Dual-functional carbon quantum dots from purple cabbage: Integrating selective Cr(VI) fluorescence sensing with free radical scavenging

Rapid and ultrasensitive detection of heavy-metal ions in aquatic environments is critical for ecological integrity and public health, however, achieving cost-effective and highly selective green fluorescent probes remains challenging. This work delivers notable novelty through a one-step nitrogen self-doping without extra nitrogen sources, dual sensing-antioxidant functionality, and superior detection limits (LOD) compared with homologous cabbage-based materials. A one-step hydrothermal approach was developed to synthesize nitrogen-doped carbon quantum dots (PC-CQDs) in situ, using purple cabbage as both carbon and nitrogen precursors. Structural, surface chemical, and optical properties were comprehensively characterized by TEM, XPS, XRD, FTIR, and fluorescence spectroscopy. PC-CQDs exhibit a pronounced and selective fluorescence response toward Cr(VI) with negligible interference from competing metal ions, and achieve a lower LOD compared with homologous cabbage-derived CQDs. Under optimized conditions, the Cr(VI) detection limit is 3.00 μg/L. In tap water, mineral water, and river water, spiked recoveries range from 97.00% to 100.50%. Additionally, PC-CQDs demonstrate strong scavenging activity toward hydroxyl and DPPH radicals, with a DPPH IC 50 of 0.37 mg/mL, indicating notable antioxidant potential—this dual sensing-antioxidant functionality is a key novelty of the work. Purple cabbage serves as a sustainable biomass precursor for the green synthesis of high-performance PC-CQDs, enabling a robust fluorescent sensing platform for rapid heavy-metal monitoring in complex environmental water matrices, together with antioxidant applications. The one-step N self-doping strategy without external nitrogen sources, combined with dual sensing-antioxidant function and superior LOD relative to cabbage-based counterparts, underscores the novelty and practical potential of this approach. Download: Download high-res image (360KB) Download: Download full-size image