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 [C₄mim]­Br) and hydrochloric acid (HCl). In this process, PEG_2000N works as the carbon source, [C₄mim]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.