Removal of lead ions from solution using chemically modified Luffa cylindrica as a method of sustainable water treatment

Abstract

Luffa cylindrica, readily available in parts of Asia, Africa and South America, when chemically treated with 4% NaOH shows an increased amount of ion exchange functionality, thereby enhancing the adsorption capacity. It is well known for loofa sponge production and it is regarded as a common waste material. Chemical modification of Luffa cylindrica also changes its structural characteristics by exposing its pores for enhanced adsorption and shows an increased BET surface area from 25.32 m2 /g to 43.10m2 /g. From the FT-IR spectra an increase in protonated hydroxyl and carboxyl functional groups was observed. The adsorption of Pb2+ onto alkali treated Luffa cylindrica (ATLC) was investigated in batch experiments as a function of pH, temperature, initial metal ion concentration and ionic strength. The ATLC was found to be the more effective in removing Pb2+ from aqueous solution as compared to the neutral treated Luffa cylindrica. Adsorption kinetic and isotherm models, pseudo second order, Langmuir, two-site Langmuir, Dubinin-Radushkevich and Sips were utilized in understanding the adsorption mechanism and the ability of the adsorption system evaluated. The maximum adsorption capacity is 24.9mg/g as described by the Langmuir isotherm and the maximum percentage uptake (efficiency) is 96.4%. The Sips model fits better than the Langmuir, two site Langmuir and Dubinin-Radushkevich model using GraphPad. The kinetics of the biosorption process was studied. A pseudo second order model shows a good correlation fit.