Preparation and characterization of poly(3 hexylthiophene)/multiwalled carbon nanotubes composites for malathion chemiresistive sensor

Chemiresistive-based sensor using poly(3-hexylthiophene-2,5-diyl) (P3HT) demonstrates high sensitivity and selectivity towards organic compound, however, P3HT can be easily oxidized in natural environment hindering its electrical
performance. Thus, highly conductive functionalize multiwalled carbon nanotubes (fMWCNT) are introduced to P3HT in order to increase its stability and sensitivity
towards malathion. To understand intermolecular interaction between f-MWCNT and P3HT, f-MWCNT (-OH, -COOH, -F and NH2) was introduced as sensing material. The P3HT/f-MWCNT nanocomposites were fabricated using filtration, spin coating, and drop-casting methods. The nanocomposite films were characterized by UV-Vis, Photoluminescence, Fourier Transform Infrared (FTIR), and Raman spectroscopies. FESEM and HR-TEM images were used to analyse the P3HT wrapped f-MWCNT nanostructures. The I-V measurement were used to examine the stability and sensitivity of the sensor. FTIR spectra of P3HT/f-MWCNT shows three major regions
of vibrational modes; (i) C-H vibration belonged to aliphatic chain of hexyl groups, (ii) C=C stretching modes, and (iii) 909 cm-1 peak that represented out-of-plane
bending vibration of cis-HC=CH- group. The last peak arises from the effect of crystallinity in P3HT chains. G-band peak shift in Raman spectra and increase of ID/IG ratio is due to formation of more ordered structures after the polymer incorporation. The origin of -π interaction between P3HT and f-MWCNT was also detected in UVvisible absorption and photoluminescence spectra. The electron images revealed noncovalent polymer wrapping on f-MWCNT as evidenced by increase in f-MWCNTs’ diameter. According to our amperometric studies, P3HT wrapped f-MWCNT showed
promising sensitivity in detecting the organophosphate (OP) simulant, malathion. The sensitivity towards malathion was examined using current-voltage characterization in range 0.1 to 500 ppb. The calculated limit of detection (LOD) was 0.07 ppb. Our findings concluded that functional group on MWCNT especially the -OH group, π-π stacking population, π-electron H interaction and hydrophobic surface play an important role in giving improved sensitivity of polymer CNT based chemiresistive sensor.