Affiner votre recherche
Résultats 2291-2300 de 4,309
Composites ZSM-5/KIT-6 Synthesized Via Assembly Modification Procedure and Mechanical Grinding Procedure, Respectively, and Their Application to CO2 Adsorption Texte intégral
2017
Lin, Zhifeng | Wei, Jianwen | Geng, Linlin | Mei, Dejun | Liao, Lei
The micro/mesoporous composite ZSM-5/KIT-6 was synthesized via the assembly procedure of preformed ZSM-5 seeds into mesostructured KIT-6, and mechanical mixtures with different contents of zeolite were prepared via a mechanical grinding procedure. These composites were used as adsorbents for the capture of CO₂ in the simulated flue gas conditions of 60 °C and 15 vol% CO₂ with a thermal gravimetric analyzer (TGA). The combination of dual-pore structures improved the adsorption performance. The composite synthesized via the assembly procedure exhibited superior adsorption capacity to the mechanical mixtures. The maximum adsorption capacity was 1.223 mmol/g. For mechanical mixtures, the adsorption capacity was dependent on the ZSM-5 content and increased with the increase of ZSM-5 content. The composite can be applied for CO₂ adsorption at flue gas temperature and desorption at regeneration temperature of 110 °C. The adsorption capacity showed only 3% attrition during five consecutive cyclic adsorption/desorption tests. The composites displayed excellent CO₂ adsorption/desorption performance.
Afficher plus [+] Moins [-]Biosorption of Lead(II) from Aqueous Solution by Sodium Hydroxide Modified Auricularia auricular Spent Substrate: Isotherms, Kinetics, and Mechanisms Texte intégral
2017
Song, Tao | Yu, Sumei | Wang, Xin | Teng, Chunying | Bai, Xin | Liang, Jinsong | Dong, Liying | Ouyang, Fengju | Qu, Juanjuan | Jin, Yu
In this study, Auricularia auricular spent substrate (AASS) was modified by sodium hydroxide and prepared as biosorbents to remove lead(II) from aqueous solution. The batch experiments showed that the biosorption capacity and biosorption percentage reached 36.35 mg g⁻¹ and 72.7% at initial concentration of 50 mg L⁻¹, pH 5, contact time of 200 min, and biosorbent dosage of 1 g L⁻¹. The biosorption of lead(II) onto modified AASS well fitted with the Langmuir isotherm model and the pseudo-second-order kinetic model with the maximum adsorption capacity(q ₘₐₓ) of 49.53 mg L⁻¹. The biosorption was an endothermic reaction and a spontaneous process based on positive value of ΔH ⁰ and negative value of ΔG ⁰. Fourier transform infrared (FTIR) analysis illuminated that amino and hydroxyl groups could bind lead(II) on biosorbent surface. Sodium hydroxide modification might enhance physical adsorption by enlarging surface area and pore volume as well as chemical adsorption by increasing ion exchange and forming crystalline species demonstrated by microscopy (SEM-EDX) and X-ray diffraction (XRD) analysis. After four regeneration cycles, the biosorption capacity of modified AASS still kept at 17.35 mg g⁻¹.
Afficher plus [+] Moins [-]Adsorptive Removal of Arsenic and Mercury from Aqueous Solutions by Eucalyptus Leaves Texte intégral
2017
Alimohammadi, Mahmood | Saeedi, Zhyar | Akbarpour, Bahman | Rasoulzadeh, Hassan | Yetilmezsoy, Kaan | Al-Ghouti, MohammadA. | Khraisheh, Majeda | McKay, G. (Gordon)
The study is a first-time investigation into the use of Eucalyptus leaves as a low-cost herbal adsorbent for the removal of arsenic (As) and mercury (Hg) from aqueous solutions. The adsorption capacity and efficiency were studied under various operating conditions within the framework of response surface methodology (RSM) by implementing a four-factor, five-level Box–Wilson central composite design (CCD). A pH range of 3–9, contact time (t) of 5–90 min, initial heavy metal (As or Hg) concentration (C ₀) of 0.5–3.875 mg/L, and adsorbent dose (m) of 0.5–2.5 g/L were studied for the optimization and modeling of the process. The adsorption mechanism and the relevant characteristic parameters were investigated by four two-parameter (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) isotherm models and four kinetic models (Lagergren’s pseudo-first order (PFO), Ho and McKay’s pseudo-second order (PSO), Weber–Morris intraparticle diffusion, and modified Freundlich). The new nonlinear regression-based empirical equations, which were derived within the scope of the study, showed that it might be possible to obtain a removal efficiency for As and Hg above 94% at the optimum conditions of the present process-related variables (pH = 6.0, t = 47.5 min, C ₀ = 2.75 mg/L, and m = 1.5 mg/L). Based on the Langmuir isotherm model, the maximum adsorption or uptake capacity of As and Hg was determined as 84.03 and 129.87 mg/g, respectively. The results of the kinetic modeling indicated that the adsorption kinetics of As and Hg were very well described by Lagergren’s PFO kinetic model (R ² = 0.978) and the modified Freundlich kinetic model (R ² = 0.984), respectively. The findings of this study clearly concluded that the Persian Eucalyptus leaves demonstrated a higher performance compared to several other reported adsorbents used for the removal of heavy metals from the aqueous environment.
Afficher plus [+] Moins [-]Simulating changes in cropping practises in conventional and glyphosate-tolerant maize. I. Effects on weeds Texte intégral
2017
Colbach, Nathalie | Fernier, Alice | Le Corre, Valérie | Messéan, Antoine | Darmency, Henri
Herbicide-tolerant (HT) crops such as those tolerant to glyphosate simplify weed management and make it more efficient, at least at short-term. Overreliance on the same herbicide though leads to the spread of resistant weeds. Here, the objective was to evaluate, with simulations, the impact on the advent of glyphosate resistance in weeds of modifications in agricultural practises resulting from introducing HT maize into cropping systems. First, we included a single-gene herbicide resistance submodel in the existing multispecific FLORSYS model. Then, we (1) simulated current conventional and probable HT cropping systems in two European regions, Aquitaine and Catalonia, (2) compared these systems in terms of glyphosate resistance, (3) identified pertinent cultural practises influencing glyphosate resistance, and (4) investigated correlations between cultural practises and species traits, using RLQ analyses. The simulation study showed that, during the analysed 28 years, (1) glyphosate spraying only results in glyphosate resistance in weeds when combined with other cultural factors favouring weed infestation, particularly no till; (2) pre-sowing glyphosate applications select more for herbicide resistance than post-sowing applications on HT crops; and (3) glyphosate spraying selects more for species traits avoiding exposure to the herbicide (e.g. delayed early growth, small leaf area) or compensating for fitness costs (e.g. high harvest index) than for actual resistance to glyphosate, (4) actual resistance is most frequent in species that do not avoid glyphosate, either via plant size or timing, and/or in less competitive species, (5) in case of efficient weed control measures, actual resistance proliferates best in outcrossing species. An advice table was built, with the quantitative, synthetic ranking of the crop management effects in terms of glyphosate-resistance management, identifying the optimal choices for each management technique.
Afficher plus [+] Moins [-]Evaluation of organic amendment on the effect of cadmium bioavailability in contaminated soils using the DGT technique and traditional methods Texte intégral
2017
Lin, Wanjing | Sun, Qin | Wang, Chao | Wang, Pei-fang | Ding, Shi-ming
Organic amendments have been widely proposed as a remediation technology for metal-contaminated soils, but there exist controversial results on their effectiveness. In this study, the effect of pig manure addition on cadmium (Cd) bioavailability in Cd-contaminated soils was systematically evaluated by one dynamic, in situ technique of diffusive gradients in thin films (DGT) and four traditional methods based on the equilibrium theory (soil solution concentration and the three commonly used extractants, i.e., acetic acid (HAc), ethylenediamine tetraacetic acid (EDTA), and calcium chloride (CaCl2). Wheat and maize were selected for measurement of plant Cd uptake. The results showed that pig manure addition could promote the growth of two plants, accompanied by increasing biomasses of shoots and roots with increasing doses of pig manure addition. Correspondingly, increasing additions of pig manure reduced plant Cd uptake and accumulation, as indicated by the decreases of Cd concentrations in shoots and roots. The bioavailable concentrations of Cd in Cd-contaminated soils reflected by the DGT technique obviously decreased with increasing doses of pig manure addition, following the same changing trend as plant Cd uptake. Changes in soil solution Cd concentration and extractable Cd by HAc, EDTA, and CaCl2 in soils were similar to DGT measurement. Meanwhile, the capability of Cd resupply from solid phase to soil solution decreased with increasing additions of pig manure, as reflected by the decreases in the ratio (R) value of CDGT to Csol. Positive correlations were observed between various bioavailable indicators of Cd in soils and Cd concentrations in the tissues of the two plants. These findings provide stronger evidence that pig manure amendment is effective in reducing Cd mobility and bioavailability in soils and it is an ideal organic material for remediation of Cdcontaminated soils.
Afficher plus [+] Moins [-]Distribution and evolution of sterols and aliphatic hydrocarbons in dated marine sediment cores from the Cabo Frio upwelling region, SW Atlantic, Brazil Texte intégral
2017
Lourenço, RafaelAndré | Martins, CésarC. | Taniguchi, Satie | Mahiques, MichelMichaelovitch | Montone, RosalindaCarmela | Magalhães, CaioAugusto | Bícego, MárciaCaruso
We report the distribution of selected lipid biomarkers specifically sterols and aliphatic hydrocarbons in sediment cores from Cabo Frio, SW Atlantic continental shelf, Brazil, corresponding approximately to the last 700 years. In the Cabo Frio region, a costal upwelling occurs as a quasi-seasonal phenomenon characterized by nutrient-rich bottom waters that intrude on the continental shelf and promote relatively high biological productivity compared to other Brazilian continental shelf areas. The results for sterols indicate the predominance of organic matter (OM) inputs related to marine organisms, mainly plankton, in all of the cores along the time scale studied. Principal component analyses show three different groups of variables, which may be associated with (i) the more effective intrusion of the nutrient-rich South Atlantic Central Water, resulting in the increase of marine lipid biomarkers such as sterols and short-chain n-alkanes; (ii) the influence of the Coastal Water with higher surface water temperature and subsequently lower primary productivity; and (iii) OM characterized by high total organic carbon and long-chain n-alkanes related to an allochthonous source. Relatively high concentrations of sterols and n-alkanes between 1450 and 1700 AD, chronologically associated with the Little Ice Age, suggest a period associated with changes in the local input of specific sources of these compounds. The concentrations of lipid biomarkers vary over core depth, but this does not suggest a notably high or low intensity of upwelling processes. It is possible that the climatic and sea surface temperature changes reported in previous studies did not affect the input of the sedimentary lipid biomarkers analyzed here.
Afficher plus [+] Moins [-]Roles of polar groups and aromatic structures of biochar in 1-methyl-3-octylimidazolium chloride ionic liquid adsorption: pH effect and thermodynamics study Texte intégral
2017
Miao, Qiuci | Bi, Erping | Li, Binghua
Adsorption mechanisms of 1-methyl-3-octylimidazolium chloride ([OMIM]Cl) on rice straw-derived biochars produced at 400, 500, and 700 °C (referred as RB400, RB500, and RB700, respectively) were evaluated. Adsorption affinity followed the order of RB700 > RB400 > RB500. Electrostatic attraction and hydrogen bond controlled adsorption of [OMIM]Cl on RB400, while π-π EDA interaction between [OMIM]Cl and the aromatic rings of biochar dominated adsorption of RB500 and RB700. With increasing solution pH, –COOH and –OH on biochar became deprotonated. Consequently, [OMIM]Cl binding to these sites changed from hydrogen bond to electrostatic attraction. Adsorption capacity of [OMIM]Cl increased with increasing pH during the adsorption process. Solid concentration induced by –OH of [OMIM]Cl was higher than that of –COOH. Thermodynamics study indicated that adsorption process was spontaneous and endothermic. ∆H ⁰ values indicated that [OMIM]Cl adsorption on biochars was a physisorption.
Afficher plus [+] Moins [-]Degradation of 5,5-diphenylhydantoin by chlorination and UV/chlorination: kinetics, transformation by-products, and toxicity assessment Texte intégral
2017
Mansor, NurAdawiyah | Tay, KhengSoo
This study investigated the reaction kinetics and mechanism of the degradation of 5,5-diphenylhydantoin (DPH) during conventional chlorination and UV/chlorination. DPH is one of the antiepileptic drugs, which has frequently been detected in the aquatic environment. For chlorination, the second-order rate constant for the reaction between DPH and free active chlorine (FAC) was determined at pH 5 to 8. At pH 6 to 8, the efficiency of chlorination in the removal of DPH was found to be dominated by the reaction involving hypochlorous acid (HOCl). The result also showed that anionic species of DPH was more reactive toward FAC as compared with neutral DPH. For UV/chlorination, the effect of FAC dosage and pH on the degradation of DPH was evaluated. UV/chlorination is a more effective method for removing DPH as compared with conventional chlorination and UV irradiation. The DPH degradation rate was found to increase with increasing FAC concentration. On the other hand, the degradation of DPH was found to be more favorable under the acidic condition. Based on the identified transformation by-products, DPH was found to be degraded through the reaction at imidazolidine-2,4-dione moiety of DPH for both chlorination and UV/chlorination. Toxicity study on the chlorination and UV/chlorination-treated DPH solutions suggested that UV/chlorination is a more efficient method for reducing the toxicity of DPH.
Afficher plus [+] Moins [-]Integrative evaluation of data derived from biomonitoring and models indicating atmospheric deposition of heavy metals Texte intégral
2017
Nickel, Stefan | Schröder, Winfried
Atmospheric deposition of heavy metals (HM) can be determined by use of numeric models, technical devices and biomonitors. Mainly focussing on Germany, this paper aims at evaluating data from deposition modelling and biomonitoring programmes. The model LOTOS-EUROS (LE) yielded data on HM deposition at a spatial resolution of 25 km by 25 km throughout Europe. The European Monitoring and Evaluation Programme (EMEP) provided model calculations on 50 km by 50 km grids. Corresponding data on HM concentration in moss, leaves and needles and soil were derived from the European Moss Survey (EMS), the German Environmental Specimen Bank (ESB) and the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (iCP Forests). The modelled HM deposition and respective concentrations in moss (EMS), leaves and needles (ESB, iCP Forests) and soil (iCP Forests) were investigated for their statistical relationships. Regression equations were applied on geostatistical surface estimations of HM concentration in moss and then the residuals were interpolated by use of kriging interpolation. Both maps were summed up to a map of cadmium (Cd) and lead (Pb) deposition across Germany. Biomonitoring data were strongly correlated to LE than to EMEP. For HM concentrations in moss, the highest correlations were found for the association between geostatistical surface estimations of HM concentration in moss and deposition (LE).
Afficher plus [+] Moins [-]Osmopriming with CaCl2 improves wheat (Triticum aestivum L.) production under water-limited environments Texte intégral
2017
Farooq, Shahid | Hussain, Mubshar | Jabran, Khawar | Hassan, Waseem | Rizwan, Muhammad S. | Yasir, Tauqeer A.
This 2-year field study investigates the potential of seed priming to mitigate losses caused by drought stress at different phenophases of wheat. Wheat seeds were soaked either in distilled water or in aerated solution of CaCl₂ (ψs −1.25 MPa) for 18 h to accomplish hydropriming and osmopriming, respectively. The soil moisture was maintained at 90–100% field capacity (well-watered) or 45–50% field capacity at vegetative (vegetative drought) and reproductive (terminal drought) phases. Allometric traits leaf area index, leaf area duration, and crop growth rate were initially more affected by vegetative drought; however, terminal drought was more severe at later stages. Drought at both phenophases, especially terminal drought, impaired the entire yield-related traits of wheat; however, osmopriming compensated the drought-induced losses up to a certain extent. Osmopriming improved the wheat grain yield, economic benefits, and allometric traits under vegetative and terminal drought as well as well-watered conditions. It is recommended that the physiological, biochemical, and genetic mechanisms of osmopriming must be explored to find more valuable insights for improving wheat productivity.
Afficher plus [+] Moins [-]