High-resolution imaging of electron beam-sensitive materials is one of the most difficult applications of transmission electron microscopy (TEM). The challenges are manifold, including the ...acquisition of images with extremely low beam doses, the time-constrained search for crystal zone axes, the precise image alignment, and the accurate determination of the defocus value. We develop a suite of methods to fulfill these requirements and acquire atomic-resolution TEM images of several metal organic frameworks that are generally recognized as highly sensitive to electron beams. The high image resolution allows us to identify individual metal atomic columns, various types of surface termination, and benzene rings in the organic linkers. We also apply our methods to other electron beam-sensitive materials, including the organic-inorganic hybrid perovskite CH
NH
PbBr
.
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•High dosage of SO42− (>10meq/L) stabilized ZnO NPs by inverting surface potential.•The electrolyte-driven aggregation of ZnO NPs was inhibited by 10mg/L SRHA.•ZnO NPs kept stable in ...a wastewater with high TOC and even high ionic strength.•High TOC and low pH compromised high ionic strength on the dissolution of ZnO NPs.
Zinc oxide nanoparticles (ZnO NPs) are widely used nanomaterials and their environmental impacts have received increasing attention. The fate and toxicity of ZnO NPs in the environment are determined by their stability and dissolution. In this study, the influence of water chemistry on aggregation, sedimentation, and dissolution of ZnO NPs was investigated. The stabilized ZnO NPs aggregated and precipitated when the aqueous pH closed to their zero point of charge (pHzpc). Counter-ions neutralized the surface charge of NPs and promoted their destabilization. However, a high concentration of counter-ion (SO42−, >10meq/L) made the NPs more stable because of the inverted surface potential. The stability of ZnO NPs was maintained by high concentration of Suwannee River humic acid (SRHA, 10mg/L) even the concentration of electrolytes was high. The influence of water chemistry on the stability and dissolution of ZnO NPs was further demonstrated in different wastewaters. In one wastewater sample, ZnO NPs was unexpectedly stable and with a high dissolution, which was due to the effects of pH value, organic matter concentration, as well as the concentration of counter ions. Our findings facilitate the predictions of the fate of stabilized ZnO NPs in the environment.
Metal-organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and ...catalysis. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square ångström to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 Å, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules.
The harvesting of solar radiation for steam generation has drawn wide attention as a future sustainable technology for the renewable production of clean water worldwide. Here, a new super‐dark ...metasurface of 200 nm thickness is presented, which reaches a solar thermal efficiency of 87% when exposed to an intensity of only 2.3 sun, maintaining a stable efficiency of 90% at higher solar intensities. The metasurface is composed of extremely robust nanoparticles, which are up to 98% recyclable and can be produced on massively large scales by wet chemistry. By employing such reusable nanoparticles on an area of 1 m2, 1.2 kg of seawater can be purified within only 1 h under natural sunshine. With such excellent performances, this nanomaterial can open new applications of high‐performance solar steam.
Large‐scale solar steam generation with biomimetic ultradark nanoparticles is presented. Each nanoparticle is composed of a nanorod and a nanosphere attached together. When a 200 nm thick membrane of nanoparticles is illuminated by sunlight, it generates steam from water with an efficiency that is higher than any other material available today. Nanoparticles are fully recyclable and produced by wet‐chemistry techniques.
Practical applications involving the magnetic bistability of single-molecule magnets (SMMs) for next-generation computer technologies require nanostructuring, organization, and protection of ...nanoscale materials in two- or three-dimensional networks, to enable read-and-write processes. Owing to their porous nature and structural long-range order, metal–organic frameworks (MOFs) have been proposed as hosts to facilitate these efforts. Although probing the channels of MOF composites using indirect methods is well established, the use of direct methods to elucidate fundamental structural information is still lacking. Herein we report the direct imaging of SMMs encapsulated in a mesoporous MOF matrix using high-resolution transmission electron microscopy. These images deliver, for the first time, direct and unambiguous evidence to support the adsorption of molecular guests within the porous host. Bulk magnetic measurements further support the successful nanostructuring of SMMs. The preparation of the first magnetic composite thin films of this kind furthers the development of molecular spintronics.
Encapsulating catalytically active components into zeolites is a way to prepare multifunctional catalysts with unique selectivity and enhanced stability. Previously reported methods for encapsulation ...were only suitable for encapsulating specific species with a limited loading capacity. Here, we report a general strategy for encapsulating various metal oxides in zeolites. Our strategy is based on the use of directly synthesized hierarchical zeolites with abundant intracrystalline mesopores. Metal oxides that are preloaded in the mesopores by impregnation become encapsulated during a secondary growth process that converts the original hierarchical structure into a bulk structure of zeolite. This method enables the encapsulation of ultrafine particles (2–4 nm) of various metal oxides (CeO2, TiO2, and MnO x ) in zeolites with loading as high as >10 wt %. Furthermore, we modify this method to achieve the encapsulation and high dispersion of noble metals (Au and Pt), which would otherwise agglomerate into large particles on the zeolite surfaces, by taking advantage of their strong interactions with metal oxides. The encapsulated metal oxides and metal oxide-supported noble metals demonstrate reactant selectivity, product selectivity, and excellent thermal stability during catalytic oxidation and hydrogenation reactions.
Cokes are inevitably generated during zeolite-catalyzed reactions as deleterious side products that deactivate the catalyst. In this study, we
in situ
converted cokes into carbons within the confined ...microporous zeolite structures and evaluated their performances as absorbing materials for solar-driven water evaporation. With a properly chosen zeolite, the coke-derived carbons possessed ordered interconnected pores and tunable compositions. We found that the porous structure and the oxygen content in the as-prepared carbons had important influences on their energy conversion efficiencies. Among various investigated carbon materials, the carbon derived from the methanol-to-olefin reaction over zeolite beta gave the highest conversion efficiency of 72% under simulated sunlight with an equivalent solar intensity of 2 suns. This study not only demonstrates the great potential of traditionally useless cokes for solar thermal applications but also provides new insights into the design of carbon-based absorbing materials for efficient solar evaporation.
Zeolite-derived cokes are used as absorbers for solar evaporation and the influences of their porous structures and compositions on energy conversion efficiency are studied.
Mixed-matrix membranes composed of mechanically strong, solution-processable polymers and highly selective ultramicroporous fillers (pore size < 7 Å) are superior candidate membrane materials for ...various energy-intensive gas separation applications because of their structural tunability to achieve enhanced gas permeability and gas–pair selectivity. However, their industrial implementation has been severely hindered because inefficient compatibility of the polymer matrices and crystalline fillers results in poorly performing membranes with low filler capacity and interfacial defects. Herein, we report for the first time a unique strategy to fabricate highly propylene/propane selective mixed-matrix membranes (MMMs) composed of a hydroxyl-functionalized microporous polyimide (PIM-6FDA-OH) and an ultramicroporous, strongly size-sieving zeolitic imidazolate framework (ZIF-8). Excellent compatibility between PIM-6FDA-OH and ZIF-8 with selective filler loading up to 65 wt % resulted from N···O–H induced hydrogen bonding as evidenced by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The newly developed MMMs demonstrated unprecedented mixed-gas performance for C3H6/C3H8 separation and outstanding plasticization resistance of up to at least 7 bar feed pressure. The reported fabrication concept is expected to be applicable to a wide variety of OH-functionalized polymers and alternative tailor-made imidazolate framework materials designed for MMMs to achieve optimal gas separation performance.
The shuttling effect of polysulfides severely hinders the cycle performance and commercialization of Li–S batteries, and significant efforts have been devoted to searching for feasible solutions to ...mitigate the effect in the past two decades. Recently, metal–organic frameworks (MOFs) with rich porosity, nanometer cavity sizes, and high surface areas have been claimed to be effective in suppressing polysulfide migration. However, the formation of large-scale and grain boundary-free MOFs is still very challenging, where a large number of grain boundaries of MOF particles may also allow the diffusion of polysulfides. Hence, it is still controversial whether the pores in MOFs or the grain boundaries play the critical role. In this study, we perform a comparative study for several commonly used MOFs, and our experimental results and analysis prove that a layer of MOFs on a separator did enhance the capacity stability. Our results suggest that the chemical stability and the aggregation (packing) morphology of MOF particles play more important roles than the internal cavity size in MOFs.
Nanomaterials are considered to be emerging contaminants because their release into the environment could cause a threat to our ecosystem and human health. This study aims to evaluate the effects of ...pH, ions, and humic acid on the destabilization and sedimentation of commercial stabilized TiO2 nanoparticles (NPs) in aquatic environments. The average hydrodynamic size of TiO2 NPs was determined to be 52 ± 19 nm by dynamic light scattering. The zero point charge (ZPC) of the commercial TiO2 NPs was found to occur at pH 6. The stability of commercial TiO2 NPs is independent of its concentration in the range of 50–200 mg/L. In the absence of NaCl, the commercial TiO2 NPs rapidly settled down near pHzpc when the aggregated nanoparticle size surpassed 1 μm. However, when the commercial TiO2 NPs aggregated with the increase of NaCl concentrations, the large aggregates (>1 μm) were found to remain suspended. For example, even at the critical aggregation concentration of NaCl (100 meq/L), TiO2 NP aggregates suspended for 45 min and then slowly deposited. This implies an increase in the exposure risk of NPs. In the presence of Suwannee river humic acid (SRHA), the commercial TiO2 NPs did not settle down until the SRHA concentration increased to 20 mg/L, and were seen to restabilize at SRHA concentrations of 50 mg/L. The uncommon behaviors of the commercial TiO2 NPs we observed may be attributed to the different destabilization mechanisms caused by different species (i.e., NaCl and SRHA) in water.
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•Stability of commercial stabilized TiO2 nanoparticles (NPs) in water was analyzed.•TiO2 NPs rapidly settled down near its pHzp once NPs aggregated >1 μm.•In the presence of electrolytes, TiO2 NPs aggregated but not settled down instantly.•The suspension of TiO2 NP aggregates could increase the exposure risk of NPs.•Humic acid more than 20 mg/L could also keep stabilized NPs from aggregating.
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