(409d) Ferromagnetic Composites of Activated Carbons and Iron Oxide Prepared From Waste Biomass

To embed iron oxide in an amorphous matrix of activated carbons can render such nano-composites enhanced properties. They could potentially enable more effective water and gas treatment processes, but could perhaps also be relevant for other applications. Here, we demonstrate that such composites with firmly embedded nanoparticles can be prepared from biomass in a two step manner. Biomass (grass cutting, horse manure, beer waste and biosludge) were first hydrothermally treated together with an iron catalyst, under which transformed to a carbon rich polymeric material with included iron. This carbon-rich polymer - hydrothermal carbonized (HTC) biomass - was subsequentially activated into activated carbons at temperatures of 600-800 °C in the flow of CO₂. Relatively large iron oxide nanoparticles formed inside the activated carbon with a particle size larger than that of the pore channel system.

The precursors for the activation (HTC biomass) were analysed with a range of tools to further relate how the compositions and molecular configurations of the precursors related to the properties of the activated carbon. Elemental analysis, X-ray Photoelectron Spectroscopy, and solid-state ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy were used. HTC beer waste and HTC grass cuttings had highly condensed molecular structures, which were similar to those of lignite. The corresponding activated carbons had micropores, with two distinct sizes of 0.7 and 1.3 nm. By contrast, HTC horse manure had less carbonized structures, which were more similar to those of peat. The corresponding activated carbon had a large fraction of mesopores. The yield for the activated carbons were 13-30 wt.%, and they displayed specific surface areas of 300-1000 m²/g. Besides of the dependencies of the molecular structures, the properties of the activated carbons also depended on the process parameters used (such as flow rate and temperature).

Transmission Electron Microscopy (TEM) and particular Electron Tomography (ET) were used to show that the nanoparticles of iron oxide were firmly embedded with in the activated carbons. X-ray diffraction showed well crystallized Fe₃O₄. ET showed embedded, well-dispersed, and crystallized 20-40 nm nanoparticles. A magnetization curve showed ferromagnetism in the nanocomposite of activated carbon and iron oxide that was produced from horse manure. The firmly embedded iron oxide and the use of biowaste could enable a low cost manufacturing of magnetic activated carbons with enhanced properties.