One-Step Synthesis of Acidophilic Highly-Photoluminescent Carbon Dots Modified by Ionic Liquid from Polyethylene Glycol

Acidophilic highly-photoluminescent ionic liquid (IL)-modified carbon dots (CDs) were fabricated directly from polyethylene glycol-2000 (PEG(2000N)) by a simple one-step hydrothermal method in a system containing an IL (1-butyl-3-methylimidazolium bromide [C(4)mim] Br) and hydrochloric acid (HCl). In this process, PEG(2000N) works as the carbon source, [ C(4)mim] Br as the modifier, and HCl as the accelerator. CDs with low photoluminescence (PL) intensity and quantum yields (QYs) were generated in the system without H+, but CDs with high PL intensity and QYs could be prepared after H+ was introduced. Moreover, with the increase of H+ concentration, the QYs of the prepared CDs increase subsequently, and the highest QY reaches up to 43%. The formation mechanism was explored, and the results showed that H+ changes the surface groups of the CDs generated without H+ into those that exist on the CDs generated with H+, which further improves the PL performance of the CDs. Different from most CDs reported in the literature, the as-prepared CDs can still exhibit high PL intensity even under strong acidic condition.