Highly Selective Xylene Sensor Based on NiO/NiMoO₄ Nanocomposite Hierarchical Spheres for Indoor Air Monitoring

Abstract

Xylene is a hazardous volatile organic compound, which should be measured precisely for monitoring of indoor air quality. The selective detection of ppm-level xylene using oxide semiconductor chemiresistors, however, remains a challenging issue. In this study, NiO/NiMoO nanocomposite hierarchical spheres assembled from nanosheets were prepared by hydrothermal reaction, and the potential of sensors composed of these nanocomposites to selectively detect xylene gas was investigated. The sensors based on the NiO/NiMoO nanocomposite hierarchical spheres exhibited high responses (maximum resistance ratio =101.5) to 5 ppm p-xylene with low cross-responses (resistance ratios <30) to 5 ppm toluene, benzene, CHOH, CHCOCH, HCHO, CO, trimethylamine, and NH. In contrast, a sensor based on pure NiO hierarchical spheres exhibited negligibly low responses to all 9 analyte gases. The gas-sensing mechanism underlying the high selectivity and response to xylene in the NiO/NiMoO nanocomposite hierarchical spheres is discussed in relation to the catalytic promotion of the xylene-sensing reaction by synergistic combination between NiO and NiMoO, gas-accessible hierarchical morphology, and electronic sensitization by Mo addition. Highly selective detection of xylene can pave the road toward a new solution for precise monitoring of indoor air pollution.

Indoor Air Pollution, Related Human Diseases, and Recent Trends in the Control and Improvement of Indoor Air Quality

“…With their small size and low cost, they are ideally suited for remote and portable monitoring systems. Recently, metal oxide semiconductor gas sensors have been considered as a viable platform for the detection of VOCs and CO in the indoor air environment [171][172][173]. It is reported that several metal oxides, including SnO 2 , ZnO, TiO 2 , In 2 O 3 , Fe 2 O 3 , MoO 3 , Co 3 O 4 , CuO, NiO, and CdO, have been utilized in IAQ-sensing applications.…”

A Review of Nanostructured Resistive-Based Vanadium Oxide Gas Sensors

“…Initially, a solution of saturated Ca(OH) 2 with a clear color was prepared. Upon introduction of xylene into the gas chamber, due to the conversion of saturated Ca(OH) 2 into CaCO 3 , its color was changed to milky, confirming the release of CO 2 as a byproduct of sensing reaction [53].…”

“…Since it is an inert gas, its detection is extremely difficult with common gas sensors Xylene is a colorless and toxic gas which is widely used in industry mostly as solvent. However, exposure to high concentrations of xylene is dangerous for human beings and, therefore, maximum allowed exposure to xylene is set to 100 ppm for 8 h [53]. Cao et al fabricated flower-like V 2 O 5 nanostructures via hydrothermal method for gas sensing studies ( Figure 4) [54].…”

A General Solution to Mitigate Water Poisoning of Oxide Chemiresistors: Bilayer Sensors with Tb4O7 Overlayer

“…For example, additives such as Pd, Rh, Sb, NiO, and CuO with high catalytic activity can significantly alter the gas selectivity of sensors. [ 21–28 ] On the other hand, the additives of Tb, Pr, and CeO 2 with moderate catalytic activity are known to increase sensor resistance excessively, while being able to maintain gas selectivity. [ 18–20,29–31 ] The former set of additives impedes the tailored design of selective gas sensors and the latter hampers the facile measurement of sensor resistance using a cost‐effective electric circuit.…”