Adsorptive performance of a new magnetic hydrochar nanocomposite for highly efficient removal of cadmium ions from water: Mechanism, modeling, and reusability studies

In this study, a novel and effective magnetic watermelon seed hydrochar (MWSHC) was successfully synthesized via hydrothermal carbonization technique and in situ co-precipitation method. The prepared magnetic watermelon seed waste hydrochar has been utilized for the elimination of cadmium ions from the aqueous environment. The structural morphology, surface properties, and thermal stability of MWSHC adsorbent were characterized using FTIR, SEM, XRD, BET surface area, and TGA analysis, which demonstrated the successful synthesis of MWSHC. An extensive study of Cd(II) adsorption was conducted by assessing the influence of contact time, adsorbent mass, pH, initial Cd(II) concentration, temperature, and coexisting cations on the adsorption process of Cd(II). The results revealed that the removal efficiency of Cd(II) was 96.60% achieved at pH 7.0, time: 300 min, and dosage: 0.01 g, T: 298 K. Adsorption isotherm and kinetic parameters were estimated. The results indicated that the Cd(II) adsorption onto MWSHC followed the Freundlich and pseudo-second-order models. Based on the Langmuir equation, the MWSHC has a maximum adsorption capacity of 347.2 mg/g at 298 K. The reusability of magnetic hydrochar nanocomposite was studied, revealing that around 84.4% Cd(II) was still removed after four cycles. In conclusion, the newly- prepared MWSHC adsorbent has the advantages of high adsorption capacity, cost-effectiveness, and easy separation, thus having promising applications in effectively removing cadmium(II) from the aqueous environment.