Synthesis and characterization of sp-sp² hybrid carbon materials

A 1,3,5-trichloro-2,4,6-triethinyl-benzene monomer was synthesized from 1,3,5-trichlorobenzene by iodination with periodic acid, followed by the substitution of iodine with trimethylsilylacetylene and finally the removal of the trimethylsilyl groups with tetrabutylammonium fluoride by the Sonogashira reaction. It was polymerized in pyridine under the catalysis of Cu⁺ to produce a gel-like polymer that was freeze-dried to give a 3D sp-sp² hybrid carbon material. A 2D sp-sp² hybrid carbon material was also made on a copper substrate which acted as both catalyst and template by first pretreating the substrate with a HCl solution,then soaking the substrate in pyridine, slowly adding a low concentration solution of 1,3,5-trichloro-2,4,6-triethinyl-benzene in pyridine,keeping it at 60 ℃ for 72 h for polymerization, rinsing the substrate consecutively with pyridine,dimethylformamide,dimethyl sulfoxide and acetone, and finally removing the substrate by FeCl₃ etching. The substituted intermediate from the first reaction, 1,3,5-trichloro-2,4,6-tri(trimethylsilylacetyl)-benzene, was stored in ether at ambient temperature for one month to yield a black solid of oligomers. Results indicated that the 3D sp-sp² hybrid carbon material consisted of carbon, chlorine and oxygen, whose composition, after oxygen was subtracted, was the same as that of the monomer. It had Raman peaks consistent with graphdiyne, and a BET surface area of 334 m²/g with a Ⅰ-Ⅱ type isotherm with a H3 hysteresis loop. The presence of a 2D graphyne-like structure was identified by HRTEM and selected area diffraction for the sp-sp² hybrid carbon on the copper substrate,indicating that it is possible for chemical synthesis of 2D graphyne by a template method. The black solid of oligomers consisted of mainly carbon,silicon and chlorine, which had a BET surface area of 382 m²/g with an ink-bottle pore texture. After it was annealed at 650 ℃ for 6 h, the chlorine was mostly eliminated, the silicon content decreased significantly and the intensities of the D and G peaks increased while the peak at 2 200 cm^-1 ascribed to graphyne disappeared producing a micro/mesoporous carbon with a surface area of 896 m²/g, an ink-bottle pore texture and pore sizes less than 30 nm, indicating that the graphyne-like structure was destroyed.