Controlled deposition of magnetic particles within the 3-D template of wood: making use of the natural hierarchical structure of wood

Abstract

This study presents a promising method to make three-dimensional lattices of structured nanomaterials by using wood templates for in situ (confined) directed growth of inorganic material in the ordered cell walls. The wood was impregnated by transition metal ion precursors (iron, manganese and cobalt) at 5 bars pressure that were further transformed into magnetic particles (Fe₃O₄, MnFe₂O₄ and CoFe₂O₄) by addition of alkaline solutions. It was found that by this method, it was possible to produce lightweight ferromagnetic functionalized wood materials in an inexpensive and environmentally friendly way. It was possible to functionalise the wood throughout the structure with a high weight percent of particles from 15–20 wt% as observed by TGA. These were not only adsorbed to the surface of the lumen, but also found by SEM-EDX throughout the cell wall and middle lamella and in higher amounts in early wood. The magnetic properties were nearly unaffected by the incorporation into the wood samples as compared to powder compacts obtained as particles that precipitated separately in the impregnation solution, both for soft and hard magnetic materials. Whereas the hard magnetic phase CoFe₂O₄ showed insignificant leaching, the soft magnetic Fe₃O₄, MnFe₂O₄ lost around 50 wt% during repeated washing in deionized water, suggesting that the CoFe₂O₄ particles were more readily attached in the structure of the wood. The crystal structure of the magnetic particles was determined to be the same in the wood structure as those formed in solution.