Browsing by Author "Carvalho, Ana"
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- Characterization of AuNPs+rGO as a functionalized layer for LSPR sensorsPublication . Fantoni, Alessandro; Stojkovic, Vladan; Carvalho, Ana; Da Costa Ribeiro, Ana Paula; Alegria, ElisabeteGraphene-based materials have been extensively explored in recent years as valuable candidates as the key material for novel structures in the field, among many other applications, of sensing devices. This work reports a study about the applicability of rGO as a support for gold nanoparticles (AuNPs) prepared with an economic and eco-friendly method using phytochemicals present in tea extract at room temperature. The overall analysis is supported by simulation results about the LSPR effect in AuNPs-rGO, obtained by Mie theory and FDTD method. The residual phytochemicals are analysed as capping agent of the nanoparticles and their influence on the LSPR properties of the nanoparticles is outlined. The resulting composite is suitable for application as a low-cost sensing layer in biomedical LSPR sensor devices.
- Characterization of plasmonic effects in AuNP+rGO composite as a sensing layer for a low-cost lab-on-chip biosensorPublication . Fantoni, Alessandro; Stojkovic, Vladan; Fernandes, Miguel; Louro, Paula; Vieira, Manuela; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Carvalho, Ana; Almeida, M. GabrielaThis work deals with the production of a low-cost disposable biosensor for point of care applications. The proposed sensor is a plasmonic structure based on the Localized Surface Plasmon Resonance (LSPR) interaction of metal nanoparticles (MNPs), embedded into a matrix of reduced Graphene Oxide (rGO). After proper functionalization with selective antibodies (Ab), the efficiency of light extinction is controlled by slight changes of the refractive coefficient induced by the concentration of biomarkers trapped by the antibodies on the sensor surface. This work reports a study about the applicability of rGO as a support for gold nanoparticles (AuNPs) for preparing the functionalized LSPR sensing layer. AuNPs are prepared with an economic and eco-friendly method using phytochemicals present in tea extract at room temperature, while a modified Hummer’s method is used to synthesize rGO. The resulting AuNPs-rGO composites are studied in terms of UV-VIS spectroscopy spectral light transmission and plasmonic resonance. The overall analysis is supported by simulation results, obtained by Mie analysis, about the LSPR effect in AuNPs-rGO and its dependence on the biomarker concentration.
- Characterization of plasmonic effects in AuNP+rGO composite as a sensing layer for a low-cost lab-on-chip biosensorPublication . Fantoni, Alessandro; Stojkovic, Vladan; Fernandes, Miguel; Louro, Paula; Vieira, Manuela; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Carvalho, Ana; Almeida, M. GabrielaThis work deals with the production of a low-cost disposable biosensor for point of care applications. The proposed sensor is a plasmonic structure based on the Localized Surface Plasmon Resonance (LSPR) interaction of metal nanoparticles (MNPs), embedded into a matrix of reduced Graphene Oxide (rGO). After proper functionalization with selective antibodies (Ab), the efficiency of light extinction is controlled by slight changes of the refractive coefficient induced by the concentration of biomarkers trapped by the antibodies on the sensor surface. This work reports a study about the applicability of rGO as a support for gold nanoparticles (AuNPs) for preparing the functionalized LSPR sensing layer. AuNPs are prepared with an economic and eco-friendly method using phytochemicals present in tea extract at room temperature, while a modified Hummer’s method is used to synthesize rGO. The resulting AuNPs-rGO composites are studied in terms of UV-VIS spectroscopy spectral light transmission and plasmonic resonance. The overall analysis is supported by simulation results, obtained by Mie analysis, about the LSPR effect in AuNPs-rGO and its dependence on the biomarker concentration.
- Eco-friendly cyclohexane oxidation by a V-scorpionate complex immobilized at hierarchical MOR zeolitePublication . Ottaviani, Davide; Van-Dúnem, Vanmira; Carvalho, Ana; Martins, Angela; Martins, LuisaThe hydrotris(3,5-dimethylpyrazol-1-yl)borate dioxido-vanadium(V) complex [VO2{HB(3,5-Me(2)pz)(3)}] (V, pz= pyrazol-1-yl) immobilized at hierarchical MOR zeolite modified through surfactant mediated technology using NaOH as alkaline agent, V@MOR_NaOH, provides an efficient (TON up to 5.2x10(2)) catalyst for the peroxidative oxidation of cyclohexane with tert-butyl hydroperoxide to KA oil (52% yield), at room temperature, and is easily recovered and reused up to four consecutive catalytic cycles with no significant leaching of vanadium. The textural modifications performed on the zeolitic matrix produced an effective support for the anchorage of the vanadium complex allowing an improved catalytic performance and reusability. This work constitutes an unprecedented use of supported vanadium B-scorpionate complexes as catalysts for the oxidation of alkanes.
- Friedel-crafts acylation reaction over hierarchical Y zeolite modified through surfactant mediated technologyPublication . Martins, Angela; Neves, Vera; Moutinho, João; Nunes, Nelson; Carvalho, AnaFriedel-Crafts acylation reaction was studied under mild conditions using hierarchical HY zeolite samples prepared through surfactant mediated technology, in the presence of NH4OH, using CTAB or DTAB as surfactants and changing the duration of treatment from 6 to 48 h. The materials were characterized by powder X-ray diffraction, low temperature N2 adsorption isotherms, SEM microscopy and pyridine adsorption followed by FTIR. The catalytic behaviour was studied in the acylation of furan by acetic anhydride. The catalytic results reflect the role of the duration of the treatment as well as the surfactant molecule used. As the time of treatment increases, the enlargement of the pores leads to an increase of the rate constant and turnover frequency (TOF), except for sample modified during longer time, 48 h, due to the occurrence of secondary reactions that produce larger products or reaction intermediates that become trapped inside the pores. The role of the surfactant molecule is also relevant since the sample modified in the presence of the larger surfactant molecule, CTAB, a significant increase in product yield and rate constant is obtained when compared with the sample prepared in the same conditions using DTAB. However, in that case, by prolonging the treatment a substantial decrease in the same parameters occurs due to the occurrence of deactivation phenomena, pointing out that the optimized modification of porosity needs to be customized according to the needs of each catalytic system.
- Improved cyclohexane oxidation catalyzed by a heterogenized Iron (II) complex on hierarchical Y zeolite through surfactant mediated technologyPublication . Van-Dúnem, Vanmira; Carvalho, Ana; Martins, Luisa; Martins, AngelaThe hydrotris (pyrazol-1-yl) methane iron (II) complex [FeCl2 (Tpm)] [Tpm=HC(C3N2H3)3] was successfully immobilized, by the incipient wetness impregnation method, in parent and hierarchical Y zeolite modified through surfactant mediated methodology using different bases (NH4OH, NaOH or TPAOH). The catalytic performance and recyclability of supported Fe complex was evaluated in the oxidation of cyclohexane with hydrogen peroxide to cyclohexanol and cyclohexanone under mild conditions and two distinct behaviors were observed: using commercial Y and modified Y with NaOH the complex is anchored mainly at the outer surface of the zeolite supports, resulting in high lixiviation after the first catalytic cycle. When NH4OH and TPAOH are used during the zeolite treatments the particular textural parameters exhibited by these two supports are able to effectively retain the complex molecules, resulting in a high recyclability observed after three consecutive cycles, especially when NH4OH treated zeolite was used as support.
- Kinetic study of Friedel-Crafts acylation reactions over hierarchical MCM-22 zeolitesPublication . Aleixo, Rodrigo; Elvas Leitao, Ruben; Martins, Filomena; Carvalho, Ana; Brigas, Amadeu; Martins, Angela; Nunes, NelsonFriedel-Crafts acylation was studied under mild conditions using hierarchical MCM-22 zeolites prepared by desilication and by desilication + acid treatment, using furan, pyrrole and anisole as substrates, and acetic anhydride as acylating agent. Enhanced catalysis was observed for furan and anisole, especially at short reaction times. Kinetic results modelling using non-linear regressions applied to a simplified Langmuir-Hinshelwood equation showed that desilication treatment followed by acid treatment improved kinetics (higher k and TOF). A QSPR methodology using nine substrate and zeolite descriptors was applied to model kinetics and adsorption. For both processes, the best QSPR model equations lead to the same descriptors, namely, Bronsted acidity, as zeolite's feature, and both van der Waals volume and Dimroth-Reichardt E-T(N) parameter (related to dipolarity and Lewis acidity) as substrates' characteristics. Normalization of descriptors allowed quantification of each descriptor's relative importance leading to a better understanding of the catalytic and adsorption processes.
- Modelling of burnt pine heartwood acid-catalysed liquefactionPublication . Ozkan, Sila; Gonçalves, Diogo; Paulo, Ivo; Queirós, Carla S. G. P.; Carvalho, Ana; Puna, Jaime; Gomes, João; Bordado, João; Santos, Rui Galhano dosThis study focused on bio-oil production by thermochemical liquefaction. For the reaction, the burnt pine heartwood was used as feedstock material, 2-Ethylhexanol (2-EHEX) was used as a solvent, p-Toluenesulfonic acid (pTSA) was used as a catalyst, and the solvent for washing was acetone. The procedure consisted of a moderate-acid-catalysed liquefaction process, and it was applied at three different temperatures, 120, 140, and 160 degrees C, and at 30, 105, and 180 min periods with 1%, 5.5%, and 10% (m/m) catalyst concentration of overall mass. Optimal results showed a bio-oil yield of 86.03% and a higher heating value (HHV) of 36.41 MJ/kg, which was 1.96 times more than the HHV of the burnt pine heartwood. A reaction surface methodology (Box-Behnken design) was performed for the liquefaction reaction optimisation. Reaction temperature, reaction time and catalyst concentration were chosen as independent variables. The obtained model showed good results with a high adjusted R-squared (0.988) and an excellent p-value (less than 0.001). The liquefied products were characterised by Fourier Transformed Infrared (FTIR) and thermogravimetric analysis (TGA), and also Scanning electron microscopy (SEM) was carried out to validate the impact of the morphological changes on the surface area of the solid samples. This study shows an excellent opportunity to validate a method to upcycle woody wastes via acid-catalysed liquefaction. In particular, this approach is of great interest to produce bio-oil with a good yield, recovering part of the values lost during wildfires.
- Neurodegeneration and choroidal vascular features on OCT in the progression to advanced age-related macular degenerationPublication . Costa, Inês; Carvalho, Ana; Andrade, Helton; Pereira, Bruno; Camacho, PedroAim: To quantify and compare longitudinal thickness changes of the ganglion cell complex (GCC) and the choroid in patients with different patterns of age-related macular degeneration (AMD) progression. Methods: Retrospective cohort analysis of anonymized data from participants aged 50y or more and diagnosed with early/intermediate AMD in at least one eye (with no evidence of advanced AMD). A total of 64 participants were included from the Instituto de Retina de Lisboa (IRL) study (IPL/2022/MetAllAMD_ESTeSL) and divided into 4 groups according to the Rotterdam classification for AMD. Spectral-domain optical coherence tomography (SD-OCT) was used to assess and quantify GCC and choroid thickness at two-time points (first visit vs last visit) with a minimum interval of 3y. Results: In the GCC inner ring, a thinner thickness (P=0.001) was observed in the atrophic AMD group (51.3±21.4 µm) compared to the early AMD (84.3±11.5 µm), intermediate AMD (77.6±16.1 µm) and neovascular AMD (88.9±16.3 µm) groups. Choroidal thickness quantification showed a generalized reduction in the central circle (P=0.002) and inner ring (P=0.001). Slight reductions in retinal thickness were more accentuated in the inner ring in the atrophic AMD (-13%; P<0.01). Conclusion: The variation of the analyzed structures could be an indicator of the risk of progression with neurodegenerative (GCC) or vascular (choroid) patterns in the intermediate and atrophic AMD. The quantification of both structures can provide important information about the risk of disease progression in the early and intermediate stages but also for the evolution pattern into late stages (atrophic or neovascular).
- Unlocking nature’s potential: modelling Acacia melanoxylon as a renewable resource for bio-oil production through thermochemical liquefactionPublication . Ozkan, Sila; Sousa, Henrique; Gonçalves, Diogo; Puna, Jaime; Carvalho, Ana; Bordado, João; Santos, Rui Galhano dos; Gomes, JoãoThis study is focused on the modelling of the production of bio-oil by thermochemical liquefaction. Species Acacia melanoxylon was used as the source of biomass, the standard chemical 2-Ethylhexanol (2-EHEX) was used as solvent, p-Toluenesulfonic acid (pTSA) was used as the catalyst, and acetone was used for the washing process. This procedure consisted of a moderate acid-catalysed liquefaction process and was applied at 3 different temperatures to determine the proper model: 100, 135, and 170 ◦C, and at 30-, 115-, and 200-min periods with 0.5%, 5.25%, and 10% (m/m) catalyst concentrations of overall mass. Optimized results showed a bio-oil yield of 83.29% and an HHV of 34.31 MJ/kg. A central composite face-centred (CCF) design was applied to the liquefaction reaction optimization. Reaction time, reaction temperature, as well as catalyst concentration, were chosen as independent variables. The resulting model exhibited very good results, with a highly adjusted R-squared (1.000). The liquefied products and biochar samples were characterized by Fourier transformed infrared (FTIR) and thermogravimetric analysis (TGA); scanning electron microscopy (SEM) was also performed. The results show that invasive species such as acacia may have very good potential to generate biofuels and utilize lignocellulosic biomass in different ways. Additionally, using acacia as feedstock for bio-oil liquefaction will allow the valorisation of woody biomass and prevent forest fires as well. Besides, this process may provide a chance to control the invasive species in the forests, reduce the effect of forest fires, and produce bio-oil as a renewable energy.