Search for: All records

While the defluorination of environmentally persistent poly‐ and perfluoroalkyl substances (PFASs) requires the development of energy‐efficient methodologies for complete mineralization, electrochemical CF bond activation remains a fundamental research challenge. Although CF activation chemistry is commonly studied using fluoromethylarenes as substrates, the stronger CF bonds in short‐chain perfluoroalkyl carboxylic acids (PFCAs), fluorinated aliphatic alcohols, and fluorotelomers are yet to be explored. Herein, we report a molecular copper(I) complex that activates the CF bonds in trifluoroacetic acid (TFA), 2,2,2‐trifluoroethanol (TFE), 2,2‐difluoroethanol (DFE), and 2‐fluoroethanol (MFE) when a constant reductive current of 6 mA is applied. 99% free fluoride was recovered fromMFEafter 12 h of electrolysis, which is comparatively higher than that ofTFE(∼15%),DFE(19.2%), orTFA(∼14%), and is attributable to the strengths of the CF bonds in these molecules. We also defluorinated four selected PFCAs bearing short‐chain CF backbones and terminal trifluoromethyl groups, which are common end products formed by the degradation of toxic perfluoroalkyl substances. In addition, we investigated the defluorination and degradation of two fluorotelomers under ambient conditions. Density functional theory calculations revealed a correlation between the %fluoride recovery and the CF bond dissociation energy of each substrate. Accordingly, we report a rare example of a molecular electrocatalytic system that activates the strong CF bonds in fluoromethylalkyls, including short‐chain PFASs, which are typical end products of common PFAS degradation processes. 

Abstract Electrosynthesis of alkyl carboxylic acids upon activating stronger alkyl chlorides at low‐energy cost is desired in producing carbon‐rich feedstock. Carbon dioxide (CO₂), a greenhouse gas, has been recognized as an ideal primary carbon source for those syntheses, and such events also mitigate the atmospheric CO₂level, which is already alarming. On the other hand, the promising upcycling of polyvinyl chloride to polyacrylate is a high energy‐demanding carbon‐chloride (C−Cl) bond activation process. Molecular catalysts that can efficiently perform such transformation under ambient reaction conditions are rarely known. Herein, we reveal a nickel (Ni)‐pincer complex that catalyzes the electrochemical upgrading of polyvinyl chloride to polyacrylate in 95 % yield. The activities of such a Ni electrocatalyst bearing a redox‐active ligand were also tested to convert diverse examples of unactivated alkyl chlorides to their corresponding carboxylic acid derivatives. Furthermore, electronic structure calculations revealed that CO₂binding occurs in a resting state to yield an η²‐CO₂adduct and that the C−Cl bond activation step is the rate‐determining transition state, which has an activation energy of 19.3 kcal/mol. A combination of electroanalytical methods, control experiments, and computational studies were also carried out to propose the mechanism of the electrochemical C−Cl activation process with the subsequent carboxylation step. 

We study the formation of oil droplets from an initially trapped large oil ganglion under surfactant flooding, using a microfluidic device consisting of a two-dimensional array of regularly spaced square posts. We observe that above a critical capillary number for oil mobilization, breakage of the ganglion results in the formation of either trapped patches spanning multiple pores or numerous mobile droplets that exit the device at a velocity comparable to the average flooding fluid velocity. These mobile droplets, however, are only observed when above a secondary capillary number threshold. The formation of these droplets is found to involve the simultaneous occurrence of three different passive droplet generation mechanisms where a droplet is formed as it is pulled by perpendicular fluid flow, as it is pulled by co-axial fluid flow, and or as it splits due to collision with a post. Our results show that oil breakthroughs only occur when the oil is in the form of mobile drop- lets, suggesting that droplet formation can be an important condition for the mobility of residual oil in porous media. Additionally, this post-array microfluidic device can be used for the production of monodisperse droplets whose size can be controlled by the spacing of the posts. 

Abstract We present Bedmap3, the latest suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60 °S. Bedmap3 incorporates and adds to all post-1950s datasets previously used for Bedmap2, including 84 new aero-geophysical surveys by 15 data providers, an additional 52 million data points and 1.9 million line-kilometres of measurement. These efforts have filled notable gaps including in major mountain ranges and the deep interior of East Antarctica, along West Antarctic coastlines and on the Antarctic Peninsula. Our new Bedmap3/RINGS grounding line similarly consolidates multiple recent mappings into a single, spatially coherent feature. Combined with updated maps of surface topography, ice shelf thickness, rock outcrops and bathymetry, Bedmap3 reveals in much greater detail the subglacial landscape and distribution of Antarctica’s ice, providing new opportunities to interpret continental-scale landscape evolution and to model the past and future evolution of the Antarctic ice sheets. 

Radio-echo sounding (RES) has revealed an internal architecture within both the West and East Antarctic ice sheets that records their depositional, deformational and melting histories. Crucially, RES-imaged internal-reflecting horizons, tied to ice-core age–depth profiles, can be treated as isochrones that record the age–depth structure across the Antarctic ice sheets. These enable the reconstruction of past climate and ice dynamical processes on large scales, which are complementary to but more spatially extensive than commonly used proxy records (e.g. former ice limits constrained by cosmogenic dating or offshore sediment sequences) around Antarctica. We review the progress towards building a pan-Antarctic age–depth model from these data by first introducing the relevant RES datasets that have been acquired across Antarctica over the last 6 decades (focussing specifically on those that detected internal-reflecting horizons) and outlining the processing steps typically undertaken to visualise, trace and date (by intersection with ice cores or modelling) the RES-imaged isochrones. We summarise the scientific applications for which Antarctica's internal architecture has been used to date and present a pathway to expanding Antarctic radiostratigraphy across the continent to provide a benchmark for a wider range of investigations: (1) identification of optimal sites for retrieving new ice-core palaeoclimate records targeting different periods; (2) reconstruction of surface mass balance on millennial or historical timescales; (3) estimation of basal melting and geothermal heat flux from radiostratigraphy and comprehensive mapping of basal-ice units to complement inferences from other geophysical and geological methods; (4) advancement of the knowledge of volcanic activity and fallout across Antarctica; and (5) refinement of numerical models that leverage radiostratigraphy to tune time-varying accumulation, basal melting and ice flow, firstly to reconstruct past behaviour and then to reduce uncertainties in projecting future ice-sheet behaviour.