arXiv subjects

Marcelo Lopes Pereira Júnior

Publications and source records attributed to Marcelo Lopes Pereira Júnior.

5 recordsLinked to original sources

arXiv2025

Electronic and Optical Properties of the Recently Synthesized 2D Vivianites (Vivianenes): Insights from First-Principles Calculations

Vivianite (Fe$_3$(PO$_4$)$_2$8H$_2$O) is a naturally occurring layered material with significant environmental and technological relevance. This work presents a comprehensive theoretical investigation of its two-dimensional (2D) counterpart, Vivianene, focusing on its structural, electronic, and optical properties. Using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, we evaluate its thermodynamic stability, band structure, density of states, and optical response. Our results confirm that Vivianene retains the main structural features of bulk Vivianite while exhibiting enhanced thermodynamic stability at room temperature. The electronic structure analysis reveals an indirect bandgap of 3.03 eV for Vivianene, which is slightly lower than the 3.21 eV observed for bulk Vivianite, deviating from the expected quantum confinement trend in 2D materials. The projected density of states (PDOS) analysis indicates that Fe d orbitals predominantly contribute to the valence and conduction bands. Optical calculations demonstrate that Vivianene exhibits a higher optical band gap (3.6 eV) than bulk Vivianite (3.2 eV), with significant absorption in the ultraviolet region. The refractive index and reflectivity analyses suggest that most of the incident light is absorbed rather than reflected, reinforcing its potential for optoelectronic applications. These findings provide valuable insights into the fundamental properties of Vivianene and highlight its potential for advanced applications in sensing, optoelectronics, and energy-related technologies.

cond-mat.mtrl-sci↗

arXiv2025

Emamectin benzoate sensing using vivianenes (2D vivianites)

The excessive application of pesticides, particularly the overreliance on insecticides for the protection of desirable crops from pests, has posed a significant threat to both ecological systems and human health due to environmental pollution. This research outlines a comprehensive approach to recognizing and quantifying the presence of insecticides through the application of spectroscopic and electrochemical sensing methods. The detection of Emamectin benzoate (EB), a commonly used insecticide, was performed utilizing vivianenes, a 2D phosphate that has been mechanically exfoliated from the naturally occurring vivianite minerals. This investigation examined the structural and compositional characteristics of vivianenes, utilizing a range of characterization methods. The spectroscopic analyses reveal the molecular interactions and structural modifications that take place during the interaction of EB with the 2D template. Electrochemical investigations employing cyclic voltammetry were performed for different concentrations of EB to enable real-time monitoring of the pesticide. The modified sensing electrode using vivianene demonstrated a linear range of from 50 mg/L to 10 micro g/L, effectively detecting EB molecules at levels significantly below the hazardous threshold. Fully atomistic molecular dynamics simulations were also carried out to obtain further insights into the interaction mechanisms of the EB with the vivianites, and the results corroborate the adsorption mechanism. Our results highlight the potential application of 2D phosphate minerals as advanced sensors to enhance agricultural monitoring and promote sustainable development.

physics.chem-ph↗

arXiv2024

Structural, mechanical, and electronic properties of single graphyne layers based on a 2D biphenylene network

Graphene is a promising material for the development of applications in nanoelectronic devices, but the lack of a band gap necessitates the search for ways to tune its electronic properties. In addition to doping, defects, and nanoribbons, a more radical alternative is the development of 2D forms with structures that are in clear departure from the honeycomb lattice, such as graphynes, with the distinctive property of involving carbon atoms with both hybridizations sp and sp2. The density and details of how the acetylenic links are distributed allow for a variety of electronic signatures. Here we propose a graphyne system based on the recently synthesized biphenylene monolayer. We demonstrate that this system features highly localized states with a spin-polarized semiconducting configuration. We study its stability and show that the system's structural details directly influence its highly anisotropic electronic properties. Finally, we show that the symmetry of the frontier states can be further tuned by modulating the size of the acetylenic chains forming the system.

cond-mat.mes-hall↗

arXiv2023

Electronic properties of two-dimensional rectangular graphyne based on phenyl-like building blocks

A rectangular graphyne sheet is composed of units similar to phenyl rings that are linked by acetylenic chains, as in hexagonal $γ$-graphyne. This system is organized over a rectangular lattice similar to that of the recently synthesized biphenylene network. We investigate the stability of this sheet from different perspectives and study its electronic structure. Rectangular graphyne is a semiconducting system in its pristine form and features a pair of highly localized states. These characteristics are correlated with the structural anisotropy of the system, since its frontier states behave like quasi--1D states embedded in the 2D lattice. We further consider modified systems in which longer acetylenic links are introduced. We discuss how a strategic choice of the position of these longer bridges can lead to specific changes of the electronic structure of the rectangular graphyne sheet.

cond-mat.mtrl-sci↗

arXiv2021

Dynamical Formation of Graphene and Graphane Nanoscrolls

Carbon nanoscrolls (CNSs) are nanomaterials with geometry resembling graphene layers rolled up into a spiral (papyrus-like) form. Effects of hydrogenation and temperature on the self-scrolling process of two nanoribbons interacting with a carbon nanotube (CNT) have been studied by molecular dynamics simulations for three configurations: (1) graphene/graphene/CNT; (2) graphene/graphane/CNT, and (3) graphane/graphane/CNT. Graphane refers to a fully hydrogenated graphene nanoribbon. Nanoscroll formation is observed for configuration (1) and (2) for temperatures 300-1000 and 300-600 K, respectively, while nanoribbons wrap CNT without nanoscroll formation for configuration (3).

cond-mat.mtrl-sci↗