Fryad Z. Henari

The study focuses on the rapid green synthesis of silver nanoparticles (AgNPs) and alginate-silver nanocomposite (Alg-AgNc) beads using sweet basil or Mashmoom (Ocimum basilicum), a common household medicinal herb in Bahrain. The aqueous extract of mashmoom was used as a reducing and stabilizing agent in the reduction of the precursor salt, silver nitrate, and formation of stable AgNPs. The Alg-AgNc beads were prepared by ionotropic gelation of sodium alginate-AgNPs solution in calcium chloride. A strong surface plasmon resonance (SPR) peak at 380 nm confirmed the formation of AgNPs. The size, morphology, and crystallinity of the nanoparticles were determined using transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). The nanoparticles were spherical and ranged in size from 32 to 45 nm. The bandgap of the nanoparticles was calculated using the Tauc equation and was found to be 2.79-2.86 eV. The AgNPs in the Alg-AgNc beads existed as randomly distributed nanoclusters in the size range of 500-900 nm. The amount of AgNPs present in the beads was 3.9 wt.% as determined by energy dispersive X-Ray spectroscopy (EDS). The nanocomposite beads proved highly effective in the catalytic degradation of the organic dye, methylene blue, achieving a maximum degradation of 92%. The rate of degradation followed pseudo-first-order reaction kinetics with two rate constants of 0.0063 min-1 and 0.033 min-1, reflecting surface adsorption followed by rapid degradation. The nanocomposite beads exhibited dose-dependent antibacterial activity against Escherichia coli.

In this work, stable and spherical silver nanoparticles (AgNPs) were synthesized in situ from silver salt (silver nitrate) using the aqueous extract of the okra plant (Abelmoschus esculentus) at room temperature and ambient pH conditions. The influences of different parts of the plant (such as the leaves, stems, and pods) on the chemical-reducing effectiveness of silver nitrate to silver nanoparticles were investigated. The aqueous extract of the leaves was found to be more effective in the chemical reduction of silver nanoparticles and in stabilizing them at the same time. The silver nanoparticles produced were stable and did not precipitate even after storage for 1 month. The extract of the stem was less effective in the reduction capacity followed by the extract of the pods. The results indicate that the different amounts of phytochemicals present in the leaves, stems, and pods of the okra plant are responsible for the chemical reduction and stabilizing effect. The silver nanoparticles were characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The surface plasmon resonance (SPR) peak at 460 nm confirmed the formation of silver nanoparticles. The nanoparticles were spherical with an average size of 16 nm and polycrystalline with face-centered cubic (fcc) structures. The z-scan technique was used to study the nonlinear refraction and absorption coefficients of AgNPs at wavelengths of 488 and 514 nm under C.W. mode excitation. The nonlinear refraction index and nonlinear absorption coefficients were calculated in the theoretical equations in the experimental data. The antibacterial properties of the nanoparticles were evaluated against Gram-positive and Gram-negative bacteria.

Iron oxide nanoparticles (α- Fe₂O₃) were synthesized using an unconventional, eco-friendly technique utilizing a Hibiscus rosa sinensis flower (common name, China rose) extract as a reducer and stabilizer agent. The microwave method was successfully used for the synthesis of iron oxide nanoparticles. Various volume ratios of iron chloride tetrahydrate to the extract were taken and heated by the microwave oven for different periods to optimize iron oxide nanoparticle production. The synthesized iron oxide nanoparticles were characterized using the ultraviolet-visible spectrometer (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray diffraction (XRD). X-ray diffraction confirmed the formation of α- Fe₂O₃ nanoparticles (hematite). The average size of iron oxide nanoparticles was found to be 51nm. The antibacterial activity of the synthesized iron nanoparticles was investigated against different bacteria such as Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia, and Escherichia coli. The results showed that the synthesized iron nanoparticles exhibited an inhabitation effect on all studied bacteria.

This study reports the synthesis of gold nanoparticles (AuNPs) using an unconventional, eco-friendly method that utilizes cinnamon bark extract as a reducing agent and stabilizer. The synthesized AuNPs were characterized using UV–Vis spectroscopy and transmission electron microscopy (TEM). UV–Vis spectrum shows the surface plasmon resonance (SPR) peak around 535 nm. TEM shows the spherical shape of AuNPs and the particle size distribution at around 35 nm. The ability of the synthesized AuNPs as a quencher of eosin Y dye was monitored using a fluorometer. It was found that in the presence of AuNPs, the fluorescence peak of eosin is quenched. The fluorescence of the mixture of eosin and AuNPs is enhanced in the presence of bovine serum albumin (BSA) protein. TEM shows that the average size of the AuNPs is reduced from 35 to 5 nm with the addition of eosin, and the size of AuNPs then increased to 26 nm upon adding BSA to the mixture of ANPs and eosin. These fluorescence fluctuations may be used for trace identification and biosensing.

In the present work, we report the results of thermally induced third-order nonlinear optical (NLO) properties of 2,4,5-trimethoxy-4[Formula: see text]-nitrochalcone (abbreviated as 2,4,5TMNC) investigated by [Formula: see text]-scan technique using continuous wave (CW) Argon ion laser at a wavelength of 488[Formula: see text]nm with adjusted power ranging from 2.5[Formula: see text]mW to 20[Formula: see text]mW. The experiments were performed by varying the concentration of the molecules in solution. The sample demonstrated strong reverse saturable absorption (RSA) and self-defocusing effect (negative nonlinear refractive index). The estimated values of the NLO absorption coefficient ([Formula: see text], nonlinear refraction ([Formula: see text] and absolute nonlinear susceptibility [Formula: see text] are found to be of the order of 10[Formula: see text][Formula: see text]m/W, 10[Formula: see text][Formula: see text]m²/W and 10[Formula: see text][Formula: see text]esu, respectively. The magnitude of the nonlinear absorption coefficient ([Formula: see text] was found to increase with concentration. The linear absorption spectrum of 2,4,5TMNC was measured using UV–Vis–NIR spectrometer. The optical band gap (Eg) value of title chalcone is obtained from the tauc’s plot of ([Formula: see text] versus [Formula: see text]. The optical limiting performance of 2,4,5TMNC is also investigated for device application. In addition to the above, the computation studies are also carried out to attain the ground state molecular geometry which is found in close to experimental results. Time-Dependent- Density Function Theory (TD-DFT) was used to determine the UV–Vis spectrum at B3LYP/6-31G* level of theory and found to be comparable with experimental data. The HOMO–LUMO energy gap was also determined and discussed. The results promote this chalcone derivative as a promising candidate for optical limiting and optical switching applications.

Nanoparticles of gold and silver were prepared by a reduction method and by employing green chemistry principles such as using curcumin as a reducing and a stabilizing agent. The formation of nanoparticles was confirmed by UV-Vis absorption spectra and TEM. Mie theory was used to determine the particle sizes. The nonlinear refraction and absorption properties of the particles were measured using the z-scan technique. A large value of third-order nonlinearities was obtained using the nanoparticles produced.

We report amplified spontaneous emission from the copolymers poly{m-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(3,4-dimethyloxy phenyl) vinylene]} (dimethoxy-PmPV) and poly{m- phenylene-co-[1,5-dioctyloxy-2,6-naphthylene-bis-2(3,4-dimethyl phenyl) vinylene]} (dimethyl-PmPV-ONV) in toluene. The copolymers are related to poly(phenylene vinylene) and have been synthesized via the Horner–Emmons polycondensation reaction. The optical gain determined from the amplified spontaneous emission intensity is dependent on the excited stripe length. Net gains of 3.4 ± 0.2 and 0.3 ± 0.3 cm⁻¹ were measured for dimethoxy-PmPV and dimethyl-PmPV-ONV respectively under nanosecond pulse excitation. The gain for rhodamine 6G was also measured under the same experimental conditions and was used to determine the stimulated emission cross-sections for both polymers; these were found to be σ_se (peak) = 2.3 × 10⁻¹⁸ cm² for dimethoxy-PmPV and σ_se (peak) = 2 × 10⁻²⁰ cm² for dimethyl-PmPV-ONV.

We report on single pass optical gain and lasing measurements on a blue-emitting copolymer, poly(m-phenylene vinylene-co-2,5-dioctyloxy-p-phenylene vinylene) under 0.5 ns pulsed photoexcitation. This soluble copolymer is designed and synthesized for light amplification and lasing applications. Blue photoluminescence is achieved by introduction of the meta linkage of the phenylene rings in the polymer backbone, which reduces the extent of delocalization of π electrons. The large Stokes shift of about 70 nm implies a low reabsorption rate, and leads to easier creation of population inversion and hence to efficient light amplification. A solution of the polymer exhibits amplified spontaneous emission evidenced by spectral narrowing and a superlinear increase of output intensity when it is photoexcited at 337 nm. By means of the variable excitation stripe length method, net gains of 18 and 24 cm⁻¹ are deduced for different pump energies of 71 and 113 μJ, respectively. Moreover, laser emission from the polymer solution is obtained in a simple cavity formed by Fresnel reflections at the cuvette–solution interfaces. A conversion efficiency as high as 27% and a wide tuning range between 470 and 492 nm in solutions are demonstrated.