Preparation and freshness detection of tofu based on In-doped CeO2 ammonia gas sensor

An ammonia (NH 3 ) sensor with high sensitivity based on indium-doped cerium oxide (In/CeO 2 ) was prepared by hydrothermal method , and its sensing mechanism was revealed by first-principles. Experimental results show that indium ion (In 3+ ) doping can effectually increase the sensitivity of NH 3 sensor based on CeO 2 , which is mainly attributed to the enhancement in the number of oxygen vacancies and oxygen free radicals on the surface of In/CeO 2 . In/CeO 2 sensor for NH 3 with a response value of 5412.93 at a concentration of 1000 ppm, which is 65 times that of CeO 2 sensor. Moreover, the low detection limit (LOD) of In/CeO 2 is 0.433 ppm and its response/recovery time to 5 ppm NH 3 is 1.1 s/1.4 s. Furthermore, the density functional theory (DFT) calculation confirmed that NH 3 has higher adsorption-induced charge transfer and adsorption energy on the surface of In/CeO 2 than other gases. This makes it easier for In/CeO 2 to adsorb NH 3 molecules and release more conduction electrons, thus improving the performance of In/CeO 2 . In addition, In/CeO 2 sensor can be effectively used to detect the freshness of tofu through the concentration of NH 3 released by the tofu in different storage environments. This work is beneficial to the safety monitoring of high protein food.