Research on synthesis of Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>/MoO<sub>3</sub> nanocomposite and trimethylamine gas sensing properties

Abstract

Aquatic products contain an incredibly high nutritional value for the human body and gradually become indispensable ingredients on the Chinese table. Trimethylamine (TMA) from the deterioration of aquatic products can serve as an indicator to measure fish freshness. It is a challenge to develop an instant, fast, convenient, and efficient gas sensor for fish freshness. In this study, a novel Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>/MoO<sub>3</sub> composite gas sensing material is prepared by introducing Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub> nanoparticles on the surface of MoO<sub>3</sub> nanobelts. The results of SEM and TEM images show that the Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub> nanoparticles are uniformly dispersed. Then, the TMA sensing performance of a resistance-type gas sensor based the prepared Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>/MoO<sub>3</sub> composite is tested at optimal operating temperature (240 °C). the results show that the sensor possesses good response (13.9) at low concentration (5×10<sup>–6</sup>), with excellent low detection limit (2×10<sup>–7</sup>). The response time is also significantly shortened. The high sensing performance of Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>/MoO<sub>3</sub> composite is attributed to the heterojunction interface, which promotes the separation of electrons from holes through its strong oxygen adsorption and catalytic effect. This significantly improves the electron transport properties and gas sensing characteristics of the composite material. Electrons flow from MoO<sub>3</sub> nanoribbons to Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>, and the Fermi level reaches equilibrium. This process results in the formation of an electron loss layer underneath MoO<sub>3</sub>, and the charge transfer channel narrows, which is consistent with previous result. When trimethylamine dissociates on the nanoribbons to release electrons, the balance of the fermi lever is disrupted, and electrons flow from MoO<sub>3</sub> to Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>. As a result, the charge transfer channel becomes thinner, resulting in resistance modulation and increased sensitivity. In addition, the enhancement of trimethylamine sensing performance of Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>/MoO<sub>3</sub> nanocomposite can be explained by the enhancement of gas adsorption and diffusion: MoO<sub>3</sub> nanoribbons as a skeleton can effectively disperse Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub> particles and increase the adsorption capacity of gas molecules. And the enhanced response of Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>/MoO<sub>3</sub> may be due to the good catalytic effect of Cu<sub>3</sub>Mo<sub>2</sub>O<sub>9</sub>, which is conducive to oxygen adsorption. This work provides a new strategy for preparing high-performance MoO<sub>3</sub>-based gas sensing materials.