RGO–MoS₂ Nano-Junction Aggregates Based Flexible Hg (II) Ion Sensors

Abstract

In this study, we demonstrated the fabrication of reduced graphene oxide reduced graphene oxide (RGO)–molybdenum disulfide (MoS2) nano-junction aggregates on flexible interdigitated electrodes (IDEs) as Hg (II) ion sensors for water quality monitoring. The as-fabricated devices showed selective sensitivity toward varying concentrations (from 3 to 12 ppb) of Hg (II) ions in solution, offering a maximum response of ~97% for 12 ppb Hg (II) ions (response time ~4 s) and a sensitivity of 2.2%/ppb (limit of detection: 1 ppb). Bending stress effects on the device were tested by subjecting it to increasing bending angles (15°–90°). They were minimally responsive (maximum variation ~2%) toward bending supported by a fitting model. The sensing performance for the device was explained via a junction-dependent mechanism with a model for supporting the same. Finally, the overall device response was determined analytically by examining the impact of the n, p, and junction regions. The analytical model’s prediction of 96% at 12 ppb was almost similar to the experimental measurement (97%). The analytical model predicted a significant response dependence on the contribution of the n-type (MoS2) and the RGO-MoS2 (pn) junction. The p-type region was less responsive toward the overall sensing performance, which may be attributed to lower hole mobility than that of electrons. The device was repeatable and stable for up to 40 days with ~7% variation in response. Hence, the proposed sensor provides a simple solution for selective Hg (II) ion sensing, challenging its complex conventional counterparts.