Chemically activated biochar layered double hydroxide composites for multifunctional water remediation: Coupled adsorption, ion exchange, and catalytic degradation mechanisms

A multifunctional Mg–Al–LDH@BC–KOH composite was successfully synthesized via chemical activation of biochar followed by in situ co-precipitation of Mg-Al layered double hydroxide nano sheets for efficient removal of organic and inorganic pollutants from wastewater. The composite had high specific surface area of 712 m² g⁻¹, pore volume of 0.82 cm³ g⁻¹, and average pore diameter of 4.6 nm, which is a 93.5 % and 78.3 % enhancement in surface area and pore volume compared to BC–KOH (540 m² g⁻¹, 0.64 cm³ g⁻¹). XRD, FTIR, FESEM, TEM, and XPS characterization confirmed the successful formation of LDH nanosheets (∼25 nm) with uniform deposition onto the biochar surface and strong chemical interaction of Mg²⁺/Al³⁺ layers with oxygen containing functional groups of biochar. The composite exhibited higher adsorption capability with maximum adsorption capacities of 243.5 mg g⁻¹ for tetracycline (TC) and 198.7 mg g⁻¹ for arsenate [As(V)], obeying well the Langmuir model (R² = 0.991 and 0.987) and pseudo-second-order kinetics (R² > 0.98). The thermodynamic analysis indicated a spontaneous endothermic adsorption process with ΔG° = −9.71 to −11.92 kJ mol⁻¹ and ΔH° = +16.4 kJ mol⁻¹. Under peroxymonosulfate (PMS) activation, Mg–Al–LDH@BC–KOH composite exhibited 94.6 % tetracycline degradation in 25 min with 87 % TOC removal and rate constant (kobs) of 0.157 min⁻¹, which is approximately five times higher than that of pure LDH. Radical scavenging experiments confirmed that SO₄•⁻, •OH, and ¹O₂ species are all involved in the oxidation process, of which MeOH and L histidine inhibited the most (TC removal dropped to 47.2 % and 58.6 %, respectively). The composite was also ideal for recyclability, the adsorption and catalytic efficiency still exceeding 90 % and 87 % after five cycles, and exhibited excellent stability under the existence of coexisting ions and varying pH conditions. The synergistic composite of Mg–Al–LDH nanosheets and KOH activated biochar created a thermally stable (28 % total weight loss), highly reactive hierarchical material that would be capable of integrating ion exchange, catalytic oxidation, and adsorption. The system was operational with minimal energy inputs (0.18 kWh m⁻³) and acceptable reusability, which suggests its potential use as an ecofriendly high efficiency platform for the removal of antibiotics and heavy metal oxyanions in real wastewater treatment.