Preparation of Ultrathin‐Walled Carbon‐Based Nanoporous Structures by Etching Pseudo‐Amorphous Silicon Oxycarbide Ceramics

Abstract

Etching polymer‐derived silicon‐oxycarbide ceramics with hydrofluoric acid creates nanoporous structures of specific surface areas as high as 600 m2/g. The change in composition upon etching shows the removal of silica, not carbon. The structure remaining after etching is postulated to consist of a scaffolding of graphene networks with their surfaces decorated with mixed bonds of tetrahedral silicon bonded to both oxygen and carbon (SiOmC4−m, where m=1, 2, or 3). The pores existing within such scaffoldings are presumed to have been filled with SiO2 tetrahedra, which are removed by etching. The measurement of the average pore size and pore volumes permits us to estimate the width of the graphitic domain walls, δW, left behind by the etching process. The smallest value of δW, which corresponds to the specimen with the highest surface area, is approximately 1 nm, which is about equal to the total width of one graphene layer and two SiOmC4–m tetrahedra, one on either side of the graphene sheet. This highest surface area specimen is also believed to have the largest size of the silica domains in the unetched samples. In specimens with smaller domains, the etching is only partially successful in removing the silica, presumably because their small size hinders the access of the etchant to the silica tetrahedra. The above behavior is found for samples with low to moderate carbon content. In one sample with a very high carbon content, the etching process removes some carbon as well as silica.

Enhanced hydrogen and methane gas storage of silicon oxycarbide derived carbon

“…The presence of amorphous silica cannot be excluded and most likely the major peak of this phase was superimposed with the broad reflections of disordered carbon in the given patterns. Both XRD patterns are in agreement with literature data reported for low and high carbon SiOC materials [22].…”

“…Studies on Si(O)C fibers reported CDC coatings, but no information on pore structure has been reported [19,20]. Albeit, it was shown that if a SiOC glass is etched for a long time (6 h) with a highly concentrated HF solution ($20%), the silica phase can be extracted leaving behind a highly porous oxycarbide-derived carbonaceous material containing SiC crystallites and Si atoms bonded to carbon, with SSA values as high as 700 m 2 /g and high pore volume up to 1.2 cm 3 /g [21,22]. It is important to note that this material can be derived from commercially available, inexpensive, easy to handle and versatile precursors such as polysiloxanes.…”

Texture and micro-nanostructure of porous silicon oxycarbide glasses prepared from hybrid materials aged in different solvents

“…3.5 nm, which is in agreement with the results published by Peña-Alonso et al for etched SiOC glasses. 40 Our results suggest that the carbon content and its distribution in the hybrid material, and therefore, the PDMS, plays an important role on the phase development of the SiOC glass. The addition of iPrOH removes the highest amount of PDMS from the hybrid network.…”

Predicting structural properties of amorphous silicon carbonitride by atomistic simulation

“…The mixed bond tetrahedron may play a critical role in the performance and properties of SiCN and other polymer derived ceramics with similar nano-domains structures. After etching polymer-derived silicon-oxycarbide ceramics with hydrofluoric acid, silica domains are removed and the remaining structure is postulated to consist of a scaffolding of graphene networks with their surfaces decorated with mixed bonds of tetrahedral silicon bonded to both oxygen and carbon (Peña-Alonso et al, 2006). In Baek's study using SiCN as candidate for anode of Li-ion batteries to replace graphite anodes (Baek et al, 2014), the mixed bond tetrahedra of Si in SiCN is believed to act as an additional lithiation site.…”