Isolation of Homogeneous Luminophores from Citric Acid and Ethylenediamine-Based Carbon Dots: pH Dependence of Their Optical Properties

Abstract

Studying the structure and mechanisms of photoluminescence (PL) formation in carbon nanoparticles, particularly carbon dots (CDs), is a topical issue in various fields of nanosensors. A key step in solving this problem is obtaining a homogeneous solution of the synthesized nanoparticles. In this study, two types of CDs with different ratios of ethylenediamine (EDA) and citric acid (CA) precursors are synthesized using a hydrothermal method. The synthesized CDs are separated into fractions using gel electrophoresis. It is found that the photoluminescence, optical density, and PL lifetime of the isolated CD fractions synthesized from EDA and CA depend significantly on the pH of the water. A theory is put forward that changes in the spectral characteristics of CD fractions with pH are due to the protonation/deprotonation of imidazole amino groups in the luminophores of these fractions.