| 4171. |
- Li, Zhe, 1987-, et al.
(författare)
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A strategic screening approach to identify transformation products of organic micropollutants along rivers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Many transformation products (TPs) from organic micropollutants are not included in routine monitoring programs due to limited knowledge of their occurrence and fate. An efficient method to identify and prioritize critical compounds in terms of environmental relevance is needed. In this study we applied a strategic screening approach based on a case-control concept to identify TPs with an increasing trend along a stretch in four wastewater-impacted rivers. Time-integrated samples were taken over one week at both ends of a river stretch downstream of a wastewater treatment plant (WWTP) outfall. The screening procedure consisted of three major steps: i) screening for parent compounds (PCs) attenuating along the stretch; ii) prediction of TPs for these PCs; and iii) screening for TPs with an increasing trend along the stretch. In total, 48 organic micropollutants were tentatively identified, of which 32 were decreasing along the stretches. From these PCs, 1315 TPs were predicted and eight out of which were tentatively identified with increasing concentrations along the stretches. Generally, good correlations were observed between the suspect screening results from this study and previous target analysis results on the same samples, suggesting high confidence of our screening approach. The case-control concept was proven efficient and reliable for identifying environmental relevant TPs formed along rivers.
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| 4172. |
- Li, Zhe, et al.
(författare)
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A strategic screening approach to identify transformation products of organic micropollutants formed in natural waters
- 2017
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2050-7887 .- 2050-7895. ; 19:4, s. 488-498
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Tidskriftsartikel (refereegranskat)abstract
- Many transformation products (TPs) from organic micropollutants are not included in routine environmental monitoring programs due to limited knowledge of their occurrence and fate. An efficient method to identify and prioritize critical compounds in terms of environmental relevance is needed. In this study, we applied a strategic screening approach based on a case-control concept to identify TPs formed along wastewater-impacted rivers. Time-integrated samples were collected over one week at both ends of a river stretch downstream of a wastewater treatment plant (WWTP) outfall and were analyzed by ultrahigh performance liquid chromatography interfaced with quadrupole time-of-flight mass spectrometry (UHPLC-QToF-MS/MS). The screening procedure of the high-resolution MS (HRMS) datasets consisted of three major steps: (i) screening for parent compounds (PCs) attenuated along the stretch; (ii) prediction of potential TPs from these PCs; and (iii) screening for TPs from this list with an increasing trend along the stretch. In total, 32 PCs decreased along the investigated river stretches. From these PCs, eight TPs had increasing concentrations along the studied stretches and could be tentatively identified. The identification of one TP (benzamide) was confirmed by its corresponding reference standard, while no standards were available for the remaining TPs.
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| 4173. |
- Li, Zhenglun, et al.
(författare)
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Catalysis with Cuii(bpy) improves alkaline hydrogen peroxide pretreatment
- 2013
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 110:4, s. 1078-1086
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Tidskriftsartikel (refereegranskat)abstract
- Copper(II) 2,2′-bipyridine (CuII(bpy))-catalyzed alkaline hydrogen peroxide (AHP) pretreatment was performed on three biomass feedstocks including alkali pre-extracted switchgrass, silver birch, and a hybrid poplar cultivar. This catalytic approach was found to improve the subsequent enzymatic hydrolysis of plant cell wall polysaccharides to monosaccharides for all biomass types at alkaline pH relative to uncatalyzed pretreatment. The hybrid poplar exhibited the most significant improvement in enzymatic hydrolysis with monomeric sugar release and conversions more than doubling from 30% to 61% glucan conversion, while lignin solubilization was increased from 36.6% to 50.2% and hemicellulose solubilization was increased from 14.9% to 32.7%. It was found that CuII(bpy)-catalyzed AHP pretreatment of cellulose resulted in significantly more depolymerization than uncatalyzed AHP pretreatment (78.4% vs. 49.4% decrease in estimated degree of polymerization) and that carboxyl content the cellulose was significantly increased as well (fivefold increase vs. twofold increase). Together, these results indicate that CuII(bpy)-catalyzed AHP pretreatment represents a promising route to biomass deconstruction for bioenergy applications
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| 4174. |
- Li, Zhenglun, et al.
(författare)
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Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar
- 2015
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Alkaline hydrogen peroxide pretreatment catalyzed by Cu(II) 2,2′-bipyridine complexes has previously been determined to substantially improve the enzymatic hydrolysis of woody plants including hybrid poplar as a consequence of moderate delignification. In the present work, cell wall morphological and lignin structural changes were characterized for this pretreatment approach to gain insights into pretreatment outcomes and, specifically, to identify the extent and nature of lignin modification. Results: Through TEM imaging, this catalytic oxidation process was shown to disrupt cell wall layers in hybrid poplar. Cu-containing nanoparticles, primarily in the Cu(I) oxidation state, co-localized with the disrupted regions, providing indirect evidence of catalytic activity whereby soluble Cu(II) complexes are reduced and precipitated during pretreatment. The concentration of alkali-soluble polymeric and oligomeric lignin was substantially higher for the Cu-catalyzed oxidative pretreatment. This alkali-soluble lignin content increased with time during the catalytic oxidation process, although the molecular weight distributions were unaltered. Yields of aromatic monomers (including phenolic acids and aldehydes) were found to be less than 0.2 % (wt/wt) on lignin. Oxidation of the benzylic alcohol in the lignin side-chain was evident in NMR spectra of the solubilized lignin, whereas minimal changes were observed for the pretreatment-insoluble lignin. Conclusions: These results provide indirect evidence for catalytic activity within the cell wall. The low yields of lignin-derived aromatic monomers, together with the detailed characterization of the pretreatment-soluble and pretreatment-insoluble lignins, indicate that the majority of both lignin pools remained relatively unmodified. As such, the lignins resulting from this process retain features closely resembling native lignins and may, therefore, be amenable to subsequent valorization.
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| 4175. |
- Li, Zhicheng, et al.
(författare)
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Growth and morphology of beta phase in an Mg-Y-Nd alloy
- 2004
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Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 58:24, s. 3021-3024
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Tidskriftsartikel (refereegranskat)abstract
- The phase precipitated in an Mg-Y-Nd alloy during ageing was studied using electron microscopy. Observations were performed along the orientations paralleling to [0001] and [11 (2) over bar0] zone axes of the matrix. The results showed that the platelike p phase has three variants growing along three <1120> directions of the matrix, the beta phase grew faster along <0001>(alpha) and <1120>(alpha) directions than along the third direction (<1 (1) over bar 00>). The morphology of the beta phases was illustrated according to the analysis of the directional misfit between the beta phase and the matrix.
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| 4176. |
- Li, Zhongqiang, et al.
(författare)
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Heat Waves Alter Macrophyte-Derived Detrital Nutrients Release under Future Climate Warming Scenarios
- 2021
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55:8, s. 5272-5281
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Tidskriftsartikel (refereegranskat)abstract
- In addition to a rise in global air and water mean temperatures, extreme climate events such as heat waves are increasing in frequency, intensity, and duration in many regions of the globe. Developing a mechanistic understanding of the impacts of heat waves on key ecosystem processes and how they differ from just an increase in mean temperatures is therefore of utmost importance for adaptive management against effects of global change. However, little is known about the impact of extreme events on freshwater ecosystem processes, particularly the decomposition of macrophyte detritus. We performed a mesocosm experiment to evaluate the impact of warming and heat waves on macrophyte detrital decomposition, applied as a fixed increment (+4 °C) above ambient and a fluctuating treatment with similar energy input, ranging from 0 to 6 °C above ambient (i.e., simulating heat waves). We showed that both warming and heat waves significantly accelerate dry mass loss of the detritus and carbon (C) release but found no significant differences between the two heated treatments on the effects on detritus dry mass loss and C release amount. This suggests that moderate warming indirectly enhanced macrophyte detritus dry mass loss and C release mainly by the amount of energy input rather than by the way in which warming was provided (i.e., by a fixed increment or in heat waves). However, we found significantly different amounts of nitrogen (N) and phosphorus (P) released between the two warming treatments, and there was an asymmetric response of N and P release patterns to the two warming treatments, possibly due to species-specific responses of decomposers to short-term temperature fluctuations and litter quality. Our results conclude that future climate scenarios can significantly accelerate organic matter decomposition and C, N, and P release from decaying macrophytes, and more importantly, there are asymmetric alterations in macrophyte-derived detrital N and P release dynamic. Therefore, future climate change scenarios could lead to alterations in N/P ratios in the water column via macrophyte decomposition processes and ultimately affect the structure and function of aquatic ecosystems, especially in the plankton community.
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| 4177. |
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| 4178. |
- Li, Z. L., et al.
(författare)
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Effect of the electronic dimensionality of electrodes on the current-voltage characteristics of single molecular devices
- 2004
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Ingår i: Wuli xuebao. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 53:5, s. 1490-1495
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Tidskriftsartikel (refereegranskat)abstract
- The electrodes can be constructed by different dimensionality of electronic systems in energy representation when the current through the molecular junction is measured. Basing on the elastic scattering Green function theory, we have developed the theoretical methods for studying the electronic transport properties of molecular junctions and paid attention to the influence of the dimensionality of electrodes. The alpha, alpha'-xylyl dithiol molecule is taken as an example and its current-voltage characteristics have been investigated for electrodes with different-dimension electronic systems. The numerical results show that dimensionality of metal contacts has strong effect on the current-voltage characteristics of molecular junction, in particular the shape of the conductance curves.
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| 4179. |
- Li, Z. -L, et al.
(författare)
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Effects of electrode distances on geometric structure and electronic transport properties of molecular 4,4'-bipyridine junction
- 2006
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 29:1, s. 110-114
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Tidskriftsartikel (refereegranskat)abstract
- Influences of electrode distances on geometric structure of molecule and on electronic transport properties of molecular junctions have been investigated by means of a generalized quantum chemical approach based on the elastic scattering Green's function method. Numerical results show that, for organic molecule 4,4'-bipyridine, the geometric structure of the molecule especially the dihedral angle between the two pyridine rings is sensitive to the distances between the two electrodes. The currents of the molecular junction are taken nonlinearly increase with the increase of the bias. Shortening the distance of the metallic electrodes will result in stronger coupling and larger conductance.
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| 4180. |
- Li, Z. L., et al.
(författare)
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Electronic transport properties of molecular bipyridine junctions : Effects of isomer and contact structures
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:7
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Tidskriftsartikel (refereegranskat)abstract
- The effects of contact structures and isomers on the current-voltage characteristics of molecular bipyridine junctions have been investigated by means of a generalized quantum chemical approach based on the elastic scattering Green's function method. For the four isomers 4,4'-bipyridine, 2,2'-bipyridine, 2,4'-bipyridine, and 2,6'-bipyridine under investigation, the 2,4'- bipyridine junction is found to be the poorest conductor owing to its nonsymmetrical arrangement. Numerical simulations of the 4,4'-bipyridine junction show that the contact structures between molecule and metallic electrodes have a noticeable effect on the electron transport characteristics of molecular junctions. The shortening of the distance between two metallic electrodes results in a stronger coupling and lower potential barrier between them, leading to larger conductance. The external electric fields cause the charge redistribution within molecule and lead to the presence of resistivity dipoles at the molecule-metal interface, and the bias voltages are mainly dropped there. The nonlinear charge transport effect on the current and conductance of 4,4'-bipyridine molecular junctions at the lower-bias region is presented. The experimental measurement has been reproduced by the theoretical calculations for a well-defined structure.
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