Ionic strength directed self-assembled polyelectrolyte single-bilayer membrane for low-pressure nanofiltration

Layer-by-layer assembly is a versatile technique for fabricating nanofiltration membranes, where multiple layers of polyelectrolytes are usually required to achieve reasonable separation performance. In this work, an ionic strength directed self-assembly procedure is described for the preparation of nanofiltration membranes consisting of only a single bilayer of poly(diallyldimethylammoniumchloride) and poly(sodium-4-styrenesulfoate). The influence of background ionic strength as well as membrane substrate properties on the formation of single-bilayer membranes are systematically evaluated. Such a simplified polyelectrolyte deposition procedure results in membranes having outstanding separation performance with permeating flux of 14.2 ± 1.5 L∙m^–2∙h^–1∙bar^–1 and Na₂SO₄ rejection of 97.1% ± 0.8% under a low applied pressure of 1 bar. These results surpass the ones for conventional multilayered polyelectrolyte membranes. This work encompasses an investigation of ionic strength induced coiling of the polyelectrolyte chains and emphasizes the interplay between-polyelectrolyte chain configuration and substrate pore profile. It thus introduces a new concept on the control of membrane fabrication process toward high performance nanofiltration.     

Understanding the Composition of Layer-by-Layer Deposited Active Layer at Buried Bottom Surface

Layer-by-layer (LbL) coating is becoming a widely used method to fabricate nonfullerene active layer films for organic solar cells. However, the vertical compositional distribution of the LbL-coated active layer, particularly at the buried bottom surface, is not clear yet. In common sense, it is believed that the LbL-coating yields a donor–mixture–acceptor (D–m–A) vertical distribution in the active layer, i.e., a thin polymer donor layer at the bottom surface, a thin acceptor layer at the top surface and a donor-acceptor mixture in the middle. In this study, it is shown that the LbL active layer vertically is an entire donor:acceptor mixture. A pure layer of polymer donor doesn't exist at the bottom surface. The LbL active layer delivers high performance in both conventional and inverted device structures. A thin polymer layer with different thicknesses (2, 6, 12 nm) is inserted at the bottom surface to study their effects on the device performance. Those inserted layers substantially deteriorate the device's performance. Furthermore, the assumption is further confirmed by X-ray photoelectron spectroscopy measurement on the exposed “originally buried” surface. This study sheds light on understanding the vertical compositional distribution of active layer via layer-by-layer solution processing.     

Modulating Carrier Kinetics in BiVO4 Photoanodes through Molecular Co4O4 Cubane Layers

Understanding the role and immobilization of molecular catalysts on photoelectrodes is essential to use their full potential for efficient solar fuel generation. Here, a Co^II₄O₄ cubane with proven catalytic performance and an active H₂O─Co₂(OR)₂─OH₂ edge-site moiety is immobilized on BiVO₄ photoanodes through a versatile layer-by-layer assembly strategy. This delivers a photocurrent of 3.3 mA cm⁻² at 1.23 V_RHE and prolonged stability. Tuning the thickness of the Co₄O₄ layer has remarkable effects on photocurrents, dynamic open circuit potentials, and charge carrier behavior. Comprehensive-time and frequency-dependent perturbation techniques are employed to investigate carrier kinetics in transient and pseudo-steady-state operando conditions. It is revealed that the Co₄O₄ layer can prolong carrier lifetime, unblock kinetic limitations at the interface by suppressing recombination, and enhance charge transfer. Additionally, its flexible roles are identified as passivation/hole trapping/catalytic layer at respective lower/moderate/higher potentials. These competing functions are under dynamic equilibrium, which fundamentally defines the observed photocurrent trends.     

自愈防腐体系的愈合机制及应用的研究进展

综述了不同自愈体系的自愈机制，根据是否需要外加修复剂，将自愈体系分为本征型和外援型两类，其中本征型自愈体系的愈合机制是指非共价键 (氢键作用、疏水作用、静电作用) 和共价键 (DA键、双硫键) 的重新结合作用；外援型自愈体系是引入修复剂，利用修复剂修复损伤。最后，对自愈体系的主要的应用技术：层层自组装技术、微胶囊封装技术和化学转化膜技术进行了综述。     

Precision Tuning of Highly Selective Polyelectrolyte Membranes for Redox-Mediated Electrochemical Separation of Organic Acids

The design of molecularly selective membranes is of paramount importance in the electrochemical separation of organic acids from complex fermentation streams, due to the presence of multicomponent species. However, current membrane-integrated electrochemical technologies have relied on ion-exchange membranes that lack intrinsic ion-selectivity, thus preventing their application for value-added recovery of organic acids from competing ions. Here, this study demonstrates a layer-by-layer polyelectrolyte functionalization approach for controlling ion-selectivity, to achieve the multicomponent separation of organic acids in a redox-flow electrodialysis platform. This study carries out a detailed investigation of the surface morphology and physicochemical properties of functionalized membranes, underlying that the selectivity of organic acids can be precisely tuned through the control of the hydrophilicity, electrostatic repulsion, and steric hindrance. Tailoring of membrane physiochemical properties enables up to complete retention of succinate, while enhancing the total flux. This organic acid retention is extended to the control over mono- and multivalent organic acids. Integration of functionalized membrane with the redox-flow system allows selective succinic acid recovery with 99.7% purity from a synthetic fermentation mixture, high energy efficiency, and membrane stability. Modulation of ion-selectivity through membrane functionalization coupled with  electrochemical architecture design enables a sustainable pathway for multicomponent separations in biomanufacturing.     

Robust and Stable Atomically Precise Metal Nanoclusters Mediated Solar Water Splitting

Atomically precise metal nanoclusters (NCs) represent an emerging sector of light-harvesting antennas by virtue of peculiar atomic stacking fashion, quantum confinement effect, and molecular-like discrete energy band structure. Nevertheless, precise control of charge carriers over metal NCs has yet to be achieved by the short carrier lifetime and intrinsic instability of metal NCs, which renders the complexity of metal NCs-based photosystems with photoredox mechanisms remaining elusive. Herein, fine tuning of charge migration over metal NCs is demonstrated by constructing directional charge transfer channels in multilayered heterostructure enabled by a facile layer-by-layer (LbL) assembly approach, wherein oppositely charged branched poly-ethylenimine (BPEI) and glutathione (GSH)-capped gold NCs [Au_x NCs, Au₂₅(GSH)₁₈ NCs] are alternately deposited on the metal oxide (MOs: TiO₂, WO₃, Fe₂O₃) substrates. TheAu_x (Au₂₅) NCs layer serves as light-harvesting antennas for engendering charge carriers, andBPEI interim layer uniformly intercalated at the interface of Au_x NCs layer constitutes the tandem hole transport channel for motivating the charge transfer cascade, resulting in the considerably enhanced photoelectrochemical water oxidation performances. Besides, poor photo-stability of Au_x NCs is surmounted by stimulating the hole transfer kinetics process.