Enhanced fluorescent intensity of graphene oxide-methyl cellulose hybrid in acidic medium: Sensing of nitro-aromatics†

Graphene oxide (GO) in acidic media (pH = 4) emits blue light but in neutral and alkaline media (pH = 7 and 9.2) the emission is negligible. On addition of 0.85, 1.7 and 3.4% (w/v) methyl cellulose (MC) to GO solution (0.005% w/v) the emission intensity increases dramatically at every pH but with an increase in pH the PL (photoluminescence) intensity decreases for every composition of the hybrid solution. The average lifetime of GO at pH = 4 increases on addition of MC. Fluorescent microscopic images of GO–MC hybrids for different MC content indicate that the morphology of the hybrids at pH 4 is ribbon type but at pH 7 and 9.2 no characteristic morphology is produced. The decrease of glass transition temperature by 9 °C of the GMC0.85 system (produced from drying GO-MC hybrid solution containing 0.85% MC solution) from that of pure MC suggests the presence of supramolecular interaction in the system. There is a drastic decrease in PL intensity on addition of nitroaromatics to the GMC0.85 system and it is very large (91%) for the addition of picric acid. Thus, the hybrid system acts as a good sensor for the detection of nitro aromatics by instantaneous photoluminescence quenching with a detectable limit of 2 ppm.