Correlation between the Carbon Nanotube Growth Rate and Byproducts in Antenna‐Type Remote Plasma Chemical Vapor Deposition Observed by Vacuum Ultraviolet Absorption Spectroscopy

For sp² or sp³ carbon material growth, it is important to investigate the precursors or intermediates just before growth. In this study, the density of ethylene (C₂H₄) outside the plasma discharge space and just before reaching the carbon nanotube (CNT) growth region is investigated by vacuum ultraviolet absorption spectroscopy for plasma discharge in an antenna‐type remote plasma chemical vapor deposition with a CH₄/H₂ system, with which the growth of very long (≈0.5 cm) CNT forests is achieved. Single‐wall CNT forests have the potential for application as electrodes in battery cells, vertical wiring for high current applications, and thermal interface materials. It is observed that the plasma discharge decomposes the CH₄ source gas and forms C₂H_x species, which reversibly reform to C₂H₄ in the plasma‐off state. In addition, the density of the formed C₂H₄ has a strong correlation to the CNT growth rate. Therefore, the C₂H₄ density is a good indicator of the density of C₂H_x species for CNT growth in the CH₄/H₂ plasma system.     

Nanostructured Metal–Organic Conjugated Coordination Polymers with Ligand Tailoring for Superior Rechargeable Energy Storage

Conjugated coordination polymers have become an emerging category of redox‐active materials. Although recent studies heavily focus on the tailoring of metal centers in the complexes to achieve stable electrochemical performance, the effect on different substitutions of the bridging bonds has rarely been studied. An innovative tailoring strategy is presented toward the enhancement of the capacity storage and the stability of metal–organic conjugated coordination polymers. Two nanostructured d‐π conjugated compounds, Ni[C₆H₂(NH)₄]_n (Ni‐NH) and Ni[C₆H₂(NH)₂S₂]_n (Ni‐S), are evaluated and demonstrated to exhibit hybrid electrochemical processes. In particular, Ni‐S delivers a high reversible capacity of 1164 mAh g^?1, an ultralong stability up to 1500 cycles, and a fully recharge ability in 67 s. This tailoring strategy provides a guideline to design future effective conjugated coordination‐polymer‐based electrodes.     

A Chemically Stable Hofmann-Type Metal−Organic Framework with Sandwich-Like Binding Sites for Benchmark Acetylene Capture

The realization of porous materials for highly selective separation of acetylene (C₂H₂) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann-type metal−organic framework (MOF), Co(pyz)[Ni(CN)₄] (termed as ZJU-74a), that features sandwich-like binding sites for benchmark C₂H₂ capture and separation is reported. Gas sorption isotherms reveal that ZJU-74a exhibits by far the record C₂H₂ capture capacity (49 cm³ g⁻¹ at 0.01 bar and 296 K) and thus ultrahigh selectivity for C₂H₂/CO₂ (36.5), C₂H₂/C₂H₄ (24.2), and C₂H₂/CH₄ (1312.9) separation at ambient conditions, respectively, of which the C₂H₂/CO₂ selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU-74a can construct a sandwich-type adsorption site to offer dually strong and cooperative interactions for the C₂H₂ molecule, thus leading to its ultrahigh C₂H₂ capture capacity and selectivities. The exceptional separation performance of ZJU-74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C₂H₂/CO₂, 1/99 C₂H₂/C₂H₄, and 50/50 C₂H₂/CH₄ mixtures under ambient conditions.     

Fabrication of diamond-like carbon film on rubber by T-shape filtered-arc-deposition under the influence of various ambient gases

Diamond-like carbon (DLC) films were prepared on rubber substrates using T-shape filtered-arc-deposition (T-FAD), which effectively removes the macrodroplets emitted from the graphite cathode spot from the processing plasma. In the present study, the influence of ambient gas (no gas, Ar, H₂, C₂H₂, C₂H₄, CH₄) was investigated. The DLC films adhered well to the rubber substrate. When the substrate was stretched, the small DLC islands were separated and clefs were opened. The deposition rate on rubber was approximately twice higher than that on a Si substrate. When hydrocarbon gas was introduced as an ambient gas, the deposition rate became higher than that for no gas and H₂ gas. In the cases of C₂H₄ and CH₄ gases, the DLC film was considered to contain a considerable amount of hydrogen. When C₂H₂ gas was used, the highest deposition rate with less surface roughness was achieved.     

A Single‐Molecule Propyne Trap: Highly Efficient Removal of Propyne from Propylene with Anion‐Pillared Ultramicroporous Materials

Propyne/propylene (C₃H₄/C₃H₆) separation is a critical process for the production of polymer‐grade C₃H₆. However, optimization of the structure of porous materials for the highly efficient removal of C₃H₄ from C₃H₆ remains challenging due to their similar structures and ultralow C₃H₄ concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF₆^2? = SIFSIX, NbOF₅^2? = NbOFFIVE) can serve as highly selective C₃H₄ traps for the removal of trace C₃H₄ from C₃H₆. Especially, it is revealed that the pyrazine‐based ultramicroporous material with square grid structure for which the pore shape and functional site disposition can be varied in 0.1–0.5 Å scale to match both the shape and interacting sites of guest molecule is an interesting single‐molecule trap for C₃H₄ molecule. The pyrazine‐based single‐molecule trap enables extremely high C₃H₄ uptake under ultralow concentration (2.65 mmol g^?1 at 3000 ppm, one C₃H₄ per unit cell) and record selectivity over C₃H₆ at 298 K (>250). The single‐molecule binding mode for C₃H₄ within ultramicroporous material is validated by X‐ray diffraction experiments and modeling studies. The breakthrough experiments confirm that anion‐pillared ultramicroporous materials set new benchmarks for the removal of ultralow concentration C₃H₄ (1000 ppm on SIFSIX‐3‐Ni, and 10 000 ppm on SIFSIX‐2‐Cu‐i) from C₃H₆.     

Laser chemical vapor deposition of TiC on tantalum

Laser chemical vapor deposition (LCVD) of titanium carbide (TiC) coatings onto tantalum substrates using hydrogen gas, titanium tetrachloride (TiCl₄) and either methane (CH₄) or acetylene (C₂H₂) source gasses was investigated. The influences of the molar ratio of the source gases and the deposition temperature on the phase assemblage, composition, and morphology of the coatings was examined. Using C₂H₂, nearly stoichiometric coatings were produced at 1000°C and at a TiCl₄/C₂H₂ ratio of 1/0.4. Stoichiometric coatings were also produced using CH₄ but the deposition temperature was 400°C higher and a much larger fraction of the carbon source was required compared to C₂H₂. Although deposition rates were much slower when using CH₄, the coatings exhibited a smoother surface finish and had a higher density compared to those produced using C₂H₂. The suitability of CH₄ and C₂H₂ as carbon sources for depositing stoichiometric, phase-pure coatings is discussed in light of these results.     

Simultaneous removal of acetaldehyde,ammonia and hydrogen sulphide from air by active carbon impregnated with p-aminobenzoic acid,phosphoric acid and metal compounds

Simultaneous removal of acetaldehyde, ammonia, and hydrogen sulphide from air by the impregnated active carbon was studied at 25C. p-Aminobenzoic acid (PABA), phosphoric acid (H₃PO₄), and metal compound such as copper (II) chloride dihydrate (CuCl₂·2H₂O), copper (II) nitrate trihydrate (Cu(NO₃)₂·3H₂O), and potassium iodide (KI) were investigated as impregnation ingredients. Acetaldehyde and ammonia were simultaneously removed from air by the active carbon impregnated with PABA and H₃PO₄. The removal was found to be made mainly through chemical reaction. Acetaldehyde, ammonia, and hydrogen sulphide were simultaneously removed from air by the active carbon impregnated with PABA, H₃PO₄, and metal compound such as CuCl₂·2H₂O, Cu(NO₃)₂·3H₂O, and KI.     

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H2/C2H2 ratios

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H₂/C₂H₂ ratios are investigated. Five kinds of carbon coatings are prepared with H₂/C₂H₂ ratios of 2, 4, 6, 8, and 10. Experimental results show that the deposition rate and surface roughness of carbon coatings decrease as the H₂/C₂H₂ ratio increases. When the H₂/C₂H₂ ratio changes from 2 to 8, the increase of H₂/C₂H₂ ratios detrimentally yields sp³ carbon atoms and sp³-CH₃ bonds in the carbon coatings. However, when the H₂/C₂H₂ ratio exceeds 8, the hydrogen retards the growth of the graphite structure. Moreover, the redundant hydrogen radicals favor bonding with the dangling bonds in the coating surface. Therefore, when the H₂/C₂H₂ ratio increases from 8 to 10, the amounts of sp³ carbon atoms and sp³-CH₃ bonds in the carbon coatings increase. At an H₂/C₂H₂ ratio of 8, the carbon coating exhibits excellent water-repellency and thermal-loading resistance, and so this ratio is the best for producing a hermetically sealed optical fiber coating.     

A High‐Capacity Negative Electrode for Asymmetric Supercapacitors Based on a PMo12 Coordination Polymer with Novel Water‐Assisted Proton Channels

The development of a negative electrode for supercapacitors is a critical challenge for the next‐generation of energy‐storage devices. Herein, two new electrodes formed by the coordination polymers [Ni(itmb)₄(HPMo₁₂O₄₀)]·2H₂O ( 1 ) and [Zn(itmb)₃(H₂O)(HPMo₁₂O₄₀)]·4H₂O ( 2 ) (itmb = 1‐(imidazo‐1‐ly)‐4‐(1,2,4‐triazol‐1‐ylmethyl)benzene), synthesized by a simple hydrothermal method, are described. Compounds 1 and 2 show high capacitances of 477.9 and 890.2 F g^?1, respectively. An asymmetric supercapacitor device assembled using 2 which has novel water‐assisted proton channels as negative electrode and active carbon as positive electrode shows ultrahigh energy density and power density of 23.4 W h kg^?1 and 3864.4 W kg^?1, respectively. Moreover, the ability to feed a red light emitting diode (LED) also demonstrates the feasibility for practical use. The results allow a better elucidation of the storage mechanism in polyoxometalate‐based coordination polymers and provide a promising direction for exploring novel negative materials for new‐generation high‐performance supercapacitors.     

An Ideal Molecular Sieve for Acetylene Removal from Ethylene with Record Selectivity and Productivity

Realization of ideal molecular sieves, in which the larger gas molecules are completely blocked without sacrificing high adsorption capacities of the preferred smaller gas molecules, can significantly reduce energy costs for gas separation and purification and thus facilitate a possible technological transformation from the traditional energy‐intensive cryogenic distillation to the energy‐efficient, adsorbent‐based separation and purification in the future. Although extensive research endeavors are pursued to target ideal molecular sieves among diverse porous materials, over the past several decades, ideal molecular sieves for the separation and purification of light hydrocarbons are rarely realized. Herein, an ideal porous material, SIFSIX‐14‐Cu‐i (also termed as UTSA‐200), is reported with ultrafine tuning of pore size (3.4 Å) to effectively block ethylene (C₂H₄) molecules but to take up a record‐high amount of acetylene (C₂H₂, 58 cm³ cm^?3 under 0.01 bar and 298 K). The material therefore sets up new benchmarks for both the adsorption capacity and selectivity, and thus provides a record purification capacity for the removal of trace C₂H₂ from C₂H₄ with 1.18 mmol g^?1 C₂H₂ uptake capacity from a 1/99 C₂H₂/C₂H₄ mixture to produce 99.9999% pure C₂H₄ (much higher than the acceptable purity of 99.996% for polymer‐grade C₂H₄), as demonstrated by experimental breakthrough curves.     

A Novel Aqueous Asymmetric Supercapacitor based on Pyrene-4,5,9,10-Tetraone Functionalized Graphene as the Cathode and Annealed Ti3C2Tx MXene as the Anode

Asymmetric supercapacitors (ASCs), employing two dissimilar electrode materials with a large redox peak position difference as cathode and anode, have been designed to further broaden the voltage window and improve the energy density of supercapacitors. Organic molecule based electrodes can be constructed by combining redox-active organic molecules with conductive carbon-based materials such as graphene. Herein, pyrene-4,5,9,10-tetraone (PYT), a redox-active molecule with four carbonyl groups, exhibits a four-electron transfer process and can potentially deliver a high capacity. PYT is noncovalently combined with two different kinds of graphene (Graphenea [GN] and LayerOne [LO]) at different mass ratios. The PYT-functionalized GN electrode (PYT/GN 4–5) possesses a high capacity of 711 F g⁻¹ at 1 A g⁻¹ in 1 M H₂SO₄. To match with the PYT/GN 4–5 cathode, an annealed-Ti₃C₂T_x (A-Ti₃C₂T_x) MXene anode with a pseudocapacitive character is prepared by pyrolysis of pure Ti₃C₂T_x. The assembled PYT/GN 4–5//A-Ti₃C₂T_x ASC delivers an outstanding energy density of 18.4 Wh kg⁻¹ at a power density of 700 W kg⁻¹. The PYT-functionalized graphene holds great potential for high-performance energy storage devices.     

Simple and efficient CVD synthesis of graphitic P-doped 3D cubic ordered mesoporous carbon at low temperature with excellent supercapacitor performance

Heteroatom doping is a promising strategy for improving the electrochemical performance of carbon materials. Herein, we spotlight an advantageous, simple, and efficient CVD synthesis of P-doped 3D cubic ordered mesoporous carbon (POMC) for the first time. The POMC was prepared by pyrolysis of acetylene/triphenylphosphine (C₂H₂/Ph₃P) mixture at relatively low temperature over Fe-KIT-6 as a sacrificial template. The ensuing P-doped OMC showed an enhanced porous texture than an undoped counterpart with a specific surface area of 403.5 m²/g, pore volume of 0.545 cm³/g, average pore size of 4.64 nm and suitable heteroatom functionalities with P and O contents of 0.13% and 9.83%, correspondingly. The obtained POMC exhibited a much higher specific capacitance of 288F/g at 0.2 A/g (175F/g for OMC), good cyclic stability of 97.6 %, and good rate capability than pristine OMC in 6 M KOH. It is equivalent to or improved than various stated mono doped and even dual doped porous carbon electrodes. Furthermore, a symmetric supercapacitor (POMC//POMC) was fabricated with 1 M Na₂SO₄ aqueous neutral electrolyte exhibits high cycling stability (89.3%) even with a wide potential window (2.0 V) and offers a relatively high energy density (10.01 Wh/kg) with a power density of 300 W/kg.     

Preparation and photocatalytic activity of TiO2 powders from titanium citrate complex using two-step hydrothermal treatments

White, almost carbon-free TiO₂ powders were prepared from a titanium citrate complex ((NH₄)₄[Ti₂(C₆H₄O₇)₂(O₂)₂]·4H₂O) using a two-step hydrothermal treatment. The product yield, carbon contamination, and crystalline phase of TiO₂ depended on both the temperature and pH value for each treatment. Titanium was precipitated as a solid phase (H₂Ti₂O₅·H₂O) using the first hydrothermal treatment in the basic condition (pH = 12) at temperatures less than 150 °C. Then white rutile or anatase powder was crystallized using the second hydrothermal treatment at 200 °C. By changing the pH condition of the second hydrothermal treatment, rutile and anatase were synthesized selectively. The photocatalytic decomposition activity of obtained rutile powder for gaseous 2-propanol under visible light was increased by Cu-grafting.     

Manufacturing of polypyrrole-FeOOH supercapacitors

The low capacitance of charge storage materials for negative electrodes of supercapacitors (SCap) is a bottleneck in the manufacturing of asymmetric SCap with high operation voltage and high power. Polypyrrole (PPR)-FeOOH-carbon nanotube (NT) electrodes with high electrochemically active material mass (AM) of 32 mg cm^?2 are manufactured for operation in a negative potential range. The manufacturing method involves the use of copolymer of styrenesulfonic and maleic acids (PSAMA) as a new poly-charged dopant for PPR and pyrocatechol violet (PCV) as a co-dispersant for NT and FeOOH. PPR-FeOOH-NT electrodes show enhanced properties in the negative potential range, compared to PPR-NT electrodes. A capacitance (C_S) of 3.8 F cm^?2 is obtained for PPR-FeOOH-NT electrodes with PPR:FeOOH mass ratio of 7:2. The electrodes offer advantages of low resistance and high ratio of AM to conductive support mass. The C_S of negative PPR-FeOOH-NT electrodes matches the C_S of positive MnO₂-NT electrodes of the same AM. Asymmetric SCap is fabricated, which shows high capacitance in a voltage range of 0–1.6 V and low resistance, high power, and energy, which make it important for industrial SCap applications.     

Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation

Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C₂H₂ capacity and selectivity over CO₂ and C₂H₄ than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C₂H₂/CO₂ (50/50, v/v) and C₂H₂/C₂H₄ (1/99, v/v), which can selectively remove C₂H₂ with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.     

Aminal-Linked Covalent Organic Frameworks with hxl-a and Quasi-hcb Topologies for Efficient C2H6/C2H4 Separation

In reticular chemistry, topology is a powerful concept for defining the structures of covalent organic frameworks (COFs). However, due to the lack of diversity in the symmetry and reaction stoichiometry of the monomers, only 5% of the two-dimensional topologies have been reported to be COFs. To overcome the limitations of COF connectivity and pursue novel topologies in COF structures, two aminal-linked COFs, KUF-2 and KUF-3,  are prepared, with dumbbell-shaped secondary building units. Linear dialdehydes and piperazine are condensed at a ratio of 1:2 to construct an aminal linkage, leading to unreported hxl-a ( KUF-2 ) and quasi- hcb ( KUF-3 ) structures. Notably, KUF-3 displays top-tier C₂H₆/C₂H₄ selectivity and C₂H₆ uptake at 298 K, outperforming most porous organic materials. The intrinsic aromatic ring-rich and Lewis basic pore environments, and appropriate pore widths enable the selective adsorption of C₂H₆, as confirmed by Grand Canonical Monte Carlo simulations. Dynamic breakthrough curves revealed that C₂H₆ can be selectively separated from a gas mixture of C₂H₆ and C₂H₄. This study suggests that topology-based design of aminal-COFs is an effective strategy for expanding the field of reticular chemistry and provides the facile integration of strong Lewis basic sites for selective C₂H₆/C₂H₄ separation.     

A Highly Active Star Decahedron Cu Nanocatalyst for Hydrocarbon Production at Low Overpotentials

The electrochemical carbon dioxide reduction reaction (CO₂RR) presents a viable approach to recycle CO₂ gas into low carbon fuels. Thus, the development of highly active catalysts at low overpotential is desired for this reaction. Herein, a high‐yield synthesis of unique star decahedron Cu nanoparticles (SD‐Cu NPs) electrocatalysts, displaying twin boundaries (TBs) and multiple stacking faults, which lead to low overpotentials for methane (CH₄) and high efficiency for ethylene (C₂H₄) production, is reported. Particularly, SD‐Cu NPs show an onset potential for CH₄ production lower by 0.149 V than commercial Cu NPs. More impressively, SD‐Cu NPs demonstrate a faradaic efficiency of 52.43% ± 2.72% for C₂H₄ production at ?0.993 ± 0.0129 V. The results demonstrate that the surface stacking faults and twin defects increase CO binding energy, leading to the enhanced CO₂RR performance on SD‐Cu NPs.     

Tuning the Trade-Off between Ethane/Ethylene Selectivity and Adsorption Capacity within Isoreticular Microporous Metal−Organic Frameworks by Linker Fine-Fluorination

The pore dimension and surface property directly dictate the transport of guests, endowing diverse gas selective adsorptions to porous materials. It is highly relevant to construct metal−organic frameworks (MOFs) with designable functional groups that can achieve feasible pore regulation to improve their separation performances. However, the role of functionalization in different positions or degrees within framework on the separation of light hydrocarbon has rarely been emphasized. In this context, four isoreticular MOFs (TKL-104−107) bearing dissimilar fluorination are rationally screened out and afforded intriguing differences in the adsorption behavior of C₂H₆ and C₂H₄. Ortho-fluoridation of carboxyl allows TKL-105−107 to exhibit enhanced structural stabilities, impressive C₂H₆ adsorption capacities (>125 cm³ g⁻¹) and desirable inverse selectivities (C₂H₆ over C₂H₄). The more modified ortho-fluorine group and meta-fluorine group of carboxyl have improved the C₂H₆/C₂H₄ selectivity and adsorption capacity, respectively, and the C₂H₆/C₂H₄ separation potential can be well optimized via linker fine-fluorination. Meanwhile, dynamic breakthrough experiments proved that TKL-105−107 can be used as highly efficient C₂H₆-selective adsorbents for C₂H₄ purification. This work highlights that the purposeful functionalization of pore surfaces facilitates the assembly of highly efficient MOF adsorbents for specific gas separation.     

New Ordered Structure of Amorphous Carbon Clusters Induced by Fullerene–Cubane Reactions

As a new category of solids, crystalline materials constructed with amorphous building blocks expand the structure categorization of solids, for which designing such new structures and understanding the corresponding formation mechanisms are fundamentally important. Unlike previous reports, new amorphous carbon clusters constructed ordered carbon phases are found here by compressing C₈H₈/C₆₀ cocrystals, in which the highly energetic cubane (C₈H₈) exhibits unusual roles as to the structure formation and transformations under pressure. The significant role of C₈H₈ is to stabilize the boundary interactions of the highly compressed or collapsed C₆₀ clusters which preserves their long‐range ordered arrangement up to 45 GPa. With increasing time at high pressure, the gradual random bonding between C₈H₈ and carbon clusters, due to “energy release” of highly compressed cubane, leads to the loss of the ability of C₈H₈ to stabilize the carbon cluster arrangement. Thus a transition from short‐range disorder to long‐range disorder (amorphization) occurs in the formed material. The spontaneous bonding reconstruction most likely results in a 3D network in the material, which can create ring cracks on diamond anvils.     

Carbon Dioxide Promotes Dehydrogenation in the Equimolar C2H2‐CO2 Reaction to Synthesize Carbon Nanotubes

The equimolar C₂H₂‐CO₂ reaction has shown promise for carbon nanotube (CNT) production at low temperatures and on diverse functional substrate materials; however, the electron‐pushing mechanism of this reaction is not well demonstrated. Here, the role of CO₂ is explored experimentally and theoretically. In particular, ¹³C labeling of CO₂ demonstrates that CO₂ is not an important C source in CNT growth by thermal catalytic chemical vapor deposition. Consistent with this experimental finding, the adsorption behaviors of C₂H₂ and CO₂ on a graphene‐like lattice via density functional theory calculations reveal that the binding energies of C₂H₂ are markedly higher than that of CO₂, suggesting the former is more likely to incorporate into CNT structure. Further, H‐abstraction by CO₂ from the active CNT growth edge would be favored, ultimately forming CO and H₂O. These results support that the commonly observed, promoting role of CO₂ in CNT growth is due to a CO₂‐assisted dehydrogenation mechanism.