Surface Functionalization of Ordered Mesoporous CarbonsA Comparative Study

Abstract

Hexagonally structured mesoporous carbons C15 and CMK-5 and cubically structured carbon C48 were synthesized using ordered silica SBA-15 and MCM-48 as templates and carbon precursors of different structures. The surfaces of these ordered carbons were chemically functionalized by employing an approach, in which the selected diazonium compounds were in situ generated and reacted with the carbon frameworks of the mesoporous carbons. The aromatic organic molecules containing chlorine, ester, and alkyl groups were covalently attached to the surface of these ordered mesoporous carbons. The presence of functional groups on the modified carbons was confirmed with Fourier transform infrared spectroscopy, thermogravimetric analysis, and nitrogen adsorption. The BET-specific surface area and the pore width of ordered carbons were significantly reduced, whereas the primary structure of these ordered carbons and their unit cells were intact. Basically, the density of grafted functional groups is related to the specific surface area of the sample, particularly the surface area of mesopores. The surface functionalization reaction takes place only on the external surface of carbon C15, while it occurs on both of the internal and external surface of CMK-5 carbon with the nanopipe structure. The presence of the micropores in CMK-5 carbon should be responsible for its lower grafting density because the small micropores are inaccessible in the reaction. It was also proposed that the preferred adsorption/reaction in C48 may be related to the observed unsymmetrical degradation of the XRD patterns for the functionalized C48 samples. The chemical modification process considerably reduced the primary mesopores in these ordered carbons by approximately 1-1.5 nm, affording carbons with micropores in the cases of C15 and C48, and mixed micropores and small mesopores in the case of CMK-5. A grafting density of approximately 0.9-1.5 micromol/m(2) was achieved under current research.

A simplified route to the synthesis of CMK-3 replica based on precipitation polycondensation of furfuryl alcohol in SBA-15 pore system

“…We attribute this effect to blocking with the SBA-15 pore system (both micro-and mesopores) and a subsequent development of micropore volume formed inside the carbon material as well as between carbon and silica walls during the carbonization step. Shrinkage of PFA-derived carbon deposited in the silica channels after thermal treatment at high temperatures was observed previously by other authors [19][20][21]. observed.…”

Covalent modification of graphitic carbon substrates by non-electrochemical methods

“…In addition to the solution methods described above, solvent-free conditions have also been used for functionalisation of high surface area graphitic carbon using aryldiazonium salts [54,55]. The procedures followed those used for carbon nanotubes [49] and involved addition of isoamyl nitrite to a dry mixture of ordered mesoporous carbon and aniline derivative, and after 1 h at room temperature, heating the stirred reaction mixture to 70 ºC.…”

Mesoporöse Kohlenstoffmaterialien: Synthese und Modifizierung

“…[45] Unsere Gruppe synthetisierte vor kurzem einen geordneten Kohlenstoff ("C48") mit MCM-48 als Templat und Mesophasenpech als Kohlenstoffvorstufe, dessen Röntgen-beugungsmuster dem von CMK-1 ähnelt. [46,47] [49] HMS wurde mit einem primä-ren Alkylamin als strukturdirigierendem Agens und mit TEOS als Silica erhalten und wies eine gleichmäßige Porengröße von etwa 3 nm und einen Röntgenreflex bei 2q = 28auf. [36,51] [51] Kurz nach der Synthese von SNU-2 beschrieb die Gruppe von Ryoo [52] die Synthese eines hochgeordneten mesoporösen Kohlenstoffs mit hexagonaler Struktur (CMK-3).…”

“…Als Templat diente dabei das hexagonale mesoporöse Silica-Molekularsieb SBA-15, das mit einem Triblockcopolymer-Tensid, Polyethylenoxid-Polypropylenoxid-Polyethylenoxid (PEO-PPO-PEO, Pluronic P123), als strukturdirigierendem Agens hergestellt wurde [26,27] [54] Die Größe der Poren in einem mit der Harttemplatmethode synthetisierten geordneten Kohlenstoff wird hauptsächlich von der Porenwandstärke des anorganischen Templats bestimmt, die sich wiederum über die Synthesebedingungen maßschneidern lässt. [27] [46] ähnlich, wird aber unter nahezu neutralen Bedingungen und mit Natriumsilicat als Silicaquelle synthetisiert. [57] Man hat auch versucht, das Triblockcopolymer (z.B.…”

“…[46,47] Auf diese Art gelang es -wie IR-Spektroskopie, Thermogravimetrie, Elektronenmikroskopie und Stickstoffadsorption bestätigten -, an der 4-Position substituierte Arylguppen (ArR, R = Cl, CO 2 R', Alkyl) mit einer hohen Ankerdichte von 0. [47] Abbildung 23.…”