# Hierarchical Porous Nickel Oxide Nanoparticles with High Specific Surface Area by Green Synthesis

## TL;DR

This paper describes a green method to create porous nickel oxide nanoparticles with high surface area using plant extracts and alcohol solutions.

## Contribution

The study introduces a green synthesis method using plant extracts and shows how extractant choice affects nanoparticle properties.

## Key findings

- Using Fumaria officinalis L. extract with isopropyl alcohol yields the highest surface area of 130.0 m2/g.
- Changing the plant extract from Fumaria officinalis L. to Origanum vulgare L. increases particle size and makes the structure more friable.
- Ethyl alcohol-based extractants for Fumaria officinalis L. result in the lowest surface area of 40.2 m2/g.

## Abstract

Porous nickel oxide nanoparticles with a hierarchical structure and high specific surface area were obtained by green synthesis followed by thermal annealing. The influence of the choice of precursor plant extract (Fumaria officinalis L. and Origanum vulgare L.) and the extractants in aqueous solutions on the parameters of the synthesized particles was studied. Characterization of the NiO morphology and composition, as well as the specific surface area, was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and the BET method of nitrogen thermal desorption. Resulting particles have a spherical shape and a size from 30 to 50 nm. According to the data obtained, it can be seen that when the precursor is changed from Fumaria officinalis L. to Origanum vulgare L., the size of the synthesized particles increases, while the structure becomes more friable. It has been revealed that certain parameters and the nature of the assembly of porous particles lead to an increase in the surface area: the highest value of the SSA of 130.0 m2/g is observed in NiO nanoparticles obtained using Fumaria officinalis L. extract based on isopropyl alcohol. Also, a relatively high SSA value of 73.5 m2/g is observed in nanoparticles obtained using the same extractant for Origanum vulgare L. extract, while the use of an ethyl alcohol-based extractant for Fumaria officinalis L. resulted in the lowest value of 40.2 m2/g. The developed semiconductor particles are promising for use in catalysis, sensors, and as part of supercapacitor electrodes and functional layers in device structures for solar cells.