Bio-inspired carbon quantum dots derived from bilimbi (Averrhoa bilimbi L.) for sustainable nanofertilizer development

Sustainable and low-toxicity nanomaterials are increasingly needed to improve agricultural productivity, yet biomass-derived carbon quantum dots (CQDs) for fertilizer applications remain limited. This study aims to address this gap by synthesizing CQDs from bilimbi (Averrhoa bilimbi L.) and evaluating their potential as environmentally friendly nano-fertilizers. Carbon quantum dots (CQDs) from bilimbi (Averrhoa bilimbi L.) were successfully prepared synthesized using a hydrothermal method. This research was conducted in three stages: synthesis, characterization, and evaluation of their activity as a fertilizer. The characterization covered optical properties, photostability, functional groups, and particle size. In the final stage, CQDs from bilimbi were tested for their effect on the growth of mung bean sprouts. The resulting CQDs appeared as a brown solution with blue fluorescence under UV light, exhibited an excitation peak at 360 nm, an emission peak at 453 nm, a quantum yield of 72.15%, and a 22.77% decrease in photostability over 30 days. FTIR characterization confirmed the presence of O–H/N–H, C–H, C = O, C = C, and C–O–C groups, while the Raman spectrum showed an ID/IG ratio of 2.85, indicating a high level of structural defects. DLS data showed an average particle size of 5.4 nm (PDI = 0.32) and a zeta potential of + 1.13 mV for CQDs, while HRTEM confirmed a size of ~ 2.62 nm. Application tests on mung bean sprouts showed that applying CQDs, especially at a concentration of 50 ppm, increased stem length, root length, and total chlorophyll content (18.37 mg/g). These results demonstrate the potential of CQDs from bilimbi as an environmentally friendly nano-fertilizer to support sustainable agriculture.