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LAYERED DOUBLE HYDROXIDES ELECTROSYNTHESIZED ON PLATINUM ELECTRODES AS MATERIALS FOR SENSORS AND SUPERCAPACITORS
Full text linkLayered Double Hydroxides (LDHs), with a general formula of [M(II)1–xM(III)x (OH)2]x+ [Aqx/q− • nH2O], where M(II) and M(III) are bivalent and trivalent metal cations, respectively, and A is the charge-balancing anion of valence x, have attracted increasing interest from both academic and industrial perspectives due to their wide applications in areas such as catalysis, separation, biotechnology, and electroanalytical chemistry. This contribution compares the performances of LDHs containing redox active metals (Co or Ni) by application of a cathodic potential to Pt soaked into solutions containing Al or Fe as trivalent metal. The electrodeposition provides an alternative route to the chemical one in order to obtain a good adhesion of the LDHs to the electrode surface which is a crucial feature for the best performances for the development of both sensors and supercapacitors. Co/Al and Ni/Al LDHs have been deeply investigated for the electrocatalytic determination of oxidizable substrates such as alcohols, sugars, phenols, amines, etc, whereas the study of their performances in the field of energy storage is more recent. This contribution compares the performances of Co/Al and Ni/Al LDHs with those displayed by the materials synthesized in the same conditions in the presence of Fe(III) instead of Al(III) as to the detection of glucose and the values of specific capacitance.
As an example, the Pt modified with a thin film of the Ni/Al LHD displays good performances as electrochemical sensor for glucose. On the contrary the presence of Fe(III) gives rise to a material where the Ni(II) are not able to act as electrocatalytic centers.
LDHs the mechanism which involves the Ni centers as redox mediators can be so summarized:
LDH-Ni(II) + OH-sol ⇄ LDH(OH-)-Ni(III) + e-
LDH(OH-)-Ni(III) + analytered LDH-Ni(II) + OH-sol + analyteox
where the second reaction is slower than the firts one since it had been demonstrated that the rate limiting step for the oxidation of alcohols and sugars was the diffusion of the substrate toward the Ni centers of LDH material.
The reason why the different behavior can be evidenced by the characterization CV in NaOH of Pt electrodes modified with Ni/Fe and Ni/Al LDHs, where it is well evidenced that the presence of iron inside the brucitic layers causes a significant decrease in the overpotential necessary for oxygen evolution.
The specific capacitances estimated for the investigated LDHs are reported and their properties as materials for supercapacitors are discussed
Laccase and tyrosinase on electrochemically reduced GO and MWCNTs hybrid for the development of polyphenols biosensors
No full textRecently, carbon-based nanomaterials have provided an interesting approach for bioanalysis platform. Among them, graphene has attracted great attention in bioanalysis applications due to its remarkable electronic structure and high surface to volume ratio which contribute to the high sensitivity of graphene-based sensor devices. The non-covalent functionalization of graphene with pyrene-based linker molecules brings great benefits, allowing to maintain unaltered the original graphene electronic properties and its low aspecific interactions with biological materials. In this work, we describe a non-covalent functionalization of graphene with a stealth-peptide bearing a terminal pyrene group (Peptide-Py), in view of the development of nanodevices such as tunable biosensor/bioanalyte concentrator. The terminal cysteine residual of the peptide would allow a further attachment of the capture antibody to the functionalized graphene. Herein, the functionalization of graphene and thus the adsorption process and self-assembly morphology of the system onto nanoscale have been demonstrated both experimentally and by computational methods carrying out simulations to investigate the adsorption of a single molecule of peptide-pyrene on the graphene layer.
Graphene was grown on copper substrates via chemical vapor deposition (CVD) technique and then transferred on Au coated quartz crystals for quartz crystal nanobalance (QCN). CVD graphene was self-assembled with the stealth peptide in flow
and the functionalization was monitored by measuring the frequency variation using a QCN. To confirm the functionalization, the samples were characterized with several techniques. Furthermore, we investigated the possibility to restore the pristine graphene layer applying a ramp of temperature, to allow the re-utilization of the sensor
Pseudocapacitors based on layered double hydroxides electrodeposited on Pt electrodes
Full text linkElectrochemical capacitors also known as supercapacitors can be divided into two categories, namely, electric double layer capacitors (EDLCs), founded on non-Faradic charge storage process, and pseudocapacitors, which use metal oxides/hydroxides as the main
electrodes since their capacitance arises from redox processes occurring at or near the solid electrode surface. Layered double hydroxides (LDHs) especially those containing transition metals are considered as ideal pseudocapacitive materials due to their peculiar properties such as efficient anion exchange capacity and high redox activity[1,2]. LDHs have the general formula [M(II)1 xM(III)x(OH)2]x+[Xqx/q−· nH2O] where M(II) and M(III) are bivalent and trivalent metal cations and X is the charge-balancing interlayer anion. Electrosynthesis is an efficient method to prepare LDH thin films suitable for sensing applications and in the last few years our group has optimised the one-step electrodeposition, mainly on Pt electrodes, of LDHs based on redox active metals as Ni or Co and Al [3]. The applications of LDH modified electrodes requires the formation of well adherent thin films and this result can be achieved if Pt surface is electrochemically pre-treated in 0.1 M H2SO4 [4]. In this work four LDHs containing Co and Ni, as bivalent and Fe and Al as trivalent cations have been synthesized on Pt by electrochemical reduction, at –0.90 V vs SCE for 30 s, of the proper electrolytic solution [5]. All the LDHs have been characterized in basic solution (0.1 and 1 M NaOH) to investigate if they behave as pseudocapacitive materials by using cyclic voltammetry and galvanostatic charge/discharge curves. The calculation of capacitance per gram of material is very important when evaluating materials for this application, so the mass deposited during the synthesis was determined using the electrochemical quartz crystal microbalance. As an example in Fig. 1 a and b the CV and the galvanostatic charge/discharge curves recorded for the LDH containing Al and Co, are shown. All the LDHs displayed good performances both in terms of specific capacitance and life cycles, as estimated by galvanostatic charge/discharge curves. As conductive support also glassy carbon was investigated in order to fabricate cheaper devices
Modified Electrodes for Energy and Sensing Applications
No full textThis thesis describes the research focused on the study of different electrode supports modified with layered double hydroxides (LDHs) on Co or Ni as M(II) and Al or Fe as M(III) or conducting polymers for energy applications. The LDHs were characterized by electrochemical techniques, FE-SEM, XRD, XPS and XAS. Glassy carbon and Pt electrodes modified with electrosynthesized LDHs were employed in order to investigate their performances as oxygen evolution reaction catalysts and as pseudocapacitor materials. Moreover, the electrochemical synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on indium tin oxide (ITO) was carried out in order to exploit an alternative route to fabricate bulk heterojunction solar cells with similar performances but less expensive than those obtained by casting. The photoactive layer was composed by [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) as electron acceptor, while as donor polymer it was employed either the commonly employed rr-poly(3-hexylthiophene) or a polythiophene copolymer, functionalized with a porphyrin derivative in order to improve the absorption in the UV/Vis region.
In the second part of the thesis, the LDHs modified electrodes were employed for sensing, taking into account the electrocatalytic oxidation of sugars. Ni/Al or Ni/Fe LDHs were studied with the aim to investigate again the effect of Fe on the electrocatalysis. LDHs prepared both by chemical and electrochemical syntheses were employed with the aim of studying the effect of the order degree on the LDHs performance since this parameter is crucial to improve the “sensing” properties. Furthermore, a sensor for the amperometric detection of sugars in flow systems, based on Co/Al LDH electrosynthesized on Pt electrodes, was developed. A mixture of sugars was submitted to high performance anion chromatography with amperometric detection, using the modified electrode as the working electrode. Moreover, to assess the applicability of the device glucose, fructose, and sucrose content in real samples were successfully determined
Amperometric biosensors based on reduced GO and MWCNTs composite for polyphenols detection in fruit juices
No full textAmperometric biosensors based on glassy carbon electrodes (GCE) modified with graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) were developed. Two types of biosensors were realized employing tyrosinase (Tyr) or laccase (Lac). Before enzyme deposition GO was reduced by electrochemical route performing cyclic voltammetry. The enzyme immobilisation on the modified GC was optimised employing different agents (bovine serum albumin and glutaraldehyde as crosslinking agent, chitosan, and Nafion). The conditions for the fabrication and the storage of the biosensors were established in order to obtain good enzyme retention, high sensitivities and long-life devices. The biosensors were used for the determination of catechol and other polyphenols, i.e., pyrogallol, epicatechin, gallic acid, 1,2-dihydroxybenzoic acid, caffeic acid, chlorogenic acid, rutin, catechin and dopamine. Eventually, their practical applicability was demonstrated by estimating the total polyphenols concentration in juice samples, expressed as epicatechin equivalents
GLASSY CARBON MODIFIED ELECTRODES WITH LAYERED DOUBLE HYDROXIDES FOR THE OXYGEN EVOLUTION REACTION
No full textGlassy carbon electrodes (GCE) were modified with a thin film of Ni/Al and Ni/Fe Layered Double Hydroxides (LDHs). The LDHs were chemically synthesized, by the double-microemulsion method according to literature data1. That modified electrodes were found to be active towards the oxygen evolution reaction (OER). The OER activity of LDHs modified electrodes was investigated in 0,1 M NaOH, at a slow scan rate of 5 mV/s, between 0 V and the OER onset potential (Ag/AgCl/3 M was used as reference electrode). During the measurements the working electrode was rotating at 1600 rpm to remove the generated oxygen bubbles from it surface. The electrochemical characterization of the Ni/Al and Ni/Fe-LDHs evidenced that the OER onset potential of those modified electrodes occurred respectively at +0.55 V and +0.53 V, showing a considerably reduced potential, compared to the values recorded in the same conditions with the bare GCE or GCE modified with a film of not redox active Mg/Al and Mg/Fe-LDHs (onset of OER current at ~1.20 V). A similar behaviour to the chemically synthesized active catalysts, was observed for the ones electrochemically synthesized from a solution of Ni(NO3)2 and Fe(NO3)3 or Al(NO3)3 (molar ratio 3:1), by applying an anodic potential of -0,9 V for 90 seconds. Furthermore the active LDHs exhibited a good stability in alkaline solution, since the chronopotentiometry curves, recorded applying a current density of 2,5 mA/cm2 for five minutes, showed that the catalysts had a nearly constant operating potential
Iron vs Aluminum Based Layered Double Hydroxides as Water Splitting Catalysts
No full textThis paper describes the electrosynthesis, characterization and electrocatalytic properties towards oxygen evolution reaction (OER) of four layered double hydroxides (LDHs) containing cobalt or nickel as divalent cation and aluminum or iron as trivalent metal. The electrochemical behaviour of the LDH modified electrodes was studied by cyclic voltammetry (CV), and the LDHs were characterized by XRD and SEM/EDS. Two materials, i.e.; platinum and glassy carbon (GC), were investigated as electrode supports recording polarization and chronopotentiometric curves, with a rotating disk electrode in alkaline solutions. LDHs containing iron exhibited higher activity for OER and all the materials showed a good stability and durability in alkaline media. When GC was used as electrode support the performances of the OER catalysts resulted to be even better than those exhibited by the same LDHs electrodeposited on Pt
Bringing Again Noble Metal Nanoparticles to the Forefront of Cancer Therapy
Full text linkNanomaterials have attracted increasing interest for their potentiality to revolutionize the diagnosis and treatment of many diseases, especially neoplasms. Interestingly, there is a huge imbalance between the number of proposed nanoplatforms and the few ones approved for clinical applications. This disequilibrium affects in particular noble metal nanoparticles (NPs), that present no-approved platform and very few candidates in clinical trials because of the issue of persistence. In this perspective, we discuss if nanomedicine is generally keeping its promises with a focus on the approach that could fill the gap between NPs and oncology in the next future: the ultrasmall-in-nano
Intercalated structures formed by platinum on epitaxial graphene on SiC(0001)
Full text linkGraphene on SiC intercalated with two-dimensional metal layers, such as Pt, offers a versatile platform for applications in spintronics, catalysis, and beyond. Recent studies have demonstrated that Pt atoms can intercalate at the heterointerface between SiC(0001) and the C-rich
R30°reconstructed surface (hereafter referred to as the buffer layer). However, key aspects such as intercalated phase structure and intercalation mechanisms remain unclear. In this work, we investigate changes in morphology, chemistry, and electronic structure for both buffer layer and monolayer graphene grown on SiC(0001) following Pt deposition and annealing cycles, which eventually led to Pt intercalation at temperatures above 500 °C. Atomic-resolution imaging of the buffer layer reveals a single intercalated Pt layer that removes the periodic corrugation of the buffer layer, arising from partial bonding of C-atoms with Si-atoms of the substrate. In monolayer graphene, the Pt-intercalated regions exhibit a two-level structure: the first level corresponds to a Pt layer intercalated below the buffer layer, while the second level contains a second Pt layer, placed between the former buffer layer and monolayer graphene, giving rise to a
superstructure relative to graphene. Upon intercalation, Pt atoms appear as silicides, indicating a reaction with Si atoms from the substrate. Additionally, charge neutral
-bands corresponding to quasi-free-standing monolayer and bilayer graphene emerge. Analysis of multiple samples, coupled with a temperature-dependent study of the intercalation rate, demonstrates the pivotal role of buffer layer regions in facilitating the Pt intercalation in monolayer graphene. These findings provide valuable insight into Pt intercalation, advancing the potential for applications
Study of hydrogen absorption in a novel three-dimensional graphene structure: Towards hydrogen storage applications
Full text linkThe use of a novel three-dimensional graphene structure allows circumventing the limitations of the two-dimensional nature of graphene and its application in hydrogen absorption. Here we investigate hydrogen-bonding on monolayer graphene conformally grown via the epitaxial growth method on the (0001) face of a porousified 4H-SiC wafer. Hydrogen absorption is studied via Thermal Desorption Spectroscopy (TDS), exposing the samples to either atomic (D) or molecular (D
) deuterium. The graphene growth temperature, hydrogen exposure temperature, and the morphology of the structure are investigated and related to their effect on hydrogen absorption. The three-dimensional graphene structures chemically bind atomic deuterium when exposed to D
. This is the first report of such an event in unfunctionalized graphene-based materials and implies the presence of a catalytic splitting mechanism. It is further shown that the three-dimensional dendritic structure of the porous material temporarily retains the desorbed molecules and causes delayed emission. The capability of chemisorbing atoms after a catalytic splitting of hydrogen, coupled to its large surface-to-volume ratio, make these structures a promising substrate for hydrogen storage devices
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