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There is an increasing demand of highly sensitive, stable and highly selective gas sensors to detect toxic gases. This is inspired by the need to monitor the concentration of these gases in order to guarantee humans, animals and environmental safety. Metal ferrites (AFe2O3, where A is a metal) based sensors are paramount in this field of sensing. Among the gases detectable using metal ferrites includes carbon monoxide (CO), liquefied petroleum gas (LPG), hydrogen sulfide (H2S), petrol and methane (CH4). This reviews presents various parameters which plays key role in the design of ferrite gas sensors. They include; operating temperatures, dopants, grain size, particle size, selectivity, surface area, concentration of the gas, sensitivity as well as recovery time. In addition, the various methods which are used to synthesize ferrite gas sensors are briefly explained. Key considerations in the designing of excellent ferrite gas sensors such as calcination temperature, working temperature, dopants, and concentration as well as optimization condition among others are outlined. In addition this paper reviews the various metal ferrites such as nickel ferrites and nickel doped ferrites, cobalt and cobalt doped ferrites, zinc and zinc doped ferrites, magnesium and magnesium doped ferrites among others that have been researched as gas sensors. [ABSTRACT FROM AUTHOR]

The selectivity of a sensor is the ability to discriminate the target from the interference molecules and display a target-specific sensor response. It is a critical trait for gas sensors that are used in real-time air pollution control, hazardous materials detection, food quality inspection and personal health monitoring. Attaining high target selectivity ensures that sensors will exhibit accurate information about the existence and concentration of a target gas, which is essential for reliable sensor response. To obtain target selectivity, it is critical to determine the optimum modification technique and receptor materials as well as to understand how each method works and how it could be designed for a specific target. For this purpose, in this review we present the working principles of the three leading chemical modification methods including catalyst decoration, composite formation, and surface functionalization, as well as the selection criteria of various recognition materials. Throughout the report, we offer a rich apprehension of these techniques by providing mechanistic insights, application areas, advantages, disadvantages, and plausible applications for the invention of the target-specific gas sensors. [ABSTRACT FROM AUTHOR]