Nature, 9 February 2023, VOL 614, ISSUE 7947
《自然》2023年2月9日，第614卷，7947期
天文学Astronomy
A dense ring of the trans-Neptunian object Quaoar outside its Roche limit
跨海王星天体创神星的致密环超越罗氏极限
▲ 作者：B. E. Morgado, B. Sicardy, F. Braga-Ribas, J. L. Ortiz, H. Salo, F. Vachier, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-05629-6
▲ 摘要：
人们观测到不仅巨型行星周围存在行星环，小天体周围也存在，如半人马座Chariklo小行星和矮行星妊神星。到目前为止，所有已知的致密环都位于离母星足够近的地方，处于罗氏极限内，即潮汐力阻止了具有合理密度的物质聚集成卫星。
研究组报道了在跨海王星天体（50000）创神星周围观测到一个不均匀环。创神星的估计半径为555千米，拥有一颗大约80千米半径的卫星（创卫一），其轨道半径为24创神星。探测到的环轨道距离中心体7.4倍半径，这远远超出了创神星的经典罗氏极限，因此表明罗氏极限并不能决定环物质的位置。
研究组的局部碰撞模拟表明，基于实验室实验的弹性碰撞可保持一个远离中心体的环。此外，创神星的环轨道接近创神星的1/3自旋轨道共振，这是Chariklo小行星环和妊神星环的共同特性，表明这种共振在小天体的环约束中起着关键作用。
▲ Abstract：
Planetary rings are observed not only around giant planets, but also around small bodies such as the Centaur Chariklo and the dwarf planet Haumea. Up to now, all known dense rings were located close enough to their parent bodies, being inside the Roche limit, where tidal forces prevent material with reasonable densities from aggregating into a satellite. Here we report observations of an inhomogeneous ring around the trans-Neptunian body (50000) Quaoar. This trans-Neptunian object has an estimated radius of 555 km and possesses a roughly 80-km satellite (Weywot) that orbits at 24 Quaoar radii. The detected ring orbits at 7.4 radii from the central body, which is well outside Quaoar’s classical Roche limit, thus indicating that this limit does not always determine where ring material can survive. Our local collisional simulations show that elastic collisions, based on laboratory experiments, can maintain a ring far away from the body. Moreover, Quaoar’s ring orbits close to the 1/3 spin–orbit resonance with Quaoar, a property shared by Chariklo’s and Haumea’s rings, suggesting that this resonance plays a key role in ring confinement for small bodies.
物理学Physics
Coherent correlation imaging for resolving fluctuating states of matter
用于分辨物质涨落状态的相干相关成像
▲ 作者：Christopher Klose, Felix Büttner, Wen Hu, Claudio Mazzoli, Kai Litzius, Riccardo Battistelli, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-05537-9
▲ 摘要：
涨落和随机跃迁在纳米尺度系统中普遍存在，特别是存在无序的情况下。然而，到目前为止，其直接观测仍受制于空间和时间分辨率之间看似基本但信号有限的权衡。
研究组开发了相干相关成像（CCI）来克服这一困境。该方法首先在傅里叶空间中对记录的相机帧进行分类。对比度和空间分辨率通过对相同状态的帧进行选择性平均而产生。通过将基于相关性的相似性度量与改进的迭代分层聚类算法相结合，实现了低至单帧采集时间的时间分辨率，独立于异常低的误分率。
研究组应用CCI来研究具有纳米尺度分辨率的高度简并磁条畴态下此前无法获知的磁涨落，并揭示了30多个离散态之间的复杂转换网络。该时空数据重建了钉扎能量景观，从而在微观水平上解释观察到的动力学。
CCI极大地扩展了新兴高相干X射线源的潜力，并为解决重大基本问题铺平了道路，例如相变中钉扎和拓扑的贡献以及高温超导中自旋和电荷有序涨落的作用等。
▲ Abstract：
Fluctuations and stochastic transitions are ubiquitous in nanometre-scale systems, especially in the presence of disorder. However, their direct observation has so far been impeded by a seemingly fundamental, signal-limited compromise between spatial and temporal resolution. Here we develop coherent correlation imaging (CCI) to overcome this dilemma. Our method begins by classifying recorded camera frames in Fourier space. Contrast and spatial resolution emerge by averaging selectively over same-state frames. Temporal resolution down to the acquisition time of a single frame arises independently from an exceptionally low misclassification rate, which we achieve by combining a correlation-based similarity metric with a modified, iterative hierarchical clustering algorithm. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state with nanometre-scale resolution. We uncover an intricate network of transitions between more than 30 discrete states. Our spatiotemporal data enable us to reconstruct the pinning energy landscape and to thereby explain the dynamics observed on a microscopic level. CCI massively expands the potential of emerging high-coherence X-ray sources and paves the way for addressing large fundamental questions such as the contribution of pinning and topology in phase transitions and the role of spin and charge order fluctuations in high-temperature superconductivity.
材料科学Materials Science
Water splitting with silicon p–i–n superlattices suspended in solution
悬浮在溶液中的硅p-i-n超晶格的水裂解
▲ 作者：Taylor S. Teitsworth, David J. Hill, Samantha R. Litvin, Earl T. Ritchie, Jin-Sung Park, James P. Custer Jr, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-05549-5
▲ 摘要：
光电化学（PEC）水裂解法生产氢燃料在50年前首次报道，但人工光合作用尚未成为一项广泛应用的技术。尽管平面硅太阳能电池已成为一种普遍存在的电能来源，在经济上可与化石燃料相媲美，但尚未实现类似的PEC器件，且标准的硅p型/n型（p-n）结不能用于水裂解，因为带隙阻碍了所需光电压的产生。
另一种范例是粒子悬浮反应器（PSR），放弃了刚性设计，而倾向于将单个PEC颗粒悬浮在溶液中，与平面系统相比，这是一种潜在的低成本选择。研究组通过合成高光电压多结硅纳米线（SiNWs）制备了硅基PSR，可协同功能化催化裂解水。
通过在单个SiNW中编码p型-本征-n型（p-i-n）超晶格，在1倍太阳光照下观察到超过10 V的可调光电压。析氧和析氢共催化剂的空间选择性光电沉积使水在高达约1050 nm的红外波长下裂解，亚波长直径SiNW的光子特性决定了制氢的效率和光谱依赖性。
尽管初始能量转换效率仍较低，但多结SiNW为PSR设计带来了可调谐介观几何结构的光子优势和硅的材料优势（包括小带隙和规模经济），为水裂解反应器提供了一种新策略。
▲ Abstract：
Photoelectrochemical (PEC) water splitting to produce hydrogen fuel was first reported 50 years ago, yet artificial photosynthesis has not become a widespread technology. Although planar Si solar cells have become a ubiquitous electrical energy source economically competitive with fossil fuels, analogous PEC devices have not been realized, and standard Si p-type/n-type (p–n) junctions cannot be used for water splitting because the bandgap precludes the generation of the needed photovoltage. An alternative paradigm, the particle suspension reactor (PSR), forgoes the rigid design in favour of individual PEC particles suspended in solution, a potentially low-cost option compared with planar systems. Here we report Si-based PSRs by synthesizing high-photovoltage multijunction Si nanowires (SiNWs) that are co-functionalized to catalytically split water. By encoding a p-type–intrinsic–n-type (p–i–n) superlattice within single SiNWs, tunable photovoltages exceeding 10 V were observed under 1 sun illumination. Spatioselective photoelectrodeposition of oxygen and hydrogen evolution co-catalysts enabled water splitting at infrared wavelengths up to approximately 1,050 nm, with the efficiency and spectral dependence of hydrogen generation dictated by the photonic characteristics of the sub-wavelength-diameter SiNWs. Although initial energy conversion efficiencies are low, multijunction SiNWs bring the photonic advantages of a tunable, mesoscale geometry and the material advantages of Si—including the small bandgap and economies of scale—to the PSR design, providing a new approach for water-splitting reactors.
Operando studies reveal active Cu nanograins for CO2 electroreduction
原位研究揭示活性铜纳米晶界助力CO2电还原
▲ 作者：Yao Yang, Sheena Louisia, Sunmoon Yu, Jianbo Jin, Inwhan Roh, Chubai Chen, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-05540-0
▲ 摘要：
二氧化碳电还原有助于燃料和化学品的可持续合成。虽然Cu能使CO2转化为多碳产物（C2+），但在操作条件下活性位点的性质仍不明确。重要的是，确定高性能铜纳米催化剂的活性位点需要纳米级、时间分辨的原位表征技术。
研究组对铜纳米催化剂生命周期中的结构动力学进行了全面的研究。7 nm的Cu纳米颗粒簇在电解后空气暴露后、完全氧化为单晶Cu2O纳米立方体之前的电解过程中，演化为金属Cu纳米晶界。
原位分析和四维电化学液体电池扫描透射电子显微镜显示，在CO2还原条件下存在金属Cu纳米晶界。相关的高能分辨率时间分辨X射线能谱表明，富含纳米晶界的金属Cu支持C-C耦合的低配位活性位点。
定量的结构-活性相关性表明，金属Cu纳米晶界占比越高，C2+选择性越高。7 nm的Cu纳米颗粒簇（整分数活性Cu纳米晶界）的C2+选择性比18 nm的Cu纳米颗粒簇（含1/3活性Cu纳米晶界）高6倍。
多模态原位技术的相关性为人们深入了解电化学条件下纳米催化剂复杂结构演化提供了一个强大的平台。
▲ Abstract：
Carbon dioxide electroreduction facilitates the sustainable synthesis of fuels and chemicals. Although Cu enables CO2-to-multicarbon product (C2+) conversion, the nature of the active sites under operating conditions remains elusive. Importantly, identifying active sites of high-performance Cu nanocatalysts necessitates nanoscale, time-resolved operando techniques. Here, we present a comprehensive investigation of the structural dynamics during the life cycle of Cu nanocatalysts. A 7 nm Cu nanoparticle ensemble evolves into metallic Cu nanograins during electrolysis before complete oxidation to single-crystal Cu2O nanocubes following post-electrolysis air exposure. Operando analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy shows the presence of metallic Cu nanograins under CO2 reduction conditions. Correlated high-energy-resolution time-resolved X-ray spectroscopy suggests that metallic Cu, rich in nanograin boundaries, supports undercoordinated active sites for C–C coupling. Quantitative structure–activity correlation shows that a higher fraction of metallic Cu nanograins leads to higher C2+ selectivity. A 7 nm Cu nanoparticle ensemble, with a unity fraction of active Cu nanograins, exhibits sixfold higher C2+ selectivity than the 18 nm counterpart with one-third of active Cu nanograins. The correlation of multimodal operando techniques serves as a powerful platform to advance our fundamental understanding of the complex structural evolution of nanocatalysts under electrochemical conditions.
化学Chemistry
Electrophotocatalytic oxygenation of multiple adjacent C–H bonds
多个邻位碳氢键的光电催化氧化
▲ 作者：Tao Shen, Yi-Lun Li, Ke-Yin Ye & Tristan H. Lambert
▲ 链接：
https://www.nature.com/articles/s41586-022-05608-x
▲ 摘要：
在复杂小分子中，含氧官能团几乎无处不在。通过选择性地同时氧化相邻C-H键来形成多个C-O键是非常理想的，但这在很大程度上是生物合成的范围。通过合成方法进行多次同时的C-H键氧化反应颇具挑战，特别是因其存在过度氧化的风险。
研究组报道了通过脱氢和氧化对两个或三个相邻C-H键进行选择性氧化，使简单的烷基芳烃或三氟乙酰胺转化为其相应的二或三乙酰氧基酯。该方法通过强效氧化催化剂的重复操作实现这种转化，但条件是有足够的选择性以避免破坏性的过度氧化。
这些反应通过光电催化来实现，这是一种利用光能和电能来促进化学反应的过程。值得注意的是，审慎的酸选择实现了二氧或三氧产物的选择性合成。
▲ Abstract：
Oxygen-containing functional groups are nearly ubiquitous in complex small molecules. The installation of multiple C–O bonds by the concurrent oxygenation of contiguous C–H bonds in a selective fashion would be highly desirable but has largely been the purview of biosynthesis. Multiple, concurrent C–H bond oxygenation reactions by synthetic means presents a challenge, particularly because of the risk of overoxidation. Here we report the selective oxygenation of two or three contiguous C–H bonds by dehydrogenation and oxygenation, enabling the conversion of simple alkylarenes or trifluoroacetamides to their corresponding di- or triacetoxylates. The method achieves such transformations by the repeated operation of a potent oxidative catalyst, but under conditions that are sufficiently selective to avoid destructive overoxidation. These reactions are achieved using electrophotocatalysis, a process that harnesses the energy of both light and electricity to promote chemical reactions. Notably, the judicious choice of acid allows for the selective synthesis of either di- or trioxygenated products.
地球科学Earth Science
Extensive global wetland loss over the past three centuries
过去三个世纪中全球湿地大面积流失
▲ 作者：Etienne Fluet-Chouinard, Benjamin D. Stocker, Zhen Zhang, Avni Malhotra, Joe R. Melton, Benjamin Poulter, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-05572-6
▲ 摘要：
湿地长期以来一直被抽取水供人类使用，严重影响了温室气体通量、防洪、营养循环和生物多样性。尽管如此，全球自然湿地损失的程度仍然非常不确定。
研究组通过将国家和次国家的排水和转换记录与土地使用地图和模拟湿地范围相结合，通过转换为1700~2020年间的七种人类土地用途，重建了湿地损失的空间分布和时间。他们估计，自1700年以来，内陆湿地损失了340（置信区间290~380）万平方千米，主要原因是湿地被转化为耕地。
全球湿地面积的净损失为21%（置信区间为16~23%），低于先前对损失严重地区不成比例地外推数据所得出的结果。湿地损失主要集中在欧洲、美国和中国，并在20世纪中期迅速扩大。
该重建阐明了全球湿地损失的时间和土地使用驱动因素，为指导评估湿地损失对地球系统进程的影响、对剩余湿地的保护规划和湿地恢复点的优先排序提供了一个改进的历史基线。
▲ Abstract：
Wetlands have long been drained for human use, thereby strongly affecting greenhouse gas fluxes, flood control, nutrient cycling and biodiversity. Nevertheless, the global extent of natural wetland loss remains remarkably uncertain. Here, we reconstruct the spatial distribution and timing of wetland loss through conversion to seven human land uses between 1700 and 2020, by combining national and subnational records of drainage and conversion with land-use maps and simulated wetland extents. We estimate that 3.4 million km2 (confidence interval 2.9–3.8) of inland wetlands have been lost since 1700, primarily for conversion to croplands. This net loss of 21% (confidence interval 16–23%) of global wetland area is lower than that suggested previously by extrapolations of data disproportionately from high-loss regions. Wetland loss has been concentrated in Europe, the United States and China, and rapidly expanded during the mid-twentieth century. Our reconstruction elucidates the timing and land-use drivers of global wetland losses, providing an improved historical baseline to guide assessment of wetland loss impact on Earth system processes, conservation planning to protect remaining wetlands and prioritization of sites for wetland restoration.
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