Competitive adsorption isotherms of rhodium 6G and methylene blue on activated carbon prepared from residual fuel oil

Usually production of activated carbon (AC) requires activation at high temperature. AC was produced from a new source of residual fuel oil at low temperature (170 °C) by chemical treatment with a mixture of sulfuric (65 vol.%), phosphoric (20 vol.%) and nitric (15 vol.%) acids. BET analysis illustrated surface area, pore volume and average pore width of 50.7 m2/g, 0.092 cm3/g and 17.18 nm, respectively. FTIR analysis showed that the surface of the AC had carbonyl (CO) and carboxyl (CO) groups. DSC-TGA illustrated a weight loss of 11% in the range of 25 °C to 210 °C. Adsorption of aqueous MB and R6G on the AC in single system provided monolayer adsorption capacity of 85.6 mg/g for MB and 64.3 mg/g for R6G. The isotherm data were fitted by Freundlich and Langmuir isotherm models and found that Freundlich model best fitted the date based on MPSD error function. Multicomponent isotherms for both dyes showed antagonism effect where MB and R6G competed on similar sites on the surface of the AC. Thermodynamic parameters, including ΔG°, ΔH°, ΔS° indicated the adsorption of MB and R6G were endothermic and exothermic, respectively, and spontaneous in the temperature range of 25-45 °C. Binary isotherm models of Non-modified, modified and extended Langmuir and extended Freundlich models were applied to fit the binary isotherm data and found that extended Freundlich isotherm model best fitted the experimental binary data adequately. This activated carbon can be used as low cost material for removal of dyes from downstream.