Construction of self-activating Z-scheme g-C3N4/AgCl heterojunctions for enhanced photocatalytic property

The Z-scheme g-C3N4/AgCl heterojunctions were prepared by precipitation method. Different loading amounts of AgCl on the surface of g-C3N4 in the g-C3N4/AgCl heterojunction photocatalysts have an important influence on the photocatalytic performance. The high anchoring amount of AgCl (From 5 to 35 wt%) on g-C3N4 leads to large interface contact areas, excellent charge transfer efficiency and many surface active points, which can promote the photocatalytic activity of g-C3N4/AgCl heterojunctions. The photocatalytic efficiency of g-C3N4/35 wt% AgCl (denoted as S4) is obviously the highest among g-C3N4/AgCl heterojunctions, pristine g-C3N4 and AgCl. It indicates that S4 exhibits enhanced degradation efficiencies, which are 96.1% of Rhodamine B (RhB) and 77.8% of Tetracycline (TC) for 120 min, respectively. The orders of removal efficiency for RhB and TC are all g-C3N4/35 wt% AgCl (S4) > g-C3N4/25 wt% AgCl (S3) > g-C3N4/15 wt% AgCl (S2) > g-C3N4/5 wt% AgCl (S1) > AgCl > C3N4 under illumination of ultraviolet–visible (UV–Vis) light or simulated sunlight. The best degradation rate constants (k) of S4 for RhB and TC are 7.46–1.71 times higher than those of pure g-C3N4 or AgCl and S1–S3, respectively. With prolonging photocatalytic time, the k of S4 becomes more and more quickly, and the photocatalytic activity can be improved due to its self-activating effect under the UV–Vis light illumination. The electron spin resonance (ESR) analysis and radical trapping experiment show that the electrons at conduction band (CB) of AgCl and the holes at valence band (VB) of g-C3N4 have no redox abilities, while the electrons at the CB of C3N4 and the holes at the VB of AgCl exhibit strong redox capability, respectively. The charge transfer of the heterojunctions follows Z-scheme mode. This Z-scheme system can change from direct Z-scheme photocatalytic system to all-solid-state Z-scheme mode due to the reduction from AgCl to Ag under light illumination, which also improves the photocatalytic performance. Additionally, the photodegradation mechanism was proposed.