New Nanostructure Breakthrough Enhances Detection of NOx for Advanced Air Quality Monitoring

Traditional chemiresistive gas sensors, which detect gases by measuring changes in material resistance, often lack selectivity and require high temperatures to operate effectively.

Scientists have developed a groundbreaking nanostructure capable of detecting nitrogen oxides (NOx) at extremely low concentrations, even at room temperature. This innovation addresses the pressing need for precise air quality monitoring in urban and industrial areas.

Gas sensors are vital for environmental monitoring, industrial safety, and healthcare diagnostics. The field of gas sensing is rapidly advancing, with ongoing research focused on improving sensitivity, selectivity, response times, and stability. Despite progress, achieving a sensor that excels in all these areas has been challenging.

Traditional chemiresistive gas sensors, which detect gases by measuring changes in material resistance, often lack selectivity and require high temperatures to operate effectively. These limitations have hindered their practical application, particularly in detecting gases at parts-per-billion (ppb) levels.

In response to these challenges, researchers from the Centre for Nano and Soft Matter Sciences (CeNS), an autonomous institute under the Department of Science and Technology (DST), have developed a gas sensor based on mixed spinel zinc ferrite (ZnFe2O4) nanostructures. This sensor detects NOx gases at ultra-low concentrations (down to 30 ppb) at room temperature, marking a significant breakthrough.

The research team, led by Mr. Vishnu G. Nath and Dr. S. Angappane, synthesized the mixed spinel ZnFe2O4 structure, where the arrangement of zinc (Zn) and iron (Fe) ions in the lattice deviates from the normal spinel configuration. Using advanced techniques such as X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the team demonstrated that the distribution of cations in the lattice could be controlled by varying the calcination temperature during nanoparticle synthesis.

The sensor showed exceptional performance in detecting NOx, with rapid response and recovery times, high selectivity, and excellent stability over long periods. It could detect NO2 concentrations as low as 9 ppb, well below the United States Environmental Protection Agency (US EPA) recommended limit of 53 ppb. The team validated the sensor's practical applicability by successfully detecting and quantifying NOx in vehicle exhaust emissions.

The energy efficiency of the sensor, combined with its low operational costs, makes it an affordable and accessible solution for environmental monitoring. Computational studies by collaborators from the National Institute of Technology Karnataka confirmed that the mixed spinel structure's unique cation distribution results in higher adsorption energy for NOx molecules, enhancing the sensor's performance.

The research, published in the Chemical Engineering Journal, highlights the potential of mixed spinel ZnFe2O4-based sensors as future high-performance gas detectors. This advancement could lead to more comprehensive air quality monitoring systems, essential for combating pollution and safeguarding public health.