Visible-light-responsive Cl/S co-doped carbon nitride nanotubes for photocatalytic denitrification: A new reaction pathway dominated by photo-electrons

In this work, we first applied metal-free polymeric catalysts to drive the photocatalytic denitrification (PCDN) reaction under visible light. We developed a hydrothermal-transverse thermal stripping method to prepare Cl/S co-doped metal-free carbon nitride nanotubes as the photocatalysts (Cl/S-TCN). With larger specific surface area, stronger light response intensity and wider light absorption range, the PCDN performance of Cl/S-TCN was 19 times higher than that of carbon nitride (GCN, obtained by direct calcination of melamine) under visible light. In hole scavenger experiments, the PCDN reaction was dominated by photo-generated electrons (e(-)) over Cl/S-TCN in acidic solutions. DFT calculations showed that surface Cl and S dopants preferentially adsorbed the O atoms in NO3- and delivered photoinduced-e(-) to N atoms through O atoms, ultimately breaking the N-O bond. Such reaction pathway was rarely reported in previous studies. Hence, this work contributes to the first insight into PCDN catalyzed by atomically modified metal-free photocatalyst under visible light.