Assessment of Adsorption Properties of Neem Leaves Wastes for the Removal of Congo Red and Methyl Orange

Abstract

 Abstract— Neem leaves were studied as plant wastes derived adsorbents for detoxification of Congo Red (CR) and Methyl Orange (MO) from aqueous solutions using batch adsorption technique. The objectives involved determining the effects of the basic adsorption parameters namely, agitation time, adsorbent dosage, adsorbents particle size, adsorbate loading concentrations and initial pH, on the adsorption process as well as characterizing the adsorbents by determining their physicochemical properties, functional groups responsible for the adsorption process using Fourier Transform Infrared (FTIR) spectroscopy and surface morphology using scanning electron microscopy (SEM) coupled with energy dispersive X - ray spectroscopy (EDS). The adsorption behaviours of the materials were tested against Langmuir, Freundlich, Temkin, Dubinin Radushkevic and Harkins Jura isotherm models. Percent adsorption increased with increase in agitation time (5 - 240 minutes), adsorbent dosage (100- 500mg), initial concentration (100-300mg/L), and with decrease in particle size (≥75μm to ≤300μm) of the adsorbents. Both processes are dye pH-dependent, increasing or decreasing percent adsorption in acidic (2-6) or alkaline (8-12) range over the studied pH (2-12) range. From the experimental data the Langmuir's separation factor (RL) suggests unfavourable adsorption for all processes, Freundlich constant (nF) indicates unfavourable process for CR and MO adsorption; while the mean free energy of adsorption �� , calculated from Dubinin-Radushkevich equation suggest a physical adsorption. Reduction in band intensities and vibrational changes observed in FTIR spectra indicate possible involvement of carbonyl (-C=O), carboxyl (-COOH) and hydroxyl (-OH) functional groups on the adsorbents' surfaces during the adsorption and interaction with the sulfonic acid groups (-SO3Na) on the dye molecules. The difference in irregular and porous texture surface morphology of fresh and dye- loaded adsorbent characterized the adsorption of the dyes by the adsorbent. While EDS analysis indicates that adsorbent consist of mainly C and O, and small amounts of, Ca, Mg, K, P and S. The result of this study shows that neem leaves are potential alternative low-cost adsorbents for the effective removal of Congo red (CR) and methyl orange (MO), from aqueous solutions. Keywords—Adsorption, Congo red, Methyl orange, Neem Leaves