Excellent visible light photocatalytic efficiency of Na and S co-doped g-C3N4 nanotubes for H2 production and organic pollutant degradation

Na and S co-doped g-C3N4 nanotubes (NaxSCNNTs) were synthesized via thermal polymerization using NaHCO3 and thiourea as Na and S source, respectively. The co-doping of Na and S in g-C3N4 nanotubes was verified by FTIR, SEM elemental mapping and XPS measurements. After loading Pt, the optimal Na0.1SCNNT produced H2 at a rate of 173.7 μmol h−1, which is 1.76 times and 14 times of that of Na0SCNNT and bulk g-C3N4, respectively. Moreover, the performance of Na0.1SCNNT was increased by 50% after replacing Pt with PtCo. The apparent quantum efficiency of Na0.1SCNNT/Pt and Na0.1SCNNT/PtCo were 6.7% and 10.2% at λ = 420 nm, respectively. Na0.1SCNNT also displayed the best photocatalytic activity for both p-chlorophenol and rhodamine B degradation, which are 3.1 and 3.4 times of that of bulk g-C3N4, respectively. Cyclic photocatalytic experiments demonstrated the high stability of Na0.1SCNNT. The enhanced photocatalytic activity of Na0.1SCNNT is resulted from the large specific surface area, narrowed bandgap, enhanced visible light absorption, and down-shifted valance band, which are supported by steady-state PL spectra and time-resolved transient PL decay, as well as photoelectrochemical analysis. Finally, the possible photocatalytic mechanisms for H2 production, and degradation of rhodamine B and p-chlorophenol are proposed.