Preparation of TiO2@ZrO2@SiO2@MAA nanocomposites and impact of layer structure on pigmentary performance

The TiO2@ZrO2@SiO2@MAA (polymethyl acrylic acid) nanocomposite was prepared with pigmentary rutile TiO2 particles as the substrates and zirconium sulfate, sodium metasilicate, and methyl acrylic acid as the coating layer precursors using the wet chemical deposition method. Continuous/compact and island-like amorphous zirconia coating layers could be alternatively deposited on pigmentary rutile TiO2 particles by adjusting pH values in the hydrolysis of zirconium sulfate. When TiO2@ZrO2 nanocomposites with continuous and compact amorphous zirconia layers were used as the substrates, continuous and compact amorphous silica coating layers were deposited on the substrates by the hydrolysis of sodium metasilicate at a higher pH value of 9.5. When TiO2@ZrO2 nanocomposites with island-like amorphous zirconia coating layers were used as the substrates, island-like amorphous silica coating layers were deposited at the same hydrolysis pH value. The amorphous zirconia and silica coating layers could anchor at their substrates through Zr-O-Ti and Si-O-Zr bonding, respectively. TiO2@ZrO2@SiO2 nanocomposites exhibited higher whiteness and brightness than rutile TiO2 particles. The coating of continuous and compact binary ZrO2/SiO2 layers on rutile TiO2 particles efficiently suppressed their photocatalytic activity. The coating of polymethyl acrylic acid molecules on TiO2@ZrO2@SiO2 nanocomposite significantly improved its dispersion stability in water.