Characteristic of Banana Plant-based Adsorbent for Removal of Organic Dyes, Cu2+ and Pb2+ Containing Aqueous Solution

The need of clean water has prompted many studies on removal of contaminants from polluted water. Amongst the water treatment methods, adsorption is simple in design and easy to use for treatment of many types of pollutants. The commonly used sorbents are activated carbon from petroleum sources, which are nonrenewable and limited. Thus, the aim of this study is to use banana stem (BSE), banana leaves (BLE) and banana stalk (BSA) as adsorbents to remove organic dyes (crystal violet dye and acid green dye) and heavy metals ions (Pb2+ and Cu2+) from aqueous solution. The BSE, BLE, and BSA sorbents were characterised using FT-IR, SEM-EDX, nitrogen adsorption and elemental analyser. The three sorbents were used in batch sorption experiments to investigate the kinetics, adsorption isotherms and effect of pH for removal of CV dye, AG dye, Pb2+ and Cu2+ ions in aqueous solution. The BSE, BLE, and BSA sorbents prior to sorption experiments show common characteristics of lignocellulosic materials. The FT-IR analysis shows the peaks of hydroxyl, CH2, CO, C-C, C-O-C and CH groups. The SEM-EDX analysis indicates irregular pores, with high amount of carbon and oxygen. The sorbents have specific surface area less than 25 m2/g, which is typical for untreated plant fibers. After sorption, the specific surface area decreases and the surface of the sorbents becomes rougher. The batch kinetics experiment indicates that the CV dye was removed using BLE sorbent at 1500 ppm, producing the highest adsorption capacity. A comparison between the CV and AG dyes show that the banana plant-based sorbents can remove CV dye better than AG dye. This highlights that the sorbents can remove positively charged ions or partially positive functional groups, due to slightly negative charge surface at almost neutral initial pH. The AG dye has to be sorbed at very low pH in order to push the equilibrium pH below 4. The metal removal using the three sorbents favours Cu2+ removal compared to Pb2+ removal. The adsorption capacities of Cu2+ removal is about 40-50% higher than Pb2+ removal, showing stronger interaction between Cu2+ ions with the sorbents. All sorbents and sorbates system were tested to be fitted well with pseudo second order kinetic model, with R > 0.97. For some system that also fits well with intraparticle and liquid film diffusion (with R > 0.9), these indicate more than one controlling step. In terms of adsorption isotherm, the CV dye removal follows Langmuir isotherm for all three sorbents, whereas the AG dye removal follows Freundlich isotherm. The effect of pH on adsorption capacities of the sorbents is not significant between initial pH of 4-10. For the AG dye, the initial pH of 2 produces the highest adsorption capacities, which drops to half of the value at higher pH. In summary, the BSE, BLE and BSA sorbents have the potential to be further utilised in removal of contaminants in water with modifications of characteristics for higher adsorption capacities