Heat treatment effect on the textural, hydrophobic and adsorptive properties of activated carbons obtained from olive waste

Activated carbon obtained from olive waste is modified via heat treatment at several temperatures (300, 400, 500, 600 and 700 °C) and under inert atmosphere in order to remove carboxylic surface functions. The porous structure characteristics of all samples are determined by nitrogen adsorption at −196 °C. Changes in surface carboxylic groups resulting from the heat treatment are examined via various techniques including Boehm’s titration, thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry–mass spectroscopy analysis (TG/MS). The improvement in performance highlighted by both cyclohexane and humidity uptake is quantified using TGA and breakthrough time measurements under different conditions. A heat treatment at 500 °C leads to a release of CO2 following the elimination of carboxylic acid functions and to a carbon with higher hydrophobicity. Above 500 °C, in addition to CO2, there is a release of CO, which results from the decomposition of other surface organic functions. This affects negatively the textural properties.

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► The carbon humidity uptake is related to the carboxylic acid group concentration.
► Carboxylic acids are selectively eliminated by heat treatment.
► 500 °C is necessary and sufficient to reduce the humidity content down to 3%.
► The efficiency is highlighted via the breakthrough time and the adsorption of cyclohexane.