Silica replication of the hierarchical structure of wood with nanometer precision

The structural features of wood were replicated in silica on all levels of hierarchy from the macroscopic to the nanoscopic level of the cellulose elementary fibrils. This was achieved by a series of processing steps on spruce wood templates. Sodium chlorite was used to partially remove the lignin matrix from the wood cell walls, exposing the cellulose fibrils. These were optionally functionalized with maleic acid anhydride to stabilize the fibrillar structure and reduce the shrinkage of the template. Repeated infiltration with tetraethyl orthosilicate in ethanol deposited silica on the fibrils. Calcination at 500 °C removed the rest of the organic template by oxidation and resulted in the fusion of the deposited material into a positive silica replica. Small-angle x-ray scattering evidenced fibrillar structures parallel to the original cellulose fibrils at length scales in the order of 10 nm, suggesting the successful nanoscopic replication of the cellulose fibrils and their orientation.