Characterization of Interleaved Zinc-Layered Hydroxide-Salicylic with Sustained Release Property: A New Promising Ultraviolet Absorber

Salicylic acid (SA) is a type of organic ultraviolet absorber that can cause health issues when used at high concentrations. Zinc-layered hydroxide (ZLH) with the chemical formula of M2+ (OH)2-x(Am-)x/m·nH2O, where M2+ is a divalent cation and Am- is a counter anion with a negative charge, was used to maximize the efficiency of SA and simultaneously reduce its side effects. Zinc-layered hydroxide-salicylic (ZSA) was synthesized using a simple direct method and then characterized. Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy showed the presence of a new peak aside from the sharp peak at 560 cm-1, corresponding to the presence of zinc oxide (ZnO). A new basal spacing formed in X-ray diffraction (XRD) study at 16.05 Ǻ and a peak disappeared between 30° and 40°. Thermogravimetric analysis/differential thermogravimetric analysis (TGA/DTG) indicated that ZSA was stable to heat exposure. Meanwhile, field emission scanning electron microscopy (FESEM) showed that ZnO has a non-uniform granular shape, whereas ZSA has a non-uniform flaky shape, indicating that SA was imbedded between the ZLH interlayer regions. Brunauer-Emmett-Teller (BET) method showed that ZSA was a mesoporous material (Type IV) after the interleave process. The sustained release properties were evaluated using ultraviolet-visible (UV-Vis) spectrophotometry to study the sustained release of different simulated media solutions. In conclusion, SA can be intercalated between the interlayer galleries of ZLH and can have a slow-release property.