Magnetic resonance studies of hierarchically ordered replicas of wood cellular structures prepared by surfactant-mediated mineralization

Hierarchically ordered positive and negative replicas of wood cellular structures prepared using surfactant templating methods under acidic and basic conditions have been studied by means of continuous flow hyperpolarized Xe-129 NMR, solid-state MAS C-13, Si-29, and 21) WISE NMR spectroscopic techniques. Xe-129 NMR data confirm a highly ordered and uniform structure with interconnected porosity in the positive silica wood replicas (SWR(+)) prepared under acidic conditions. In contrast, nonuniform porosity with irregular pore structures is inferred from similar data for negative silica wood replicas (SWR(-)) prepared under basic conditions. This contrasts with results from N-2 adsorption and TEM measurements that indicate regular nanoporous channels in both cases. From C-13 MAS NMR spectra, significant leaching of wood lignin was found to occur under acidic but was not evident for samples subjected to basic treatment. Si-29 MAS NMR spectra revealed higher hydroxylation levels for the silica replica prepared under acidic conditions compared to those observed in samples prepared under basic conditions. 21) WISE NMR experiments showed increased mobility of protons associated with the organic functional groups in cellulose after acidic treatment when compared with the dry and base-treated wood. Reported NMR data provide compelling evidence for the proposed mechanism of surfactant directed mineralization of wood cellular structures in acidic and basic solutions.