Hollow urchin Co-Fe2O3 with outstanding selectivity and fast responding for ppb level NH3 sensing via Lewis acid-base effect

Layered double hydroxides (LDH) represent a category of stratified compounds, garnering interest in the research community due to their expansive specific surface area and superior catalytic attributes. In the current study, urchin-like Co-Fe2O3 was synthesized through the topological transformation of Co-Fe LDH. Microscopic observations confirmed the uniform distribution of burrs on its surface with diameters ranging approximately between 3 and 5 nm. The urchin-like Co-Fe2O3 exhibited exceptional sensitivity towards NH3, marked by impressive repeatability, robust stability, and selectivity, achieving an ultra-low detection threshold of 10 ppb (with a response of 5%). When exposed to 10 ppm NH3 at 275 °C, the sensor demonstrated a response rate of 298%, accompanied by swift response/recovery times (7.2/5.4 s). BET analysis highlighted a specific surface area of 114.5 m2/g for the urchin-like Co-Fe2O3, suggesting increased sites conducive to gas adsorption and interaction. Comprehensive analyses using XPS, Raman, and FTIR spectra revealed the substitution of certain Co2+ ions in the place of Fe3+, leading to a proliferation of oxygen vacancies that augmented the activity of the sensitive material. The inherent small size effect coupled with the p-n junction amplified the adsorption potential of the material. Further, a combined influence of the Lewis acid-base reaction and the catalytic properties of Co3O4 markedly elevated the sensor's selectivity to NH3. An in-depth discourse on the growth mechanisms and principles underlying Co-Fe LDH offers innovative perspectives for the regulated synthesis of LDH. Conclusively, urchin-like Co-Fe2O3 emerges as a potent gas-sensitive substrate for the precise and expedited detection of ammonia.