•Furfural is selectively rearranged to cyclopentanone.•High selectivity is attributed to furfuryl alcohol polymers.•The polymers are formed on catalyst surface by side-reaction.•Modified catalysts ...inhibit cyclopentanone hydrogenation.•Desorption of cyclopentanone is responsible for high selectivity.
The influence of furanic polymers upon the activity and selectivity of Ni, Pd, Pt catalysts in rearrangement of furfural to cyclopentanone, and its consecutive hydrogenation to cyclopentanol in an aqueous phase has been studied. The coverage of surface of heterogeneous catalyst by the furanic polymers suppresses or almost completely inhibits hydrogenation of cyclopentanone to cyclopentanol. Furanic polymers are created on catalyst surface by partial polymerization reaction of furfuryl alcohol which is in aqueous medium catalyzed by H+ protons formed by dissociation of water at reaction temperatures. Thermogravimetric and XPS measurements confirmed the presence of polymers on catalyst surface. Owing to the modification of catalyst surface by the polymer bearing furan moieties constituents the dominant reaction product is despite high reaction temperature (175°C) and hydrogen pressure (80bar), cyclopentanone, and not expected more stable cyclopentanol. Very high selectivity of furfural rearrangement to cyclopentanone can be achieved by influencing the balance between the rates of formation of furfuryl alcohol polymers on the catalyst surface and their decomposition.
Smart protective coatings and devices are currently of great interest. In particular, they can absorb or reflect harmful waves of electromagnetic interference (EMI). In this work, novel binary and ...ternary composites with highly amorphous poly(vinyl alcohol) (HAVOH) as a matrix and single-walled carbon nanotubes (SWCNTs) and MXenes as nanofillers were prepared. HAVOH is a recently patented kind of poly(vinyl alcohol) (PVOH) that was modified with diol monomers. MXenes are a new type of inorganic two-dimensional (2D) nanoparticle consisting of carbides, nitrides and carbonitrides. Three series of composites, HAVOH/SWCNTs, HAVOH/MXenes and HAVOH/SWCNTs/MXenes, were prepared using the solvent casting method. Samples were tested with various methods to study their structure, electrical properties, thermal behavior and EMI-shielding properties. HAVOH/3.0 wt.% SWCNTs/3.0 wt.% MXene specimens revealed a shielding effectiveness of 55 dB, which is 122 times better than that of the neat matrix. These results are promising for the fabrication of films with protective effects against EMI.
Tetrafluoroborate salts of diazotized Azure A (AA-N2 +), Neutral Red (NR-N2 +) and Congo Red (CR-N2 +) dyes were prepared and reacted with multiwalled carbon nanotubes (MWCNTs) at room temperature, ...in water without any reducing agent. The as-modified MWCNTs were examined by IRATR, Raman spectroscopy, XPS, TGA, TEM, and cyclic voltammetry. The diazonium band located at ∼2350 cm–1 in the diazotized dye IR spectra vanished after attachment to the nanotubes whereas the Raman D/G peak ratio slightly increased after dye covalent attachment at a high initial diazonium/CNT mass ratio. XPS measurements show the loss of F 1s from the BF4 – anion together with a clear change in the high-resolution C 1s region from the modified nanotubes. Thermogravimetric analyses proved substantial mass loadings of the organic grafts leveling off at 40.5, 34.3, and 50.7 wt % for AA, NR, and CR, respectively. High-resolution TEM pictures confirmed the presence of 1.5–7-nm-thick continuous amorphous layers on the nanotubes assigned to the aryl layers from the dyes. Cyclic voltammetry studies in acetonitrile (ACN) confirmed the grafting of the dyes; the latter retain their electrochemical behavior in the grafted state. The experimental results correlate remarkably well with quantum chemical calculations that indicate high binding energies between the dyes and the CNTs accounting for true covalent bonding (140–185 kJ/mol with the CNT-aryl distance <1.6 nm), though attachment by π stacking also contributes to obtaining stable hybrids. Finally, the pH-responsive character of the robust hybrids was demonstrated by a higher degree of protonation of Neutral Red-grafted CNTs at pH 2 compared to that of the neutral aqueous medium. This work demonstrates that diazotized dyes can be employed for the surface modification of MWCNTs in a very simple and efficient manner in water and at room temperature. The hybrids could be employed for many purposes such as optically pH-responsive materials, biosensors, and optothermal composite actuators to name a few.
NaSICON fast-ionic conductors have been largely considered as a viable solution for the development of energy storage units. Chemical doping is a popular technique to improve their electrochemical ...performance, and the widely accepted criterion is an aliovalent substitution, to increase the cationic density, and/or an isovalent substitution with larger species, to enlarge the bottleneck, as widely speculated for the LATP series. However, this study demonstrates through electrochemical impedance spectroscopy that the ionic conductivity of a Na3Fe2(PO4)3 NaSICON isovalently doped with smaller Al3+ ions to form a Na3AlxFe2-x(PO4)3 NaSICON series can be improved up to 4 times. We resorted to X-ray diffraction and ab initio simulation to show that the NaSICON bottlenecks are enlarged despite the lattice shrinkage and the long-range diffusion path is unlocked for x ≥ 0.5. Moreover, the Al-doping sizeably increases the cohesive energy of the monoclinic lattice, thus stabilizing it. As a result, the cyclic voltammetry and galvanostatic charge-discharge tests of the half-cell battery with Na3AlxFe2-x(PO4)3 as the composite cathode showed better capacity and no decay. We believe that this out-of-the-scheme work will clarify the effects of Al-doping on NaSICON compounds and at the same time contribute to reviving the interest around this highly-sustainable Fe3+-based NaSICON.
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•The isovalent doping is the simplest case to study the aluminum effect on NaSICON.•Contrary to the current view, alumimun doping improves the ionic conductivity.•Despite the shrinkage of the unit-cell, the bottlenecks are enlarged.•Two Al-octahedra per unit-cell are necessary to enlarge a long-range diffusion path.
Persistent microbial contamination of medical implant surfaces is becoming a serious threat to public health. This is principally due to antibiotic-resistant bacterial strains and the formation of ...bacterial biofilms. The development of novel antibacterial materials that will effectively fight both Gram-positive and Gram-negative bacteria and prevent biofilm formation represents a big challenge for researchers in the last few decades. In the present work, we report an antibacterial hydrophobic carbon quantum dots/polyurethane nanocomposite (hCQD-PU), with enhanced antibacterial properties induced by pre-treatment with gamma-irradiation. Hydrophobic quantum dots (hCQDs), which are capable of generating reactive oxygen species (ROS) upon irradiation with low-power blue light (470 nm), have been integrated into the polyurethane (PU) polymer matrix to form a photoactive nanocomposite. To modify its physical and chemical properties and improve its antibacterial efficacy, various doses of gamma irradiation (1, 10, and 200 kGy) in the air environment were applied to the formed nanocomposite. Gamma-irradiation pre-treatment significantly influenced the rise in ROS production, therefore, the prooxidative activity under the blue-light illumination of hCQD-PU was also significantly improved. The best antibacterial activity was demonstrated by the hCQD-PU nanocomposite irradiated with a dose of 200 kGy, with the complete eradication of Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria after 15 min of exposure to the blue lamp.
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•Gamma-irradiation of hydrophobic carbon quantum dots/polyurethane nanocomposites.•Increase of the production of reactive oxygen species after the gamma-irradiation.•Visible-light triggered fast and efficient antibacterial activity.•Low toxicity of gamma-irradiated nanocomposites.•Excellent candidates for various antibacterial surfaces and bio-interfaces.
Industrialization today leads to a significant increase in the environmental pollution, with number of phenols, pesticides, paints, solvents and other organic pollutants with potentially carcinogenic ...effect in natural resources. Investigation of some new semiconductor materials and their photocatalytic properties for removal of pollutants is a challenging work. However, limited usage of photoactive materials still requires the testing of new materials with photoactive properties. The current work introduces the swift and easy approach for synthesis of (metal–free) N–doped carbon quantum dots in water using microwave reactor. Synthesis was performed from glucose water solution by heating in microwave reactor for only 1 min, at low temperature and applied microwave power. The synthesized N–doped carbon quantum dots show remarkable photocatalytic activity for removal of toxic organic dye (Rose Bengal) under visible light irradiation. Almost 93% of the dye degradation is achieved after only 30 min of radiation. The uninspected result, that the pH of the medium has a significant effect on the performance of the synthesized material in the presence of organic dye, indicates that dots show dual behavior. In the neutral and basic conditions, they have the ability to degrade organic dye, whereas, by shifting the medium pH into acidic medium, they form a stable conjugate with Rose Bengal.
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•Exfoliated poly(glycidyl methacrylate)/clay nanocomposites were prepared by free radical photopolymerization.•The bentonite clay was intercalated with mercaptosilane prior to ...photopolymerization.•The clay-silane/polymer nanocomposite served as hybrid nanofiller for epoxy matrix.•Poly(glycidyl methacrylate) permits to disperse clay in- and to couple it to the epoxy matrix through the aminated hardener.•Thermal and mechanical properties of hybrid filler-reinforced epoxy are superior to those of epoxy–pristine clay composites.
Poly(glycidyl methacrylate) (PGMA)/clay nanocomposites were prepared by free radical in situ photopolymerization using intercalated chain transfer agent (3-mercaptopropyl)trimethoxysilane (MPS) in the layers of bentonite (B) clay. The natural bentonite was treated with MPS (at 1–5% v/v) which acts as both intercalant and chain transfer agent. Glycidyl methacrylate (GMA) was photopolymerized in situ in the presence of the silanized bentonite (B-MPS) using 2,2-azobisisobutyronitrile (AIBN). The intercalation ability of MPS and exfoliated nanocomposite structure were evidenced by both X-ray diffraction spectroscopy (XRD) and transmission electron microscopy (TEM). Surface analysis and morphologies of the resultant nanocomposites were also studied. The mass loading of PGMA reached 81wt.% while XPS spectra, particularly the high resolution C1s region, resemble those of pure PGMA. The primary B-MPS/PGMA nanocomposite was then used in the preparation of nanocomposite coatings by mixing it with di-glycidyl ether of bisphenol A (DGEBA) epoxy matrix and 4,4-diaminodiphenyl sulfone (DDS) hardener in order to obtain ternary Epoxy/B-MPS/PGMA. The latter was cured and then was compressed into 5mm thick sheets; it was found to be transparent with mixed intercalated/exfoliated structure. The thermal and mechanical performances of Epoxy/B-MPS/PGMA are by far superior to those of the reference epoxy–pristine bentonite nanocomposite.
Five different polypyrroles (PPys) with four different oxidants, namely, FeCl3, FeCl3·6H2O, Fe2(SO4)3, and (NH4)2S2O8, were prepared by chemical oxidative polymerization and studied during aging. In ...the case of FeCl3, the anionic surfactant dodecylbenzenesulfonic acid (DBSA) was used as a co-dopant to improve the stability. The prepared PPys were aged (>400 days) in ambient air at a temperature of 24 ± 2 °C in our laboratory, where they were not directly exposed to the sun. A clear increase in the oxygen content could be seen on the surface of all the prepared samples. There was no significant difference between PPy prepared using FeCl3 and FeCl3·6H2O as oxidants. The incorporation of the anionic surfactant dodecylbenzenesulfonic acid into the PPy structure did not lead to a longer effective conjugation length but did lead to the superior stability of the prepared PPy in ambient air. PPy prepared with Fe2(SO4)3 and (NH4)2S2O8 showed inferior stability of electrical conductivity among the samples studied. The samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), and elemental analysis (EA), and the chemical changes during aging were confronted with measurements of the electrical conductivity.
Novel elastomer/modified carbon nanotube nanocomposites were prepared by melt mixing ethylene vinyl acetate (EVA) matrix with dye-grafted multiwalled carbon nanotubes (MWCNTs, CNTs in short). The ...latter were prepared by spontaneous reactions of diazotized Azure A (AA-N2+), Neutral Red (NR-N2+) and Congo Red (CR-N2+) dyes with CNTs in water at RT. The dispersion of the dye-modified CNTs was facilitated with cholesteryl 1-pyrenecarboxylate (PyChol) surfactant. The EVA/modified CNT nanocomposites were employed as optothermal actuators. The photo-actuation measurements were performed on the un-stretched as well as the stretched strips of pristine EVA and EVA/CNT-dye nanocomposites using a dynamic mechanical analyzer (DMA) equipped with a red light emitting diode (red LED) at a wavelength of 627 nm illuminated either 10 s or 30 s. The concentration of modified dyes, the use of PyChol surfactant and the applied pre-strain were the parameters investigated in this work.
To sum up, the nanocomposites prepared so far could be regarded as promising optothermal actuators used for touch displays visually impaired people.
•Dye-grafted CNT hybrids were prepared through diazonium chemistry.•The hybrids are remarkable light harvesters.•Elastomer/CNT-Dye nanocomposites respond to light and exhibit optothermal behavior.•Elastomer/CNT-Dye nanocomposite thin films are highly promising optothermal actuators.
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