Photocatalytic Activity and Stability of Carbon Nitride-Pyrite Composites

In photocatalysis, the photoabsorber plays a crucial role in the reaction. The most important parameters are stability, cost and optical band gap. In this work, a prominent class of absorbers, namely carbon nitrides (CN), has been investigated. In the literature, CN is most often described as stable, although photodegradation has been observed. In order to retain the beneficial properties of CN while improving stability, a crystalline phase poly(triazine imide) (PTI) of carbon nitride was investigated and compared to polymeric CN in photocatalytic hydrogen generation experiments. In order to improve the charge separation for the photoinduced hydrogen evolution reaction, pyrite (FeS2) was used as a surface co-catalyst with a loading of 1, 5 and 10 wt %. At the same time, any photodegradation products in solution were investigated by ion chromatography. Interestingly, PTI shows hardly any photocorrosion compared to defective carbon nitride, indicating its higher photostability in hydrogen evolution experiments. However, FeS2 produces ammonium as a degradation product when synthesised from nitrogen-containing precursors. When made from nitrogen-free precursors, FeS2 together with photostable PTI releases little ammonia, making it a photostable, earth-abundant composite for photocatalytic hydrogen generation.