Elvis Lopez - Academia.edu (original) (raw)

Papers by Elvis Lopez

Materials Today Sustainability

Open Chemistry, 2021

In the last years, supercapacitors (SCs) have been proposed as a promising alternative to cover t... more In the last years, supercapacitors (SCs) have been proposed as a promising alternative to cover the power density deficiency presented in batteries. Electrical double-layer SCs, pseudocapacitors, and hybrid supercapacitors (HSCs) have shown very attractive features such as high-power density, long cycle life, and tunable specific capacitance. The advances of these energy storage devices made by transition metal oxides (TMOs) and their production in pseudocapacitors and HSCs depend on chemical composition, crystalline structure, morphology, theoretical capacitance, and oxidation states. In this way, this critical review considers several metal oxides (RuO2, MnO2, V2O5, and Co3O4) and their different configurations with diverse carbon-based materials. Energy storage mechanisms and fundamental principles to understand the promising effect of metal oxides in SCs devices are thoroughly described. Special attention as regards to the energy storage mechanisms relative to the specific capac...

Materials Chemistry and Physics, 2019

Hydroxyapatite (HA) is the main constituent of bone mineral in vertebrates and is widely used as ... more Hydroxyapatite (HA) is the main constituent of bone mineral in vertebrates and is widely used as a biomaterial in biomedical studies and medical clinics. The synthesis of this calcium phosphate phase is a crucial factor in its potential use in various applications as well as in understanding the nucleation and growth processes in biological mineralization (biomineralization). In this work, a sequential analysis of the different steps of HA synthesis in aqueous media was performed by using cryotransmission electron microscopy (Cryo-TEM), which allows preservation of the specimens at different stages of the synthesis process, preventing their modification during drying. X-ray energy dispersive spectroscopy and electron diffraction, in addition to high-resolution imaging, were performed on vitrified samples. We showed that drying a specimen from the synthesis solution induces the crystallization of nanoparticles into an HA phase after 30 min of reaction, while when analyzed by Cryo-TEM, crystalline nanoparticles were detected only after 15 h. Calcium phosphate nanoparticles presented three different morphologies: irregular shapes characterized by low contrast in TEM (5 min), isotropic shapes with well-defined contrast (10 min) and needle-like shapes (after 30 min). The long axis of the HA needle-like nanoparticles can be associated with the c-axis direction of the hexagonal unit cell, which can thus be assigned to the preferential crystallization direction. However, a diffraction signal of the nanoparticles in vitreous ice that "mimics" the original solution was detected by Cryo-TEM only after 15 h of synthesis. These apparently controversial results are discussed

New Journal of Chemistry, 2018

Functional groups may alter the optical and electrical characteristics of graphene quantum dots a... more Functional groups may alter the optical and electrical characteristics of graphene quantum dots and lead to unusual properties and related applications.

physica status solidi (a), 2018

In this work, the authors present a study of the resistive switching effect (RS) in Co 0.2 TiO 3.... more In this work, the authors present a study of the resistive switching effect (RS) in Co 0.2 TiO 3.2 (CTO) in a thin film structure Pt/CTO/ITO. The identification of a structure of low crystallinity with different deposition times is seen in the diffractograms with a certain tendency of orientation in the plane (311) of the inverted spinel of space group Fd-3m. Electrical measurements I-V highlight the appearance of RS effect predominated by unipolar filamentary mechanism. The retention of charge in the device shows good stability and separation of HRS-LRS states with R OFF /R ON %10 6 ratio. The authors are able to demonstrate that Co 0.2 TiO 3.2 presents promising performance for application in non-volatile memories.

RSC Adv., 2017

In this study, magnetic nanocomposites were developed and used as adsorbents for lead and copper ... more In this study, magnetic nanocomposites were developed and used as adsorbents for lead and copper from aqueous media. Structural, surface, magnetic and textural properties of functionalized maghemite nanoparticles synthesized by alkaline co-precipitation were studied. The surfaces of the iron oxide nanoparticles (Nps) were modified with different chemical agents such as fatty and amino acids, silica (SiO 2), mesoporous silica (SBA-15), hydroxyapatite, multiwall carbon nanotubes (MWCNTs) and ethylenediaminetetraacetic acid (EDTA), obtaining NPs with mean particle sizes ranging from 7 to 16 nm according to Rietveld refinement and TEM images analysis. The physicochemical surface properties of the functionalized materials were studied via zeta potential (z) and Fourier transform infrared (FTIR) spectroscopy. Mössbauer spectroscopy (MS) as a function of temperature and DC magnetometry were used to study the magnetic properties. The superparamagnetic relaxation was studied by MS. The resolved spectra at 20 K confirm the presence of nanomaghemite phase. Besides, the saturation magnetization varies from 12 to 62 emu g À1. A nitrogen adsorption-desorption technique was used to determine the specific surface area and to study the porous structure. The functionalized g-Fe 2 O 3 Nps exhibited a Brunauer-Emmett-Teller (BET) specific surface area ranging from 74 to 214 m 2 g À1 and revealed remarkable uptake capacities to remove Cu(II) and Pb(II) species from aqueous solutions.

Advanced Materials Technologies, 2017

Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric... more Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric in wearable devices. In this work, copper selenide films are achieved by a novel low‐temperature technique, namely pulsed hybrid reactive magnetron sputtering (PHRMS). A brief introduction to the basic chemistry and physics involved during growth is included to explain its fundamentals. PHRMS is a single‐step, room temperature (RT), fabrication process carried out in another ways conventional vacuum sputtering system. It does not require high‐temperature post‐annealing to obtain films with great thermoelectric performance. It is, therefore, compatible with polymeric substrates like Kapton tape. Several sets of films covering a large exploratory compositional range (from Cu/Se = 1 to 9) are deposited and their microstructure and thermoelectric properties are analyzed at RT. Power factors as high as 1.1 mW m−1 K−2 in the in‐plane direction and thermal conductivities as low as κ = 0.8 ± 0....

Materials science & engineering. C, Materials for biological applications, 2017

Insulin-loaded calcium phosphate nanoparticles have been proposed as a potential drug delivery sy... more Insulin-loaded calcium phosphate nanoparticles have been proposed as a potential drug delivery system for the oral treatment of diabetes and to stimulate bone cell proliferation and bone mineralization. The kinetics of insulin incorporation onto hydroxyapatite (HA) and Sr (SrHA)- and Zn (ZnHA)-substituted hydroxyapatite nanoparticles was investigated using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, zeta potential measurements and circular dichroism (CD) spectroscopy. The increase in insulin concentration on HA, SrHA and ZnHA was a typical physical adsorption process controlled by electrostatic forces and followed a Freundlich isotherm model. Zn substitution enhanced the capacity of the apatite surface to adsorb insulin, whereas Sr substitution inhibited insulin uptake. The surface stoichiometry and mesopore specific area induced by Zn and Sr substitution are proposed as the main causes of the difference in insulin adsorption. Despite the ...

Colloids and surfaces. B, Biointerfaces, 2014

For gene and drug delivery applications, carbon nanotubes (CNTs) have to be functionalized in ord... more For gene and drug delivery applications, carbon nanotubes (CNTs) have to be functionalized in order to become compatible with aqueous media and bind with genetic materials. In this study, combination of polyethyleneimine (PEI) grafted multi-walled carbon nanotubes (PEI-g-MWCNTs) and chitosan substrate is used as an efficient gene delivery system for transfection of hard-to-transfect bone marrow mesenchymal stem cells (BMSCs) with enhanced green fluorescent protein (EGFP) gene. Fourier transform infrared (FT-IR) spectra, dynamic light scattering (DLS) analysis and zeta potential measurements are used to characterize binding of PEI, particle size distribution and colloidal stability of the functionalized CNTs, respectively. DNA binding affinity, cellular uptake, transfection efficiency and possible cytotoxicity are also tested by agarose gel electrophoresis, flow cytometry, cytochemisty and MTT assay. The results demonstrate that cytotoxic effect of PEI-g-MWCNTs is negligible under op...

Revista Ciencias …, 2007

Revista Ciencias Técnicas Agropecuarias Universidad Agraria de La Habana paneque@isch.edu.cu ISSN... more Revista Ciencias Técnicas Agropecuarias Universidad Agraria de La Habana paneque@isch.edu.cu ISSN (Versión impresa): 1010-2760 CUBA ... 2007 Elvis López B. / Ciro Iglesias C. / Amado Cruz C. / Miguel Herrera S. / Omar González ... C AUMENTO DE LA ...

ACS Applied Materials & Interfaces, 2013

Right angle radio frequency magnetron sputtering technique (RAMS) was redesigned to favor the pro... more Right angle radio frequency magnetron sputtering technique (RAMS) was redesigned to favor the production of high-quality hydroxyapatite (HA) thin coatings for biomedical applications. Stoichiometric HA films with controlled crystallinity, thickness varying from 254 to 540 nm, crystallite mean size of 73 nm, and RMS roughness of 1.7 ± 0.9 nm, were obtained at room temperature by tuning the thermodynamic properties of the plasma sheath energy. The plasma energies were adjusted by using a suitable high magnetic field confinement of 143 mT (1430 G) and a substrate floating potential of 2 V at the substrate-tomagnetron distance of Z = 10 mm and by varying the sputtering geometry, substrate-to-magnetron distance from Z = 5 mm to Z = 18 mm, forwarded RF power and reactive gas pressure. Measurements that were taken with a Langmuir probe showed that the adjusted RAMS geometry generated a plasma with an adequate effective temperature of T ef f ≈ 11.8 eV and electron density of 2.0 × 10 15 m −3 to nucleate nanoclusters and to further crystallize the nanodomains of stoichiometric HA. The deposition mechanism in the RAMS geometry was described by the formation of building units of amorphous calcium phosphate clusters (ACP), the conversion into HA nanodomains and the crystallization of the grain domains with a preferential orientation along the HA [002] direction.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.