Recent advances in flower-like nanomaterials: Synthesis, characterization, and advantages in gas sensing applications

With the rapid development of the industry, studies on environmental pollution, health, and safety are increasing. Air pollutants, toxic gases, and volatile organic compounds can threaten human health and need sensitive detection of their concentration. Gas sensors are indispensable because of their promising characteristics for detecting these gases. Gas sensors are promised to play a critical role in environmental monitoring, personal safety, and supervising toxic gases that are released from industries, fossil fuel consumption, etc. Gas sensors are low-cost, sensitive, and portable devices with intensively studied to develop their sensing performances. These can be improved by using flower-like metal oxide nanostructures, including ZnO, SnO2, and In2O3, due to the increased surface area material's selectivity to gas molecules. The other advantage of flower-like nanostructures is a large number of surface sites. Thanks to this recent development of gas sensors, the ppb levels of target gas molecules can be measured. The recent developments in detecting some common volatile organic compounds, including ethanol, NOx, formaldehyde, and H2S, were presented through gas sensors based on flower-like nanostructured metal oxides. This review also focuses on the attention of synthesis techniques and characterizations of flower-like nanomaterials. The most preferred synthesis techniques are hydrothermal and sol-gel.