Depression of deintercalation of 4-hydroxy-3-methoxybenzoic acid from Zn2Al layered double hydroxide by direct coating with silica

Organic ultraviolet (UV) ray absorbents have been used as sunscreen materials, but may pose a safety problem when used at high concentration. In order to prevent direct contact of organic UV ray absorbent to the human skin, a typical organic UV absorbent, 4-hydroxy-3-methoxybenzoic acid (HMBA) was intercalated into Zn2Al layered double hydroxide (Zn2Al-LDHs) by coprecipiation reaction. The problem of deintercalation of organic molecules from LDHs by the anion exchange reaction with carbonate ion could be greatly depressed by forming a protection film of silica on the surface. Zn2Al-LDH/4-hydroxy-3-methoxybenzoic acid was direct coated with silica by means of polymerization technique based on the Stober method. The deintercalation behavior as well as U-V-shielding properties was investigated for coated particles. (C) 2004 Elsevier B.V. All rights reserved.