Zinc oxide nanowires in chemical bath on seeded substrates: Role of hexamine

Ceria-doped alumina sol-gel materials were obtained by two synthesis methods at low temperature; using method A, 2-propanol-diluted cerium precursor was slowly added at the time of the aluminum sol formation in acidic environment; using method B, the cerium salt was mixed with the aluminum alkoxide before sol formation in a basic environment. The supports were characterized by N₂ physisorption, thermogravimetric and thermal differential analyses (TGA and DTA), X-ray diffraction (XRD), ²⁷Al Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR), 2-propanol reactions, and ammonia temperature-programmed desorption (NH₃-TPD). The samples obtained by Method B present similar values in properties such as specific areas, pore volumes, pore size distribution, and acidity compared to those of pure alumina; the alumina structure was not modified, but segregated crystallites of CeO₂ were found in samples calcined at 1000 ^∘C, as observed by XRD. The ceria-containing materials synthesized by method A show a thermal behavior similar to that of alumina, with no appreciable segregation of CeO₂ detected by XRD and modifications in the amounts of tetra, penta, and octa-hedral aluminum coordination as determined by NMR. 2-propanol reactions showed a good correlation with acid density determined by NH₃-TPD. As the percentage of ceria in the material increases, surface area, pore volume, and acidity decrease. These changes can be correlated with an increase of pentacoordinated aluminum content. The results indicate that CeO₂ is well dispersed in the alumina framework when method A is used, but synthesis method B does not have the same effect on the CeO₂incorporation.     

Synthesis,characterization, and mesomorphic investigations of diester-substituted salicylaldimines and their copper (II) complexes

A novel homologous series of N-[4-[4′-n-alkoxy)benzoyloxy-2-hydroxybenzylidene)-4-carbethoxy anilines, H_2n+1C_nOC₆H₄C(O)OC₆H₃(OH)C(H)?NC₆H₄COOC₂H₅ (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes have been synthesized. All these compounds have been characterized by suitable spectroscopic techniques. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The ligands exhibit wide range of enantiotropic smectic A and nematic phases as confirmed by their typical optical texture under polarizing microscope. The square planar copper(II) complexes of the ligands show only an isotropic phase at higher temperature and no mesogenic nature is observed. DFT calculations have been performed using GAUSSIAN-03 program at B3LYP level to obtain the stable electronic structure of the ligand with decyloxy chain length and its copper(II) complex.     

Viability of clathrate hydrates as CO2 capturing agents: a theoretical study

Capture and sequestration of green house gas CO(2) is a major challenge for scientists and identifying right materials for this purpose is a task of outstanding importance. Through reliable computational studies, we have demonstrated that the clathrate cages (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4), and 5(12)6(8)) have a great potential to store CO(2). All the considered clathrates and their CO(2) inclusion complexes are optimized at B3LYP/6-31G(d) level of theory. The impact of DFT-D, M05-2X, and MP2 functionals on interaction energy were tested using various basis sets. Although different functionals and basis sets show variation in absolute IE values, the trend is consistent and does not depend on the level of the calculations. Dispersion was found important for these complexes and DFT-D shows comparable IE values with MP2 functional. The optimum and maximum cage occupancy for all the considered cages were tested on the basis of quantum chemical calculations. The maximum cage occupancy for all five considered cages (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4), and 5(12)6(8)) is one, two, two, two, and seven CO(2) molecules, respectively, and the optimum cage occupancy is one, one, one, two, and five CO(2) molecules, respectively. Thus, 5(12)6(8) cages can host up to 7 CO(2) molecules, resulting in about 32 wt %, which makes them highly promising materials.     

Cellulose Acetate–Poly(N‐isopropylacrylamide)‐Based Functional Surfaces with Temperature‐Triggered Switchable Wettability

Temperature‐triggered switchable nanofibrous membranes are successfully fabricated from a mixture of cellulose acetate (CA) and poly(N‐isopropylacrylamide) (PNIPAM) by employing a single‐step direct electrospinning process. These hybrid CA‐PNIPAM membranes demonstrate the ability to switch between two wetting states viz. superhydrophilic to highly hydrophobic states upon increasing the temperature. At room temperature (23 °C) CA‐PNIPAM nanofibrous membranes exhibit superhydrophilicity, while at elevated temperature (40 °C) the membranes demonstrate hydrophobicity with a static water contact angle greater than 130°. Furthermore, the results here demonstrate that the degree of hydrophobicity of the membranes can be controlled by adjusting the ratio of PNIPAM in the CA‐PNIPAM mixture.

     

Synthesis, characterization and photoluminescence properties of Ce3+-doped ZnO-nanophosphors

The present study involves the synthesis of Ce³⁺ doped ZnO nanophosphors by the zinc nitrate and cerium nitrate co-precipitation method. The synthesized nanophosphors were characterized with respect to their crystal structure, crystal morphology, particle size and photoluminescence (PL) properties using X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive X-ray (EDX), transmission electron microscopy (TEM)/Energy-dispersive X-ray spectroscopy (EDS) and PL-spectroscopy respectively. XRD results revealed that ZnO nanophosphors are single phase and cubic type structures. Further, PL spectra of ZnO:Ce³⁺ nanophosphors showed green emission because of the charge transfer at single occupied oxygen vacancies with ZnO holes and red emission due to the cerium ion transitions. Intensity and fine structure of the Ce³⁺ luminescence and its temperature dependence are strongly influenced by the doping conditions. The formation of ZnO:Ce³⁺ nanophosphors was confirmed by Fourier transform infrared (FTIR) and XRD spectra.     

Flame spray pyrolysis for the one-step fabrication of transition metal oxide films: Recent progress in electrochemical and photoelectrochemical water splitting

Developing large scale deposition techniques to fabricate thin porous films with suitable opto-electro nic properties for water catalysis is a necessity to mitigate climate change and have a sustainable environment.In this review,flame spray pyrolysis(FSP)technique,a rapid and scalable methodology to synthesize nanostructured transitional metal oxide films with designed functionalities,is firstly introduced.Furthermore,applications in electrochemical(EC)and photoelectrochemical(PEC)water splitting for the production of hydrogen fuel is also presented.The high combustion temperature and the aggregation of flame aerosol ensure that the FSP-made films possess high crystallinity,tunable porosity and high surface areas,making this method suitable either as catalysts for EC water splitting or as efficient semiconductor materials for PEC water splitting.Finally,a perspective on the next generation FSP engineered films with potential applications in energy storage and conversion is described.     

Elasticity and photoelasticity relationships for polyethylene terephthalate fiber networks by molecular simulation

We present a framework for the development of elasticity and photoelasticity relationships for polyethylene terephthalate fiber networks, incorporating aspects of the primary molecular structure. Semicrystalline polymeric fiber networks are modeled as sequentially arranged crystalline and amorphous regions. Rotational isomeric states-Monte Carlo simulations of amorphous chains of up to 360 bonds (degree of polymerization, DP=60), confined between and bridging infinite impenetrable crystalline walls, have been characterized by Omega, the probability density of the intercrystal separation h, and Deltabeta, the polarizability anisotropy. ln Omega and Deltabeta have been modeled as functions of h, yielding the chain deformation relationships. The development has been extended to the fiber network to yield the photoelasticity relationships. We execute our framework by fitting to experimental stress-elongation data and employing the single fitted parameter to directly predict the birefringence-elongation behavior, without any further fitting. Incorporating the effect of strain-induced crystallization into the framework makes it physically more meaningful and yields accurate predictions of the birefringence-elongation behavior.     

The redox behaviour of ferrocene derivatives : III. Ferrocenylacyl complexes (η-C5H5) Fe(η-C5H4-COER3 E = C, Si or Ge; R = Me or Ph

The electrochemical behaviour of the ferrocenylacyl derivatives [FcCOER₃] (E = C, Si or Ge; R = Me or Ph) is examined. One-electron oxidations to the substantially stable monocations [FcCOER₃]⁺ occur at potentials significantly higher than that observed with ferrocene, but only minor differences hold within the series, independent of the nature of both E and R. In contrast the EPR spectra of the monocations for E = C show that the unpaired electron resides mainly on the iron, whereas for E = Si or Ge the electron density is essentially localized on the C₅H₄COER₃ fragment.     

Role of hydrogen bonding in the photophysical properties of isomeric tetrapyridylporphyrins in aprotic solvent

Extensive photophysical properties of isomeric tetra-2-pyridylporphyrin (TpyP(2)), tetra-3-pyridylporphyrin (TpyP(3)), and tetra-4-pyridylporphyrin (TpyP(4)) have been studied in the presence of a series of phenols of increasing hydrogen bonding power in dichloromethane solution by employing UV/vis spectroscopy; steady-state, time-resolved fluorescence spectroscopy; and transient absorption spectroscopic techniques. The change of absorption spectra of all three porphyrins as a function of different phenol concentrations established the preference of hydrogen bonded complex formation to the peripheral pyridyl nitrogen rather than the pyrrole nitrogen of the porphyrin macrocycle. The fluorescence behaviors of the porphyrins which were observed upon addition of different phenols point to a marked dependence on the nature of the added phenols. Phenols with an electron withdrawing group do not quench the fluorescence of porphyrins, whereas phenols with an electron donating group quench the singlet porphyrin both in static and dynamic pathways. A remarkable difference in quenching behaviors of singlet excited porphyrin by 4-methylphenol (4-MePhOH) and 4-MeOPhOH/4-EtOPhOH (4-EtOPhOH = 4-ethoxyphenol) are observed. The quenching of singlet excited porphyrins by 4-MePhOH is attributed to be purely static in nature, and the H-bond provides a strong nonradiative channel to singlet excited porphyrins. However, the quenching of singlet excited porphyrins by 4-MeOPhOH/4-EtOPhOH is mostly dynamic, and it is ascribed to be the reductive quenching of single excited porphyrins. Picosecond transient absorption study with TpyP(2) and 4-MeOPhOH provides the evidence of porphyrin radical anion and phenol radical cation of equal lifetime, which indicates the fact that electron transfer occurs from phenol to singlet excited porphyrin. The temperature effect on dynamic quenching by 4-MeOPhOH/4-EtOPhOH and kinetic deuterium isotope effect established the reaction to be a photoinduced concerted proton coupled electron transfer.