Structural studies of TiO2/wood coatings prepared by hydrothermal deposition of rutile particles from TiCl4 aqueous solutions on spruce (Picea Abies) wood

Abstract A low temperature approach was developed for the deposition of rutile TiO 2 particles on a wood surface by hydrolysis of TiCl 4 in aqueous solutions acidified with HCl, and crystallization at 75 and 90 °C (1 h). Prior to hydrothermal treatment, Picea Abies wood was first soaked in a 0.5 mmol/l aqueous solution containing anionic surfactant sodium dodecyl sulphate (SDS, Sigma Aldrich) for 2 h at 80 °C. The crystal structure of the hydrothermally made rutile particles was determined with XRD, while the morphology of the deposited TiO 2 particles and their distribution in the wood were examined with SEM and EDX measurements. The penetration and amount of deposited rutile particles could be modified by changing the deposition conditions. Thicker layers were obtained from more concentrated aqueous TiCl 4 solutions with and without added HCl, and with longer deposition times and higher temperatures of the hydrothermal treatment. The interaction of TiO 2 particles with hemicellulose and lignin in wood was established from infrared attenuated total reflection (FT-IR ATR) and Raman spectra measurements, from which the spectra of wood were subtracted. Analysis of the subtraction spectra showed the presence of titania particles on the wood surface, revealing also the establishment of TiO 2 -wood coordinative bonds of titanium ions with hemicellulose and lignin. The red frequency shift of the OH stretching modes suggested interaction of the TiO 2 particles with water molecules of wood. TiO 2 deposited on wood treated with SDS became hydrophobic (water contact angles (WCA) of 150°), contrasting the properties of untreated wood with a deposited TiO 2 particle coating, which remained hydrophilic.