Zn/Al LDH immobilized onto coconut fiber biochar for Pb (II) removal: effect of pyrolysis temperature

In light of the escalating environmental concerns surrounding heavy metal pollution, particularly the widespread presence of lead, Pb(II) contaminants, there is a pressing need to advance our methods for efficient remediation. This urgency underscores the significance of developing innovative adsorbents, such as biochar functionalized with layered double hydroxide (LDH), as a promising solution to enhance the removal of Pb(II) pollutants from various environmental matrices. This study used co-precipitation to synthesize coconut fiber biochar/zinc-aluminium layered double hydroxide (CFBC-Zn/Al LDH). The CFBC-Zn/Al LDH serves as an adsorbent for removing Pb(II) in a series of batch adsorption tests. Three samples pyrolyzed at 500 °C, 600 °C, and 700 °C immobilized Zn-Al LDH. The chemical structure, surface area, and morphology analysis for the CFBC-Zn/Al LDH were investigated by analyzing X-ray Diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and Brunauer–Emmett–Teller (BET). The SEM–EDX analysis revealed the presence of finely crystalline LDH within the textured surfaces of the original CFBC samples. Additionally, confirmation of the successful creation of Zn/Al LDH composites with CFBC was established through the appearance of corresponding peaks in both XRD and FTIR analyses. The removal of Pb(II) by the CFBC-Zn/Al LDH was studied by varying the pH of the solution, the initial concentration of Pb(II), and the contact time. A batch adsorption experiment demonstrated that the 700 °C pyrolyzed CFBC had great adsorption performance towards Pb(II). The maximum adsorption capacity for CFBC-Zn/Al LDH-700 Pb(II) samples was 163.89 mg/g at pH 6 for 200 mg/L. The Pb(II) removal for CFBC-Zn/Al LDH is greater than pristine CFBC samples. The adsorption was found to follow Langmuir and pseudo-second-order, respectively, according to both adsorption and kinetic isotherms models. Hence, the incorporation of Zn/Al LDH onto cost-effective coconut fiber biochar demonstrated superior adsorption efficiency for Pb(II) when compared to the unmodified coconut fiber biochar.