UV Blocking by Mg-Zn-Al Layered Double Hydroxides for the Protection of Asphalt Road Surfaces

MgaZnbAlc-CO3 layered double hydroxides (LDHs) with varying magnesium/zinc ratios have been synthesized by a method involving separate nucleation and aging steps. The resulting LDHs were analyzed by powder X-ray diffraction, laser particle size analysis, scanning electron microscopy, and diffuse reflectance UV spectroscopy. The results show that the UV blocking properties of MgaZnbAlc-CO3-LDHs depend on both the proportion of zinc and the particle size distribution. The UV absorbing properties of MgaZnbAlc-CO3-LDHs increase with the content of zinc, which can be ascribed to the decrease in the band gap energy, as has been observed experimentally and confirmed by density functional theory calculations. The UV screening properties of Zn4Al2-CO3-LDHs were found to increase with increasing particle size, which can be explained by Mie scattering theory. Moreover, in accelerated UV light irradiation aging tests, LDH-modified asphalt samples showed excellent resistance to UV aging, with the efficacy of the LDH increasing with increasing zinc content.