Elucidating the low-frequency ultrasound effect on mass transfer resistances during phenol adsorption over microporous materials

To improve the adsorption rate of pollutants on microporous materials, a comparative study of the adsorption of phenol on activated carbon pellets (ACP) in the presence of conventional agitation and low-frequency ultrasound (US) was accomplished. Additionally, the effect of chemical and textural properties over the equilibrium and adsorption rate was evaluated by modifying the ACP with a physical reactivation process at different times. The textural properties of the adsorbents were obtained by physisorption of N2 at-196 & DEG;C and CO2 at 0 ?, while the functional groups were identified using XPS spectroscopy. The phenol adsorption equilibrium was studied at 25 and 45 ?, while the adsorption rate was conducted by varying the initial phenol concentration, stirring speed, and ultrasound amplitude. The results showed that the reactivation process improves the average micropore width and mesopore volume, which allows better diffusion of phenol towards the microporosity of the material, increasing the adsorption capacity from 164 to 217 mg/g at pH & AP;7 and 25 ?. The concentration decay curves of phenol were predicted using a 3D-diffusional model. The results evidenced that in absence or presence of US, the overall adsorption rate is controlled by intraparticle diffusion. Moreover, the surface diffusion mechanism proved to be more important than the pore volume diffusion for both scenarios. Finally, it was demonstrated that US decreases the equilibrium times by enhancing the intraparticle diffusion causing a 2.36-fold increase in the value of the surface diffusion coefficients. Finally, the external mass transport was enhanced exclusively for ultra-microporous materials.

Automated summary

This study compared the adsorption performance of activated carbon pellets (ACP) for phenol under conventional agitation and low-frequency ultrasound. The effects of modifying the ACP with a physical reactivation process and the chemical and textural properties on the adsorption rate were evaluated. The results showed that the reactivation process improved the adsorption capacity, and ultrasound enhanced the adsorption rate.