A.M. Ferraria

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.

Microwave plasmas applied for the synthesis of free standing graphene sheets

Self-standing graphene sheets were synthesized using microwave plasmas driven by surface waves at 2.45 GHz stimulating frequency and atmospheric pressure. The method is based on injecting ethanol molecules through a microwave argon plasma environment, where decomposition of ethanol molecules takes place. The evolution of the ethanol decomposition was studied in situ by plasma emission spectroscopy. Free gas-phase carbon atoms created in the plasma diffuse into colder zones, both in radial and axial directions, and aggregate into solid carbon nuclei. The main part of the solid carbon is gradually withdrawn from the hot region of the plasma in the outlet plasma stream where nanostructures assemble and grow. Externally forced heating in the assembly zone of the plasma reactor has been applied to engineer the structural qualities of the assembled nanostructures. The synthesized graphene sheets have been analysed by Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The presence of sp3 carbons is reduced by increasing the gas temperature in the assembly zone of the plasma reactor. As a general trend, the number of mono-layers decreases when the wall temperature increases from 60 to 100 °C. The synthesized graphene sheets are stable and highly ordered.

Controlled growth of Cu2O nanoparticles bound to cotton fibres

A green, safe and fast procedure is presented for in situ generation of nanoparticles (NPs) of cuprous oxide (Cu2O) onto cotton fibres at room temperature using water as a solvent. The method is based on a mild surface oxidation of cellulose fibres to generate in a controlled way carboxylic groups acting as a binding site for the adsorption of Cu(2+) via electrostatic coordination. Then, the adsorbed Cu(2+) ions were readly converted into Cu2O by dipping the treated cotton fibres into a aqueous solution of a reducing agent. Field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), as well as UV-vis absorption and emission spectroscopic methods were used to analyse the size, morphology, chemical composition and the crystalline structure of the generated nanoparticles on the fabrics. The morphology of the ensuing Cu2O nanoparticles was shown to be dependent on the reduycing agent used. Antibacterial properties of the modified fibres were also investigated.

Grafting of Porphyrins on Cellulose Nanometric Films

Ultrathin films of cellulose were functionalized with iron protoporphyrin IX (FePP). Spin-coating allows the production of silylated cellulose films in a controlled way. Cellulose regeneration is achieved through the hydrolyzation of the silane groups, exposing the film to acidic vapors. To enhance the reactivity of the cellulose surface to the protoporphyrin, carbonyldiimidazole (CDI) was used as an activator. The effect of different spacers on the porphyrin grafting such as 1,8-diaminooctane and 1,4-phenylenediamine was studied. The highest level of cellulose functionalization with FePP was achieved when both the cellulose film and FePP were activated by CDI and a diaminoalkane was used as a spacer between the surface and the FePP. ATR/MIR (attenuated total reflection in multiple internal reflections) was performed in situ to follow the kinetics of the different chemical reactions with the cellulose surface. ATR/MIR proved again to be a powerful tool for probing the surface reaction. X-ray photoelectron spectroscopy permitted the elemental analysis of the cellulose surface after the chemical modification.

Sugarcane bagasse cellulose fibres and their hydrous niobium phosphate composites: synthesis and characterization by XPS, XRD and SEM

AbstractCellulose fibres obtained from sugarcane bagasse were submitted to a purification process, which consisted of an acid hydrolysis for elimination of the major part of lignin and hemicellulose. This was followed by a delignification process carried out in two steps to yield crude cellulose (CCell) fibres in the first one and with a subsequent bleaching in order to yield bleached cellulose fibres (BCell). Composites of crude and bleached cellulose fibres with hydrous niobium phosphate, cell/NbOPO4·nH2O, were subsequently synthesized. Scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction characterization of the obtained materials showed CCell/NbOPO4·nH2O and BCell/NbOPO4·nH2O are real composites. The nature of the cellulose (CCell or BCell) has an important role on the composites obtained, namely on the niobium salt composition at the composite surface. The synthesis of membranes of both cellulose and mixed matrix cellulose/NbOPO4·nH2O was only possible when the bleached cellulose was used.

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.

Energy Thresholds of DNA Damage Induced by UV Radiation: An XPS Study

This work stresses on damage at the molecular level caused by ultraviolet radiation (UV) in the range from 3.5 to 8 eV, deoxyribonucleic acid (DNA) films observed by X-ray photoelectron spectroscopy (XPS). Detailed quantitative XPS analysis, in which all the amounts are relative to sodium-assumed not to be released from the samples, of the carbon, oxygen, and particularly, nitrogen components, reveals that irradiation leads to sugar degradation with CO-based compounds release for energies above 6.9 eV and decrease of nitrogen groups which are not involved in hydrogen bonding at energies above 4.2 eV. Also the phosphate groups are seen to decrease to energies above 4.2 eV. Analysis of XPS spectra allowed to conclude that the damage on bases peripheral nitrogen atoms are following the damage on phosphates. It suggests that very low kinetic energy photoelectrons are ejected from the DNA bases, as a result of UV light induced breaking of the phosphate ester groups which forms a transient anion with resonance formation and whereby most of the nitrogen DNA peripheral groups are removed. The degree of ionization of DNA was observed to increase with radiation energy, indicating that the ionized phosphate groups are kept unchanged. This result was interpreted by the shielding of phosphate groups caused by water molecules hydration near sodium atoms.

Hybrid cotton–anatase prepared under mild conditions with high photocatalytic activity under sunlight

Cotton fibres were coated with nanolayers of TiO2, anatase, using a new approach based on a non-hydrolytic sol–gel process followed by a mild hydrothermal treatment at a temperature lower than 140 °C. The crystallization process was followed by Raman spectroscopy and XRD, and the change in the chemical environment of Ti resulting from the hydrothermal temperature was analyzed using XPS. Changes in the morphology of the ensuing NPs on the different cotton samples were studied by FE-SEM. UV-Vis absorption spectra and the luminescence properties of the TiO2, as well as their thermal properties, were also investigated. To explain the TiO2 crystallization at temperatures much lower than 350 °C, a growth mechanism of TiO2 nanocrystallites (diameter < 15 nm) was proposed to proceed via coordination and ligand exchange of Ti(OBu)4 with the cotton surface hydroxyl groups followed by edge-sharing polycondensation during the hydrothermal process. Also the presence of acetic acid was revealed crucial in the mechanism. The hybrid cotton–TiO2 was shown to exhibit a good photocatalytic activity for the degradation of an organic dye – Remazol Brilliant Blue R. The preparation technique is reliable, easy to implement and can be also applied to cotton fabrics to create self-cleaning and protection textiles under visible irradiation. Reusability of the cotton samples was investigated.

TiO2-CdS Nanocomposites

Nanocomposites TiO2-CdS with different relative contents of CdS molar ratios Cd/Ti = 0.02, 0.03, 0.05, 0.1, 0.2, and 0.5 were studied. The structural, photophysical, and chemical properties were investigated using XRD, Raman spectroscopy, XPS, GSDR, and LIL. XRD and Raman results confirmed the presence of TiO2 and CdS with intensities dependent on the ratio Cd/Ti. The presence of CdSO4 was detected by XPS at the surface of all TiO2-CdS composites. The relative amount of sulphate was dependent on the CdS loading. Luminescence time-resolved spectra clearly proved the existence of an excitation transfer process from CdS to TiO2 through the luminescence emission from TiO2 after excitation of CdS at λexc=410 nm, where no direct excitation of TiO2 occurs. Photodegradation of a series of aromatic carboxylic acids—benzoic, salicylic, 4-bromobenzoic, 3-phenylpropionic, and veratric acids—showed a great enhancement in the photocatalytic efficiency of the TiO2-CdS composites, which is due, mainly, to the effect of the charge carriers’ increased lifetime. In addition, it was shown that the oxidation of CdS to CdSO4 did not result in the deactivation of the photocatalytic properties and even contributed to enhance the degradation efficiency.

Erratum to: Highly transparent nanocomposite films based on polybutylmethacrylate and functionalized cellulose nanocrystals

Efficient surface functionalization of cellulose nanocrystals (CNC) with hydroxyl butyl acrylate monomer (HBA) was carried on under mild condition using N,N′-carbonyldiimidazole as an activator. The grafting of the acrylic monomer was shown to bring about the high yield grafting of polymer chains on the functionalized CNC during in situ polymerization process. Surface functionalization of CNC with HBA and the polymer grafting on the modified CNC were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Nanocomposite film prepared from in situ polybutylmethacrylate polymerization process using HBA functionalized nanocrystals exhibited high transparency degree here assigned to improved dispersion. DMA analysis proved that the best mechanical/rheological performance is obtained for HBA–CNC contents of 4 %.