EDTA-treated fibrillated cellulose bio-adsorbents from okra plant biomass and their performance on toxic divalent metal ions attenuation from aqueous solution

In this study, we highlight the valorization of agro-biomass okra fiber through a chemical modification that is cost-effective, efficient, and sustainable handy bio-adsorbent of toxic metal ions (Pb⁺², Hg⁺², and Cd⁺²). The fibrillated cellulose (FC) was extracted from the okra plant and then modified with EDTA in the presence of dimethylformamide solvent for 6, 9, and 12 h. The EDTA-modified FC (EDTA-FCX) was characterized by FTIR spectroscopy, SEM, XRD, and TGA. The absorption band for ester linkage at 1758 cm⁻¹ and amide linkage at 1629 cm⁻¹ confirm the covalent binding of EDTA with cellulose chain. The surface morphology ascribes the irregular attachment of EDTA with the groovy-like shape of FC. Consequently, the percentage of crystallinity of EDTA-FCX decreased with the increases in EDTA treatment time. The effect of the initial concentration (C₀) of Pb²⁺, Hg²⁺, and Cd²⁺ ions on the adsorption capacity of FC and EDTA-FCX was investigated. The EDTA-FCX adsorbents exhibited higher adsorption capacity (q) of metal ions than the FC adsorbent. The q values of the adsorbents were shown highest at C₀ = 200 ppm. The affinity of EDTA-FCX toward the metal ions was varied in the order of Hg²⁺  > Pb²⁺  > Cd²⁺. The ionic size and chelate formation tendency of metal ions are responsible for affecting the adsorption preference. The Freundlich and Langmuir adsorption isotherms models were developed using equilibrium adsorption data. The results obtained from the isotherms, i.e., R², 1/n, K_F, K_L, R_L, and q_m suggest that the EDTA-FCX bio-adsorbent has good potential to remove toxic metal ions from wastewater.