Abstract
Detection of poisonous and flammable gases for health and security purpose
utilizing semiconductor metal oxides (SMO) based sensors has fascinated ample
attention owing to their incomparable advantages, such as a flawless evidence in
variation of their sensor resistance when exposed to either reducing or oxidizing
gases. Moreover, their rapid response and recovery times as well as their
remarkable sensitivity make them appealing. It is well-known that an anticipated
gas sensor ought to possess a combination of enhanced sensitivity, excellent
selectivity, rapid response-recovery times, long-term stability and low working
temperature. These factors are mostly reliant on surface area to volume ratio,
higher relative concentration of defects and crystal structure of the SMO sensing
layer. Moreover, this work is justified by the demand of gas sensors globally, with
the market estimated to reach approximately R38.4-billion by 2020. According to
World Health Organization (WHO) and World Bank, about 5.5 million deaths
happen annually costing the world economy R70-trillion a year due to air
pollution. While in South Africa about 20 000 deaths occur every year, costing
the economy nearly R300-million due to air pollution. Recently, WHO has
indicated that most of the cities in SA (such as Pretoria, Johannesburg, etc.)
exceed the limit of air quality (AQ) with roughly five times the WHO
recommendation, while over 90% of the world's population live in areas that
exceed WHO limits on air pollution.