Phase‐Engineered Graphene/1T‐Tungsten Disulfide Heterostructure for Sustainable Trace‐Level Mercury Monitoring in Water Systems

ABSTRACT Here, we present a two‐terminal van der Waals (vdW) heterostructure‐based ultra‐sensitive sensor for the real‐time detection of mercury (Hg ^{2 +} ) ions. The sensing receptor is a heterostructure of semi‐metallic graphene and metallic 1T‐tungsten disulfide (1T‐WS ₂ ) (i.e., graphene/1T‐WS ₂ ), and it shows a highly conductive interface with strong interfacial charge‐transfer properties. The device also shows an ultrawide detection range from 100 ppt (parts‐per‐trillion) to 100 ppm (parts‐per‐million) with extraordinary sensitivity of ∼154.95 µA ppb ⁻¹ at a reasonably low operating voltage of only 10 mV. The sensor has a high selectivity toward Hg ²⁺ ions over other heavy metal ions, such as Sodium ion (Na ⁺ ), Calcium ion (Ca ²⁺ ), Cobalt(II) ion (Co ²⁺ ), Chromium (III) ion (Cr ³⁺ ), Nickel(II) ion (Ni ²⁺ ), Cadmium(II) ion (Cd ²⁺ ), Manganese(II) ion (Mn ²⁺ ), Copper(II) ion (Cu ²⁺ ), and Lead(II) ion (Pb ²⁺ ). The electrical characterization shows a systematic decrease in the sensor's current with increasing Hg ^{2 +} ions concentration, ascribed to strong analyte‐induced charge depletion at the graphene/1T‐WS ₂ interface. A remarkably low detection limit of ∼58.8 ppt, which is well below the permissible limits, emphasizes its usefulness in the detection of Hg ²⁺ ions. The results demonstrate the vdW heterostructure engineering strategy as an effective platform in the development of ultrasensitive, highly selective, and energy‐efficient heavy metal ion detectors.