Efficient synthesis of carbon nanotubes with improved surface area by low-temperature solvothermal route from dichlorobenzene

The synthesis of well-aggregated carbon nanotubes in the form of bundles was achieved by the catalytic reduction of 1,2-dichlorobenzene by a solvothermal approach. The use of 1,2-dichlorobenzene as a carbon source yielded a comparably good percentage of carbon nanotubes in the range of 60–70 %, at a low reaction temperature of 200°C. The products obtained were analysed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques. The X-ray diffraction studies implied the presence of pure, crystalline, and well-ordered carbon nanotubes. The scanning electron and transmission electron microscopic images revealed the surface morphology, dimensions and the bundled form of the tubes. These micrographs showed the presence of multi-walled carbon nanotubes with an outer diameter of 30–55 nm, inner diameter of 15–30 nm, and lengths of several hundreds of nanometers. Brunauer-Emmett-Teller-based N₂ gas adsorption studies were performed to determine the surface area and pore volume of the carbon nanotubes. These carbon nanotubes exhibit a better surface area of 385.30 m² g^?1. In addition, the effects of heating temperature, heating time, amount of catalyst and amount of carbon source on the product yield were investigated.     

Giant gain enhancement in surface‐confined resonant Stimulated Brillouin Scattering

The notion that Stimulated Brillouin Scattering (SBS) is primarily defined by bulk material properties has been overturned by recent work on nanoscale waveguides. It is now understood that boundary forces of radiation pressure and electrostriction appearing in such highly confined waveguides can make a significant contribution to the Brillouin gain. Here, this concept is extended to show that gain enhancement does not require nanoscale or subwavelength features, but generally appears where optical and acoustic fields are simultaneously confined near a free surface or material interface. This situation routinely occurs in whispering gallery resonators (WGRs), making gain enhancements much more accessible than previously thought. To illustrate this concept, the first full‐vectorial analytic model for SBS in WGRs is developed, including optical boundary forces, and the SBS gain in common silica WGR geometries is computationally evaluated. These results predict that gains 10⁴ times greater than the predictions of scalar theory may appear in WGRs even in the 100 μm size range. Further, trapezoidal cross‐section microdisks can exhibit very large SBS gains approaching 10² m⁻¹W⁻¹. With resonant amplification included, extreme gains on the order of 10¹² m⁻¹W⁻¹ may be realized, which is 10⁸ times greater than the highest predicted gains in linear waveguide systems.

     

Phosphonate-Modified UiO-66 Brønsted Acid Catalyst and Its Use in Dehydra-Decyclization of 2-Methyltetrahydrofuran to Pentadienes

Phosphorus-modified all-silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well-defined sites, we report the incorporation of Brønsted acidity to metal–organic frameworks with the UiO-66 topology, achieved by attaching phosphonic acid to the 1,4-benzenedicarboxylate ligand and using it to form UiO-66-PO₃H₂ by post-synthesis modification. Characterization reveals that UiO-66-PO₃H₂ retains stability similar to UiO-66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF). For the later reaction, the reported catalyst exhibits site-time yields and selectivity approaching that of phosphoric acid on all-silica zeolites. Using solid-state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.     

Volumetric Studies of 2,2,2-Cryptand in Aqueous and Aqueous KBr Solutions at 298.15 K: An Example Involving Solvent-Induced Hydrophilic and Hydrophobic Interactions

Density measurements of good precision are reported for aqueous and aqueous salt (KBr) solutions containing 2,2,2-cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) (~0.009 to ~0.24 mol·kg^?1) for the binary systems and for the ternary system with ~0.1 mol·kg^?1 2,2,2-cryptand and varying KBr concentrations (~0.06 to ~ 0.16 mol·kg^?1) at 298.15 K. The density data have been used to study the variation of apparent molar volume (\( \varphi_{V} \)) of 2,2,2-cryptand and of KBr as a function of concentration. 2,2,2-Cryptand is a diamine and hence it is hydrolyzed in aqueous solutions and needs an appropriate methodology to obtain meaningful thermodynamic properties. We have adopted a method of hydrolysis correction developed initially by Cabani et al. and later by Kaulgud et al. to analyze our volumetric data for the aqueous solutions. The method is described and we were successful in obtaining the limiting partial molar volume of the bare (free) cryptand in water at 298.15 K. Volumes of ionization as well as volumes of complexation (with KBr) are calculated. Estimations of the apparent molar volume of 2,2,2-cryptand in CCl₄ are also reported. There is a loss in volume for the cryptand on transferring it from CCl₄ to water. The volume changes due to ionization for the cryptand in water are calculated to be –20.5 and –0.6 cm³·mol^?1 for the mono- and di-protonation equilibria respectively, while the volume of complexation for K⁺ is +24.5 cm³·mol^?1. The results are discussed in terms of conformation, protonation equilibria and selective encapsulation of K⁺ ions in cryptand cavities. The solution volume properties seem to depend upon water–solute interaction as well on the solute–solute association because of hydrophobic interactions caused by lowering of the charge density on formation of cryptand-K⁺ species in solution.     

Tea‐Bag‐Like Polymer Nanoreactors Filled with Gold Nanoparticles

Gold‐containing polymer nanotubes, which showed both catalytic activity and resistance to leaching, were prepared by the “tubes by fiber templates” (TUFT) process. For this purpose, electrospun polymer nonwovens with incorporated poly(L ‐lactide)‐stabilized gold nanoparticles were coated with poly(p‐xylylene) by the chemical vapor deposition process, and then the inner fiber templates were removed. The resulting polymer tubes carried encapsulated gold nanoparticles which were shown to be immobilized and featured pronounced catalytic activity towards the hydrolytic oxidation of dimethylphenylsilane and the alcoholysis of dimethylphenylsilane with n‐butanol. The macroscopic nonwovens could be used as tea‐bag‐like catalyst systems and showed excellent reusability.     

Structural Isomerization of the Gas‐Phase 2‐Norbornyl Cation Revealed with Infrared Spectroscopy and Computational Chemistry

In an attempt to produce the 2‐norbornyl cation (2NB⁺) in the gas phase, protonation of norbornene was accomplished in a pulsed discharge ion source coupled with a supersonic molecular beam. The C₇H₁₁⁺ cation was size‐selected in a time‐of‐flight mass spectrometer and investigated with infrared laser photodissociation spectroscopy using the method of “tagging” with argon. The resulting vibrational spectrum, containing sharp bands in the C? H stretching and fingerprint regions, was compared to that predicted by computational chemistry. However, the measured spectrum did not match that of 2NB⁺, prompting a detailed computational study of other possible isomers of C₇H₁₁⁺. This study finds five isomers more stable than 2NB⁺. The spectrum obtained corresponds to the 1,3‐dimethylcyclopentenyl cation, the global minimum‐energy structure for C₇H₁₁⁺, which is produced through an unanticipated ring‐opening rearrangement path.     

Heine’s method and $$A_{n}$$ A n to $$A_{m}$$ A m transformation formulas

The Ramanujan Journal - We apply Heine’s method—the key idea Heine used in 1846 to derive his famous transformation formula for $$_2\phi _1$$ series—to multiple basic series over...     

Existence of local and global solutions of fractional-order differential equations

We study the existence of local and global mild solutions of the fractional-order differential equations in an arbitrary Banach space by using the semigroup theory and the Schauder fixed-point theorem. We also give some examples to illustrate the applications of abstract results.