Environmentally friendly synthesis of In₂O₃ nano octahedrons by cellulose nanofiber template-assisted route and their potential application for O₃ gas sensing

Cellulose has recently been utilized as a green and eco-friendly substrate template for synthesizing semiconductor oxide materials. This paper introduces a novel and sustainable method for obtaining In2O3 nano octahedrons, using cellulose nanofibers (CNF) as sacrificial templates. To demonstrate the importance and advantages of the CNF template, a parallel synthesis was conducted under the same conditions, but with no CNF. The as-prepared In2O3 compounds were thoroughly characterized by XRD, SEM, and XPS techniques. The CNF template-assisted route resulted in an approximately 3000 % particle size reduction and a narrow distribution compared to the sample prepared with no CNF as a template. Notably, the sensing performance towards ozone (O-3) gas was also substantially enhanced in the CNF template-assisted sample and a significantly higher response (Rg/Ra = 42 @ 70 ppb O-3) was observed compared to the In2O3 sample with no CNF (Rg/Ra = 3.5 @ 70 ppb O-3). Furthermore, sensors based on CNF-assisted In2O3 octahedra synthesis showed greater selectivity towards O-3 than towards NO2, another oxidizing gas, and a relatively lower operation temperature (200 degrees C). The enhancement in gas sensing properties for O-3 detection was attributed mainly to the higher concentration of chemically adsorbed oxygen species and surface defects, such as oxygen vacancies, which were promoted by the reduction in the particle size and the removal of CNF, respectively. The sustainable and CNF template-assisted approach represents a promising result for environmentally-friendly synthesis and advanced gas sensing applications.