Silica coating and photochemical properties of layered double hydroxide/4,4′-diaminostilbene-2,2′-disulfonic acid nanocomposite

Organic ultraviolet (UV) rays absorbents have been used as sunscreen materials, but they 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, 4,4'diaminostilbene-2,2'-disulfonic acid (DASDSA), was intercalated into Zn2Al layered double hydroxide (Zn2Al-LDH) by coprecipitation reaction. However, deintercalation of DASDSA from Zn2Al-LDH, by the anion exchange reaction with carbonate ion, was observed. Therefore, Zn2Al-LDH/DASDSA was directly coated with silica by means of polymerization technique based on the Stober method. Silica coating effectively depressed the deintercalation of DASDSA from Zn2Al-LDH. The amorphous silica was confirmed by XRD, SEM, TEM and FT-IR. The deintercalation behaviors as well as UV-shielding properties were investigated for coated particles. (c) 2005 Elsevier Inc. All rights reserved.