A conducting cotton fabric with a resistance of <1.5 k cm −2 was obtained by dip coating of multiwalled carbon nanotubes (MWCNTs) dispersed in a surfactant, sodium dodecyl sulphate (SDS). The dip coating was repeated up to 20 times to increase the loading of MWCNT as observed from optical absorption spectra (λ max = 442 nm). The field emission scanning electron microscopy (FE-SEM) image of coated fabric at different magnifications shows micro-fibril structure. Energy-dispersive X-ray analysis (EDXA) spectra show peaks for carbon and other constituent elements of SDS, Na and S. In order to improve the functionality of loaded MWCNT, the coated fabric was treated with 5% HNO 3 for 3 h. For such a sample, the resistance decreased significantly to 1.5 k cm −2 , whereas it is 2.0 and 2.5 k cm −2 for untreated and KOH-treated sample. This is in corroboration with I−V characteristics, and is attributed to increased loading of MWCNT through hydrogen bonding with glycosidic group present in cotton (cellulose) fibres. The series capacitance of the MWCNT-coated fabric is about 40 μF cm −2 , which is found to decrease with the increase in frequency, close to zero at about 20 kHz. A capacitor formed by placing two MWCNT-coated fabrics between etched PCB plates (terminal contacts) shows the charging capacity of about 1 F.
Today, resistance gas sensors which are mainly realized from metal oxides are among the most used sensing devices. However, generally, their sensing temperature is high and other materials with a lower operating temperature can be an alternative to them. Graphene and its derivatives with a 2D structure are among the most encouraging materials for gas-sensing purposes, because a 2D lattice with high surface area can maximize the interaction between the surface and gas, and a small variation in the carrier concentration of graphene can cause a notable modulation of electrical conductivity in graphene. However, they show weak sensing performance in pristine form. Hence, doping, and in particular N doping, can be one of the most promising strategies to enhance the gas-sensing features of graphene-based sensors. Herein, we discuss the gas-sensing properties of N-doped graphene and its derivatives. N doping can induce a band gap inside of graphene, generate defects, and enhance the conductivity of graphene, all factors which are beneficial for sensing studies. Additionally, not only is experimental research reviewed in this review paper, but theoretical works about N-doped graphene are also discussed.
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