Accelerated proton dissociation in an excited state induces superacidic microenvironments around graphene quantum dots.

Abstract

Investigating proton transport at the interface in an excited state facilitates the mechanistic investigation and utilization of nanomaterials. However, there is a lack of suitable tools for in-situ and interfacial analysis. Here we addresses this gap by in-situ observing the proton transport of graphene quantum dots (GQDs) in an excited state through reduction of magnetic resonance relaxation time. Experimental results, utilizing 0.1 mT ultra-low-field nuclear magnetic resonance relaxometry compatible with a light source, reveal the light-induced proton dissociation and acidity of GQDs' microenvironment in the excited state (Hammett acidity function: -13.40). Theoretical calculations demonstrate significant acidity enhancement in -OH functionalized GQDs with light induction ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>p</mi> <msubsup><mrow><mi>K</mi></mrow> <mrow><mi>a</mi></mrow> <mrow><mo>*</mo></mrow> </msubsup> </math>  = -4.62, stronger than that of H₂SO₄). Simulations highlight the contributions of edge and phenolic -OH groups to proton dissociation. The light-induced superacidic microenvironment of GQDs benefits functionalization and improves the catalytic performances of GQDs. Importantly, this work advances the understanding of interfacial properties of light-induced sp²-sp³ carbon nanostructure and provides a valuable tool for exploring catalyst interfaces in photocatalysis.