Synthesis of titanium dioxide by ultrasound assisted sol–gel technique: Effect of amplitude (power density) variation

Titanium dioxide was successfully synthesized by utilizing sol–gel technique modified by incorporation of ultrasound as a reaction aid. The effect of amplitude of irradiation (power input varied from 19.9 to 80.8 W) on % Rutile, % yield, % crystallinity, crystallite size and morphological (scanning electron microscopy) properties of the obtained nano-TiO₂ was studied. Calcination temperatures of all the samples were kept constant at 750 °C. With increasing ultrasonic irradiation amplitude it is observed that the values of % Rutile (after calcination) increased and reached a peak value after which further increase in amplitude resulted in a decrease in the % Rutile. A similar trend was observed in the case of % crystallinity and % yield of the reaction. On the basis of these results an optimum operating ultrasonic irradiation amplitude for the reaction has been suitably established.     

Synthesis of chalcone (3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one): advantage of sonochemical method over conventional method

In this work, an attempt was made to synthesize chalcone (3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one) by condensation of 4-fluorobenzaldehyde with 1-(4-methoxyphenyl)ethanone under basic conditions by using both conventional (NUS) and sonochemical (US) methods. A simple condensation reaction of 4-fluorobenzaldehyde and 1-(4-methoxyphenyl)ethanone using potassium hydroxide as a base was carried out for the study. The synthesized chalcone derivative was characterized for FTIR, NMR, elemental analyses and studied for XRD, PSM, TGA and SEM properties to evaluate its performance obtained under ultrasonic energy. It was observed that complete conversion to chalcone occurred in 10 min by sonochemical method and in 4h by conventional method. Also it was found that crystallinity of the US synthesized chalcone was found to be increased by 63% than that of NUS synthesized chalcone. Finally, it has been observed that chalcone synthesis using sonochemical method is an energy efficient technique over conventional method (almost 90% of energy saving).     

Electronic structure, molecular electrostatic potentials, vibrational spectra in substituted calix[n]arenes (n = 4, 5) from density functional theory

Electronic structure, molecular electrostatic potential, and vibrational frequencies of para-substituted calix[n]arene CX[n]-R (n = 4, 5; R = H, NH(2), t-Bu, CH(2)Cl, SO(3)H, NO(2)) and their thia analogs (S-CX[n]-R; with R = H and t-Bu) in which sulfur bridges two aromatic rings of CX[n] have been derived from the density functional theory. A rotation around CH(2) groups connecting the phenol rings engenders four, namely, cone, partial cone, 1,2-alternate, and 1,3-alternate CX[n]-R conformers. Of these, the cone conformer comprising of large number of O1-H1···O1' interactions turns out to be of lowest energy. Normal vibration analysis reveal the O1-H1 stretching frequency of unsubstituted CX[n] shifts to higher wavenumber (blue shift) on substitution of electron-withdrawing (NO(2) or SO(3)H) groups, while electron-donating substituents (NH(2), t-Bu) engender a shift of O1-H1 vibration in the opposite direction (red shift). The direction of frequency shifts have been analyzed using natural bond orbital analysis and molecular electrostatic potential (MESP) topography. Furthermore, calculated (1)H NMR chemical shift (δ(H)) in modified CX[n] hosts follow the order: H1 > H3/H5 > H7(a) > H7(b). The δ(H) values in CX[4] are in consonant with the observed (1)H NMR spectra.     

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

Ultrasound and deep eutectic solvent (DES): A novel blend of techniques for rapid and energy efficient synthesis of oxazoles

The present work deals with the synthesis of novel oxazole compounds by using effective combination of ultrasound (US) and deep eutectic solvent (DES). The reaction was also conducted by thermal method (NUS) and the comparative studies are provided. It was observed that applying ultrasound not only improved yields and reduced reaction times but also saved more than 85% energy as shown by energy consumption calculations. The advantages of using DES as reaction medium is highlighted from the fact that it is bio-degradable, non-toxic, recyclable and could be easily prepared using inexpensive raw materials. The recyclability for DES was studied wherein it was found that ultrasound has no negative effects on DES even up to four runs. In addition, the present work is the first report on the combinative use of DES and US in organic synthesis.     

Comparative material study and synthesis of 4-(4-nitrophenyl)oxazol-2-amine via sonochemical and thermal method

The present paper deals with the synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as medium. It was observed that ultrasound-assisted method gave 90% yield in just 8 min as against 3.5 h required to get 69% yield by thermal method. One of the compounds 4-(4-nitrophenyl)-1,3-oxazol-2-amine synthesized by both methods were subjected to material characterization study via XRD, TGA and SEM analysis. It was observed that use of ultrasound not only increased the rate of reaction but also improved the quality of product obtained. The crystallinity of the product from ultrasound method was 21.12% whereas thermal method fetched only 8.33% crystallinity thereby improving crystallinity by almost 60%. In addition, sonochemical synthesis also saved more than 70% energy as depicted by energy calculations.     

Cavitation milling of natural cellulose to nanofibrils

Cavitation holds the promise of a new and exciting approach to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure. The collapse process occurs supersonically and generates a host of physical and chemical effects. We have made an attempt to fabricate natural cellulose material using hydrodynamic as well as acoustic cavitation. The cellulose material having initial size of 63 micron was used for the experiments. 1% (w/v) slurry of cellulose sample was circulated through the hydrodynamic cavitation device or devices (orifice) for 6 h. The average velocity of the fluid through the device was 10.81 m/s while average pressure applied was 7.8 kg/cm². Cavitation number was found to be 2.61. The average particle size obtained after treatment was 1.36 micron. This hydrodynamically processed sample was sonicated for 1 h 50 min. The average size of ultrasonically processed particles was found to be 301 nm. Further, the cellulose particles were characterized with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to see the effect of cavitation on crystallinity (X_c) as well as on melting temperature (T_m). Cellulose structures consist of amorphous as well as crystalline regions. The initial raw sample was 86.56% crystalline but due to the effect of cavitation, the crystallinity reduced to 37.76%. Also the melting temperature (T_m) was found to be reduced from 101.78 °C of the original to 60.13 °C of the processed sample. SEM images for the cellulose (processed and unprocessed) shows the status and fiber–fiber alignment and its orientation with each other. Finally cavitation has proved to be very efficient tool for reduction in size from millimeter to nano scale for highly crystalline materials.     

Interfacing High-Energy Charge-Transfer States to a Near-IR Sensitizer for Efficient Electron Transfer upon Near-IR Irradiation

Push–pull systems comprising of triphenylamine–tetracyanobutadiene (TPA-TCBD), a high-energy charge-transfer species, are linked to a near-IR sensitizer, azaBODIPY, for promoting excited-state CS. These systems revealed panchromatic absorption owing to intramolecular CT and near-IR absorbing azaBODIPY. Using electrochemical and computational studies, energy levels were established to visualize excited state events. Fs-TA studies were performed to monitor excited state CT events. From target analysis, the effect of solvent polarity, number of linked CT entities, and excitation wavelength dependence in governing the lifetime of CS states was established. Electron exchange between two TPA-TCBD entities in 3 seem to prolong lifetime of the CS state. We have been successful in demonstrating efficient CS upon both high-energy CT and low-energy near-IR excitations, signifying importance of these push–pull systems for optoelectronic applications operating in the wide optical window.