查看更多>>摘要：Developing new approaches to fulfill the enantioseparation of nanocluster racemates and construct cluster-based nanomaterials with optical activity remains highly desired in cluster science,because it is an essential prerequisite for fundamental research and extensive applications of these nanomaterials.We herein propose a strategy termed"active-site exposing and partly re-protecting"to trigger the symmetry breaking of highly symmetrical nan-oclusters and to render cluster crystals optically active.The vertex PPh3 of the symmetrical Ag29(SSR)12(PPh3)4(SSR=1,3-benzenedithiol)nanocluster was firstly dissociated in the presence of counterions with large steric hindrance,and then the exposed Ag active sites of the obtained Ag29(SSR)12 nanocluster were partly re-protected by Ag+,yielding an Ag29(SSR)12-Ag2 nanocluster with a symmetry-breaking construction.Ag29(SSR)12-Ag2 fol-lowed a chiral crystallization mode,and its crystal displayed strong optical activity,derived from CD and CPL characterizations.Overall,this work presents a new approach(i.e.,active-site exposing and partly re-protecting)for the symmetry breaking of highly symmetrical nanoclusters,the enantioseparation of nanocluster racemates,and the achievement of highly optical activity.
查看更多>>摘要：The electrochemical oxidation of biomass molecules coupling with hydrogen production is a promising strat-egy to obtain both green energy and value-added chemicals;however,this strategy is limited by the compet-ing oxygen evolution reactions and high energy consumption.Herein,we report a hierarchical CoNi layered double hydroxides(LDHs)electrocatalyst with abundant Ni vacancies for the efficient anodic oxidation of 5-hydroxymethylfurfural(HMF)and cathodic hydrogen evolution.The unique hierarchical nanosheet structure and Ni vacancies provide outstanding activity and selectivity toward several biomass molecules because of the finely regulated electronic structure and highly-exposed active sites.In particular,a high faradaic efficiency(FE)at a high current density(99％at 100 mA cm-2)is achieved for HMF oxidation,and a two-electrode electrolyzer is assembled based on the Ni vacancies-enriched LDH,which realized a continuous synthesis of highly-pure 2,5-furandicarboxylic acid products with high yields(95％)and FE(90％).
查看更多>>摘要：The development of stereodivergent synthetic methods to access all four stereoisomers of biologically impor-tant α-fluoro γ-butyrolactones containing vicinal stereocenters is of great importance and poses a formidable challenge owing to ring strain and steric hindrance.Herein,a novel asymmetric[3+2]annulation of α-fluoro α-azaaryl acetates with vinylethylene carbonate was successfully developed through Cu/Ir-catalyzed cascade allylic alkylation/lactonization,affording a variety of enantioenriched α-fluoro γ-butyrolactones bearing vicinal stere-ogenic centers with high reaction efficiency and excellent levels of both stereoselectivity and regioselectivity(up to 98％yield,generally＞20∶1 dr and＞99％ee).Notably,all four stereoisomers of these pharmaceutically valu-able molecules could be accessed individually via simple permutations of two enantiomeric catalysts.In addition,other azaaryl acetates bearing α-methyl,α-chlorine or α-phenyl group were tolerated well in this transformation.Reaction mechanistic investigations were conducted to explore the process of this bimetallic catalysis based on the results of reaction intermediates,isotopic labelling experiments,and kinetic studies.
查看更多>>摘要：Despite its existence for more than 80 years,the titanium industry is still challenged by massive carbon emis-sions,high production costs,and large resource waste.More than one hundred million tons of Ti-bearing blast furnace slag(TB-slag)has been discarded in China because of the difficulty of reutilization,which requires ef-ficient titanium extraction and recovery technologies.This paper describes a low-cost,carbon-emission-free method for Ti extraction and oxygen evolution via molten oxide electrolysis(MOE)vacuum distillation.After a comprehensive analysis of the binding energies and activities of liquid metals,the highlights of our study are as follows.1)Sb has the best preferential deposition of Ti among a series of high-Ti-affinitive liquid metal cathodes(Cu,Ni,Pb,Sn,and Sb).2)The Ir anode was first used in TB-slag with IrO2 formed on its surface to protect it from further corrosion.3)An alloy containing Ti and Ca can be obtained by MOE,and Ti and Ca metals can be refined by further vacuum distillation.4)A closed loop is formed in the overall process owing to the recyclable Sb cathode and continuous feeding of TB-slag into the electrolyte.This simple,low-cost,and environmentally friendly method can realize the efficient utilization of Ti resources and achieve carbon neutrality.
查看更多>>摘要：Iconic memory and short-term memory are not only crucial for perception and cognition,but also of great im-portance to mental health.Here,we first showed that both types of memory could be improved by improving limiting processes in visual processing through perceptual learning.Normal adults were trained in a contrast detection task for ten days,with their higher-order aberrations(HOA)corrected in real-time.We found that the training improved not only their contrast sensitivity function(CSF),but also their iconic memory and baseline information maintenance for short-term memory,and the relationship between memory and CSF improvements could be well-predicted by an observer model.These results suggest that training the limiting component of a cognitive task with visual perceptual learning could improve visual cognition.They may also provide an empirical foundation for new therapies to treat people with poor sensory memory.
查看更多>>摘要：Oceanic uptake and storage of anthropogenic CO2(CANT)are regulated by ocean circulation and ventilation.To decipher the storage and redistribution of CANT in the western North Pacific,where a major CANT sink develops,we investigated the water column carbonate system,dissolved inorganic radiocarbon and ancillary parameters in May and August 2018,spanning the Kuroshio Extension(KE,35-39 °N),Kuroshio Recirculation(KR,27-35 °N)and subtropical(21-27 °N)zones.Water column CANT inventories were estimated to be 40.5±1.1 mol m-2 in the KR zone and 37.2±0.9 mol m-2 in the subtropical zone.In comparison with historical data obtained in 2005,relatively high rates of increase of the CANT inventory of 1.05±0.20 and 1.03±0.12 mol m-2 yr-1 in the recent decade were obtained in the KR and subtropical zones,respectively.Our water-mass-based analyses suggest that formation and transport of subtropical mode water dominate the deep penetration,storage,and redistribution of CANT in those two regions.In the KE zone,however,both the water column CANT inventory and the decadal CANT accumulation rate were small and uncertain owing to the dynamic hydrology,where the naturally uplifting isopycnal surfaces make CANT penetration relatively shallow.The findings of this study improve the understanding of the spatiotemporal variations of CANT distribution,storage,and transport in the western North Pacific.
查看更多>>摘要：Charcoal is commonly preserved in both natural and artificial sediments,and is intensively used in paleonto-logical,paleoenvironmental,and archaeological studies due to the abundant bio-information it contains.The biochemical properties of charcoal are also used for paleoclimatic reconstruction;however,the reliability of this approach has been challenged due to a lack of clarity on how physicochemical properties change during the charring process,as well as the temperatures required for charcoalification.To address this lack,in this study,Qinghai spruce and Chinese pine wood samples from the northeastern Tibetan Plateau were heated at different temperatures and for different lengths of time under restricted oxygen conditions.The reflectance;carbon,nitro-gen,and oxygen content;and tracheid morphology were quantified before and after heating to assess changes related to the charring process.Archaeological charcoal remains were then evaluated to determine the char-coalification temperatures by comparing with the experimental results.The minimum temperature required for wood charcoalification was～300 ℃,while temperatures recorded by archaeological charcoal were concentrated at 400-500 ℃.During the charring experiments,the tracheid cell walls gradually homogenized,and tracheid cell wall thickness and lumen area decreased by～20％.On average,50％mass losses were observed;the car-bon and oxygen content(％wt.)approximately changed from 47％to 60％and 48％to 35％respectively,while the nitrogen content(％wt.)fluctuated around 0.2％.The reflectance increased slightly from 0％to 0.5％.We propose that the charcoalification of wood tissue refers to charring(in restricted air)and carbonization(in the almost absence of air)when the wood is exposed to a heat source,which then finally transforms into a black,inert solid.This quantitative study provided valuable data and a thorough assessment of the process of wood charcoalification,as well as accurately estimated the feasibility of using charcoal physicochemical properties in paleoclimatic research.
查看更多>>摘要：The most important optical component in an optical fiber endoscope is its objective lens.To achieve a high imaging performance level,the development of an ultra-compact objective lens is thus the key to an ultra-thin optical fiber endoscope.In this work,we use femtosecond laser 3D printing to develop a series of micro objective lenses with different optical designs.The imaging resolution and field-of-view performances of these printed micro objective lenses are investigated via both simulations and experiments.For the first time,multiple micro objective lenses with different fields of view are printed on the end face of a single imaging optical fiber,thus realizing the perfect integration of an optical fiber and objective lenses.This work demonstrates the considerable potential of femtosecond laser 3D printing in the fabrication of micro-optical systems and provides a reliable solution for the development of an ultrathin fiber endoscope.
查看更多>>摘要：Solar-driven CO2-to-fuel conversion assisted by another major greenhouse gas CH4 is promising to concurrently tackle energy shortage and global warming problems.However,current techniques still suffer from drawbacks of low efficiency,poor stability,and low selectivity.Here,a novel nanocomposite composed of interconnected Ni/MgAlOx nanoflakes grown on SiO2 particles with excellent spatial confinement of active sites is proposed for direct solar-driven CO2-to-fuel conversion.An ultrahigh light-to-fuel efficiency up to 35.7％,high production rates of H2(136.6 mmol min-1g-1)and CO(148.2 mmol min-1g-1),excellent selectivity(H2/CO ratio of 0.92),and good stability are reported simultaneously.These outstanding performances are attributed to strong metal-support interactions,improved CO2 absorption and activation,and decreased apparent activation energy under direct light illumination.MgAlOx@SiO2 support helps to lower the activation energy of CH*oxidation to CHO*and improve the dissociation of CH4 to CH3*as confirmed by DFT calculations.Moreover,the lattice oxygen of MgAlOx participates in the reaction and contributes to the removal of carbon deposition.This work provides promising routes for the conversion of greenhouse gasses into industrially valuable syngas with high efficiency,high selectivity,and benign sustainability.
查看更多>>摘要：Stretchable power sources,especially stretchable lithium-ion batteries(LIBs),have attracted increasing atten-tion due to their enormous prospects for powering flexible/wearable electronics.Despite recent advances,it is still challenging to develop ultra-stretchable LIBs that can withstand large deformation.In particular,stretch-able LIBs require an elastic electrolyte as a basic component,while the conductivity of most elastic electrolytes drops sharply during deformation,especially during large deformations.This is why highly stretchable LIBs have not yet been realized until now.As a proof of concept,a super-stretchable LIB with strain up to 1200％is created based on an intrinsically super-stretchable polymer electrolyte as the lithium-ion conductor.The super-stretchable conductive system is constructed by an effective diblock copolymerization strategy via photocuring of vinyl functionalized 2-ureido-4-pyrimidone(VFUpy),an acrylic monomer containing succinonitrile and a lithium salt,achieving high ionic conductivity(3.5 x 10-4 mS cm-1 at room temperature(RT))and large deformation(the strain can reach 4560％).The acrylic elastomer containing Li-ion conductive domains can strongly increase the compatibility between the neighboring elastic networks,resulting in high ionic conductivity under ultra-large deformation,while VFUpy increases elasticity modulus(over three times)and electrochemical stability(voltage window reaches 5.3 V)of the prepared polymer conductor.At a strain of up to 1200％,the resulting stretchable LIBs are still sufficient to power LEDs.This study sheds light on the design and development of high-performance intrinsically super-stretchable materials for the advancement of highly elastic energy storage devices for powering flexible/wearable electronics that can endure large deformation.
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