Graded Junction ZnO on rGO Conduction Layer for Ultraselective Cu(II) Ion Detection

The discharge of noxious effluents from industries into water bodies results in an increase in the contamination of consumable water with heavy metal ions. This study illustrates a graded junction-based reduced graphene oxide (rGO)/ZnO heterojunction device that is capable of detecting Cu(II) ions in water at an ultrafast and highly selective rate. The voltage-assisted chemical bath deposition (CBD) technique was employed to fabricate the graded junction ZnO on the rGO carrier transport layer (CTL). The device exhibited a maximum response of 99% for 40 ppm of Cu(II) when exposed to controlled quantities of Cu(II) ions. The response and recovery times were rapid, at 0.31 and 0.58 s, respectively, and the limit of detection (LOD) was 0.1 ppm at room temperature at 5 V. In comparison to other analogous ions, the sensor has been demonstrated to be highly selective toward Cu(II). The device was determined to be highly repeatable for a 45-day period, with a maximal error of 1.9% and a response deviation of 2.4%. The device’s high sensitivity in comparison to its existing counterparts was facilitated by the graded ZnO structure and its variable bandgap and depletion layer modulation. Additionally, the incorporation of the CTL facilitated the high-speed detection of Cu(II) ions. The graded junction-assisted adsorption mechanism elucidated the device’s unconventional behavior as it was fabricated. Consequently, this device can be used as a suitable replacement for its conventional counterparts in the detection of Cu(II) ions in solution.