Work

Dual selective sensing of CH4 and ultra-low NO gas utilizing Ag-decorated CeO2-CuO nanorods: Role of humidity in p-n conductivity transition

Year: 2025

Type: article

Abstract: Detecting hazardous gases like methane (CH 4 ) and nitric oxide (NO) under real-world conditions is a significant challenge for gas sensors. Herein, pure and (0.5–2 wt%) ag-decorated CeO 2 -CuO nanorods were prepared using a hydrothermal approach and tested as dual-gas sensors for NO and CH 4 , with controlled relative humidity (RH). The crystal structures, optical properties, surface adsorption states, and chemical states of the materials were probed using various analytical techniques. The sensors were tested at different temperatures for multiple gases, including benzene, acetone, xylene, carbon monoxide, and CH 4 . At 175 °C, a 2 wt% ag-decorated CeO 2 -CuO nanorods demonstrated a superior response and selectivity towards 10,000 ppm CH 4 gas. In comparison, at 200 °C, the 0.5 wt% ag-decorated CeO 2 -CuO nanorods showed a remarkable selectivity towards a trace level of (5–100 ppb) NO gas. The sensor showed a notable p-n transition in its electrical response based on gas and humidity levels. However, an opposite response emerged under humid conditions (RH >50 %), indicating a switch to n-type conductivity. This shift is due to humidity-driven surface hydroxylation, electron donation from ag nanoparticles, and charge effects at the CeO 2 -CuO interface. Water molecules on the surface change band bending and increase electron accumulation, promoting n-type behaviour. The sensing mechanism associated with humidity-controlled conduction reversal is discussed in detail • Pure and (0.25–1 wt%) Ag/CeO 2 -CuO nanorods were prepared using a microwave hydrothermal. • At 175 °C, 2 wt% Ag/CeO 2 -CuO demonstrated a superior response towards 10,000 ppm CH 4 gas. • At 200 °C, 0.5 wt% Ag/CeO 2 -CuO showed a remarkable selectivity towards a trace level of NO gas. • Notable p-n transition in electrical response based on the gas and humidity levels was observed.

Source: Inorganic Chemistry Communications

DOI: 10.1016/j.inoche.2025.116098

Authors: Maphia G. Pholoana, Gerald F. Malgas, Katlego L. Morulane, James Tshilongo, Hendrik C. Swart, David E. Motaung

Institutions: University of the Western Cape, University of the Free State, Mintek

Language: English

Topic: Gas Sensing Nanomaterials and Sensors

Subfield: Electrical and Electronic Engineering

Field: Engineering

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,550

Funders: Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS), National Research Foundation, Department of Science and Technology, Republic of South Africa