Carbon quantum dots-ZnFe2O4 nanocomposite for dual-function applications: Adsorption-assisted photocatalysis and fluorescence quenching-based sensing of Hg2+ and Fe3+ ions

Carbon quantum dots/ZnFe 2 O 4 nanocomposite (CQDs/ZnFe NC) was successfully synthesized via a hydrothermal approach and characterized using XRD, HR-TEM, UV–Vis/DRS, PL spectroscopy and zeta potential analysis. The PL results revealed enhanced separation efficiency of photogenerated charge carriers in the CQDs/ZnFe NC. HR-TEM analysis confirmed the formation of quasi-spherical nanoparticles with an average particle size of approximately 18 nm. EDS spectra further verify the presence of Zn, Fe, N, O and C elements in synthesized nanocomposite. The prepared CQDs/ZnFe NC was employed for both metal ion sensing and photocatalytic degradation of methylene blue dye. The nanocomposite exhibited selective sensing performance toward Fe 3+ and Hg 2+ ions with limits of detection values of 1.3 and 2.8 μm, respectively. In addition, the photocatalytic activity of ZnFe NPs and CQDs/ZnFe NC was also evaluated under visible light irradiation for MB degradation. The CQDs/ZnFe NC demonstrated superior MB removal, achieving nearly 80% degradation within 3 h. The higher overall MB removal observed for CQDs/ZnFe NC is attributed to enhanced dark-phase adsorption by CQDs, followed by efficient charge carrier separation that promoted photocatalytic degradation during visible-light irradiation.