Ni-doped CdO/CdSe in-situ heterojunctions: Tunable composition engineering for low-concentration formaldehyde detection.

Realizing low-concentration formaldehyde (HCHO) detection remains pivotal for air quality monitoring yet challenging due to insufficient sensitivity and selectivity of conventional sensors. This work presents a Ni-doped CdO/CdSe heterostructure synthesized via a one-step hydrothermal strategy coupled with controlled calcination, where Ni content governs the in-situ formation of tunable heterointerfaces. The optimized 5Ni-CdO/CdSe sensor achieves an exceptional response (Ra/Rg = 14.56) to 10 ppm HCHO at 250 °C with ultrafast response/recovery times (13/20 s), outperforming most reported metal oxide-based counterparts. Notably, it demonstrates an ultralow actual detection limit (0.08 ppm) and dual-linear response across 0.1-50 ppm (R² = 0.9738) and 100-1000 ppm (R² = 0.9553), enabling precise quantification in real-world scenarios. Long-term stability over 30 days further underscores its practicality. Mechanistic studies reveal that Ni doping modulates the CdO/CdSe composition ratio, which synergistically enhances interfacial electron depletion and facilitates charge transfer. This work establishes a heterojunction-component engineering strategy via dopant-mediated in-situ composition tuning, advancing the design of high-performance HCHO sensors.