Sediment oxygen demand in streams : lab measurements underestimate in situ rates substantially

Global warming is expected to affect stream metabolism significantly; and higher temperatures may lead to higher respiration and thus higher risk of oxygen depletion. It is, therefore, crucial to obtain reliable data on the oxygen dynamics in the different stream compartments. Determination of sediment oxygen demand (SOD) is typically based on lab or field measurement using cores or benthic chamber in which the actual physical conditions in the streams are not possible to mimic perfectly. We compared SOD based on lab core incubations with SOD measured in situ in stream sections where the oxygen exchange between water and air was eliminated artificially. The in situ SOD increased with increasing oxygen concentrations and both the temperature and the oxygen dependency of SOD increased with increasing organic content in the surface sediment. The laboratory rates reached 17 - 83% of the rates obtained in situ. The percentages were especially low at low stream velocity, likely reflecting a pure imitation of the physical conditions near the sediment in the lab when the sediment organic content was high (at low velocity). Therefore, alternative methods, simulating the natural horizontal water flow, are needed to provide reliable information on SOD in streams.

Supercritical hydrothermal synthesis of silver nanoparticles, composites, and their characterizations

Silver nanoparticles (AgNPs) and silver nanoparticles doped activated carbon (AC-Ag) composite materials were synthesized by hydrothermal processes in supercritical water conditions (29 MPa and 400 °C) using batch reactor. We studied the influence of the precursor solution concentration, reaction temperature under the hydrothermal conditions, and synthesis time on the properties of synthesized materials. The properties of plain AgNPs and AC-Ag composite materials synthesized in supercritical water, including crystallinity, particle size, and molecular interactions between AC and Ag were investigated, comprehensively. Compared to the plain AgNPs, the activated carbon-supported Ag nanocomposite was synthesized faster due to the active functional groups of activated carbon. Furthermore, the FTIR results reveal that the silver nanoparticles are attached to the activated carbon surface in the presence of oxygen bonded carbonyl and carboxyl groups. The nano-sized metal silver particles were observed on the AC surface when analyzed by TEM and XRD. All results imply that the supercritical water condition allows the formation of silver particles less than 100 nm either in the form of plain particles or deposited on the activated carbon surface using the silver acetate precursor solution. This environmentally benign supercritical hydrothermal process can replace the conventional method and become a novel synthesis method for preparing various new materials.

Preface - volume 22(48), 2021

No Abstract in English

Electrical and optical properties of dip coated Al-doped ZnO thin films

Undoped and Aluminum doped Zinc Oxide thin films were synthesized by dip coating technique. The electrical properties of the films were studied due to the Aluminum doping, starting solution aging and sample aging. The sheet resistance of ZnO:Al films was minimum at 2.5 at % whereas carrier concentration is maximum. Both undoped and aluminum doped Zinc Oxide thin films were found to be highly transparent lying in between 65 - 79 % in the wavelength range 367 nm to 1038 nm. The band gap of deposited films changed slightly from 3.22 eV to 3.27 eV.

Synthesis of cuprous oxide nanocubes combined with chitosan nanoparticles and its application to p-nitrophenol degradation

For the first time, cuprous oxide nanocubes (Cu2O NCBs) were successfully combined with chitosan nanoparticles (CS NPs) to generate Cu2O NCBs/CS NPs composites material with highly optical property and photocatalytic activity using a simple and eco-friendly synthetic approach at room temperature for 30 min. The synthesized Cu2O NCBs NPs/CS NPs were determined characterizations by Ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), X – ray Diffraction (XRD), Transmission Electron Microscope (TEM) and Energy-dispersive X-ray spectroscopy (EDX). Results show that the Cu2O NCBs/CS NPs composites have an average particle size of ~3-5 nm; in which, Cu2O has the form of nanocubes (Cu2O NCBs) with size ~3-4 nm and chitosan nanoparticles with spherical shape (CS NPs) with size ~4-5 nm. In addition, the percent (%) composition of elements present in Cu2O NCBs/CS NPs composites material have been obtained respective: Cu (23.99%), O (38.18%), and C (33.61%). Moreover, Cu2O NCBs/CS NPs composites material was also investigated for photocatalytic activity applied in p-nitrophenol degradation. The obtained results showed that the catalytic capability of Cu2O NCBs/CS NPs for p-nitrophenol reduction reached the highest efficiency >55% in the treatment time of 25 min, and this efficiency was higher than that result of using ZnO@chitosan nanoparticles (ZnO@CS NPs) catalyst under the same conditions for comparison.

The general characteristics and organic matters of therapeutic mud from Lake Noot (Mongolia)

In this investigation, we examined the chemical composition, physicochemical properties, and organic matter of therapeutic mud from Lake Noot in the Arkhangai province of Mongolia. The therapeutic mud from “Lake Noot” is used in the pelotherapy of local health care services for some time but without deep characterization. Due to this, a study of therapeutic mud samples was required. Our research concentrated on identifying general characteristics, organic matter, mineralogical, and chemical composition of therapeutic mud at two different Lake Noot sites. Results showed that the therapeutic mud belongs to the continental hydrogen sulfide sticky mud type. The total organic matter in the therapeutic mud of Lake Noot was 14.44%. Total organic matter contains a humic substance of 42.17%, lipid 16.62%, and carbohydrate 7.13%. A total of 172 compounds were identified in the dissoluble organic matter of therapeutic mud, mainly of natural origin, using the gas chromatography-mass spectrometry (GC/MS) method. The dominant compounds were saturated and unsaturated hydrocarbons with 13–44 carbon atoms and carboxylic acids and their ethers. Some of the identified organic compounds have been reported antimicrobial, anti-inflammatory, antibacterial, and antifungal properties.

Synthetic fatty acid from crude oil of Tamsagbulag petroleum deposit (Mongolia)

In this work, we studied to obtain synthetic fatty acids raw materials to produce surfactants and various detergents from paraffin. The solid paraffin extracted from the Tamsagbulag petroleum deposit was 46 mass%, distilled 350-450°C, by complexing with urea. Experimental study indicates paraffin's physicochemical characteristics from this petroleum are more suitable to use in the production of synthetic fatty acids. By solid paraffin oxidation, we obtained 33.01% of the synthetic fatty acids containing monocarboxylic acids.We suggest obtaining the synthetic fatty acid by oxidation process in normal condition from petroleum paraffin.

The study on the antioxidant activity of polysaccharides isolated from Polygonatum odoratum (Mill.) Druce

The polysaccharides isolated from Polygonatum odoratum (Mill.) Druce (POPs) by water extraction, after precipitation with ethanol were purified through deproteinization, decolorization, dialysis, and column chromatography leading to a purified polysaccharide (POPs-I) content of 90.7 %. The scavenging of oxygen free radicals and inhibition of lipid peroxidation (LPO) by POPs-I were analyzed using a colorimetric method. The results showed that the hydroxyl radical scavenging ability of the polysaccharides was weaker than that of benzoic acid, but stronger than those of ascorbic acid and mannitol, and that the superoxide anion radical scavenging ability was inferior to those of all three. When the concentration was higher than 1.0 mg/mL, the POPs-I could inhibit LPO by superoxide anion radicals to a certain degree. Therefore, this work suggests that POPs-I are potential antioxidant agents in medicine and functional food.

Preface - vol. 20

No Abstract in English

Phytochemical and antioxidant properties of Diodia sarmentosa swartz leaves

This research studied proximate, phytochemical and antioxidant properties of Diodia sarmentosa leaves. The ethanol and aqueous extracts of the leaves significantly inhibited 2,2-diphenyl-1-picrylhydrazyl (DPPHo) radical formation with IC50 values of 10.994 and 10.121 μg/mL respectively, compared to the ascorbic acid standard (IC50 value = 17.916 μg/mL).The aqueous extract exhibited more inhibitory effect on thiobarbituric acid-reactive species (TBARS) with IC50 values of 2.657 μg/mL while the ethanol extract had an IC50 value of 8.53 μg/mL compared to butylated hydroxytoluene standard (IC50 = 2.142 μg/mL). For the total antioxidant capacity assay, the aqueous extract had higher ascorbic acid equivalent values than the ethanol extract. However, the two solvent extracts showed antioxidant activity. Diodia sarmentosa leaves possess useful phytochemicals which are indicative of its antioxidant properties.