Enhanced Pb(II) Adsorption by a Ternary MnO₂/NH₂-MIL-101(Fe)/Graphitic Carbon Nitride Nanocomposite Through...

Severe heavy metal pollution in aquatic environments demands the engineered development of structurally optimized, highly selective adsorbents. Herein, we report the intentional fabrication of a novel ternary MnO₂/NH₂-MIL-101(Fe)/g-C₃N₄ nanocomposite via an integrated in situ interfacial growth pathway. The true architectural novelty of this multi-component assembly lies in utilizing the 3D mesoporous metal-organic framework (MOF) scaffolding to structurally isolate the 2D g-C₃N₄ layers and prevent the self-aggregation of redox-active MnO₂ nanoparticles. Comprehensive characterization via PXRD, FTIR, TEM, Raman, and high-resolution XPS confirmed that this unique interfacial hybridization maximizes the spatial exposure of unblocked chemical binding sites. Batch extraction trials demonstrated a high Pb²⁺ removal efficiency of 99.5 ± 2.7% at an optimized pH of 6.0, yielding a superior maximum monolayer adsorption capacity (q_max) of 431.8 mg.g^-1. Competitive selectivity matrices containing co-existing ions (Cu²⁺, Cd²⁺, Ni²⁺, and Cr³⁺) revealed noticeable selectivity toward Pb²⁺ ions, driven by soft Lewis's acid-base affinities, while background electrolyte tests identified SO₄^2- as the most influential competing anion. Non-linear isotherm modeling showed a better agreement with the Langmuir model, suggesting dominant monolayer adsorption on accessible surface sites, while kinetic data followed the pseudo-second-order model. Spectroscopic profiling proved that this heightened performance is dictated by a multi-modal integrated network operating via cooperative inner-sphere Mn-OH complexation, oxygen-vacancy trapping, exocyclic framework amine (-NH₂) chelation, and g-C₃N₄ triazine dative configurations. These findings establish the ternary system as an advanced, highly recyclable benchmark for targeted heavy metal decontamination.