Showing: 10 from total: 19 publications
1. Drivers of FDI in small states
Forte, R ; Neves, C
Article in Press,  Indexed in: crossref, scopus, wos 
Abstract This paper examines the determinants of FDI in small states, as only a small number of studies have analyzed the determinants of FDI in these countries. Small states have particular features that justify the need for a deeper analysis. Based on a panel data for 42 small states between 2005 and 2019, results clearly indicate the importance of the quality of human capital and the availability of infrastructures as the strongest drivers of FDI in small states. The country's level of openness, the availability of natural resources, the level of corporate tax and control of corruption also seems to play a relevant role therein. Moreover, the results suggest that the determinants differ depending on the region to which the country belongs and differ between island and non-island countries. These results can help small countries in defining policies that help them to attract FDI, which is crucial for their sustainable development.

2. Energetic vs structural study of two biomass degradation derivatives: 2-Cyclopentenone and 3-methyl-2-cyclopentenone
Silva, ALR ; Moura, C ; Ribeiro da Silva, MDMCR
in JOURNAL OF CHEMICAL THERMODYNAMICS, 2019, ISSN: 0021-9614,  Volume: 132, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The standard molar enthalpies of formation in the gaseous state, at T= 298.15 K, of the 2-cyclopentenone and 3-methyl-2-cyclopentenone were derived from their standard molar energies of combustion and from their standard molar enthalpies of vaporization, obtained from static-bomb combustion calorimetry measurements and high-temperature Calvet microcalorimetry, respectively. The enthalpies of hydrogenation of the two cyclopentenones were derived from their gas-phase enthalpies of formation and the gas-phase enthalpies of formation of the corresponding cycloalkanones. The gas-phase standard molar enthalpy of formation of the compounds studied were also obtained using high level ab initio calculations and are in very good agreement with the experimental ones. In addition, thermochemical parameters associated to 2-cyclopentenone and 3-methyl-2-cyclopentenone transformations were investigated using the G3(MP2)//B3LYP level of theory. The conversions of both compounds to longer chain alkanes were found to be thermodynamically favourable. (C) 2019 Elsevier Ltd.

3. Cationic imprinting of Pb(II) within composite networks based on bovine or fish chondroitin sulfate
Ferreira, VRA ; Azenha, MA ; Teresa Mena, MT ; Moura, C ; Pereira, CM ; Perez Martin, RI ; Vazquez, JA ; Fernando Silva, AF
in JOURNAL OF MOLECULAR RECOGNITION, 2018, ISSN: 0952-3499,  Volume: 31, 
Article,  Indexed in: crossref, scopus, wos 
DOI: 10.1002/jmr.2614 P-00N-2MD
Abstract Imprinting chondroitin sulfate (CS)/silica composites with Pb(II) and Cu(II) cations was explored with CS of bovine and different fish species origin. The process was based on the assumption that particular arrangements of the linear CS chains in aqueous solution, induced so as to accommodate cross complexation with the cations, would be embodied into a tridimensional matrix created through an organoalkoxysilane sol-gel scheme. The presence of Cu(II) in the synthesis of the composites did not result in the production of significantly stronger Cu(II)-oriented binding arrangements, and therefore, the imprinting was not successful. Inversely, for Pb(II), the materials obtained exhibited a memory effect for the Pb(II) ions, expressed in the observation of stronger (13%-44%) binding as compared to the nonimprinted counterparts, and increased selectivity (1.5-2 folds) against Cd(II). The imprinting features observed were dependent on the CS source. However, it was not possible to identify, among a set of their properties (carboxylate and sulfate abundance, percent of disulfated units, 4S/6S ratio, and molecular weight), any that correlated directly with the observed imprinting features. The augmented selectivity provided by the cation-imprinting process may be advantageous in areas such as analytical separation, remediation, purification, sensing, and others, particularly in those cases where a certain cation is of special interest within a mixture of them.

4. Novel hybrid based on a poly[Ni(salen)] film and WO3 nanoparticles with electrochromic properties
Nunes, M ; Moura, C ; Hillman, AR ; Freire, C
in ELECTROCHIMICA ACTA, 2017, ISSN: 0013-4686,  Volume: 238, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The strategy of combining electroactive polymers and inorganic nanomaterials has been widely explored in recent years in order to improve some of their properties, namely electrocatalysis and electrochromism. This report focuses on a new composite prepared through the electropolymerization of the transition metal complex [Ni(3-Mesalen)], designated as [1] in the presence of WO3 nanoparticles (NPs) and its electrochromic (EC) performance. The WO3 NPs were prepared using tungsten metal powder; their characterization indicated quasi-spherical morphology, high crystallinity and particle sizes in the range 30-40 nm. The nanocomposite WO3@poly[1] films displayed similar electrochemical responses to those of pristine poly[1] films in LiClO4/CH3CN, but higher electroactive surface coverages, an advantage of NPs incorporation in the nanocomposite. The presence of the WO3 NPs in the poly[1] matrix was assessed by X-ray photoelectron spectroscopy and scanning electronic microscopy. The nanocomposite presented similar electronic spectra to those of poly[1], indicating that the electronic structure of the pristine film is maintained in the nanocomposite, but exhibited lower e-values for bands associated with charge transfer transitions for high oxidised states, revealing an enhanced stability towards ligand over-oxidation. The WO3@ poly[1] nanocomposite showed more favourable EC properties in LiClO4/CH3CN than the pristine film. For typical coverages ( Gamma = 0.06-0.10 mu mol cm (2)) the composite showed lower switching times (tau = 1.3 - 3.6 s), higher optical contrast (Delta T approximate to 31%, an improvement of ca. 40%) and better colouration efficiencies (in the range eta = 104 - 115 cm(2)C (1), improvement of ca. 13 - 22%).

5. Multicolour Electrochromic Film Based on a TiO2@poly[Ni(sa/en)] Nanocomposite with Excellent Electrochemical Stability
Nunes, M ; Moura, C ; Hillman, AR ; Freire, C
in LANGMUIR, 2017, ISSN: 0743-7463,  Volume: 33, 
Article,  Indexed in: crossref, scopus, wos 
Abstract We report the electrochromic properties of a polymeric nanocomposite prepared by potentiodynamic deposition of transition-metal complex [Ni(3-Mesalen)], designated as [1], in the presence of TiO2 nanoparticles (NPs) with an average size of 9.7 +/- 1.1 nm. Entrapment of TiO2 NPs in the poly[1] matrix was confirmed by several techniques. The nanocomposite TiO2@poly[1] films showed similar electrochemical responses to the original (nanoparticle-free) poly[1] films, but with higher electroactive surface coverages (G), showing the advantage of the nanocomposite preparation. The results indicated that the electronic structure of poly[1] was retained in the nanocomposite; nonetheless, a lower e value was obtained for the charge-transfer band of the former, revealing superior stability of the nanocomposite for ligand high oxidation states. The TiO2@poly[1] nanocomposite showed interesting color changes, from yellow (reduced state) to green and russet (oxidized states), with enhanced electrochemical stability, demonstrated by a charge loss of only 7.3% over ca. 10?000 redox cycles surpassing the original polymer film stability: the loss of electroactivity is a factor of ca. 2 less than for pristine poly[1]. Furthermore, an enhancement of 16.7% in the optical modulation (Delta OD = 0.48) was also observed for the nanocomposite, confirming the benefit of TiO2 incorporation into the EC properties of the original polymer film.

6. Graphene-poly(nickel complex) as novel electrochromic nanocomposite for the fabrication of a robust solid-state device
Araujo, MP ; Nunes, M ; Fonseca, J ; Moura, C ; Hillman, R ; Freire, C
in JOURNAL OF COLLOID AND INTERFACE SCIENCE, 2017, ISSN: 0021-9797,  Volume: 504, 
Article,  Indexed in: crossref, scopus, wos 
Abstract An electrochromic nanocomposite based on a nickel-salen polymeric film - poly[Ni(3-Mesalen)], Mesalen = N,N'-bis(3-methylsalicylideneiminate) - and graphene nanoplatelets (GFNPs) with enhanced electrochromic stability was successfully prepared by anodic electropolymerization. Although the electrochemical processes typical of the polymer film were not changed by the presence of graphene, higher electroactive surface coverages could be obtained for nanocomposite films, which suggest the incorporation of GFNPs into the polymeric network. The nanocomposite showed multi-electrochromic behavior, with color changes between yellow (reduced state) and green (oxidized state). The inclusion of GFNPs into the poly[Ni(3-Mesalen)] structure accelerates the switching process, with the response time for green coloration decreasing by 50.7% and for yellow coloration by 60.0%, for films prepared with 30 electropolymerization cycles. In terms of electrochemical stability, after 10,000 electrochemical cycles the loss of charge was 7% for the graphene nanocomposite. The nanocomposite film was used as electrochromic material to assemble a flexible solid-state electrochromic device (ECD), which exhibited an outstanding electrochemical stability - only 3% of charge loss after 15 days of continuous activity.

7. Metal cation sorption ability of immobilized and reticulated chondroitin sulfate or fucoidan through a sol-gel crosslinking scheme
Ferreira, VRA ; Azenha, MA ; Bustamante, AG ; Teresa Mena, MT ; Moura, C ; Pereira, CM ; Fernando Silva, AF
in MATERIALS TODAY COMMUNICATIONS, 2016, ISSN: 2352-4928,  Volume: 8, 
Article,  Indexed in: crossref, scopus, wos 
Abstract An immobilization scheme, via glycidyloxypropyl-trimethoxysilane sol-gel crosslinking, of chondroitin sulfate (CS) or fucoidan (Fd), inspired by the biological silicate bridge found in CS, is presented here. It revealed to constitute a simple and effective way of producing biopolymer-silicate composites without compromising the carboxylate- and sulfate- groups of the biopolymers, those which play a determinant role in the binding to metal cations. In the case of the Fd composite, the immobilization process resulted in the similar to 4-fold enhancement of the negatively charged sorption sites, probably due to unfolding effects induced by the synthesis conditions. Textural analysis of the composites showed a microporous, low surface area (6-12 m(2)/g), microstructure which did not prevent the observation of relevant sorption features for metal cations, especially for Pb(II) and Cd(II). Rate constants (1-14 g/mg min(-1)) and affinity constants (79-370L/mg) in the same order of magnitude of chitosan-based sorbents were determined, whereas capacities (2-24 mg/g) were smaller than the generality of those same sorbents. Globally, the sorption of metal cations by the Fd composite was superior to that by the CS composite. Furthermore, high stability of the sorbents and acceptable reproducibility of the synthesis was observed. Overall, the developed scheme of immobilization of CS and Fd appears capable of providing an effective way for integrating these biopolymers into metal cation-related applications such as biosorption, sensing or separation.

8. High-Performance Electrochromic Devices Based on Poly[Ni(salen)]-Type Polymer Films
Nunes, M ; Araujo, M ; Fonseca, J ; Moura, C ; Hillman, R ; Freire, C
in ACS APPLIED MATERIALS & INTERFACES, 2016, ISSN: 1944-8244,  Volume: 8, 
Article,  Indexed in: crossref, scopus, wos 
Abstract We report the application of two poly[Ni(salen)]-type electroactive polymer films as new electrochromic materials. The two films, poly[Ni(3-Mesalen)] (poly[1]) and poly[Ni(3-MesaltMe)] (poly[2]), were successfully electrodeposited onto ITO/PET flexible substrates, and their voltammetric characterization revealed that poly[1] showed similar redox profiles in LiClO4/CH3CN and LiClO4/propylene carbonate (PC), while poly[2] showed solvent-dependent electrochemical responses. Both films showed multielectrochromic behavior, exhibiting yellow, green, and russet colors according to their oxidation state, and promising electrochromic properties with high electrochemical stability in LiClO4/PC supporting electrolyte. In particular, poly[1] exhibited a very good electrochemical stability, changing color between yellow and green (lambda = 750 nm) during 9000 redox cycles, with a charge loss of 34.3%, an optical contrast of Delta T = 26.2%, and an optical density of Delta OD = 0.49, with a coloration efficiency of ? = 75.55 cm(2) C-1. On the other hand, poly[2] showed good optical contrast for the color change from green to russet (Delta T = 58.5%), although with moderate electrochemical stability. Finally, poly[1] was used to fabricate a solid-state electrochromic device using lateral configuration with two figures of merit: a simple shape (typology 1) and a butterfly shape (typology 2); typology 1 showed the best performance with optical contrast Delta T = 88.7% (at lambda = 750 nm), coloration efficiency eta = 130.4 cm(2) C-1, and charge loss of 37.0% upon 3000 redox cycles.

9. MnFe2O4@CNT-N as novel electrochemical nanosensor for determination of caffeine, acetaminophen and ascorbic acid
Fernandes, DM ; Silva, N ; Pereira, C ; Moura, C ; Magalhaes, JMCS ; Bachiller Baeza, B ; Rodriguez Ramos, I ; Guerrero Ruiz, A ; Delerue Matos, C ; Freire, C
in SENSORS AND ACTUATORS B-CHEMICAL, 2015, ISSN: 0925-4005,  Volume: 218, 
Article,  Indexed in: crossref, scopus, wos 
Abstract For the first time, a glassy carbon electrode (GCE) modified with novel N-doped carbon nanotubes (CNTN) functionalized with MnFe2O4 nanoparticles (MnFe2O4@CNT-N) has been prepared and applied for the electrochemical determination of caffeine (CF), acetaminophen (AC) and ascorbic acid (AA). The electrochemical behaviour of CF, AC and AA on the bare GCE, CNT-N/GCE and MnFe2O4@CNT-N/GCE were carefully investigated using cyclic voltammetry (CV) and square-wave voltammetry (SWV). Compared to bare GCE and CNT-N modified electrode, the MnFe2O4@CNT-N modified electrode can remarkably improve the electrocatalytic activity towards the oxidation of CF, AC and AA with an increase in the anodic peak currents of 52%, 50% and 55%, respectively. Also, the SWV anodic peaks of these molecules could be distinguished from each other at the MnFe2O4@CNT-N modified electrode with enhanced oxidation currents. The linear response ranges for the square wave voltammetric determination of CF, AC and AA were 1.0 x 10(-6) to 1.1 x 10(-3) mol dm(-3), 1.0 x 10(-6) to 1.0 x 10(-3) mol dm(-3) and 2.0 x 10(-6) to 1.0 x 10(-4) mol dm(-3) with detection limit (S/N= 3) of 0.83 x 10(-6), 0.83 x 10(-6) and 1.8 x 10(-6) mol dm(-3), respectively. The sensitivity values at the MnFe2O4@CNT-N/GCE for the individual determination of AC, AA and CF and in the presence of the other molecules showed that the quantification of AA and CF show no interferences from the other molecules; however, AA and CF interfered in the determination of AC, with the latter molecule showing the strongest interference. Nevertheless, the obtained results show that MnFe2O4@CNT-N composite material acted as an efficient electrochemical sensor towards the selected biomolecules.

10. Sucrose-derived activated carbons: electron transfer properties and application as oxygen reduction electrocatalysts
Nunes, M ; Rocha, IM ; Fernandes, DM ; Mestre, AS ; Moura, CN ; Carvalho, AP ; Pereira, MFR ; Freire, C
in RSC ADVANCES, 2015, ISSN: 2046-2069,  Volume: 5, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The development of carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) is one of the most attractive topics in fuel cell field. Herein, we report the application of two sustainable sucrose-based activated carbons (ACs), denominated SC800 and SH800, as ORR electrocatalysts. In alkaline medium the ACs showed similar onset potentials at E-onset approximate to -0.20 V vs. Ag/AgCl (0.76 V vs. E-RHE), which are 0.06 V more negative than that observed for 20 wt% Pt/C used as a reference. Higher diffusion-limiting current densities (j(L(-1.0 V, 1600 rpm)) = -3.44 mA cm(-2)) were obtained for the SH800 electrocatalyst, in contrast to SC800 (j(L(-1.0 V, 1600 rpm)) = -3.04 mA cm(-2)). These differences can be related with their different textural properties. The SH800 electrocatalyst revealed a higher specific surface area (A(BET) approximate to 2500 m(2) g(-1)), larger micropores (widths between 0.7 and 2 nm) and sponge-like morphology. Conversely, SC800 showed a spherical shape, A(BET) approximate to 1400 m(2) g(-1) and narrow micropores with pore width <0.7 nm. Both ACs were neither selective to 2- or 4-electron ORR processes, opposing Pt/C which showed selectivity towards direct O-2 reduction to water. SH800 and SC800 showed very similar Tafel plots, but with SH800 showing in both low and high current density regions, the lowest slopes values 53/171 mV dec(-1) vs. 68/217 mV dec(-1). Furthermore, the ACs presented excellent tolerance to methanol, with the SH800 electrocatalyst also showing greater long-term electrochemical stability than the Pt/C electrocatalyst which are very important advantages. The ACs-based electrocatalysts also showed ORR catalytic activity in acidic media, which makes them promising candidates for applications with acidic electrolytes (e.g. proton exchange fuel cells). In this case, E-onset = 0.06 V vs. Ag/AgCl (0.41 V vs. E-RHE) for SC800 and E-onset = -0.01 V vs. Ag/AgCl (0.34 V vs. E-RHE) for SH800, and the diffusion-limiting current densities are very similar for both ACs (jL = -2.59/-2.76 mA cm(-2) at -1.3 V vs. Ag/AgCl, at 1600 rpm). SH800 and SC800 Tafel plots also showed two different slopes, but with higher values in both low and high current density regions, when compared with those obtained in an alkaline medium; still SH800 continues to show the lowest slopes.