CARBON NANOFILLERS BASED THIN FILMS FOR TOXIC GAS SENSOR APPLICATIONS

Abstract

There are various kinds of natural, chemical and artificial species available in our surrounding environment, some of them are very essential while others are more harmful or less. The essential gases/species like oxygen (O2), nitrogen (N2) and humidity should be maintained at sufficient level in global atmosphere while excess emission of hazardous or toxic gases can harm living atmosphere. In this regard, burning of fossil fuels (e.g. Coal, petroleum, and natural gas) is a major concern for global air pollution [1-3]. On burning, compounds containing carbon, nitrogen, and sulfur generate gaseous oxides by reacting with air. These toxic gases are harmful in living atmosphere in parts per million (ppm) or even parts per billion (ppb). Among these gases, increase emission of carbon dioxide (CO2) and other greenhouse gases since the mid-20th century has been thought to be the cause of the increase in the average near-surface air and ocean temperature of the earth, a phenomenon known as global warming. In particular, CO2 detection in ambient air has continued to be a challenge due to oxidizing stability of the compound and interferences from several species, such as nitrogen dioxide (N2O) and carbon monoxide (CO). In many fields, such as industrial emission control, household security, and vehicle emission control, monitoring of CO2 is mandatory. Further, a CO2 sensor can be greatly beneficial to a wide range of applications, including breath and blood analysis for medical diagnosis [4-6], portable gas detector for personal protection and gas monitoring for climate control [7]. In view of safety regulation, a confined workplace should have CO2 concentration level below 5000 ppm in 8 h average; even lower concentration can cause discomfort, headache, respiratory problem, and other sensitive health issues [8-9]. In related to various chemical compounds, volatile organic compounds (VOCs) also attract much more interest from the last few decades in abundant significant fields like R&D laboratories, industrial productions etc. due to its toxicity, flammability, environmentally hazardousness, and explosiveness [10-11]. So, a rapid detection of VOCs is desired to maintain their concentration within permissible limit and avoid exposure associated health hazards. Chronic exposure of VOCs such as benzene, toluene, ethyl benzene and methanol poses serious health concerns such as skin and sensory irritation, carcinogenesis, mutagenesis, central nervous system depression and respiratory system damage [12-13]. Among VOCs, methanol (MeOH) has been used as an important raw chemicals in various industries as well as household products (drugs, perfumes, colors, dyes, antifreeze, etc) [14]. It is also a valuable alternative automobile fuel as it has already been used for fuel motor vehicles in many 2 countries [14]. On the other hand, methanol has also been strongly injurious to human health as well as environment monitoring due to its toxicity, flammability etc. [15-16]. Inhalation of ~20 mL methanol can lead to blindness, while ~60 mL may cause to fatal accident, if not immediately treated. Hence, early detection of methanol vapor makes a high demand for safety purpose. Though many researchers have developed low power consuming CO2 as well as methanol sensor with remarkable sensitivity, stability and selectivity [16-19] but, still there is a demand due to high sensitivity, small in size, low cost, and modest operation at room temperature. Even, development of CO2 sensor operating at room temperature under different humid condition makes another challenge.