Sustainable Thermochemical Single-Step Process to Obtain Magnetic Activated Carbons from Chestnut Industrial Wastes

Abstract

A novel thermochemical process based on a single step was optimized to obtain magnetic activated carbons from an industrial biomass waste. Anhydrous iron chloride was used as an activating agent and mixed directly with the chestnut shell waste. The effect of the activation temperature (220-800 °C) on the chemical, morphological, textural, and magnetic properties of the materials was studied. The results demonstrated the presence of different iron compounds depending on the activation temperature set as well as their influence on morphological and textural development of the magnetic activated carbons (BET specific surface area, S up to 568 m g, total pore volume, V, up to 0.294 cm g vs 1 m g and 0.007 cm g, respectively, for the raw biomass waste). The techniques employed, especially Mössbauer spectroscopy, showed relative contributions of the different iron compounds (magnetite, maghemite, metallic iron, and so on) in the materials. The higher activation temperature (800 °C) favored the formation of metal Fe and iron carbide. Additionally, the magnetic properties measured by vibrating sample magnetometry confirmed the coexistence of different ferromagnetic phases with the remanent magnetization, M, (up to 3.88 emu/g) and coercivity, H, (up to 140 Oe), being larger as the activation temperature increases. A higher activation temperature favored the development and evolution toward other iron compounds, while at low temperature, 220 °C, the presence of these compounds were null, and their behavior resembled the results obtained for the original biomass waste.