title: Eliminated Phototoxicity of TiO2 Particles by an Atomic-Layer-Deposited Al2 O3 Coating Layer for UV-Protection Applications.
abstract: We demonstrate the conformal coating of an ultrathin Al2 O3 layer on TiO2 nanoparticles through atomic layer deposition by using a specifically designed rotary reactor to eliminate the phototoxicity of the particles for cosmetic use. The ALD reactor is modified to improve the coating efficiency as well as the agitation of the particles for conformal coating. Elemental and microstructural analyses show that ultrathin Al2 O3 layers are conformally deposited on the TiO2 nanoparticles with a controlled thickness. Rhodamine B dye molecules on Al2 O3 -coated TiO2 exhibited a long life time under UV irradiation, that is, more than 2 h, compared to that on bare TiO2 , that is, 8 min, indicating mitigation of photocatalytic activity by the coated layer. The effect of carbon impurities in the film resulting from various deposition temperatures and thicknesses of the Al2 O3 layer on the photocatalytic activity are also thoroughly investigated with controlled experimental condition by using dye molecules on the surface. Our results reveal that an increased carbon impurity resulting from a low processing temperature provides a charge conduction path and generates reactive oxygen species causing the degradation of dye molecule. A thin coated layer, that is, less than 3 nm, also induced the tunneling of electrons and holes to the surface, hence oxidizing dye molecules. Furthermore, the introduction of an Al2 O3 layer on TiO2 improves the light trapping thus, enhances the UV absorption.
authors.affiliation: Department of Advanced Materials Engineering, Hanyang University, Ansan, 15588, Republic of Korea.
authors.forename: Eunyong
authors.initials: E
authors.lastname: Jang
authors.affiliation: Department of Materials Science Engineering & Chemical Engineering, Hanyang University, Ansan, 15588, Republic of Korea.|Department of Physics, National Institute of Technology Karnataka, Surathkal, P.O. Srinivasnagar, Mangaluru, 575025, India.
authors.forename: Kishore
authors.initials: K
authors.lastname: Sridharan
authors.affiliation: Surface Technology Group, Korea Institute of Industrial Technology (KITECH), Incheon, 31056, Republic of Korea.
authors.forename: Young Min
authors.initials: YM
authors.lastname: Park
authors.affiliation: Department of Advanced Materials Engineering, Hanyang University, Ansan, 15588, Republic of Korea. tjp@hanyang.ac.kr.|Department of Materials Science Engineering & Chemical Engineering, Hanyang University, Ansan, 15588, Republic of Korea. tjp@hanyang.ac.kr.
authors.forename: Tae Joo
authors.initials: TJ
authors.lastname: Park
keywords: Al2O3; TiO2; UV protection; atomic layer deposition; photocatalysis