Selective Adsorption of Lead in Mixed Metals Wastewater System by Lignin-Carbon-Supported Titanate Nanoflower BC@TNS Adsorbent: Performance and Mechanism

This study introduced a novel type of biochar–titanate nanosheet (BC@TNS) composite for the selective adsorption of Pb(II) from wastewater containing various heavy metal ions. The biochar derived from lignin–carbon pyrolysis forms the scaffold, while titanate nanosheets coat it via an alkaline hydrothermal reaction. The synthesis was confirmed through analytic characterizations, revealing a distinctive morphology of TNS nanoflowers consisting of numerous nanosheets incorporated into the BC support. BC@TNS achieved maximum adsorption capacities of 37.89 mg/g for Pb(II), 13.38 mg/g for Cd(II), and 8.47 mg/g for Zn(II), demonstrating its remarkable selectivity for Pb(II). Kinetic studies using Weber–Morris, PFO, and PSO models indicated that Pb(II) adsorption was primarily driven by chemisorption, whereas Cd(II) and Zn(II) adsorption were predominantly governed by physisorption. Isotherm analysis using Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin models revealed that Pb(II) adsorption involved both monolayer and multilayer processes, while Cd(II) and Zn(II) adsorption were primarily monolayer. Detailed insights from scanning electron microscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) analyses further elucidated these mechanisms. The superior selectivity of BC@TNS for Pb(II) was further validated in multicomponent simulated HMs containing 10 co-existing metal ions, maintaining a high Pb(II) adsorption efficiency of 75.68%, highlighting its potential for selective Pb recovery. Moreover, the adsorbent demonstrated excellent regeneration capacity and recyclability. The BC@TNS adsorbent shows great potential for the selective and efficient removal of Pb(II) ions from wastewater, offering a sustainable solution for environmental protection.