K.H. Mahmoud

Thermal analysis and infrared study of Nb2O5–TeO2glasses

Tellurite glasses of the xNb2O5–(100–x) TeO2, (3 ≤ x ≤ 20 mol%) system have been prepared and studied by IR spectroscopy and differential thermal analysis to explore the role of Nb2O5 on their structure. IR analysis indicates that NbO6 transforms TeO4 units into tellurite structural TeO3 units, with a shift of lattice vibrations towards higher wavenumbers. The stretching force constant of the tellurite structural units increases with Nb2O5 content, a feature that is attributed to the higher bond strength and higher coordination number of Nb2O5 relative to TeO2. The crystallization kinetics has been studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results are analyzed, and both the activation energy of the crystallization process and the crystallization mechanism are characterized. The thermal stability of these glasses are characterized in terms of characteristic temperatures, such as the glass-transition temperature, T g, the temperature of onset of crystallization, T in, the temperature corresponding to the maximum crystallization rate, T p, and two kinetic parameters, K(T g) and K(T p). The results reveal that thermal stability increases with increasing Nb2O5 content. XRD diffraction of the studied glasses indicates the presence of microcrystallites of α-tellurite, γ-telluride, Nb2Te4O13 and an amorphous matrix.

Dielectric characterization and catalytic activity studies of nickel chloride doped carboxymethyl cellulose films.

Cast technique was used to prepare films of sodium carboxymethyl cellulose (CMC) doped with different ratios of NiCl(2)·6H(2)O in the range of 0-40Ni(2+) wt.%. Thermal analysis (DTA) in the range of 25-600°C and dielectric properties in the temperature range of 30-150°C and frequency range of 0.1-100 kHz were measured for the prepared samples. DTA analysis showed new exothermic peaks which were attributed to structural phase transitions. Different molecular motions are separated via dielectric relaxation spectroscopy. In the high temperature range (higher than 100°C), the σ-relaxation, which is associated with the hopping motion of ions through polymer material, was detected. The detailed analysis of the results showed that the dielectric dispersion consists of both dipolar and interfacial polarization. Measurements of ac conductivity as a function of frequency at different temperatures indicated that the correlated barrier hopping model (CBH) is the most suitable mechanism for the ac conduction behavior. The catalytic activity of CMC doped with Ni(2+) was tested in the reduction of the hazardous pollutant 4-nitrophenol to the functional 4-aminophenol with an excess amount of NaBH(4). Ni-free CMC did not exhibit any catalytic activity for the studied reaction. However, Ni(2+)-doped CMC showed a significant catalytic activity that is proportional to the ratio of Ni(2+) included in CMC. The activation energy (E(a)) was estimated in the temperature range of 25-40°C. The estimated value of E(a) decreased with increasing the ratio of Ni(2+). Finally, the optimum catalyst mass was found to be ≈0.6 g/l.

Synthesis, characterization, optical and antimicrobial studies of polyvinyl alcohol-silver nanocomposites.

Silver nanoparticles (Ag NPs) were synthesized by chemical reduction of silver salt (AgNO3) through sodium borohydride. The characteristic surface plasmon resonance band located at around 400nm in the UV-Visible absorption spectrum confirmed the formation of Ag nanoparticles. Polyvinyl alcohol-silver (PVA-Ag) nanocomposite films were prepared by the casting technique. The morphology and interaction of PVA with Ag NPs were examined by transmission electron microscopy and FTIR spectroscopy. Optical studies show that PVA exhibited indirect allowed optical transition with optical energy gap of 4.8eV, which reduced to 4.45eV under addition of Ag NPs. Optical parameters such as refractive index, complex dielectric constant and their dispersions have been analyzed using Wemple and DiDomenco model. Color properties of the nanocomposites are discussed in the framework of CIE L(∗)u(∗)v(∗) color space. The antimicrobial activity of the nanocomposite samples was tested against Gram positive bacteria (Staphylococcus aureus NCTC 7447 &Bacillus subtillis NCIB 3610), Gram negative bacteria (Escherichia coli, NTC10416 &Pseudomonas aeruginosa NCIB 9016) and fungi (Aspergillus niger Ferm - BAM C-21) using the agar diffusion technique. The antimicrobial study showed that PVA has moderate antibacterial activity against B. subtillis and the 0.04wt% Ag NPs composite sample effect was strong against S. aureus.

Synthesis, characterization and optical properties of gelatin doped with silver nanoparticles

In this study, silver nanoparticles were synthesized by chemical reduction of silver salt (AgNO3) solution. Formation of nanoparticles was confirmed by UV-visible spectrometry. The surface plasmon resonance peak is located at 430 nm. Doping of silver nanoparticles (Ag NPs) with gelatin biopolymer was studied. The silver content in the polymer matrix was in the range of 0.4-1 wt%. The formation of nanoparticles disappeared for silver content higher than 1 wt%. The morphology and interaction of gelatin doped with Ag NPs was examined by transmission electron microscopy and FTIR spectroscopy. The content of Ag NPs has a pronounced effect on optical and structural properties of gelatin. Optical parameters such as refractive index, complex dielectric constant were calculated. The dispersion of the refractive index was discussed in terms of the single--oscillator Wemple-DiDomenico model. Color properties of the prepared samples were discussed in the framework of CIE L(*)u(*)v(*) color space.

Optical properties of hydroxyethyl cellulose film treated with nitrogen plasma.

Hydroxyethyl cellulose (HEC) film has been prepared by casting technique. The prepared sample has been treated with nitrogen plasma at different exposure times. The optical absorption was recorded at room temperature in the wavelength range of 200-800 nm. Absorbance fitting procedure curves revealed a direct allowed transition with optical band gap, Eopt, of 4.9 eV for pristine film, and this value decreases to 4.30 eV for 20 min plasma treatment time. The band tail values (Ee) were found to be increased under plasma time treatment from 1.74 eV in case of the pristine film to 2.20 eV for 20 min. The dispersion of refractive index and complex dielectric constants under plasma treatment was also studied. Variation of color parameters under effect of the plasma treatment is analyzed in the framework of CIE L*U*V* color space.

Judd–Ofelt analysis of luminescence spectra of an erbium chloride-doped carboxy methyl cellulose film

Optical absorption and photoluminescence properties of an ErCl3-doped carboxy methyl cellulose film have been studied. From measured intensities of various absorption bands of film, the Judd–Ofelt parameters Ω2, Ω4 and Ω6 have been calculated. The Judd–Ofelt theory has been applied to characterize the photoluminescence spectra of the investigated film. From this theory, various radiative properties, such as transition probability A T, branching ratio β r, radiative life time τ r and emission cross section , for various emission levels have been determined and reported.

Optical properties of polyvinyl alcohol film irradiated with Nd:YAG laser

Casting solution method has been used to prepare Polyvinyl alcohol (PVA) film. The prepared film has been irradiated with a laser beam of 6ns Q-switched Nd:YAG laser (Lotus II) operating at 10Hz and fourth harmonic wavelength, 266nm, at different irradiation times. Optical absorbance of the irradiated sample was studied in the wavelength region between 200 and 800nm. The absorption peak shift of 272nm towards the longer wavelengths region and the increase of absorption as the irradiation time increases, are related to the increase in crosslinking network. The fitting technique of the absorbance revealed an indirect allowed transition with optical energy gap of 4.22eV for the pristine PVA sample, and 2.85eV after 2h of laser irradiation. The index of refraction and the dielectric function showed dispersion in the studied wavelength range. The analysis of color parameters of PVA showed an observable change after laser irradiation.