Mechanisms Of Stucture-controlled Construction Of SiO₂,ZrO₂,AlOOH,and MAA Composite Nanofilms On Rutile TiO₂ Particle Surface And Performance Investigation

The application performance of rutile TiO₂ produced by sulfuric acid method is far inferior to that of chloric acid method in whiteness,brightness,hiding power and other aspects,which makes the domestic rutile TiO₂ products have a very low share in the high-end market.Surface coating treatment can effectively improve the application performance of rutile TiO₂ and enhance the competitiveness of its products.In this paper,the pigmentary rutile TiO₂ nano-powder as the substrate,SiO₂,ZrO₂,Al OOH,and MAA（polymethacrylic acid）composite nanofilms with different microstructure were constructed on its surface.The mechanism of nanofilm formation,the interaction between nanofilm and substrate,and the effects of composite nanofilm on pigment properties,photocatalytic activity and water dispersion stability of rutile TiO₂ were studied.The results are summarized as follows.The TiO₂@ZrO₂@SiO₂@MAA nanocomposite were prepared by the wet chemical deposition method.Continuous/compact and island-like ZrO₂ nanofilms could be alternatively deposited on rutile TiO₂ particles by adjusting p H values in the hydrolysis of zirconium sulfate.When TiO₂@ZrO₂ nanocomposites composed of continuous and compact ZrO₂ nanofilms coated with TiO₂were used as the substrates,continuous and compact SiO₂nanofilms were deposited on the substrates by the hydrolysis of sodium metasilicate at a higher p H value of 9.5.When TiO₂@ZrO₂ nanocomposites composed of island-like ZrO₂nanofilms coated with TiO₂were used as the substrates,island-like SiO₂ nanofilms were deposited at the same p H value.The amorphous ZrO₂ and SiO₂ nanofilms could anchor at their substrates through Zr-O-Ti and Si-O-Zr bonding,respectively.TiO₂@ZrO₂@SiO₂nanocomposites exhibited higher whiteness and brightness than rutile TiO₂particles.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.The dense and island-like SiO₂ nanofilms were alternatively coated on pigmentary rutile TiO₂ particles by adjusting the p H values in the hydrolysis of sodium metasilicate.When the TiO₂@SiO₂ nanocomposites with uniform and dense SiO₂ nanofilms were used as the substrates,uniform and dense ZrO₂ layers were coated on the substrates by the hydrolysis of zirconium sulfate at a lower p H value.The amorphous SiO₂ and ZrO₂ nanofilms anchored at their substrates by the formation of Si-O-Ti and Zr-O-Si bonds,respectively.The brightness and whiteness of the pigmentary rutile TiO₂ particles were improved by coating binary SiO₂/ZrO₂ composite nanofilms.The photocatalytic activity of the pigmentary rutile TiO₂ particles was efficiently suppressed by coating uniform and dense binary SiO₂/ZrO₂composite nanofilms.When polymethyl acrylic acid molecules anchored at TiO₂@SiO₂@ZrO₂ nanocomposite by in situ polymerization,the as-prepared TiO₂@SiO₂@ZrO₂@MAA nanocomposite exhibited a higher dispersion stability in water.The TiO₂@ZrO₂@Al OOH@MAA nanocomposites were prepared by successive hydrolysis of zirconium sulfate and sodium meta-aluminate and in situ polymerization of methyl acrylic acid in aqueous solutions.Uniform,compact,and island-like hydrous ZrO₂nanofilms could be controllably coated on rutile TiO₂ particles by adjusting hydrolysis p H value.At 1wt%alumina loading,boehmite nanoparticles were deposited on ZrO₂ nanofilms to form an island-like Al OOH nanofilms whereas at 2wt%alumina loading,in addition to the island-like Al OOH nanofilms,flocculent Al OOH nanofilms was deposited.The ZrO₂and Al OOH nanofilms anchored at their substrates through Zr-O-Ti and Al-O-Zr bonding,respectively.The ZrO₂ nanofilms layer obviously improved the whiteness and brightness of the pigmentary rutile TiO₂ powder.The binary ZrO₂/Al OOH composite nanofilms completely suppressed the photocatalytic activity of the rutile TiO₂ powder under UV light irradiation.The Al OOH nanofilms with a large amount of OH groups caused the aggregation of nanocomposites.Anchoring polymethyl acrylic acidmolecules at TiO₂@ZrO₂@Al OOH nanocomposite improved its dispersion stability in water.