Papers 2015 by Victor Guerrero
Titanium dioxide in nanoparticle form is of great technological interest since it may be used in ... more Titanium dioxide in nanoparticle form is of great technological interest since it may be used in several industrial applications. In this work, titanium dioxide nanoparticles in anatase phase were synthesized by sol-gel method using titanium oxysulphate as the precursor. Calcination temperatures used were 300 and 500°C, and calcination times were 30 and 60 minutes. FT-IR, SEM, TEM and XRD analysis were used to characterize the samples obtained. According to the results obtained, nanoparticles smaller than 10 nm can be synthetized with a calcination at 500°C during 1 hour.
Papers by Victor Guerrero
Minerals, 2022
Black mineral sands are widely used to obtain titanium dioxide, titanium, and, more recently, a v... more Black mineral sands are widely used to obtain titanium dioxide, titanium, and, more recently, a variety of iron–titanium oxide nanostructures. Highly corrosive mineral acids or alkalis are commonly employed for this purpose. Hence, it is desirable to find eco-friendly ways to process these minerals, deriving high-added value materials. In this study, an Ecuadorian mineral sand precursor (0.6FeTiO3∙0.4Fe2O3 solid solution) was treated with oxalic acid aqueous solutions under subcritical water conditions. The synthesis was conducted in a batch reactor operating at 155 °C, 50 bar, and 700 rpm for 12 h, varying the oxalic acid concentration (0.1, 0.5 to 1.0 M). The as-obtained compounds were physically separated, dried, and analyzed by X-ray powder diffraction, scanning electron microscopy, and Raman spectroscopy. The characterization showed that the precursor was completely converted into two main products, ferrous oxalate, and titanium dioxide polymorphs. Rutile was always found in th...
Revista Politécnica (Quito. En línea), 2017
La síntesis de nanopartículas de óxidos de hierro ha captado gran interés en las últimas décadas ... more La síntesis de nanopartículas de óxidos de hierro ha captado gran interés en las últimas décadas debido a sus interesantes aplicaciones, entre ellas la remoción de contaminantes. En este trabajo se sintetizaron nanopartículas de magnetita mediante el método de co-precipitación y se estudió el efecto de la velocidad de agitación y el tiempo de reacción sobre el rendimiento, el tamaño y la distribución de tamaños, además, se estudió la influencia del pH del medio de dispersión en la aglomeración de las nanopartículas. Las nanopartículas fueron caracterizadas mediante microscopía electrónica de transmisión (MET), dispersión dinámica de luz (DLS), difracción de rayos X (DRX) y espectroscopía Raman. Se observó que la velocidad de agitación y el tiempo de reacción influyen positivamente en el rendimiento de la reacción (85 a 94 %), tamaño (23 ± 13 a 7 ± 4 nm) y distribución de tamaño de las nanopartículas. Para las mejores condiciones de síntesis se obtuvieron nanopartículas de magnetita ...
Materials, 2022
Magnetic composites obtained by impregnation of lignocellulosic biomass with magnetite nanopartic... more Magnetic composites obtained by impregnation of lignocellulosic biomass with magnetite nanoparticles were used for zinc(II) removal from aqueous synthetic solutions. Laurel, canelo and eucalyptus sawdust, with a particle size between 74 and 150 µm were used as support. Structural and morphological examinations of the composites confirmed the presence of magnetite nanoparticles in the lignocellulosic support. Transmission Electron Microscopy showed nanoparticles with diameters of about 20 nm. The maximum removal efficiencies for 7 g L−1 of modified adsorbent were increased to 98.9, 98.8 and 97.6% for laurel, canelo and eucalyptus magnetic composites, respectively, in comparison to 60.9, 46.0 and 33.3%, for corresponding unmodified adsorbents. Adsorption data was analyzed using pseudo-first, pseudo-second order and intra-particle diffusion kinetic models and various isotherm models. The results determined that Freundlich isotherm fits the Zn ions adsorption on magnetite modified adsor...
Resumen: El dioxido de titanio nanoparticulado es de gran interes tecnologico pues se puede utili... more Resumen: El dioxido de titanio nanoparticulado es de gran interes tecnologico pues se puede utilizar en diversas aplicaciones industriales. En este trabajo se sintetizaron nanoparticulas de TiO2 en fase anatasa mediante el metodo de sol-gel, utilizando oxisulfato de titanio como precursor. Las condiciones de sintesis ensayadas incluyeron temperaturas de 300 y 500 °C y tiempos de 30 y 60 minutos para la calcinacion. Las nanoparticulas fueron caracterizadas mediante espectrofotometria de infrarrojo, dispersion dinamica de luz, microscopia electronica de transmision y difraccion de rayos X. Los resultados obtenidos permitieron determinar que las mejores condiciones de sintesis incluyen calcinacion a 500 °C durante 1 hora, con lo cual se obtuvo particulas de tamano menor a 10 nm.Abstract: Titanium dioxide in nanoparticle form is of great technological interest since it may be used in several industrial applications. In this work, titanium dioxide nanoparticles in anatase phase were synt...
Resumen: Se obtuvo carbon activado a partir de 3 tipos de aserrin de madera: laurel, canelo y euc... more Resumen: Se obtuvo carbon activado a partir de 3 tipos de aserrin de madera: laurel, canelo y eucalipto, mediante activacion quimica. El proceso de activacion consistio en impregnar al aserrin con acido fosforico al 40 % w/w en proporcion 1:1, posteriormente el material se carbonizo a 500 °C durante 2 h y finalmente fue lavado para eliminar los residuos de acido y alcanzar un pH neutro. Se obtuvo el mayor rendimiento con el laurel (29.3 %) para un tamano de particula mayor a 2 mm. Mediante microscopia electronica de barrido (SEM) se observaron las estructuras porosas que se formaron a partir del proceso de activacion. La capacidad de adsorcion se evaluo mediante el indice de yodo, donde se obtuvo que el canelo presenta el mayor valor correspondiente a 740 mg I 2 /g para la muestra de tamano de particula entre 74 y 150 µm. Con base en los resultados obtenidos se puede evidenciar que para una misma variedad de madera, a menor tamano de particula, aumenta la capacidad de adsorcion. Abs...
IOP Conference Series: Earth and Environmental Science, 2021
The removal of heavy metals from water is one of the major challenges that humanity must address ... more The removal of heavy metals from water is one of the major challenges that humanity must address to avoid negative potential impacts on the environment and human health. During the last few years, several adsorbents have been examined, in a search for highly efficient and cost-effective materials. In this work, we investigated the use of laurel, canelo and eucalyptus lignocellulosic sawdust residues (LRs) impregnated with magnetite nanoparticles (MNP), to remove Cr6+ ions. Each LR was added to an aqueous solution in which MNP were being synthesized by coprecipitation. Two composite adsorbents were obtained, with LR:MNP ratios of 1:1 and 3:1. The materials obtained were characterized by X-ray diffraction, scanning and transmission electron microscopy, and infrared and Raman spectroscopy. The results obtained showed that the laurel composite was the best adsorbent, reaching a maximum removal efficiency and capacity of 99.8 % and 30.5 mg/g, respectively. The optimal contact time was 30...
Resumen: En este trabajo se sintetizaron nanoparticulas de oxido de zirconio mediante el metodo d... more Resumen: En este trabajo se sintetizaron nanoparticulas de oxido de zirconio mediante el metodo de sol-gelutilizando como precursor oxicloruro de zirconio octahidratado y acetato de calcio monohidratado como estabilizadorde las estructuras de zirconia, en una relacion molar precursor/estabilizante de 0,84/0,16. Ademas, se utilizoetilenglicol como disolvente polimerizable, glicina como regulador del pH y agua destilada como agente hidrolizante.Los parametros que se tomaron en consideracion para la sintesis fueron el tiempo de reaccion, pH y agitacion. Lasvariables estudiadas fueron las temperaturas y el tiempo de calcinacion del sol-gel obtenido en la sintesis. Al finalizareste proceso se obtuvo un polvo fino y blanco, con estructura cristalina cubica, de acuerdo con lo establecido mediantedifraccion de rayos X. El tamano de las nanoparticulas obtenidas fue de 5 o 7 nm, aproximadamente, dependiendo sila calcinacion se realiza a 600 o 550 °C durante 30 min. Para determinar estos taman...
Journal of Materials Research and Technology, 2020
Summary Inorganic nanotubes are promising fillers for polymer composites. Among them, pristine pr... more Summary Inorganic nanotubes are promising fillers for polymer composites. Among them, pristine protonated titanate nanotubes (p-TTNT), with high specific surface area and abundant hydroxyl surface groups, are good candidates for reinforcing amine-cured epoxy systems. Thus, epoxy composites filled with p-TTNT (≤3.0 wt. %, i.e. ≤ 1.1 vol. %) were prepared and their effect on the mechanical properties of the polymer matrix was studied. Young’s modulus (E) and hardness (H) of the composites increased up to 19 and 17 %, respectively, as demonstrated by microindentation tests, for 3.0 wt. % of p-TTNT, without functionalization. These increments could be attributed to the mutual compatibility, derived from the polar natures of p-TTNT and amine-cured epoxy, through the formation of hydrogen bonds. The wear resistance (H/E) of composites was maintained, independently of the p-TTNT content. Additionally, micromechanical models were successfully employed to predict the influence of the p-TTNT filler on the Young’s modulus and hardness of the as-prepared composites.
Minerals, 2021
Ecuadorian black mineral sands were used as starting material for the production of iron-titanium... more Ecuadorian black mineral sands were used as starting material for the production of iron-titanium oxide nanostructures. For this purpose, two types of mineral processing were carried out, one incorporating a pre-treatment before conducting an alkaline hydrothermal synthesis (NaOH 10 M at 180 °C for 72 h), and the other prescinding this first step. Nanosheet-assembled flowers and nanoparticle agglomerates were obtained from the procedure including the pre-treatment. Conversely, nanobelts and plate-like particles were prepared by the single hydrothermal route. The nanoscale features of the product morphologies were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The ilmenite and hematite molar fractions, within the ilmenite-hematite solid solution, in the as-synthetized samples were estimated by Brown’s approach using the computed values of unit-cell volumes from Le Bail adjustments of X-ray powder diffraction (XRPD) patterns. The re...
Data in Brief, 2020
Data revealing the phase and chemical compositions of natural black sands from "El Ostional" beac... more Data revealing the phase and chemical compositions of natural black sands from "El Ostional" beach, located in the northern Ecuadorian Pacific coast have been presented. The samples were collected from six points over the shore area of approximately 500 × 40 m 2. The data on crystalline phases (iron titanium oxide, orthoclase feldspar and zircon) were determined by X-ray powder diffraction (XRPD), while semiquantitative chemical analyses of major (Fe and Ti) and trace elements were obtained by X-ray fluorescence spectroscopy (XRF). The phase composition was verified by scanning electron microscopy (SEM), using backscattered electron (BSE) mode and energy dispersive spectroscopy (EDS). These comprehensive data are a contribution to valorize ilmenitehematite solid solutions from natural resources towards the identification of novel technological applications.
Science of The Total Environment, 2020
Biofiltration is one of the main alternatives developed to improve wastewater quality and increas... more Biofiltration is one of the main alternatives developed to improve wastewater quality and increase its recyclability. Support materials are extremely important when using this technology since they impact the cost of the treatment. In this work, we study the use of wood chips/peanut shell as support medium within biofilters incorporating microorganisms (BM), plants and microorganisms (BPM), earthworms and microorganisms (BEM) and all organisms (hybrid biofilters, HB). These typologies were evaluated to remove organic matter from synthetic domestic wastewater. For this purpose, twelve biofilters were operated in parallel under three different nominal hydraulic rates (0.5, 1 and 1.5 m3 m-2 day-1). Previously, support materials were individually characterized and acute/chronic toxicity tests on plants (Eleocharis palustris (L.) Roem. & Schult.) and earthworms (Eisenia foetida Savigny) were driven. Results showed that both materials have good adsorbent properties, providing adequate environmental conditions for biofiltration. Moreover, non toxicological response was reported when a 25 v/v % peanut shell fraction was selected. With this fraction used in every biofilter studied, the average hydraulic conductivity was between 321 and 502 mm h-1, reaching organic matter removal efficiencies close to 80% (measured as COD), and between 40 and 63% (measured as VS). Higher efficiencies, attributed to the longer contact times, and lower clogging were observed at lower hydraulic rates. The incorporation of earthworms and plants improved the solids removal and reduced clogging. The statistical analysis indicated that the results obtained for biofilters operating at 0.5 m3 m-2 day-1 showed significant differences (p < 0.05) with respect to the other rates. Moreover, BEM were the ones that presented significant differences. As a conclusion, low-cost organic materials (wood chip/peanut shell mix) can be successfully used as support medium, since they provide adequate environmental conditions for plants and earthworms, improving the operation and maintaining contaminant (organic matter) removal within biofiltration typologies.
Journal of Materials Science, 2002
The tailoring of the thermoelectric properties (the sign and magnitude of the absolute thermoelec... more The tailoring of the thermoelectric properties (the sign and magnitude of the absolute thermoelectric power) was achieved by composite engineering. The techniques involved the choice of the reinforcing fibers (continuous or short) in a structural composite and the choice of the particulate filler between the laminae in a continuous fiber composite. The tailoring resulted in thermoelectric structural composites, including continuous
ACS Applied Nano Materials, 2019
Polymeric-based microparticles and fibers are tailorable for a wide range of common industrial an... more Polymeric-based microparticles and fibers are tailorable for a wide range of common industrial and biomedical applications, while multi-walled carbon nanotubes (MWCNTs) are among the most useful macromolecules based on their outstanding electronic, mechanical, and optical properties at the nanoscale. By combining these nanostructures with various polymeric precursors, their range of potential applications becomes even greater. One of the simplest and most affordable methods for fabricating micro and nanostructures is electrospinning. Herein we demonstrate how MWCNTs may be used to produce tailor-made organic-organic poly(vinylpyrrolidone) (PVP) microparticles and fibers via electrospinning by studying their structural, vibrational, rheological and mechanical properties’ dependence on their solvent (ethanol (EtOH) or dimethylformamide (DMF)) and resulting morphology. Specifically, we find clear differences in morphologies from perfectly spherical and isolated microparticles to fibers mats, or a combination...
In this work, the effect of adding montmorillonite nanoclays as reinforcement to a polypropylene ... more In this work, the effect of adding montmorillonite nanoclays as reinforcement to a polypropylene (PP) matrix is studied. The reinforcing clay was used as powder and masterbatch, with loads of 3, 5, 7 wt%. Maleic anhydride grafted polypropylene (PP g MA) was also added as compatibilizer, in 1:2; 1:1 and 2:1 ratios of PP-g- MA: clay. The clays and the compatibilizer were added to the PP matrix using a twin screw extruder. The obtained nanocomposite pellets were injected to obtain tensile, bending and impact test specimens according to standards ASTM D638-10, D7264-07 and D256-10, respectively. Thermal stability of the materials was analyzed using thermogravimetric analysis (TGA). The 5 wt% nanocomposites showed the best mechanical properties compared to the original matrix; with improvements of 4% in tensile strength and 59% in elastic modulus. Enhancements of 40% in the bending strength and 57% in bending modulus were also observed. Nonetheless, a reduction in the impact strength of ...
The search for inexpensive and environmentally friendly alternatives for used motor oil (UMO) pur... more The search for inexpensive and environmentally friendly alternatives for used motor oil (UMO) purification has become a topic of research. In this study, the use of bentonite clay modified by acid activation is proposed. Sulfuric acid, acetic acid (v-acid/w-clay ratio=20, 40 and 60%) and sulfuric/acetic mixtures (1:1 ratio) were used in the bentonite clay activation. The activated clays were used in the UMO treatment in a ratio of 1:4 w/v, using batch adsorption processes (contact time=12 min). To determine the structural and morphological modifications produced by the acid activation process, the clays were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The oil clarification efficiency was quantified by UV-Vis spectroscopy, acidity, alkalinity and viscosity index. It was determined that sulfuric acid and the sulfuric/acetic activations presented a similar bentonite structure transformation, which appears in the cations ...
Resumen —La eliminacion de metales pesados de las aguas residuales es un problema de interes mund... more Resumen —La eliminacion de metales pesados de las aguas residuales es un problema de interes mundial, debido a los efectos perjudiciales sobre el medio ambiente. El uso de arcillas activadas es uno de los metodos de tratamiento prometedor que se esta siendo investigando. En este trabajo se estudia la capacidad de remocion de niquel (II) de soluciones sinteticas utilizando arcillas modificadas quimicamente. En cuanto al proceso de modificacion quimica, se muestra que el uso de una sal de sodio aumenta la capacidad de intercambio cationico de 32 meq/100 g de arcilla a 50 meq/100 g de arcilla. Esto es debido al cambio del espacio interlaminar entre las capas de la arcilla.Para la medicion de la capacidad de remocion de niquel (II) utilizando la arcilla activada, se prepararon varias soluciones sinteticas de niquel usando 1 g/l de niquel (II) y se vario el pH y la concentracion de arcilla. La arcilla se caracterizo por tecnicas instrumentales tales como la difraccion de rayos X (DRX) ,d...
En este trabajo se utilizo el proceso de estratificacion manual para obtener compuestos de matriz... more En este trabajo se utilizo el proceso de estratificacion manual para obtener compuestos de matriz poliester reforzados con fibra de abaca. Se usaron fibras continuas unidireccionales y fibras cortas distribuidas aleatoriamente. Las longitudes consideradas para la fibra corta fueron 5 y 10 mm. Para las dos configuraciones de refuerzo se propusieron cuatro fracciones volumetricas nominales:0.20; 0.25; 0.30; y 0.35. El objetivo del trabajo fue estudiar la influencia de las variables descritas en las propiedades mecanicas de los materiales formulados. Para este proposito, los especimenes fabricados fueron sometidos a ensayos de traccion y flexion. Los resultados obtenidos mostraron que el compuesto unidireccional reforzado con una fraccion volumetrica de fibra de abaca de 0.30 exhibio las mejores propiedades mecanicas. La resistencia y el modulo a traccion de este material fueron aproximadamente 270 y 124% mayores que en la matriz. La resistencia y el modulo a flexion mejoraron alrededo...
Se sintetizaron nanoparticulas de plata utilizando el metodo de poliol mediante reduccion de nitr... more Se sintetizaron nanoparticulas de plata utilizando el metodo de poliol mediante reduccion de nitrato de plata con etilenglicol. Se estudio el efecto de la temperatura y de la cantidad de polivinilpirrolidona (PVP) anadida. Las temperaturas utilizadas fueron 100, 120 y 140 °C y se usaron tres relaciones de porcentaje en peso de PVP/AgNO3: 0.00; 0.25 y 0.50 a fin de controlar el crecimiento de las particulas. Se obtuvieron tamanos entre 15 y 30 nm al trabajar a 120°C y porcentaje en peso de PVP/AgNO3 de 0.50 y pudieron ser observadas con ayuda del microscopio electronico de transmision. Se utilizo la tecnica de inmersion, secado y curado para depositar las nanoparticulas de plata en dos telas de algodon en concentraciones de 10 y 20 ppm. A fin analizar las propiedades bactericidas adquiridas por las telas se las sometio a la accion de la bacteria Gram positiva Staphylococcus Aureus 25923. Los resultados indicaron que la tela tipo 1 impregnada con 20 ppm mostro las mejores caracteristi...
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Papers 2015 by Victor Guerrero
Papers by Victor Guerrero