Holey Carbon Nanotubes from Controlled Air Oxidation

Abstract

Defects in various nanomaterials are often desirable to enable enhanced functional group attachments and attain properties that are not available with their intact counterparts. A new paradigm in the defective low-dimensional carbon nanomaterials is to create holes on the graphitic surfaces via partial etching. For example, holey graphene, graphene sheets with throughthickness holes, is synthesized using several different partial etching approaches and found useful for various applications such as field-effect transistors, sensors, energy storage devices, and separation membranes. In these applications, the presence of holes leads to unique advantages, such as bandgap widening, chemical functionalization of hole edges, and improved accessible surface area. Here, a facile and scalable method to prepare holey carbon nanotubes via controlled air oxidation is presented. Although no additional catalyst is added, the residual iron nanocatalysts encapsulated in the nanotube cavity from nanotube manufacturing significantly contributed to the hole generation through the nanotube walls. The holey carbon nanotube products exhibit enhanced surface area, pore volume, and oxygen-containing functional groups, which lead to their much enhanced electrochemical capacitive properties (increased over 100% in capacitance). Synthesis and characterization details of this novel class of holey carbon nanomaterials are presented, and their potential applications are discussed.

Yolk–Shell Carbon Nanospheres with Controlled Structure and Composition by Self-Activation and Air Activation

“…Moreover, the shortened diffusion distance between yolk and shell can accelerate the EDLC behavior and Faradaic reactions. , Table compares the electrochemical performances of as-prepared carbon nanospheres with literature values. A-HPS@PPy 100–10 exhibited higher specific capacitances and electrochemical cycle stability than most carbon materials as previously reported, including hierarchical yolk–shell carbon nanospheres, ,, heteroatom-doped hollow carbon nanospheres, , N-doped solid carbon nanospheres, , and air-activated carbon nanotubes , or graphene . This superior electrochemical performance of the yolk–shell carbon nanospheres in this work was attributed to their hierarchical porous structures and abundant heteroatoms.…”

“…Moreover, active elements such as nitrogen can be easily removed due to the severe environment under chemical activation . Alternatively, direct heating carbon materials in the air under appropriate conditions (termed air activation treatment) can increase the specific surface areas and introduce more oxygen functional groups for carbon materials. , An excessive air activation treatment decreases the conductivity of carbon materials and causes the structural collapse . Thus, it is important to explore the controllable air activation conditions to prepare carbon materials with desirable structures and surface properties.…”

Controlled Air‐Etching Synthesis of Porous‐Carbon Nanotube Aerogels with Ultrafast Charging at 1000 A g−1

“…High‐resolution TEM images clearly exhibit a highly porous tube wall structure consisting of densely packed pores throughout the entire wall (Figure e,f). Compared with previously reported porous carbon materials mainly in the form of particles, carbon nanotubes (CNTs), and carbon nanofibers, here we have obtained 1D nanotubes with a uniform porous structure along both the axial and radial directions.…”

“…The process of pore creation in PCNs was supposed as follows: 1) HNO 3 treatment provides full anion doping throughout the entire PPy nanotube; 2) parts of the C and N atoms were consumed and escaped as gases during the heat process in Ar, leading to the formation of micropore sites; 3) when temperature arose to 1000 °C, low‐concentration air flow (oxygen was supposed to be the main reactant) was introduced to further consume the C and N atoms around the micropore sites and produce uniform micro‐ and mesopores in the PCN walls. This controlled low‐concentration air etching during the annealing process and the HNO 3 treatment are two critical conditions for creating uniform micropores throughout the PCN walls both in axial direction and radial direction evenly, whereas directly etching graphitic materials by a large amount of O 2 usually produces mesopores, even macropores with irregular distribution, rather than uniform micropores . From a microscopic view, the pore formation process is initiated by the reaction between the N and C atoms with both the anion dopants and air, which would release NO x and CO x gases to leave sub‐nanometer pores .…”

Local Oxygen Reconstruction Enables Dual‐Ion Active Sites in Carbon Cathode for High Energy Density Sodium‐Ion Capacitors

“…[ 25 ] With increasing oxidation temperature, there was a slight increase observed in the specific surface area and average pore diameter of carbon materials due to enhanced etching effects caused by oxygen on carbon materials. [ 26 ] The specific surface areas for CRPC0, CRPC390, CRPC420, and CRPC450 were determined as 783, 937, 1003, and 949 m 2 g −1 respectively. The relative decrease in specific surface area for CRPC450 may be attributed to excessive etching resulting in reduced micropore content along with increased mesoporous and macroporous content.…”