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

Abstract

Mg_aZn_bAl_c–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 Mg_aZn_bAl_c–CO₃–LDHs depend on both the proportion of zinc and the particle size distribution. The UV absorbing properties of Mg_aZn_bAl_c–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