Fabrication of Iron Oxide–Based Chitosan/CNF Bio-Green Composite for Pb(II) Removal from Synthetic Wastewater: Isotherm and Regeneration Studies

Bio-green adsorbents for contaminant removal from wastewater are trending due to various advantages over traditional adsorbents such as low cost, eco-friendly nature, low toxicity, and high adsorption performance. In this, we report the synthesis of metal-based chitosan/CNF porous composite (Fe/Ch/CNF-P). Iron oxide was used as a metal base which was mixed with chitosan and cellulose nanofiber (CNF) to form the composite. Sol–gel was used as a sustainable method of fabrication. The composite was characterized via SEM, FTIR, XRD, and TGA. It was shown that the structure of the synthesized composite was porous with pore size ranging from 0.20 to 1.20 µm. Moreover, XRD peaks confirmed the fusion of iron oxide into the matrix with peaks at 35.5° and 53°, while the FTIR confirmed removal of lignin and cellulose with absence of stretching at 460 cm⁻¹ and 1740 cm⁻¹ respectively. With impressive properties, the green and cellulosic composite was investigated for Pb(II) removal from aqueous solution through pH, adsorbent dose, temperature, and contact time experiments. In pH results, the highest removal of 98% was achieved by the composite at pH of 4. In dose experiments, 0.5 g of composite removed 99% of the Pb(II) ions. Moreover, the removal of 98% was maintained till 50 °C after which it declined significantly. Furthermore, the contact time of 30 min was found to be optimum time for maximum removal. When the adsorption data was analyzed through isotherms, it best fitted Langmuir isotherm with R² value of 0.98 and maximum adsorption capacity (q_m) of 98 mg/g. When the removal capacity was compared with reported studies, it was higher than that of various traditional composite adsorbents. Moreover, the composite indicated reusability performance of more than 50% for up to four cycles after which it lost its efficiency to below 50% in the 5th and 6th cycles. With such impressive adsorption performance for Pb(II), this composite can be a potential adsorbent for other heavy metals from the synthetic as well as real wastewater.