Synthesized uniform-different sizes silver nanoparticles using TSC and SBH simultaneously for antibacterial application.

Silver nanoparticles (AgNPs) in the form of nanospheres from a few nm to 100 nm in diameter were synthesized in a controlled manner using a combination of two reducing agents: sodium borohydride (SBH) and trisodium citrate (TSC). The influence of the size of AgNPs on antibacterial activity was investigated with different concentrations of AgNPs on two types of bacteria:Pseudomonas aeruginosa(PA) andStaphylococcus aureusresistant (SA) while the positive control wasAmpicillin (Amp)50µg/ml and the negative control was water. AgNPs were investigated for morphology, size and size distribution using transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. The optical properties of the AgNPs were investigated by recording their UV-vis absorption spectra. The antimicrobial activity of AgNPs was determined using the disc diffusion method. The results showed that the antibacterial ability of AgNPs depends on both concentration and particle size. With a particle concentration of 50µg ml-1, the antibacterial ability is the best. The smaller the particle size, the higher the antibacterial ability. The simultaneous use of two reducing agents TSC and SBH is the novelty of the article to synthesize AgNPs particles that are uniform in shape and size while controlling the particle size. On that basis, their antibacterial performance is increased.

First-principles study of SiC and GeC monolayers with adsorbed non-metal atoms.

Chemical adsorption of non-metal atoms may lead to the emergence of novel features in two-dimensional (2D) materials. In this work, the electronic and magnetic properties of graphene-like XC (X = Si and Ge) monolayers with adsorbed H, O, and F atoms are investigated using spin-polarized first-principles calculations. Deeply negative adsorption energies suggest strong chemical adsorption on XC monolayers. Despite the non-magnetic nature of both host monolayer and adatom, SiC is significantly magnetized by H adsorption inducing the magnetic semiconductor nature. Similar features are observed in GeC monolayers upon adsorbing H and F atoms. In all cases, an integer total magnetic moment of 1 µB is obtained, originating mainly from adatoms and their neighbor X and C atoms. In contrast, O adsorption preserves the non-magnetic nature of SiC and GeC monolayers. However, the electronic band gaps exhibit significant reduction of the order of 26% and 18.84%, respectively. These reductions are consequences of the middle-gap energy branch generated by the unoccupied O-pz state. The results introduce an efficient approach to develop d0 2D magnetic materials to be applied in spintronic devices, as well as to widen the working region of XC monolayers in optoelectronic applications.

The Mosquito Larvicidal Activity of Essential Oils from Cymbopogon and Eucalyptus Species in Vietnam.

The larvicidal activity of essential oils (EOs) extracted from Cymbopogon citratus, Cymbopogon winterianus, Eucalyptus citriodora, and Eucalyptus camaldulensis aromatic plants grown in Vietnam was evaluated on Aedes aegypti larvae. The EOs were hydro-distilled in a Clevenger-type apparatus. The EOs were analyzed by gas chromatography-mass spectrometry (GC-MS). The mortality rates obtained from the bioassays were used to calculate the lethal concentrations (LC50) of the EOs by the probit analysis method. These essential oils exhibited toxicity to the larvae of Aedes aegypti. Results were obtained for Cymbopogon citratus (LC50 = 120.6 ppm), Cymbopogon winterianus (LC50 = 38.8 ppm), Eucalyptus citriodora (LC50 = 104.4 ppm), and Eucalyptus camaldulensis (LC50 = 33.7 ppm). The essential oils of Eucalyptus camaldulensis and Cymbopogon winterianus were found to be the most efficient, and their respective values of LC50 were 33.7 ppm, 38.8 ppm. In conclusion, this research adds to the growing body of literature on natural larvicides from essential oils against Aedes aegypti mosquitoes.

A 3-Step Chemiluminescence Method for Chemical Oxygen Demand Measurement.

Direct chemiluminescence emission from the reaction of acidic permanganate and organic compounds was employed for determining the chemical oxygen demand (COD) in water (1-step CL COD). Due to the diversity of organic pollutants in water, there are no standards for COD measurements, and many compounds do not show any chemiluminescence signal in the 1-step CL COD method. As a result, this method shows a low correlation with the conventional CODMn method. In this study, a new 3-step CL COD method was developed to overcome these drawbacks. The basic principle of the 3-step CL COD method is based on the principle of "back titration" in the CODMn method: (i) the sample is treated with permanganate under heating, (ii) the excess permanganate is treated with pyrogallol, and (iii) the excess pyrogallol is measured by the chemiluminescence reaction with permanganate. The reagent concentration, sample volume, and heating temperature were optimized, and the 3-step CL COD method successfully obtained the signal from some samples that cannot be detected by 1-step CL COD method. The calibration graph is linear in the range of 0 - 12.86 mg/L with a detection limit of 0.082 mg/L. This method is continuous, sensitive and low cost compared with the conventional method, and is applicable for on-site monitoring. The effect of the chloride ion was investigated, and showed an insignificant effect after two-times dilution of high-salinity samples. The correlation with the CODMn method for various organic compounds showed a good coefficient of determination, R2 = 0.9773 (n = 16).