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As one of the basic bismuth nitrates, Bi₂O₂(OH)(NO₃) (denoted as BION) has been reported to exhibit powerful photodegradation activity for various contaminants. However, pure BION could only be irradiated by UV light due to broad bandgap ($\sim$3.14eV). Herein, Bi₂S₃/Bi₂O₂(OH)(NO₃) (denoted as BS-BION) heterojunction was prepared by an in situ ion exchange reaction between BION and aqueous thiourea solution ($\mathrm{\text{pH}}\approx 3$). The resulting heterojunction possessed good visible light absorption and closely contacted interfaces, which benefited effective separation and transfer of photogenerated charges, thus leading to excellent photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation. Furthermore, the as-prepared heterojunction photocatalyst also presented high photochemical stability, which may be of great significance for practical application.

Silver nanoparticles (NPs) and related semiconductors are a family of very important and widely applied photocatalysts. However, the preparation of high stability and activity of this photocatalyst is still a challenge. In this work, we report a stable Ag/AgCl/AgBi(MoO${}_4{)}_2$ heterojunction photocatalyst fabricated via a simple in situ anion-exchange reaction followed by the photoreduction treatment. In the treatment of tetracycline (TC) wastewater under visible light, the AC-0.4 sample (prepared with 0.4mmol KCl) exhibits the significantly improved activity (degradation ratio, DR of 71.3%) compared with the pristine AgBi(MoO${}_4{)}_2$ (30% DR) and Ag/AgCl sample (synthesized by the photoreduction of AgCl) (37% DR) under identical experimental conditions. This activity promotion is from the fast interfacial electron transfer between the heterojunction phases of AgCl/AgBi(MoO${}_4{)}_2$ and the SPR effect of Ag NPs. After five successive recycles, the AC-0.4 sample still maintains good stability and activity for TC degradation, which shows a great potential to be used in practical application. Through the ESR and controlled scavenged experiments, we found the $•$OH and $•$O${}_2^{-}$ are the major reactive intermediate species in the TC photodegradation reaction. Our work provides a new insight into the synthesis of stable and high efficient Ag-based heterojunction photocatalysts for the application of wastewater treatment.