Visible LED-based photo-redox properties of sulfur and nitrogen-doped carbon dots designed by solid-state synthesis

Abstract

Nitrogen-doped and sulfur, nitrogen co-doped carbon dots (CDs) were synthesized using a solid-state, solvent-free, microwave synthesis technique at 250 °C. CDs were synthesized using citric acid as the carbon precursor and urea or thiourea as the nitrogen and sulfur precursor. The solid-state synthesis produced crystalline nitrogen-doped CDs (N-CDs) and nitrogen/sulfur co-doped CDs (S,N-CDs) with a broad absorption band in the visible region. The photoredox catalytic properties of the as-prepared CDs were demonstrated by investigating the model photoreduction of methyl viologen using 410 nm and 455 nm light-emitting diodes (LEDs). The highest concentration of the methyl viologen radical cation was monitored in the presence of N-CDs in comparison with S,N-CDs. The results indicate that nitrogen-doped graphitic CDs feature higher charge extraction for photoredox catalysis in comparison to nitrogen, sulfur co-doped CDs.