Adsorption of methyl red on activated carbon derived from custard apple (Annona squamosa) fruit shell: Equilibrium isotherm and kinetic studies

Abstract

Activated carbon prepared from custard apple (Annona squamosa) shell by K2CO3 (ACCO3) and H3PO4 (ACPO4) activation were used to study the removal of methyl red (MR) from aqueous medium. The BET surface area, pore volume and pore size of the ACCO3 was 431.3m2/g, 0.054cm3/g and 21.63Ǻ and that of ACPO4 was 1065.0, 0.269cm3/g and 31.91Ǻ, suggesting mesoporous nature of the activated carbons. The FT-IR spectra established the occurrence of –COOH and –OH functional groups. SEM images suggested porous and heterogeneous surface. The contact time, adsorbent dose, initial concentration of MR, initial solution pH and temperature were optimized by batch method. The isotherm modeling of the adsorption data over the concentration range (80–130mg/L) at 303, 313 and 323K was performed using non-linear regression analysis. The data best described by Langmuir isotherm over the entire concentration range. The negative ΔG° and positive ΔH° values indicated spontaneous and endothermic adsorption process. The kinetic modeling revealed that the experimental data followed the pseudo-first order and pseudo-second order rate equations for ACPO4 and ACCO3, respectively.