Hydrothermally Synthesized Carbon Quantum Dots from Amomum compactum for Fluorescence-Based Fe³⁺ Sensing

This study reports the green synthesis of carbon quantum dots (CQDs) derived from Amomum compactum via a simple hydrothermal method for the sensitive and selective fluorescence-based detection of Fe³⁺ ions. Compared with previously reported biomass-derived CQD sensors, the developed system offers a simple synthesis route without additional surface modification, high selectivity toward Fe³⁺, and reliable sensing performance in real water samples. The obtained CQDs exhibit nanoscale dimensions (2.92 nm), strong blue emission, and excitation-dependent optical behavior attributed to quantum confinement effects and abundant oxygen-containing functional groups. These surface characteristics facilitate strong interactions with metal ions, where Fe³⁺ induces a pronounced fluorescence quenching response through coordination interactions and electron transfer with oxygen-containing surface groups, compared to other tested ions, demonstrating high selectivity. The sensing system shows a linear response over a concentration range of 0.001–5 ppm with a low detection limit of 0.085 ppm, which is competitive with several previously reported CQD-based Fe³⁺ fluorescent sensors, meeting requirements for environmental monitoring. Application in real water samples confirms high accuracy and precision, with recovery values ranging from 95.1% to 101.2%. Overall, this work highlights an eco-friendly, cost-effective sensing platform that supports sustainable water quality monitoring, contributing to Sustainable Development Goals (SDGs), particularly SDG 6.