Tandem Conversion of Cyano-/Amino-Organics into N-Doped Carbon Nanotubes and Harmless Off-Gas.

We reported a new technology for transforming N-containing organic wastes (such as aniline, adiponitrile, and tar from preoxidized PAN fibers) into N-doped carbon nanotubes (N-CNTs) with nanosized iron or nickel catalysts in two consecutive reactors at 650-800 °C. Most of the reactants were converted, and N-CNTs in large amounts were produced in the first stage of the reactor, while the reactants could be completely removed in the second stage of the reactor. The doping content of N-species on CNTs easily approached 10-22 wt %, much higher than most of the earlier reported methods. The results were potentially useful for the treatment of toxic cyano-organics and the production of high-end products simultaneously.

Fluidization and Application of Carbon Nano Agglomerations.

Carbon nanomaterials are unique with excellent functionality and diverse structures. However, agglomerated structures are commonly formed because of small-size effects and surface effects. Their hierarchical assembly into micro particles enables carbon nanomaterials to break the boundaries of classical Geldart particle classification before stable fluidization under gas-solid interactions. Currently, there are few systematic reports regarding the structural evolution and fluidization mechanism of carbon nano agglomerations. Based on existing research on carbon nanomaterials, this article reviews the fluidized structure control and fluidization principles of prototypical carbon nanotubes (CNTs) as well as their nanocomposites. The controlled agglomerate fluidization technology leads to the successful mass production of agglomerated and aligned CNTs. In addition, the self-similar agglomeration of individual ultralong CNTs and nanocomposites with silicon as model systems further exemplify the important role of surface structure and particle-fluid interactions. These emerging nano agglomerations have endowed classical fluidization technology with more innovations in advanced applications like energy storage, biomedical, and electronics. This review aims to provide insights into the connections between fluidization and carbon nanomaterials by highlighting their hierarchical structural evolution and the principle of agglomerated fluidization, expecting to showcase the vitality and connotation of fluidization science and technology in the new era.

Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst.

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situ analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situ X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO2 methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by in situ XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2 and H2 dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2 methanation reaction pathway while hindering coking and fostering high selectivity toward methane.

Imaging of Single Molecular Behaviors Under Bifurcated Three-Centered Hydrogen Bonding.

The mechanism for interaction and bonding of single guest molecules with active sites fundamentally determines the sorption and subsequent catalytic processes occurring in host zeolitic frameworks. However, no real-space studies on these significant issues have been reported thus far, since atomically visualizing guest molecules and recognizing single Al T-sites in zeolites remain challenging. Here, we atomically resolved single thiophene probes interacting with acid T-sites in the ZSM-5 framework to study the bonding behaviors between them. The synergy of bifurcated three-centered hydrogen bonds and van der Waals interactions can "freeze" the near-horizontal thiophene and make it stable enough to be imaged. By combining the imaging results with simulations, direct atomic observations enabled us to precisely locate the single Al T-sites in individual straight channels. Then, we statistically found that the thiophene bonding probability of the T11 site is 15 times higher than that of the T6 site. For different acid T-sites, the variation in the interaction synergy changes the inner angle of the host-guest O-H⋅⋅⋅S hydrogen bond, thereby affecting the stability of the near-horizontal thiophene and leading to considerable bonding inhomogeneities.

Point CNN:3D Face Recognition with Local Feature Descriptor and Feature Enhancement Mechanism.

Three-dimensional face recognition is an important part of the field of computer vision. Point clouds are widely used in the field of 3D vision due to the simple mathematical expression. However, the disorder of the points makes it difficult for them to have ordered indexes in convolutional neural networks. In addition, the point clouds lack detailed textures, which makes the facial features easily affected by expression or head pose changes. To solve the above problems, this paper constructs a new face recognition network, which mainly consists of two parts. The first part is a novel operator based on a local feature descriptor to realize the fine-grained features extraction and the permutation invariance of point clouds. The second part is a feature enhancement mechanism to enhance the discrimination of facial features. In order to verify the performance of our method, we conducted experiments on three public datasets: CASIA-3D, Bosphorus, and Lock3Dface. The results show that the accuracy of our method is improved by 0.7%, 0.4%, and 0.8% compared with the latest methods on these three datasets, respectively.

Process Simulation of Diesel into Aromatics and Carbon Nanotubes: A Techno and Economic Analyses.

With the sustainable increase of renewable energy and the maturation of heavy vehicle market, diesel consumption would face a downward trend worldwide. Herein, we have proposed a new route for hydrocracking of light cycle oil (LCO) into aromatics and gasoline and the tandem conversion of C1-C5 hydrocarbons (byproducts) into carbon nanotubes (CNTs) and H2, and by combining the simulation with Aspen Plus software and the experimental study of C2-C5 conversion, we have built a transformation network including LCO to aromatics/gasoline, C2-C5 to CNTs and H2, the conversion of CH4 into CNTs and H2, and the cycle use of H2 with pressure swing adsorption. Mass balance, energy consumption, and economic analysis were discussed as a function of varying CNT yield and CH4 conversion. 50% of H2 required for hydrocracking of LCO can be supplied by the downstream chemical vapor deposition processes. This can greatly reduce the cost of high-priced hydrogen feedstock. If the sale price of CNTs exceeds 2170 CNY per ton, the entire process would break even for a process of dealing with 520,000 t/a LCO. These results imply the great potential of this route, considering the vast demand and the current high price of CNTs.

VBlock: A Blockchain-Based Tamper-Proofing Data Protection Model for Internet of Vehicle Networks.

The rapid advancement of the Internet of Vehicles (IoV) has led to a massive growth in data received from IoV networks. The cloud storage has been a timely service that provides a vast range of data storage for IoV networks. However, existing data storage and access models used to manage and protect data in IoV networks have proven to be insufficient. They are centralized and usually accompanied by a lack of trust, transparency, security, immutability, and provenance. In this paper, we propose VBlock, a blockchain-based system that addresses the issues of illegal modification of outsourced vehicular data for smart city management and improvement. We introduce a novel collusion-resistant model for outsourcing data to cloud storage that ensures the network remains tamper-proof, has good data provenance and auditing, and solves the centralized problems prone to the single point of failure. We introduced a key revocation mechanism to secure the network from malicious nodes. We formally define the system model of VBlock in the setting of a consortium blockchain. Our simulation results and security analysis show that the proposed model provides a strong security guarantee with high efficiency and is practicable in the IoV environment.

Atomic imaging of zeolite-confined single molecules by electron microscopy.

Single-molecule imaging with atomic resolution is a notable method to study various molecular behaviours and interactions1-5. Although low-dose electron microscopy has been proved effective in observing small molecules6-13, it has not yet helped us achieve an atomic understanding of the basic physics and chemistry of single molecules in porous materials, such as zeolites14-16. The configurations of small molecules interacting with acid sites determine the wide applications of zeolites in catalysis, adsorption, gas separation and energy storage17-21. Here we report the atomic imaging of single pyridine and thiophene confined in the channel of zeolite ZSM-5 (ref. 22). On the basis of integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM)23-25, we directly observe the adsorption and desorption behaviours of pyridines in ZSM-5 under the in situ atmosphere. The adsorption configuration of single pyridine is atomically resolved and the S atoms in thiophenes are located after comparing imaging results with calculations. The strong interactions between molecules and acid sites can be visually studied in real-space images. This work provides a general strategy to directly observe these molecular structures and interactions in both the static image and the in situ experiment, expanding the applications of electron microscopy to the further study of various single-molecule behaviours with high resolution.

Modulating inherent lewis acidity at the intergrowth interface of mortise-tenon zeolite catalyst.

The acid sites of zeolite are important local structures to control the products in the chemical conversion. However, it remains a great challenge to precisely design the structures of acid sites, since there are still lack the controllable methods to generate and identify them with a high resolution. Here, we use the lattice mismatch of the intergrown zeolite to enrich the inherent Lewis acid sites (LASs) at the interface of a mortise-tenon ZSM-5 catalyst (ZSM-5-MT) with a 90° intergrowth structure. ZSM-5-MT is formed by two perpendicular blocks that are atomically resolved by integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). It can be revealed by various methods that novel framework-associated Al (AlFR) LASs are generated in ZSM-5-MT. Combining the iDPC-STEM results with other characterizations, we demonstrate that the partial missing of O atoms at interfaces results in the formation of inherent AlFR LASs in ZSM-5-MT. As a result, the ZSM-5-MT catalyst shows a higher selectivity of propylene and butene than the single-crystal ZSM-5 in the steady conversion of methanol. These results provide an efficient strategy to design the Lewis acidity in zeolite catalysts for tailored functions via interface engineering.

In situ imaging of the sorption-induced subcell topological flexibility of a rigid zeolite framework.

The crystallographic pore sizes of zeolites are substantially smaller than those inferred from catalytic transformation and molecular sieving capabilities, which reflects flexible variation in zeolite opening pores. Using in situ electron microscopy, we imaged the straight channels of ZSM-5 zeolite with benzene as a probe molecule and observed subcell flexibility of the framework. The opening pores stretched along the longest direction of confined benzene molecules with a maximum aspect change of 15%, and the Pnma space group symmetry of the MFI framework caused adjacent channels to deform. This compensation maintained the stability and rigidity of the overall unit cell within 0.5% deformation. The subcell flexibility originates mainly from the topologically soft silicon-oxygen-silicon hinges between rigid tetrahedral SiO4 units, with inner angles varying from 135° to 153°, as confirmed by ab initio molecular dynamics simulations.

Rational Design of Zinc/Zeolite Catalyst: Selective Formation of p-Xylene from Methanol to Aromatics Reaction.

The production of p-xylene from the methanol to aromatics (MTA) reaction is challenging. The catalytic stability, which is inversely proportional to the particle size of the zeolite, is not always compatible with p-xylene selectivity, which is inversely proportional to the external acid sites. In this study, based on a nano-sized zeolite, we designed hollow triple-shelled Zn/MFI single crystals using the ultra-dilute liquid-phase growth technique. The obtained composites possessed one ZSM-5 layer (≈30 nm) in the middle and two silicalite-1 layers (≈20 nm) epitaxially grown on two sides of ZSM-5, which exhibited a considerably long lifetime (100 % methanol conversion >40 h) as well as an enhanced shape selectivity of p-xylene (>35 %) with a p-xylene/xylene ratio of ≈90 %. Importantly, using this sandwich-like zeolite structure, we directly imaged the Zn species in the micropores of only the ZSM-5 layer and further determined the specific structure and anchor location of the Zn species.

Ultrafast Nonvolatile Ionic Liquids-Based Supercapacitors with Al Foam-Enhanced Carbon Electrode.

The ultrafast frequency response supercapacitor is a promising candidate for alternating current line filtering. We report the fabrication of a special structured ionic liquid-based supercapacitor with an ultrafast response of only 1.5 ms. The three-dimensional aluminum (Al) foam in situ coated with carbon layer (∼500 nm) serves as the novel, highly efficient electrode-current collector. The high porosity (95%) of Al foam allows the rapid ion diffusion and the as-obtained Al/C interface with atomic-level mixing allows the fast electron transfer, two crucial factors for ultrafast response. Hence, it possesses an excellent specific mass capacitance of 68 mF g-1 at 120 Hz, as well as an ultrahigh rate of up to 3000 V s -1. The supercapacitors exhibit frequency modulation performance in the range of 20 kHz to 16 MHz. They exhibit the similar even better alternating current filtering performance, as compared to the commercial aluminum electrolytic capacitors, detected at 10 Hz, 60 Hz, 100 Hz and 1 M Hz. These results suggest that, although ILs have high viscosity and low ion mobility, the IL-based supercapacitor has a great potential to be used as a device for alternating current line filtering, as well as providing nonvolatile and nonflammability safety.

High-Performance Graphene/Carbon Nanotube-Based Adsorbents for Treating Diluted o-Cresol in Water in a Pilot-Plant Scale Demo.

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 <1.12 mg/kg in a continuous and reversible adsorption-desorption apparatus, which could last for 99 h with a space velocity of 30 h-1 and a total wastewater capacity of 5 tons per day. Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Raman spectroscopy all suggested that the surface properties and pore structure of the spent adsorbents remain unchanged after recycling at both low-temperature adsorption and high-temperature desorption in vacuum. These results provided an effective reversible adsorbent system for removing aromatic organics and prompted the scaled-up applications of carbon nanomaterials in the treatment of wastewater.

A single-molecule van der Waals compass.

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.

Resolving atomic SAPO-34/18 intergrowth architectures for methanol conversion by identifying light atoms and bonds.

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.

Monochromatic Carbon Nanotube Tangles Grown by Microfluidic Switching between Chaos and Fractals.

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.

The Application of Carbon Nanotube/Graphene-Based Nanomaterials in Wastewater Treatment.

The treatment of organic wastewater is of great significance. Carbon nanotube (CNT)/graphene-based nanomaterials have great potential as absorbent materials for organic wastewater treatment owing to their high specific surface area, mesoporous structure, tunable surface properties, and high chemical stability; these attributes allow them to endure harsh wastewater conditions, such as acidic, basic, and salty conditions at high concentrations or at high temperatures. Although a substantial amount of work has been reported on the performance of CNT/graphene-based nanomaterials in organic wastewater systems, engineering challenges still exist for their practical application. Herein, the adsorption mechanism of CNT- and graphene-based nanomaterials is summarized, including the adsorption mechanism of CNTs and graphene at the atomic and molecular levels, their hydrophilic and hydrophobic surface properties, and the structure-property relationship required for adsorption to occur. Second, the structural modification and recombination methods of CNT- and graphene-based adsorbents for various organic wastewater systems are introduced. Third, the engineering challenges, including the molding of macroscopically stable adsorbents, adsorption isotherm models and adsorption kinetic behaviors, and reversible adsorption performance compared to that of activated carbon (AC) are discussed. Finally, cost issues are discussed in light of scalable and practical application of these materials.

Highly selective conversion of methanol to propylene: design of an MFI zeolite with selective blockage of (010) surfaces.

As an important catalyst of methanol-to-propylene (MTP) conversion, the ZSM-5 zeolite has an anisotropic diffusion path and a large pore size, resulting in the formation of undesirable heavy aromatic by-products. Herein, we developed a surface-specific silica deposition method to block straight channels of nanosized ZSM-5 crystals selectively. By such a coating method, we can selectively suppress the yield of aromatics from the original 13% to 2.4% at 100% conversion of methanol. Trapped hydrocarbon pool species are directly confirmed by aberration-corrected S/TEM for the first time. Such a method of trapping and restricting hydrocarbon pool species in a multiscale zeolite with 10-membered rings would significantly increase its catalytic efficiency and olefin diffusion. Moreover, this provides new methodologies for zeolite structure construction and will be greatly beneficial for the industrial MTP process.

Perspective to the Potential Use of Graphene in Li-Ion Battery and Supercapacitor.

Graphene is a hot star in materials science with various potential application aspects, including in Li-ion battery and supercapacitor. The burst of scientific papers in this area seems to validate the performance of graphene, but also arouses large dispute. Herein, we share our judgment of these trends to all, encouraging the discussion and enhancing the understanding of the structure-performance relationship of graphene.

Enhanced production of aromatics from propane with a temperature-shifting two-stage fluidized bed reactor.

A temperature-shifting two-stage fluidized bed reactor technology was used to convert propane and its intermediate products into aromatics. The first stage served for the aromatization of propane with a Ga/ZSM-5 catalyst at 570 °C. The second stage served for the alkylation of the intermediates of olefins at 300 °C. The increased yield of aromatics was attributed to the effective transformation of C2-C3 olefins as well as due to the suppression of the hydrogen transfer effect of the olefins.