Gas-phase HO-initiated reactions of elemental mercury: kinetics, product studies, and atmospheric implications

Mercury is an environmentally volatile toxic fluid metal that is assumed to have a long atmospheric residence time and hence is subject to long-range transport. The speciation and chemical transformation of mercury in the atmosphere strongly influences its bioaccumulation potential in the human food chain as well as its global cycling. To investigate the oxidation of Hg0 by HO, the dominantdaytime atmospheric oxidant, we performed kinetic and product studies over the temperature range 283-353 K under near atmospheric pressure (100+/-0.13 kPa) in air and N2 diluents. Experiments were carried out by the relative rate method using five reference molecules and monitored by gas chromatography with mass spectroscopic detection (GC-MS). The HO were generated using UV photolysis of isopropyl nitrite at 300 < or = lambda < or = 400 nm in the presence of NO. The room-temperature rate constant was found to be (9.0+/-1.3) x 10(-14) cm3 molecule(-1) s(-1). The temperature dependence of the reaction can be expressed as a simple Arrhenius expression (in unit of 10(-14) cm3 molecule(-1) s(-1)) using ethane as the reference molecule: kHg + HO = 3.55 x 10(-14) exp((294+/-16)/T). The major reaction product, HgO, was identified in the gaseous form, as aerosols and as deposits on the container walls, using chemical ionization mass spectrometry (CI-MS), electron impact mass spectrometry (EI-MS), GC-MS, and cold vapor atomic fluorescence spectrometry (CVAFS). Experimental results reveal that ca. 6% of the reaction products were collected on a 0.2 microm filter as suspended aerosol, ca. 10% were in the gaseous form, and about 80% were deposited on the reaction vessel wall. The potential implications of our results in the understanding of tropospheric mercury transformation are herein discussed.     

Imaging a single-electron quantum dot

Images of a single-electron quantum dot were obtained in the Coulomb blockade regime at liquid He temperatures using a cooled scanning probe microscope (SPM). The charged SPM tip shifts the lowest energy level in the dot and creates a ring in the image corresponding to a peak in the Coulomb-blockade conductance. Fits to the line shape of the ring determine the tip-induced shift of the energy of the electron state in the dot. SPM manipulation of electrons in quantum dots promises to be useful in understanding, building, and manipulating circuits for quantum information processing.     

Evaluating the ability of separation and adsorption of SO<Subscript>2</Subscript> by nano-CuO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> in high concentrations and moderate temperatures

Nano CuO-Fe₂O₃/TiO₂ adsorbents were made with different compositions of metal oxides using precipitation- desorption method. The adsorbents were applied for adsorption of SO₂ at high concentrations ranging from 10,000 to 30,000 ppm and temperatures between 523 and 627 K. Adsorption experiments were applied for adsorbents in a laboratory fixed bed adsorption column. The adsorption capacity was measured by calculating the area under the adsorption curve using the integral method. The results showed that temperature is the most affecting factor on the adsorption capacity. The highest adsorption capacity was obtained by using 17, 8 and 75 wt% of CuO, Fe₂O₃ and nano TiO₂, respectively. Characteristics of the best sorbent were determined by using Fe-SEM, XRD and nitrogen adsorption-desorption analyses.     

Combination of surface texturing and nanostructure coating for reduction of light reflection in ZnO/Si heterojunction thin film solar cell

In this study, we report a single heterojunction solar cell based on n-type zinc oxide/p-type silicon. Three different solar cells were fabricated based on ZnO thin film on Si substrate, ZnO nanorods on Si substrate, and ZnO nanorods on micro-pyramidal structure of Si substrate. The comparison between these three kinds of solar cells was studied. Pyramidal structure of silicon was fabricated using chemical etching technique of p-type Si (100). The chemical solution consists of NaOH, isopropyl alcohol and hydrazine hydrate. The results showed that Si micro-pyramids can enhance optical absorption of Si substrates by increasing surface area and entrapping of incident light. For fabrication of uniform ZnO nanorods, a seed layer of ZnO was deposited on Si substrates via radio frequency magnetron sputtering technique. This layer can be used as an active n-type material in heterojunction solar cells as well. ZnO nanostructures can increase light absorption due to their high specific surface area. The combination of ZnO nanorods and Si micro-pyramids can enhance light trapping effect and increase the efficiency of solar cells. The structural and morphology of samples were studied using field-emission scanning electron microscopy, atomic force microscopy and X-ray diffractometry while the optical properties were investigated using photoluminescence and reflectance spectrometry. The efficiency and fill factor of solar cells were obtained from current–voltage characteristics using a solar simulator and a source-meter. The results showed that the efficiency of solar cell based on nanostructures of ZnO/micropyramids of Si is highly increased due to high anti-reflective behavior of this sample.     

Improved performance of Bis-GMA dental composites reinforced with surface-modified PAN nanofibers

Journal of Materials Science: Materials in Medicine - Skeletal muscle is an electrically and mechanically active tissue that contains highly oriented, densely packed myofibrils. The tissue has...     

Robust design of a sustainable and resilient bioethanol supply chain under operational and disruption risks

Clean Technologies and Environmental Policy - In this work, we propose a mixed-integer linear programming model to address the design and planning of a multi-feedstock lignocellulosic bioethanol...     

Sugar cane juice concentration via CO2 gas hydrate formation

Sugar cane juice concentration via evaporation is the traditional method, though the downside in this technique is the product loss due to sucrose inversion. Gas hydrate separation is an emerging technology applied in desalination, carbon capture, and in this study, for concentrating fruit juice by trapping the water in the form of crystalline cages. A 750 cm³ hydrate reactor was used for hydrate formation experiments to concentrate the sugar cane juice, with a sampling of the concentrate to determine the final solids content. Hydrate formation experiments showed the successful concentration of a 0.12 mass fraction feed to approximately 0.56 mass fraction using four batchwise concentration stages. A comparison of the energy usage between the evaporation train as used in sugar factories and a single batch hydrate formation stage, to concentrate a 0.12 mass fraction feed to 0.30 mass fraction showed an energy reduction of approximately 20% for the hydrate method.     

Fabrication and characterization of alginate/chitosan hydrogel combined with honey and aloe vera for wound dressing applications

Hydrogels can be one of the best polymeric wound dressings due to the desirable properties of wound healing. In this study, emphasizing the use of natural biomaterials such as Aloe vera and honey in the structure of cross-linked polymers, a novel hydrogel was produced that might be applied to healing wounds. In the beginning, four hydrogel groups were made from a combination of Sodium Alginate and Chitosan with Aloe vera extract and honey in optimum concentrations. Then the structure of those was evaluated by SEM and FTIR. After confirming hydrogels' structural properties, their physical properties, including swelling, porosity, density, mass loss, stability, and WVTR, were examined. Besides, the hydrogel biocompatibility was assessed by analyzing the cell viability and hemolytic activity. Adhesion of the cells to the hydrogel was also observed by SEM imaging. The results showed that the designed hydrogel has a porous structure with interconnected cavities, which their size can provide suitable conditions for cell adhesion, migration, and proliferation. Also, their physical and structural properties can be a strong suit to wound healing. Although honey's application can weaken the hydrogel structure, honey has beneficial properties due to its complex biomolecules. In contrast, Aloe vera in hydrogel generally improved the hydrogel's specificity for wound healing. According to the results of this study, taking advantage of hydrogels containing honey and Aloe vera based on alginate and chitosan polymers led to the formation of an acceptable structure and biocompatibility that can be used in future researches to repair tissues, especially wounds.     

Swelling and auramine-<Emphasis Type="Italic">O</Emphasis> adsorption of carboxymethyl cellulose grafted poly(methyl methacrylate)/Cloisite 30B nanocomposite hydrogels

Carboxymethyl cellulose (CMC) grafted poly(methyl methacrylate)/Cloisite 30B nanocomposite hydrogels were prepared for adsorptive removal of auramine-O (as a cationic dye model) from wastewater. For the synthesis of nanocomposite hydrogel by free radical polymerization method, potassium persulfate (KPS), methyl methacrylate (MMA), N,N′-methylene bisacrylamide (MBA) and Cloisite 30B were used as initiator, monomer, cross-linker and nano-filler, respectively. The nanocomposite hydrogels were characterized by FTIR, TGA, SEM and XRD techniques. The FTIR results showed that the monomer was grafted onto carboxymethyl cellulose chains successfully. Swelling behavior of nanocomposite hydrogel as a function of KPS, MBA, MMA concentration and CMC/Cloisite 30B weight ratio was studied by Taguchi method using Minitab 16 software. According to ANOVA results, the most effective factor of equilibrium swelling of nanocomposite hydrogel was CMC/Cloisite 30B weight ratio. Addition of Cloisite 30B to hydrogel up to a certain amount improved swelling, though its high amount decreased swelling. The effects of pH and ionic strength on swelling of optimum hydrogels were investigated. Maximum swelling of nanocomposite hydrogel occurred at pH 7.0. The kinetic data of adsorption fitted well to pseudo-second-order model. The best isotherm for investigation of adsorption mechanism was Langmuir model suggesting the formation of a monolayer on the adsorbent surface. FTIR results, before and after auramine-O adsorption, showed that complexation is the main mechanism of adsorption. High adsorption capacity of nanocomposite hydrogels made them more efficient in wastewater treatment application.     

Evaluating recyclability of fly ash reinforced polyvinyl chloride foams

Using fly ash as a reinforcing filler can be very cost effective; however, the recycling of postconsumer products containing fly ash is of a considerable concern. In this study, the recycling of processed polyvinyl chloride (PVC) foam reinforced with fly ash was investigated by evaluating the effect of regrind content (up to 40 wt%) and fly ash content (up to 20 wt%) on the physical, mechanical, microstructural, and processing properties of the composites. Experimental results show an increase in the foam density with increasing regrind and fly ash contents. The melt viscosity increased with increasing the regrind concentration; however, it dropped with increasing the fly ash content. The tensile strength increased with increasing the regrind content, indicating a good degree of gelation in the composites. Meanwhile, the charpy impact strength of the composites decreased due to the high rigidity of fly ash particles. Dynamic mechanical analysis show that the storage modulus improved with both the addition and increasing the amount of regrind, which confirmed good stress transformation between the polymer foam matrix and the fly ash particles. The polymer matrix morphology, as was determined by scanning electron microscopy (SEM), confirmed uniform foam structure even with the addition of 40 wt% regrind in the virgin PVC. J. VINYL ADDIT. TECHNOL., 24:154–161, 2018. © 2016 Society of Plastics Engineers