Embedding Ag nanoparticles to construct BiOI/Ag/PANI with enhanced photoelectrocatalytic activity: A demonstration of the switch from type-II to Z-scheme

Abstract

Conventional type-II and Z-scheme heterojunctions are two typical models of the composite photocatalyst. However, it is still a challenge to rationally design a strategy to realize the switch from type-II to Z-scheme. Here, a Z-scheme BiOI/Ag/PANI (BAP) heterojunction was constructed by embedding Ag nanoparticles at the interface of the type-II BiOI/PANI heterojunction (BP), in which Ag nanoparticles not only acted as the shuttle charge mediator for Z-scheme but also brought about the surface plasmon resonance (SPR) effect. The Z-scheme BAP-10 photoelectrode exhibited significantly boosted photoelectrocatalytic efficiencies for degradation of RhB and reduction of Cr(VI), the kinetic constants of which were approximately 5 and 12 times respectively higher than those of type-II BP, attributed to enhanced charge separation efficiency and stronger redox capacity of the Z-scheme mechanism and the excellent light absorption efficiency from the SPR effect of Ag. Photocurrent response, electrochemical impedance spectroscopy and the time-resolved photoluminescence spectra revealed that the separation of photo-generated charge in BAP was accelerated. Importantly, the Z-scheme mechanism was proved by electron spin resonance, terephthalic acid photoluminescence probing technique. The charge transfer pathways of Z-scheme were further studied by linear-sweep voltammogram and especially surface photovoltage spectra. The work provided an excellent reference for rationally converting the type-II heterojunction to the Z-scheme heterojunction and deep insight for the charge transfer mechanism of the Z-scheme.