Adsorption from aqueous phenol and 2,3,4-trichlorophenol solutions on nanoporous carbon prepared from poly(ethylene terephthalate)

Abstract

Highly microporous poly(ethylene terephthalate) based activated carbon exhibits a Brunauer—Emmett—Teller surface area of 1170 m²/g and a total pore volume of 0.625 cm³/g. It contains mesopores in a sufficient proportion of 42% of the total pore volume, which promotes the diffusion availability of the micropore region. The surface possesses an amphoteric nature owing to the oxygen functionalities present; however, the majority of the groups are basic. The adsorption properties from aqueous solution of weak acids, such as phenol and 2,3,4-trichlorophenol, depend both on the pH of the solutions and on the pK _a of the phenols, as the pH influences both the surface chemistry of the carbon and the dissociation of the weak acids used. In the case of phenol, a competitive adsorption takes place, as the interactions are weak in the three media investigated (pH 3, unbuffered and pH 11). The triple chlorine substitution in 2,3,4-trichlorophenol significantly enhances the surface interactions. Owing to the smaller pK _a value of trichlorophenol in an unbuffered medium, ionic interaction occurs as has been concluded from the outstandingly high value of the adsorption equilibrium constant. At pH 11 the adsorption of the phenols is hindered by electrostatic repulsion.