Bio-inspired green synthesis of reclaimable ZnO nanoclusters using Parkia speciosa Hassk pods and its potential photocatalytic removal of water-borne pollutant and antioxidant activities

ZnO nanoclusters (NCs) were synthesized by hydrothermal method following biogenic route using cost-effective, environment-friendly precursor material like the extract of Parkia speciosa Hassk pods. The as-synthesized ZnO NCs were characterized by various techniques, such as transmission electron microscope, powder X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, etc. The biosynthesized ZnO NCs were made of particles of size ranging from 10 to 22 nm with an average size of the particle of 15 nm. XRD and EDX analyses showed that as-synthesized ZnO NCs using Parkia speciosa Hassk or Stink beans extract resulted in the formation of ZnO NCs with high purity. FTIR studies showed the presence of various functional groups of biomolecules on the surface of ZnO NCs and confirm their role as capping and complexing agent in the formation of ZnO NCs. Further, the biosynthesized ZnO NCs were utilized as an efficient reclaimable photocatalyst for the degradation of 98.8% naphthol green B dye from the aqueous phase under UV₂₅₄ light within 32 min. The morphological and structural study of the reclaimed ZnO NCs confirmed that it was highly stable and could be used up to 6 cycles without losing any significant catalytic activity. Additionally, the biosynthesized ZnO NCs also showed decent antioxidant property with the IC₅₀ value of 109.61 ± 0.23 μg/mL.