commonly used insecticide in agriculture, but its high toxicity to organisms and humans makes it a concern. It has been established that the plasmon resonances of all the studied GNRs occur at the same frequency as chlorpyrifos-methyl, which is 0.95 THz. Our findings can serve as a useful guide for future experiments

Proving Surface Plasmons in Graphene Nanoribbons Organized as 2D Periodic Arrays and Potential Applications in Biosensors

Surface-plasmon-based biosensors have become excellent platforms for detecting biomolecular interactions. While there are several methods to exciting surface plasmons, the major challenge is improving their sensitivity. In relation to this, graphene-based nanomaterials have been theoretically and experimentally proven to increase the sensitivity of surface plasmons. Notably, graphene nanoribbons display more versatile electronic and optical properties due to their controllable bandgaps in comparison to those of zero-gap graphene. In this work, we use a semi-analytical approach to investigate the plasmonic character of two-dimensional graphene nanoribbon arrays, considering free-standing models, i.e., models in which contact with the supporting substrate does not affect their electronic properties. Our findings provide evidence that the plasmon frequency and plasmon dispersion are highly sensitive to geometrical factors or the experimental setup within the terahertz regime. More importantly, possible applications in the molecular detection of lactose, α-thrombin, chlorpyrifos-methyl, glucose, and malaria are discussed. These predictions can be used in future experiments, which, according to what is reported here, can be correctly fitted to the input parameters of possible biosensors based on graphene nanoribbon arrays

THz Surface Plasmons in Wide and Freestanding Graphene Nanoribbon Arrays

Graphene is a thin-film carbon material that has immense potential as a key ingredient in new nanoelectronic and nanophotonic devices due to its unique characteristics. In particular, plasmons in graphene appear as a practical tool for the manipulation of light with potential applications from cancer treatment to solar cells. A motivating tunability of graphene properties has been observed in graphene nanoribbons (GNRs) due to their geometrically controllable bandgaps that, in turn, influence the plasmonic properties. The formidable effort made over recent years in developing GNR-based technologies is, however, weakened by a lack of predictive approaches that draw upon available semi-analytical electromagnetic models. An example of such a framework is used here, focusing on experimentally realized GNRs from 155 to 480 nm wide and organized as two-dimensional (2D) GNR arrays. The results show that the plasmon frequency behavior is highly affected by the experimental setup or geometrical factors. In particular, the bandgap of the analyzed systems is of the order of a few meV with a density of states opening around zero energy (Fermi level) in contrast to what is observed in graphene. From the plasmonic part, it is observed in all 2D GNR arrays that the frequency–momentum trend follows a q-like plasmon dispersion whose plasmon frequency can be increased substantially by increasing the ribbon width or charge density concentration. Forbidden plasmon regions are observed for high values of plasmon excitation angle or electron relaxation rate. From a sensing point of view, the important finding is the fact that 2D GNR arrays of 155 nm wide with high values of electron relaxation rate have plasmon responses similar to those observed for α−thrombin in water. Our predictions are projected to be of fast support for detecting plasmons in more complex designs of ribbon nanodevices with potential applications in molecular sensing of aqueous molecules

Calibration of Fermi Velocity to Explore the Plasmonic Character of Graphene Nanoribbon Arrays by a Semi-Analytical Model

We present an analysis of the electronic and plasmonic behavior of periodic planar distributions of sufficiently wide graphene nanoribbons, for which a thorough ab initio investigation is practically unfeasible. Our approach is based on a semi-analytical model whose only free parameter is the charge carrier velocity, which we estimate by density-functional theory calculations on graphene. By this approach, we show that the plasmon resonance energies of the scrutinized systems fall in the lower THz band, relevant for optoelectronic and photonic applications. We further observe that these energies critically depend on the charge carrier concentration, ribbon width, electron relaxation rate, and in-plane transferred momentum angle, thus, suggesting a tunability of the associated light-matter modes