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Morant, Carmen

Publications and source records attributed to Morant, Carmen.

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Biomimetic Catalysts Based on Au@ZnO–Graphene Composites for the Generation of Hydrogen by Water Splitting

For some decades, the scientific community has been looking for alternatives to the use of fossil fuels that allow for the planet’s sustainable and environmentally-friendly development. To do this, attempts have been made to mimic some processes that occur in nature, among which the photosystem-II stands out, which allows water splitting operating with different steps to generate oxygen and hydrogen. This research presents promising results using synthetic catalysts, which try to simulate some natural processes, and which are based on Au@ZnO–graphene compounds. These catalysts were prepared by incorporating different amounts of gold nanoparticles (1 wt.%, 3 wt.%, 5 wt.%, 10 wt.%) and graphene (1 wt.%) on the surface of synthesized zinc oxide nanowires (ZnO NWs), and zinc oxide nanoparticles (ZnO NPs), along with a commercial form (commercial ZnO) for comparison purposes. The highest amount of hydrogen (1127 μmol/hg) was reported by ZnO NWs with a gold and graphene loadings of 10 wt.% and 1 wt.%, respectively, under irradiation at 400 nm. Quantities of 759 μmol/hg and 709 μmol/hg were obtained with catalysts based on ZnO NPs and commercial ZnO, respectively. The photocatalytic activity of all composites increased with respect to the bare semiconductors, being 2.5 times higher in ZnO NWs, 8.8 times higher for ZnO NPs, and 7.5 times higher for commercial ZnO. The high photocatalytic activity of the catalysts is attributed, mainly, to the synergism between the different amount of gold and graphene incorporated, and the surface area of the composites.

Machín, Abniel (ORCID:0000000341343344)↗
DOE OSTI2020

0D-1D Hybrid Silicon Nanocomposite as Lithium-Ion Batteries Anodes

Lithium ion batteries (LIBs) are the enabling technology for many of the societal changes that are expected to happen in the following years. Among all the challenges for which LIBs are the key, vehicle electrification is one of the most crucial. Current battery materials cannot provide the required power densities for such applications and therefore, it makes necessary to develop new materials. Silicon is one of the proposed as next generation battery materials, but still there are challenges to overcome. Poor capacity retention is one of those drawbacks, and because it is tightly related with its high capacity, it is a problem rather difficult to address with common and scalable fabrication processes. Here we show that combining 0D and 1D silicon nanostructures, high capacity and stability can be achieved even using standard electrode fabrication processes. Capacities as high as 1200 mAh/g for more than 500 cycles at high current densities (2 A/g) were achieved with the produced hybrid 0D/1D electrodes. In this research, it was shown that while 0D nanostructures provide good strain relaxation capabilities, 1D nanomaterials contribute with enhanced cohesion and conductive matrix integrity.

0D↗
DOE OSTI2019

Synthesis Procedure of Highly Densely Packed Carbon Nanotube Forests on TiN

The goal of this research was to obtain high-density single-walled carbon nanotube forests (SWNTs) on conductive substrates for different applications, including field emission. For this, dip-coating was chosen as the catalyst deposition method, to subsequently grow SWNTs by Alcohol Catalytic Chemical Vapor Deposition (AC-CVD). Si (100) was chosen as the substrate, which was then coated with a TiN thin film. By sputtering with Ar, it was possible to generate alternating TiN and Si lanes, with a different wettability and, therefore, a different affinity for the catalysts. As a result, the Mo-Co catalyst was mainly deposited on TiN and not on sputtered-Si, which allowed the selective growth of SWNT forests on the TiN conductive surfaces. These as-synthesized SWNTs were used for field emission measurements in a high vacuum chamber.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis and characterization of amorphous SiO 2 nanowires directly grown on Cu substrates

In this work, a novel procedure for the growth of Silica nanowires directly from Cu substrates is reported. The singlestep synthesis procedure consists of a thermal treatment at 900 °C in Ar-H 2 atmosphere, without the need for additional catalysts. Nanowires grow from Cu protrusions generated on the surface during annealing via Vapor–Liquid–Solid method, giving rise to a branched structure. These SiO 2 nanostructures present an amorphous structure as evidenced by transmission electron microscopy. Silica nanowires grown on Cu and Si substrates have been characterized by XPS. Additionally, room-temperature photoluminescence measurements show a blue-green emission peak at ca. 509 nm (2.44 eV) attributed to oxygen deficiencies in the structure. The success of this procedure allows for future possible incorporation of these nanowires in optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Facile synthesis of ZnO nanoparticles and its photocatalytic activity in the degradation of 2-phenylbenzimidazole-5-sulfonic acid

Sphere-shaped zinc oxide nanoparticles were synthesized following an eco-friendly synthesis method, at mild temperature, using zinc acetate dihydrate as precursor. For this work, a comparative characterization was performed with and without a post-calcined step at 300 °C during 15 min. The synthesized zinc oxide nanoparticles were characterized by FE-SEM, EDS, XRD, BET and UV–vis spectroscopy. After the calcined step, wurtzite was the only crystalline structure present in the sample. The photocatalytic activity of the calcined zinc oxide nanoparticles proved to be high since more than 90% of degradation of 2-phenylbenzimidazole-5-sulfonic acid was reached after 180 min of reaction time. Furthermore, the effects of different factors (i.e. radiation source, oxygen source, and catalyst) on the catalytic reaction were evaluated and, as expected, it was found that all these factors are required, and act synergistically in the photodegradation process.

2-phenylbenzimidazole-5-sulfonic acid↗
DOE OSTI2016

Graphene Synthesis by Plasma-Enhanced CVD Growth with Ethanol

A modified route to synthesize graphene flakes is proposed using the Chemical Vapor Deposition (CVD) technique, by using copper substrates as supports. The carbon source used was ethanol, the synthesis temperature was 950°C and the pressure was controlled along the whole process. In this CVD synthesis process the incorporation of the carbon source was produced at low pressure and 950°C inducing the appearance of a plasma blue flash inside the quartz tube. Apparently, the presence of this plasma blue flash is required for obtaining graphene flakes. The synthesized graphene was characterized by different techniques, showing the presence of non-oxidized graphene with high purity.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis and photocatalytic activity of TiO 2 nanowires in the degradation of p-aminobenzoic acid: A comparative study with a commercial catalyst

The photocatalytic degradation of p-aminobenzoic acid was studied using TiO 2 nanowires as the catalyst synthesized through a hydrothermal procedure. The as-synthesized TiO 2 nanowires were fully characterized by SEM, TEM, XRD and Raman with a very high surface area of 512 m 2 g -1 . In addition, the photocatalytic degradation of p-aminobenzoic acid was carried out under 180 min of constant radiation and the results were compared with P25 as commercial catalyst. Optimal experimental conditions were determined for TiO 2 nanowires with a catalyst dosage of 1.0 g L -1 under acidic conditions with a 20 μM p-aminobenzoic acid solution obtaining 95% of degradation. Under similar experimental conditions comparative studies were performed obtaining 98% of degradation when P25 is employed. Finally, in both systems, a pseudo first order reaction was found to provide the best correlations, with constant rates of 2.0 x 10 -2 min -1 and 2.4 x 10 -2 min -1 for TiO 2 nanowires and P25, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanomaterials for Sensor Applications

A large part of the advances in nanotechnology have been directed towards the development of highspeed electronics, more efficient catalysts, and sensors. This latter group of applications has great relevance and unprecedented development potential for the coming years. Some of the main objectives for the development of sensors have focused on making more sensitive, effective and specific sensing devices. The improvement of these systems and the increase of specificity are clearly associated with a decrease in size of the components, which can lead to obtaining more rapid action, almost in real time. Nanomaterials currently used in sensor development include a long list of nanostructured systems, as for example: Metal nanotubes, nanowires, nanofibers, nanocomposites, nanorods, nanoparticles, nanostructured polymers, and different allotropes of carbon as carbon nanotubes, graphene or fullerenes, among others [1]. These nanomaterials are characterized by having unique physicochemical properties, including high electrical and thermal conductivity, extremely high surface area/volume ratio, high mechanical strength and even excellent catalytic properties [1] [2]. These materials, may exhibit relevant physicochemical behavior, such as quantization or electronic confinement effects, which can be used in the development of all kinds of sensors [2]. So far, sensors have been developed for determination and quantification of gases, radiation, biomolecules, microorganisms, etc. [2] [3]. The sensors developed so far usually use the system lock and key, wherein the selective receptor (lock) is selectively anchored to the analyte of interest (or key). This system has great limitations when analyzing the analyte in the presence of other analytes, which can alter the sensitivity or specificity of the measure, as occurs in sensors used in biomedical applications [3] [4]. One possible solution is based on the development of sensor arrays, consisting of a combination of different and specific sensors, which may enable simultaneous measurements of one or more analytes in a less favorable environment [5] in these cases. These sensors are now a reality, although there is still a long way to go before the levels of precision and accuracy are reached. Future challenges for the development and commercialization of efficient sensors are mainly focused on improving the specificity, reproducibility, and the ability to detect trace levels. We hope that in the coming years nanotechnology and nanomaterials allow reaching previously unimaginable advances in the development of these systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Nanomaterials for Drugs Delivery

Nanotechnology has revolutionized engineering, biology, chemistry, physics and medicine of today. These disciplines are evolving thanks to the ongoing development of new materials and applications. Nanomedicine, as application of nanotechnology in the field of health care, has undergone unprecedented development. Some of these changes have real applications as, for example, the use of nanoparticles in MRI imaging, in hyperthermia, in immunotherapy, or to improve the bioavailability of drugs, among others. Furthermore, when a drug is administered to a patient, the blood distributes it throughout the body. In the case of very localized diseases (i.e. tumors), only a small fraction of the drug reaches the target. Chemotherapy is one of the most aggressive treatment options used in some types of cancer, and is usually administered intravenously. The drug circulates throughout the body, reaching and destroying healthy and cancerous tissues, producing side effects throughout the body, sometimes with serious consequences for the health of the patient (nephrotoxicity, cardiotoxicity, peripheral neuropathy, anemia, etc.) in this type of therapy. Among the many applications of nanotechnology, the fabrication of nanostructures capable of safely transporting these drugs is seen as a strategy for reducing these side effects. Nanoparticles are able to carry and release the drug in the right place and with the required dose, greatly reducing the problems associated with direct treatment with these drugs. In recent years, there have been continuous improvements in the design and development of new tailor-made drug delivery systems, including hollow magnetic nanoparticles, liposomal structures, dendrimers, nanoporous silicon, etc. These structures can be obtained with different molecular weights (in the case of polymers), structures, shapes, and even with the appropriate functional groups for interaction at the desired positions. But, a great effort is still required to solve many of the current problems, including toxicity, aggregation, solubility and stability in the human body, physiological processes of elimination, identification of targets by highly specific receptors, controlled drug release over time, etc.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Photocatalytic hydrogen production by water splitting using novel catalysts under UV-vis light irradiation

In this work, photocatalytic hydrogen generation by water splitting (H 2 O (l) →H 2 (g) +1/2O 2 (g) ) has been studied on photocatalysts based on Zn, Cd, Fe and Cu, synthesized by coprecipitation. Iron and copper nanoparticles were incorporated as cocatalysts to enhance the photocatalytic activity of the ZnCd solid solution. The effect of the different synthesis parameters (temperature, elemental atomic ratios, amount of Cu and Fe incorporated in the catalyst and calcination temperature) on the photocatalytic production of hydrogen has been studied in order to determine the best experimental synthesis conditions. The catalysts have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and BET. The experiments of photocatalytic water splitting were performed in aqueous solution of the photocatalysts previously dispersed in a soft ultrasound bath. The photocatalysts were irradiated under different lights ranging from 220 to 700 nm. Furthermore, the photocatalytic activity was found to be clearly dependent on the specific area of the photocatalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Microspheres for the growth of silicon nanowires via vapor-liquid-solid mechanism

Silicon nanowires have been synthesized by a simple process using a suitable support containing silica and carbon microspheres. Nanowires were grown by thermal chemical vapor deposition via a vapor-liquid-solid mechanism with only the substrate as silicon source. The curved surface of the microsized spheres allows arranging the gold catalyst as nanoparticles with appropriate dimensions to catalyze the growth of nanowires. Here, the resulting material is composed of the microspheres with the silicon nanowires attached on their surface.

25 ENERGY STORAGE↗