Direct electrochemical detection of trace heavy metal ions in untreated seawater using a porous defect-rich g-C3N4/Bi@Bi2O3 composite

Traditional electrochemical methods often face challenges in accurately detecting heavy metal ions in seawater due to high salinity and complex organic matrices. Herein, a porous, defect-rich graphitic carbon nitride/bismuth–bismuth oxide (pdr-g-C 3 N 4 /Bi@Bi 2 O 3 ) composite was fabricated via two-step calcination and hydrothermal assembly, and applied for simultaneous Cd(II) and Pb(II) detection by SWASV. The unique porous structure and abundant defect sites facilitate efficient ion preconcentration and electron transfer, leading to high sensitivity and selectivity. Under optimized conditions in sodium acetate–acetic acid buffer (pH 6.0), the sensor exhibits linear detection ranges of 5–200 ppb for both Cd(II) and Pb(II), with limits of detection (LOD) of 0.513 ppb and 0.313 ppb, respectively. Remarkably, the sensor demonstrates excellent stability and accuracy even in unprocessed seawater samples, achieving LODs of 0.32 ppb for Cd(II) and 10.13 ppb for Pb(II). These results confirm the feasibility of direct, on-site detection of trace heavy metals in complex marine environments, offering a practical strategy for rapid environmental monitoring.