Optical Sensing and Photocatalytic Dye Degradation Using Blue‐Luminescent Graphene Quantum Dots

Colloidal graphene quantum dots (GQDs) are synthesized via a pyrolysis method using air‐stable hydrazine hydrate. The optical and structural properties of GQDs are investigated by optical absorption, photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The colloidal GQDs are blue luminescent with defect free amorphous structure, indicating the formation of high‐quality GQDs. The average estimated size of the GQDs is 2.2 nm with a uniform particle size distribution from TEM measurement. The colloidal GQDs are employed as an optical sensor for the detection of L‐cysteine based on the PL spectra and exhibit an effective and selective response within the linear range of 10–200 µM, estimated detection limit of 7.64 µM. Additionally, the photocatalytic performance of the GQDs is evaluated through the degradation of Rhodamine B (RhB) and Methylene Blue (MB) under mercury vapor lamp irradiation. The photodegradation efficiencies for RhB and MB are 82.36% and 60.90%, respectively, at 210 min, highlighting their potential as efficient photocatalysts. These findings demonstrate the multifunctionality of GQDs in both optical sensing and environmental remediation applications.