Abstract
Narrow band gap zinc oxide (ZnO) nanoparticles (NPs) were synthesized using unboiled and boiled leaf extracts of Costus woodsonii. The as-synthesized NPs were characterized using a range of techniques. The as-synthesized ZnO NPs were crystalline with a hexagonal wurtzite structure similar to the commercial ZnO (ZnO-C). The maximum absorbance was observed at similar to 390 nm for ZnO-C and the as-synthesized ZnO NPs (ZnO-UL and ZnOBL) showed a red shift, i.e. similar to 448 nm to similar to 462 nm, hence, a lower band gap of similar to 2.68-2.77 eV. The band gap energy of the as-synthesized ZnO NPs was lower than that of commercial ZnO. The surface of ZnO was coated/modified with the components of the leaf extract. The as-synthesized ZnO NPs showed similar particle sizes and were spherical in shape. These studies confirmed the green synthesis of ZnO NPs using Costus woodsonii and the significantly reduced band gap (E-g = similar to 2.68 eV to similar to 2.77 eV) of the as-synthesized ZnO NPs compared to the ZnO-C (E-g = 3.18 eV).