A thermal-assisted electrochemical strategy to synthesize carbon dots with bimodal photoluminescence emission

Although several groups have reported bimodal emissive carbon dots (B-CDs) and paid considerable attention to their ratiometric fluorescent sensing application in recent years, the establishment of convenient yet robust strategies that can generate B-CDs from various low-cost and extensive carbon sources is still required. Here a novel thermal-assisted electrochemical strategy for preparing B-CDs from low-cost carbon sources, including graphite and raw coal, is reported. The as-prepared B-CDs exhibit bimodal photoluminescence (PL) emission at 415 and 510 nm under single-wavelength excitation. Furthermore, the origination of the bimodal emissive characteristics of the as-prepared B-CDs was investigated in detail. Under thermal induction, the carbonyl-related surface state PL centers are generated at the surface of B-CDs, and the co-existence of the carbonyl-related surface state and core state PL centers results in bimodal PL emission. Finally, to demonstrate its practical application, a ratiometric PL nanoprobe was developed to sense pH. This thermal-assisted electrochemical strategy is versatile and potentially suitable to a wide range of low-cost carbon sources.