Remarkable surface area engineering of nanosheet-assembled hierarchical p-n Ag-loaded NiO-CeO2 heterostructure for superior ethanol sensing performance
Boiketlo R.J. Thamaga, Thabang J. Theka, Rapelang G. Motsoeneng, Liza Coetsee-Hugo, H.C. Swart, David E. Motaung
Abstract
The creation of ultra-high surface areas of heterostructures based on p-n NiO-CeO2 hierarchical nanospheres and nanosheet-assembled Ag-loaded p-n NiO-CeO2 is reported, employing a straightforward hydrolysis method. A porous NiO-CeO2 heterostructure was produced by an improved 24 h urea synthesis reaction time, while the addition of Ag nanoparticles reduced the grain size and produced a remarkable surface area of 472 m2 g-1 with a significant number of adsorption sites. For the 1.0 wt.% Ag-loaded p-n NiO-CeO2 heterostructure, the optical band decreased from 3.01 to 2.37 eV. Photoluminescence experiments revealed larger surface defects for the 1.0 wt.% Ag-loaded NiO-CeO2 heterostructure provided additional evidence for the reduced band. Therefore, compared to its counterparts, the 1.0 wt.% Ag-loaded NiO-CeO2 demonstrated superior ethanol sensing, an excellent sensitivity of 0.81 ppm−1, and an ultra-low limit of detection of 1.23 ppb, towards ethanol vapor at 100 °C. The sensing mechanism illustrated that the greater gas-sensing characteristics were associated with the catalytic effect and electronic sensitization of AgO and the engineering of nanosheet-assembled hierarchical heterostructures with an extraordinary specific surface area providing sufficient active sites for the adsorption of ethanol gas, highly porous structures, and an interlayer gap, which accelerated the ethanol diffusion, leading to enhanced sensitivity and response speed of the sensor. Therefore, this study provided a simplistic approach to engineering the nanosheet-assembled hierarchical 1.0 wt.% Ag/NiO-CeO2 microspheres with enhanced ethanol sensing performance.