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A field study of colloid transport in surface and subsurface flows
Zhang, Wei,Tang, Xiang-Yu,Xian, Qing-Song,Weisbrod, Noam,Yang, Jae E.,Wang, Hong-Lan Elsevier, etc 2016 Journal of hydrology Vol.542 No.-
<P><B>Abstract</B></P> <P>Colloids have been recognized to enhance the migration of strongly-sorbing contaminants. However, few field investigations have examined combined colloid transport via surface runoff and subsurface flows. In a headwater catchment of the upper Yangtze River, a 6m (L) by 4m (W) sloping (6°) farmland plot was built by cement walls to form no-flow side boundaries. The plot was monitored in the summer of 2014 for the release and transport of natural colloids via surface runoff and subsurface flows (i.e., the interflow from the soil-mudrock interface and fracture flow from the mudrock-sandstone interface) in response to rain events. The water sources of the subsurface flows were apportioned to individual rain events using a two end-member model (i.e., mobile pre-event soil water extracted by a suction-cup sampler <I>vs</I>. rainwater (event water)) based on <I>δ</I> <SUP>18</SUP>O measurements. For rain events with high preceding soil moisture, mobile pre-event soil water was the main contributor (generally >60%) to the fracture flow. The colloid concentration in the surface runoff was 1–2 orders of magnitude higher than that in the subsurface flows. The lowest colloid concentration was found in the subsurface interflow, which was probably the result of pore-scale colloid straining mechanisms. The rainfall intensity and its temporal variation govern the dynamics of the colloid concentrations in both surface runoff and subsurface flows. The duration of the antecedent dry period affected not only the relative contributions of the rainwater and the mobile pre-event soil water to the subsurface flows but also the peak colloid concentration, particularly in the fracture flow. The <10μm fine colloid size fraction accounted for more than 80% of the total suspended particles in the surface runoff, while the colloid size distributions of both the interflow and the fracture flow shifted towards larger diameters. These results highlight the need to avoid the application of strongly-sorbing agrochemicals (e.g., pesticides, phosphorus fertilizers) immediately before rainfall following a long no-rain period because their transport in association with colloids may occur rapidly over long distances via both surface runoff and subsurface flows with rainfall.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Subsurface flow was apportioned into rainwater and mobile pre-event soil water. </LI> <LI> The duration of no-rain period affects peak colloid concentration. </LI> <LI> Rainfall intensity and its temporal variation govern colloid discharge dynamics. </LI> </UL> </P>
Wang, Dong,Zhang, Wei,Drewett, Nicholas E.,Liu, Xiaofei,Yoo, Seung Jo,Lee, Sang-Gil,Kim, Jin-Gyu,Deng, Ting,Zhang, Xiaoyu,Shi, Xiaoyuan,Zheng, Weitao American Chemical Society 2018 ACS central science Vol.4 No.1
<▼1><P/><P>Graphitic carbon anodes have long been used in Li ion batteries due to their combination of attractive properties, such as low cost, high gravimetric energy density, and good rate capability. However, one significant challenge is controlling, and optimizing, the nature and formation of the solid electrolyte interphase (SEI). Here it is demonstrated that carbon coating via chemical vapor deposition (CVD) facilitates high electrochemical performance of carbon anodes. We examine and characterize the substrate/vertical graphene interface (multilayer graphene nanowalls coated onto carbon paper via plasma enhanced CVD), revealing that these low-tortuosity and high-selection graphene nanowalls act as fast Li ion transport channels. Moreover, we determine that the hitherto neglected parallel layer acts as a protective surface at the interface, enhancing the anode performance. In summary, these findings not only clarify the synergistic role of the parallel functional interface when combined with vertical graphene nanowalls but also have facilitated the development of design principles for future high rate, high performance batteries.</P></▼1><▼2><P>We explored an anti-T-shaped graphene surface-coating concept which offers a low-tortuosity, sieve-like interface that may be exploited for optimized Li-based anodes.</P></▼2>