Federico González

Coatings of Fe3O4 Nanoparticles as Selective Solar Absorber

Cost-effective and pollution-free green chemical method has been employed for synthesizing Fe3O4 nanoparticles which can be used as a solar absorbent and characterized further for their structural, optical and morphological properties using X-ray diffraction and UV-VIS-IR spectrophotometry and transmission electron microscopy techniques, respectively. Presence of Fe 2+ and Fe 3+ in nanoparticles is confirmed from the X-ray photoelectron spectroscopy analysis. The nanometric grain-size allows deposition of thin films, and the resulting coatings onto copper substrate show a relatively low thermal emittance in a range of 0.05-0.10. The solar absorptance values are between 0.76 and 0.85, which can provide an acceptable selectivity. Attempt is also made to find influence of the thickness effect on the selectivity having 15.2 as best value for one layer coating.

Improving the contact properties of CdS-decorated TiO2 nanotube arrays using an electrochemical/thermal/chemical approach

Decoration of TiO2 nanotube films (TiO2 nanotube arrays (TNAs)) with CdS nanoparticles has been pursued for a broad range of applications that goes from solar cells to biological sensors. In most synthesis methods, the scale-up of devices has been challenging due to the poor contact at the chalcogenide/oxide interface. In this work, we validate the electrochemical/thermal/chemical route as a superior strategy to sensitize TNAs with CdS nanoparticles when compared with conventional methods. The process consisted of (i) electrodeposition of cadmium on TNAs to ensure strong bonding between TiO2 and Cd precursor particles, (ii) air annealing of Cd-decorated TNAs to thermally oxidize cadmium to cadmium oxide, and (iii) total sulfurization of cadmium oxide to obtain CdS in an hexagonal phase matching that of TNAs. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses indicated the complete transformation of cadmium precursor particles into CdS and a good surface coverage of the internal/external walls of TNAs. When compared to samples prepared by successive ionic layer adsorption and reaction (SILAR), electrochemical impedance spectroscopy data revealed the improvement of the electrical properties of the TNA matrix due to the sulfurization process and a lower contact resistance at the CdS/TNA interface. These improvements explain the superior photoelectrochemical response of CdS/TNA photoelectrodes obtained by the electrochemical/thermal/chemical route.

On Trapping Porphyrin Free-Bases Between Graphene Oxide Plates

A synergistic combination of properties between graphene oxide (GO) nanosheets and porphyrin molecules has been accomplished via the entrapment of the latter species within the pore space formed by parallel plates of the carbon material. A hybrid material, synthesized in this manner, would likely lead to the development of efficient photovoltaic cells, given the high capacity of porphyrin molecules to absorb sunlight or radiation of wavelength shorter than 700 nm as well as because of the excellent electron conduction and fine solar energy capture that can be achieved by the graphene substrate. Herein, materials consisting of trapped porphyrin molecules in-between GO plates have been prepared to develop preliminary solar cell devices for an efficient capture of sunlight energy. The hybrid systems created this way can be physicochemically characterized through diverse techniques, which include fluorescence emission to confirm and avail both the presence and manifest luminescent characteristics of the tetrapyrrolic species that are captured and retained in-between GO plates.