Highly Ordered Mesoporous Silicon Carbide Ceramics with Large Surface Areas and High Stability

Abstract

Highly ordered mesoporous silicon carbide ceramics have been successfully synthesized with yields higher than 75 % via a one‐step nanocasting process using commercial polycarbosilane (PCS) as a precursor and mesoporous silica as hard templates. Mesoporous SiC nanowires in two‐dimensional (2D) hexagonal arrays (p6m) can be easily replicated from a mesoporous silica SBA‐15 template. Small‐angle X‐ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images show that the SiC nanowires have long‐range regularity over large areas because of the interwire pillar connections. A three‐dimensional (3D) bicontinuous cubic mesoporous SiC structure (Ia3d) can be fabricated using mesoporous silica KIT‐6 as the mother template. The structure shows higher thermal stability than the 2D hexagonal mesoporous SiC, mostly because of the 3D network connections. The major constituent of the products is SiC, with 12 % excess carbon and 14 % oxygen measured by elemental analysis. The obtained mesoporous SiC ceramics are amorphous below 1200 °C and are mainly composed of randomly oriented β‐SiC crystallites after treatment at 1400 °C. N2‐sorption isotherms reveal that these ordered mesoporous SiC ceramics have high Brunauer–Emmett–Teller (BET) specific surface areas (up to 720 m2 g–1), large pore volumes (∼ 0.8 cm3 g–1), and narrow pore‐size distributions (mean values of 2.0–3.7 nm), even upon calcination at temperatures as high as 1400 °C. The rough surface and high order of the nanowire arrays result from the strong interconnections of the SiC products and are the main reasons for such high surface areas. XRD, N2‐sorption, and TEM measurements show that the mesoporous SiC ceramics have ultrahigh stability even after re‐treatment at 1400 °C under a N2 atmosphere. Compared with 2D hexagonal SiC nanowire arrays, 3D cubic mesoporous SiC shows superior thermal stability, as well as higher surface areas (590 m2 g–1) and larger pore volumes (∼ 0.71 cm3 g–1).

Visible Light-Induced Metal Free Surface Initiated Atom Transfer Radical Polymerization of Methyl Methacrylate on SBA-15

“…Briefly, 20 g of Pluronic 123 was dissolved under stirring in 600 mL of 2M HCl and 150 mL of deionized water at 40 ℃. Then 42.5 g of tetraethlorthosilicate (TEOS) was [8]added. The resultant solution was stirred for 24 h at 40 ℃ before transferring into a Teflon bottle sealed in an autoclave, which was then heated to 130 ℃ for 24 h in an oven.…”

“…In particular, ordered mesoporous materials such as SBA-15 are ideal candidates for functionalization due to their high hydrothermal stability, desired morphology, adjustable pore sizes (2−30 nm), and thick walls that can be easily functionalized using silanol chemistry [7,8]. In this context, the covering of a silica surface with different polymers seems to be a potentially useful strategy for incorporating a range of organic functional groups which could modify the properties of these materials and open up new fields for novel applications.…”

Synthesis of Inorganic–Organic Diblock Copolymers as a Precursor of Ordered Mesoporous SiCN Ceramic

“…On the other hand, the preparation of mesoporous silicon carbide with a unique stability and strength using hard templates has attracted considerable interest. [4][5][6][7][8] However, hard-template routes are not suitable for the industrial production of powder materials due to engineering difficulties, and require a harmful etching step, most commonly with strong acid, which limits the coating processiblity to substrates. Therefore, soft-template routes using surfactants and block copolymers have attracted substantial attention for the creation of well-ordered nanostructured materials with facile applications on a large scale.…”

Fabrication of SiC-Based Ceramic Microstructures from Preceramic Polymers with Sacrificial Templates and Lithographic Techniques-A Review

“…Highly ordered mesoporous SiC ceramics were synthesized via a one-step nanocasting process using commercial polycarbosilane PCS as a precursor and mesoporous silica materials, SBA-15 and KIT-6, as hard templates. 31 The obtained mesoporous SiC ceramics with 12ಚ excess of carbon were amorphous below 1200c C, and were composed of ran- …”