One-pot synthesis of biogenic nickel oxide nanoparticles for enhanced water photoremediation

Nickel oxide nanomaterials present interesting catalytic and electronic properties, which strongly depend on the preparation conditions. This work reports on the synthesis and characterization of biogenic nickel oxide particles (NiOxBIO), prepared by precipitation using Lemna minor (duckweed) as a capping agent. The properties of the biogenic NiOxBIO have been compared to those nickel oxide particles obtained in water through steric stabilization (NiOxCl). In particular, the samples have been morphologically and optically characterized. The size distribution of the two samples, determined by SEM and DLS measurements, indicate that NiOxBIO presents about 40 % smaller average diameter (27 nm) compared to NiOxCl (50 nm), likely due to the templating effects of duckweed extracts; furthermore a corona of residual extract layer is present on the surface of NiOxBIO with an average thickness of 1.5 nm. XRD measurements, Raman measurement and diffuse reflectance spectra demonstrate that the use of bio-based capping agent does not alter crystalline domains, and the electronic properties of the colloids. Comparative photocatalytic performance tests reveal that NiOxBIO is is able to photodegrade Rhodamine B dye in water more efficiently (up to 75 %, in 120 min) under UV-visible irradiadiation, using ledsources, than NiOxCl sample (about 60 % in 120 min). More importantly, the photocatalytic activity of NiOxBIO is not reduced with increasing irradiation time, as observed for the NiOxCl sample. These findings indicate that biogenic corona is able to protect the photoactive sites of the Ni oxide colloids. Thus, the enhanced photocatalytic activity of NiOxBIO highlights the potential of biogenic synthesis as an eco-friendly and sustainable approach for producing nanostructured materials for environmental remediation to treat polluted water.