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Papers by Nicolás Carvajal

Research paper thumbnail of Studies of Multi-walled Carbon Nanotubes and Their Capabilities of Hydrogen Adsorption

Nanostructured Materials for Energy Related Applications, 2019

Over the last decade, there has been a significant interest of the scientific community in the sy... more Over the last decade, there has been a significant interest of the scientific community in the synthesis of carbonaceous materials due to its wide range of application, as well on the hydrogen storage problem. Since the discovery of carbon nanotubes by Iijima, carbon nanotubes have been one of the candidate nanomaterials for hydrogen storage. However, experimental studies on hydrogen storage capacity of carbon nanotubes are still very few, and the mechanism of how hydrogen is stored into carbon nanotubes and the factors affecting the adsorption remains still unclear.

Research paper thumbnail of Fabrication of ZnSe nanoparticles: Structural, optical and Raman Studies

Journal of Luminescence, 2017

In this work, a simple, effective, reproducible and green fabrication process for the production ... more In this work, a simple, effective, reproducible and green fabrication process for the production of high-quality, pure ZnSe nanoparticles at low temperature is presented. The structural and optical properties of these nanoparticles have been examined by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Ultraviolet-Visible spectroscopy (UV-vis), photoluminescence (PL), and Raman spectroscopy. TEM analysis confirms that the formed products are ZnSe particles with size less than 10 nm, respectively. Strong blue shift absorption with energy band gap of 3.85 eV is observed from UV-vis spectrophotometry. Photoluminescence measurements showed that the nanoparticles exhibit a strong UV emission peak at 380 nm. The blue emission could be attributed to the quantum size effect of ZnSe nanocrystals. Raman spectroscopy of the ZnSe NPs showed a clear shift of transverse optical (TO) and longitudinal optical (LO) phonon modes, as well as a broadening of the LO phonon mode. 2.2. Characterization The samples were characterized on a Tecnai F20 FEG-S/TEM

Research paper thumbnail of Mineral magnetite as precursor in the synthesis of multi-walled carbon nanotubes and their capabilities of hydrogen adsorption

International Journal of Hydrogen Energy, 2015

Mineral magnetite was used as metallic oxide catalysts in the synthesis of Multi-Walled Carbon Na... more Mineral magnetite was used as metallic oxide catalysts in the synthesis of Multi-Walled Carbon Nanotubes (MWCNTs) by Aerosol Assisted Chemical Vapor Deposition (AACVD). The structural and morphological information of MWCNTs was obtained by X-ray Diffraction (XRD), Raman Spectroscopy (RS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The hydrogen storage capacity and the gas adsorption kinetics of the MWCNTs exposed to H 2 at different pressures were determined using a quartz crystal microbalance (QCM). It was found that the hydrogen adsorption capacity was strongly dependent on the chemical, structural and morphological characteristics of the MWCNTs which, in turn, depend on the proportion of the starting materials (mineral magnetite and zeolite) used for the synthesis by AACVD. However, no a clear correlation was found between each one of these characteristics and the adsorption properties since the sample was affected by gas exposure during the H 2 loading/unloading cycles. The maximum adsorption capacity was 1.76 wt% at 44 Torr of H 2 exposure pressure. The adsorption kinetics was determined by in situ monitoring the QCM resonance frequency. As expected, a faster H 2 adsorption kinetics of the MWCNTs occurred when the sample was exposed to higher H 2 pressures. In general, there are measurable H 2 adsorption between 60 s and 100 s before reaching saturation.

Research paper thumbnail of Low temperature synthesis and blue photoluminescence of ZnS submicronparticles

Materials Letters, 2014

Submicronparticles of ZnS were synthesized at low temperature using a top-down fabrication proces... more Submicronparticles of ZnS were synthesized at low temperature using a top-down fabrication process by ultrasonication. The obtained ZnS particles were characterized by scanning transmission electron microscopy (S/TEM), energy dispersive X-ray analysis (EDAX), Fourier transform infra-red spectroscopy (FTIR), UV-visible spectrophotometry (UV), and photoluminescence spectroscopy (PL). The results showed that the formed products are ZnS particles with size less than 200 nm and exhibit a strong luminescence in the blue region. The origin of the blue emission could be attributed to the quantum size effect of ZnS nanocrystals.

Research paper thumbnail of Characterization and hydrogen storage in multi-walled carbon nanotubes grown by aerosol-assisted CVD method

Diamond and Related Materials, 2014

The characterization and hydrogen storage capacity of multi-walled carbon nanotubes (MWCNTs) have... more The characterization and hydrogen storage capacity of multi-walled carbon nanotubes (MWCNTs) have been studied in the present work. MWCNTs with high purity and bulk yield were achieved from a mixture of camphor/alcohol on a Ni/zeolite support by aerosol-assisted chemical vapor deposition (AACVD). The morphology, surface quality and structure of MWCNTs were characterized by transmission electron microscopy (TEM). Crystallinity and defects of the MWCNTs were studied by Raman spectroscopy and thermo gravimetric analysis (TGA). Hydrogen storage properties of MWCNTs were investigated using a quartz crystal microbalance (QCM). Values between 1.2 and 2.0 wt.% of adsorbed H 2 were reached depending on the exposure pressure. The results also showed that the remaining zeolite present in the as-prepared MWCNT powder adsorbs hydrogen, allowing better adsorption performance of the CNT12 and CNT13 samples. The hydrogen adsorption behavior of CNTs is significantly affected by their structural and morphological characteristics.

Research paper thumbnail of Studies of Multi-walled Carbon Nanotubes and Their Capabilities of Hydrogen Adsorption

Nanostructured Materials for Energy Related Applications, 2019

Over the last decade, there has been a significant interest of the scientific community in the sy... more Over the last decade, there has been a significant interest of the scientific community in the synthesis of carbonaceous materials due to its wide range of application, as well on the hydrogen storage problem. Since the discovery of carbon nanotubes by Iijima, carbon nanotubes have been one of the candidate nanomaterials for hydrogen storage. However, experimental studies on hydrogen storage capacity of carbon nanotubes are still very few, and the mechanism of how hydrogen is stored into carbon nanotubes and the factors affecting the adsorption remains still unclear.

Research paper thumbnail of Fabrication of ZnSe nanoparticles: Structural, optical and Raman Studies

Journal of Luminescence, 2017

In this work, a simple, effective, reproducible and green fabrication process for the production ... more In this work, a simple, effective, reproducible and green fabrication process for the production of high-quality, pure ZnSe nanoparticles at low temperature is presented. The structural and optical properties of these nanoparticles have been examined by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Ultraviolet-Visible spectroscopy (UV-vis), photoluminescence (PL), and Raman spectroscopy. TEM analysis confirms that the formed products are ZnSe particles with size less than 10 nm, respectively. Strong blue shift absorption with energy band gap of 3.85 eV is observed from UV-vis spectrophotometry. Photoluminescence measurements showed that the nanoparticles exhibit a strong UV emission peak at 380 nm. The blue emission could be attributed to the quantum size effect of ZnSe nanocrystals. Raman spectroscopy of the ZnSe NPs showed a clear shift of transverse optical (TO) and longitudinal optical (LO) phonon modes, as well as a broadening of the LO phonon mode. 2.2. Characterization The samples were characterized on a Tecnai F20 FEG-S/TEM

Research paper thumbnail of Mineral magnetite as precursor in the synthesis of multi-walled carbon nanotubes and their capabilities of hydrogen adsorption

International Journal of Hydrogen Energy, 2015

Mineral magnetite was used as metallic oxide catalysts in the synthesis of Multi-Walled Carbon Na... more Mineral magnetite was used as metallic oxide catalysts in the synthesis of Multi-Walled Carbon Nanotubes (MWCNTs) by Aerosol Assisted Chemical Vapor Deposition (AACVD). The structural and morphological information of MWCNTs was obtained by X-ray Diffraction (XRD), Raman Spectroscopy (RS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The hydrogen storage capacity and the gas adsorption kinetics of the MWCNTs exposed to H 2 at different pressures were determined using a quartz crystal microbalance (QCM). It was found that the hydrogen adsorption capacity was strongly dependent on the chemical, structural and morphological characteristics of the MWCNTs which, in turn, depend on the proportion of the starting materials (mineral magnetite and zeolite) used for the synthesis by AACVD. However, no a clear correlation was found between each one of these characteristics and the adsorption properties since the sample was affected by gas exposure during the H 2 loading/unloading cycles. The maximum adsorption capacity was 1.76 wt% at 44 Torr of H 2 exposure pressure. The adsorption kinetics was determined by in situ monitoring the QCM resonance frequency. As expected, a faster H 2 adsorption kinetics of the MWCNTs occurred when the sample was exposed to higher H 2 pressures. In general, there are measurable H 2 adsorption between 60 s and 100 s before reaching saturation.

Research paper thumbnail of Low temperature synthesis and blue photoluminescence of ZnS submicronparticles

Materials Letters, 2014

Submicronparticles of ZnS were synthesized at low temperature using a top-down fabrication proces... more Submicronparticles of ZnS were synthesized at low temperature using a top-down fabrication process by ultrasonication. The obtained ZnS particles were characterized by scanning transmission electron microscopy (S/TEM), energy dispersive X-ray analysis (EDAX), Fourier transform infra-red spectroscopy (FTIR), UV-visible spectrophotometry (UV), and photoluminescence spectroscopy (PL). The results showed that the formed products are ZnS particles with size less than 200 nm and exhibit a strong luminescence in the blue region. The origin of the blue emission could be attributed to the quantum size effect of ZnS nanocrystals.

Research paper thumbnail of Characterization and hydrogen storage in multi-walled carbon nanotubes grown by aerosol-assisted CVD method

Diamond and Related Materials, 2014

The characterization and hydrogen storage capacity of multi-walled carbon nanotubes (MWCNTs) have... more The characterization and hydrogen storage capacity of multi-walled carbon nanotubes (MWCNTs) have been studied in the present work. MWCNTs with high purity and bulk yield were achieved from a mixture of camphor/alcohol on a Ni/zeolite support by aerosol-assisted chemical vapor deposition (AACVD). The morphology, surface quality and structure of MWCNTs were characterized by transmission electron microscopy (TEM). Crystallinity and defects of the MWCNTs were studied by Raman spectroscopy and thermo gravimetric analysis (TGA). Hydrogen storage properties of MWCNTs were investigated using a quartz crystal microbalance (QCM). Values between 1.2 and 2.0 wt.% of adsorbed H 2 were reached depending on the exposure pressure. The results also showed that the remaining zeolite present in the as-prepared MWCNT powder adsorbs hydrogen, allowing better adsorption performance of the CNT12 and CNT13 samples. The hydrogen adsorption behavior of CNTs is significantly affected by their structural and morphological characteristics.