Synthesis of Nitrogen-Doped Carbon Dots and Their Effects on Crop Seed Germination and Seedling Growth

Nanomaterials are helping to transform agricultural production, playing a crucial role in achieving sustainable development, increasing crop yields, and addressing the safety of fertilizer use. The advantages of carbon dots (CDs) in the application of new agriculture are apparent. This study combined the advantages of CDs to explore the positive effects of CDs doped with essential elements on plant growth. In this regard, for the first time, we prepared nitrogen-doped CDs (N-CDs) with blue fluorescence emission by a microwave reaction with succinic acid using <i>m</i>-phenylenediamine (MPD) as the nitrogen source, and studied their effects on crop growth and development. The morphology, structure, and fluorescence properties of the N-CDs were analyzed using various characterization methods. N-CDs exhibited good stability with an average particle size of 2.20 nm. The optimal emission wavelength was 360 nm, the maximum fluorescence emission peak was 452 nm, and the absolute quantum yield (QY) was 35.60%. The results of the effect of N-CDs on crop growth and development showed that the highest germination rate (86.67%, 68.33%), vigor index (127.76%, 15.31%), and biomass in maize and tomato were observed after treatment with 0.010 mg/mL N-CDs. With increasing N-CDs concentration, the indices first increased and then decreased, with significant growth inhibition observed at excessively high concentrations. Therefore, appropriate concentrations of N-CDs can enhance the development of crop seedlings. This study lays the foundation for the nanofertilization applications of CDs, which could be further doped with potassium, phosphorus, and other important plant nutrients.