Vol. 5, Issue 4, Part G (2019)

Abstract
Adsorption is one of physiochemical approaches which can effectively be used for the removal of different pollutant in gaseous and liquid phases. Even though, different types of adsorbents are used for the removal of pollutant by the adsorption, activated carbon is frequently used as an adsorbent at industrial level due to its effective adsorptive capacity. However, the use of environmental friendly, naturally abundant and non-conventional adsorbents is becoming more popular for removal of pollutants since commercial adsorbents are quite expensive. Even though, several adsorption studies of Neem leaf powder have been reported, comparative study of adsorption by leaf, bark, seed coat and seed kernel has not been conducted. Therefore, in this study, it was attempted to evaluate the adsorption capacity of non-conventional adsorbents derived from Neem (Azadirachta indica) leaf, bark, seed coat and seed kernel compare their adsorption capacity and identify the adsorption mechanism using isotherm models. Four type of adsorbents were prepared using Neem leaf, bark, seed outer shell and seed kernel. The different plant parts were washed, dried (105°C) and powdered. The particle size less than 0.71mm was used as adsorbents for the study. Before the experiment, the characterization of adsorbents was performed. Methylene blue dye was used as the pollutant since it is frequent used dye for adsorption studies. Series of batch experiments were performed to evaluate the adsorption capacity of different adsorbents using different doses of adsorbents (1, 2 and 3g) and different initial adsorbate concentrations (50, 100, 150 and 200mg/L). One hundred milliliter of adsorbate in each concentration was taken into 250mL beaker and predetermined amount of adsorbent dose from each type was added, shaken in mechanical shaker (30min), allowed for settling. Then, adsorbate concentration in aqueous phase was determined using maximum absorbance wavelength (660nm) by a UV-visible spectrophotometer. Seed coat showed highest adsorption capacity of 87%. The adsorption capacity of leaf, bark and seed kernel was 83%, 80% and 69% respectively. Adsorption rate increases with adsorbent dose and decreases with increases of adsorbate initial concentration. Langmuir and freundlich isotherm were examined to understand the adsorption process. Langmuir isotherm showed high coefficient of determination more than 97% for all adsorbents except seed coat. Both Langmuir separation factor (R_L) and Freundlich constant (n_F) suggests the favorable adsorption of the dye onto the adsorbents. Adsorption process of all adsorbents except seed coat belongs to monolayer adsorption. Based on the study, it can be concluded that the adsorbents prepared for seed coat, bark and leaf can be used as an alternative adsorbent for the removal of pollutants from aqueous media.