Development of Novel Nano-materials and Mathematical Modeling for Selective Separation and Efficient Removal of Heavy Metals from Environmental Matrices

Source abstract

Graphene oxide (GO) was synthesized from natural graphite clay (58% graphite) via modified Hummers method was dual-functionalized to GO-SH-CE by covalent grafting of thiol and benzo-18-crown-6 ether. Characterization confirmed successful synthesis. XRD showed GO peaks at 38.0° (002) and 44.23° (100), with (001) shifting from 10.5° (0.84 nm) to 8.2° (1.08 nm) after functionalization, confirming intercalation. SEM revealed wrinkled sheets becoming rough with particulate deposits; EDS showed C 75.1 wt%; FTIR evidenced GO bands at 1013 cm⁻¹ (C-O), 1580 cm⁻¹ (C=C), 1830 cm⁻¹ (C=O) and new bands at 2550 cm⁻¹ (-SH), 1100 cm⁻¹ (C-O-C crown) and 1650 cm⁻¹ (amide), confirming covalent grafting. Pristine GO was non-selective: Pb²⁺ 248.56 mg/g > Cd²⁺ 179.56 > Cu²⁺ 149.54 mg/g at pH 5.5-6.0, Ks 1.38-1.66, Langmuir R² 0.97-0.99, equilibrium 120 min, but poor reusability (72.3% to 28.4% by cycle 5) and severe matrix suppression (78.5% in DI to 18.6% in 100-fold hard water) due to Ca²⁺ aggregation. GO-SH-CE showed enhanced performance. Optimum pH 5.5 gave qe-Pb 298.2 mg/g. Kinetics followed pseudo-second-order (R²>0.99, k₂=0.0018 g mg⁻¹ min⁻¹) indicating chemisorption via Pb-S/O coordination. Isotherms fitted Langmuir (R²>0.98) with qm Pb²⁺ 312.5 mg/g >> Cu²⁺ 85.3 > Cd²⁺ 68.7 mg/g, 2.7-fold higher than GO (115.2 mg/g). KL Pb (0.184 L mg⁻¹) > Cu (0.042) > Cd (0.031), consistent with DFT energies -220.0 > -193.5 > -173.8 kJ mol⁻¹. In ternary system, Kd was 2450 L/g (Pb), 68 (Cu), 42 (Cd), giving selectivity αPb/Cu=36.0 and αPb/Cd=58.3 vs GO ∼1.5, attributed to HSAB soft-soft interaction and size-fit of Pb²⁺ (1.19 Å) into crown cavity. GO-SH-CE retained 87.3% capacity after 5 cycles and achieved 98.2%, 94.5% and 91.8% Pb removal in tap, river and synthetic wastewater with 100-fold excess Na⁺/K⁺/Ca²⁺/Mg²⁺, proving practical applicability.