Xerogels for the study of porosity in photochemistry: Adsorption and photodegradation of yellow-5.

ARENILLAS, A.; MENÉNDEZ, J.A.; MATOS, J.:
Satellite Symposium to CARBON 2019. Beyond Adsorption II, JULY 20th, LEXINGTON, KY.

Abstract

Carbon xerogels were prepared from formaldehyde/resorcinol mixtures. The pore size distribution and the mean pore diameters were carefully tailored varying from 5-100 nm. The influence of these parameters upon the capacity of adsorption and the photodegradation of yellow-5 (Y5) were verified. The pseudo first-, second-, and intraparticle diffusion models, as well as the Langmuir and Freundlich adsorption isotherms for the Y5 adsorption were studied. In addition, pseudo-first, pseudo-second order and intraparticle diffusion models were verified for the kinetics of Y5 adsorption and results were correlated with the photochemical activity. It was found that the mean pore diameter influenced the kinetic constants for Y5 adsorption, and accordingly, the surface density of molecules adsorbed on carbon xerogels is highly dependent of the mean pore size. This parameter affected the reaction-rate of Y5 photodegradation. In terms of the first- and second-order apparent rate-constants, the maxima photocatalytic activity was observed for 20 nm mean pore diameter. Despite of the present xerogels were clearly lower in pholoactivily in comparison to commercial TiO2, the binary composites prepared by mixing the best carbon Xerogel with TiO2 showed interesting results. The influence of the initial concentration of the azo-dye (from 1 up to 10 ppm) was verified. It was found that 1 ppm, an important synergy effect up to 6 times more pholoactivity was observed while Increasing the concentration to 10 ppm, the synergy decreased to only 1.4 times higher. This effect was ascribed to an enhancement in the influence of the mass-diffusion limitation of the azo-dye from the bulk of solution to the pores of the xerogel. The present work opens new opportunities for carbon xerogels to be efficiently used in environmental remediation in aqueous phase.

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