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Abstract Here, a comprehensive study on the synthesis, characterization, and reactivity of grain‐boundary (GB)‐rich noble metal nanoparticle (NP) assemblies is presented. A facile and scalable synthesis of Pt, Pd, Au, Ag, and Rh NP assemblies is developed, in which NPs are predominantly connected via Σ3 (111) twin GBs, forming a network. Driven by water electrolysis, the random collisions and oriented attachment of colloidal NPs in solution lead to the formation of Σ3 (111) twin boundaries and some highly mismatched GBs. This synthetic method also provides convenient control over the GB density without altering the crystallite size or GB type by varying the NP collision frequency. The structural characterization reveals the presence of localized tensile strain at the GB sites. The ultrahigh activity of GB‐rich Pt NP assembly toward catalytic hydrogen oxidation in air is demonstrated, enabling room‐temperature catalytic hydrogen sensing for the first time. Finally, density functional theory calculations reveal that the strained Σ3(111) twin boundary facilitates oxygen dissociation, drastically enhancing the hydrogen oxidation rate via the dissociative pathway. This reported large‐scale synthesis of the Σ3 (111) twin GB‐rich structures enables the development of a broad range of high‐performance GB‐rich catalysts. 

The increasing use of Gd-based contrast agents for magnetic resonance imaging at hospitals and research centers has led to the rapidly growing demand for Gd and Gd anomalies in surface waters. Recycling Gd from hospital effluents could simultaneously address Gd demand and severe concerns about Gd contamination. Here, we present a study relevant to the extraction and preconcentration of Gd from hospital effluents that contain parts per billion-level Gd via the ligand-assisted electrochemical aerosol formation (LEAF) process. We demonstrate that the LEAF process extracts ∼75% GdIII from 50 ppb Gd-spiked water samples, including diluted artificial urine samples while preconcentrating Gd by up to 390-fold. Mechanistic studies confirm that the surface activity of the Gd-binding ligand is essential for successful LEAF extraction. The ligands are recyclable by performing electrophoretic separation in an origami paper device, followed by water extraction. The steep pH gradient and strong electric field in the origami paper device enabled the dissociation of Gd-ligand complexes, spatial separation of Gd and ligand, and precipitation of GdIII as Gd(OH)3. Approximately 80% of the ligands were recovered from the paper device by water extraction and reused in subsequent extraction cycles. This straightforward and green method could also be adapted to other aqueous rare earth metal wastes in the future. 

Gas bubbles are easily accessible and offer many unique characteristic properties of a gas/liquid two-phase system for developing new analytical methods. In this minireview, we discuss the newly developed analytical strategies that harness the behaviors of bubbles. Recent advancements include the utilization of the gas/liquid interfacial activity of bubbles for detection and preconcentration of surface-active compounds; the employment of the gas phase properties of bubbles for acoustic imaging and detection, microfluidic analysis, electrochemical sensing, and emission spectroscopy; and the application of the mass transport behaviors at the gas/liquid interface in gas sensing, biosensing, and nanofluidics. These studies have demonstrated the versatility of gas bubbles as a platform for developing new analytical strategies.