A Rapid, Green and Cost-Effective Synthesis of pH- and Hydroxyl Group Sensitive Carbon Dots for Sensing Applications

Abstract

A rapid, green, and cost-effective method for synthesizing carbon dots (CDs) was developed using non-toxic, low-cost precursors via a simple combustion process. The resulting CDs exhibit strong and tunable photoluminescence, high photostability, and excellent dispersibility in aqueous media. Structural and spectroscopic analyses confirmed the presence of a partially crystalline graphene-like carbon core surrounded by polymeric surface functionalities. The synthesized CDs display dual environmental sensitivity: continuous emission shifts were observed across a broad pH range (1–14), as well as distinct spectral responses depending on the presence and nature of hydroxyl groups in organic solvents. Infrared (IR) spectroscopy revealed dynamic surface interactions and structural transformations during solvent evaporation, particularly in methanol and ethanol. UV–Vis absorption and photoluminescence spectroscopy demonstrated that the emission wavelength and intensity of the CDs vary significantly depending on solvent polarity, hydroxyl group content, and carbon chain length. In aqueous media, increasing pH induced a blue shift and enhanced emission intensity, while in alcohols, red shifts were observed. The unique sensitivity of the CDs to both pH and hydroxyl-rich environments highlights their potential utility as label-free, real-time sensors. Given their biocompatibility, photostability, and solvent-responsiveness, the synthesized CDs offer promising applications in biomedical diagnostics, food safety (e.g., methanol detection), and environmental monitoring. The study demonstrates how a sustainable and scalable synthetic route can yield multifunctional carbon-based nanomaterials with advanced sensory properties.