Recycling of plastic bag waste into carbon quantum dots using optimized pyrolysis-hydrothermal methods for selective Fe (III) sensing

Developing carbon-based nanomaterials from waste sources has offered versatile applications and a sustainable solution to environmental pollution. A sustainable approach to recycle plastic bag waste into carbon quantum dots (CQDs) using modified pyrolysis and hydrothermal methods with a low concentration of hydrogen peroxide as an oxidant (< 7 wt%) was proposed. Parameter optimization, such as pyrolysis product mass, hydrothermal time, and hydrogen peroxide concentration, was investigated. In this study, CQDs with a high quantum yield of 10.04% were successfully synthesized in a short time of 10 h. Compared to standalone pyrolysis or hydrothermal methods, the integrated pyrolysis-hydrothermal approach enhanced CQDs synthesis efficiency by achieving a shorter reaction time, lower processing temperature, and improved quantum yield. In addition, remarkable fluorescence stability of CQDs was acquired under UV light exposure, in various ionic strengths, and during prolonged storage. The size distribution of CQDs was 1.5–4.5 nm with a defected graphitic structure caused by incorporated oxygenated functional groups, such as carboxyl, carbonyl, and hydroxyl. The presence of these functional groups facilitated selective interaction between CQDs and Fe3+ ions. Therefore, these CQDs showed high selectivity and sensitivity for Fe3+ ions in water, with a good correlation coefficient of 0.9983 and a low limit of detection of 9.50 µM. This research highlighted the potential of converting plastic waste into valuable nanomaterials, offering a cost-effective and eco-friendly solution for using plastic waste in advanced sensing materials for metal ion