Development of Morphologically engineered Flower-like
Hafnium-Doped ZnO with Experimental and DFT Validation for Low-Temperature
and Ultrasensitive Detection of NOX Gas
posted on 2022-04-22, 19:08authored bySrijita Nundy, Sankar Ganesh Ramaraj, Manoharan Muruganathan, Aritra Ghosh, Asif Ali Tahir, Tapas Kumar Mallick, Joon-Shik Park, Hoo-Jeong Lee
Substitutional
doping and different nanostructures of ZnO have
rendered it an effective sensor for the detection of volatile organic
compounds in real-time atmosphere. However, the low selectivity of
ZnO sensors limits their applications. Herein, hafnium (Hf)-doped
ZnO (Hf-ZnO) nanostructures are developed by the hydrothermal method
for high selectivity of hazardous NOX gas in the atmosphere,
substantially portraying the role of doping concentration on the enhancement
of structural, optical, and sensing behavior. ZnO microspheres with
5% Hf doping showed excellent sensing and detected 22 parts per billion
(ppb) NOX gas in the atmosphere, within 24 s, which is
much faster than ZnO (90 s), and rendered superior sensing ability
(S = 67) at a low temperature (100 °C) compared
to ZnO (S = 40). The sensor revealed exceptional
stability under humid air (S = 55 at 70% RH), suggesting
a potential of 5% Hf-ZnO as a new stable sensing material. Density
functional theory (DFT) and other characterization analyses revealed
that the high sensing activity of 5% Hf-ZnO is attributed to the accessibility
of more adsorption sites arising due to charge distortion, increased
oxygen vacancies concentration, Lewis acid base, porous morphology,
small particle size (5 nm), and strong bond interaction amidst NO2 molecule with ZnO-Hf-Ovacancy sites, resulting
from the substitution of the host cation (Zn2+) with doping
cation (Hf4+).