Synthesis, Characterization, and Multifunctional Applications of Moosa Balbeesiaana Peel-Derived NCQDs-PEG-400 Composite in Photocatalysis and Electrochemical Energy Storage

The degradation analysis of toxic and non-biodegradable dyes, widely used in textiles, paper, plastics, and food industries, is critical for protecting aquatic ecosystems. Additionally, the use of bio-waste for designing high-performance electrodes for supercapacitors aligns with environmental conservation efforts. In this study, we report the synthesis and characterization of a composite of metal oxide/nitrogen-doped carbon quantum dots (NCQDs) and polyethylene glycol-400 (PEG-400) using Moosa balbeesiaana peels extract. The photocatalytic degradation potential of the composite was investigated for malachite green (MG) and rhodamine B (Rh-B) dyes. Furthermore, the degradation potential of the composite without PEG-400 was examined for fluorescein (Fl) and methylene blue (MB) dyes. The correlation coefficients for the composite with PEG-400 in zero-order, first-order, and second-order kinetics were 0.8802, 0.9654, and 0.8144, respectively, for MG, and 0.8256, 0.8378, and 0.8497, respectively, for Rh-B. For the composite without PEG-400, the respective values for Fl were 0.9452, 0.9514, and 0.9519, while for MB, they were 0.8882, 0.8879, and 0.8874. Electrochemical analysis was conducted using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrical impedance spectroscopy (EIS), and cyclic stability (Csta) measurements. The specific capacitance values were found to be 1873.14 (F/g) at 10 mVs−1 and 1806.27 (F/g) at 1 Ag−1. EIS measurements showed a series resistance (Rs) of 13.79 Ω, a charge transfer resistance (Rct) of 28.56 Ω, and a Warburg impedance (Zw) of 1.15 × 10–7 Ω. The capacitance retention of 110% from 1500 to 5000 cycles demonstrated excellent stability over 5000 cycles.