Solar-to-H2 O2 Catalyzed by Covalent Organic Frameworks.

Benefiting from the excellent structural tunability, robust framework, ultrahigh porosity, and rich active sites, covalent organic frameworks (COFs) are widely recognized as promising photocatalysts in chemical conversions, and emerged in the hydrogen peroxide (H2 O2 ) photosynthesis in 2020. H2 O2 , serving as an environmental-friendly oxidant and a promising liquid fuel, has attracted increasing researchers to explore its potential. Over the past few years, numerous COFs-based photocatalysts are developed with encouraging achievements in H2 O2 production, whereas no comprehensive review articles exist to summarize this specific and significant area. Herein we provide a systematic overview of the advances and challenges of COFs in photocatalytic H2 O2 production. We first introduce the priorities of COFs in H2 O2 photosynthesis. Then, various strategies to improve COFs photocatalytic efficiency are discussed. The perspective and outlook for future advances of COFs in this emerging field are finally offered. This timely review will pave the way for the development of highly efficient COFs photocatalysts for practical production of value-added chemicals not limited to H2 O2 .

Pd-conformally coated, one-end-embedded gold nanowire percolation network for intrinsically stretchable, epidermal tattoo fuel cell.

Soft, conformal and wearable epidermal fuel cells may offer promising energy solutions to power next-generation on-skin electronics on-demand anytime anywhere. However, it is non-trivial to design intrinsically stretchable electrode in order to maintain the fuel cell performance under real-world and dynamic mechanical deformations. Here, we present a tattoo-like epidermal fuel cell based on Pd conformally-coated, one-end-embedded percolation gold nanowire (EP-AuNW/EP-AuPdNW) networks, which are in essence the combination of in-plane percolation conductivity and out-plane anisotropic conductivity. Both EP-AuNW and EP-AuPdNW are intrinsically stretchable conductors for anode and cathode in fuel cell. Compared to non-conformal counterparts, a 6-times greater power density was achieved for conformal system. Importantly, EP-NW based fuel cell can function under various mechanical deformations including stretching, compression, bending, and twisting; the power density showed negligible changes to the tensile strain up to ∼50% and could maintain its 75% performance even under 80% strain. Furthermore, a dragon-tattoo epidermal fuel cell was fabricated, demonstrating on-demand power generation with real-world ethanol sources.

Omnidirectional Hydrogen Generation Based on a Flexible Black Gold Nanotube Array.

Solar-driven hydrogen generation is emerging as an economical and sustainable means of producing renewable energy. However, current photocatalysts for hydrogen generation are mostly powder-based or rigid-substrate-supported, which suffer from limitations, such as difficulties in catalyst regeneration or poor omnidirectional light-harvesting. Here, we report a two-dimensional (2D) flexible photocatalyst based on elastomer-supported black gold nanotube (GNT) arrays with conformal CdS coating and Pt decoration. The highly porous GNT arrays display a strong light-trapping effect, leading to near-complete absorption over almost the entire range of the solar spectrum. In addition, they offer high surface-to-volume ratios promoting efficient photocatalytic reactions. These structural features result in high H2 generation efficiencies. Importantly, our elastomer-supported photocatalyst displays comparable photocatalytic activity even when being mechanically deformed, including bending, stretching, and twisting. We further designed a three-dimensional (3D) tree-like flexible photocatalytic system to mimic Nature's photosynthesis, which demonstrated omnidirectional H2 generation. We believe our strategy represents a promising route in designing next-generation solar-to-fuel systems that rival natural plants.

Thermoresponsive chiral plasmonic nanoparticles.

Chiral metallic nanoparticles can exhibit novel plasmonic circular dichroism (PCD) in the ultraviolet and visible range of the electromagnetic spectrum. Here, we investigate how thermoresponsive dielectric nanoenvironments will influence such PCD responses through poly(N-isopropylacrylamide) (PNIPAM) modified chiral gold nanorods (AuNRs). We observed the temperature-dependent chiral plasmonic responses distinctly from unmodified counterparts. As for the modified systems, the PCD peaks for both L-AuNRs and D-AuNRs at 50 °C red shifted simultaneously with enhanced intensities compared to the results at 20 °C. In contrast, the unmodified L-AuNRs and D-AuNRs exhibited no peak shift with reduced intensities. Subsequent simulation and experimental studies demonstrated that the enhanced PCD was attributed to PNIPAM chain collapse causing the increase of the refractive index by expelling minute water out of the corona surrounding chiral plasmonic AuNRs. Notably, such thermoresponsive chiral plasmonic responses are reversible, general, and extendable to other types of chiral plasmonic nanoparticles.

Cell Sheet-Like Soft Nanoreactor Arrays.

Tissues, which consist of groups of closely packed cell arrays, are essentially sheet-like biosynthesis plants. In tissues, individual cells are discrete microreactors working under highly viscous and confined environments. Herein, soft polystyrene-encased nanoframe (PEN) reactor arrays, as analogous nanoscale "sheet-like chemosynthesis plants", for the controlled synthesis of novel nanocrystals, are reported. Although the soft polystyrene (PS) is only 3 nm thick, it is elastic, robust, and permeable to aqueous solutes, while significantly slowing down their diffusion. PEN-associated palladium (Pd) crystallization follows a diffusion-controlled zero-order kinetics rather than a reaction-controlled first-order kinetics in bulk solution. Each individual PEN reactor has a volume in the zeptoliter range, which offers a unique confined environment, enabling a directional inward crystallization, in contrast to the conventional outward nucleation/growth that occurs in an unconfined bulk solution. This strategy makes it possible to generate a set of mono-, bi-, and trimetallic, and even semiconductor nanocrystals with tunable interior structures, which are difficult to achieve with normal systems based on bulk solutions.

Seagrass-inspired design of soft photocatalytic sheets based on hydrogel-integrated free-standing 2D nanoassemblies of multifunctional nanohexagons.

Natural leaves are virtually two-dimensional (2D) flexible photocatalytic system. In particular, seagrass can efficiently harvest low-intensity sunlight to drive photochemical reactions continuously in an aqueous solution. To mimic this process, we present a novel 2D hydrogel-integrated photocatalytic sheet based on free-standing nanoassemblies of multifunctional nanohexagons (mNHs). The mNHs building blocks is made of plasmonic gold nanohexagons (NHs) decorated with Pd nanoparticles in the corners and CdS nanoparticles throughout their exposed surfaces. The mNHs can self-assemble into free-standing 2D nanoassemblies and be integrated with thin hydrogel films, which can catalyze chemical reactions under visible light illumination. Hydrogels are translucent, porous, and soft, allowing for continuous photochemical conversion in an aqueous environment. Using methylene blue (MB) as a model system, we demonstrate a soft seagrass-like photodegradation design, which offers high efficiency, continuous operation without the need of catalyst regeneration, and omnidirectional light-harvesting capability under low-intensity sunlight irradiation, defying their rigid substrate-supported random aggregates and solution-based discrete counterparts.

Self-assembled Janus plasmene nanosheets as flexible 2D photocatalysts.

A leaf is a free-standing photocatalytic system that can effectively harvest solar energy and convert CO2 and H2O into carbohydrates in a continuous manner without the need for regeneration or tedious product extraction steps. Despite encouraging advances achieved in designing artificial photocatalysts, most of them function in bulk solution or on rigid surfaces. Here, we report on a 2D flexible photocatalytic system based on close packed Janus plasmene nanosheets. One side of the Janus nanosheets is hydrophilic with catalytically active palladium, while the opposite side is hydrophobic with plasmonic nanocrystals. Such a unique design ensures a stable nanostructure on a flexible polymer substrate, preventing dissolution/degradation of plasmonic photocatalysts during chemical conversion in aqueous solutions. Using catalytic reduction of 4-nitrophenol as a model reaction, we demonstrated efficient plasmon-enhanced photochemical conversion on our flexible Janus plasmene. The photocatalytic efficiency could be tuned by adjusting the palladium thickness or types of constituent building blocks or their orientations, indicating the potential for tailor-made catalyst design for desired reactions. Furthermore, the flexible Janus plasmene nanosheets were designed into a small 3D printed artificial tree, which could continuously convert 30 mL of chemicals in 45 minutes.

Orientation-Dependent Soft Plasmonics of Gold Nanobipyramid Plasmene Nanosheets.

In parallel to the burgeoning field of soft electronics, soft plasmonics focuses on the design and fabrication of plasmonic structures supported on elastomers and to understand how their properties respond to mechanical deformations. Here, we report on a partial ligand-stripping strategy to fabricate elastomer-supported gold nanobipyramid (NBP) plasmene nanosheets. Unlike spherelike building blocks, NBP-building blocks display complex orientation-dependent plasmonic responses to external strains. By collecting polarized plasmonic resonance spectra in conjunction with electrostatic eigenmode modeling, we reveal simultaneous changes in interparticle spacing and spatial orientations of NBP building blocks under mechanical strains. Such changes are directly related to initial NBP packing orders. Further analysis of strain sensitivities for various NBP plasmenes indicated that plasmonic spectra of ∼45° oriented samples are mostly susceptible to strain at acute polarized angles. The results presented may enable novel applications in future soft optoelectronic devices in sensing, encryption, and data storage.

Stretchable gold fiber-based wearable electrochemical sensor toward pH monitoring.

Sweat pH is a key health indicator related to metabolism and homeostasis level through hydrogen ion concentration in biological bio-fluid. Therefore, increasing research efforts have been directed to develop wearable pH sensors towards continuous non-invasive monitoring of sweat pH values in the out-of-hospital environments. Herein, we report a stretchable gold fiber-based electrochemical pH sensor based on our recently developed elastomer-bonded gold nanowire coating technology. The densely packed gold film offers superior strain-insensitive conductivity, high stretchability and large electrochemical active surface area (EASA). By electrodepositing polyamine (PANI) and Ag/AgCl onto the gold fibers, we could selectively detect the pH based on open circuit potentials in an ion-selective electrode design. The obtained fiber-based pH sensors feature a great sensitivity (60.6 mV per pH), high selectivity against cationic interference and high stretchability (up to 100% strain). One of the attributes for the fiber-based sensors is that they can be weaved into textiles, holding great potential for integration into everyday clothing for "unfeelable" personal health monitoring.

X-ray-activated long persistent phosphors featuring strong UVC afterglow emissions.

Phosphors emitting visible and near-infrared persistent luminescence have been explored extensively owing to their unusual properties and commercial interest in their applications such as glow-in-the-dark paints, optical information storage, and in vivo bioimaging. However, no persistent phosphor that features emissions in the ultraviolet C range (200-280 nm) has been known to exist so far. Here, we demonstrate a strategy for creating a new generation of persistent phosphor that exhibits strong ultraviolet C emission with an initial power density over 10 milliwatts per square meter and an afterglow of more than 2 h. Experimental characterizations coupled with first-principles calculations have revealed that structural defects associated with oxygen introduction-induced anion vacancies in fluoride elpasolite can function as electron traps, which capture and store a large number of electrons triggered by X-ray irradiation. Notably, we show that the ultraviolet C afterglow intensity of the yielded phosphor is sufficiently strong for sterilization. Our discovery of this ultraviolet C afterglow opens up new avenues for research on persistent phosphors, and it offers new perspectives on their applications in terms of sterilization, disinfection, drug release, cancer treatment, anti-counterfeiting, and beyond.

Doping-Enhanced Short-Range Order of Perovskite Nanocrystals for Near-Unity Violet Luminescence Quantum Yield.

All-inorganic perovskite nanocrystals (NCs) have emerged as a new generation of low-cost semiconducting luminescent system for optoelectronic applications. The room-temperature photoluminescence quantum yields (PLQYs) of these NCs in the green and red spectral range approach unity. However, their PLQYs in the violet are much lower, and an insightful understanding of such poor performance remains missing. We report a general strategy for the synthesis of all-inorganic violet-emitting perovskite NCs with near-unity PLQYs through engineering local order of the lattice by nickel ion doping. A broad range of experimental characterizations, including steady-state and time-resolved luminescence spectroscopy, X-ray absorption spectra, and magic angle spinning nuclear magnetic resonance spectra, reveal that the low PLQY in undoped NCs is associated with short-range disorder of the lattice induced by intrinsic defects such as halide vacancies and that Ni doping can substantially eliminate these defects and result in increased short-range order of the lattice. Density functional theory calculations reveal that Ni doping of perovskites causes an increase of defect formation energy and does not introduce deep trap states in the band gap, which is suggested to be the main reason for the improved local structural order and near-unity PLQY. Our ability to obtain violet-emitting perovskite NCs with near-perfect properties opens the door for a range of applications in violet-emitting perovskite-based devices such as light-emitting diodes, single-photon sources, lasers, and beyond.

Cs4PbBr6/CsPbBr3 Perovskite Composites with Near-Unity Luminescence Quantum Yield: Large-Scale Synthesis, Luminescence and Formation Mechanism, and White Light-Emitting Diode Application.

All-inorganic perovskites have emerged as a new class of phosphor materials owing to their outstanding optical properties. Zero-dimensional inorganic perovskites, in particular the Cs4PbBr6-related systems, are inspiring intensive research owing to the high photoluminescence quantum yield (PLQY) and good stability. However, synthesizing such perovskites with high PLQYs through an environment-friendly, cost-effective, scalable, and high-yield approach remains challenging, and their luminescence mechanisms has been elusive. Here, we report a simple, scalable, room-temperature self-assembly strategy for the synthesis of Cs4PbBr6/CsPbBr3 perovskite composites with near-unity PLQY (95%), high product yield (71%), and good stability using low-cost, low-toxicity chemicals as precursors. A broad range of experimental and theoretical characterizations suggest that the high-efficiency PL originates from CsPbBr3 nanocrystals well passivated by the zero-dimensional Cs4PbBr6 matrix that forms based on a dissolution-crystallization process. These findings underscore the importance in accurately identifying the phase purity of zero-dimensional perovskites by synchrotron X-ray technique to gain deep insights into the structure-property relationship. Additionally, we demonstrate that green-emitting Cs4PbBr6/CsPbBr3, combined with red-emitting K2SiF6:Mn4+, can be used for the construction of WLEDs. Our work may pave the way for the use of such composite perovskites as highly luminescent emitters in various applications such as lighting, displays, and other optoelectronic and photonic devices.

Ion-Exchangeable Microporous Polyoxometalate Compounds with Off-Center Dopants Exhibiting Unconventional Luminescence.

The synthesis of luminescent polyoxometalates (POMs) typically relies on the assembly of POM ligands with rare earth or transition metals, placing significant constraints on the composition, structure, and hence the luminescence properties of the resultant systems. Herein, we show that the ion-exchange strategy can be used for the synthesis of novel POM-based luminescent materials. We demonstrate that introducing bismuth ions into an ion-exchangeable, microporous POM compound yields an unconventional system luminescing in the near-infrared region. Experimental characterization, coupled with quantum chemical calculations, confirms that bismuth ions site-specifically occupy an off-center site in the lattice, and have an asymmetric coordination geometry unattainable by other means, thus giving rise to peculiar emission. Our findings offer an effective strategy for the synthesis of POM-based luminescent materials, and the design concept may potentially be adapted to the creation of POM-based systems with other functionalities.

Controlling Crystallization of All-Inorganic Perovskite Films for Ultralow-Threshold Amplification Spontaneous Emission.

All-inorganic lead halide perovskites have gained considerable interest owing to their potential applications in an array of high-performance optoelectronic devices. However, producing highly luminescent, nearly pinhole-free, all-inorganic perovskite films through a simple solution process remains challenging. Here, we provide a detailed investigation of the crystallization control of inorganic perovskite films fabricated by a one-step spin-coating process. Our results reveal that the coating temperature in the fabrication process is of paramount importance in influencing perovskite crystallization and that lowering the coating temperature and fine stoichiometry modification of the precursors favor the suppression of trap states in CsPbBr3 perovskite films. A broad range of experimental characterizations help us identify that nonsynergistic assembly of solutes, resulting from poor diffusion capability of inorganic salts, is the dominant cause for the inhomogeneous element distribution, low luminescence yield, and poor surface coverage of the resulting films. Importantly, we find that polyethylene glycol can also be used for tailoring the crystallization process, which enables the attainment of high-quality CsPbBr3 films with a maximum luminescence yield of ∼30%. Finally, we demonstrate that amplification spontaneous emission with an ultralow threshold can be readily accomplished by using the developed film as an emissive component. Our findings provide deep insights into the crystallization control of CsPbBr3 perovskite films and establish a systematic route to high-quality all-inorganic perovskite films, paving the way for widespread optoelectronic applications.

Ultrabroad Photoluminescence and Electroluminescence at New Wavelengths from Doped Organometal Halide Perovskites.

Doping of semiconductors by introducing foreign atoms enables their widespread applications in microelectronics and optoelectronics. We show that this strategy can be applied to direct bandgap lead-halide perovskites, leading to the realization of ultrawide photoluminescence (PL) at new wavelengths enabled by doping bismuth (Bi) into lead-halide perovskites. Structural and photophysical characterization reveals that the PL stems from one class of Bi doping-induced optically active center, which is attributed to distorted [PbI6] units coupled with spatially localized bipolarons. Additionally, we find that compositional engineering of these semiconductors can be employed as an additional way to rationally tune the PL properties of doped perovskites. Finally, we accomplished the electroluminescence at cryogenic temperatures by using this system as an emissive layer, marking the first electrically driven devices using Bi-doped photonic materials. Our results suggest that low-cost, earth-abundant, solution-processable Bi-doped perovskite semiconductors could be promising candidate materials for developing optical sources operating at new wavelengths.