Design and optimization of polyindole-integrated bimetallic composites (PLN/CuO–NiO and PLN/Mn–Cu) for efficient photocatalytic degradation of imidacloprid under sunlight irradiation

Abstract

The present study demonstrated the fabrication of novel polyindole (PLN)-based bimetallic nanocomposites (PLN/Mn–Cu and PLN/CuO–NiO) via coprecipitation, hydrothermal, and in situ polymerization methods for the photodegradation of imidacloprid (IMI) pesticide. Fourier transform infrared spectroscopy showed that PLN was successfully loaded onto the bimetallic nanocomposites' surface. X-ray diffraction analysis revealed that PLN/Mn–Cu exhibited a cubic phase with a crystallite size of 75 nm, while PLN/CuO–NiO retained cubic CuO and monoclinic NiO phases with a size of 54 nm. Scanning electron microscopy analysis showed that PLN/CuO–NiO featured spherical but irregular structures, while PLN/Mn–Cu exhibited a granular and uneven surface morphology. UV–visible analysis showed band gaps of 2.15 eV (PLN/Mn–Cu) and 2.13 eV (PLN/CuO–NiO), with strong absorption between 250 and 350 nm, confirming their visible-light photocatalytic potential. Photocatalytic activity of PLN/Mn–Cu and PLN/CuO–NiO composites exhibited 91% and 98% degradation efficiency of IMI pesticide under optimum conditions of pH = 10 and 4, catalyst dose = 5 mg L⁻¹, irradiation time = 120 min and 60 min, and pesticide dose = 2 and 6 mg L⁻¹, respectively. The kinetic study showed that the Behnajady–Modirshala–Ghanbery model fitted best with the experimental data. The study on reusability showed that catalysts can be used for five consecutive cycles. The work also demonstrates a sustainable and promising route for designing PLN-functionalized bimetallic nanocomposites for environmental remediation applications.