Avocado seeds derived carbon dots for highly sensitive Cu (II)/Cr (VI) detection and copper (II) removal via flocculation

• Green and sustainable synthesis of carbon dots using avocado seeds as carbon source. • Increase in limit of detection with an increase in carbonization temperature. • Carbon dots applied as optical sensors with high selectivity towards Cr 6+ and Cu 2+ . • Real water remediation demonstrated through removal of Cu 2+ via flocculation. • Measured limit of detection in river water was 0.04 and 0.09 nM for Cr 6+ and Cu 2+ respectively. Sustainable, scalable and green carbon dots (CDs) were derived from avocado seeds using carbonization at different temperatures (250, 400, and 600 °C) and were applied as fluorescent nanoprobes for the detection of heavy metal ions. The CDs were found to be highly selective towards Cr 6+ and Cu 2+ ions and acted as fluorescent turn-off sensors. An increase in the carbonization temperature not only decreased the dimensions of the CDs from 4.6 to 3.2 nm, but also enhanced the crystallinity and sensitivity towards Cu 2+ /Cr 6+ . Although the CDs act as accurate optical sensors at low concentration range for Cu 2+ ions, at higher concentration flocculation (visible to the naked eye) takes place and hence their applicability for possible water treatment is elucidated. The high sensitivity of CDs synthesized at 600 °C is revealed through a low limit of detection (LOD), i.e., 0.04 nM and 0.09 nM for Cr 6+ and Cu 2+ ions respectively. The efficacy of the proposed particles has been successfully demonstrated in the possible real-life applications via sensitivity tests in river/tap water samples.