<p>In this paper, dual luminescence nitrogen-doped carbon quantum dots (By-CQDs) were prepared using green hazelnut kernel shells and o-phenylenediamine. Through systematic optimization of reaction conditions, including temperature and time, a stable and reproducible preparation protocol was established. This approach has yielded significant results through straightforward preparation and characterization techniques, enabling the high-sensitivity multi-target detection of pollutants such as Fe³⁺, Cu²⁺, and OFX. These pollutants can cause water and soil contamination, further affecting ecosystems and public health. The By-CQDs selectively detected Fe³⁺, Cu²⁺ and OFX with detection limits of 0.21&#xa0;µM, 0.55&#xa0;µM and 54.18&#xa0;nM, respectively. Notably, when detecting both Fe³⁺ and Cu²⁺ simultaneously, the detection signals of the two ions did not interfere with each other. This feature allows for accurate quantitative analysis of metal ions within the same detection system, significantly enhancing detection efficiency. Furthermore, By-CQDs were successfully applied to detect Fe³⁺ and Cu²⁺ in brown sugar with recoveries ranging from 97.60 to 109.60% and to detect OFX in real samples with recoveries ranging from 97.55 to 102.32%. This study provides an innovative and reliable method for multifunctional fluorescent sensors for waste resource utilization and multi-target substance detection, which has a promising future for practical applications.</p>