Preparation and Characterization of Carbon Quantum Dots (CQD) and CuFe₂O₄–CQD Composite Materials for Photo and Electrochemical Applications

The Carbon quantum dots (CQD) is prepared from ascorbic acid, and the photophysical, structural, and metal sensing behavior of the CQD is investigated in detail. The negatively charged CQD, along with the vibrant functional groups, can absorb the positive charge ferric ion (Fe³⁺) and copper(II) ion or cupric ion (Cu²⁺) ions with the help of electrostatic attractive forces. In this process, the aggregation of CQD around the Fe³⁺ and Cu²⁺ ions results in confirmation that CQD is a fluorescence sensor probe that forms a metal complex, CQD-Fe³⁺ and CQD-Cu²⁺. The composite structural and functional group properties are investigated by the different analytical techniques. Moreover, the copper ferrite (CuFe²O⁴–CQD) electrochemical performances are evaluated in three and two-electrode systems by Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) techniques. The CuFe²O⁴–CQD electrode's specific capacitance value is 410 F g⁻¹ at 2 A g⁻¹ with 100% capacitance retention after 3000 cycles. Moreover, the methylene blue dye degradation efficiency of CuFe²O⁴–CQD is 91% in 120 min. The CuFe²O⁴–CQD composite has a synergistic effect between the CQD and CuFe²O⁴, which delivers a higher photocatalytic effect because which reduced recombination and enhancing charge transport.