Adsorption of Cu(II) ion from aqueous solution onto mesoporous chitosan-functionalized watermelon rind composite

The increased release of copper ions (Cu²⁺) into the ecosystem as a result of numerous anthropogenic activities and its potentially detrimental impact on public health is a cause for serious concern. However, among various heavy metal removal techniques, the adsorption technique is thought to be the most promising. This, therefore, necessitated the present study which aimed at the synthesis of watermelon rind-chitosan composite (WMR-CH) as an effective bio-sorbent for Cu²⁺ uptake from copper ion-polluted wastewater. The scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the composite. Batch adsorption was performed by varying operational conditions such as dosage, temperature, pH, dose, temperature, contact time, and initial metal concentration. The FTIR spectra of WMR-CH confirmed the existence of carbonyl, hydroxyl, and amine groups, while the SEM micrograph showed a porous composite. Optimum Cu²⁺ uptake of 96.5% was observed at pH 6 with 0.45 g adsorbent dose. The experimental data was best described  by Langmuir–Freundlich with R² = 0.9952 and the lowest error value of 0.2508 was obtained. The kinetics of the adsorption of Cu²⁺ onto WMR-CH is best fitted into the pseudo-first-order model with R² = 0.9800, thereby suggesting an interaction between the Cu²⁺ and the adsorbent. The thermodynamics parameters ΔH° and ΔG° show that the uptake of Cu²⁺ from its solution is endothermic and spontaneous. The cost analysis shows that WMR-CH composite is a cost-effective substitute for commercial activated carbon. According to the study’s findings, WMR-CH composite is a potential bio-sorbent material for the treatment of Cu²⁺-polluted wastewater.