Direct Z-scheme Layered N-doped H.sup.+Ti.sub.2NbO.sub.7.sup.-/g-C.sub.3N.sub.4 Heterojunctions for Visible-light-driven Photocatalytic H.sub.2 Production and RhB Degradation

There are increasing concerns of environmental-pollution and energy issues. Herein, an exfoliation-restacking process was firstly employed to synthesize H.sup.+-restacked H.sup.+Ti.sub.2NbO.sub.7.sup.- nanosheets (HTNS), and then heated with melamine at 510 °C to obtain direct Z-scheme layered N-doped H.sup.+Ti.sub.2NbO.sub.7.sup.-/g-C.sub.3N.sub.4 (TCN) heterojunctions with an increased specific surface area. Two-dimensional (2D) g-C.sub.3N.sub.4 material was in-situ formed on the surface of HTNS to achieve a layered heterostructure between two components, which could maximize interfacial contact area and minimize interfacial distance for the efficient charge carrier separation. Simultaneously, the surface of HTNS was doped by nitrogen atoms to form visible-light-responsive N-doped HTNS. All TCNx (x = 1, 2 and 3) composites exhibited the enhanced photocatalytic activity for both hydrogen (H.sub.2) production and rhodamine B (RhB) degradation. As an optimal sample, the resulted TCN2 composite exhibited the best photocatalytic efficiency for H.sub.2 production and RhB degradation. The enhanced photocatalytic activity was assigned to the combined effects of layered heterojunction, N-doping and large specific surface area. According to trapping experiments and electron spin resonance (ESR) spectra, the holes (h.sup.+), superoxide (·O.sub.2.sup.-) and hydroxyl (·OH) radicals were responsible for photocatalytic RhB degradation and especially the ·O.sub.2.sup.- was the key active specie. A possible charge transfer pathway was analyzed in detail. This work will hopefully provide some guidance on designing Z-scheme layered heterojunction photocatalyst systems with highly photocatalytic efficiency.