Scientific Papers in SCI

Triboelectric nanogenerators (TENGs) have emerged as potential energy sources, as they are capable of harvesting energy from low-frequency mechanical actions such as biological movements, moving parts of machines, mild wind, rain droplets, and others. However, periodic mechanical motion can have a detrimental effect on the triboelectric materials that constitute a TENG device. This study introduces a self-healable triboelectric layer consisting of an Ecoflex-coated self-healable polydimethylsiloxane (SH-PDMS) polymer that can autonomously repair mechanical injury at room temperature and regain its functionality. Different compositions of bis(3-aminopropyl)-terminated PDMS and 1,3,5-triformylbenzene were used to synthesize SH-PDMS films to determine the optimum healing time. The SH-PDMS films contain reversible imine bonds that break when the material is damaged and are subsequently restored by an autonomous healing process. However, the inherent stickiness of the SH-PDMS surface itself renders the material unsuitable for application in TENGs despite its attractive self-healing capability. We show that spin-coating a thin layer (approximate to 32 mu m) of Ecoflex on top of the SH-PDMS eliminates the stickiness issue while retaining the functionality of a triboelectric material. TENGs based on Ecoflex/SH-PDMS and nylon 6 films show excellent output and fatigue performance. Even after incisions were introduced at several locations in the Ecoflex/SH-PDMS film, the TENG spontaneously attained its original output performance after a period of 24 h of healing. This study presents a viable approach to enhancing the longevity of TENGs to harvest energy from continuous mechanical actions, paving the way for durable, self-healable mechanical energy harvesters.

Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) experiments have been carried out in N-2 and N-2-H2O atmospheres on a Pt-based catalyst physically mixed with an Eu-doped ZrO2 ionic conductor as a function of temperature under realistic conditions of the water gas shift (WGS) reaction. This work aims to demonstrate the significant effect of having active H2O on the ionic conductor surface at reaction temperatures to provide it to Pt metal sites. The ionic conductor, Eu-doped zirconia matrix, presents defects (oxygen vacancies, O-v) that allows upon H2O dissociation the formation of a hydrogen-bonded molecular water layer favoring diffusion through a Grotthuss mechanism below 300 degrees C. In the presence of H2O, the O-v are occupied by hydroxyl species as observed in the Eu 4d spectra, which differentiate two types of Eu oxidation states. The Eu3+-to-Eu2+ atomic ratio increases with the occupancy of the O-v by hydroxyls. Moreover, while the Pt-based catalyst alone is unable to create Pt-OH bonds, the physical mixture of the Pt-based catalyst and the ionic conductor allows the formation of Pt-OH bonds from room temperature up to 300 degrees C. These data demonstrate that the increase in molecular water concentration on the ionic conductor surface up to 300 degrees C acts as a reservoir to provide water to the Pt surface, enhancing the catalyst performance in the WGS reaction, supporting the importance of the surface H2O concentration in the reaction kinetics.

In heterogeneous photocatalysis, different reactive species generated from the excitation of the semiconductor are responsible for the degradation of different contaminants in aqueous solution. In order to evaluate the influence of each of these reactive species on the photocatalysis process, it is common to perform an analysis using different chemical compounds, which (in theory) react selectively with only one reactive species, preventing this species from participating in the process. Questioning this analysis is the aim of this work and the reasons that lead us to this will be described and discussed. For this, different investigations were selected where this analysis was carried out on two model substrates, Rhodamine B and Phenol. With this, it was possible to determine which compounds are most used as scavengers for the different reactive species, and how these compounds influence the photodegradation process. It was possible to shown that none of the commonly used scavengers react selectively with only one reactive species, since it can also influence other reactions, either by reacting with other reactive species, with the surface of the catalyst, or with the substrate under study, among others. In our opinion, the conclusions obtained by using scavenger analysis should be carefully considered, and the compounds used should be renamed as interfering species of the photocatalytic process.

The garnet aluminates RE3Al5O12 (RE = Gd - Lu, Y) are an important class of optical materials with a range of applications. Typically, they do not tolerate large deviations from ideal stoichiometry, and their luminescence properties are controlled by dopant selection rather than modification of the host structure. Here, we use glass crystallization as a nonequilibrium synthesis route to a new family of highly nonstoichiometric gadolinium aluminate garnets, of formula Gd3+xAl5-xO12 with x <= 0.60. Remarkably, this range is much broader than the previously reported Y3+xAl5-xO12 series (x <= 0.4), despite the vast size contrast between Al3+ and Gd3+, which are forced to share a crystallographic site in the nonstoichiometric materials: the endmember Gd3.6Al4.4O12 lies halfway between ideal garnet and perovskite stoichiometries, with 30% of its octahedral Al3+ sites substituted by Gd3+. In principle, this crystal chemistry should allow the synthesis of phosphor systems with rare-earth activators distributed over two different cation sublattices. To probe the response of luminescence properties to extreme nonstoichiometry in Gd3+xAl5-xO12, we synthesized three model phosphor systems by doping with Ce3+, Tb3+, or Tm3+/Yb3+ and found that upconversion (Tm3+/Yb3+) phosphors have the most potential to be tuned by this approach. These results demonstrate that highly nonstoichiometric garnet aluminates are not limited to small rare-earth hosts such as YAG, opening new opportunities for development of different garnet-based optical and magnetic materials.