Silica coating of Zn₂Al/4-hydroxy-3-methoxybenzoic acid nanocomposites via seeded polymerization technique

Organic ultraviolet (UV) rays 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-rays absorbent to the human skin a typical organic UV-absorbent, 4-hydroxy3-methoxybenzoic acid (HMBA) was intercalated into Zn₂Al layered double hydroxide (Zn ₂Al-LDHs) by coprecipiation reaction. But deintercalation of organic molecules from Zn₂ Al-LDHs, by the anion exchange reaction with carbonate ion, was observed. Therefore, Zn ₂Al-LDH/4-hydroxy-3-methoxybenzoic acid is directly coated with silica by means of polymerization technique based on the Stöber method. Silica coating effectively depress the deintercalation of 4-hydroxy-3-methoxybenzoic acid from Zn₂Al-LDHs. The amorphous silica is confirmed by X-ray diffraction, scanning electron microscope and FT-IR. The deintercalation behavior as well as UV-shielding properties is investigated for coated particles.