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3D ZnO/Ag surface-enhanced Raman scattering on disposable and flexible cardboard platforms
Publication . Pimentel, Ana; Araújo, Andreia; Coelho, Beatriz J.; Nunes, Daniela; Oliveira, Maria J.; Mendes, M. J.; Águas, Hugo; Martins, Rodrigo; Fortunato, Elvira; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; Molecular Diversity Preservation International (MDPI)
In the present study, zinc oxide (ZnO) nanorods (NRs) with a hexagonal structure have been synthesized via a hydrothermal method assisted by microwave radiation, using specialized cardboard materials as substrates. Cardboard-type substrates are cost-efficient and robust paper-based platforms that can be integrated into several opto-electronic applications for medical diagnostics, analysis and/or quality control devices. This class of substrates also enables highly-sensitive Raman molecular detection, amiable to several different operational environments and target surfaces. The structural characterization of the ZnO NR arrays has been carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical measurements. The effects of the synthesis time (5-30 min) and temperature (70-130 °C) of the ZnO NR arrays decorated with silver nanoparticles (AgNPs) have been investigated in view of their application for surface-enhanced Raman scattering (SERS) molecular detection. The size and density of the ZnO NRs, as well as those of the AgNPs, are shown to play a central role in the final SERS response. A Raman enhancement factor of 7 × 105 was obtained using rhodamine 6 G (RG6) as the test analyte; a ZnO NR array was produced for only 5 min at 70 °C. This condition presents higher ZnO NR and AgNP densities, thereby increasing the total number of plasmonic "hot-spots", their volume coverage and the number of analyte molecules that are subject to enhanced sensing.
Tailoring Upconversion and Morphology of Yb/Eu Doped Y2O3 Nanostructures by Acid Composition Mediation
Publication . Nunes, Daniela; Pimentel, Ana; Matias, Mariana; Freire, Tomas; Araujo, A.; Silva, Filipe; Gaspar, Patricia; Garcia, Silvia; Carvalho, Patricia A.; Fortunato, Elvira; Martins, Rodrigo; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; MDPI AG
The present study reports the production of upconverter nanostructures composed by a yttrium oxide host matrix co-doped with ytterbium and europium, i.e., Y2O3:Yb3+/Eu3+. These nanostructures were formed through the dissociation of yttrium, ytterbium and europium oxides using acetic, hydrochloric and nitric acids, followed by a fast hydrothermal method assisted by microwave irradiation and subsequent calcination process. Structural characterization has been carried out by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM) both coupled with energy dispersive X-ray spectroscopy (EDS). The acid used for dissociation of the primary oxides played a crucial role on the morphology of the nanostructures. The acetic-based nanostructures resulted in nanosheets in the micrometer range, with thickness of around 50 nm, while hydrochloric and nitric resulted in sphere-shaped nanostructures. The produced nanostructures revealed a homogeneous distribution of the doping elements. The thermal behaviour of the materials has been investigated with in situ X-Ray diffraction and differential scanning calorimetry (DSC) experiments. Moreover, the optical band gaps of all materials were determined from diffuse reflectance spectroscopy, and their photoluminescence behaviour has been accessed showing significant differences depending on the acid used, which can directly influence their upconversion performance.
Paper-based nanoplatforms for multifunctional applications
Publication . Matias, M. L.; Nunes, D.; Pimentel, A.; Ferreira, S. H.; Borda D’Agua, R.; Duarte, M. P.; Fortunato, E.; Martins, R.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); MEtRICS - Centro de Engenharia Mecânica e Sustentabilidade de Recursos; DCTB - Departamento de Ciências e Tecnologia da Biomassa (ex-GDEH); John Wiley and Sons Ltd
In this work, zinc oxide (ZnO) and titanium dioxide (TiO2) nanostructures were grown on different cellulose paper substrates, namely, Whatman, office, and commercial hospital papers, using a hydrothermal method assisted by microwave irradiation. Pure ZnO and TiO2 nanostructures were synthesized; however, the growth of TiO2 above ZnO was also investigated to produce a uniform heterostructure. Continuous ZnO nanorod arrays were grown on Whatman and hospital papers; however, on office paper, the formation of nanoplates originating nanoflower structures could be observed. TiO2 nanoparticles homogeneously covered all the substrates, in some conditions forming uniform TiO2 films. Structural characterization was carried out by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The optical characterization of all the materials was carried out. The produced materials were investigated for multifunctional applications, like photocatalyst agents, bacterial inactivators, and ultraviolet (UV) sensors. To evaluate the photocatalytic activity under UV and solar radiations, rhodamine B was the model-test contaminant indicator and the best photocatalytic activity was achieved with Whatman paper. Hospital paper with TiO2 nanoparticles showed significant antibacterial properties against Staphylococcus aureus. ZnO-based UV sensors demonstrated a responsivity of 0.61 μA W-1.
Metal oxide nanostructures for sensor applications
Publication . Nunes, D.; Pimentel, A.; Gonçalves, A.; Pereira, S.; Branquinho, R.; Barquinha, P.; Fortunato, E.; Martins, R.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Institute of Physics Publishing
Electrorheological fluids have been paying a lot of attention due to their potential use in active control of various devices in mechanics, biomedicine or robotics. An electrorheological fluid consisting of polarizable particles dispersed in a non-conducting liquid is considered to be one of the most interesting and important smart fluids. This work presents the effect of the dopant, camphorsulphonic acid or citric acid, on the electrorheological behaviour of suspensions of doped polyaniline nanostructures dispersed in silicone oil, revealing its key role. The influence of carbon nanoparticle concentration has also been studied for these dispersions. All the samples showed an electrorheological effect, which increased with electric field and nanostructure concentration and decreased with silicone oil viscosity. However, the magnitude of this effect was strongly influenced not only by carbon nanoparticle concentration but also by the dopant material. The electrorheological effect was much lower with a higher carbon nanoparticle concentration and doped with citric acid. The latter is probably due to the different acidities of the dopants that lead to a different conductivity of polyaniline nanostructures. Furthermore, the effect of the carbon nanoparticles could be related to its charge trapping mechanism, while the charge transfer through the polymeric backbone occurs by hopping. Polyaniline/camphorsulphonic acid composite nanostructures dispersed in silicone oil exhibited the highest electrorheological activity, higher than three decades increase in apparent viscosity for low shear rates and high electric fields, showing their potential application as electrorheological smart materials.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BPD/76992/2011