Impact of the crystallinity of mesoporous polymeric graphitic carbon nitride on the photocatalytic performance under UV and visible light

- Highly active mesoporous graphitic carbon nitrides were prepared.
- Photocatalytic activity in ibuprofen degradation was studied.
- High crystallinity combined with mesoporosity yielded highest active mpg-C3N4.
- Soft thermal activation increases disorder and break down activity completely.
- High-temp. annealing reestablishes crystallinity/activity by polymer relaxation.

Mesoporous polymeric graphitic carbon nitrides (mpg-C3N4) were prepared by combined soft templated solvothermal synthesis method and detailed post-thermal treated starting from low temperature. The materials were structurally characterized by powder X-ray diffraction and ATR-FTIR spectroscopy. The morphology and texture of the samples were studied by TEM, STEM and nitrogen adsorption desorption isotherm measurements. The photocatalytic activity was tested in the degradation of the harmful and recalcitrant pharmaceutical pollutant ibuprofen. New photocatalytic results were obtained by testing the degradation at low catalyst content and low catalyst to substrate ratio of four under sun light equivalent UV and visible room light. The mineralization of the organics to carbon dioxide and water was followed by TOC measurements. The formation of reaction intermediates was further checked by ESI-TOF-MS measurements. Highly active mesoporous polymeric pure mpg-C3N4 photocatalysts were obtained. It was found that the crystallinity of the mpg-C3N4 has a pronounced impact on the photocatalytic activity. Especially, post-synthesis low temperature exposure led to complete loss of the photocatalytic activity. Therefore, the pretreatment had a decisive effect on the final photocatalytic performance. The scavenger experiments showed that super oxide radical anions and hydroxyl radicals were the active reactive oxidative species with mesoporous polymeric carbon nitride. Mpg-C3N4 is a “green” photocatalyst because the number of formed by-products is limited.

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