A signal-on photoelectrochemical sensor based on the target-triggered double-ion exchange reaction for Hg2+ under visible light

A photoelectrochemical (PEC) sensor driven by visible light has been developed to detect Hg2+ with a signal output "turn-on" mode on basic of the double ZIF-Cds@Zns@HgS type-II heterojunction formed by a target-triggered double-ion exchange reaction. The type-II heterojunction photocatalysts ZIF-CdS@ZnS were prepared through growing ZnS nanoparticles onto ZIF-CdS hollow nanocages which were innovatively synthesized using ZIF-67 as a template by MOF-engaged directional deposition strategy. An obvious photocurrent amplification effect induced by mercury ions is evident in ZIF-CdS@ZnS modified ITO electrodes, compared to ZIF-CdS or pure ZnS modified electrodes. The ZIF-CdS@ZnS heterojunction would successfully utilize visible light to promote the photoelectric response process due to the synergistic effect of the narrow band gap component and cavity structure. More importantly, the photocurrent can be greatly amplified by the target-triggered double-ion exchange reaction, which results in the generation of double type-II heterostructures HgS@ZnS@CdS, where an electrical field resulting from the unification of the fermi level facilitates the separation of photogenerated charges and increases the output photocurrent. Besides, the target-triggered double ion exchange strategy can provide guidance for the design of signal-on PEC sensors to detect other heavy metal ions sensitively.