For safer geologic CO2 sequestration (GCS), it is important to understand CO2-brine-cement interactions, which affect wellbore integrity. However, potential effects of sulfate and magnesium ions on cement degradation under GCS conditions are not well understood. Here Class H Portland cement were reacted in brines containing 0.05M sulfate and/or magnesium ions under both GCS (50°C and 100atm CO2) and control (50°C and atmospheric pressure) conditions. Using optical microscopy and scanning electron microscope coupled with energy dispersive spectrometry and electron back scattered electron (SEM-EDS/BSE), slower cement carbonation rates were observed in the presence of sulfate under GCS conditions, because of gypsum precipitation on cement surfaces. Calcite rather than gypsum formed in both the inner layers of cement samples reacted under GCS conditions, and on cement surfaces reacted under atmospheric pressure conditions. Under GCS conditions, the dissolved CO2 lowered the pH of the solution surrounding cement surfaces, thus favoring the formation of gypsum over calcite on cement surfaces; while the high pH condition in pore solution inside cement favors the formation of calcite over gypsum. The presence of magnesium had no significant effect on cement degradation under GCS conditions, as brucite, magnesium carbonates and magnesium calcite did not form, due to the low pH at cement surface and the limited diffusion of Mg into cement inner layers.
AimsTopography has long been recognized as an important factor in shaping species distributions. Many studies revealed that species may show species–habitat associations. However, few studies investigate how species assemblages are associated with local habitats, and it still remains unclear how the community–habitat associations vary with species abundance class and life stage. In this study, we analyzed the community–habitat associations in a subtropical montane forest.MethodsThe fully mapped 25-ha (500×500 m) forest plot is located in Badagongshan Nature Reserve in Hunan Province, Central China. It was divided into 625 (20×20 m) quadrats. Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics. Indicator species analysis was used to identify the most important species for structuring species assemblages. We also compared the community–habitat associations for two levels of species abundances (i.e. abundant and rare) and three different life stages (i.e. saplings, juveniles and adults), while accounting for sample size effects.Important FindingsThe Badagongshan plot was divided into five distinct habitat types, which explained 34.7% of the variance in tree species composition. Even with sample size taken into account, community–habitat associations for rare species were much weaker than those for abundant species. Also when accounting for sample size, very small differences were found in the variance explained by topography for the three life stages. Indicator species of habitat types were mainly abundant species, and nearly all adult stage indicator species were also indicators in juvenile and sapling stages. Our study manifested that topographical habitat filtering was important in shaping overall local species compositions. However, habitat filtering was not important in shaping rare species’ distributions in this forest. The community–habitat association patterns in this forest were mainly shaped by abundant species. In addition, during the transitions from saplings to juveniles, and from juveniles to adults, the relative importance of habitat filtering was very weak.
Anaerobic denitrification has been proved to be negatively affected by ZnO nanomaterials (NPs), but little is known about how ZnO NPs affects aerobic denitrification. In this study, inhibition of ZnO NPs to an aerobic denitrifier, Pseudomonas stutzeri PCN-1, was firstly reported. The results showed total nitrogen removal efficiency was decreased from 100% to 1.70% with the increase of ZnO NPs from 1 to 128 mg/L. The presence of ZnO NPs caused significant inhibition of gene expressions and catalytic activities of nitrate reductase and nitrite reductase, which finally led to delayed nitrate reduction and high nitrite accumulation. Further studies revealed that the deposition of nanoparticles on the bacterial surface caused by electrostatic forces and the generation of reactive oxygen species (ROS) were responsible for the cytotoxicity of ZnO NPs, where ROS played a more important role. These results were of significance to evaluating the potential ecological toxicity and risks of nanomaterials. (C) 2017 Elsevier Ltd. All rights reserved.
A novel Z-scheme AgI/Bi2MoO6 hybrid photocatalyst was fabricated via a solvothermal-precipitation approach to disinfect bacteria in water. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopic (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscope (HRTEM), UV-vis diffuse reflectance spectra (DRS), as well as photoluminescence spectra (PL) were employed to characterize the fabricated photocatalyst. Due to the stronger redox potential and better separation of charge carriers induced by the Z-scheme structure, the optimal synthesized AgI/Bi2MoO6 exhibited excellent disinfection activity towards both Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) under visible light irradiation. 5.0 × 107 CFU mL−1 of E. coli and S. aureus cells were completely disinfected within 30 min and 90 min, respectively. Ag+ ions did not contribute to the disinfection activity, while active species including h+, ·O2−, e-, and H2O2 contributed to the cell inactivation. By changing the interaction force and being involved in the photocatalytic reactions, the common anions (Cl−, NO3−, SO42−, and H2PO4−) would affect the disinfection activity. Moreover, AgI/Bi2MoO6 exhibited effective disinfection activity in four consecutive reused cycles. Thus, AgI/Bi2MoO6 could be used as a promising photocatalyst for water disinfection.
Decabromodiphenyl ether (decaBDE) is a highly brominated flame retardant that recent studies have identified as a potential persistent organic pollutant. Large amounts of decaBDE have been consumed and released in the environment in China, while no emission inventory has been available until now. In this study, a substance flow analysis was applied to establish the emission inventory of decaBDE in China from 1982 (the first year of decaBDE production in China) until 2013 based on activity data, transfer coefficients, and emission factors. The results show that the stock of decaBDE continually increased, reaching a peak of 290,000 tons in 2007. The annual processing capacity of decaBDE also increased, and the processing capacity in 2013 was 49,000 tons. Historical accumulative emissions were estimated to be 313.3 tons from 1982 to 2013, and the annual emissions peaked in 2003 at 27.5 tons. On average, decaBDE processing was the major source (58.4%) of total emissions, followed by treatment, production, and usage processes. From 1982 to 2013, decaBDE was released mainly into water sources, accounting for 50.7% of the accumulative emissions. At the provincial level, Guangdong, Shandong, and Zhejiang provinces were the largest producers in China. Simulations produced by the level III fugacity model showed that the projected concentration was very consistent with the measured value. The stock of decaBDE in the soil and sediment phases accounted for 99.8% of the total stock, and the transfer among the four environmental phases occurred mainly at the atmosphere–soil interface.
Chlorinated paraffins (CPs) are used as flame retardants, plasticizers, and metalworking fluids, which have varying contents of toxic short-chain chlorinated paraffins (SCCPs). Based on the study of several relevant production and consumption sectors, this paper classifies the consumption of CPs among sectors and provides an emission inventory and the provincial emission distribution of SCCPs in China in 2010–2014 based on the consumption patterns and emission factors of each sector. The total emissions of SCCPs in China in 2014 were 3083.88 tons, with emissions to the atmosphere and water accounting for 894.81 tons and 2189.07 tons, respectively. The largest emission source was from metalworking fluids, with total emissions of 2459.12 tons, of which 756.65 tons went to the atmosphere and 1702.47 tons to water. Our results show that SCCP emissions were mainly concentrated in the eastern, more developed regions and that Jiangsu Province was the biggest producer in China, with total emissions of 1853.06 tons, of which 562.61 tons were to the atmosphere and 1290.46 tons to water.
Discrepancies in emission estimates of carbon tetrachloride (CCl 4 , CTC), between bottom-up and top-down methods, have been shown since the 1990s at both the global and regional scale. This study estimates the emissions of China from 1992 to 2014 based on emission functions and aggregated activity information given reasonable uncertainties. The results show that emissions increase from 7.3Gg/yr (5.6–9.1Gg/yr at 95% confidential interval) to 14.0 (9.1–19.5) Gg/yr with a growth rate of 6.7 (1.9–11.4) %/yr during 1992–2002 and then decrease to a minimum of 4.3 (1.9–8.0) Gg/yr in 2011. More than 54% of the emissions during 1992–2009 are from the process agents sector. The estimates are comparable with those of other studies and those in this study based on observations during 2011–2014 using the interspecies correlation method. China's contribution to global emissions increases from 7.5% to 19.5% during 1992–2009, but the contribution is reduced to 9.9% and 8.0% in 2010 and 2011, respectively, indicating the effectiveness of compliance with the Montreal Protocol and its subsequent Amendments and Adjustments, whereby CTC emissions are phased-out. The results of this study are beneficial for narrowing the gap between bottom-up estimates and top-down emission calculations of CTC in China.
In order to apply classical micromechanics in predicting the effective prop-erties of nanocomposites incorporating interface energy, a concept of equivalent inclusion (EI) is usually adopted. The properties of EI are obtained by embedding a single inclusion with the interface into an infinite matrix. However, whether such an EI is universal for different micromechanics-based methods is rarely discussed in the literature. In this pa-per, the interface energy theory is used to study the applicability of the above mentioned EI. It is found that some elastic properties of the EI are related only to the properties of the inclusion and the interface, whereas others are also related to the properties of the matrix. The former properties of the EI can be applied to both the classical Mori-Tanaka method (MTM) and the generalized self-consistent method (GSCM). However, the latter can be applied only to the MTM. Two kinds of new EIs are proposed for the GSCM and used to estimate the effective mechanical properties of nanocomposites.
In order to apply classical micromechanics in predicting the effective prop-erties of nanocomposites incorporating interface energy, a concept of equivalent inclusion (EI) is usually adopted. The properties of EI are obtained by embedding a single inclusion with the interface into an infinite matrix. However, whether such an EI is universal for different micromechanics-based methods is rarely discussed in the literature. In this pa-per, the interface energy theory is used to study the applicability of the above mentioned EI. It is found that some elastic properties of the EI are related only to the properties of the inclusion and the interface, whereas others are also related to the properties of the matrix. The former properties of the EI can be applied to both the classical Mori-Tanaka method (MTM) and the generalized self-consistent method (GSCM). However, the latter can be applied only to the MTM. Two kinds of new EIs are proposed for the GSCM and used to estimate the effective mechanical properties of nanocomposites.