Effects of non-oxidant and oxidant acid treatments on the surface properties of an activated carbon with very low ash content

An activated carbon obtained from olive stones and with very low ash content (0.10%) was treated with either HCl, HF or HNO3. The changes in surface area and porosity resulting from the acid treatments were studied by N-2 and CO2 adsorption at 77 and 273 K, respectively and by mercury porosimetry. The changes in surface chemistry were studied by temperature-programmed desorption and Fourier transformed infrared spectroscopy. The treatments with HCl yielded activated carbons on which some chlorine remained chemisorbed, whereas the HF treatment did not fix any fluorine. Due to this, the HCl treatment had a slight effect on the microporosity of the samples. Moreover, the HF treatment increased the amount of CO-evolving surface groups. The treatment with HNO3 destroyed the pore walls to a large extent, fixing a large amount of oxygen surface groups. The nature and structure of the CO- and CO2-evolving groups will be discussed in detail. (C) 1997 Elsevier Science Ltd All rights reserved.