Mesoporous carbon nitride–silica composites by a combined sol–gel/thermal condensation approach and their application as photocatalysts

Abstract

Mesoporous carbon nitrides, silicas and their composites have been prepared by a combined sol-gel and thermal condensation approach. Precursors for the carbon nitride (cyanamide) and silica (TEOS) are mixed and condensed simultaneously. After condensation and heat treatment it is observed that the carbon nitride and silica formed highly interpenetrating mesophases which leads either to the formation of mesoporous carbon nitride or silica after selective removal of one of the phases. Importantly, the carbon nitride preserves its graphitic stacking even in the spatial confinement introduced by the surrounding silica phase. As both precursors are liquids this approach allows convenient shaping into thin and thick films or monoliths of mesoporous carbon nitrides. Enhanced photocatalytic activity is observed for the production of hydrogen from water when these mesoporous carbon nitrides are applied as photocatalyst in comparison to the bulk, but also to other mesoporous carbon nitrides, prepared by the reported two-step, hard templating approach.

Bioinspired hollow semiconductor nanospheres as photosynthetic nanoparticles

“…The solid-state 13 C CP-NMR spectra (Fig. 2c) further confirms the presence of heptazine tectons in the g-C 3 N 4 solids, and the signals at approximately 155.6 and 164.3 ppm related to the formation of a poly(tri-s-triazine) structure characteristic of melem, melon and the final carbon nitride 21,36,37 . The presence of sharper lines in the NMR spectrum of the HCNS sample than the bulk g-C 3 N 4 could be due to a reduced inhomogeneous broadening of the hollow sphere samples, which would indicate an improved condensation and local organization in the thin shell structure.…”

Quantification of photocatalytic hydrogen evolution

“…[9][10][11][12][13][14] Herein, a recently developed sol-gel/thermal condensation route was employed to synthesize continuous mesoporous structures of carbon nitrides. 15 In general, a comparison of published results regarding photocatalytic efficiency of many photocatalysts for H 2 or O 2 evolution is often impossible due to completely different reaction conditions or test reactors. To perform photocatalytic hydrogen evolution reactions with UV or visible light irradiation using homogenous or heterogeneous photocatalysts, three types of photo reactors are commonly used: reactors with (a) inner irradiation, 16 (b) top irradiation, 17,18 and (c) side irradiation 19 ( Fig.…”

Cyanamide route to calcium–manganese oxide foams for water oxidation

“…Heat treatment of cyanamide yield, over several polycondensation steps, a polymeric carbon nitride, which acted as a hard template to create the porosity in the silica. 21 Herein we used a comparable approach, namely mixing Ca-Mn oxide precursors with cyanamide and additional heat treatment. However, here the organic porogen decomposed already at lower temperatures leaving behind a porous, foam-like Ca-Mn oxide.…”