Freezing efficiency of feldspars is affected by their history of previous freeze-thaw events.

Among the different aerosol mineral particles that contribute to induce ice nucleation (IN) in the troposphere, feldspars have been identified as the most active. Nevertheless, which surface properties make some feldspars more efficient than others, i.e. able to induce IN at higher temperatures, is still unclear. In addition to that, surface properties of such materials can change as they are exposed to a variety of environmental conditions while traveling through the troposphere. Here, freezing temperature of water droplets deposited on feldspar minerals has been measured as a function of consecutive freeze-thaw cycles. We found an increase of the freezing temperature for the initial cycles followed by approximately constant freezing temperature for consecutive cycles. We call this a "history effect". This effect is more evident for samples aged in standard room conditions and it disappears if the sample is exposed to oxygen plasma. Oxygen plasma generates OH groups at the surface, facilitating IN and cleans the surface from organic contamination, unblocking pores at the surface, believed to be the most active IN sites on feldspars. A similar process is suggested to happen during the history effect, when consecutive freeze-thaw events unblock IN sites.

Studying Ice with Environmental Scanning Electron Microscopy.

Scanning electron microscopy (SEM) is a powerful imaging technique able to obtain astonishing images of the micro- and the nano-world. Unfortunately, the technique has been limited to vacuum conditions for many years. In the last decades, the ability to introduce water vapor into the SEM chamber and still collect the electrons by the detector, combined with the temperature control of the sample, has enabled the study of ice at nanoscale. Astounding images of hexagonal ice crystals suddenly became real. Since these first images were produced, several studies have been focusing their interest on using SEM to study ice nucleation, morphology, thaw, etc. In this paper, we want to review the different investigations devoted to this goal that have been conducted in recent years in the literature and the kind of information, beyond images, that was obtained. We focus our attention on studies trying to clarify the mechanisms of ice nucleation and those devoted to the study of ice dynamics. We also discuss these findings to elucidate the present and future of SEM applied to this field.

Charge transfer in steam purified arc discharge single walled carbon nanotubes filled with lutetium halides.

In the present work, the effect of doping on electronic properties in bulk purified and filled arc-discharge single-walled carbon nanotubes samples is studied for the first time by in situ Raman spectroelectrochemical method. A major challenge to turn the potential of SWCNTs into customer applications is to reduce or eliminate their contaminants by means of purification techniques. Besides, the endohedral functionalization of SWCNTs with organic and inorganic materials (i.e. metal halides) allows the development of tailored functional hybrids. Here, we report the purification and endohedral functionalization of SWCNTs with doping affecting the SWCNTs. Steam-purified SWCNTs have been filled with selected lutetium(iii) halides, LuCl3, LuBr3, LuI3, and sealed using high-temperature treatment, yielding closed-ended SWCNTs with the filling material confined in the inner cavity. The purified SWCNTs were studied using TGA, EDX, STEM and Raman spectroscopy. The lutetium(iii) halide-filled SWCNTs (LuX3@SWCNTs) were characterized using STEM, EDX, Raman spectroscopy and in situ Raman spectroelectrochemistry. It was found that there is a charge transfer between the SWCNTs and the encapsulated LuX3 (X = Cl, Br, I). The obtained data testify to the acceptor doping effect of lutetium(iii) halides incorporated into the SWCNT channels, which is accompanied by the charge transfer from nanotube walls to the introduced substances.

Water adsorption, dissociation and oxidation on SrTiO3 and ferroelectric surfaces revealed by ambient pressure X-ray photoelectron spectroscopy.

Water dissociation on oxides is of great interest because its fundamental aspects are still not well understood and it has implications in many processes, from ferroelectric polarization screening phenomena to surface catalysis and surface chemistry on oxides. In situ water dissociation and redox processes on metal oxide perovskites which easily expose TiO2-terminated surfaces, such as SrTiO3, BaTiO3 or Pb(Zr,Ti)O3, are studied by ambient pressure XPS, as a function of water vapour pressure. From the analysis of the O1s spectrum, we determine the presence of different types of oxygen based species, from hydroxyl groups, either bound to Ti4+ and metal sites or lattice oxygen, to different peroxide compounds, and propose a model for the adsorbate layer composition, valid for environmental conditions. From the XPS analysis, we describe the existing surface redox reactions for metal oxide perovskites, occurring at different water vapour pressures. Among them, peroxide species resulting from surface oxidative reactions are correlated with the presence of Ti4+ ions, which are observed to specifically promote surface oxidation and water dissociation as compared to other metals. Finally, surface peroxidation is enhanced by X-ray beam irradiation, leading to a higher coverage of peroxide species after beam overexposure and by ferroelectric polarization, demonstrating the enhancement of the reactivity of the surfaces of ferroelectric materials due to the effect of internal electric fields.

Quantitative monitoring of the removal of non-encapsulated material external to filled carbon nanotube samples.

The endohedral functionalization of carbon nanotubes with both organic and inorganic materials allows the development of tailored functional hybrids whose properties benefit from the synergistic effects of the constituent compounds. Bulk filling of carbon nanotubes (CNTs) results in samples that contain a large amount of non-encapsulated material external to the CNTs. The presence of the external material is detrimental to the processing and application of the resulting hybrids. Here we introduce the use of UV-Vis spectroscopy to monitor the cleaning process, i.e. the elimination of non-encapsulated compounds. Chrome azurol S has been employed to assess the bulk removal of external samarium(iii) chloride from filled single-walled carbon nanotubes. Chrome azurol S is of interest since it can be used to quantify a large variety of materials in a fast, accurate and reliable manner. The parameters that control the cleaning process have been optimized, including the time, temperature, volume and sonication, to achieve a fast and complete removal of the external material.

Production of water-soluble few-layer graphene mesosheets by dry milling with hydrophobic drug.

A novel, fast, and easy mechano-chemistry-based (dry milling) method has been developed to exfoliate graphene with hydrophobic drugs generating few-layer graphene mesosheets (< 10 nm in thickness and ∼1 µm in width). The electronic properties of the graphitic structure were partially preserved after the milling treatment compared with graphene oxide prepared by Hummers' method. Several characterization techniques such as thermogravimetric analysis, Raman spectroscopy, atomic force microscopy, electron microscopy, and molecular dynamics simulation were used to characterize this material. The drug-exfoliated mesosheets were pharmacologically inactive, offering a new approach for making water-soluble few-layer graphene mesosheets upon dry milling with hydrophobic drugs, mainly used as exfoliating agents.

Size-dependent dissociation of carbon monoxide on cobalt nanoparticles.

In situ soft X-ray absorption spectroscopy (XAS) was employed to study the adsorption and dissociation of carbon monoxide molecules on cobalt nanoparticles with sizes ranging from 4 to 15 nm. The majority of CO molecules adsorb molecularly on the surface of the nanoparticles, but some undergo dissociative adsorption, leading to oxide species on the surface of the nanoparticles. We found that the tendency of CO to undergo dissociation depends critically on the size of the Co nanoparticles. Indeed, CO molecules dissociate much more efficiently on the larger nanoparticles (15 nm) than on the smaller particles (4 nm). We further observed a strong increase in the dissociation rate of adsorbed CO upon exposure to hydrogen, clearly demonstrating that the CO dissociation on cobalt nanoparticles is assisted by hydrogen. Our results suggest that the ability of cobalt nanoparticles to dissociate hydrogen is the main parameter determining the reactivity of cobalt nanoparticles in Fischer-Tropsch synthesis.

A reaction cell with sample laser heating for in situ soft X-ray absorption spectroscopy studies under environmental conditions.

A miniature (1 ml volume) reaction cell with transparent X-ray windows and laser heating of the sample has been designed to conduct X-ray absorption spectroscopy studies of materials in the presence of gases at atmospheric pressures. Heating by laser solves the problems associated with the presence of reactive gases interacting with hot filaments used in resistive heating methods. It also facilitates collection of a small total electron yield signal by eliminating interference with heating current leakage and ground loops. The excellent operation of the cell is demonstrated with examples of CO and H2 Fischer-Tropsch reactions on Co nanoparticles.

Experimental and theoretical investigation of the electronic structure of Cu2O and CuO thin films on Cu(110) using x-ray photoelectron and absorption spectroscopy.

The electronic structure of Cu(2)O and CuO thin films grown on Cu(110) was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The various oxidation states, Cu(0), Cu(+), and Cu(2+), were unambiguously identified and characterized from their XPS and XAS spectra. We show that a clean and stoichiometric surface of CuO requires special environmental conditions to prevent loss of oxygen and contamination by background water. First-principles density functional theory XAS simulations of the oxygen K edge provide understanding of the core to valence transitions in Cu(+) and Cu(2+). A novel method to reference x-ray absorption energies based on the energies of isolated atoms is presented.

The Role of Temperature on the Degree of End-Closing and Filling of Single-Walled Carbon Nanotubes.

Carbon nanotubes (CNTs), owing to their high surface area-to-volume ratio and hollow core, can be employed as hosts for adsorbed and/or encapsulated molecules. At high temperatures, the ends of CNTs close spontaneously, which is relevant for several applications, including catalysis, gas storage, and biomedical imaging and therapy. This study highlights the influence of the annealing temperature in the range between 400 and 1100 °C on the structure and morphology of single-walled CNTs. The nitrogen adsorption and density functional theory calculations indicate that the fraction of end-closed CNTs increases with temperature. Raman spectroscopy reveals that the thermal treatment does not alter the tubular structure. Insight is also provided into the efficacy of CNTs filling from the molten phase, depending on the annealing temperature. The CNTs are filled with europium (III) chloride and analyzed by using electron microscopy (scanning electron microscopy and high-resolution transmission electron microscopy) and energy-dispersive X-ray spectroscopy, confirming the presence of filling and closed ends. The filling yield increases with temperature, as determined by thermogravimetric analysis. The obtained results show that the apparent surface area of CNTs, fraction of closed ends, and amount of encapsulated payload can be tailored via annealing.

Functionalization of filled radioactive multi-walled carbon nanocapsules by arylation reaction for in vivo delivery of radio-therapy.

Functionalized multi-walled carbon nanotubes (MWCNTs) containing radioactive salts are proposed as a potential system for radioactivity delivery. MWCNTs are loaded with isotopically enriched 152-samarium chloride (152SmCl3), the ends of the MWCNTs are sealed by high temperature treatment, and the encapsulated 152Sm is neutron activated to radioactive 153Sm. The external walls of the radioactive nanocapsules are functionalized through arylation reaction, to introduce hydrophilic chains and increase the water dispersibility of CNTs. The organ biodistribution profiles of the nanocapsules up to 24 h are assessed in naïve mice and different tumor models in vivo. By quantitative γ-counting, 153SmCl3@MWCNTs-NH2 exhibite high accumulation in organs without leakage of the internal radioactive material to the bloodstream. In the treated mice, highest uptake is detected in the lung followed by the liver and spleen. Presence of tumors in brain or lung does not increase percentage accumulation of 153SmCl3@MWCNTs-NH2 in the respective organs, suggesting the absence of the enhanced permeation and retention effect. This study presents a chemical functionalization protocol that is rapid (∼one hour) and can be applied to filled radioactive multi-walled carbon nanocapsules to improve their water dispersibility for systemic administration for their use in targeted radiotherapy.

Neutron Activated 153Sm Sealed in Carbon Nanocapsules for in Vivo Imaging and Tumor Radiotherapy.

Radiation therapy along with chemotherapy and surgery remain the main cancer treatments. Radiotherapy can be applied to patients externally (external beam radiotherapy) or internally (brachytherapy and radioisotope therapy). Previously, nanoencapsulation of radioactive crystals within carbon nanotubes, followed by end-closing, resulted in the formation of nanocapsules that allowed ultrasensitive imaging in healthy mice. Herein we report on the preparation of nanocapsules initially sealing "cold" isotopically enriched samarium (152Sm), which can then be activated on demand to their "hot" radioactive form (153Sm) by neutron irradiation. The use of "cold" isotopes avoids the need for radioactive facilities during the preparation of the nanocapsules, reduces radiation exposure to personnel, prevents the generation of nuclear waste, and evades the time constraints imposed by the decay of radionuclides. A very high specific radioactivity is achieved by neutron irradiation (up to 11.37 GBq/mg), making the "hot" nanocapsules useful not only for in vivo imaging but also therapeutically effective against lung cancer metastases after intravenous injection. The high in vivo stability of the radioactive payload, selective toxicity to cancerous tissues, and the elegant preparation method offer a paradigm for application of nanomaterials in radiotherapy.

Surface charged species and electrochemistry of ferroelectric thin films.

The combination of scanning probe microscopy and ambient pressure X-ray photoelectron spectroscopy opens up new perspectives for the study of combined surface chemical, electrochemical and electromechanical properties at the nanoscale, providing both nanoscale resolution of physical information and the chemical sensitivity required to identify surface species and bulk ionic composition. In this work, we determine the nature and evolution over time of surface chemical species obtained after water-mediated redox reactions on Pb(Zr0.2,Ti0.8)O3 thin films with opposite as-grown polarization states. Starting with intrinsically different surface chemical composition on the oppositely polarized films (as a result of their ferroelectric-dominated interaction with environmental water), we identify the reversible and irreversible electrochemical reactions under an external electric field, distinguishing switching and charging events. We find that while reversible ionic displacements upon polarization switching dominate screening in the bulk of the sample, polarization dependent irreversible redox reactions determine surface chemical composition, which reveals itself as a characteristic fingerprint of the ferroelectric polarization switching history.

Determination of the length of single-walled carbon nanotubes by scanning electron microscopy.

A methodology is presented to determine the length of well individualized single-walled carbon nanotubes (SWCNTs) by means of scanning electron microscopy (SEM). Accurate measurements on wide areas of the sample can be achieved in an easy, fast and trustworthy manner. We have tested several supports and solvents to optimize the dispersion of SWCNTs, as well as the SEM imaging conditions. The optimal methodology goes via dispersion of the sample in ortho-dichlorobenzene, deposition onto a continuous carbon film supported on a copper TEM grid, and SEM imaging at 2 kV in secondary electrons mode using a through-in-lens detector. •Individualization of SWCNTs is achieved by dispersion of SWCNTs in ortho-dichlorobenzene and deposition onto TEM grids•Individual SWCNTs are imaged by SEM•Length determination by SEM is as precise as AFM.

Evaluation of the immunological profile of antibody-functionalized metal-filled single-walled carbon nanocapsules for targeted radiotherapy.

This study investigates the immune responses induced by metal-filled single-walled carbon nanotubes (SWCNT) under in vitro, ex vivo and in vivo settings. Either empty amino-functionalized CNTs [SWCNT-NH2 (1)] or samarium chloride-filled amino-functionalized CNTs with [SmCl3@SWCNT-mAb (3)] or without [SmCl3@SWCNT-NH2 (2)] Cetuximab functionalization were tested. Conjugates were added to RAW 264.7 or PBMC cells in a range of 1 µg/ml to 100 µg/ml for 24 h. Cell viability and IL-6/TNFα production were determined by flow cytometry and ELISA. Additionally, the effect of SWCNTs on the number of T lymphocytes, B lymphocytes and monocytes within the PBMC subpopulations was evaluated by immunostaining and flow cytometry. The effect on monocyte number in living mice was assessed after tail vein injection (150 µg of each conjugate per mouse) at 1, 7 and 13 days post-injection. Overall, our study showed that all the conjugates had no significant effect on cell viability of RAW 264.7 but conjugates 1 and 3 led to a slight increase in IL-6/TNFα. All the conjugates resulted in significant reduction in monocyte/macrophage cell numbers within PBMCs in a dose-dependent manner. Interestingly, monocyte depletion was not observed in vivo, suggesting their suitability for future testing in the field of targeted radiotherapy in mice.

Carbon nanotubes allow capture of krypton, barium and lead for multichannel biological X-ray fluorescence imaging.

The desire to study biology in situ has been aided by many imaging techniques. Among these, X-ray fluorescence (XRF) mapping permits observation of elemental distributions in a multichannel manner. However, XRF imaging is underused, in part, because of the difficulty in interpreting maps without an underlying cellular 'blueprint'; this could be supplied using contrast agents. Carbon nanotubes (CNTs) can be filled with a wide range of inorganic materials, and thus can be used as 'contrast agents' if biologically absent elements are encapsulated. Here we show that sealed single-walled CNTs filled with lead, barium and even krypton can be produced, and externally decorated with peptides to provide affinity for sub-cellular targets. The agents are able to highlight specific organelles in multiplexed XRF mapping, and are, in principle, a general and versatile tool for this, and other modes of biological imaging.

Design of antibody-functionalized carbon nanotubes filled with radioactivable metals towards a targeted anticancer therapy.

In the present work we have devised the synthesis of a novel promising carbon nanotube carrier for the targeted delivery of radioactivity, through a combination of endohedral and exohedral functionalization. Steam-purified single-walled carbon nanotubes (SWCNTs) have been initially filled with radioactive analogues (i.e. metal halides) and sealed by high temperature treatment, affording closed-ended CNTs with the filling material confined in the inner cavity. The external functionalization of these filled CNTs was then achieved by nitrene cycloaddition and followed by the derivatization with a monoclonal antibody (Cetuximab) targeting the epidermal growth factor receptor (EGFR), overexpressed by several cancer cells. The targeting efficiency of the so-obtained conjugate was evaluated by immunostaining with a secondary antibody and by incubation of the CNTs with EGFR positive cells (U87-EGFR+), followed by flow cytometry, confocal microscopy or elemental analyses. We demonstrated that our filled and functionalized CNTs can internalize more efficiently in EGFR positive cancer cells.

The interaction of carbon nanotubes with an in vitro blood-brain barrier model and mouse brain in vivo.

Carbon nanotubes (CNTs) are a novel nanocarriers with interesting physical and chemical properties. Here we investigate the ability of amino-functionalized multi-walled carbon nanotubes (MWNTs-NH3(+)) to cross the Blood-Brain Barrier (BBB) in vitro using a co-culture BBB model comprising primary porcine brain endothelial cells (PBEC) and primary rat astrocytes, and in vivo following a systemic administration of radiolabelled f-MWNTs. Transmission Electron microscopy (TEM) confirmed that MWNTs-NH3(+) crossed the PBEC monolayer via energy-dependent transcytosis. MWNTs-NH3(+) were observed within endocytic vesicles and multi-vesicular bodies after 4 and 24 h. A complete crossing of the in vitro BBB model was observed after 48 h, which was further confirmed by the presence of MWNTs-NH3(+) within the astrocytes. MWNT-NH3(+) that crossed the PBEC layer was quantitatively assessed using radioactive tracers. A maximum transport of 13.0 ± 1.1% after 72 h was achieved using the co-culture model. f-MWNT exhibited significant brain uptake (1.1  ±  0.3% injected dose/g) at 5 min after intravenous injection in mice, after whole body perfusion with heparinized saline. Capillary depletion confirmed presence of f-MWNT in both brain capillaries and parenchyma fractions. These results could pave the way for use of CNTs as nanocarriers for delivery of drugs and biologics to the brain, after systemic administration.

Revealing correlation of valence state with nanoporous structure in cobalt catalyst nanoparticles by in situ environmental TEM.

Simultaneously probing the electronic structure and morphology of materials at the nanometer or atomic scale while a chemical reaction proceeds is significant for understanding the underlying reaction mechanisms and optimizing a materials design. This is especially important in the study of nanoparticle catalysts, yet such experiments have rarely been achieved. Utilizing an environmental transmission electron microscope equipped with a differentially pumped gas cell, we are able to conduct nanoscopic imaging and electron energy loss spectroscopy in situ for cobalt catalysts under reaction conditions. Studies reveal quantitative correlation of the cobalt valence states with the particles' nanoporous structures. The in situ experiments were performed on nanoporous cobalt particles coated with silica, while a 15 mTorr hydrogen environment was maintained at various temperatures (300-600 °C). When the nanoporous particles were reduced, the valence state changed from cobalt oxide to metallic cobalt and concurrent structural coarsening was observed. In situ mapping of the valence state and the corresponding nanoporous structures allows quantitative analysis necessary for understanding and improving the mass activity and lifetime of cobalt-based catalysts, for example, for Fischer-Tropsch synthesis that converts carbon monoxide and hydrogen into fuels, and uncovering the catalyst optimization mechanisms.