Sunlight-driven photocatalytic degradation of methylene blue using ZnO/biochar nanocomposite derived from banana peels

Abstract This study describes the preparation of zinc oxide nanocomposite and its application as photocatalyst in the degradation of methylene blue under sunlight irradiation. Zinc oxide-coated biochar (ZnO/BC) nanocomposite was prepared using the hydrothermal method from banana peels and zinc acetate dihydrate as precursors. The biochar (BC), ZnO nanoparticles (ZnONPs), and ZnO/BC nanocomposite were characterized, and the results showed that ZnONPs had definite crystallinity and a regular surface morphology, with particles approximately 18 nm in size, and a XRD pattern corresponding to ZnONPs. In contrast, the ZnO/BC nanocomposite exhibited a more amorphous structure consistent with wurtzite (ZnO) and an irregular surface morphology with clusters of white particles measuring around 20–30 nm. Tauc’s plot was used to calculate the band gaps energy of ZnONPs (3.04 eV) and ZnO/BC nanocomposite (2.89 eV). Catalyst-free, ZnONPs, and ZnO/BC nanocomposite were utilized for the photocatalytic degradation of methylene blue (MB) under sunlight irradiation for 0 to 120 min in which ZnO/BC nanocomposite showed excellent photocatalytic degradation of MB under sunlight irradiation at 0 to 120 min due to lower band gap energy and synergetic effect between ZnO and BC. Dosages of 100 mg (ZnO/BC nanocomposite) and 10 ppm (MB) were optimized to obtain the best photocatalytic degradation efficiency (92 %) under sunlight irradiation with 0 to 120 min. The process was conducted with various parameters like dosage variation, concentration of MB, and different pH 3, 5, 8, and 10 to improve the photocatalytic degradation of MB from wastewater. The results indicated that the optimal conditions for the photocatalytic degradation of MB (92% after 120 min) were a catalyst dosage of 100 mg, an MB concentration of 10 ppm, and a pH of 10. This work demonstrates the potential of ZnO/BC nanocomposite photocatalyst for application in wastewater treatment and environment remediation.