Abstract
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 Zn
2Al layered double hydroxide (Zn
2Al-LDH) by coprecipitation reaction. However, deintercalation of DASDSA from Zn
2Al-LDH, by the anion exchange reaction with carbonate ion, was observed. Therefore, Zn
2Al-LDH/DASDSA was directly coated with silica by means of polymerization technique based on the Stöber method. Silica coating effectively depressed the deintercalation of DASDSA from Zn
2Al-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.
It is clear that coating with silica greatly suppressed the deintercalation of the DASDSA from the layer structure. The deintercalation percent decreased from 85% to less than 10% after silica coating. Deintercalation profiles of DASDSA from Zn
2Al-LDH/DASDSA non-coated and coated with different amounts of silica in 0.02 mol dm
−3 Na
2CO
3 aqueous solution at 50 °C. (a) Non-coated Zn
2Al-LDH/DASDSA, (b), (c), (d) and (e) were coated with 5, 10, 15 and 20 wt% SiO
2 using TEOS, whereas (f) and (g) were coated with 5.5 and 21.3 wt% SiO
2 using Na
2SiO
3.