Creating a built-in electric field (BIEF) can effectively modulate the performance of functional materials. However, the effect of BIEF on adsorbents at the single-particle level has not been explored. Here, we employ in situ dark-field optical microscopy (DFM) imaging to track the reaction of single Cu2O microcrystals and Cu2O@BiOBr core-shell structures with I-. At high concentrations of I-, selective etching occurs in the Cu2O core, while the pristine Cu2O remains inactive. This illustrates the enhanced reactivity of p-type Cu2O when coupled with the n-type BiOBr shell. Mechanistic studies reveal that the BIEF in the p-n interface region drives directional migration of I-, accelerating mass transfer and increasing local concentration, thus significantly enhancing the reactivity of Cu2O@BiOBr. The reactivity improvement is further validated by batch adsorption at low I- concentration, and Cu2O@BiOBr is also employed for μCi-level radioactive 131I- uptake. These findings highlight the critical role of the BIEF in adsorbent activity and may provide a general design principle for high-performance adsorbents.

Covalent organic frameworks (COFs) are promising photocatalysts, but improving their performance requires enhanced light harvesting and suppressed electron-hole recombination, often via postprotonation or conformational modulation. Here, using in situ liquid-phase dark-field optical microscopy (DFM), we directly image in real time that the chloroacetic acid (MCA) interacts with COF-300 as a prototype COF host to form a highly protonated and twisted host-guest complex (MCA@COF-300) at the single-particle level, whereas acetic acid or trichloroacetic acid induces only weak effects. Further real-time single-particle photocatalytic imaging experiments show the high activity of MCA@COF-300. Combining ensemble characterizations and theoretical calculations, the coexistence of deep protonation and twist modulation in MCA@COF-300 is uncovered to favor visible light absorption and single-triplet intersystem crossing, leading to the formation of long-lived charge-separated states for boosting photocatalysis. Moreover, we apply the MCA@COF-300 photocatalyst to capture ultratrace radioactive 131I- from an aqueous solution. These findings provide key insights into the photocatalysis of the COFs.

Meperidine, morphine, and sufentanil exhibit a critical duality in contemporary medicine: while serving as essential clinical anesthetics with well-established therapeutic value, they have paradoxically contributed to a severe public health crisis due to their widespread abuse. In response to the pressing demands of contemporary anesthetic regulation and drug control initiatives, this study employs a home-made atmospheric pressure corona discharge ion mobility spectrometer. By introducing an ammonia dopant to suppress the ionization of specific proton-binding sites in morphine, the technical challenge of overlapping mobility peaks between meperidine and morphine is overcome. Experimental results reveal that under optimized drift tube temperature conditions (40–100°C), the drift time of these anesthetics decreases as temperature rises, while the signal intensities of meperidine exhibit a pronounced increasing trend. Through an exploration of signal response characteristics during multi-component simultaneous detection, the competitive ionization mechanisms among the three anesthetics are comprehensively elucidated. This research provides significant value by successfully applying the method of ammonia dopant to additional opioid anesthetic compounds while simultaneously developing and refining the methodological approach.

In the field of 3D detection, mainstream 3D feature extraction methods usually follow the paradigm of voxelization and downsampling to BEV (Bird's Eye View). The feature extraction process is crucial for the quality of BEV during dimension reduction. However, mainstream methods encounter information disconnection issue when dealing with excessively sparse voxels, preventing the extraction of sufficient geometric features for large-scale object detection before dimension reduction. In this paper, we propose a novel convolutional module, termed Asterisk Sparse Convolution (Asterisk Conv), to address the aforementioned issue. Additionally, we have devised a lightweight feature extraction network to extract and balance features across various scales, enhancing overall detection accuracy. Our method achieves competitive accuracy on large targets such as trucks and buses, and significantly improves overall accuracy compared to baseline on the nuScenes benchmark.

Single-crystal covalent organic frameworks (COFs) have received increasing interest due to their well-defined structures and exceptional performance. However, the reaction pathways of the facet development during growth of single-crystal COFs remains unclear, limiting the regulation of their shapes and functions. We report the dynamic imaging of the facet development during single-crystal COF-300 microcrystal growth using in situ dark-field optical microscopy. Our observations reveal that the concentration of terephthalaldehyde (BDA) linkers not only influences the morphology of the primary COF-300 crystal seeds but also governs the facet evolution, leading to the generation of differently shaped COF-300 microcrystals. Mechanistic studies reveal that the observed shape evolution of COF-300 single crystals arises from distinct kinetically or thermodynamically controlled growth pathways, depending on the BDA concentration. Moreover, we uncover the shape-dependent deformation capacity after solvent uptake, demonstrating the impact of COF-300 crystal morphology on its performance. These discoveries elucidate the COF facet transition mechanism and offer guidance for the future design of single-crystal COFs.

Au nanoclusters (AuNCs) have attracted significant attention in electrochemiluminescence (ECL) owing to their excellent luminescent properties; however, achieving high-efficient ECL remains a formidable challenge. Despite the extensively reported emphasis on enhancing radiative transitions, it is imperative to acknowledge that both radiation and excitation play crucial roles in ECL, thereby requiring a dual-enhanced strategy for improving ECL efficiency. Herein, we introduced PTCA-COF, a dual-functional covalent organic frameworks (COFs) with the effect of “kill two birds with one stone” to achieve this purpose. The PTCA-COF not only acted as a carrier to effectively suppress the rotational vibration of surface ligands and reduce self-quenching by minimizing non-radiative transitions, but also acted as an electrosensitiser that facilitated the generation of electrogenerated holes, thereby promoting efficient transfer of hot electrons and enhancing excitation of AuNCs due to favorable energy level alignment. As a proof of concept, by utilizing cadmium ions (Cd2+) as a model analyte, the ECL aptasensing platform fabricated based on the dual-enhancement AuNCs-COFs ECL system demonstrated a broad linear response spanning from 1 pM to 5nM and achieved an impressive low detection limit of 0.66 pM (S/N=3) with exceptional reproducibility and selectivity. The findings of this study not only presented a novel approach for the rational dual-enhancement of ECL efficiency, but also contributed to the advancement of their potential applications in the field of environmental monitoring.

Monitoring and understanding the photocatalytic reactions at individual covalent organic framework (COF) photocatalysts are crucial for gaining insights into their structure-activity relationships. Here, we report real-time imaging of the guest-induced structural torsion in single COF-300 microcrystals for enhanced photocatalysis utilizing in situ dark-field optical microscopy (DFM). Upon inclusion of ethyl acetate (EAC) into the COF-300 framework, deformed EAC-encapsulated COF-300 (EAC@COF-300) microcrystals with twisted diimine linkers are generated, resulting in an inert-to-active photocatalytic reactivity transformation. Impressively, this host-guest-enhanced photocatalysis strategy is also applicable to other guests. The combination of single-particle imaging, spectral characterizations, and theoretical calculations elucidates that structurally twisted EAC@COF-300 boosts the intersystem crossing process and spin-orbit coupling, facilitating the separation of photogenerated electron-hole pairs. Furthermore, the twisted EAC@COF-300 realizes the photocatalytic removal of radioactive 131I- at the pg level. Our findings provide a general strategy for the rational design of efficient COF photocatalysts via twist engineering.

After dispersal into soil, explosive compounds such as TNT undergo dissolution and rapid aging through interactions with soil components. In arid, nutrient-poor soils, the adsorption and transformation of TNT by soil minerals critically influence its environmental behavior. Adsorption onto minerals and metals triggers redox and hydrolysis reactions, facilitating its degradation. A dark-field imaging methodology was established to visualize particle-organic pollutant interactions by leveraging light-scattering properties and chromogenic reactions. Studies revealed that TNT interactions with minerals and metals primarily involve three mechanisms: Physical adsorption (e.g., Fe2O3, Al2O3, Fe3O4, SiO2, CuO, Pb), adsorption-reduction (e.g., Cu, Al), adsorption-hydrolysis (e.g., MgO). Dark-field microscopy enables semi-quantitative assessment of TNT contamination in soils but highlights uneven adsorption across particle surfaces and crystal facets. Mineral adsorption alters TNT pyrolysis behavior, with chemically adsorbed TNT exhibiting higher thermal decomposition temperatures than physically adsorbed forms. Soil magnesium content is a key factor influencing TNT bioavailability. TNT adsorbed onto MgO resists extraction by hydroxypropyl-beta-cyclodextrin (HPCD), significantly reducing bioavailability of TNT. Magnesium-rich minerals (e.g., montmorillonite) further suppress TNT bioavailability, positioning montmorillonite as a potential remediation agent. Combined with XRD for mineral identification and pollutant fractionation, dark-field microscopy and scattering spectroscopy provide high spatial resolution and reveal adsorption heterogeneity among soil particles.

Three-dimensional covalent organic frameworks are promising multifunctional materials for applications in adsorption, separation, and catalysis. However, despite the continuous synthesis of an increasing number of three-dimensional covalent organic frameworks, little is known about the crystal growth pathways. Here, we report the real-time visual observation of the crystal growth process of COF-300 and LZU-79, two typical three-dimensional covalent organic frameworks, using in situ dark-field optical microscopy. Our dark-field optical microscopy imaging results reveal that two crystal-growth pathways are simultaneously operative during the liquid growth of COF-300 and LZU-79 microcrystals, including classical crystal growth modes and non-classical oriented attachment mechanisms. Specifically, detailed tracking of the trajectories between two rod-shaped single-crystal COF-300 pairs suggests that the oriented attachment process undergoes several distinct stages such as approach, alignment at (021) facets, tip-to-tip attachment, fusion, and shaping. Theoretical simulation results show that (021) facets of COF-300 microcrystals, which have a lower repulsive energy barrier due to steric solvation forces from intervening solvents, are energetically more favorable than (010) facets, inducing the oriented attachment between adjacent facets. This work enables a fundamental understanding of how three-dimensional covalent organic framework microcrystals grow dynamically, which can aid the further design of three-dimensional covalent organic frameworks with enhanced performances.

Covalent organic frameworks (COFs) represent attractive crystalline porous materials for the capture of radioactive iodate anions (IO3-). However, the optimization and improvement of COF performances have mainly relied on trial-and-error approaches using bulk ensemble samples, and high-performance COFs for IO3- treatment are still lacking. Here we image the encapsulation of formic acids in a model single LZU-111 COF (FA@LZU-111) to react with IO3- using in situ dark-field optical microscopy (DFM) and quantitatively unveil the stepwise reduction kinetics of IO3- into I2/I3- in real time. Sequential DFM analysis, supplementary characterization, and theoretical simulation reveal that FA@LZU-111 COFs serve as reductants, microreactors, and optical microcavities during IO3- reduction. Guided by mechanistic understanding, the bulk performance of FA@LZU-111 for IO3- was evaluated under visible light irradiation, showing a record-high removal capacity (2817.5 mg·g-1) and excellent selectivity. This study highlights how single-particle imaging reveals structure-activity relationships in a bottom-up approach and aids the rational design of high-performance COF materials.

Metal-organic frameworks (MOFs) have emerged as promising templates and precursors that can be converted to a series of functional materials. Probing the dynamic conversion processes within individual MOF crystal particles in real-time is key to understanding the structure-activity relationship, but this remains challenging, particularly for anisotropic MOF crystals. Here, using dark-field optical microscopy, we visually in situ image and quantify the dynamic oxidation conversion of a single bismuth-based metal-organic framework (Bi-MOF) into bismuth oxides by NaClO. The reactivity of single rod-shaped Bi-MOFs is anisotropic, and its two ends have higher activity than those in the middle regions, which depend on the aspect ratio. Through analysis of the channel directions and theoretical diffusion coefficients, this anisotropic behavior may be attributed to the inherently low diffusion barrier of the NaClO oxidant due to the larger accessible rectangular channels at both ends along the c-axis. Our findings unveil comprehensive kinetic information about the MOF conversion reaction at the subparticle level, favoring the design of future MOF-derived materials.

The interlayer shifting of two-dimensional (2D) covalent organic frameworks (COFs) is a critical issue affecting their sorption and catalytic properties. However, current analytical tools often measure static and averaged stacking properties from bulk samples, restricting a comprehensive understanding of the interlayer shifting process in individual 2D COFs. Here, we report real-time dynamic imaging of the solvent exchange-induced interlayer shifting in single 2D COFs using in situ dark-field optical microscopy (DFM). The increase in pore size from quasi-AB stacking to AA stacking in triphenylbenzene (TPB)-terephthaldehyde-COF and TPB-dimethoxyterephthaldehyde-COF in organic solvent and water facilitates the accommodation of more guest molecules, leading to a higher scattering intensity. By using the grayscale intensity of DFM images as a quantitative indicator, we visually observe that the solvent exchange-triggered interlayer shifting dynamics not only exhibits a significant particle-to-particle heterogeneity but also is sensitive to the solvent viscosity and interlayer interaction strength of 2D COFs. Moreover, theoretical simulations elucidate that this interlayer shifting process is governed by crystal stacking energies and follows a thermodynamically preferred pathway during the water-to-organic exchange process. This imaging methodology provides a useful way for direct observation of solvent exchange-induced interlayer shifting in single 2D COFs and understanding its dynamics.

Bismuth-based metal-organic frameworks (Bi-MOFs) have emerged as important photocatalysts for pollutant degradation applications. Understanding the photocatalytic degradation mechanism is key to achieving technological advantage. Herein, we apply dark-field optical microscopy (DFM) to realize in situ multicolor imaging of the photocatalytic degradation process of permanganate (MnO4-) on single CAU-17 Bi-MOFs. Three reaction kinetic processes such as surface adsorption, photocatalytic reduction, and disproportionation are revealed by combining the time-lapsed DFM images with optical absorption spectra, indicating that the photocatalytic reduction of purple MnO4- first produces beige red MnO42- through a one-electron pathway, and then MnO42- disproportionates into yellow MnO2 on CAU-17. Meanwhile, we observe that the deposition of MnO2 cocatalysts enhances the surface adsorption reaction and the photocatalytic reduction of MnO4- to MnO42-. Unexpectedly, it is found that isopropanol as a typical hole scavenger can stabilize MnO42-, avoiding disproportionation and causing the alteration of the photocatalytic reaction pathway from a one-electron avenue to a three-electron (1 + 2) process for producing MnO2 on CAU-17. This research opens up the possibility of comprehensively tracking and understanding the photocatalytic degradation reaction at the single MOF particle level.

Colorimetric assays are inexpensive and attractive tools for the detection of fentanyl (FTN), yet further enhancing their sensitivity remains a major challenge. Herein, we develop a halogen-bond mediated visual competitive colorimetric assay for FTN using Erythrosine B (EB) as a probe. The addition of poly(ethylene oxide)-block-poly (propylene oxide)-block-poly(ethylene oxide (F-127) induces the EB aggregation, strongly suppressing the background signal. Upon the introduction of FTN, the subsequent competitive reaction displaces F-127 to generate EB-FTN charge-transfer complexes via N...I halogen bonds between electron-rich amine groups and electron-deficient iodine sites, accompanying a significant absorbance wavelength shift and pink-to-purple color change. The limits of detection of this approach for FTN are 2 mg center dot L- 1 by the naked eye and 0.19 mg center dot L- 1 by UV-vis spectroscopy, which are approximately 3.7-fold to 4 orders of magnitude more sensitive than the reported colorimetric assays. Meanwhile, the present method is well applied for FTN-spiked domestic sewage samples, and an easy-to-use smartphone-based digital image colorimetry is also fabricated. It is expected that such an assay can play a key role in alleviating the worldwide opioid overdose crisis.

The core-shell microstructures are attracting much interest, most notably for their superior performance compared with their pure counterparts because of the interfacial effect. Comprehensively understanding the mechanism of the interfacial effect is critical but still elusive. Here, we report real-time dark-field optical microscopy (DFM) imaging of the selective etching in the core region of single cuprous oxide-bismoclite (Cu2O@BiOCl) core-shell microcrystals by I-. In situ DFM observations reveal that the reaction activity of Cu2O is significantly improved after coating the BiOCl shell layer, and the I- diffuses through the BiOCl shell and approaches the interface region, followed by etching the Cu2O core. During the etching process, two distinct reaction pathways, such as interfacial Cu2+-driven redox etching and confinement-governed dissolution, are identified. The interfacial Cu2+ is generated due to the coordination number difference at the core-shell interface. Moreover, according to the in situ DFM single-crystal imaging results, the ensemble adsorption capacity improvement for I- is also demonstrated in Cu2O@BiOCl core-shell microcrystals. These findings provide deep insights into the interfacial effect of core-shell microcrystals and establish a bridge between microscopic imaging and macroscopic practical application.

In this contribution, we report on the visualization of 12-crown-4 molecular diffusion behavior within a single-crystal particle of covalent organic framework-300 (COF-300) using operando dark-field optical microscopy. The diffusion area and front of 12-crown-4 are directly tracked in real time, offering key information for quantifying the diffusion coefficient (D). The direction of the diffusion and variation of D reveal intraparticle and interparticle heterogeneity. Notably, an unexpected hydration-accelerated diffusion process of 12-crown-4 within the pore channels of COF-300 is captured, in which a relatively low concentration of 12-crown-4 aqueous solution induces a fast diffusion, whereas the pure 12-crown-4 liquid cannot access the framework. The observed acceleration diffusion is demonstrated to arise from the hydrogen-bonding interactions between surface water molecules of hydrated 12-crown-4 and the imine groups of COF-300. These findings expand the mechanistic understanding of the noncovalent interactions between COFs and crown ethers (CEs), which will help to design and prepare CE-based COFs with improved performance.

Zinc-ion capacitors (ZICs) have attracted great attention due to a series of advantages. However, the cathode materials are still the bottleneck for high-performance ZICs to be achieved. Therefore, ZIF-8-derived porous carbons are one of the most promising candidates but ZIF-8 nanoparticles with different sizes exhibited various electrochemical performances in ZICs. Herein, a series of monodispersed ZIF-8 nanoparticles are first prepared by a temperature-controlled process to fabricate the corresponding ZIF-8-based porous carbon nanoparticles with pre-designed sizes. The as-prepared materials have been tested as cathode materials in ZICs. Thus, their size effect allowed us to disclose its correlation with other factors such as ion transport/storage and capacitance. The results reveal that the optimal-sized porous carbon particles can effectively shorten the ion transport distance and accelerate the ion diffusion rate, resulting in lower electrical resistance, larger ion diffusion coefficients, and faster electron transport. The presented findings can facilitate the design of new advanced cathode materials paving the way for the development of high-performance cathode materials for ZICs in the future.

Achieving anion capture with metal-organic frameworks (MOFs) usually relies on anion exchange reactions. Here, we report the direct visual imaging of the anion binding process within a charge-neutral Bi-based MOF (UU-200) in water at the single-particle level using in situ dark-field optical microscopy. Notably, an unexpected anion-induced structural shrinkage of UU-200 is mapped, and concentration-dependent responses are applied to determine the association constants. The resulting anion affinity is correlated with its basicity, demonstrating that charge-dense anions such as F-, SO32-, and SO42- feature strong binding with the UU-200 framework. Moreover, the unusual anion binding processes are identified as the C-H hydrogen-bonding interactions between electron-deficient hydrogen atoms on the channel wall and negatively charged anions by combining imaging results, nuclear magnetic resonance spectroscopy, and theoretical simulation. These discoveries reshape and strengthen our fundamental understanding of the anion capture within MOFs, favoring the rational design of MOF-based anion receptors.

By combining dark-field optical microscopy with an in situ thermochemical aqueous solution system, we report a single-particle imaging strategy to investigate the host-guest interactions between covalent organic framework-300 (COF-300) as a representative COF host and a series of linear-chain fatty amines. The thermodynamic parameters, such as dissociation constant, Gibbs free energy changes, enthalpy changes, and entropy changes for the binding events within COF-300 are quantified. Correlation between the hydrophobicity of various amines and other data suggests that the mechanism of the host-guest bindings arises from the entropy-driven noncovalent interactions such as hydrogen bonds and van der Waals forces. These mechanistic insights allow for the rational design and preparation of COF-300-encapsulated n-octylamine with enhanced trapping performance of radioactive I-131(-). This study not only provides thermodynamic insights into the host-guest interactions within the COF framework but also establishes a structure-property relationship between fatty amines and energetic magnitude information.

The development of efficient, robust, and cost‐effective electrocatalysts remains a significant challenge for practical water electrolysis. Here, a metallic glass (MG)‐based catalyst with surface‐enriched Ir and Pt‐alloyed active sites, demonstrating superior electrocatalytic performance, is reported. The dealloyed catalyst, characterized by an Ir and Pt‐rich honeycombed nanoporous surface and an interior flexible MG substrate, can directly serve as a bifunctional electrode, enabling efficient hydrogen and oxygen evolution reactions with low overpotentials of 19 and 223 mV to achieve a current density of 10 mA cm−2, respectively. Notably, the mass activity of the catalyst surpasses that of commercial Pt/C and Ir/C catalysts by 13.9 and 16.5 times, respectively. Additionally, the catalyst exhibits exceptional stability with negligible activity decay even under an ampere‐level current density (i.e., ≥1 A cm−2). Theoretical calculations reveal the optimization of atomic configuration and regulation of electronic interactions through lattice strain induced by the co‐alloying of Ir and Pt, contributing to superior electrocatalytic performance. Furthermore, the unique honeycombed nanoporous architecture, shaped by the surface migration and enrichment of the noble metals, offers abundant active sites for accelerating the electrocatalytic reactions. This work presents a novel approach to cost‐effectively design high‐performance alloy catalysts by engineering surface catalytically active sites.