Effect of confinement of anionic organic ultraviolet ray absorbers into two-dimensional zinc hydroxide nitrate galleries

Abstract

Anionic ultraviolet (UV) ray absorbers (4-methoxybenzoate, N-acetylanthranilate, 4-methoxycinnamate and 4,4'-diamino-2,2'- stilbenedisulfonate) were intercalated into zinc hydroxide nitrate, either by direct alkaline co-precipitation or topotactic exchange reactions. The intercalation was confirmed by X-ray powder diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA/DTA), scanning electron microscopy (SEM), selected area electron diffraction (SAED), elemental analysis and ultraviolet visible (UV-Vis) spectroscopy. In the co-precipitation reactions full intercalation was achieved, while during the exchange reactions nitrate anions were not completely replaced by the organic anions. After the intercalation, the UV absorption capacity was similar to that of the solid salts and acids, the effect being attributed to the confinement of the anionic species in the host two-dimensional gallery. This observation opens new opportunities for the use of organic anions immobilized in alternative layered matrixes for the formulation of sunscreens. © 2011 Sociedade Brasileira de Química.