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Surface and interface, with unique local characteristics different from bulk structure, are of great significance in various applications of metal-organic frameworks (MOFs), which should be studied by real-space imaging methods, such as electron microscopy. However, it is still challenging to atomically resolve these local structures in MOFs, because they are even more sensitive to electron irradiation. Here, we use integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) to achieve the atomic imaging of both the metal nodes and organic linkers in UiO-66 (Zr) nanocrystals and their assembly. After adding acetic acid, we modulate the whole process of MOF assembly and observe the organic linkers at both the surfaces and twin interfaces in the chemically assembled UiO-66 (Zr) crystals by the iDPC-STEM. These results bring us a deeper understanding on the role of acid modulators that promote the MOF assembly by generating the missing-linker defects on the crystal surface.

Graphene/carbon nanotube (CNT)-based adsorbents were fabricated on a kilogram scale by extrusion processing (where graphene is used as the major adsorption material and CNTs make up the backbone to enhance the mechanical strength) and then mixed and bonded with poly(tetrafluoroethylene). Kilogram-scale adsorbents were used to treat the content of o-cresol in wastewater to be

Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level1–6. Van der Waals interactions at the sub-nanometre scale strongly influence various molecular behaviours under confinement conditions7–11. Inspired by the traditional compass12, here we use a para-xylene molecule as a rotating pointer to detect the host–guest van der Waals interactions in the straight channel of the MFI-type zeolite framework. We use integrated differential phase contrast scanning transmission electron microscopy13–15 to achieve real-space imaging of a single para-xylene molecule in each channel. A good correlation between the orientation of the single-molecule pointer and the atomic structure of the channel is established by combining the results of calculations and imaging studies. The orientations of para-xylene help us to identify changes in the van der Waals interactions, which are related to the channel geometry in both spatial and temporal dimensions. This work not only provides a visible and sensitive means to investigate host–guest van der Waals interactions in porous materials at the molecular level, but also encourages the further study of other single-molecule behaviours using electron microscopy techniques. The orientation of a rotating para-xylene molecule in the nanochannel of a zeolite framework can be visualised by electron microscopy to determine the host–guest van der Waals interaction inside the channel.

The micro-structures of catalyst materials basically affect their macro-architectures and catalytic performances. Atomically resolving the micro-structures of zeolite catalysts, which have been widely used in the methanol conversion, will bring us a deeper insight into their structure-property correlations. However, it is still challenging for the atomic imaging of silicoaluminophosphate zeolites by electron microscopy due to the limits of their electron beam sensitivity. Here, we achieve the real-space imaging of the atomic lattices in SAPO-34 and SAPO-18 zeolites, including the Al–O–P atoms and bonds, by the integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). The spatial distribution of SAPO-34 and SAPO-18 domains in SAPO-34/18 intergrowths can be clearly resolved. By changing the Si contents and templates in feed, we obtain two SAPO-34/18 catalysts, hierarchical and sandwich catalysts, with highly-mixed and separated SAPO-34 and SAPO-18 lattices respectively. The reduced diffusion distances of inside products greatly improve the catalytic performances of two catalysts in methanol conversion. Based on the observed distributions of lattices and elements in these catalysts, we can have a preliminary understanding on the correlation between the synthesis conditions and structures of SAPO-34/18 intergrowth catalysts to further modify their performances based on unique architectures., The micro-structures of zeolite catalysts affect their macroarchitectures and catalytic performances. Here, the different SAPO-34/18 intergrowth catalysts are atomically resolved, and the correlation between synthesis conditions and zeolite structures is revealed to further enhance their performances in methanol conversion.

Graphene/carbon nanotube (CNT)-based adsorbents were fabricated on a kilogram scale by extrusion processing (where graphene is used as the major adsorption material and CNTs make up the backbone to enhance the mechanical strength) and then mixed and bonded with poly(tetrafluoroethylene). Kilogram-scale adsorbents were used to treat the content of

Single-molecule imaging with atomic resolution is a notable method to study various molecular behaviours and interactions

Extraordinary properties and great application potentials of carbon nanotubes (CNT) and graphene fundamentally rely on their large‐scale perfect sp2 structure. Particularly for high‐end applications, ultralow defect density and ultrahigh selectivity are prerequisites, for which metal‐catalyzed chemical vapor deposition (CVD) is the most promising approach. Due to their structure and peculiarity, CNTs and graphene can themselves provide growth templates and nonlocal dual conductance, serving as template autocatalysts with tunable bandgap during the CVD. However, current growth kinetics models all focus on the external factors and edges. Here, the growth kinetics of sp2 nanocarbons is elaborated from the perspective of template autocatalysis and holistic electronic structure. After reviewing current growth kinetics, various representative works involving CVD growth of different sp2 nanocarbons are analyzed, to reveal their bandgap‐coupled kinetics and resulting selective synthesis. Recent progress is then reviewed, which has demonstrated the interlocking between the atomic assembly rate and bandgap of CNTs, with an explicit volcano dependence whose peak would be determined by the environment. In addition, the topological protection for perfect sp2 structure and the defect‐induced perturbation for the interlocking are discussed. Finally, the prospects for the kinetic selective growth of perfect nanocarbons are proposed., The developments toward perfect nanocarbon structures are presented, and the importance of bandgap‐coupled template autocatalysis kinetics is emphatically demonstrated. The protection provided by large formation energies of topological defects for perfect sp2 structure is revealed. Furthermore, the bandgap‐coupled autocatalysis growth kinetics, which could modulate detailed structure of nanocarbons due to their slight difference in bandgap, are manifested by various evidences.

The nature of chaos is in that elusive flow that is an advanced order out of our vision. It is wise to take advantage of chaos after recognizing or modifying its unique fractal properties. Here, a magnetron weaving strategy was developed for producing chaotic but monochromatic carbon nanotube tangles (CNT-Ts) under Kelvin-Helmholtz instability (KHI). The self-similarity characteristic facilitated individual ultralong CNTs to manipulate their entropy-driven fractal geometry, resulting in ∼104 μm2 CNT-Ts with variable curvature radius. In addition, based on the rate-selected mechanism, 85% metallic and ∼100% semiconducting CNT-Ts were synthesized and separated simultaneously at different length positions. After ex situ modifying their fractal into aligned CNTs with hydrogel, these CNT-Ts delivered a current of 10 μA μm-1 in transistors with an on/off ratio >107. It has provided the third route as a paradigm of applying one-dimensional nanomaterials by switching between chaos and fractal, in parallel with that of direct synthesis and postseparation.

Imaging the single molecules is always challenging under the diverse microscopes, but highly demanded for investigating the intermolecular interactions at the molecular level1-6. The van der Waals (vdW) interactions at sub-nanometer scale will deeply influence various molecular behaviors under the confinement conditions7-11. Here, inspired by the traditional compass12, we introduce a classical strategy using a vertical para-xylene (PX) molecule as a rotating pointer to detect the vdW potential field in a MFI straight channel. Based on the integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM)13-17, we achieve the real-space imaging of single PX molecule pointer in each channel with a certain orientation. The solid relation between the pointer orientation and atomic channel structure in this vdW compass is established by combining the calculations and imaging results. Thus, these PX orientations help us identify the varied vdW potential field related to the channel geometry both in the spatial and temporal dimensions. This work not only provides a visible and sensitive pointer to investigate the host-guest vdW interactions in porous materials at the molecular level, but also promotes the further imaging and study of other single-molecule behaviors by the iDPC-STEM.

Carbon nanotubes (CNTs) are one of the strongest known materials. When assembled into fibres, however, their strength becomes impaired by defects, impurities, random orientations and discontinuous lengths. Fabricating CNT fibres with strength reaching that of a single CNT has been an enduring challenge. Here, we demonstrate the fabrication of CNT bundles (CNTBs) that are centimetres long with tensile strength over 80 GPa using ultralong defect-free CNTs. The tensile strength of CNTBs is controlled by the Daniels effect owing to the non-uniformity of the initial strains in the components. We propose a synchronous tightening and relaxing strategy to release these non-uniform initial strains. The fabricated CNTBs, consisting of a large number of components with parallel alignment, defect-free structures, continuous lengths and uniform initial strains, exhibit a tensile strength of 80 GPa (corresponding to an engineering tensile strength of 43 GPa), which is far higher than that of any other strong fibre.

Carbon nanotubes (CNTs) are promising candidates for smart electronic devices. However, it is challenging to mediate their bandgap or chirality from a vapor-liquid-solid growth process. Here, we demonstrate rate-selected semiconducting CNT arrays based on interlocking between the atomic assembly rate and bandgap of CNTs. Rate analysis confirms the Schulz-Flory distribution which leads to various decay rates as length increases in metallic and semiconducting CNTs. Quantitatively, a nearly ten-fold faster decay rate of metallic CNTs leads to a spontaneous purification of the predicted 99.9999% semiconducting CNTs at a length of 154 mm, and the longest CNT can be 650 mm through an optimized reactor. Transistors fabricated on them deliver a high current of 14 μA μm−1 with on/off ratio around 108 and mobility over 4000 cm2 V−1 s−1. Our rate-selected strategy offers more freedom to control the CNT purity in-situ and offers a robust methodology to synthesize perfectly assembled nanotubes over a long scale., Carbon nanotubes are considered promising materials for microelectronics, but it is challenging to separate semiconducting tubes from their metallic counterparts. Here, the authors report a self-purification growth process that allows them to obtain long, highly pure semiconducting carbon nanotubes.

Finding the source of their durability Many high-strength materials can fail after repeated exposure to subcritical loading; therefore, understanding the causes of fatigue is key to extending the longevity of the material in use. Bai et al. used chemical vapor deposition to produce centimeter-long carbon nanotubes. They then decorated these nanotubes with titanium dioxide nanoparticles for optical visualization and studied them using noncontact acoustic resonance tests. The authors determined that fatigue lifetime is dependent on the formation of the first defects on straining and is higher at lower temperatures. Science , this issue p. 1104

Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level

Chirality is a significant structural feature for chemistry, biology, physics, and materials science, and especially determines the electrical, mechanical, and optical properties of diverse tubular structures, such as carbon nanotubes (CNTs). To recognize the chirality of nanotubes, templates are introduced as potential tools to obtain crystalline samples with visible chiral fringes under electron microscopes. However, few efforts show optimistic results, and new understanding is desired to control the sample quality with CNT templates. Here, a synthesis strategy of single-crystalline molybdenum trioxide (α-MoO3 ) nanotubes (MONTs) on CNT surfaces is reported to build a 1D van der Waals (vdW) heterostructure. The chirality of the MONTs can be directly "seen" and their structural selectivity is revealed. First, the centralized distribution of the chiral angles of the MONTs indicates a preferential orientation due to the anisotropic bending rigidity of the 2D layers. Then, the interlayer mismatching rejects the radial stacking of α-MoO3 to maintain the single-walled nature. These results provide a spontaneous strategy for the efficient recognition and control of chirality, and open up a new avenue for CNT-based functional 1D vdW heterostructures.

A novel polymerizable amphiphilic purple dye, 4-((4-(p-toluidino)anthraquinone-1-yl)oxy)-N-(2-(methacryloyloxy)ethyl)-N,N-dimethylbutan-1-aminium bromide (TAQMAB), was first designed and synthesized, and then used to prepare cationic covalently purple copolymer latexes through semi-continuous emulsion polymerization using water-soluble 2,2′-azobis(2-methylpropionamide) dihydrochloride (AIBA) as initiator. The chemical structure and properties of the dye were confirmed and characterized. Results showed that the critical micelle concentration and the hydrophilic lipophilic balance of TAQMAB were 975 mg L−1 and 32.8, respectively. The amphiphilic structure of TAQMAB gave the dye considerable water solubility and an ability to migrate from the monomer droplets into the latex particles during emulsion polymerization, which overcame the limitation of solubility, dye conversion, color depth of the latexes, and made the polymerization proceed smoothly. The total monomer conversion decreased gradually with dye amount increasing, while the dye still kept a relatively high conversion when an adequate amount of AIBA was used. Both the total monomer conversion and the dye conversion decreased with AIBA amount decreasing. The light fastness of the covalently colored film was significantly enhanced compared with the noncovalently colored one, which was ascribed to electrons flowing through the polymer chains.

Energy storage in a proper form is an important way to meet the fast increase in the demand for energy. Among the strategies for storing energy, storage of mechanical energy via suitable media is widely utilized by human beings. With a tensile strength over 100 GPa, and a Young's modulus over 1 TPa, carbon nanotubes (CNTs) are considered as one of the strongest materials ever found and exhibit overwhelming advantages for storing mechanical energy. For example, the tensile-strain energy density of CNTs is as high as 1125 Wh kg-1 . In addition, CNTs also exhibit great potential for fabricating flywheels to store kinetic energy with both high energy density (8571 Wh kg-1 ) and high power density (2 MW kg-1 to 2 GW kg-1 ). Here, an overview of some typical mechanical-energy-storage systems and materials is given. Then, theoretical and experimental studies on the mechanical properties of CNTs and CNT assemblies are introduced. Afterward, the strategies for utilizing CNTs to store mechanical energy are discussed. In addition, macroscale production of CNTs is summarized. Finally, future trends and prospects in the development of CNTs used as mechanical-energy-storage materials are presented.

Supersaturation formulation is an effective way to improve the oral bioavailability of poorly water-soluble drugs, and water-soluble polymers are commonly used to prolong the supersaturation. However, the mechanism for such supersaturation prolonging effect is not clearly understood. Using the hydrocortisone/hydroxypropyl methylcellulose (HPMC) pair as a model system, we found that HPMC prolongs hydrocortisone supersaturation by inducing the formation of a metastable crystal polymorph of higher solubility, hence lowering the actual supersaturation level in the solution. A possible mechanism is proposed to explain the selective polymorph formation in the presence of polymers.

Identifying the atomic structures of porous materials in spatial and temporal dimensions by (scanning) transmission electron microscope ((S)TEM) is significant for their wide applications in catalysis, separation and energy storage. However, the sensitivity of materials to electron beams made it difficult to reduce the electron damage to specimens while maintaining the resolution and signal-to-noise ratio. It is therefore still challenging to capture multiple images of the same area in one crystal to image the temporal changes of lattices. Usings integrated differential phase contrast (iDPC) STEM, atomic-resolution imaging of beam-sensitive zeolite frameworks is achieved with an ultralow dose of 40 e- A-2 , 2-3 orders of magnitude lower than that of conventional STEM. Based on the iDPC technique, not only the atomic 3D architecture of ZSM-5 crystals but also the changes of frameworks are observed during in situ experiments. Local structures and light-element aromatics in ZSM-5 crystals can also be revealed directly under iDPC-STEM. These results provided not only an efficient tool to image beam-sensitive materials with ultralow beam current but also a new strategy to observe and investigate the hydrocarbon pools in zeolite catalysts at the single-molecule scale.

Because of the outstanding mechanical and electrical properties of carbon nanotubes (CNTs), a CNT-based torsion pendulum is demonstrated to show great potential in nano-electromechanical systems. It is also expected to achieve various manipulations for further characterization and increase device sensitivity using ultrlong CNTs and macroscale moving parts. However, the reported top-down method limits the CNT performance and device size by introducing inevitable contamination and destruction, which greatly hinders the development of single-molecule devices. Here, a bottom-up method is introduced to fabricate heterostructures of anthracene flakes (AFs) and suspended CNTs, providing a nondamaging CNT mechanical measurement before further applications, especially for the twisting behavior, and providing a controllable and clean transfer method to fabricate CNT-based electrical devices under ambient conditions. Based on the unique geometry of CNT/AF heterostructures, various complex manipulations of single-CNT devices are conducted to investigate CNT mechanical properties and prompt novel applications of similar structures in nanotechnology. The AF-decorated CNTs show high Young's modulus (≈1 TPa) and tensile strength (≈100 GPa), and can be considered as the finest and strongest torsional springs. CNT-based torsion balance enables to measure fN-level forces and the torsional spring constant is two orders of magnitude lower than previously reported values.