Morphology controlled copper-rich covellite nanoarchitectures for methyl orange degradation and supercapacitor applications

Covellite (CuS) nanostructures were synthesized via a chelation-assisted hydrothermal route using EDTA and PEG, followed by annealing at 100 and 200 °C, to regulate their structural, optical, and electrochemical properties for organic pollutant degradation and energy storage applications. X-ray diffraction confirms a hexagonal covellite phase for all samples, with chelating agents promoting preferential (110) growth. PEG-assisted annealing induces a morphological transition from irregular aggregates to uniform nanoflower architectures, most pronounced for PEG–CuS annealed at 200 °C. BET analysis shows that CuS–PEG has a higher surface area (28.70 m² g⁻¹, 15.7 nm pores) than CuS–EDTA (27.58 m² g⁻¹, 23.30 nm), with uniform mesopores that enhance active sites and ion diffusion. XPS verifies availability of Cu and S. The bandgap is tunable from 1.1 to 1.4 eV and correlates with crystallite size, enabling strong visible-light absorption, while suppressed electron–hole recombination enhances charge separation. Under natural sunlight, methyl orange acts as a photosensitizer, injecting excited electrons into the CuS conduction band and significantly improving photocatalytic activity. Scavenger studies and DFT-based Fukui function analysis confirm a dominant photo-sensitized charge-transfer pathway, with hydroxyl radicals as secondary reactive species. Beyond photocatalysis, PEG-derived CuS nanoflowers demonstrate excellent electrochemical performance as the positive electrode in an asymmetric supercapacitor, delivering 415 F g⁻¹ at 1 A g⁻¹, an energy density of 147 Wh kg⁻¹ at 856 W kg⁻¹, and 98% capacitance retention after 10,000 cycles. Three-electrode tests reveal pseudo-capacitance with up to 716 F g⁻¹ (1 A g⁻¹), a low Rct (2.15 Ω), and ideal EIS. The enhanced performance originates from the PEG-directed hierarchical CuS nanoflower architecture, which facilitates rapid electron transport and efficient ion diffusion.