Ronaldo Batista - Academia.edu (original) (raw)

Papers by Ronaldo Batista

The Journal of Physical Chemistry C

Materials Research

The characterization studies of tailings from mining are crucial for the development of its reuse... more The characterization studies of tailings from mining are crucial for the development of its reuse processes and the reduction of impacts caused by its conditioning on the earth's surface. This study characterizes the magnetic tailings from phosphate-rock processing using X-ray diffraction, X-ray fluorescence spectrometry and quantitative electron microscopy techniques. Samples were obtained from the magnetic tailings deposit of a mining company in the Alto Paranaíba region, Minas Gerais. The tailings are mainly composed of hematite/magnetite (74.92%), ilmenite (8.91%), fluorapatite (8.8%), anatase (3.07%), calcite (1.67%), goethite (1.62%), and quartz (1.02%). The particle size of the tailings is smaller than that specified for the production of sinter feed. The hematite/magnetite phase is strongly associated with ilmenite and fluorapatite. New stages of comminution and separation are needed due to the low degree of liberation of these minerals for a possible reuse of the components.

Materials Chemistry and Physics, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Microporous and Mesoporous Materials, 2018

grafted into mesoporous silica nanoparticles as benznidazol carrier for Chagas diseases treatment... more grafted into mesoporous silica nanoparticles as benznidazol carrier for Chagas diseases treatment, Microporous and Mesoporous Materials (2018),

Journal of the Mechanical Behavior of Biomedical Materials, 2021

Economic viability and eco-friendliness are important characteristics that make implants availabl... more Economic viability and eco-friendliness are important characteristics that make implants available to the population in a sustainable way. In this work, we evaluate the performance of a low-cost, widely available, and eco-friendly material (talc from soapstone) relative to reduced graphene oxide as reinforcement to brittle hydroxyapatite coatings. We employ a low-cost and straightforward technique, electrodeposition, to deposit the composite coatings on the titanium substrate. Corrosion, wear, and biocompatibility tests indicate that the reduced graphene oxide can be effectively replaced by talc without reducing the mechanical, anticorrosion, and biocompatible composite coatings properties. Our results indicate that talc from soapstone is a promising material for biomedical applications.

Journal of Materials Science, 2022

Carbon, 2021

Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental effo... more Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental efforts to obtain such structures are in initial stage. Recent high-pressure experiments provided significant advancements in the field, however, expected properties of a 2D-like diamond such as sp 3 content, transparency and hardness, have not been observed together in a compressed graphene system. Here, we compress few-layer graphene samples on SiO 2 /Si substrate in water and provide experimental evidence for the formation of a quenchable hard, transparent, sp 3-containing 2D phase. Our Raman spectroscopy data indicates phase transition and a surprisingly similar critical pressure for two-, five-layer graphene and graphite in the 4e6 GPa range, as evidenced by changes in several Raman features, combined with a lack of evidence of significant pressure gradients or local non-hydrostatic stress components of the pressure medium up to z 8 GPa. The new phase is transparent and hard, as evidenced from indentation marks on the SiO 2 substrate, a material considerably harder than graphene systems. Furthermore, we report the lowest critical pressure (z 4 GPa) in graphite, which we attribute to the role of water in facilitating the phase transition. Theoretical calculations and experimental data indicate a novel, surfaceto-bulk phase transition mechanism that gives hint of diamondene formation.

We have investigated the diffusion and structure of TIP4P/2005 water confined in carbon nanotubes... more We have investigated the diffusion and structure of TIP4P/2005 water confined in carbon nanotubes subjected to external electric fields. A wide range of diameters has been used to show a highly size-dependent behavior of the water diffusion. We also found that the diffusion is extremely affected by the intensity of the applied field. However, is the relative direction between the field and the tube axis that causes the most intriguing behavior. Electric fields forming angles of 0^∘ and 45^∘ with the tube axis were found to slow down the water dynamics by increasing organization, while fields perpendicular to the tube axis can enhance water diffusion in some cases by decreasing the hydrogen bond formation. Remarkably, for the 1.2 nm diameter long (9,9) nanotube, the field along the tube axis melts the water structure increasing the water mobility. These results points out that the structure and dynamics of confined water are extremely sensitive to external fields and suggest the use ...

We investigate by means of DFT/GGA+U calculations the electronic and structural properties of mag... more We investigate by means of DFT/GGA+U calculations the electronic and structural properties of magnetic nanotubes composed of an iron oxide monolayer and (n,0) Boron Nitride (BN) nanotubes, with n ranging from 6 up to 14. The formation energy per FeO molecule of FeO covered tubes is smaller than the formation energy of small FeO nanoparticles which suggest that the FeO molecules may cover the BN nanotubes rather than to aggregate to form the FeO bulk. We propose a continuous model for the FeO covered BN nanotubes formation energy which predicts that BN tubes with diameter of roughly 13 \AA are the most stable. Unlike carbon nanotubes, the band structure of FeO covered BN nanotubes can not be obtained by slicing the band structure of a FeO layer, the curvature and the interaction with the BN tube is determinant for the electronic behavior of FeO covered tubes. As a result the tubes are semiconductors, intrinsic half-metals or semi-half-metals that can become half-metals charged with e...

Water desalination through nanopores has been shown to be a promising alternative to the currentl... more Water desalination through nanopores has been shown to be a promising alternative to the currently water purification processes. In spite the results in this direction obtained by means of computational simulations were animating there are still pending issues to be resolved. For example, water desalination involves macro numbers (in size and time) but in such a scale it is literally impossible to attack this problem using all-atoms simulations. It is common to extrapolate results from nano to macro sizes in order to estimate quantities of interest, which must be taken with care. Here we present a simple model which mimics the separation of salt from water, which may help to attack bigger problems on water desalination subjects. Besides, we show that the investigation of a restrict space of parameters imposed by expensive models may hidden interesting, important features involved in the water desalination problem. Finally, we present an analytical calculation which explains the rich...

Biointerface Research in Applied Chemistry, 2021

The incorporation of nanoparticles on polymer films is possible to obtain materials with desired ... more The incorporation of nanoparticles on polymer films is possible to obtain materials with desired properties. In the present work, we address the physical-chemical influence of nanoparticles in polymer films by producing and characterizing polyaniline hybrids with SiO2 and Au nanoparticles and comparing them with films with TiO2 nanoparticles. The hybrid films were characterized by SEM, EDS, UV-Vis, AFM, Raman, and cyclic voltammetry. Unlike TiO2 nanoparticles, SiO2 and Au nanoparticles do not promote any noticeable change in polyaniline oxidation state in less acid environments (pH 5.9 and 6.15). However, in those environments, the presence of nanoparticles significantly increases the film's conductivity. At a pH of 1.5 and 3.9, all three kinds of nanoparticles are screened by ions from the solution diminishing their physical-chemical effects on polyaniline. Thus, our results suggest that, in general, nanoparticles don't have any physical-chemical effects on polyaniline film...

Bulletin of the American Physical Society, 2008

We perform first-principles calculations to investigate electronic and structural properties of g... more We perform first-principles calculations to investigate electronic and structural properties of graphene with a layer of deposited Au nanoparticles. We consider Au38 nanoparticles that can be either covered with methylthiol molecules, or not. We also consider that the nanoparticles are arranged in a hexagonal lattice, and we focus on the effect of net charge, applied electric fields, and molecular coverage

We investigate the diffusion and structure of TIP4P/2005 water confined in carbon nanotubes under... more We investigate the diffusion and structure of TIP4P/2005 water confined in carbon nanotubes under the effect of electric field. For nanotubes with distinct diameters we vary the intensity and the direction of the electric field. We show that the nanotube diameter, the field intensity and the relative direction between field and tube axis change the water diffusion. For the (9,9) nanotube, the field along the tube axis melts the water structure increasing the water mobility. Our results suggest the use of electric field as a facilitator for filtration processes.

Surface and Coatings Technology, 2020

Abstract Mechanical resistant bioactive materials are of high interest for biomedical application... more Abstract Mechanical resistant bioactive materials are of high interest for biomedical applications. In this work, we address the improvement in mechanical properties of HA coatings by the addition of a cheap and widely available secondary phase material, the talc from soapstone. The composites hydroxyapatite/talc (HA/talc) were successfully obtained by pulsed electrodeposition and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, corrosion and wear resistance and biocompatibility tests. We found that the addition of talc greatly improves the mechanical properties of coatings (i. e., wear track and friction coefficient in wear tests were significantly diminished) without diminishing corrosion resistance and biocompatibility. Alamar Blue® tests, alkaline phosphatase activity, and collagen production indicate that the biocomposites are biocompatible and talc itself induce bone maturation.

The Journal of Physical Chemistry C, 2018

We propose, based on results of first-principles calculations, that nanoporous graphene and h-BN ... more We propose, based on results of first-principles calculations, that nanoporous graphene and h-BN might be efficiently produced from B–C–N layers as precursors. In our calculations, we find that the removal of the h-BN islands that naturally occur in BN-doped graphene, forming nanoporous graphene, requires less energy than if pristine graphene is used as a precursor. The same reduction ΔEf in pore formation energy is found for nanoporous h-BN obtained from graphene-doped BN as a precursor. ΔEf is found to increase linearly as a function of the number of B–C and N–C bonds at the island boundary, with the slope being nearly the same for either porous graphene or porous h-BN. This is explained by an analytical bond-energy model. In the case of porous graphene, we find that the pore formation energy would be further reduced by passivation by pyridinic and quaternary remnant nitrogen atoms at the pore edges, a mechanism that is found to be more effective than the passivation by hydrogen atoms. Both mechanisms f...

Physica A: Statistical Mechanics and its Applications, 2018

ACS nano, Jan 22, 2018

Graphene is regarded as the toughest two-dimensional material (highest in-plane elastic propertie... more Graphene is regarded as the toughest two-dimensional material (highest in-plane elastic properties) and, as a consequence, it has been employed/proposed as an ultrathin membrane in a myriad of microfluidic devices. Yet, an experimental investigation of eventual variations on the apparent elastic properties of a suspended graphene membrane in contact with air or water is still missing. In this work, the mechanical response of suspended monolayer graphene membranes on a microfluidic platform is investigated via scanning probe microscopy experiments. A high elastic modulus is measured for the membrane when the platform is filled with air, as expected. However, a significant apparent softening of graphene is observed when water fills the microfluidic system. Through molecular dynamics simulations and a phenomenological model, we associate such softening to a water-induced uncrumpling process of the suspended graphene membrane. This result may bring substantial modifications on the desig...

ACS nano, Jan 25, 2018

The ability to create materials with improved properties upon transformation processes applied to... more The ability to create materials with improved properties upon transformation processes applied to conventional materials is the keystone of materials science. Here, hexagonal boron nitride (h-BN), a large-band-gap insulator, is transformed into a conductive two-dimensional (2D) material- bonitrol-that is stable at ambient conditions. The process, which requires compression of at least two h-BN layers and hydroxyl ions, is characterized via scanning probe microscopy experiments and ab initio calculations. This material and its creation mechanism represent an additional strategy for the transformation of known 2D materials into artificial advanced materials with exceptional properties.