Apple Tree Root-Derived Biochar/Iron Oxide Triphasic Nanocomposite for Wastewater Treatment and Microwave Absorption

In this work, two major sources of pollution: (1) Water pollution due to heavy metals, and (2) Electromagnetic wave (EMW) pollution, often regarded as the fourth category of pollution (after air, water, and soil pollution) are addressed. A unique bio-based triphasic nanocomposite (Fe₃O₄/α-Fe₂O₃/carbon) is synthesized and its superior properties are demonstrated to address both types of environmental pollution. The nanocomposite, derived from lightweight apple tree roots, is used for Pb (II) ion removal from aqueous solutions via adsorption and magnetic separation. The biomass-derived highly porous biochar decorated with iron-oxide showed adsorption efficiency of nearly 100% and corresponding capacity of 149 mg.g⁻¹ under optimal conditions for initial Pb (II) concentration of 50 mg.L⁻¹. Furthermore, a remarkable adsorption capacity of 731 mg.g⁻¹ is achieved using lower amount of the adsorbent for a slightly lower efficiency (97%). In addition, the mesoporous composite showed excellent EMW absorption efficiency with effective absorption bandwidth of 7.8 GHz and reflection loss of −61.7 dB, arising from very good impedance matching, and high dielectric and magnetic losses. This work establishes the multifunctional properties of the synthesized composite, and addresses the UN Sustainable Development Goal (SDG) 6 (Clean water and sanitation) and SDG 13 (Climate action, including pollution management).