Virginia Ruiz

• PhD
• Senior Researcher at University of Burgos

Polyacrylonitrile (PAN) nanofibrous membranes incorporating graphene quantum dots (GQD) as photoantibacterial additives were prepared by electrospinning. GQD encapsulation in the composite GQD-PAN membranes proved very stable, with negligible GQD leakage after 1 month immersed in neutral phosphate buffer solutions. A series of GQD-PAN membranes wit...

On‐paper microsupercapacitors (MSCs) are a key energy storage component for disposable electronics that are anticipated to essentially address the increasing global concern of electronic waste. However, nearly none of the present on‐paper MSCs combine eco‐friendliness with high electrochemical performance (especially the rate capacity). In this wor...

Reactive oxygen species (ROS) are important in regulating normal cell physiological functions, i.e., cell death, proliferation and differentiation. Redox modulation could have significant implications providing an opportunity for the development of new strategies to improve clinical therapeutic outcomes in the treatment of diabetes, hypertension, a...

Graphene oxide quantum dots (GOQD) covalently immobilized in hydrogels have shown great promise as artificial enzymes for the photodegradation of the organic dye rhodamine B (RhB). Suitably functionalized with cross-linkable 3-(triethoxysilyl)propyl methacrylate (MPS) units, GOQD-MPS were incorporated by free radical copolymerization into poly[2-(M...

Graphene quantum dots (GQD) are promising visible‐light photocatalysts for organic dye degradation. Besides having improved visible‐light activity compared with commercial TiO2, GQD are versatile photocatalysts as their chemical composition and, consequently, optical properties can be tuned synthetically, with a direct impact on photoactivity. Howe...

Poly(ethylene glycol)(PEG)chains were covalently grafted onto carbon black (CB)using a PEG-terminated trimethoxysilane, yielding PEGylated CB additives (CB-SiPEG)with different SiPEG contents. Unlike pristine CB, CB-SiPEG was readily dispersed in PEG200 base oil, with CB-SiPEG hydrodynamic particle sizes being considerably smaller than those of pri...

We report a method to encapsulate graphene quantum dots (GQD) in polyacrylonitrile (PAN) nanofibrous membranes to manufacture robust filtering membranes by electrospinning. GQD-PAN membranes with different nanofiber diameter were prepared tuning the electrospinning parameters, all exhibiting the characteristic fluorescence fingerprint of the GQD pr...

The antioxidant activity of graphene quantum dots (GQD) with different chemical composition and sp²-hybridized carbon content has been evaluated and compared to that of a standard antioxidant, ascorbic acid. GQD were prepared by top down and bottom up synthetic approaches from three different precursors (carbon black, glucose and pyrene) in order t...

Changes in the optical properties of Graphene Quantum Dots (GQD) during electrochemical reduction and oxidation were investigated by photoluminescence (PL) spectroelectrochemistry, which provided direct in-situ evidence of the dependence of GQD luminescence on their redox state. We demonstrated that GQD PL intensity was enhanced upon reduction (qua...

A simple and versatile method to produce filtration membranes with graphene quantum dots (GQD) and their excellent performance as turn-off fluorescence sensing platforms for Cr (VI) detection in water is presented. Suitably functionalized GQD were immobilized on various types of membranes (nylon, cellulose and glass fiber) and the resulting GQD-mod...

Optically transparent electrodes (OTEs) are needed for a wide range of applications such as solar cells, printable electronics, touch screens, light emitting diodes or flexible displays. Furthermore, OTEs are required for normal transmission spectroelectrochemistry measurements to obtain simultaneously electrochemical and spectroscopic responses. T...

Direct alcohol fuel cells are viewed as a promising candidate for powering portable electronics due to the high volumetric energy density of alcohols. Methanol is often used as the fuel because its electro-oxidation is relatively simple. However, ethanol is more preferable as it is non-toxic and has higher energy density but on the other hand, its...

Cellulose nanocrystal-stabilized graphene (GR-CNC) was produced by liquid phase exfoliation of graphite assisted by cellulose nanocrystals (CNC), a recently reported method that allows stabilization of resulting graphene flakes in aqueous dispersions. Using a simple and environmentally friendly process, GR-CNC was incorporated into poly(vinyl alcoh...

A room temperature graphene quantum dots (GQDs) based sensing material for relative humidity monitoring is presented. GQDs are synthesized by pyrolysis of citric acid and are deposited on a metallic interdigitated microelectrodes by drop-casting technology. GQDs are nanosheets around 20 nm in average lateral size and an average height of 2.7 ± 0.9...

UV-Visible, NIR and Raman spectroelectrochemistry techniques have been used for the in-situ study of Pt nanoparticles (PtNPs) electrosynthesis on an electrochemically generated poly(3,4-ethylenedioxythiophene) film. Two electrochemical steps have been used to obtain in a reproducible way PtNPs with catalytic properties towards methanol oxidation: 1...

Modification of electrodes with metal nanoparticles (NPs) is attracting intense interest because the widespread applications of these electrodes as sensors in electroanalysis. In the present study, we have analysed the electrodeposition of gold nanoparticles (Au NPs) on a platinum electrode in presence of polyvinylpyrrolidone using UV/Vis spectroel...

Nitrogen-doped graphene nanoplatelets (N-GNP) with 1.6-3.3 at.% nitrogen content were synthesized by thermal annealing of GNP functionalized with a series of imidazole-based nitrogen-containing precursors of different nature, charge and nitrogen content. The imidazole derivatives included one ionic liquid, 1-butyl-3-methylimidazolium tetrafluorobor...

This work describes the fabrication of a new lactate biosensor. The strategy is based on the use of a novel hybrid nanomaterial for amperometric biosensors i.e. platinum nanoparticles (PtNps) supported on graphitized carbon nanofibers (PtNps/GCNF) prepared by chemical reduction of the Pt precursor at GCNF surfaces. The biosensors were constructed b...

Reduced graphene oxide (RGO) films have been electrodeposited on indium tin oxide coated polyethylene terephthalate substrates (ITO-PET) from graphene oxide (GO) solutions and the resulting flexible transparent electrodes have been used in electrochromic devices of ethyl viologen (EtV2+). The electrochromic performance of devices with bare ITO-PET...

Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric–sulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by mean...

A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highly graphitized carbon nanofibers (CNFs) was carried out using fluorine-19 nuclear magnetic resonance spectroscopy. On the basis of the values obtained for the equilibrium constant (Keq , derived from Langmuir isotherm), the ionomer has varying affinities...

Durability issues have recently been given much attention in Proton Exchange Membrane Fuel Cell (PEMFC) research. It gives fundamental definition for cell life time, capital cost, system stability and technique reliability. Loss of catalyst surface area due to corrosion of supporting material (normally carbon black) is one of the essential degradat...

UV/Vis spectroelectrochemistry has been used to study the electrochemical synthesis of gold nanoparticles using a novel multipulse method. Evolution of the spectra during nanoparticle formation indicates that oxidized gold plays an essential role to obtain metal agglomerates with different size. Spectroelectrochemistry allowed us to perform in-situ...

The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion� contents (30, 50 and 70 wt% or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in...

The counter electrodes (CEs) for flexible dye solar cells (DSCs) are normally prepared by sputtering platinum on indium tin oxide (ITO) plastic substrate. However both ITO and platinum are expensive materials that need to be replaced with cheaper alternatives in large scale production of low-cost DSCs. We fabricated a flexible and completely carbon...

Spatial scanning spectroelectrochemistry is a new analytical technique that provides spectral information at different distances from an electrified liquid/liquid interface where an electrochemical process takes place. As a proof of concept, we have studied two different electrochemical processes at the electrified liquid/liquid interface: (1) Ru(b...

PtRu catalysts with similar particle size and composition were deposited on three different carbon supports: Vulcan, graphitized carbon nanofibers (GNF) and few-walled carbon nanotubes (FWCNT) and their performance for methanol oxidation was studied in an electrochemical cell and in a single cell DMFC. The electrochemical results indicate that with...

In this paper, we report the preparation of highly stable gold nanoparticles/poly(3,4-ethylendioxythiophene) nanocomposites by a one-pot chemical route in aqueous medium without surfactants to increase the solubility of the monomer (3,4-ethylendioxythiophene, EDOT) or to stabilize gold nanoparticles (Au NPs). The generation of the nanocomposite was...

Coating a carbon electrode surface, specifically highly oriented pyrolytic graphite (HOPG) with an ultrathin film of poly-(3,4-ethylenedioxythiophene), PEDOT, provides a support on which a high density of uniformly dispersed Pt nanoparticles (NPs) can readily be formed by electrodeposition. The NPs tend to be much smaller, have a higher surface cov...

Graphitised carbon nanofibres (G-CNFs) show superior thermal stability and corrosion resistance in PEM fuel cell environment over traditional carbon black (CB) and carbon nanotube catalyst supports. However, G-CNFs have an inert surface with only very limited amount of surface defects for the anchorage of Pt catalyst nanoparticles. Modification of...

We report a simple and rapid method to prepare multifunctional free-standing single-walled carbon nanotube (SWCNT) films with variable thicknesses ranging from a submonolayer to a few micrometers having outstanding properties for a broad range of exceptionally performing devices. We have fabricated state-of-the-art key components from the same sing...

A new combination of a low-resolution Raman spectrometer with a minipotentiostat is presented in this work to perform in situ Raman measurements during electrochemical experiments with low-cost instrumentation. The instrumental setup has been used to study the electrochemical oxidation of transparent single walled carbon nanotube (SWCNT) films supp...

Second CARISMA International Conference on Progress in MEA Materials for Medium and High Temperature Polymer Electrolyte Fuel Cells, Progress MEA 2010. La Grande Motte, FR, 19 - 22 Sept. 2010, 122 Vapor grown carbon fibers (VGCF) by Showa Denko are highly graphitized carbon nanofibers with a diameter of 150 nm. VGCFs show superior thermal stability...

Pyrroloquinoline quinone (PQQ) was immobilized on glassy-carbon electrodes (GCE) modified with single-walled carbon nanotubes (SWCNT), few-walled carbon nanotubes (FWCNT) and carbon black (Vulcan XC72R). Modified electrodes were prepared by drop-casting. Immobilization was achieved with an extremely simple dipping procedure and without any further...

Poly(3,4-ethylenedioxythiophene) and tungsten oxide films with enhanced electrochromism were prepared by templated electrodeposition on flexible transparent carbon nanotube electrodes. The nanostructured porous architectures obtained by coating the nanotube templates exhibited high contrast with faster switching response, higher coloration efficien...

The use of a thin carbon nanotube (CNT) counter electrode (CE) on plastic in a dye solar cell (DSC) is demonstrated as an alternative to expensive indium tin oxide and platinum materials. Optically transparent, single-walled CNT films synthesized by the aerosol CVD method and dry-printed on PET plastic substrates functioned as both the catalyst and...

We present two novel UV–vis absorption spectroelectrochemical cells for the study of electrochemical processes at polarized liquid|liquid interfaces based on the parallel incidence of the light beam with respect to the interface. The first one is a crude design (Cell 1) based on an existing cylindrical cell for liquid|liquid electrochemistry. The s...

We present a fast and effective electrochemical method to purify random networks of single-walled carbon nanotubes (SWCNTs) that leads to total removal of metal catalyst without apparent detrimental effect on the electrochemical properties of the electrodes. The efficiency of the electrochemical purification has been compared with that of conventio...

We present a simple and reproducible method to produce single-walled carbon nanotube (SWCNT) optically transparent electrodes (OTEs) for optical transmission spectroelectrochemistry on flexible and insulating Polyethylene terephthalate (PET) supports. SWCNTs grown by aerosol chemical vapor deposition (CVD) and collected directly from the gas phase...

A new composite material based on the electrochemical generation of a layer-by-layer structure of polyaniline (PANI) and Pt particles has been prepared. The number of layers and the nature of the external layer (PANI or Pt) determine the electrocatalytic performance of the composite for the oxidation of methanol. We demonstrate that the layer-by-la...

This article reports on the charging behavior of thin films of alkanethiol protected gold nanoparticles, socalled monolayer protected clusters (MPCs), immersed in aqueous solution. We demonstrate that the oxidation of the MPCs is controlled by the transfer of counter-ions across the aqueous/MPC film interface. A model is developed to describe this...

Metal nanoparticles coated with an organic monolayer, so-called monolayer protected clusters (MPCs), can show quantised charging at room temperature due to their sub-attofarad capacitance arising from the core size and the nature of the protecting monolayer. In this tutorial review, we examine the factors affecting the energetics of MPC charging. I...

A synthesis strategy to obtain monodisperse hexanethiolate-protected Au38 clusters based on their resistance to etching upon exposure to a hyperexcess of thiol is reported. The reduction time in the standard Brust-Schiffrin two-phase synthesis was optimized such that Au38 were the only clusters that were fully passivated by the thiol monolayer whic...

This paper shows that oligomers are retained inside the polymer film during the electrosynthesis of poly(3,4-ethylenedioxythiophene), PEDOT, in aqueous media. The behavior of the electrochemically generated PEDOT film is highly dependent on the presence of these oligomers. A detailed study of the release of oligomers trapped in the PEDOT film has b...

UV-vis reflection spectroelectrochemistry has proven to be a very useful multiresponse technique to evaluate the quality of bismuth films obtained by electrochemical deposition on glassy carbon electrodes (GCEs). Bismuth films have recently emerged as a promising and environmental friendly alternative to mercury electrodes for stripping analysis. S...

We demonstrate that scanning electrochemical microscopy (SECM) can be used to determine the conductivity of nanoparticle assemblies as a function of assembly potential. In contrast to conventional electron transport measurements, this method is unique in that electrical connection to the film is not required. The electrochemical potential of the as...

Luminescent ruthenium trisbipyridine complexes containing one or two mercapto-alkyl chain(s) on one of the bipyridyl units have been synthesized through a new strategy. The electrochemical and photophysical properties, determined in solution and in the solid state were compared. Deposition on electrode surfaces (gold, platinum and indium tin oxide)...

For hydrophobic redox films immersed in aqueous electrolyte, electron transfer at the electrode/film interface is coupled to ion transfer across the film/solution interface. Here we consider how differences in ion solvation in the film versus the electrolyte phase can control the apparent redox properties of model electroactive thin films.

A new procedure for the electrosynthesis of polyaniline (PANI), based on the electropolymerization of aniline on a PANI-modified electrode, is proposed. The procedure is controlled by the chemical reaction between the aniline and the highest oxidized form of PANI. A spectroelectrochemical flow cell has been used to study the influence of the flow r...

The spectroelectrochemistry of multilayer films of hexanethiolate-protected Au147 clusters (C6-Au147 MPCs) supported on gold electrodes has been investigated by UV−vis reflectance spectroelectrochemical quartz crystal microbalance in aqueous solutions containing electrolyte anions with different degrees of hydrophobicity (PF6-, ClO4-, BF4-, and NO3...

The spectral changes occurring in multilayer films of hexanethiolate monolayer-protected Au147 clusters (C6–Au147 MPCs) as a consequence of quantized MPC core charging have been investigated in aqueous solutions using a multiresponse technique, UV–vis reflectance spectroelectrochemical quartz crystal microbalance (SEQCM). The joint technique, a com...

UV–vis bidimensional spectroelectrochemistry has been applied to the study of the electrochemical stability of conducting polymer films during p- and n-doping processes. Specifically, poly(4,4′-bis(butylthio)-2,2′-bithiophene) has been chosen as example to prove the usefulness and suitability of this multi-response technique to characterize polymer...

Ultrathin Langmuir-Schaeffer (LS) films were fabricated from blends of regioregular poly(3-hexylthiophene) (P3HT) and highly monodispersed dodecanethiolate-capped gold nanoparticles (Au NPs) mixed in varying weight ratios. The morphology of the ultrathin films was investigated by UV-visible absorption spectroscopy, atomic force microscopy (AFM) and...

Bidimensional spectroelectrochemistry is an analytical technique that provides simultaneously one electrochemical and two spectroscopic signals. Taking the plane of the electrode surface as a spatial reference, normal-beam and parallel-beam UV–Vis absorbance signals are simultaneously obtained, which convey important information about the electroch...

Scanning electrochemical microscopy (SECM) has been employed in the feedback mode to assess the electrochemical behavior of two-dimensional networks of single-walled carbon nanotubes (SWNTs). It is shown that, even though the network comprises both metallic and semiconducting SWNTs, at high density (well above the percolation threshold for metallic...

Degradation of polyaniline films electrodeposited on optically transparent gold electrodes has been followed by thin-layer bidimensional spectroelectrochemistry. The influence of the anodic potential reached during multiple potential scans has been assessed. Correlation of changes in the spectral signals in normal and parallel arrangement has enabl...

A new spectroelectrochemical flow cell is presented and its capability to provide a better understanding of reaction mechanisms is illustrated with the study of the electrosynthesis and characterization of a conducting polymer, polyaniline (PANI). A spectroelectrochemical study of electropolymerization of aniline under flow conditions has been perf...

Multilayer films of Au147 hexanethiolate monolayer-protected clusters (C6-Au MPCs) of 1.6-nm diameter cores were formed onto indium tin oxide electrodes and the film optical changes arising from sequential single electron removal from the MPC cores in aqueous solutions were followed by UV–vis absorption spectroelectrochemistry. The film absorbance...

Quantized optical changes accompanying discrete core charging of hexanethiolate-protected Au-cluster films was evidenced by UV/Vis absorption spectroelectrochemistry. The film absorbance is found to respond proportionally and reversibly to the nanoparticle core charge in aqueous solutions (see Figure), where ion-induced rectification of the quantiz...

This paper reports the first comparison of the structure and electrical conductivity properties of spin cast (SC) and Langmuir-Schaeffer (LS) films of regioregular poly(3-hexylthiophene) (P3HT). In addition, the effect of incorporating highly monodisperse Au nanoparticles (NPs), with a core diameter of approximately 5 nm, into SC and LS P3HT films...

Incorporation of non-luminescent dodecanethiolate-protected gold clusters into regioregular poly(3-hexylthiophene) films results in a 6-fold increase in the visible photoluminescence (PL) of the polymer, which arises predominantly from NP-induced structural changes in the composite films.

In order to perform an in-depth study on the electropolymerization mechanism of bis(alkyl)-substituted bithiophenes, poly[4,4′-bis(metylbutylthio)-2,2′-bithiophene] (poly-MBTBT) has been electrogenerated by using both potentiodynamic and potentiostatic techniques under different experimental conditions. Bidimensional spectroelectrochemical data hav...

This article reports the use of the scanning electrochemical microscope (SECM) to investigate the electronic properties of Langmuir monolayers of alkane thiol protected gold nanocrystals (NCs). A substantial increase in monolayer conductivity upon mechanical compression of the Au NC monolayer is reported for the first time. This may be the room tem...

Electrogeneration of soluble Prussian Blue (PB) during the oxidation–reduction of the Fe(CN)63−/Fe(CN)64− system has been detected using bidimensional spectroelectrochemistry (BSEC). This new technique allows us to obtain simultaneously two different spectroscopic signals together with an electrochemical signal, each one containing different inform...

An advanced electroanalytical technique, scanning electrochemical microscopy (SECM), is used as a new approach to measure both the lateral (in-plane) and cross-film electron transport in multilayer polymer/nanoparticle films. The sensitivity of SECM is such that the conductivity of a single nanoparticle monolayer can be quantified. The increase in...

A digital simulation model has been developed taking into account the simultaneous acquisition of one electrical and two spectroscopic signals generated in a bidimensional spectroelectrochemistry experiment. In this type of measurements, light absorption is simultaneously considered in both the normal and parallel directions to a plane electrode su...

Scanning electrochemical microscopy has been used to quantify both the charge injection energetics between a solution redox couple and a monolayer of hexanethiol stabilised gold nanoparticles and the subsequent lateral charge transport in the monolayer.

The first observation of 15 voltammetric quantized charging peaks for a solution of hexanethiol-capped gold nanoparticles (so-called monolayer protected clusters MPCs) at room temperature is reported where the variation in peak spacing with increasing charge stored in the metal core is discussed in terms of MPC capacitance.

Hexacyanoferrate(III)/(II) system has been studied by UV-visible long-pathway spectroelectrochemistry. Three different methodologies, based on potentiodynamic techniques, have been successfully used in the thermodynamic characterization of the system. Formation of soluble Prussian Blue has been detected during the electrode process. The values of t...

Bidimensional chronoabsorptometry is a novel spectroelectrochemical technique that monitors simultaneously three different signals: current and absorbance both normal to the electrode plane and parallel to this plane during a time in which a fixed potential is imposed. This technique is applied in the visible range to the study of the electropolyme...

The electropolymerization mechanism of 4,4′-bis(butylthio)-2,2′-bithiophene (1) was studied by means of bidimensional spectroelectrochemistry. Simultaneous electrochemical and spectroscopic signals were analyzed with the aim of obtaining information about the role of the low-molecular-weight oligomers in the polymerization process. Experiments in e...

A new methodology is presented to offer the possibility of simultaneously obtaining two different spectroscopic signals in a single spectroelectrochemical experiment. Taking the plane of the electrode surface as a spatial reference, normal-beam and parallel-beam UV-vis absorbance signals are jointly analyzed, revealing important experimental differ...

Single-walled carbon nanotube (SWCNT) networks have emerged as very promising alternative to conventional transparent conducting oxides (TCO) for optically transparent electrodes, exhibiting comparable sheet resistance and optical transmittance but outperforming TCO in terms of mechanical and chemical robustness. Here the advantages of SWCNT films...