X-ray photoelectron spectroscopy investigation of nanoporous NiO electrodes sensitized with Erythrosine B

Nanoporous NiO thin films were prepared onto FTO glass substrates by means of screen-printing and were sensitized with Erythrosine B (EryB) dye. The obtained material was electrochemically treated and characterized with ex-situ X-ray photoelectron spectroscopy in order to gain information beneficial to the application of sensitized NiO as photocathodes of p-type dye-sensitized solar cells (p-DSCs). In particular, EryB-sensitized NiO films underwent a series of electrochemical treatments in LiClO4/Acetonitrile (ACN) electrolyte devised so as to simulate possible conditions the electrode might encounter during operation in the photoelectrochemical cell. Upon potential-cycling in a range where the two NiO faradic events Ni(II)→Ni(III) and Ni(III)→Ni(IV) occur, X-ray photoelectron spectroscopy revealed that Erythrosine B dye experiences a partial detachment from the NiO surface. This detachment seems to be paralleled by the formation of stable (Ni)+(ClO4)- couples. Overall, the EryB dye displayed an acceptable electrochemical stability onto the surface of NiO electrode up to 50 cyclic voltammetries in the range -0.27÷+1.13V vs. Ag/AgCl. These results are useful for the evaluation of electrochemical stability of the dye when this is immobilized onto an electrode surface and are beneficial for a better comprehension of the degradation phenomena operating in real photoconversion device. © 2017 Elsevier B.V

Progress, highlights and perspectives on NiO in perovskite photovoltaics

The power conversion efficiency of NiO based perovskite solar cells has recently hit a record 22.1%. Here, the main advances are reviewed and the role of NiO in the next breakthroughs is discussed

Photoemission study of ferrocenes: insights into the electronic structure of Si-based hybrid materials

We present here the results of synchrotron radiation-excited UV-photoemission investigation and DFT calculations on vinylferrocene (VFC), a redox molecule suitable for applications in molecular electronics. A detailed assignment is discussed of the valence photoelectron spectra (UPS), which provides new data on the electronic structure and offers a partial re-interpretation of previous assignments on VFC based on theoretical and experimental evidences. Furthermore, the present results can allow for a meaningful comparison of photoemission results from the corresponding hybrid obtained by covalently attaching VFC to Si oriented surfaces. © 2008 IOP Publishing Ltd

Self-Assembling Peptide-Based Magnetogels for the Removal of Heavy Metals from Water

In this study, we present the synthesis of a novel peptide-based magnetogel obtained through the encapsulation of ?-Fe2O3-polyacrylic acid (PAA) nanoparticles (?-Fe(2)O(3)NPs) into a hydrogel matrix, used for enhancing the ability of the hydrogel to remove Cr(III), Co(II), and Ni(II) pollutants from water. Fmoc-Phe (Fluorenylmethoxycarbonyl-Phenylalanine) and diphenylalanine (Phe(2)) were used as starting reagents for the hydrogelator (Fmoc-Phe(3)) synthesis via an enzymatic method. The PAA-coated magnetic nanoparticles were synthesized in a separate step, using the co-precipitation method, and encapsulated into the peptide-based hydrogel. The resulting organic/inorganic hybrid system (?-Fe(2)O(3)NPs-peptide) was characterized with different techniques, including FT-IR, Raman, UV-Vis, DLS, ?-potential, XPS, FESEM-EDS, swelling ability tests, and rheology. Regarding the application in heavy metals removal from aqueous solutions, the behavior of the obtained magnetogel was compared to its precursors and the effect of the magnetic field was assessed. Four different systems were studied for the separation of heavy metal ions from aqueous solutions, including (1) ?-Fe(2)O(3)NPs stabilized with PAA, (?-Fe(2)O(3)NPs); (2) Fmoc-Phe(3) hydrogel (HG); (3) ?-Fe(2)O(3)NPs embedded in peptide magnetogel (?-Fe(2)O(3)NPs@HG); and (4) ?-Fe(2)O(3)NPs@HG in the presence of an external magnetic field. To quantify the removal efficiency of these four model systems, the UV-Vis technique was employed as a fast, cheap, and versatile method. The results demonstrate that both Fmoc-Phe(3) hydrogel and ?-Fe(2)O(3)NPs peptide magnetogel can efficiently remove all the tested pollutants from water. Interestingly, due to the presence of magnetic ?-Fe(2)O(3)NPs inside the hydrogel, the removal efficiency can be enhanced by applying an external magnetic field. The proposed magnetogel represents a smart multifunctional nanosystem with improved absorption efficiency and synergic effect upon applying an external magnetic field. These results are promising for potential environmental applications of ?-Fe(2)O(3)NPs-peptide magnetogels to the removal of pollutants from aqueous media

Targeting the antifungal activity of carbon dots against Candida albicans biofilm formation by tailoring their surface functional groups

Carbon dots (CDs) are an emerging class of carbon nanoparticles, which for their characteristics have found applications in many fields such as catalysis, materials and biomedicine. Within this context, the application of CDs as antibacterial agents has received much attention in very recent years, while their use as antifungal nanoparticles has been scarcely investigated. Here we report a systematic investigation of the surface functional groups of CDs to study their influence on these nanoparticles' against Candida albicans. Three classes of CDs have been synthesised and fully characterized. A thorough in vitro and in vivo biological screening against C. albicans was performed to test their antifungal, antiadhesion and antibiofilm formation activities. Moreover, the interaction with C. albicans cells was investigated by microscopic analysis. Our results evidence how the presence of a positively polarised surface results crucial for the internalization into COS-7 cells. Positively charged nanoparticles were also able to inhibit adhesion and biofilm formation, to interact with the cellular membrane of C. albicans, and to increase the survival of G. mellonella infected larvae after the injection with positive nanoparticles. The antifungal activity of CDs and their extremely low toxicity may represent a new strategy to combat infections sustained by C.albicans

Adsorption behavior of I3(-) and I(-) ions at a nanoporous NiO/acetonitrile interface studied by X-ray photoelectron spectroscopy

The adsorption of I- and I3 - anions, i.e., the two species constituting the most common redox couple of dye-sensitized solar cells (DSCs), onto the surface of screen-printed nanoporous NiO was studied by means of X-ray photoelectron spectroscopy (XPS). Nanoporous NiO films were deposited on transparent metallic fluorine-doped tin oxide (FTO) and polarized as working electrodes in a three-electrode cell with differently concentrated I-/I3 - electrolytes to simulate the different conditions experienced by the NiO cathodes during the lifecycle of a p-type DSC (p-DSC) at those atomic sites not passivated by the dye. Bare NiO films were tested also as photocathodes of nonsensitized p-DSCs. The ex situ XPS analysis of I 4d ionization region of both reference and electrochemically treated NiO films showed that the presence of native and electrochemically generated Ni3+ and Ni4+ centers induces fast adsorption/desorption of I- ions and catalyzes their oxidation to I3 - ions. The adsorption phenomena generated by I- and I3 - species on nanoporous NiO electrodes can also induce an effect of electrochemical passivation toward a fraction of charged Ni sites. Such an effect would render these sites inactive for the further realization of those photoelectrochemical processes at the basis of the operation of a p-DSC. © 2016 American Chemical Society

Enhancement of the performance in Li-O2cells of a NiCo2O4based porous positive electrode by Cr(III) doping

Here we discuss the incorporation of Cr(III) as dopant in the spinel lattice of the NiCo2O4cubic phase and its beneficial effect on the electro-catalytic activity of this material in aprotic Li-O2cells. To this aim, we synthesized highly porous carbon-free self-standing electrodes constituted by nanostructured undoped and Cr-doped NiCo2O4grown on open nickel mesh. These materials were characterized by X-ray diffraction, field emission scanning electron microscopy coupled with energy dispersive spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The performance in aprotic Li-O2cells of the undoped and Cr-doped NiCo2O4electrodes were tested in galvanostatic cycling using a LiTFSI 1 m in tetraethylene glycol dimethyl ether electrolyte without the incorporation of any carbon conductive agent. Cr(III) doping discloses a remarkable enhancement of more than 300% of the discharge capacity at J = 0.1 mA cm−2. Moreover, the Cr-doped NiCo2O4material is capable to give reversible limited capacity ORR/OER for 52 and 45 cycles at 0.2 mA cm−2/0.1 mAh cm−2and 0.1 mA cm−2/0.2 mAh cm−2, respectively, without oxygen flow in static Ar/O2overpressures (pO2= 1bar). Pseudo-Tafel data derived by galvanostatic titrations highlight the beneficial effect of Cr(III) doping on the electrode kinetics both for ORR and OER