A green and facile one-pot synthesis of Ag–ZnO/RGO nanocomposite with effective photocatalytic activity for removal of organic pollutants

In this study, Ag–ZnO/reduced graphene oxide (Ag–ZnO/RGO) composite was synthesized by a green and facile one-step hydrothermal process. Aqueous suspension containing Ag and ZnO precursors with graphene oxide (GO) sheets was heated at 140 °C for 2 h. The morphology and structure of as-synthesized particles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and Photoluminescence (PL) spectroscopy which revealed the formation of composite of metal, metal oxide and RGO. It was observed that the presence of Ag precursor and GO sheets in the hydrothermal solution could sufficiently decrease the size of ZnO flowers. The hybrid nanostructure, with unique morphology, obtained from this convenient method (low temperature, less time, and less number of reagents) was found to have good photocatalytic and antibacterial activity. The perfect recovery of catalyst after reaction and its unchanged efficiency for cyclic use showed that it will be an economically and environmentally friendly photocatalyst.     

Uranium recovery from coal ash dumps of Mongolia

The concentration of natural radionuclides and the feasibility of recovery of uranium from browncoal ash of a Mongolian cogeneration plant were investigated. The concentrations of the elements were determined by instrumental gamma-activation (IGAA) and X-ray fluorescence (XRF) analysis. Uranium from brown-coal ash was leached with an 8 M HNO₃ + HF (10%) mixture. The extraction of uranium from the solution and its purification for the removal of accompanying elements were carried out on an anion exchanger. An ash sample after leaching contains neither natural radioactive elements (²³⁸U and ²³²Th) nor their decay products, thereby allowing for the use of the ash as a building material.     

Antibacterial and photocatalytic properties of Ag/TiO2/ZnO nano-flowers prepared by facile one-pot hydrothermal process

In this paper, a simple and efficient strategy of one-pot synthesis of Ag doped TiO₂/ZnO photocatalyst was developed using hydrothermal process. Simultaneous crystallization of Ag and ZnO crystals from their precursor solution containing P25 (TiO₂) NPs could form effectively bonded Ag/TiO₂/ZnO composite photocatalyst during hydrothermal treatment. Several analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), FT-IR spectroscopy, and photoluminescence spectroscopy have been used to characterize the resulting Ag/TiO₂/ZnO photocatalyst. Results showed that ZnO nano-flowers doped with TiO₂ and Ag NPs were formed by this simple facile one-step process. The unique properties of Ag NPs on binary semiconductor composite not only provide the decreased rate of electron–hole separation but also prevent from the loss of photocatalyst during recovery due to the fixed attachment of Ag and TiO₂ NPs on the surface of flower shaped large ZnO particles. Therefore, as-synthesized composite is an economically and environmentally friendly photocatalyst.     

Mercury exposure in female artisanal small-scale gold miners (ASGM) in Mongolia: An analysis of human biomonitoring (HBM) data from 2008

Background

Many poor in developing countries have turned to artisanal small-scale gold mining (ASGM) in an attempt to improve their situation. However, the mercury used to extract gold from ore is discharged in vaporized form into the environment, where it poses a hazard for human health.

Methods

As part of an environmental epidemiological study in Mongolia—to evaluate the burden of environmental mercury contamination—urine, blood and hair samples were collected from residents of areas with or without mercury contamination. A total of 200 blood, urine and hair samples were analyzed for mercury and divided into three subgroups according to mercury content: (1) occupational exposure (high/medium); (2) environmental exposure (low); and (3) no exposure. Internal mercury distributions of the subgroups were compared using the Kruskal-Wallis and Mann-Whitney U-test. The Chi-square test and likelihood ratio proportion were used to compare the findings with threshold limits.

Results

The highest values and greatest differences were seen in the urine samples (p < 0.001, Kruskal-Wallis). The occupational group showing the highest exposure with a median mercury level of 4.36 μg/l (control group: 0.10 μg/l, p < 0.001), 7.18 μg/g creatinine and 12 results above the threshold limit HBM I (Human Biomonitoring I). Even participants from the low-exposure subgroup showed elevated mercury levels (median 2.88 μg/l urine and 2.98 μg/g creatinine, p < 0.001), with 10 individuals above the HBM I threshold limits.

Discussion

The body burden resulting from the use of mercury in artisanal gold mining is high not only in the miners themselves, an increased mercury hazard was also found for inhabitants of mining areas who were not actively involved in mining. Public health support measures are urgently needed to alleviate the situation.     

Vacancy‐Driven Gelation Using Defect‐Rich Nanoassemblies of 2D Transition Metal Dichalcogenides and Polymeric Binder for Biomedical Applications

A new approach of vacancy‐driven gelation to obtain chemically crosslinked hydrogels from defect‐rich 2D molybdenum disulfide (MoS₂) nanoassemblies and polymeric binder is reported. This approach utilizes the planar and edge atomic defects available on the surface of the 2D MoS₂ nanoassemblies to form mechanically resilient and elastomeric nanocomposite hydrogels. The atomic defects present on the lattice plane of 2D MoS₂ nanoassemblies are due to atomic vacancies and can act as an active center for vacancy‐driven gelation with a thiol‐activated terminal such as four‐arm poly(ethylene glycol)–thiol (PEG‐SH) via chemisorption. By modulating the number of vacancies on the 2D MoS₂ nanoassemblies, the physical and chemical properties of the hydrogel network can be controlled. This vacancy‐driven gelation process does not require external stimuli such as UV exposure, chemical initiator, or thermal agitation for crosslinking and thus provides a nontoxic and facile approach to encapsulate cells and proteins. 2D MoS₂ nanoassemblies are cytocompatible, and encapsulated cells in the nanocomposite hydrogels show high viability. Overall, the nanoengineered hydrogel obtained from vacancy‐driven gelation is mechanically resilient and can be used for a range of biomedical applications including tissue engineering, regenerative medicine, and cell and therapeutic delivery.     

Characterization and Photocatalytic Efficiency of TiO2 /Ti Beads Fabricated by Simple Heat-Treatment

The goal of the present study was to investigate the photocatalytic efficiency of titanium dioxide (TiO 2) formed on titanium (Ti) bead substrate (referred herein as TiO 2 /Ti beads) by heat treatment when exposing to ultraviolet (UV) light irradiation.Escherichia coli was used as the model test organism.The results show 4-log and 7-log decrease in bacterial concentration after a test time of 15 and 120 min,respectively,using TiO 2 /Ti beads irradiated with UV light in a tin-foil covered beaker.This article presents the potential of TiO 2 on Ti bead substrate formed by simple heat-treatment together with UV light for bacterial inactivation.     

The determination of water‐soluble vitamins and in vitro digestibility of selected Czech cheeses

Water‐soluble vitamins, in vitro organic matter digestibility (OMD) and dry matter digestibility (DMD) values were determined in various different Czech cheeses. An HPLC method for the simultaneous determination of niacin, pantothenic acid and pyridoxine in cheese was established. Different hydrolysis conditions and enzymes were used to release these vitamins from their complex form. The cheeses contained on average 2.04 mg of niacin, 3.24 mg of pantothenic acid and 2.16 mg of pyridoxine per 100 g of fresh mass. An enzymatic method was applied for the evaluation of OMD and DMD in cheeses. In vitro digestibility values ranged from 83.29% to 99.99% for organic matter (OMD) and 83.33% to 99.87% for dry matter (DMD) after two different enzymatic digestions (pepsin, pancreatin). In addition, cheeses incubated with pepsin plus pancreatin, OMD and DMD were strongly digested (99.04–99.83%, 97.73–99.74%).     

Effect of annealing on the phase transition and morphology of Ag NPs on/in TiO2 rods synthesized by a polyol method

In this study, we report the effect of annealing (250–700 ^oC) on the phase transition and morphology of silver (Ag) nanoparticles (NPs) on/in titanium dioxide (TiO₂) rods prepared using a polyol method. The annealed samples showed not only morphological change, i.e., a solid-to-liquid (melting) transition of Ag NPs due to its partial dissolution into the TiO₂ rods, but also early stage anatase crystallization and anatase–rutile transformation of TiO₂ rods under low annealing temperatures. Such findings, together with XRD and FE-SEM analyses, confirm that, upon higher annealing treatment, diffusion and coalescence leads to changes in the size and shape of the metal particles not only in the outermost regions, but also a random distribution and progressive growth of Ag clusters in the inner interface region. Here, it was shown that annealing can induce changes in morphology, as well as the chemical state and structure of Ag–TiO₂. The present polyol-synthesized Ag–TiO₂ composite also showed improved thermal stability.     

A new “fluoride” synthesis route for successive ionic layer deposition of the ZnxZr(OH)yFz·nH2O nanolayers

It was for the fist time shown that hydroxo-fluoride nanolayers with the general formula M_xZr(OH)_yF_z·nH₂O can be synthesized by the successive ionic layer deposition method using soluble complexes of metal fluorides as reagents. By an example of the Zn_xZr(OH)_yF_z·nH₂O nanolayers on silicon surfaces, the effect of pH, the reagent concentration, and the number of the deposition cycles was examined. The composition and structure of these layers were determined by X-ray photoelectron and FTIR transmission spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), while the growth kinetics was evaluated by ellipsometry.