Research progress on the preparation of iron-carbon composites from agricultural and forestry biomass and their application in improving environmental pollution

Abstract: An ever-increasing number of pollutants have posed serious hazards to human health and ecological environment, especially industrial wastewater, dye wastewater, and heavy-metal carcinogenic substances with the development of industrialization and urbanization in recent years. Fortunately, the iron-carbon composites can be expected to prepare using agricultural and forestry wastes. Among them, ferromagnetic additives have been widely used in the treatment of environmental pollution, due to the high specific surface area, better porosity, and abundant surface functional groups. The current preparation of iron-carbon composites includes hydrothermal synthesis, solvent heat, chemical co-precipitation, arc discharge, impregnation pyrolysis, and microwave. In this review, the latest research progress was summarized for the pros and cons of various syntheses. Among them, the hydrothermal environment accelerated the physicochemical interaction between the biomass and the aqueous solution in the hydrothermal synthesis. In turn, the formation of oxygen-containing functional groups was promoted on the surface of the carbonized materials. The solvent heat method was utilized to effectively inhibit the oxidation of products for the preparation of high-purity substances. The impregnation pyrolysis greatly contributed to a large number of pore structures in the carbonized products. The chemical co-precipitation was able to attach the metal ions and metal oxides to the surface of carbon materials or inside the pore channels. The arc discharge was used to precisely control the synthesis of nanoparticles via the varying electrode potential and current density. The microwave method was applied to realize the internal heating for less reaction time. The prepared iron-carbon composites exhibited excellent adsorption performance, easy separation, and high recycling rate. Extensive application prospects can be expected in the potential treatment of pollutants. A systematic investigation was then focused on the application progress of iron-carbon composites prepared from agricultural and forestry wastes in environmental pollution management, especially, the removal of heavy metals (Zn, Pb, Cd, Cr, Co, Ca, Mg, and Ni) from the wastewater, the treatment of dye wastewater, and the soil heavy metal pollution. More importantly, the removal of heavy metals and dyeing wastewater contained a combination of multiple adsorptions. Among them, the physical adsorption was caused by the Van der Waals forces between the molecules on the surface of iron-carbon composites and heavy metal or dye pollutant ions. The chemisorption was the process in the presence of elements via the redox reactions, especially the change of valence state. The optimal adsorption was achieved under the various chemical behavior, biological effectiveness, and migration ability of heavy metals. As such, the heavy metals were remediated in the soil pollutants, due to the significant effect of the iron-carbon composites on the immobilization of metal ions in the soil. Specifically, the iron-carbon composites with positive surfaces shared a great ability to immobilize anionic pollutants, whereas, the iron-carbon composites with negative surfaces mainly immobilized the cationic pollutants. The modified biochar can be expected to serve as a very promising immobilizer for soil heavy metal pollution. Therefore, the iron-carbon composites were prepared from the agricultural and forestry wastes in the environmental pollution remediation applications. Therefore, the low-cost, high-performance, high-efficiency adsorbent and remediation agent can provide great potential to leading technology and material for future environmental pollution treatment.