Development of Morphologically engineered Flower-like Hafnium-Doped ZnO with Experimental and DFT Validation for Low-Temperature and Ultrasensitive Detection of NO_X Gas

Abstract

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 NO X 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) NO X 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 NO 2 molecule with ZnO-Hf-O vacancy sites, resulting from the substitution of the host cation (Zn 2+ ) with doping cation (Hf 4+ ).

Roll-to-Roll Processing of Hybrid MOF and Nylon Membranes for High Efficiency Removal of Toxic Gases, Heavy Metals, and Dyes

“…On account of rapid industrialization over the past decades, one of the biggest challenges facing the world is environmental pollution due to contaminated wastewater and smoke from factories, power plants, automobile exhausts, and waste disposal. , Many people suffer symptoms from toxic gases, such as hydrogen sulfide (H 2 S), ammonia (NH 3 ), NO x , and SO x . This problem has attracted the attention of scientists worldwide to prevent harmful and toxic chemicals from being released into the environment.…”