Extended π‑conjugated system of 3D carbon-rich carbon nitride microspheres for boosting photoelectrochemical 4-chlorophenol sensing

4-Chlorophenol (4-CP) is one of the water pollutants with high toxicity and low biodegradability. Accurate detection against 4-CP is of great value to maintain human life. A photoelectrochemical (PEC) sensor based on three-dimensional carbon-rich carbon nitride (named 3D-CN) material was proposed for monitoring 4-CP from water environment. 3D-CN material was prepared by a low-temperature supramolecular self-assembly combined with thermal-polymerization strategy. 3D and carbon rich structure endow 3D-CN material with significantly extended π-conjugated system and enhanced charge mobility, which not only easily activates inherent π → π* electronic transition, but also awakens n → π* electronic transition in 3D-CN material. The n → π* electronic transition can further extend the absorption band edge, results into excellent PEC performance of 3D-CN material. The constructed PEC 4-CP sensor showed excellent selectivity, stability, reproducibility, and accuracy for actual water sample detection. Furthermore, the sensor provided a wide detection range (1.6–3200 μg L–1) and a low limit detection (0.53 μg L–1). This work proposes a new idea for the development of graphitic carbon nitride (g-C3N4) materials with high PEC performance by introducing a synergistic regulation strategy of carbon rich and 3D structure, and broadens the application of g-C3N4-based materials in the field of PEC sensors.