Fig. 4.

a Illustration of the electron transition processes in Zn-PCN. b C K-edge and N K-edge XANES spectra of BCN and Zn-PCN(4.79%) with or without illumination. The inset in b shows the spectral difference between being in dark and light. c Steady-state PL emission spectra and d time-resolved transient PL decay spectra of BCN and Zn-PCN. The excitation wavelength for all samples is 337 nm. e SPV spectra of BCN and Zn-PCN(4.79%) and f corresponding phase spectra. The inset in e shows the schematic setup for the SPV measurements. g Electrochemical impedance spectra of BCN and Zn-PCN at 0.8 V versus Ag/AgCl in 0.5 M Na₂SO₄ aqueous solution under light irradiation. The left inset in g is an equal circuit for the catalyst/electrolyte interfaces. R_s is the electrolyte resistance. R_ct and CPE is the charge transfer resistance from the bulk to the surface of photocatalyst and the constant phase element, respectively. The right inset in g presents the corresponding R_ct values. h Transient photocurrent density curves of BCN and Zn-PCN at 0.2 V versus Ag/AgCl in 0.5 M Na₂SO₄ aqueous solution under sequential illumination condition with an interval of 10 s on/off switch