Synthesis of tiny carbon dots with high quantum yield using multi-walled carbon nanotubes as support for selective “turn-off-on” detection of rutin and Al³⁺

The solid-phase pyrolysis method is widely used in the synthesis of fluorescent carbon dots (CDs) because of its large scale and solvent-saving advantages. However, CDs are inclined to agglomerate during the synthesis process, resulting in low quantum yield (QY) and inhomogeneous distribution of particle sizes. Here, a simple and effective solid dispersion surface pyrolysis method was used for the synthesis of tiny-carbon dots (T-CDs) with a high QY. Multi-walled carbon nanotubes (MWCNTs) were used as a support and 2-(N-morpholino)ethanesulfonic acid (MES) as a precursor. MES was uniformly dispersed on the surface of MWCNTs by hydrogen bonding and π-π interactions. Due to the excellent thermal conductivity and rigidity of MWCNTs, the precursor is carbonized without agglomeration. Compared with the CDs obtained by the direct pyrolysis method without the use of a solid support, the particle size of the T-CDs is small (0.69 ± 0.14 nm) and the QY increased from 17.8 to 42.8%. It is anticipated that this method will lead to the improvement of the QY of CDs. Applications of the T-CDs included fluorescence detection of rutin in pharmaceuticals, human urine, and human serum samples, and determination of Al³⁺ in tap water samples.