The effects of acid leaching on porosity and surface functional groups of cocoa (Theobroma cacao)-shell based activated carbon

Cocoa shell pellets were converted into activated carbon (CSAC) by carbonization at 800 °C followed by activation at 850 °C in CO2 flow until reaching burn off at approximately 48%. The CSAC was treated with hydrochloric acid (HCl) using response surface methodology (RSM), where the effect of soaking times (1, 2 and 4 h), temperatures (30, 50, 70 °C) and concentration of HCl (0.1, 1 and 2 M) were studied. CSAC treated with 1 M HCl at higher temperatures (>60 °C) yielded CSAC with low ash content (<10%). Acid-treatment process parameters, particularly the reaction temperature, determined the composition and types of functional groups existing in the CSAC. High concentrations of oxygen functional groups were detected in both untreated CSAC and CSAC treated at low acid concentration (1 M). High concentrations of nitrogen functional groups were detected only in CSAC treated at acid concentration (2 M).

► Treatment at low concentration does not change activated carbon structure.
► Treatment at high concentration could form the amorphous silica.
► Dissolution of cations occurred at high concentration treatment.