Rate kinetics and isotherm study of step functionalised carbon nanotubes gas sensor for NO2 adsorption

Abstract

The rate kinetics of adsorption of environmentally hazardous gas NO2 on pristine and SnO2 functionalized carbon nanotubes was studied using pseudo first and second order kinetic models, Elovich model and intraparticle diffusion model. Pristine carbon nanotubes were functionalized with 0.1 mg, 0.2 mg and 1 mg SnO2. The experimental data obtained for the exposure of NO2 (concentrations varying from 2 ppm to 20 ppm) to pristine and SnO2 functionalized nanotubes had been correlated with rate laws to understand the adsorption process in the duration of the reaction. Of the various kinetic models tested, the experimental data was seen to fit best with the intraparticle diffusion model. The straight line obtained for intraparticle diffusion model suggested that adsorption process in the present study might be mainly governed by intraparticle diffusion. Henry, Langmuir and Freundlich isotherm models also presented a good data fit for the studied NO2 adsorption with Freundlich model giving the highest regression coefficient. The obtained constants clearly indicate the improved adsorption process in terms of the rate of the reaction and adsorption capacity for functionalized carbon nanotubes as compared to pristine with an optimum response obtained at 0.1 mg SnO2. This may be attributed to increase in active nano sites and heterogeneity in functionalized carbon nanotubes.