Surface State Passivation Ignited Photoelectrochemical Sensing of Thallium(I) with Ultrathin In₂S₃ Nanosheets

Tl+ has long been known for its high toxicity and can cause various illnesses, but its sensing is seldom explored compared with other heavy metal ions. Here, we report for the first time a photoelectrochemical (PEC) sensor for Tl+ with a highly porous In2S3 anode which is assembled by ultrathin nanosheets. The photoanode shows a notable peak in photocurrent J–V curve at −0.65 V vs Ag/AgCl, resulting from oxidation of rich sulfide (surface states) in the surface of In2S3 by photogenerated holes. Upon combination of surface sulfide with Tl+, such a peak can be evidently quenched as a function of the concentration of Tl+. Therefore, a PEC sensor based on the unique mechanism of surface state passivation is thus developed. Benefiting from the sensitivity of surface states to guest materials, the proposed system offers a detection limit of 0.36 μM. Unexpectedly, the sensor also exhibits higher selectivity to Tl+ than to other metal ions, possibly due to the high affinity between Tl+ and sulfide, as well as the applied low bias potential that avoids direct oxidation of analytes. The successful application of such a mechanism in the detection of Tl+ brings perspectives for the exploration and design of the PEC sensing system.