Hydrothermally synthesized Copper Oxide (CuO) superstructures for ammonia sensing

Abstract

According to environmental protection agencies (EPA), the emission threshold of NH3 in air is 1000kg/yr which is now about 20Tg/yr. Hence, there is a rapid increase in need of NH3 sensors to timely detect and control NH3 emissions. Metal oxide nanostructures such as CuO with special features are potential candidates for NH3 sensing. In the present study, morphology controlled 3-dimensional CuO superstructures were synthesized by surfactant-free hydrothermal method for NH3 detection. In addition to conventional hydrothermal method where water as solvent, a modified approach using a mixture of water and ethylene glycol (EG) was used as solvent to control the growth process. Hierarchical superstructures namely, snowflake-like, flower-like, hollow-sphere-like and urchin-like feature with particle dimensions ranging from 0.3 to 1μm were obtained by varying water/EG ratio and reaction temperature. The synthesized nanostructures exhibited morphology dependent luminescence and gas sensing properties. The surface area and pore distribution determined by BET surface analysis also largely influenced by the presence of EG in the reaction system. The average pore diameter enhanced from 6nm to 14nm by the addition of 10ml EG as solvent. The room temperature ammonia sensing behavior of all samples was studied using an indigenous gas sensing set-up. It was found that hollow-sphere like CuO nanostructures showed a maximum sensitivity of 150% towards 600ppm ammonia with a response and recovery time of 6min. The hydrothermal synthesis strategy reported here has the advantage of producing shape controlled hierarchical materials are highly suitable for various technological applications.