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Resultados 4681-4690 de 4,924
Catalytic hydrolysis of cellulose by phosphotungstic acid–supported functionalized metal-organic frameworks with different electronegative groups
2019
Han, Jinye | Wang, Yan | Wan, Jinquan | Ma, Yongwen
It is found that strong electronegative groups can selectively adsorb cellulose by hydrogen bonds. Grafting strong negatively charged groups onto catalysts to achieve the functionalization of the catalyst can give it the ability to selectively adsorb cellulose without affecting its catalysis, which is of great significance for the hydrolysis of cellulose. In this study, PTA@MIL-101–X (X = –Br, –NH₂, –Cl, –NO₂) materials were synthesized to investigate the effect of grafting different electronegative groups on carriers to the directional hydrolysis of cellulose. The synthesized catalysts used phosphotungstic acid as the catalytic center while treated MIL-101 structure as the carrier. The grafting of different electronegative groups changed the crystal structure of the metal organic framework without affecting its stability during the reaction. The strong negative functional groups can selectively adsorb cellulose by forming hydrogen bonds with cellulose hydroxyl groups and weaken the hydrogen bonds within cellulose molecules. This hydrogen bond can reduce the side reaction of glucose, lighten the difficulty of cellulose hydrolysis, and improve the efficiency of cellulose conversion at the same time. The hydrolysis rate of cellulose increased with the electronegativity enhancement of the grafted functional groups, and the grafted –NO₂ catalyst PTA@MIL-101–NO₂ obtained the highest glucose yield of 16.2% in the cellulose-directed hydrolysis. The –NH₂ can form a chemical linkage with PTA through electrostatic interaction to get the highest immobilization stability and exhibit excellent stability in the recycling of catalysts. Graphical abstract
Mostrar más [+] Menos [-]Determinants of renewable energy consumption in Africa
2019
Ergun, Selim Jürgen | Owusu, Phebe Asantewaa | Rivas, María Fernanda
Although the role that renewable energy consumption plays on economic growth and emissions has been widely studied, there are relatively few papers focusing on the determinants of renewable energy consumption, and only one study focuses on the factors related to the share of renewables in the energy consumption in Africa. This paper contributes to the literature by filling the gap in knowledge by exploring the nexus between the share of renewables in energy consumption and social and economic variables, for a panel consisting of 21 African countries for the period between 1990 and 2013, extending the set of variables and the time span used by a previous study. Estimating a random-effects generalized least squares regression, we find that countries with a higher Human Development Index and a higher gross domestic product per capita have a lower share of renewable energy in the national grid. On the other hand, an increase in foreign direct investment has been found to be related to higher renewable energy integration. The level of democracy, measured by the Freedom House political rights and civil liberties ratings, does not directly affect the integration level of renewable energy sources. The negative relationship between gross domestic product per capita and the share of renewables contradicts previous findings for developed countries. This contradiction and policy implications are discussed in the light of the review of the energy mix of the selected countries.
Mostrar más [+] Menos [-]In situ resuspension rate monitoring method in the littoral zone with multi-ecotypes of a shallow wind-disturbed lake
2019
Qi, Chuang | Xu, Xiao-guang | Shi, Kuan | Zhang, Li-min | Zhou, Yang | Lin, Hui | Wu, Xin-ting | Wang, Guo-xiang | Meng, Han
Sediment resuspension has been recognized as a crucial internal process in aquatic ecosystems. However, there is still a lack of reliable measuring methods due to the complex hydrodynamic conditions in large shallow eutrophic lakes. In this study, sequential sediment traps (SST) and instantaneous multiple point (IMP) methods were compared at 6 sites located in the littoral zone of Zhushan Bay in Lake Taihu. Results show that the average resuspension rates (RRs) estimated using the IMP method at sites 1 to 6 were 266.39, 272.79, 235.17, 254.95, 392.25, and 483.85 g·m⁻²d⁻¹, respectively. While the RRs estimated using the SST method were 195.16, 236.99, 116.76, 156.23, 389.53, and 509.85 g·m⁻²d⁻¹, respectively. In wind-disturbed areas, both methods were suitable for RR analysis in large and shallow eutrophic lakes and SST provides high-resolution temporal RR estimations. However, in the areas with cyanobacterial blooms and vegetation cover, the IMP method overestimated the RR. Therefore, SST was more suitable across different conditions in large and shallow eutrophic lakes, providing a simple, accurate, and high-resolution temporal estimation of RR, while furthering our understanding of lake evolution processes.
Mostrar más [+] Menos [-]Monitoring of environmental persistent organic pollutants in hair samples collected from wild terrestrial mammals of Primorsky Krai, Russia
2019
Iatrou, Evangelia I. | Tsygankov, Vasiliy | Seryodkin, Ivan | Tzatzarakis, Manolis N. | Vakonaki, Elena | Barbounis, Emmanouil | Zakharenko, Alexander M. | Chaika, Vladimir V. | Sergievich, Alexander A. | Tsatsakis, Aristidis M. | Golokhvast, Kirill
Persistent organic pollutants (POPs) constitute a wide range of chemicals. Their release into the environment has raised great concern due to their potentially harmful impact in humans and wildlife species. The aim of this current study was to detect selected POPs in hair samples of wild terrestrial mammals from Primorsky Krai, Russia, so as to assess potential environmental exposure. The tested wild species were leopard cat, musk deer, wolf, amur hedgehog, and raccoon dog. The targeted organochlorines were hexachlorobenzene (HCB) and DDTs (opDDE, ppDDE, and opDDD), polychlorinated biphenyl (PCB) congeners (28, 52, 101, 118, 138, 153, and 180), and polycyclic aromatic hydrocarbons (PAHs) (acenaphylene (ACEN), fluorene (FLU), anthracene (ANTH) phenathrene (PHEN), and pyrene (PYR)). The detection of POPs was conducted in hair samples by a one-step hair extraction method, by using a headspace solid-phase microextraction technique (HS-SPME) and analyzed then by GC-MS. The majority of the wild animal hair samples were found positive in all tested pollutants. More specifically, the percentage of positive hair samples for HCB was 93.3% and for DDTs, PCBs, and PAHs, 20.0 to 100.0%, 6.7 to 100.0%, and 75.0 to 100.0%, respectively. DDT, PCB, and PAH detection ranged from 1.26 to 52.06 pg mg⁻¹, 0.73 to 31.34 pg mg⁻¹, and 2.59 to 35.00 pg mg⁻¹, respectively. The highest mean concentration levels of all tested pollutants were found for musk deer (PCBs 12.41 pg mg⁻¹, DDTs 21.87 pg mg⁻¹, PAHs 22.12 pg mg⁻¹) compared to the other wild species. To the best of our knowledge, this is the first study that provides results regarding contamination in different terrestrial mammals by POP exposure. The use of hair as a matrix is proven to be an effective tool for nondestructive biological monitoring of POP contamination in terrestrial ecosystems.
Mostrar más [+] Menos [-]Performance of Aeluropus lagopoides (mangrove grass) ecotypes, a potential turfgrass, under high saline conditions
2019
Zamin, Muhammad | Khattak, Abdul Mateen | Salim, Abdul Mohsin | Marcum, Kenneth B. | Shakūr, Muḥammad | Shah, Shahen | Jan, Ibadullah | Shah, Fahad
Climate change has become a real threat, and its impacts are being felt throughout the world. Temperature is considered one of the significant elements by the recent consequences of climate change and global warming, specially the salinity which is increased at higher temperature. Turfgrasses are adversely affected due to an increasing trend in salinity. The main aim of this investigation was to find out salt-tolerant ecotypes from native species of UAE to mitigate the salinity problem. Performance of a native grass, Aeluropus lagopoides, was investigated under high saline conditions during the year 2014 under the UAE climatic conditions. The experiment was planned under randomised complete block design (RCBD) with two factors and four replications. During the experiment, 50 ecotypes of Aeluropus lagopoides, alongside Paspalum vaginatum (as control), were tested at different salt levels, i.e. 0, 15, 30, 45, 60 and 75 dSm⁻¹. Significant differences were found among various ecotypes as well as salinity levels for different agronomic traits including green cover, canopy stiffness, leaf colour and salinity of leaf rinseates. Most of the ecotypes tolerated salinity up to 30 dSm⁻¹, maintaining the quality, but beyond this level the quality declined. However, some of the ecotypes survived under high salinity, even beyond sea level (75 dSm⁻¹). All the ecotypes, except RUA2, RUA3 and RUA1, showed better performance than P. vaginatum, the prevailing commercial turfgrass in the UAE. Based on their performance, the ecotypes RUDA7, FA5, RA3, RUDA2 and RA2 could be used for turf purposes under saline conditions.
Mostrar más [+] Menos [-]Spatiotemporal evolution of environment based on integrated remote sensing indexes in arid inland river basin in Northwest China
2019
Wei, Wei | Guo, Zecheng | Xie, Binbin | Zhou, Junju | Li, Chuanhua
Arid inland river basin has been regarded as environmental vulnerable and an important protective area in northwest China. Shiyang River Basin (SRB) is one of the most typical areas in arid inland rivers basin in China. The environmental quality evaluation of different periods is significant for environmental control and management of SRB. In this paper, the normalized differential vegetation index (NDVI), wetness index (WI), albedo, index-based built-up index (IBI), salinization index (SI), and land surface temperature (LST) were obtained through Landsat TM and OLI images in 1995, 2000, 2005, 2010, and 2016. Besides, three methods including spatial principal component analysis (SPCA), analytic hierarchy process (AHP), and remote-sensing spatial distance model (RSSDM) were compared to select a reasonable method for environmental evaluation. The AHP method was determined as the final method for objectively evaluating spatiotemporal changes of environment from 1995 to 2016 in SRB. The results showed that the environment deteriorated in 1995–2000 and improved in 2000–2016. The effect of environmental governance was significant in 2010–2016 because of the longtime environmental management between multiple departments. The results indicated that the environmental quality of SRB was generally improved from 1995 to 2016. We found that the improvement areas were mainly concentrated in the oasis and marginal areas, while environmental damage areas were mainly distributed in the urban regions. However, in most areas of the SRB, the environment was still below average level of China, and the roads of the environment management still had a long way to go. We found that spatiotemporal pattern analysis of the environment was of great importance for the formulation of plans for development of this basin and environmental protection measures.
Mostrar más [+] Menos [-]The effect of the earthworm Lumbricus rubellus on the bioavailability of cadmium and lead to the springtail Folsomia candida in metal-polluted field soils
2019
Ardestani, Masoud M. | Giska, Iwona | Gestel, Cornelis A. M. van
The bioavailability of metals can be influenced not only by soil properties but also by other species living at polluted sites. However, in laboratory experiments, usually only one test species is used to estimate bioavailability. In this study, a two-species approach was applied to assess the impact of the earthworm Lumbricus rubellus on the bioavailability of cadmium and lead to the springtail Folsomia candida using natural soils from a gradient of metal pollution. Earthworms were kept in half of the soil replicates for 4 weeks. Subsequently, the uptake and elimination kinetics of cadmium and lead in F. candida exposed for 21 days to the soils was determined. Earthworm activity affected soil properties but did not significantly affect metal uptake rate constants in springtails. The slightly higher uptake due to the presence of earthworms, which was consistent in all tested soils and for both metals, suggests that further research is needed on the role of species interactions in affecting metal bioavailability in soil.
Mostrar más [+] Menos [-]Synthesis and characterization of Ag2O/B2O3/TiO2 ternary nanocomposites for photocatalytic mineralization of local dyeing wastewater under artificial and natural sunlight irradiation
2019
Tijani, Jimoh Oladejo | Momoh, Ufon Ojogbane | Salau, Rasaq Bolakale | Bankole, Mercy Temitope | Abdulkareem, Ambali Saka | Roos, Wiets Dániel
In this work, Ag₂O/B₂O₃/TiO₂ ternary nanocomposite was synthesized by a combination of green and precipitation method involving mixing of different concentrations of silver nitrate, boric acid, and titanium (IV) isopropoxide precursor with Plumeria acuminate leaf extract. The extract was obtained by boiling the mixture of distilled water and the powdered leaves in a beaker for few minutes followed by filtration. The microstructure, morphology, chemical composition, surface area, phase structure, and optical properties of the various prepared nanomaterials were determined by HRTEM, HRSEM, UV-Vis/DRS, BET, XRD, and XPS. The photocatalytic potential of TiO₂ nanoparticles and Ag₂O/B₂O₃/TiO₂ nanocomposites to degrade local dyeing wastewater under artificial and natural sunlight irradiation was investigated. The extent of degradation of the organic pollutants was measured using chemical oxygen demand (COD) and total organic carbon (TOC) as indicator parameters. The XRD pattern of Ag₂O/B₂O₃/TiO₂ nanocomposites revealed that the formation of pure anatase TiO₂ phase and the addition of both silver and boron precursors did not influenced the phase structure of the nanocomposites. The oxidation states of +1 and +3 for both Ag and B on the surface of Ag₂O/B₂O₃/TiO₂ nanocomposites were confirmed by XPS. Optical characterization of the sample revealed reduction of band gap energy from 2.6 to 2.0 eV for TiO₂ and Ag₂O/B₂O₃/TiO₂, respectively. The Ag₂O/B₂O₃/TiO₂ nanocomposites demonstrated excellent photocatalytic activity under natural sunlight and artificial light than mono and binary oxide systems with TOC and COD degradation efficiencies of 86.11% and 75.69%, respectively. The kinetics of degradation of organic dyes in the wastewater followed the order of Langmuir–Hinshelwood pseudo-first-order > Freundlich > Zero > Parabolic diffusion model. The coupling effect of Ag₂O and B₂O₃ onto TiO₂ framework was responsible for the enhanced photochemical stability of the nanocomposites even after five repeated cycles.
Mostrar más [+] Menos [-]Synthetic agrochemicals: a necessary clarification about their use exposure and impact in crop protection
2019
Marchand, Patrice A.
Synthetic pesticides are largely decried. A common attitude against the synthetic agrochemicals is to avoid, criticise or ban these substances. Along with chemical pesticides to defend crops from bioagressors are microorganisms, semiochemical and natural substances used as plant protection products including biocontrol agents (BCAs) and crop protection products in organic production. Nevertheless, a natural substance status does not confer or imply safety, security or absence of residues (in the context of plant protection). Although in this paper we do not consider the toxicological perspective of highly toxic chemicals with adverse effects on humans and non-target organisms sprayed on crops, we have applied ourselves to working on the safe use of synthetic agrochemicals. Thus, along with biopesticides (either BCA or others) allowed in organic farming, we show that some synthetic chemical pesticides may be used in safe manner. HIGHLIGHTS: • Synthetic agrochemicals are widely criticised. • Some pesticide usages are not sprayed on crops. • Some biocontrol agents are of synthetic origin.
Mostrar más [+] Menos [-]Exposure to phthalates and bisphenol A is associated with higher risk of cardiometabolic impairment in normal weight children
2019
Mansouri, Vahid | Ebrahimpour, Karim | Poursafa, Parinaz | Riahi, Roya | Shoshtari-Yeganeh, Bahareh | Hystad, Perry | Kelishadi, Roya
Some obese individuals have normal metabolic profile, and some normal-weight persons have impaired metabolic status. Our hypothesis was that one of the potential underlying factors for such differences in cardiometabolic profiles might be the exposure to some environmental chemicals. This study aimed to investigate the association of serum bisphenol A (BPA) and phthalate metabolites with cardiometabolic risk factors in children and adolescents independent of their weight status. This case–control study was conducted on a subsample of 320 participants of a national school-based surveillance program in Iran. We measured serum BPA and phthalate metabolites by gas chromatography mass spectrophotometry. We compared them in children and adolescents with and without excess weight and those with and without cardiometabolic risk factors (80 in each group). We categorized the concentrations of chemicals to tertiles and then we applied logistic regression models after adjustment for potential confounding factors. The concentrations of BPA and some metabolites of phthalates were significantly different in the four groups studied. MEHP concentration was associated with higher odds ratio of cardiometabolic risk factors in participants with normal weight (OR, 95% CI 2.82, 1.001–7.91) and those with excess weight (OR, 95% CI 3.15, 1.27–7.83). MBP concentration increased the odds ratio of cardiometabolic risk factors only in normal weight children and adolescents (OR, 95% CI 6.59, 2.33–18.59, P < 0.001). In participants without cardiometabolic risk factor, MMP and MEHHP were significantly associated with increased risk of excess weight (OR, 95% CI 5.90, 1.21–28.75 and 7.82, 1.5–41.8, respectively). This study showed that the association of BPA and phthalate with cardiometabolic risk factors is independent of the weight status. Our findings suggest that the metabolic impairment in some normal weight children and normal metabolic profile of some obese children can be, in part, related to exposure to these environmental chemicals. Graphical abstract
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