The thermal degradation of Nomex poly(m-phenylene isophthalamide) impregnated with phosphoric acid has been investigated by the analysis of the corresponding pyrolysis products, which were ...fractionated into gases, liquids, and char. Gas chromatography (GC) and/or gas chromatography/mass spectrometry (GC/MS) were used to study the volatiles evolved whereas the solid residue was examined by elemental analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). For the sake of comparison, a parallel study of unimpregnated Nomex was carried out in the same conditions. The main product of unimpregnated Nomex degradation in the conditions of this work was found to be m-benzenediamine, which is the result of a heterolytic process. Aromatic nitriles are also produced through homolytic reactions. Most of the products of impregnated Nomex degradation were also detected with its unimpregnated counterpart, except for isophthalic acid, carbon monoxide, and elemental phosphorus. Aromatic nitriles are the pre-eminent products from pyrolysis of unimpregnated Nomex, there being no trace of m-benzenediamine. Reaction mechanisms for impregnated Nomex degradation consistent with these findings are proposed, including a nonhomolytic process for the formation of nitriles in the presence of phosphoric acid.
The development of porosity upon pyrolysis of Nomex poly (m-phenylene isophthalamide) fibres has been investigated up to a temperature of 1173 K through physical adsorption of N2 (77 K) and CO2 (273 ...K). The carbonisation temperatures were chosen on the basis of thermal analysis studies (TG and DTA). The results of porous texture characterisation were compared with characteristic features in the TG and DTA curves. A temperature of 1073 K was chosen as appropriate for pyrolysis regarding activated carbon fibres preparation.
To overcome the challenges of Na-O2 batteries with respect to efficiency, capacity, and cycle life as well as to develop cheap, metal-free, and abundant electrocatalysts, we explored boron and ...nitrogen-functionalized graphene aerogels prepared by the hydrothermal self-assembly of graphene oxide with subsequent thermal reduction. The results showed an improve of both the cycling overpotential and the coulombic efficiency for the functionalized graphene aerogels. However, the nitrogen-containing cathode presented a shortened cycle life and decreased charging stability. The postmortem analysis of the full discharge, and the full discharge and charge cathodes demonstrated that nitrogen functionalization triggered the formation of solid parasitic products that passivate the cathode surface, thus resulting in a poorer electrochemical performance. By contrast, functionalization with boron-containing groups demonstrated to be a more promising strategy due to minimized parasitic products, leading to lower oxygen reduction and evolution overpotentials with a concomitantly enhanced cell efficiency vs. the undoped cathodes. This resulted in a cycle life of 70 cycles at a relatively high current density of 0.1 mA cm−2 with a capacity cut-off of 0.5 mAh cm−2. Our study underscores that functionalization with heteroatoms simultaneously alters multiple characteristics of graphene-based materials, including their chemistry, texture and morphology, which in turn presents a critical impact on the electrochemical response of the resultant Na-O2 cells.
In the present work, the textural evolution of a series of activated carbon fibers with increasing burn-off degree, prepared by the pyrolysis and steam activation of Nomex aramid fibers, is followed ...by measurements of physical adsorption of N
2 (77 K) and CO
2 (273 K) and immersion calorimetry into different liquids (dichloromethane, benzene, cyclohexane). The immersion calorimetry results are discussed in depth, paying special attention to the choice of the reference material. The activated carbon fibers studied possess an essentially homogeneous microporous texture, which suggests that these materials may be applied in gas separation, either directly or with additional CVD treatment.
The swelling of a polymer surface has been monitored in real time on the nanometer scale by atomic force microscopy (AFM). After modification by oxygen plasma treatment, poly(p-phenylene ...terephthalamide) (PPTA) displays a characteristic nanostructured surface morphology consisting of high-lying features alternating with topographically depressed areas. Selective swelling of the least cross-linked, depressed areas after the adsorption of ambient water or water from saturated humid atmospheres was observed by tapping mode AFM operated in the attractive interaction regime. The swollen areas could be distinguished from the nonswollen ones by local variations in the sample indentation made by the AFM tip when imaging in the tapping mode repulsive interaction regime. Monitoring the swelling of the plasma-treated polymer surface provided a means to reveal the nanometer-scale heterogeneity that this type of treatment creates on the polymer surface, which is something that would not be possible otherwise. Measurement of AFM tip−sample adhesion forces evidenced rapid water adsorption onto the oxygen plasma-treated surface, supporting the idea of water-induced swelling. This high hydrophilicity was interpreted as arising from the incorporation of polar oxygen functionalities, as demonstrated by X-ray photoelectron spectroscopy (XPS).
Graphene nanosheets in the form of chemically reduced graphene oxide have been prepared in organic media without the need to chemically functionalise the starting graphene oxide nanosheets. The ...preparation procedure is simple and similar to that previously used for the production of stable aqueous dispersions of graphene nanosheets. The resulting organic dispersions are homogeneous, exhibit long-term stability and are made up of graphene sheets a few hundred nanometres large. The ability to prepare graphene dispersions in organic media facilitates their combination with polymers, such as polyacrylonitrile and poly(methyl methacrylate), to yield homogeneous composites.
Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS
and WS
, have recently emerged as nanomaterials with potential use in biomedicine. An attractive means to favor their interaction ...with biological media is the use of proper biomolecules as exfoliating/dispersing agents. Here, MoS
flakes were stabilized with different small functional biomolecules such as adenosine monophosphate (AMP), guanosine monophosphate (GMP) and flavin mononucleotide (FMN) through the strong nucleotide-MoS
interaction of Lewis acid-base type, rather than just on the weak dispersive and hydrophobic forces commonly associated with the use of many surfactants. The impact of the nucleotide-stabilized MoS
flakes on the viability and cell proliferation, on the production of intracellular reactive oxygen species (ROS), and on the preosteoblast differentiation process (early stage) has been also evaluated, as well as the incorporation and intracellular localization of the nanomaterials by MC3T3-E1 and Saos-2 cells. The nucleotide-stabilized MoS
flakes were found to exhibit excellent biocompatibility. Furthermore, their incorporation did not affect the integrity of the cell plasma membrane, which makes them ideal candidates for delivering drug/gene directly into cells. The in vitro cell response of tumor cells to these nanomaterials differs from that of undifferentiated cells, which provides the basis for their potential use in cancer therapy.
Activated carbon fibers (ACFs) prepared from highly ordered polymers, such as aramid fibers, have been proven to possess an outstanding homogeneity in pore size. Taking advantage of this feature, ...microporous carbon molecular sieves for separating gaseous mixtures such as CO2/CH4 and O2/N2 (air separation) have been prepared through chemical vapor deposition (CVD) of benzene on ACFs obtained from Nomex aramid fiber. Two batches of carbon fibers steam-activated to different burnoffs (BOs), namely, 21% and 42%, were subjected to CVD of benzene for different periods of time. The micropore size distribution of the resulting materials was assessed by immersion calorimetry into liquids of different molecular sizes (dichloromethane, benzene, and cyclohexane). Their validity for separating CO2/CH4 and O2/N2 was tested by performing the corresponding kinetics of adsorption experiments. Carbon molecular sieves with good selectivity for these two separations and showing acceptable adsorption capacities were obtained from ACFs activated to the two chosen BOs.
Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS2 and WS2, have recently emerged as nanomaterials with potential use in biomedicine. An attractive means to favor their ...interaction with biological media is the use of proper biomolecules as exfoliating/dispersing agents. Here, MoS2 flakes were stabilized with different small functional biomolecules such as adenosine monophosphate (AMP), guanosine monophosphate (GMP) and flavin mononucleotide (FMN) through the strong nucleotide−MoS2 interaction of Lewis acid-base type, rather than just on the weak dispersive and hydrophobic forces commonly associated with the use of many surfactants. The impact of the nucleotide-stabilized MoS2 flakes on the viability and cell proliferation, on the production of intracellular reactive oxygen species (ROS), and on the preosteoblast differentiation process (early stage) has been also evaluated, as well as the incorporation and intracellular localization of the nanomaterials by MC3T3-E1 and Saos-2 cells. The nucleotide-stabilized MoS2 flakes were found to exhibit excellent biocompatibility. Furthermore, their incorporation did not affect the integrity of the cell plasma membrane, which makes them ideal candidates for delivering drug/gene directly into cells. The in vitro cell response of tumor cells to these nanomaterials differs from that of undifferentiated cells, which provides the basis for their potential use in cancer therapy.
•MoS2 flakes stabilized through the strong nucleotide−MoS2 interaction of Lewis acid-base type.•300 nm nucleotide-stabilized MoS2 flakes were successfully incorporated by cells.•Incorporation higher as the nanomaterial concentration increased for both types of cells.•Cellular incorporation higher as the exposure time increased in tumor cells.•Independent incorporation of exposure time for undifferentiated cells.
Metal-free electrocatalysts for the electrochemical conversion of gases constitute an important asset for a sustainable energy transition. Nucleotides act as redox mediators in the electron transport ...chain to reduce oxygen in cellular respiration. The biomimicry of such an efficient natural mechanism could be utilized to address the challenges associated with electrochemical gas conversion technologies, such as sluggish kinetics and high overpotentials. Multiple descriptors are generally reported to benchmark the activity of electrocatalysts where the turnover frequency (TOF) is claimed to be the most accurate criterion. Here, a library of graphene nanosheets-nucleotide hybrid materials was prepared, and the electrocatalytic performance towards ORR/OER reactions of a graphene-flavin mononucleotide hybrid was evaluated by rotating disc electrode experiments and TOF estimation. The determination of catalyst loading and dispersion is especially relevant when assessing the intrinsic activity of a catalyst and, therefore, the amount of nucleotide electrocatalyst loaded into the graphene support was thoroughly quantified by a combination of characterization techniques. Density functional theory calculations supported the observed experimental trends, both on the adsorption rate of a given nucleotide on graphene and the catalytic activity of a specific hybrid material. This work constitutes an avenue to predict nature-mimicking electrocatalysts for efficient energy storage.
Sustainable metal-free nucleotide/graphene hybrids are prepared as promising electrocatalysts for gas conversion reactions. Non-covalent π-π interactions are facilitated through liquid adsorption and the amount of adsorbed nucleotide in graphene is assessed using various techniques. The trend observed experimentally aligns consistently with the adsorption energies computed through DFT calculations. The riboflavin-containing hybrid shows a better ability to catalyze OER than graphene. Display omitted
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