High-performance photocatalytic degradation of methylene blue from industrial wastewater using bio-inspired ZnO nanoparticles under visible light

Water pollution caused by organic pollutants and dyes, such as methylene blue (MB), is a significant environmental concern. Traditional wastewater treatment methods often have limitations in effectively removing these pollutants. Photocatalysis, a green and sustainable technology, has developed as a favourable approach to this issue. The main objectives of this study were the biosynthesis of ZnO nanoparticles (NPs) using citrus peel extract, which acts as a biological capping and reducing agent; this approach was employed to produce economic, pure, and more stable ZnO NPs. The second aim was to use the bio-synthesized ZnO NPs in the photocatalytic degradation of MB dyes under visible light irradiation. The structures of bio-synthesized ZnO NPs were deeply described by TGA, XRD, BET, SEM, PL, UV-Vis spectroscopy and TEM measurements. The UV–visible absorption analysis of ZnO NPs showed a characteristic absorption band at 355 nm, and a calculated energy band gap was 3.1 eV. Under optimized conditions (1.0 g/L catalyst, 50 mg/L MB, pH 8, visible light with λ ≥ 420 nm), the ZnO NPs achieved a remarkable degradation efficiency of 94.5 %. This research seeks to develop an efficient and eco-friendly method for eliminating organic pollutants from wastewater using ZnO NPs under visible light, with successful seven cycles. • Facile, one-step green synthesis of ZnO NPs using citrus peel, eliminating hazardous chemicals and high energy inputs. • Effectively valorizes agricultural waste into a high-performance functional nanomaterial, supporting the circular economy. • The synthesized ZnO NPs showed highly visible-light photocatalytic wastewater treatment efficiency using solar energy. • ZnO NPs band gap was 3.16 eV, and low electron-hole recombination rate for degradation of Methylene blue dye pollutants. • The maximum ZnO NPs-photocatalytic degradation of MB was 94 % after 90 min.