Synthesis of Iron-Doped Carbon Nanodots from Waste Expanded Polystyrene and its Application in Carbon Monoxide Gas Detection

Herein, a one-pot solvothermal method was employed to synthesize Fe-doped carbon nanodots using waste expanded polystyrene as the carbon source and ferric chloride hexahydrate for iron doping. Three synthesis parameters-reaction time, temperature, and dopant weight-were optimized using Response Surface Methodology (RSM) based on Box-Behnken design, with relative fluorescence (FL) intensity as the response. Model validation showed a percentage error of 0.66% between replication experiments and predicted maximum intensity, confirming the model's reliability to maximize FL intensity in synthesis. FTIR spectroscopy identified the presence of a medium peak at 538 cm - ¹, associated with Fe-O stretching, indicating successful Fe doping, supported by EDX analysis. TEM analysis confirmed the nanosized properties of Fe-CDs, with an average particle size of 1.84 nm, and HR-TEM revealed an onion-like structure with a lattice spacing of 0.369 nm, and the presence of amorphous shells, suggesting structural heterogeneity. The synthesized doped and undoped CDs were employed in a drop-casting method to produce films that were used for carbon monoxide detection. Results displayed significant effects of operating temperature and gas concentration on the gas response of Fe-CDs and CDs films on resistance. The significant statistical difference in gas response between Fe-CDs and undoped CDs suggests that Fe doping enhances electron mobility, due to more pronounced changes in resistivity, yielding higher responses to carbon monoxide gas.