Attachment of Magnetic Nanoparticles on Carbon Nanotubes and Their Soluble Derivatives

The magnetic modification of carbon nanotubes is described here. Pyrene can be noncovalently attached on the carbon nanotube surface. A carboxylic derivative of pyrene is used as interlinker for the binding of capped magnetic nanoparticles on the carbon nanotubes. The increased organophilic character of the capped nanoparticles induces high solubility in organic media for the modified carbon nanotubes

<i>H</i>‑Shaped Copolymer of Polyethylene and Poly(ethylene oxide) under Severe Confinement: Phase State and Dynamics

The self-assembly and the dynamics of an H-shaped copolymer composed of a polyethylene midblock and four poly­(ethylene oxide) arms (PE-b-4PEO) are investigated in the bulk and under severe confinement into nanometer-spaced LAPONITE clay particles by means of small- and wide-angle X-ray diffraction (SAXS, WAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), rheology, and dielectric spectroscopy (DS). Because of the H-shaped architecture, the PE midblock is topologically frustrated and thus unable to crystallize. The superstructure formation in the bulk is dictated solely by the PEO arms as inferred by the crystallization/melting temperature relative to the PEO homopolymer. Confinement produced remarkable changes in the interlayer distance and PEO crystallinity but left the local segmental dynamics unaltered. To reconcile all structural, thermodynamic, and dynamic effects, a novel morphological picture is proposed with interest in emulsions. Key parameters that stabilize the final morphology are the severe chain confinement with the associated entropy loss and the presence of interactions (hydrophobic/hydrophilic) between the LAPONITE and the PEO/PE blocks

DataSheet1_Effect of Graphite Oxide on the Catalytic Behavior of (S)-Selective Amine Transaminases.PDF

Graphite oxide (GO) has been used for the immobilization of several classes of enzymes, exhibiting very interesting properties as an immobilization matrix. However, the effect the nanomaterial has on the enzyme cannot be predicted. Herein, the effect GO has on the catalytic behavior of several (S)-selective amine transaminases [(S)-ATAs] has been investigated. These enzymes were the focus of this work as they are homodimers with pyridoxal 5′-phosphate in their active site, significantly more complex systems than other enzymes previously studied. Addition of GO (up to 0.1 mg/ml) in the reaction medium leads to activation (up to 50% improved activity) for most enzymes studied, while they maintain their temperature profile (they perform better between 40 and 45°C) and their stability. However, the effect is not universal and there are enzymes that are negatively influenced by the presence of the nanomaterial. More profound is the effect on the (S)-ATA from Chromobacterium violaceum which loses almost 50% of its activity in the presence of 0.1 mg/ml GO, while the stability was significantly decreased, losing its activity after 2 h incubation at 40°C, in the presence of 25 μg/ml GO. This negative effect seems to rise from minor secondary structure alterations; namely, a loss of α-helices and subsequent increase in random coil (∼3% in the presence of 25 μg/ml GO). We hypothesize that the effect the GO has on (S)-ATAs is correlated to the surface chemistry of the enzymes; the less negatively-charged enzymes are deactivated from the interaction with GO. This insight will aid the rationalization of ATA immobilization onto carbon-based nanomaterials.</p

Effective Improvement of Water-Retention in Nanocomposite Membranes Using Novel Organo-Modified Clays as Fillers for High Temperature PEMFCs

Toward an enhanced water-retention of polymer electrolyte membranes at high temperatures, novel organo-modified clays were prepared and tested as fillers for the creation of hybrid Nafion nanocomposites. Two smectite clays (Laponite and montmorillonite), with different structural and physical parameters, were loaded with various cationic organic molecules bearing several hydrophilic functional groups (−NH2, −OH, −SO3H) and incorporated in Nafion by solution intercalation. The resulted hybrid membranes were characterized by a combination of powder X-ray diffraction, FTIR spectroscopy, and thermal analysis (DTA/TGA) showing that highly homogeneous exfoliated nanocomposites were created where the individual organoclay layers are uniformly dispersed in the continuous polymeric matrix. In this paper, water-transport properties were investigated by NMR spectroscopy, including pulsed-field-gradient spin–echo diffusion and spectral measurements conducted under variable temperature. Organo-montmorillonite nanofillers demonstrate a considerable effect on the Nafion polymer in terms both of water absorption/retention and water mobility with a remarkable behavior in the region of high temperatures (100–130 °C), denoting that the surface modifications of this clay with acid organic molecules significantly improve the performance of the final composite membrane. 1H NMR spectral analysis allowed a general description of the water distribution in the system and an estimation of the number of water molecules involved in the hydration shell of the sulfonic groups as well as that absorbed on the organoclay particles

Nanocomposites of Polystyrene‑<i>b</i>‑Poly(isoprene)‑<i>b</i>‑Polystyrene Triblock Copolymer with Clay–Carbon Nanotube Hybrid Nanoadditives

Polystyrene-<i>b</i>-polyisoprene-<i>b</i>-polystyrene (PS-<i>b</i>-PI-<i>b</i>-PS), a widely used linear triblock copolymer of the glassy-rubbery-glassy type, was prepared in this study by anionic polymerization and was further used for the development of novel polymer nanocomposite materials. Hybrid nanoadditives were prepared by the catalytic chemical vapor deposition (CCVD) method through which carbon nanotubes were grown on the surface of smectite clay nanolayers. Side-wall chemical organo-functionalization of the nanotubes was performed in order to enhance the chemical compatibilization of the clay–CNT hybrid nanoadditives with the hydrophobic triblock copolymer. The hybrid clay–CNT nanoadditives were incorporated in the copolymer matrix by a simple solution-precipitation method at two nanoadditive to polymer loadings (one low, i.e., 1 wt %, and one high, i.e., 5 wt %). The resulting nanocomposites were characterized by a combination of techniques and compared with more classical nanocomposites prepared using organo-modified clays as nanoadditives. FT-IR and Raman spectroscopies verified the presence of the hybrid nanoadditives in the final nanocomposites, while X-ray diffraction and transmission electron microscopy proved the formation of fully exfoliated structures. Viscometry measurements were further used to show the successful incorporation and homogeneous dispersion of the hybrid nanoadditives in the polymer mass. The so prepared nanocomposites exhibited enhanced mechanical properties compared to the pristine polymer and the nanocomposites prepared by conventional organo-clays. Both tensile stress and strain at break were improved probably due to better interfacial adhesion of the clay–CNT hybrid of the flexible rubbery PI middle blocks of the triblock copolymer matrix

Incorporation of Fullerene Derivatives into Smectite Clays: A New Family of Organic−Inorganic Nanocomposites

Three fulleropyrrolidine derivatives, characterized by the presence of positive charges, were introduced in the interlayer space of montmorillonite. The composites were characterized by powder X-ray diffraction and differential thermal and thermogravimetric (DTA−TGA) analysis, in conjunction with FTIR, UV−Vis, Raman, and 57Fe-Mössbauer spectroscopies. Organophilic derivatives were intercalated into organically modified clays, while water-soluble fulleropyrrolidines were introduced into the clay galleries through ion exchange. The experiments, complemented by computer simulations, show that not all the clay−clay platelets are intercalated by the fullerene derivatives and that a sizable amount of charge transfer takes place between the host and the guests

Water-Triggered Conduction Mediated by Proton Exchange in a Hygroscopic Fulleride and Its Hydrate

Impedance spectroscopy is employed to probe the impact of water on the dc conductivity and ac dielectric response of the polycrystalline C₆₀(ONa)₂₄ fulleride, both in its bulk-hydrate form, stable only below 370 K, and in the pure form, obtained by heating to high temperature. Exposure of the pure material to ambient air results in the condensation of water vapor on the crystallites’ surface, which in turn leads to an enhancement of the room-temperature conductivity by 4 orders of magnitude due to charge transport through the hydration layer. Electrical conduction in the hydrate between 320 and 380 K is dominated by a nonequilibrium contribution associated with the structural water, which leads to a value of the dc conductivity that is higher than that of the pure material by almost two decades at 360 K. Both conductivity enhancements are most likely due to a proton exchange mechanism. All impedance spectra exhibit, in the radiofrequency range, a dielectric loss feature related to accumulation of free charges at grain boundaries, whose strength is strongly affected by the presence of hydration water

Nanocomposite Catalysts Producing Durable, Super-Black Carbon Nanotube Systems: Applications in Solar Thermal Harvesting

A novel two-step approach for preparing carbon nanotube (CNT) systems, exhibiting an extraordinary combination of functional properties, is presented. It is based upon nanocomposite films consisting of metal (Me = Ni, Fe, Mo, Sn) nanoparticles embedded into diamond-like carbon (DLC). The main concept behind this approach is that DLC inhibits the growth of Me, resulting in the formation of small nanospheres instead of layers or extended grains. In the second step, DLC:Me substrates were used as catalyst templates for the growth of CNTs by the thermal chemical vapor deposition (T-CVD) process. X-ray photoelectron spectroscopy (XPS) has shown that at the T-CVD temperature of 700 °C DLC is completely graphitized and NiC is formed, making DLC:Ni a very effective catalyst for CNT growth. The catalyst layers and the CNT systems have been characterized with a wide range of analytical techniques such as Auger electron spectroscopy and X-ray photoelectron spectroscopy (AES/XPS), X-ray diffraction, reflectivity and scattering, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and optical and electrical testing. The produced CNTs are of excellent quality, without needing any further purification, durable, firmly attached to the substrate, and of varying morphology depending on the density of catalyst nanoparticles. The produced CNTs exhibit exceptional properties, such as super-hydrophobic surfaces (contact angle up to 165°) and exceptionally low optical reflection (reflectivity <10^–4) in the entirety of the visible range. The combination of the functional properties makes these CNT systems promising candidates for solar thermal harvesting, as it is demonstrated by solar simulation experiments

Antibacterial and Algicidal Effects of Porous Carbon Cuboid Nanoparticles

Here, we have studied the antibacterial effects of a newly synthesized carbon structure with excellent properties, named porous carbon cuboid (PCC) nanoparticles, upon Gram-negative Escherichia coli and Gram-positive Corynebacterium glutamicum bacterial cells and its algicidal effects upon Chlamydomonas reinhardtii microalgal cells. More specifically, the antibacterial properties of PCCs enriched with acid treatment (PCC-ox) or metal encapsulation (PCC-Cu and PCC-Ag) were investigated under various concentrations of PCCs and their interaction times. Additionally, the impact of PCCs upon microalgal growth was estimated by measuring the total chlorophyll level during their cultivation. As a result, E. coli and C. glutamicum were shown to be substantially inhibited by PCCs, depending on their special characteristics, dose, and bacterial strain. Moreover, it has been proven that the antibacterial effect is time-dependent. Growth of C. reinhardtii was inhibited by PCCs in a material-dependent manner, whereas PCC-Ag had the highest registered effect. These results suggest that PCCs could be used as an effective antibacterial material, although consideration should be given to issues involving the disposal of PCCs after usage, given their level of toxic effect on the environment

Effect of [Fe(CN)₆]^4– Substitutions on the Spin-Flop Transition of a Layered Nickel Phyllosilicate

A 3 to 1 Ni/Si antiferromagnetic layered phyllosilicate, Ni₃Si­(C₃H₆NH₃)­F_0.65O_1.9(OH)_4.45(CH₃COO)_1.1·<i>x</i>H₂O, was modified with K₄[Fe­(CN)₆]·3H₂O. This compound retained its ordering as proved by X-ray diffraction, while infrared spectra revealed the presence of [Fe­(CN)₆]^4– groups and X-ray photoelectron spectroscopy showed that the latter partially substitute the acetate groups. Both the parent and the modified compound are canted antiferromagnets with an anisotropy perpendicular to the layers and show spin-flop transitions. For the parent compound, a single step spin-flop occurs at <i>H</i> = 24 kOe. The modified compound shows increased antiferromagnetic canting and a two-step transition (<i>H</i>₁ = 24 kOe, <i>H</i>₂ = 48 kOe). These results testify to the existence of competing interactions that depend sensitively on the grafted species