virginia ferreira | Universidade de Lisboa (original) (raw)

Papers by virginia ferreira

Research paper thumbnail of Monocamadas Auto-Montadas de Alcanotióis - das Superfícies Planas à Estabilização de Nanopartículas de Ouro

Research paper thumbnail of In situ synthesis and modification of cotton fibers with bismuthoxychloride and titanium dioxide nanoparticles for photocatalytic applications

Journal of Photochemistry and Photobiology A: Chemistry, 2018

Highlights-Novel Cotton-BiOCl composites have been successfully prepared-Fibers modification by s... more Highlights-Novel Cotton-BiOCl composites have been successfully prepared-Fibers modification by straightforward in situ room temperature approach-Cotton-NPs composites display photocatalytic properties towards dye degradation

Research paper thumbnail of Electrochemical, microgravimetric and AFM studies of polythionine films. Application as new support for the immobilisation of nucleotides

Sensors and Actuators, B: Chemical, 2006

The experimental conditions for the thionine potentiodynamic electropolymerisation in acidic medi... more The experimental conditions for the thionine potentiodynamic electropolymerisation in acidic media are optimised in order to achieve polythionine (PTN) modified electrodes with high stability and reproducible redox behaviour in acidic and biological compatible media. The data obtained by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) show that under the selected conditions, polythionine films growth, presents a non-linear relation between mass and electroactivity which suggests structural changes during electropolymerisation, that are corroborated by atomic force microscopy (AFM). The pH effect in the redox switching of PTN films is studied in solutions with pH from 1.3 to 12 where two processes with different dependence on protons occurs in the interval from 5.5 to 9, indicating a complex behaviour. PTN redox conversion in acidic media is film thickness sensitive and a non-permselective behaviour is found in acidic and neutral media, being the mass change dependent on the electrolyte nature. The presence of free amino functions in the polymer structure enable the nucleotide immobilisation by adsorption and covalent attachment, which was simultaneously monitored by EQCM and open circuit potential. The nucleotidic phosphate groups reactivity is enhanced by adding coupling agents leading to an higher amount of mass immobilisation.

Research paper thumbnail of Synthesis and properties of Polythionine/Co-doped titanate nanotubes hybrid materials

Electrochimica Acta, 2013

ABSTRACT The synthesis of polythionine (PTN)/cobalt-doped titanate nanotubes (CoTNTs) hybrid cond... more ABSTRACT The synthesis of polythionine (PTN)/cobalt-doped titanate nanotubes (CoTNTs) hybrid conducting films with distinct layouts, using electropolimerization, is reported. The CoTNTs nanocrystalline elongated particles were obtained by a hydrothermal treatment, using an amorphous Co-doped material as precursor. The adsorption ability of the prepared CoTNTs to remove organic dyes from aqueous media was investigated, using thionine (Th). The total amount of Th removed by the nanocrystalline CoTNTs powder was 340.06 mg g−1. During this process, and due to the CoTNTs structural properties, the combination of dye adsorption and intercalation was considered. After dye sensitization, the Th/CoTNTs were characterized and used for Th electropolymerization studies, in order to produce hybrid polythionine (PTN) electroactive films. The electroactivity of the Th molecules after immobilization in the CoTNTs surface is maintained. After electropolymerization, stable and electroactive nanostructured CoTNTs-PTN modified electrodes were obtained. The influence of the experimental parameters in the final electrical and morphological properties of the obtained hybrid films was studied, mainly the presence of the monomer in solution, adsorbed or intercalated in CoTNTs.

Research paper thumbnail of Attachment of noble metal nanoparticles to conducting polymers containing sulphur – preparation conditions for enhanced electrocatalytic activity

Electrochimica Acta, 2011

ABSTRACT Taking advantage of the spontaneous deposition of noble metals on polymers containing su... more ABSTRACT Taking advantage of the spontaneous deposition of noble metals on polymers containing sulphur, the inclusion of gold and platinum in poly(3-methylthiophene) and poly(3,4-ehylenedioxythiophene) (PEDOTh) layers, achieved by immersion of the polymer into the metal nanoparticles suspension, is reported in the present work.Platinum and gold nanoparticles (NPs), with diameters between 3 and 17nm, have been prepared from colloidal methods (citrate or borohydride reduction in the presence of citrate capping agent) and characterized by transmission electron microscopy, ultraviolet–visible spectrophotometry and X-ray diffraction (XRD). The electropolymerization was carried out under potentiostatic and potentiodynamic conditions, imparting distinct morphologies, as revealed by atomic force microscopy. After polymer films immersion in the colloidal solutions, evidence of the NPs confinement and distribution was provided by XRD analysis and scanning electron microscopy. For thin layers, the quantity of attached metal NPs could be estimated from quartz crystal microbalance data collected throughout the films immersion.The influence of the polymer type and morphology, NPs nature, size and incorporated amount on the electrocatalytic activity of the so-prepared modified electrodes towards the hydrazine oxidation, in phosphate buffer solution, has been investigated by cyclic voltammetry. The results clearly show the superior properties of potentiodynamically prepared PEDOTh films attaching very small (3nm) freshly prepared Pt-NPs.

Research paper thumbnail of Electrochemical copolymerisation of luminol with aniline: A new route for the preparation of self-doped polyanilines

Electrochimica Acta, 2008

Electrochemical copolymerisation of luminol and aniline from acidic aqueous medium onto gold elec... more Electrochemical copolymerisation of luminol and aniline from acidic aqueous medium onto gold electrodes has been investigated. Cyclic voltammetry in combination with electrochemical quartz crystal microbalance (EQCM) have been used to study both the in situ growth and redox switching process. In monomer free solution, the deposited polymers are stable and electrochemically active but distinct behaviour is shown by poly(luminol-aniline) films

Research paper thumbnail of Progress in the understanding of surface structure and surfactant influence on the electrocatalytic activity of gold nanoparticles

Electrochimica Acta, 2011

The preparation of gold nanoparticles (Au-NPs) displaying specific shape, size and surface crysta... more The preparation of gold nanoparticles (Au-NPs) displaying specific shape, size and surface crystallographic domains has been investigated aiming to clarify the effect of the surface crystallographic orientation, of the synthesised nanoparticles, and surfactant influence on the electrochemical response of the ITO/Au-NPs modified electrodes. Polymorphic and nanorod-shaped Au-NPs have been obtained using distinct synthetic procedures in the presence of cetyltrimethylammonium bromide (CTAB), through seed-mediated growth methods, displaying distinct surface crystallographic domains confirmed by transmission electron microscopy, X-ray diffraction analysis and under potential deposition (UPD) of lead. The nanoparticles have been physically immobilised by casting on indium tin oxide (ITO) surfaces and the electrocatalytic activity of the Au-NPs evaluated using the ascorbic acid (AA) oxidation reaction, by cyclic voltammetry. The polymorphic and distinct surface crystallographic orientations of the Au-NPs were reflected in an irreproducible electrochemical response. Using gold nanorods comprising (1 1 1) and (1 1 0) facets and gold nanocubes consisting of faces displaying (1 0 0) surface domains, by contrasting the behaviour of CTAB-stabilised and clean particles, it has been possible to verify that the distinct voltammetric results are due to the exposure of specific crystallographic orientations owing to dissimilar interaction strength of CTAB with those facets.

Research paper thumbnail of One-pot approach to modify nanostructured gold surfaces through in situ dithiocarbamate linkages

Electrochimica Acta, 2012

This work describes a simple methodology to bio-functionalize flat Au(1 1 1) electrodes through t... more This work describes a simple methodology to bio-functionalize flat Au(1 1 1) electrodes through the onestep reaction between gold nanoparticles (AuNPs), carbon disulfide and a secondary amine (epinephrine) and an aminoacid (tryptophan). The process relies on the in situ dithiocarbamate formation between carbon disulphide and amine groups and also on the strong linkage between sulfur and gold. The redox behavior of modified gold with epinephrine or tryptophan, prepared from both ethanolic and aqueous solutions confirms their covalent immobilization and reveals a significant increase of their amount on the electrode due to the presence of AuNPs. Electrochemical reductive desorption in basic solution provided qualitative information on the amount of sulfur linked the gold surface and complements the redox studies. The co-immobilization of an enzyme (glucose oxidase, GOx) and gold nanoparticles, using carbon disulfide has been also tested. The presence of GOx on modified Au(1 1 1) electrodes has been confirmed by electrochemical detection of the catalytic oxidation of glucose in the presence of a redox mediator and through the evaluation of H 2 O 2 reduction, formed during the catalytic reaction. XPS analysis, topographic and phase imaging by atomic force microscopy (AFM) further confirmed surface modification by AuNPs and also their functionalization. The successful one-step amine adsorption, in the presence of AuNPs, from aqueous solutions reveals the potential of this method in the construction of nanostructured biosensing interfaces.

Research paper thumbnail of Electrochemical and STM Study of α,ω-alkanedithiols Self-assembled Monolayers

Chemical and Biochemical Engineering Quarterly

Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions cont... more Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions containing α,ω-alkanedithiol, n-alkanethiol or mixed thiol/dithiol solutions, with 6, 9 and 10 carbon atoms in the alkyl chain, have been investigated. The amount of adsorbate and the SAM stability in alkaline medium is evaluated by reductive desorption of the prepared monolayers by cyclic voltammetry. An upright orientation of the dithiol self-assembled molecules and disulfide bonding at the SAM/solution interface are suggested by the higher reductive desorption charge of the dithiol monolayers (relative to thiol SAMs) for n = 6 and 9. The results show that an improvement on the stability of these dithiol SAMs is obtained by the presence of monothiols, resulting in mixed monolayers. Mixed SAMs prepared from longer alkane chain thiols, n = 10, allow to overcome the increased possibility of loop formation and therefore lower surface coverage is obtained for the 1,10-decanedithiol monolayers. ...

Research paper thumbnail of Novel one-pot synthesis and sensitisation of new BiOCl–Bi2S3 nanostructures from DES medium displaying high photocatalytic activity

RSC Advances, 2016

A novel one-pot synthetic procedure yields hierarchically nanostructured BiOCl–Bi2S3 nanoparticle... more A novel one-pot synthetic procedure yields hierarchically nanostructured BiOCl–Bi2S3 nanoparticles with improved photocatalytic activity towards degradation of rhodamine B.

Research paper thumbnail of Titanate nanofibers sensitized with nanocrystalline Bi2S 3 as new electrocatalytic materials for ascorbic acid sensor applications

, Titanate nanofibers sensitized with nanocrystalline Bi 2 S 3 as new electrocatalytic materials ... more , Titanate nanofibers sensitized with nanocrystalline Bi 2 S 3 as new electrocatalytic materials for ascorbic acid sensor applications,

Research paper thumbnail of Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

Materials Chemistry and Physics, 2013

Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes... more Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The influence of the synthesis temperature, autoclave dwell time and metal doping on the structural and microstructural as well as on the optical properties of the synthesized titanate nanotubes is studied and discussed. The optical band gaps of the CoTNT samples are red shifted in comparison with the values determined for the undoped samples, such red shifts bringing the absorption edge of the CoTNT samples into the visible region. CoTNT materials also demonstrate particular high adsorption ability for methylene blue, the amount of the adsorbed dye being higher than the one predictable for a monolayer formation. This suggests the possibility of intercalation of the dye molecule between the TiO 6 layers of the TNT structure. It is also shown that the methylene blue sensitized Co-doped nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region.

Research paper thumbnail of New hybrid titanate elongated nanostructures through organic dye molecules sensitization

Journal of Nanoparticle Research, 2013

ABSTRACT This study reports on a novel chemical route to synthesize new elongated titanates nanos... more ABSTRACT This study reports on a novel chemical route to synthesize new elongated titanates nanostructured hybrid materials by the combination of titanate nanofibers (TNFs) with organic dye molecules. The influence of the sodium/proton replacement on the adsorption and intercalation characteristics of the TNFs materials was analysed. Depending on the sodium/proton content, materials with surface areas in the 21.08–38.90 m2/g range were obtained. Due to their molecule size and shape, and anticipating their intercalation between the TiO6 layers, the cationic molecules chosen for this study were thionine, methylene blue, crystal violet and rhodamine 6G. The sample with the highest sodium content was the best material on up taking dyes from aqueous media. The amount of the immobilized dyes was higher than the one predictable for the formation of a monolayer in an adsorption process. The intercalation of thionine, methylene blue and crystal violet between the TiO6 layers was accomplished. The characterisation results obtained by adsorption, XRD and FTIR are in agreement with the production of these new hybrid structures, with the organic molecules located within the TiO6 layers. The results also demonstrate that only the thionine was incorporated in the protonated titanate structure, due to the smaller distance between the layers. The optical characterisation of the prepared materials by DRS also indicates that intercalated and adsorbed dyes have strong influence on the optical properties of the new hybrid materials prepared.

Research paper thumbnail of Ion transfer dynamics of poly(3,4-ethylenedioxythiophene) films in deep eutectic solvents

Electrochimica Acta, 2013

Mechanistic studies are reported for redox switching (doping/undoping) of Au-supported poly(3,4et... more Mechanistic studies are reported for redox switching (doping/undoping) of Au-supported poly(3,4ethylenedioxythiophene) (PEDOT) films exposed to LiClO 4 /CH 3 CN (a conventional electrolyte based on a molecular solvent) and to Ethaline and Propaline (two choline chloride-based deep eutectic solvent (DES) media). A combination of electrochemical, acoustic (quartz crystal microbalance, QCM) and optical (probe beam deflection, PBD) methods was used to monitor the exchange of mobile species between the film and the bathing electrolyte. Qualitatively, film responses to a potentiodynamic control function showed that the redox switching mechanisms are quite different in all three media. When exposed to acetonitrile, anion transfer is dominant, with some accompanying solvent transfer but negligible cation transfer; application of the convolution protocol allowed these transfers to be quantified. Analogous observations in the DES media could be interpreted qualitatively in terms of dominant cation transfer, but the convolution protocol could not be used to quantify the contributions of individual species; in these viscous media, this is a consequence of the long transit times from the film/solution interface to the optical detection zone. Chronoamperometric experiments, in which the measurement time was an order of magnitude (or more) longer permitted the diffusional processes driven by the polymer/DES interfacial population changes to reach the optical detection zone.

Research paper thumbnail of Polímeros condutores e monocamadas auto-montadas na concepção de novas arquitecturas contendo nanopartículas metálicas: preparação, caracterização e …

Nanopartículas (NPs) de ouro e de platina, com distribuições homogéneas em tamanho e forma, são s... more Nanopartículas (NPs) de ouro e de platina, com distribuições homogéneas em tamanho e forma, são sintetizadas via química e analisadas por espectroscopia de UV-vis, DRX e TEM. A caracterização electroquímica das Au-NPs, por deposição a sub-potencial de chumbo, ...

Research paper thumbnail of Novel one-pot synthesis and sensitisation of new BiOCl–Bi 2 S 3 nanostructures from DES medium displaying high photocatalytic activity

A novel route to synthesise Bi 2 S 3-sensitised BiOCl nanoparticles from deep eutectic solvent me... more A novel route to synthesise Bi 2 S 3-sensitised BiOCl nanoparticles from deep eutectic solvent medium at room temperature by a one-pot approach is reported. The influence of the temperature, sulphur source, concentration of reactants and presence of water, on the morphological, structural and microstructural, optical and photocatalytic properties of the synthesised nanoparticles is analysed and discussed. Stable and crystalline BiOCl hybrid structures with shapes from sheet-like to flower-like hierarchical aggregates and (001) and (110) dominant crystallographic orientation were obtained. The sensitisation of BiOCl with Bi 2 S 3 was successfully achieved in situ during synthesis by an ion-exchange process and the relative proportion of the components (BiOCl and Bi 2 S 3) was controlled by the Bi : S ratio in the synthesis medium and by the sulphur precursor. The sensitiser nanomaterial (Bi 2 S 3) extends the BiOCl photoactive region to the visible range. Also it favours charge separation and reducing the electron/hole pair recombination and therefore increasing the photocatalytic performance. The prepared composite materials show high ability to adsorb rhodamine B cationic dye and the complete photocatalytic degradation was achieved within 45 min (75 mg per g of catalyst).

Research paper thumbnail of Novel one-pot synthesis and sensitisation of new BiOCl–Bi2S3 nanostructures from DES medium displaying high photocatalytic activity

A novel route to synthesise Bi2S3-sensitised BiOCl nanoparticles from deep eutectic solvent mediu... more A novel route to synthesise Bi2S3-sensitised BiOCl nanoparticles from deep eutectic solvent medium at room temperature by a one-pot approach is reported. The influence of the temperature, sulphur source, concentration of reactants and presence of water, on the morphological, structural and microstructural, optical and photocatalytic properties of the synthesised nanoparticles is analysed and discussed. Stable and crystalline BiOCl hybrid structures with shapes from sheet-like to flower-like hierarchical aggregates and (001) and (110) dominant crystallographic orientation were obtained. The sensitisation of BiOCl with Bi2S3 was successfully achieved in situ during synthesis by an ion-exchange process and the relative proportion of the components (BiOCl and Bi2S3) was controlled by the Bi : S ratio in the synthesis medium and by the sulphur precursor. The sensitiser nanomaterial (Bi2S3) extends the BiOCl photoactive region to the visible range. Also it favours charge separation and reducing the electron/hole pair recombination and therefore increasing the photocatalytic performance. The prepared composite materials show high ability to adsorb rhodamine B cationic dye and the complete photocatalytic degradation was achieved within 45 min (75 mg per g of catalyst).

Research paper thumbnail of Application of the combined electrochemical quartz crystal microbalance and probe beam deflection technique in deep eutectic solvents

Electrochimica Acta, 2014

ABSTRACT The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) h... more ABSTRACT The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) have been widely used to study interfacial processes in molecular solvent-based electrolytes. However, there has been limited use of the EQCM and none of PBD in room temperature ionic liquids, including deep eutectic solvents (DES). Here we explore the use of the combined EQCM/PBD technique to the study of Ag and Sn electrodeposition from a DES comprising a 1:2 mixture of choline chloride and ethylene glycol. While overcoming the effect of viscous loss in the acoustic wave (EQCM) part of the experiment is understood, the optical (PBD) technique fails to provide a meaningful response in slow scan rate voltammetric experiments; this contrasts sharply with the straightforward behaviour seen in aqueous media. Solution transport considerations reveal this to be a consequence of long surface-to-beam transit times in the viscous DES. The problem can be overcome by operating at scan rates 1-2 orders of magnitude slower, permitting application of this powerful technique to novel media of technological interest. The PBD responses reveal unanticipated chemical effects: multiple complexes in the Ag system and solubility limitations in the Sn system, neither of which is evident from the electrochemical or QCM responses.

Research paper thumbnail of Electrochemical and Morphological Characterization of New Architectures Containing Self-Assembled Monolayers and Au-NPs

Pure 1,10-decanedithiol (C 10 -SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled mo... more Pure 1,10-decanedithiol (C 10 -SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free -SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN) 6 3-, in KNO 3 solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C 10 -SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free -SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C 10 -SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C 10 -SH SAM upon layer-by-layer modification was performed ex situ in air.

Research paper thumbnail of Conducting polymers with attached platinum nanoparticles towards the development of DNA biosensors

Based on the strong interaction of noble metal particles with the sulphur atoms of thiophene deri... more Based on the strong interaction of noble metal particles with the sulphur atoms of thiophene derivatives, platinum nanoparticles (Pt-NPs)-dispersed poly(3-methylthiophene) (P(3-MeTh)) thin films have been successfully prepared. Evidence of the Pt-NPs confinement in the polymer was provided by the electrocatalytic activity of the modified electrodes towards the dissolved oxygen reduction reaction. The efficient immobilization by self-assembly of thiolated oligonucleotides on the embedded Pt-NPs could be monitored by electrochemical quartz crystal microbalance (EQCM) as well as the subsequent hybridization with the complementary sequence. The good conducting properties and high surface area of P(3-MeTh)/Pt-NPs modified electrodes also allowed the detection of both processes by cyclic voltammetry.

Research paper thumbnail of Monocamadas Auto-Montadas de Alcanotióis - das Superfícies Planas à Estabilização de Nanopartículas de Ouro

Research paper thumbnail of In situ synthesis and modification of cotton fibers with bismuthoxychloride and titanium dioxide nanoparticles for photocatalytic applications

Journal of Photochemistry and Photobiology A: Chemistry, 2018

Highlights-Novel Cotton-BiOCl composites have been successfully prepared-Fibers modification by s... more Highlights-Novel Cotton-BiOCl composites have been successfully prepared-Fibers modification by straightforward in situ room temperature approach-Cotton-NPs composites display photocatalytic properties towards dye degradation

Research paper thumbnail of Electrochemical, microgravimetric and AFM studies of polythionine films. Application as new support for the immobilisation of nucleotides

Sensors and Actuators, B: Chemical, 2006

The experimental conditions for the thionine potentiodynamic electropolymerisation in acidic medi... more The experimental conditions for the thionine potentiodynamic electropolymerisation in acidic media are optimised in order to achieve polythionine (PTN) modified electrodes with high stability and reproducible redox behaviour in acidic and biological compatible media. The data obtained by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) show that under the selected conditions, polythionine films growth, presents a non-linear relation between mass and electroactivity which suggests structural changes during electropolymerisation, that are corroborated by atomic force microscopy (AFM). The pH effect in the redox switching of PTN films is studied in solutions with pH from 1.3 to 12 where two processes with different dependence on protons occurs in the interval from 5.5 to 9, indicating a complex behaviour. PTN redox conversion in acidic media is film thickness sensitive and a non-permselective behaviour is found in acidic and neutral media, being the mass change dependent on the electrolyte nature. The presence of free amino functions in the polymer structure enable the nucleotide immobilisation by adsorption and covalent attachment, which was simultaneously monitored by EQCM and open circuit potential. The nucleotidic phosphate groups reactivity is enhanced by adding coupling agents leading to an higher amount of mass immobilisation.

Research paper thumbnail of Synthesis and properties of Polythionine/Co-doped titanate nanotubes hybrid materials

Electrochimica Acta, 2013

ABSTRACT The synthesis of polythionine (PTN)/cobalt-doped titanate nanotubes (CoTNTs) hybrid cond... more ABSTRACT The synthesis of polythionine (PTN)/cobalt-doped titanate nanotubes (CoTNTs) hybrid conducting films with distinct layouts, using electropolimerization, is reported. The CoTNTs nanocrystalline elongated particles were obtained by a hydrothermal treatment, using an amorphous Co-doped material as precursor. The adsorption ability of the prepared CoTNTs to remove organic dyes from aqueous media was investigated, using thionine (Th). The total amount of Th removed by the nanocrystalline CoTNTs powder was 340.06 mg g−1. During this process, and due to the CoTNTs structural properties, the combination of dye adsorption and intercalation was considered. After dye sensitization, the Th/CoTNTs were characterized and used for Th electropolymerization studies, in order to produce hybrid polythionine (PTN) electroactive films. The electroactivity of the Th molecules after immobilization in the CoTNTs surface is maintained. After electropolymerization, stable and electroactive nanostructured CoTNTs-PTN modified electrodes were obtained. The influence of the experimental parameters in the final electrical and morphological properties of the obtained hybrid films was studied, mainly the presence of the monomer in solution, adsorbed or intercalated in CoTNTs.

Research paper thumbnail of Attachment of noble metal nanoparticles to conducting polymers containing sulphur – preparation conditions for enhanced electrocatalytic activity

Electrochimica Acta, 2011

ABSTRACT Taking advantage of the spontaneous deposition of noble metals on polymers containing su... more ABSTRACT Taking advantage of the spontaneous deposition of noble metals on polymers containing sulphur, the inclusion of gold and platinum in poly(3-methylthiophene) and poly(3,4-ehylenedioxythiophene) (PEDOTh) layers, achieved by immersion of the polymer into the metal nanoparticles suspension, is reported in the present work.Platinum and gold nanoparticles (NPs), with diameters between 3 and 17nm, have been prepared from colloidal methods (citrate or borohydride reduction in the presence of citrate capping agent) and characterized by transmission electron microscopy, ultraviolet–visible spectrophotometry and X-ray diffraction (XRD). The electropolymerization was carried out under potentiostatic and potentiodynamic conditions, imparting distinct morphologies, as revealed by atomic force microscopy. After polymer films immersion in the colloidal solutions, evidence of the NPs confinement and distribution was provided by XRD analysis and scanning electron microscopy. For thin layers, the quantity of attached metal NPs could be estimated from quartz crystal microbalance data collected throughout the films immersion.The influence of the polymer type and morphology, NPs nature, size and incorporated amount on the electrocatalytic activity of the so-prepared modified electrodes towards the hydrazine oxidation, in phosphate buffer solution, has been investigated by cyclic voltammetry. The results clearly show the superior properties of potentiodynamically prepared PEDOTh films attaching very small (3nm) freshly prepared Pt-NPs.

Research paper thumbnail of Electrochemical copolymerisation of luminol with aniline: A new route for the preparation of self-doped polyanilines

Electrochimica Acta, 2008

Electrochemical copolymerisation of luminol and aniline from acidic aqueous medium onto gold elec... more Electrochemical copolymerisation of luminol and aniline from acidic aqueous medium onto gold electrodes has been investigated. Cyclic voltammetry in combination with electrochemical quartz crystal microbalance (EQCM) have been used to study both the in situ growth and redox switching process. In monomer free solution, the deposited polymers are stable and electrochemically active but distinct behaviour is shown by poly(luminol-aniline) films

Research paper thumbnail of Progress in the understanding of surface structure and surfactant influence on the electrocatalytic activity of gold nanoparticles

Electrochimica Acta, 2011

The preparation of gold nanoparticles (Au-NPs) displaying specific shape, size and surface crysta... more The preparation of gold nanoparticles (Au-NPs) displaying specific shape, size and surface crystallographic domains has been investigated aiming to clarify the effect of the surface crystallographic orientation, of the synthesised nanoparticles, and surfactant influence on the electrochemical response of the ITO/Au-NPs modified electrodes. Polymorphic and nanorod-shaped Au-NPs have been obtained using distinct synthetic procedures in the presence of cetyltrimethylammonium bromide (CTAB), through seed-mediated growth methods, displaying distinct surface crystallographic domains confirmed by transmission electron microscopy, X-ray diffraction analysis and under potential deposition (UPD) of lead. The nanoparticles have been physically immobilised by casting on indium tin oxide (ITO) surfaces and the electrocatalytic activity of the Au-NPs evaluated using the ascorbic acid (AA) oxidation reaction, by cyclic voltammetry. The polymorphic and distinct surface crystallographic orientations of the Au-NPs were reflected in an irreproducible electrochemical response. Using gold nanorods comprising (1 1 1) and (1 1 0) facets and gold nanocubes consisting of faces displaying (1 0 0) surface domains, by contrasting the behaviour of CTAB-stabilised and clean particles, it has been possible to verify that the distinct voltammetric results are due to the exposure of specific crystallographic orientations owing to dissimilar interaction strength of CTAB with those facets.

Research paper thumbnail of One-pot approach to modify nanostructured gold surfaces through in situ dithiocarbamate linkages

Electrochimica Acta, 2012

This work describes a simple methodology to bio-functionalize flat Au(1 1 1) electrodes through t... more This work describes a simple methodology to bio-functionalize flat Au(1 1 1) electrodes through the onestep reaction between gold nanoparticles (AuNPs), carbon disulfide and a secondary amine (epinephrine) and an aminoacid (tryptophan). The process relies on the in situ dithiocarbamate formation between carbon disulphide and amine groups and also on the strong linkage between sulfur and gold. The redox behavior of modified gold with epinephrine or tryptophan, prepared from both ethanolic and aqueous solutions confirms their covalent immobilization and reveals a significant increase of their amount on the electrode due to the presence of AuNPs. Electrochemical reductive desorption in basic solution provided qualitative information on the amount of sulfur linked the gold surface and complements the redox studies. The co-immobilization of an enzyme (glucose oxidase, GOx) and gold nanoparticles, using carbon disulfide has been also tested. The presence of GOx on modified Au(1 1 1) electrodes has been confirmed by electrochemical detection of the catalytic oxidation of glucose in the presence of a redox mediator and through the evaluation of H 2 O 2 reduction, formed during the catalytic reaction. XPS analysis, topographic and phase imaging by atomic force microscopy (AFM) further confirmed surface modification by AuNPs and also their functionalization. The successful one-step amine adsorption, in the presence of AuNPs, from aqueous solutions reveals the potential of this method in the construction of nanostructured biosensing interfaces.

Research paper thumbnail of Electrochemical and STM Study of α,ω-alkanedithiols Self-assembled Monolayers

Chemical and Biochemical Engineering Quarterly

Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions cont... more Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions containing α,ω-alkanedithiol, n-alkanethiol or mixed thiol/dithiol solutions, with 6, 9 and 10 carbon atoms in the alkyl chain, have been investigated. The amount of adsorbate and the SAM stability in alkaline medium is evaluated by reductive desorption of the prepared monolayers by cyclic voltammetry. An upright orientation of the dithiol self-assembled molecules and disulfide bonding at the SAM/solution interface are suggested by the higher reductive desorption charge of the dithiol monolayers (relative to thiol SAMs) for n = 6 and 9. The results show that an improvement on the stability of these dithiol SAMs is obtained by the presence of monothiols, resulting in mixed monolayers. Mixed SAMs prepared from longer alkane chain thiols, n = 10, allow to overcome the increased possibility of loop formation and therefore lower surface coverage is obtained for the 1,10-decanedithiol monolayers. ...

Research paper thumbnail of Novel one-pot synthesis and sensitisation of new BiOCl–Bi2S3 nanostructures from DES medium displaying high photocatalytic activity

RSC Advances, 2016

A novel one-pot synthetic procedure yields hierarchically nanostructured BiOCl–Bi2S3 nanoparticle... more A novel one-pot synthetic procedure yields hierarchically nanostructured BiOCl–Bi2S3 nanoparticles with improved photocatalytic activity towards degradation of rhodamine B.

Research paper thumbnail of Titanate nanofibers sensitized with nanocrystalline Bi2S 3 as new electrocatalytic materials for ascorbic acid sensor applications

, Titanate nanofibers sensitized with nanocrystalline Bi 2 S 3 as new electrocatalytic materials ... more , Titanate nanofibers sensitized with nanocrystalline Bi 2 S 3 as new electrocatalytic materials for ascorbic acid sensor applications,

Research paper thumbnail of Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

Materials Chemistry and Physics, 2013

Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes... more Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The influence of the synthesis temperature, autoclave dwell time and metal doping on the structural and microstructural as well as on the optical properties of the synthesized titanate nanotubes is studied and discussed. The optical band gaps of the CoTNT samples are red shifted in comparison with the values determined for the undoped samples, such red shifts bringing the absorption edge of the CoTNT samples into the visible region. CoTNT materials also demonstrate particular high adsorption ability for methylene blue, the amount of the adsorbed dye being higher than the one predictable for a monolayer formation. This suggests the possibility of intercalation of the dye molecule between the TiO 6 layers of the TNT structure. It is also shown that the methylene blue sensitized Co-doped nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region.

Research paper thumbnail of New hybrid titanate elongated nanostructures through organic dye molecules sensitization

Journal of Nanoparticle Research, 2013

ABSTRACT This study reports on a novel chemical route to synthesize new elongated titanates nanos... more ABSTRACT This study reports on a novel chemical route to synthesize new elongated titanates nanostructured hybrid materials by the combination of titanate nanofibers (TNFs) with organic dye molecules. The influence of the sodium/proton replacement on the adsorption and intercalation characteristics of the TNFs materials was analysed. Depending on the sodium/proton content, materials with surface areas in the 21.08–38.90 m2/g range were obtained. Due to their molecule size and shape, and anticipating their intercalation between the TiO6 layers, the cationic molecules chosen for this study were thionine, methylene blue, crystal violet and rhodamine 6G. The sample with the highest sodium content was the best material on up taking dyes from aqueous media. The amount of the immobilized dyes was higher than the one predictable for the formation of a monolayer in an adsorption process. The intercalation of thionine, methylene blue and crystal violet between the TiO6 layers was accomplished. The characterisation results obtained by adsorption, XRD and FTIR are in agreement with the production of these new hybrid structures, with the organic molecules located within the TiO6 layers. The results also demonstrate that only the thionine was incorporated in the protonated titanate structure, due to the smaller distance between the layers. The optical characterisation of the prepared materials by DRS also indicates that intercalated and adsorbed dyes have strong influence on the optical properties of the new hybrid materials prepared.

Research paper thumbnail of Ion transfer dynamics of poly(3,4-ethylenedioxythiophene) films in deep eutectic solvents

Electrochimica Acta, 2013

Mechanistic studies are reported for redox switching (doping/undoping) of Au-supported poly(3,4et... more Mechanistic studies are reported for redox switching (doping/undoping) of Au-supported poly(3,4ethylenedioxythiophene) (PEDOT) films exposed to LiClO 4 /CH 3 CN (a conventional electrolyte based on a molecular solvent) and to Ethaline and Propaline (two choline chloride-based deep eutectic solvent (DES) media). A combination of electrochemical, acoustic (quartz crystal microbalance, QCM) and optical (probe beam deflection, PBD) methods was used to monitor the exchange of mobile species between the film and the bathing electrolyte. Qualitatively, film responses to a potentiodynamic control function showed that the redox switching mechanisms are quite different in all three media. When exposed to acetonitrile, anion transfer is dominant, with some accompanying solvent transfer but negligible cation transfer; application of the convolution protocol allowed these transfers to be quantified. Analogous observations in the DES media could be interpreted qualitatively in terms of dominant cation transfer, but the convolution protocol could not be used to quantify the contributions of individual species; in these viscous media, this is a consequence of the long transit times from the film/solution interface to the optical detection zone. Chronoamperometric experiments, in which the measurement time was an order of magnitude (or more) longer permitted the diffusional processes driven by the polymer/DES interfacial population changes to reach the optical detection zone.

Research paper thumbnail of Polímeros condutores e monocamadas auto-montadas na concepção de novas arquitecturas contendo nanopartículas metálicas: preparação, caracterização e …

Nanopartículas (NPs) de ouro e de platina, com distribuições homogéneas em tamanho e forma, são s... more Nanopartículas (NPs) de ouro e de platina, com distribuições homogéneas em tamanho e forma, são sintetizadas via química e analisadas por espectroscopia de UV-vis, DRX e TEM. A caracterização electroquímica das Au-NPs, por deposição a sub-potencial de chumbo, ...

Research paper thumbnail of Novel one-pot synthesis and sensitisation of new BiOCl–Bi 2 S 3 nanostructures from DES medium displaying high photocatalytic activity

A novel route to synthesise Bi 2 S 3-sensitised BiOCl nanoparticles from deep eutectic solvent me... more A novel route to synthesise Bi 2 S 3-sensitised BiOCl nanoparticles from deep eutectic solvent medium at room temperature by a one-pot approach is reported. The influence of the temperature, sulphur source, concentration of reactants and presence of water, on the morphological, structural and microstructural, optical and photocatalytic properties of the synthesised nanoparticles is analysed and discussed. Stable and crystalline BiOCl hybrid structures with shapes from sheet-like to flower-like hierarchical aggregates and (001) and (110) dominant crystallographic orientation were obtained. The sensitisation of BiOCl with Bi 2 S 3 was successfully achieved in situ during synthesis by an ion-exchange process and the relative proportion of the components (BiOCl and Bi 2 S 3) was controlled by the Bi : S ratio in the synthesis medium and by the sulphur precursor. The sensitiser nanomaterial (Bi 2 S 3) extends the BiOCl photoactive region to the visible range. Also it favours charge separation and reducing the electron/hole pair recombination and therefore increasing the photocatalytic performance. The prepared composite materials show high ability to adsorb rhodamine B cationic dye and the complete photocatalytic degradation was achieved within 45 min (75 mg per g of catalyst).

Research paper thumbnail of Novel one-pot synthesis and sensitisation of new BiOCl–Bi2S3 nanostructures from DES medium displaying high photocatalytic activity

A novel route to synthesise Bi2S3-sensitised BiOCl nanoparticles from deep eutectic solvent mediu... more A novel route to synthesise Bi2S3-sensitised BiOCl nanoparticles from deep eutectic solvent medium at room temperature by a one-pot approach is reported. The influence of the temperature, sulphur source, concentration of reactants and presence of water, on the morphological, structural and microstructural, optical and photocatalytic properties of the synthesised nanoparticles is analysed and discussed. Stable and crystalline BiOCl hybrid structures with shapes from sheet-like to flower-like hierarchical aggregates and (001) and (110) dominant crystallographic orientation were obtained. The sensitisation of BiOCl with Bi2S3 was successfully achieved in situ during synthesis by an ion-exchange process and the relative proportion of the components (BiOCl and Bi2S3) was controlled by the Bi : S ratio in the synthesis medium and by the sulphur precursor. The sensitiser nanomaterial (Bi2S3) extends the BiOCl photoactive region to the visible range. Also it favours charge separation and reducing the electron/hole pair recombination and therefore increasing the photocatalytic performance. The prepared composite materials show high ability to adsorb rhodamine B cationic dye and the complete photocatalytic degradation was achieved within 45 min (75 mg per g of catalyst).

Research paper thumbnail of Application of the combined electrochemical quartz crystal microbalance and probe beam deflection technique in deep eutectic solvents

Electrochimica Acta, 2014

ABSTRACT The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) h... more ABSTRACT The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) have been widely used to study interfacial processes in molecular solvent-based electrolytes. However, there has been limited use of the EQCM and none of PBD in room temperature ionic liquids, including deep eutectic solvents (DES). Here we explore the use of the combined EQCM/PBD technique to the study of Ag and Sn electrodeposition from a DES comprising a 1:2 mixture of choline chloride and ethylene glycol. While overcoming the effect of viscous loss in the acoustic wave (EQCM) part of the experiment is understood, the optical (PBD) technique fails to provide a meaningful response in slow scan rate voltammetric experiments; this contrasts sharply with the straightforward behaviour seen in aqueous media. Solution transport considerations reveal this to be a consequence of long surface-to-beam transit times in the viscous DES. The problem can be overcome by operating at scan rates 1-2 orders of magnitude slower, permitting application of this powerful technique to novel media of technological interest. The PBD responses reveal unanticipated chemical effects: multiple complexes in the Ag system and solubility limitations in the Sn system, neither of which is evident from the electrochemical or QCM responses.

Research paper thumbnail of Electrochemical and Morphological Characterization of New Architectures Containing Self-Assembled Monolayers and Au-NPs

Pure 1,10-decanedithiol (C 10 -SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled mo... more Pure 1,10-decanedithiol (C 10 -SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free -SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN) 6 3-, in KNO 3 solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C 10 -SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free -SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C 10 -SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C 10 -SH SAM upon layer-by-layer modification was performed ex situ in air.

Research paper thumbnail of Conducting polymers with attached platinum nanoparticles towards the development of DNA biosensors

Based on the strong interaction of noble metal particles with the sulphur atoms of thiophene deri... more Based on the strong interaction of noble metal particles with the sulphur atoms of thiophene derivatives, platinum nanoparticles (Pt-NPs)-dispersed poly(3-methylthiophene) (P(3-MeTh)) thin films have been successfully prepared. Evidence of the Pt-NPs confinement in the polymer was provided by the electrocatalytic activity of the modified electrodes towards the dissolved oxygen reduction reaction. The efficient immobilization by self-assembly of thiolated oligonucleotides on the embedded Pt-NPs could be monitored by electrochemical quartz crystal microbalance (EQCM) as well as the subsequent hybridization with the complementary sequence. The good conducting properties and high surface area of P(3-MeTh)/Pt-NPs modified electrodes also allowed the detection of both processes by cyclic voltammetry.