Study of modified biomass of Gossypium hirsutum as heavy metal biosorbent

The presence of heavy metals in aqueous media can cause serious threats to living organisms. Consequently, for the efficient and economic removal of heavy metals from water, a wide range of biomass as biosorbents has been investigated. The present study was designed to deploy Gossypium hirsutum stem powder as a biosorbent for efficient removal of toxic heavy metals including Pb²⁺, Cu²⁺, Zn²⁺ and Ni²⁺ ions from aqueous media. The biomass was modified through acid and base treatment prior to its deployment as biosorbent. Different instrumental techniques such as FTIR, SEM and TGA were used to analyze the structural, morphological, and thermal characteristics of biosorbent. AAS, and UV spectrophotometer were used to quantify the metal ions in solutions. Nonlinear models of Langmuir and Freundlich isotherms was explored for practical use in real sample analysis, and adsorption parameters were optimized systematically. The adsorption isotherms followed the non-linear Langmuir model, which best fit four heavy metals with an R² value (0.99) in both acidic and base-modified biomass. The base treated biomass showed relatively higher maximum uptake capacity for the investigated heavy metals (Pb²⁺ 121.24, Cu²⁺ 117.09, Zn²⁺ 130.65, and Ni²⁺ 111.09 mg g⁻¹) than that of acid treated biomass. Thermogravimetric analysis revealed the degradation pattern of designed adsorbent. Fourier transform infrared spectroscopy confirmed the presence of OH and Cl groups which were added during pretreatment. Scanning electron microscopy showed that the modified material has rough surface area which can contribute in enhancing the adsorption of heavy metals. The regeneration studies of modified biosorbent using 0.1 M HNO₃ solution demonstrated that the biosorbent can be effectively utilized for further five biosorption cycles without significant loss in its adsorption capability. The findings of the study revealed that acid and base modified Gossypium hirsutum stem could be efficiently utilized as a biosorbent for the removal of heavy metals in water at pH 5.5 with an adsorbent dose of 0.5 g and equilibrium time of 35 min.