Synthesis and characterization of high surface area nanosilica from rice husk ash by surfactant-free sol–gel method

A nanosilica powder was obtained by thermal treatment of rice husk ash using the sol–gel method without adding any extra surfactant, and was characterized by several techniques. Fourier transform infrared measurements revealed the similarity of the absorption curves of both standard nanosilica and synthesized nanosilica. From the nitrogen adsorption–desorption analysis followed that the nanosilica showed very high surface area of 653 m²/g, total pore volume of 0.64647 mL/g, and narrow pore radius of about 1.98 nm. Scanning electron microscopy of the nanosilica sample dried at 120 °C showed separated particles, while the particles of the sample sintered at 700 °C were aggregated. The analysis of transmission electron microscopy (TEM) micrographs and showed that about 69 % of particles had their sizes in the range of 20–25 nm. X-ray diffraction measurements showed the amorphous nature of the synthesized silica. Applying the Debye–Scherrer formula provided the value of the mean crystallite size around 26 nm which agreed with the one determined from TEM. The purity of the prepared nanosilica was higher than 95 % silica which was confirmed by means of energy dispersive X-ray analysis.     

Design and synthesis of D-π-A fluorescent dyes based on nicotinonitrile and azobenzene derivatives

Study the synthesis and fluorescent properties of a new series of D-π-A fluorescent dyes based on nicotinonitrile and azobenzene is the main objective for this work. Reduction with Zn/HCl, diazotization with HCl/NaNO₂, and coupling using catalytic NaOH or AcONa are simple applied methods. Where, nicotinonitrile 3 was synthesized via reduction of nitro derivative 1 followed by diazotization with HCl/NaNO₂ in acetic acid. The formed benzene diazonium chloride was coupled with several activated phenols, aniline, and α-CH acids to yield the respective azo dyes 4-11 in moderate to good yield. Dyes 11a-d subjected to intermolecular cyclization with hydrazine hydrate resulted in pyrazole dyes 12-15 in moderate yield. Dyes containing pyrazole moiety or electron-withdrawing groups at the sixth position of pyridine nucleus exhibit stronger blue-green emission (λ_fl.max = 503, 507, 500, 501, 502, 493, and 514 nm) than that of the rest of compounds.     

Improving the Thermal Behavior and Flame-Retardant Properties of Poly(o-anisidine)/MMT Nanocomposites Incorporated with Poly(o-anisidine) and Clay Nanofiller

The synthesis of MMT and poly(o-anisidine) (MMT/POA) clay nanocomposites was carried out by using the chemical oxidative polymerization of POA and MMT clay with POA, respectively. By maintaining the constant concentration of POA, different percentage loads of MMT clay were used to determine the effect of MMT clay on the properties of POA. The interaction between POA and MMT clay was investigated by FTIR spectroscopy, and, to reveal the complete compactness and homogeneous distribution of MMT clay in POA, were assessed by using scanning-electron-microscope (SEM) analysis. The UV–visible spectrum was studied for the optical and absorbance properties of MMT/POA ceramic nanocomposites. Furthermore, the horizontal burning test (HBT) demonstrated that clay nanofillers inhibit POA combustion.     

Synthesis and Biological Activity of Pyrazolo(3,4-D)-8-Amino-1-Azaquinoxaline Dimethine Cyanine Dyes

New asymmetrical dimethine cyanines (V_a–f) and their bases (VI_a,b), incorporating pyrazolo(3,4-d)-8-amino-1-azaquinoxaline moiety or its ethiodide, have been prepared and tested for their antibacterial and fungicidal activities.