Oxygen Vacancies Modulation of Ammonium Tungsten Bronze by NH ₄ ⁺ ‐Assisted Heat Treatment for Highly Sensitive Detection of NO ₂

ABSTRACT Introducing oxygen vacancies has emerged as an essential strategy to affect the sensing properties of nanomaterials. However, existing methods for manipulating oxygen require high cost, complex operation, and harsh conditions. Herein, a simple NH 4 + ‐assisted heat treatment approach was designed to regulate the concentration of oxygen vacancies of ammonium tungsten bronze ((NH 4 ) 0.25 WO 3 , named as NWO). The resultant NWO‐300 sensor exhibited an extremely high response of 118 to 1 ppm NO 2 at 40°C. It achieved a detection limit as low as 10 ppb. Such outstanding sensing properties of NWO‐300 were ascribed to the modulated electronic structure and increased active sites caused by oxygen vacancies. The formation of a large number of oxygen vacancies in NWO‐300 is due to the H and N atoms in NH 3 can extract O atoms on the surface of materials, which was confirmed by X‐ray photoelectron spectroscopy (XPS) and thermogravimetric‐mass spectrometry (TG‐MS) techniques. Moreover, the excellent NO 2 detection ability of the NWO‐300 sensor enables the detection of air quality under different floors, and its development can be utilized in the field of environmental monitoring applications.