Abstract
Activated carbon (AC), a porous material with high pore volume, attracts increasing attention owing to its potential applications in several fields. The development of a porous structure in AC marginally relies on both the treatment methods and the type of precursor. Thus far, both renewable and nonrenewable precursor sources have been used to synthesize AC with high surface area and pore volume. This study presents the synthesis of AC via physicochemical treatment of waste oil fly ash (OFA), a waste material produced from power plants. The aim was to produce AC by adding surface pores and surface functional groups to the basal plane of OFA. Toward this objective, OFA was first chemically leached/activated with various combinations of H2SO4 and H3PO4, and then physically activated with CO2 at 900 °C. The chemical activation step, synergistically combined with CO2 activation, resulted in an increase of 24 times the specific surface area of the OFA. The maximum increase in surface area was obtained for the sample physicochemically treated with 100% H2SO4 . Moreover, the spectroscopic analysis confirmed the presence of acid functional groups after the chemical treatment step. To explore the surface heterogeneity, adsorptive potential distribution in terms of surface energy was also discussed as a function of the surface coverage. Following chemical activation, the OFA surface became heterogeneous. A major portion of the AC showed surface energy in the range of 40–50 erg/K, which was further increased as a result of physical activation at a higher temperature. Thus, the synergism created by physicochemical activation resulted in a material with high surface area and pore volume, and excellent adsorption characteristics. From the findings of this study, it was concluded that OFA is a cost-effective and environmentally benign precursor for the synthesis of AC.
Highlights
Activated carbon (AC), as defined by the International Union of Pure and Applied Chemistry (IUPAC), is a well-developed porous structure with several surface functionalities [1]
Chemical activation using different metal salts and oxidizing agents, like FeCl 3, zinc chloride (ZnCl 2), potassium hydroxide (KOH), ammonium hydroxide (NH 4 OH), phosphoric acid (H 3 PO 4), and HCl, leads to the pyrolysis of raw material, which allows the synthesis of AC with high carbon content, tunable porosity, and surface chemistry [11,12,13,14,15,16,17]
Both renewable and nonrenewable precursor sources have practiced the synthesization of AC with high surface area and pore volume
Summary
Activated carbon (AC), as defined by the International Union of Pure and Applied Chemistry (IUPAC), is a well-developed porous structure with several surface functionalities [1]. A study of the literature revealed that the choice of good precursor is as important as the activating agent or treatment method in the synthesis process [20] To date, both renewable and nonrenewable precursor sources have practiced the synthesization of AC with high surface area and pore volume. To achieve this objective, OFA was modified by following a 2-step treatment method: 1) chemical modification using different compositions of acid mixtures and 2) physical activation of the material synthesized in step 1 using CO 2 under elevated temperatures. The change in porosity of raw OFA and modifications in the surface functional groups were analyzed by porosity and spectroscopic analyzers
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