The Role of Hydrogen Incorporation into Amorphous Carbon Films in the Change of the Secondary Electron Yield.

Over the last few years, there has been increasing interest in the use of amorphous carbon thin films with low secondary electron yield (SEY) to mitigate electron multipacting in particle accelerators and RF devices. Previous works found that the SEY increases with the amount of incorporated hydrogen and correlates with the Tauc gap. In this work, we analyse films produced by magnetron sputtering with different contents of hydrogen and deuterium incorporated via the target poisoning and sputtering of CxDy molecules. XPS was implemented to estimate the phase composition of the films. The maximal SEY was found to decrease linearly with the fraction of the graphitic phase in the films. These results are supported by Raman scattering and UPS measurements. The graphitic phase decreases almost linearly for hydrogen and deuterium concentrations between 12% and 46% (at.), but abruptly decreases when the concentration reaches 53%. This vanishing of the graphitic phase is accompanied by a strong increase of SEY and the Tauc gap. These results suggest that the SEY is not dictated directly by the concentration of H/D, but by the fraction of the graphitic phase in the film. The results are supported by an original model used to calculate the SEY of films consisting of a mixture of graphitic and polymeric phases.

Heterogenization of Heteropolyacid with Metal-Based Alumina Supports for the Guaiacol Gas-Phase Hydrodeoxygenation.

Because of the global necessity to decrease CO2 emissions, biomass-based fuels have become an interesting option to explore; although, bio-oils need to be upgraded, for example, by catalytic hydrodeoxygenation (HDO), to reduce oxygen content. This reaction generally requires bifunctional catalysts with both metal and acid sites. For that purpose, Pt-Al2O3 and Ni-Al2O3 catalysts containing heteropolyacids (HPA) were prepared. HPAs were added by two different methods: the impregnation of a H3PW12O40 solution onto the support and a physical mixture of the support with Cs2.5H0.5PW12O40. The catalysts were characterized by powder X-ray diffraction, Infrared, UV-Vis, Raman, X-ray photoelectron spectroscopy and NH3-TPD experiments. The presence of H3PW12O40 was confirmed by Raman, UV-Vis and X-ray photoelectron spectroscopy, while the presence of Cs2.5H0.5PW12O40 was confirmed by all of the techniques. However, HPW was shown to strongly interact with the supports, especially in the case of Pt-Al2O3. These catalysts were tested in the HDO of guaiacol, at 300 °C, under H2 and at atmospheric pressure. Ni-based catalysts led to higher conversion and selectivity to deoxygenated compound values, such as benzene. This is attributed to both a higher metal and acidic contents of these catalysts. Among all tested catalysts, HPW/Ni-Al2O3 was shown to be the most promising, although it suffered a more severe deactivation with time-on-stream.

Luminescent Carbon Dots from Wet Olive Pomace: Structural Insights, Photophysical Properties and Cytotoxicity.

Carbon nanomaterials endowed with significant luminescence have been synthesized for the first time from an abundant, highly localized waste, the wet pomace (WP), a semi-solid by-product of industrial olive oil production. Synthetic efforts were undertaken to outshine the photoluminescence (PL) of carbon nanoparticles through a systematic search of the best reaction conditions to convert the waste biomass, mainly consisting in holocellulose, lignin and proteins, into carbon dots (CDs) by hydrothermal carbonization processes. Blue-emitting CDs with high fluorescence quantum yields were obtained. Using a comprehensive set of spectroscopic tools (FTIR, Raman, XPS, and 1H/13C NMR) in combination with steady-state and time-resolved fluorescence spectroscopy, a rational depiction of WP-CDs structures and their PL properties was reached. WP-CDs show the up-conversion of PL capabilities and negligible cytotoxicity against two mammalian cell lines (L929 and HeLa). Both properties are excellent indicators for their prospective application in biological imaging, biosensing, and dynamic therapies driven by light.

Photocatalytic activity of layered MoS2 in the reductive degradation of bromophenol blue.

Molybdenum disulphide (MoS2) is a layered material with interesting photocatalytic properties. In this study, a layered MoS2 was produced using a hydrothermal method. The obtained material was characterised by XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), SEM (scanning electron microscopy), UV-Vis spectroscopy, DLS (dynamic light scattering), and zeta potential analysis. For the evaluation of the photocatalytic properties of layered MoS2, a solution of bromophenol blue (BPB) and the catalyst was illuminated for 120 minutes. According to the experimental results, MoS2 exhibited excellent catalytic activity in BPB degradation. The MoS2 preparation method enabled improved light harvesting, avoided fast charge recombination (related to bulk MoS2), and created a large number of suitable electron transfer sites for photocatalytic reactions. Simulation of BPB decay and bromide production was carried out for a further understanding of MoS2 photocatalytic action. The simulation results proved the reduction mechanism of BPB photodegradation.

Effect of Graphene vs. Reduced Graphene Oxide in Gold Nanoparticles for Optical Biosensors-A Comparative Study.

Aiming to develop a nanoparticle-based optical biosensor using gold nanoparticles (AuNPs) synthesized using green methods and supported by carbon-based nanomaterials, we studied the role of carbon derivatives in promoting AuNPs localized surface plasmon resonance (LSPR), as well as their morphology, dispersion, and stability. Carbon derivatives are expected to work as immobilization platforms for AuNPs, improving their analytical performance. Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4·3H2O using phytochemicals (from tea) which act as both reducing and capping agents. UV-Vis spectroscopy, transmission electron microscopy (TEM), zeta potential (ζ-potential), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNPs and nanocomposites. The addition of reduced graphene oxide (rGO) resulted in greater dispersion of AuNPs on the rGO surface compared with carbon-based nanomaterials used as a support. Differences in morphology due to the nature of the carbon support were observed and are discussed here. AuNPs/rGO seem to be the most promising candidates for the development of LSPR biosensors among the three composites we studied (AuNPs/G, AuNPs/GO, and AuNPs/rGO). Simulations based on the Mie scattering theory have been used to outline the effect of the phytochemicals on LSPR, showing that when the presence of the residuals is limited to the formation of a thin capping layer, the quality of the plasmonic resonance is not affected. A further discussion of the application framework is presented.

Unprecedented Mechanochemical Synthesis and Heterogenization of a C-Scorpionate Au(III) Catalyst for Microwave-Assisted Biomass Valorization.

The transformation of biomass, a carbon resource presenting a huge potential to produce valuable chemicals, requires the search for sustainable catalytic routes. This work proposes the microwave-assisted oxidation of biomass -derived substrates, such as glycerol and the furfural derivatives 5-(hydroxymethyl)furfural (HMF) and 5-hydroxymethyl-2-furancarboxylic acid (HFCA), using the C-scorpionate dichloro-gold(III) complex [AuCl2(κ2-Tpm)]Cl (Tpm = HCpz3; pz = pyrazol-1-yl) as a catalyst, as prepared and supported on graphene, in solvent-free conditions. The unprecedented application of a mechanochemical procedure (in a planetary ball mill, in solid state) to synthesize a C-scorpionate complex, the [AuCl2(κ2-Tpm)]Cl, is disclosed. The immobilization of [AuCl2(κ2-Tpm)]Cl on graphene was performed using different methods, including some (e.g., microwave irradiation and liquid assisted grinding) for the first time. The structural properties and the performance of the prepared catalytic materials are presented and discussed.

Dataset for the synthesis, characterisation and application of cobalt and nitrogen co-doped TiO2 anatase nanoparticles on triclosan photodegradation using visible LED light.

The growing threat of emerging waterborne contaminants is a global concern, fuelled in part by the ineffectiveness of current remediation strategies. One of the most prominent remediation strategies is catalytic photodegradation, particularly with TiO2 nanoparticles (NPs), but its full utilization is hampered by using only UV radiation, which is scarce in sunlight. To fully benefit from the sunlight abundance, several efforts are focused on the tailoring of TiO2 to make it more active in visible (Vis) light. However, this target is yet to be met, sought for new developments. In a recent research paper entitled "Visible light-driven photodegradation of triclosan and antimicrobial activity against Legionella pneumophila with cobalt and nitrogen co-doped TiO2 anatase nanoparticles" [ 1 ], we investigated the co-doping potential of cobalt and nitrogen in TiO2 NPs for water decontamination, focusing on its application for the degradation of triclosan (TCS) under Vis LED light irradiation. Herein, the synthesis methodology for the preparation of doped TiO2 with nitrogen is described in detail, along with complementary data on the characterisation of all previously synthesised photocatalysts in the form of specific surface area determination (B.E.T. method) based on the obtained physisorption isotherms, X-ray photoelectron spectroscopy (XPS), and the automatic determination of bandgap energy through the diffuse reflectance spectra (DRS) analysis by using the GapExtractor© software. This dataset article also includes optimised photocatalytic reaction conditions, specifically conducted under monochromatic LED light irradiation. The employed LED irradiation conditions can support photocatalytic research in the field, since LED systems are costless and have a long-life span compared to most conventional UV-Vis systems. In addition, raw UV-Vis spectra and high-performance liquid chromatography (HPLC) chromatograms for monitoring the TCS degradation reaction are also included, as are powder X-ray diffractograms (XRD) of recycled doped-TiO2 photocatalysts, confirming the renewable efficiency of the synthesised photocatalysts to pursue green chemistry principles.

Catalytic Performance of a Magnetic Core-Shell Iron(II) C-Scorpionate under Unconventional Oxidation Conditions.

For the first time, herein is reported the use of a magnetic core-shell support for a C-scorpionate metallic complex. The prepared hybrid material, that consists on the C-scorpionate iron(II) complex [FeCl2{κ3-HC(pz)3}] (pz, pyrazolyl) immobilized at magnetic core-shell particles (Fe3O4/TiO2), was tested as catalyst for the oxidation of secondary alcohols using the model substrate 1-phenylethanol. Moreover, the application of alternative energy sources (e.g., ultrasounds, microwaves, mechanical or thermal) for the peroxidative alcohol oxidation using the magnetic heterogenized iron(II) scorpionate led to different/unusual outcomes that are presented and discussed.

Hydrophilic Carbon Nanomaterials: Characterisation by Physical, Chemical, and Biological Assays.

A highly hydrophilic carbon nanomaterial was generated by using an electrochemical approach, and its structure, chemical composition, redox properties, antioxidant activity and effects on cells were characterised. It was found that the nanomaterial possesses a structure dominated by sp2 carbon atoms in a non-ordered carbon network formed by small clusters (<2 nm) of a carbonaceous material. This material has an outstanding capability for donating electrons and an unusual ability to bind metal cations. Antioxidant activity assays showed that it displays a high scavenging activity against both 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals, and a concentration-dependent ability to protect mitochondrial lipids and intracellular thiol groups from oxidation promoted by external oxidising agents. Cell-based assays also revealed that the nanomaterial has the ability to protect neuronal cells against oxidative damage and toxicity promoted by tert-butyl hydroperoxide and amyloid-ß1-42 peptide. These results, combined with the attractive methodology for generating this hydrophilic carbon-based nanomaterial, make this study the first step in addressing the therapeutic application of this new material.

Synergistic catalytic action of vanadia-titania composites towards the microwave-assisted benzoin oxidation.

Intensification of chemical processes according to the motto "faster, simpler, greener" is among the main concerns nowadays. One of the ways of intensification is the application of synergistic catalytic effects when the overall efficiency of a composite catalyst is much higher than the sum of the component activities. Here, we report on the preparation of synergistic catalytic materials by a simple and straightforward ball milling procedure. Oxidation of benzoin was selected as a model reaction to demonstrate the viability of the concept. For the V2O5-TiO2 (95 : 5) composite material, the synergistic effect is triggered by low power microwave irradiation with more than a tenfold jump in the catalytic activity in comparison to the activities of the individual components.

Comparison of microwave and mechanochemical energy inputs in the catalytic oxidation of cyclohexane.

The effect of microwave and mechanochemical ball milling energy inputs was studied for the peroxidative oxidation (with aqueous H2O2) of cyclohexane to cyclohexanol and cyclohexanone, over CoCl2 and/or V2O5 dispersed (µm scale) catalysts. A maximum total yield of cyclohexanol and cyclohexanone of 43% after 1 h of reaction at 30 °C, in acetonitrile and under microwave irradiation (5 W), was achieved over the CoCl2-V2O5 (3 : 1) catalyst prepared by ball milling. Cyclohexanol is the main final product with a selectivity of up to 93% over cyclohexanone. Conducting the oxidation reaction under microwave irradiation under the same conditions but without any mechanochemical treatment of the catalyst prior to use resulted in a lower total yield of 30% with a lower selectivity (69%) towards cyclohexanol over cyclohexanone. The sole application of mechanochemical treatment for the catalyst preparation and the catalytic oxidation of cyclohexane allowed to reach yields of 29% after 1 h of reaction, at room temperature, without microwave irradiation and any additive and in the absence of any organic solvent. Ball milling is shown to provide a convenient, solvent-free method to disperse these solid catalysts and to promote the above cyclohexane oxidation, although, in the latter case, not so effectively as microwave irradiation.

Effect of Phenolic Compounds on the Synthesis of Gold Nanoparticles and its Catalytic Activity in the Reduction of Nitro Compounds.

Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4 with polyphenols from tea extracts, which act as both reducing and capping agents. The obtained AuNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet⁻visible spectroscopy (UV⁻vis), and X-ray photoelectron spectroscopy (XPS). They act as highly efficient catalysts in the reduction of various aromatic nitro compounds in aqueous solution. The effects of a variety of factors (e.g., reaction time, type and amount of reducing agent, shape, size, or amount of AuNPs) were studied towards the optimization of the processes. The total polyphenol content (TPC) was determined before and after the catalytic reaction and the results are discussed in terms of the tea extract percentage, the size of the AuNPs, and their catalytic activity. The reusability of the AuNP catalyst in the reduction of 4-nitrophenol was also tested. The reactions follow pseudo first-order kinetics.

Imidazolium-based ionic liquids used as additives in the nanolubrication of silicon surfaces.

In recent years, with the development of micro/nanoelectromechanical systems (MEMS/NEMS), the demand for efficient lubricants of silicon surfaces intensified. Although the use of ionic liquids (ILs) as additives to base oils in the lubrication of steel/steel or other types of metal/ metal tribological pairs has been investigated, the number of studies involving Si is very low. In this work, we tested imidazolium-based ILs as additives to the base oil polyethylene glycol (PEG) to lubricate Si surfaces. The friction coefficients were measured in a nanotribometer. The viscosity of the PEG + IL mixtures as well as their contact angles on the Si surface were measured. The topography and chemical composition of the substrates surfaces were determined with atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. Due to the hygroscopic properties of PEG, the first step was to assess the effect of the presence of water. Then, a series of ILs based on the cations 1-ethyl-3-methylimidazolium [EMIM], 1-butyl-3-methylimidazolium [BMIM], 1-ethyl-3-vinylimidazolium [EVIM], 1-(2-hydroxyethyl)-3-methylimidazolium [C2OHMIM] and 1-allyl-3-methylimidazolium [AMIM] combined with the anions dicyanamide [DCA], trifluoromethanesulfonate [TfO], and ethylsulfate [EtSO4] were added to dry PEG. All additives (2 wt %) led to a decrease in friction coefficient as well as an increase in viscosity (with the exception of [AMIM][TfO]) and improved the Si wettability. The additives based on the anion [EtSO4] exhibited the most promising tribological behavior, which was attributed to the strong interaction with the Si surface ensuring the formation of a stable surface layer, which hinders the contact between the sliding surfaces.

Facile functionalization of cotton with nanostructured silver/titania for visible-light plasmonic photocatalysis.

In the present work, a simple, reliable and cost-effective approach to functionalize cotton fabrics with Ag-TiO2 nanoparticles strongly bound to the fibres and with visible-light-responsive photo-activity is presented. The hybrid cotton-Ag-TiO2 fabrics were characterized by Raman, AFM, FE-SEM, TGA, XPS GSDR, and LIL to confirm the generation of metallic Ag nanoparticles and crystalline TiO2 and investigate how the concentration of Ag and TiO2 precursors affected the morphology and the luminescence properties of the nanostructured layer grafted on the cotton fibres. The photocatalytic activity of the cotton-Ag-TiO2 hybrid systems was evaluated by the discoloration of Remazol Brilliant Blue R in water under a xenon lamp irradiation (sunlight simulator) equipped with selective filters. The extended photocatalytic activity to the visible is here explained by a synergistic effect of both the excitation of the Ag NPs plasmon resonance by visible light and a delayed electron-hole recombination rate caused by Ag NPs, as it can be observed by UV absorption.

Voltage-polarity dependent multi-mode resistive switching on sputtered MgO nanostructures.

Resistive switching in metal-insulator-metal nanosctructures is being intensively studied for nonvolatile memory applications. Here, we report unipolar resistive switching in Pt/MgO/Ta/Ru structures, with a 30 nm oxide barrier. A forming process was needed to initiate the resistive switching, which was then observed for all Set and Reset voltage polarity combinations. We studied the influence of the voltage polarity on the variability of the Set/Reset voltages and ON/OFF resistances and revealed the importance of a thin TaOx layer working as an oxygen revervoir for resistive switching. The mechanism behind this phenomenon can be understood in terms of conductive filaments formation/rupture with a contribution from Joule heating. Resistance change is thus caused by a voltage-driven oxygen vacancy motion in the MgO layer and a filament model was proposed for each polarity mode. A OFF/ON resistance ratio of at least 2 orders of magnitude was obtained with resistive states stable up to 104 s. Our results open the prospect to improve switching performance in other resistive switching systems, by proving a better understanding of the differences between operation modes.

Antimicrobial Contact-Active Oligo(2-oxazoline)s-Grafted Surfaces for Fast Water Disinfection at the Point-of-Use.

Water is one of the most valuable resources today and its purity is crucial to health and society well-being. The access to safe drinking water is decreasing in the world, which can have a huge socio-economic impact especially in developing countries, more prone to water-associated diseases. The goal of this work was to develop an innovative, fast, and cost-effective 3D material capable of decontaminating water. We have used an eco-friendly strategy, combining plasma surface activation and supercritical fluid technology to produce, for the first time, a 2-oxazoline-grafted 3D surface with broad-spectrum contact-active antimicrobial properties. Oligo(2-methyl-2-oxazoline) quaternized with N,N-dimethyldodecylamine and grafted to a chitosan (CHT) scaffold (CHT-OMetOx-DDA) efficiently and quickly (<3 min) killed >99.999% of Staphylococcus aureus and Escherichia coli cells upon direct contact and avoided bacterial adhesion to the materials surface, which is important for the prevention of biofilm formation. As a proof of concept, CHT-OMetOx-DDA scaffold was demonstrated to be suitable for water purification efficiently killing the microorganisms present in different water samples within minutes of contact and without leaching to the water. Additionally, we report for the first time a new method to clearly distinguish two mechanisms of action of bioactive surfaces: contact-active and releasing systems.

Synthesis, characterization and heterogeneous catalytic application of copper integrated mesoporous matrices.

Ordered copper integrated mesoporous silicate catalysts (CuMSC) have been synthesized by the utilization of the amphiphilic tri-block copolymer pluronic F127 as a structure directing agent (SDA) under acidic aqueous conditions. The mesophase of the materials was investigated using small-angle powder X-ray diffraction and transmission electron microscopic (TEM) image analysis. N2 adsorption-desorption studies show that the BET surface area of CuMSC (214-407 m(2) g(-1)) is lower than that of pure silica (611 m(2) g(-1)) and has smaller average pore dimensions (4.0-5.0 nm), both prepared following the same synthetic route. The reduction of pore size and surface area points to incorporation of copper within the silicate network. FEG-SEM results suggest that the materials have a plate-like morphology and are composed of very tiny nanoparticles. EDS surface chemical analysis was utilized for the detection of the distribution of Si, O and Cu in the matrix. The FT IR spectral study suggests the complete removal of the surfactants from the calcined materials and the presence of Si-O-Cu bonds for high nominal contents. X-ray photoelectron spectroscopy (XPS) and UV-vis reflectance spectra show the oxidation state of copper and coordination mode, respectively. These mesoporous materials display a good catalytic activity in the oxidation of cyclohexane to cyclohexanone and cyclohexanol in the presence of the green oxidant hydrogen peroxide. The maximum yield (cyclohexanone and cyclohexanol) was ca. 29% and the TON (turnover number) was 276 under optimal reaction conditions. The good catalytic activity could be attributed to the large surface area and the presence of a high number of active sites located at the surface of the material, as well as to its stability. The catalysts showed negligible loss of activity after five cycles.

Role of a disperse carbon interlayer on the performances of tandem a-Si solar cells.

We report the effect of a disperse carbon interlayer between the n-a-Si:H layer and an aluminium zinc oxide (AZO) back contact on the performance of amorphous silicon solar cells. Carbon was incorporated to the AZO film as revealed by x-ray photoelectron spectroscopy and energy-dispersive x-ray analysis. Solar cells fabricated on glass substrates using AZO in the back contact performed better when a disperse carbon interlayer was present in their structure. They exhibited an initial efficiency of 11%, open-circuit voltage Voc = 1.6 V, short-circuit current JSC = 11 mA cm-2 and a filling factor of 63%, that is, a 10% increase in the JSC and 20% increase in the efficiency compared to a standard solar cell.

Interaction of self-assembled monolayers of DNA with electrons: HREELS and XPS studies.

We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.

New hybrid films based on cellulose and hydroxygallium phthalocyanine. Synergetic effects in the structure and properties.

Hydroxygallium phthalocyanine (HOGaPc) and cellulose (from a trimethylsilyl derivative) have been used as native elements for the preparation of a novel family of hybrid films. By spin-coating, both components allow the building of films with different configurations on various substrates in a controlled way. The particularities of these hybrid films have been characterized by a range of techniques such as Fourier transform infrared spectroscopy (FTIRS) in attenuated total reflection using multiple internal reflections (ATR/MIR), absorption ultraviolet and visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surface potential measurements using the Kelvin-Zisman vibrating capacitor probe (KP). This enabled determination of the influence of cellulose on the arrangement of HOGaPc and, consequently, control of the relation between the structure and the properties of the films. Finally, gas sensor tests were performed to check the potentialities of these hybrid films. In particular, the synergetic behavior between the film-forming materials allows a fast and sensible change in surface potential after cyclic exposures to ozone (O3, 100 ppb) and nitrogen. Overall, we present the advantages of combining phthalocyanine with cellulose in enhancing the properties of the final product. Introduction of cellulose as a host material opens up a new area of hybrid films.