Plasma-Driven Tuning of Dielectric Permittivity in Graphene.

Materials with tunable negative electromagnetic performance, i.e., where dielectric permittivity becomes negative, have long been pursued in materials research due to their peculiar electromagnetic (EM) characteristics. Here, this promising feature is reported in materials on the case of plasma-synthesized nitrogen-doped graphene sheets with tunable permittivity over a wide (1-40 GHz) frequency range. Selectively incorporated nitrogen atoms in a graphene scaffold tailor the electronic structure in a way that provides an ultra-low energy (0.5-2 eV) 2D surface plasmon excitation, leading to subunitary and negative dielectric constant values in the Ka-band, from 30 up to 40 GHz. By allowing the tailoring of structures at atomic scale, this novel plasma-based approach creates a new paradigm for designing 2D nanomaterials like nanocarbons with controllable and tunable permittivity, opening a path to the next generation of 2D metamaterials.

Valorisation of spent tire rubber as carbon adsorbents for Pb(II) and W(VI) in the framework of a Circular Economy.

Spent tire rubber-derived chars and their corresponding H3PO4 and CO2-activated chars were used as adsorbents in the recovery of Pb(II) ion and (W(VI)) oxyanion from synthetic solutions. The developed chars (both raw and activated) were thoroughly characterized to have insight about their textural and surface chemistry properties. H3PO4-activated chars presented lower surface areas than the raw chars and an acidic surface chemistry which affected the performance of these samples as they showed the lowest removals of the metallic ions. On the other hand, CO2-activated chars presented increased surface areas and increased mineral content compared to the raw chars, having presented higher uptake capacities for both Pb(II) (103-116 mg/g) and W(VI) (27-31 mg/g) ions. Cation exchange with Ca, Mg and Zn ions was appointed as a mechanism for Pb removal, as well as surface precipitation in the form of hydrocerussite (Pb3(CO3)2(OH)2). W(VI) adsorption might have been ruled by strong electrostatic attractions between the negatively charged tungstate species and the highly positively charged carbons' surface.The results shown in this work allow concluding that the valorisation of spent tire rubber through pyrolysis and the subsequent activation of the obtained chars is an alternative and a feasible option to generate adsorbent materials with a high uptake capacity of critical metallic elements.

Bactericide Activity of Cellulose Acetate/Silver Nanoparticles Asymmetric Membranes: Surfaces and Porous Structures Role.

The antibacterial properties of cellulose acetate/silver nanoparticles (AgNP) ultrafiltration membranes were correlated with their integral asymmetric porous structures, emphasizing the distinct features of each side of the membranes, that is, the active and porous layers surfaces. Composite membranes were prepared from casting solutions incorporating polyvinylpyrrolidone-covered AgNP using the phase inversion technique. The variation of the ratio acetone/formamide and the AgNP content resulted in a wide range of asymmetric porous structures with different hydraulic permeabilities. Comprehensive studies assessing the antibacterial activity against Escherichia coli (cell death and growth inhibition of bacteria in water) were performed on both membrane surfaces and in E. coli suspensions. The results were correlated with the surface chemical composition assessed by XPS. The silver-free membranes presented a generalized growth of E. coli, which is in contrast with the inhibition patterns displayed by the membranes containing AgNP. For the surface bactericide test, the growth inhibition depends on the accessibility of E. coli to the silver present in the membrane; as the XPS results show, the more permeable membranes (CA30 and CA34 series) have higher silver signal detected by XPS, which is correlated with a higher growth inhibition. On the other hand, the inhibition action is independent of the membrane porous structure when the membrane is deeply immersed in an E. coli inoculated suspension, presenting almost complete growth inhibition.

Cotton decorated with Cu2O-Ag and Cu2O-Ag-AgBr NPs via an in-situ sacrificial template approach and their antibacterial efficiency.

Cotton fabrics decorated with Cu2O-Ag and Cu2O-Ag-AgBr NPs have been prepared using chemically immobilized Cu2O NPs as sacrificial templates. The objective is to prepare Cu2O-Ag heterostructures with Ag being intimately in contact with Cu2O NPs by galvanic replacement reactions without addition of any external reducing agent. Field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis were used to study the morphology and the chemical composition of the nanocomposites formed on the fabrics. The morphology of the ensuing nanostructures was shown to be dependent on the Ag precursor, AgNO3, concentration. The antimicrobial activity of the treated fabrics was evaluated against Staphylococcus aureus and Escherichia coli as model strains of gram-negative and gram-positive, respectively. The results showed that the fabrics loaded with Cu2O-Ag and Cu2O-Ag-AgBr nanocomposites exhibited enhanced sterilization activity compared to the Cu2O treated fabric.

Preclinical In Vitro Assessment of Submicron-Scale Laser Surface Texturing on Ti6Al4V.

Loosening of orthodontic and orthopedic implants is a critical and common clinical problem. To minimize the numbers of revision surgeries due to peri-implant inflammation or insufficient osseointegration, developments of new implant manufacturing strategies are indicated. Ultrafast laser surface texturing is a promising contact-free technology to modify the physicochemical properties of surfaces toward an anti-infectious functionalization. This work aims to texture Ti6Al4V surfaces with ultraviolet (UV) and green (GR) radiation for the manufacturing of laser-induced periodic surface structures (LIPSS). The assessment of these surface modifications addresses key aspects of topography, morphology and chemical composition. Human primary mesenchymal stromal cells (hMSCs) were cultured on laser-textured and polished Ti6Al4V to characterize the surfaces in terms of their in vitro biocompatibility, cytotoxicity, and metal release. The outcomes of the in vitro experiment show the successful culture of hMSCs on textured Ti6Al4V surfaces developed within this work. Cells cultured on LIPSS surfaces were not compromised in terms of their viability if compared to polished surfaces. Yet, the hMSC culture on UV-LIPSS show significantly lower lactate dehydrogenase and titanium release into the supernatant compared to polished. Thus, the presented surface modification can be a promising approach for future applications in orthodontics and orthopedics.

Cotton fabrics decorated with nanostructured Ag/AgX (X:Cl,Br) as reusable solar light-mediated bactericides: A comparative study.

In this study, cotton fabrics decorated with Ag/AgCl and Ag/AgBr NPs were produced by a simple hydrothermal treatment using AgCl and AgBr as precursors. Their morphological features as well as, chemical composition and structural and luminescence properties were compared. Their water disinfection aptitude against E. coli and S. aureus was also investigated under solar illumination in batch as well asin dynamic conditions. The highest activity was observed for Cot-Ag/AgCl with a quasi-complete inactivation of E. coli and S. aureus(1.5 × 107cfu mL-1) within 15 min illumination. Disinfection efficiency under continuous flow was also tested using a home-made photoreactor and the cotton fabrics with the most efficient photocatalyst (Ag/AgCl). It has shown to be efficient at least for 10 cycles revealing the robustness of the functionalization. The mechanism of photocatalytic disinfection was explained in terms of the surface plasmon resonance (SPR) induced by the presence of Ag NPs, the resulting holes, h+, being one of the most intervenient species in the disinfection mechanism. The difference in the photocatalytic efficiency between AgCl and AgBr functionalized cotton was attributed to differences in the carriers (h+and e-) lifetime. This work provides a proof of concept for the potential applicability of Cot-Ag/AgCl or Cot-Ag/AgBr for in-flow potabilization of water under solar illumination.

Cell and tissue response to nanotextured Ti6Al4V and Zr implants using high-speed femtosecond laser-induced periodic surface structures.

In this paper, the effect of femtosecond laser nanotexturing of surfaces of Ti6Al4V and Zr implants on their biological compatibility is presented and discussed. Highly regular and homogeneous nanostructures with sub-micrometer period were imprinted on implant surfaces. Surfaces were morphologically and chemically investigated by SEM and XPS. HDFa cell lines were used for toxicity and cell viability tests, and subcutaneous implantation was applied to characterize tissue response. HDFa proliferation and in vivo experiments evidenced the strong influence of the surface topography compared to the effect of the surface elemental composition (metal or alloy). The effect of protein adsorption from blood plasma on cell proliferation is also discussed.

Silver Nanoparticles on Cellulose Surfaces: Quantitative Measurements.

In this work, cellulose films pre-activated with carbonyldiimidazole (CDI) and grafted with 1,6-hexanediamine, were decorated with silver nanoparticles (AgNPs). The generation of AgNPs was followed by quartz crystal microbalance (QCM). The obtained films were characterized by X-Ray Photoelectron Spectroscopy (XPS) and imaged by atomic force microscopy (AFM). XPS confirmed the synthesis in situ of AgNPs on the film attesting their oxidation state. The results from the three techniques were compared showing how sound the quantitative treatment of the results issued from these techniques can be. The main objective of this work is exactly to show that the quantitative exploration of the results of different characterization techniques can and should be practiced systematically instead of just comparing them qualitatively.

Hybrid chitosan-TiO2/ZnS prepared under mild conditions with visible-light driven photocatalytic activity.

Thin films of chitosan (CS) coated on glass substrates were used as support for the immobilization of nanostructures TiO2/ZnS via a mild chemical process followed by a hydrothermal treatment at 90 °C. The preparation route involved the coating of the CS film on the glass substrate followed by the deposition of a thin layer of Ti(OBu)4 precursor and immersion in a solution of Zn(O2CCH3)2 and Na2S. After a hydrothermal treatment at 90 °C, an even layer of TiO2 anatase decorated by ZnS nanorods was generated. Evidence of the formation of TiO2 anatase and ZnS was confirmed by XRD, Raman and XPS, and the morphology of the TiO2 layer and ZnS nanoparticles was analyzed by FE-SEM observations. The photocatalytic activity of the CS-TiO2-ZnS systems was evaluated by the degradation of a wide range of organic compounds including aromatic amines and carboxylic acids under a conventional halogen lamp.

Unraveling the reaction mechanism of silver ions reduction by chitosan from so far neglected spectroscopic features.

Metallic silver nanoparticles were synthesized in aqueous solution using chitosan, as both reducing and stabilizing agent, and AgNO3 as silver precursor aiming the production of solid ultra-thin films. A systematic characterization of the resulting system as a function of the initial concentrations was performed. The combination of UV-vis absorption - and its quantitative analysis - with X-ray photoelectron spectra, light scattering measurements and atomic force microscopy allowed obtaining a rational picture of silver reduction mechanism through the identification of the nature of the formed reduced/oxidized species. Nanoparticle mean sizes and sizes distributions were rather independent from the precursors initial absolute and relative concentrations ([AgNO3]/[chitosan]). This work clarifies some points of the mechanism involved showing experimental evidence of the early stages of the very fast silver reduction in chitosan aqueous solutions through the spectral signature of the smallest silver aggregate (Ag2+) even at room temperature. The characterized system is believed to be useful for research fields where silver nanoparticles completely exempt of harmful traces of inorganic ions, coming from additional reducing agents, are needed, especially to be used in biocompatible in films.

Interrogating the Role of Receptor-Mediated Mechanisms: Biological Fate of Peptide-Functionalized Radiolabeled Gold Nanoparticles in Tumor Mice.

To get a better insight on the transport mechanism of peptide-conjugated nanoparticles to tumors, we performed in vivo biological studies of bombesin (BBN) peptide functionalized gold nanoparticles (AuNPs) in human prostate tumor bearing mice. Initially, we sought to compare AuNPs with thiol derivatives of acyclic and macrocyclic chelators of DTPA and DOTA types. The DTPA derivatives were unable to provide a stable coordination of (67)Ga, and therefore, the functionalization with the BBN analogues was pursued for the DOTA-containing AuNPs. The DOTA-coated AuNPs were functionalized with BBN[7-14] using a unidentate cysteine group or a bidentate thioctic group to attach the peptide. AuNPs functionalized with thioctic-BBN displayed the highest in vitro cellular internalization (≈ 25%, 15 min) in gastrin releasing peptide (GRP) receptor expressing cancer cells. However, these results fail to translate to in vivo tumor uptake. Biodistribution studies following intravenous (IV) and intraperitoneal (IP) administration of nanoconjugates in tumor bearing mice indicated that the presence of BBN influences to some degree the biological profile of the nanoconstructs. For IV administration, the receptor-mediated pathway appears to be outweighed by the EPR effect. By contrast, in IP administration, it is reasoned that the GRPr-mediated mechanism plays a role in pancreas uptake.

Cellulose films: designing template-free nanoporous cellulose films on semiconducting surfaces.

In this work, we report the preparation of ultrathin submicro- and nanoporous cellulose films onto Si (100). The effect of different experimental conditions of preparation on the film surface morphology was studied, namely the role of the film casting method (spin- versus dip-coating), solvent (toluene or tetrahydrofuran), substrate pretreatment (hydrophilicity degree), and regeneration procedure with HCl vapors (two consecutive dips followed by regeneration or regeneration after each dip). The surface morphological structures presented in this work were never obtained before without the use of templates. A rather regular two-dimensional pore network was obtained onto the less hydrophilic Si substrate (contact angle≅68°), after two consecutive dips (with an intercalary rotation of 180º) in trimethylsilyl cellulose diluted in toluene and regeneration at the end. All the surfaces were characterized by atomic force microscopy.

Uniform arrays of ZnO 1D nanostructures grown on Al:ZnO seeds layers by hydrothermal method.

In obtaining uniform array of ZnO 1D nanostructures, especially using solution based methods, the thickness and the morphology of the epitaxial seeds layer are very important. The paper presents the effect of the thickness and the morphology of the Al:ZnO seeds layer on the morphology and properties of ZnO nanowires array grown by hydrothermal method. Compact and vertically aligned ZnO 1D nanostructures were obtained. Concentration of 0.02 M of zinc nitrate was found to be optimal for growing nanowires with diameters up to 50 nm and lengths between 1.5 and 2.5 microns. Using 0.04 M solution, nanorods with diameter between 50 and 100 nm were obtained. The correlation between the crystal structure and optical properties of ZnO nanowires is discussed. From electrical measurements on single nanowire, resistivity value of 9 x 10(-2) omega cm was obtained. The I-V curves of single ZnO NWs show quasi diode characteristic when an e-beam is irradiating the NWs, and a typical semiconductive behaviour when the e-beam is turned off.

Hybrid systems of silver nanoparticles generated on cellulose surfaces.

A method to produce hybrid systems of cellulose ultrathin films containing immobilized silver nanoparticles (Ag NPs) generated and grown at the surface is presented. Ag NPs were produced via a mild wet chemistry technique on cellulose ultrathin films spin-coated on GaAs substrates and on modified films after grafting of diaminoalkanes activated by N,N'-carbonyldiimidazole. Appended amine groups operate as anchoring centers of the silver NPs enabling selective generation and immobilization of Ag NPs. The different phases of the modification process were followed by Fourier transform infrared spectroscopy (FTIRS) in attenuated total reflection in multiple internal reflections (ATR/MIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The generation of NPs is observed even on untreated cellulose surfaces with sizes ranging from 7 to 30 nm but not specifically at the surface. For modified surfaces with diaminoalkanes, higher NP density regions including extensive plates are obtained, which are specifically located at the film extreme surface. The highest NP density is achieved when the NP generation is performed on these modified surfaces in the presence of a carboxylic salt.

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.