Binary heterojunctions of Mg/Al-LDH and carbon-based matrixes derived from self-assembly synthesis for inhibition of pyrene photopolymerizing: Elucidation of LDHs protecting bitumen against UV aging

Abstract

Layered double hydroxides (LDHs) have been found to protect bitumen against UV aging that was a culprit to shorten service life of new paved roads and burden environment with toxic volatiles in case of repaving roads time and again. Utilizing LDHs to improve the UV resistance to bitumen is desirable but the corresponding mechanism is still not be clarified. In this work, a simple self-assembly strategy is used to synthesize binary-heterojunction catalysts consisting of Mg/Al-LDH and carbon-based matrixes, aiming at obtaining copious mesopores and tailoring photocatalytic routes. The specific surface areas of the binary-heterojunction catalysts reached 193.94 and 156.31 m2/g for Mg/Al-LDH@biocarbon and Mg/Al-LDH@g-C3N4, respectively. It was found that the as-synthesized catalyst of Mg/Al-LDH@g-C3N4 was an outstanding inhibitor in photopolymerizing polycyclic aromatics, which was verified by photochemical experiments using pyrene (PY) as a target. The Mg/Al-LDH@g-C3N4 enabled to decrease the proportion of exciplex of PY to 8.63% upon UV irradiation, while the proportion was as high as 39.81% in the absence of Mg/Al-LDH@g-C3N4. The test results revealed that photogenerated holes and photogenerated electrons were responsible for accelerating the photodegradation process of PY and suppressing the photopolymerization of PY molecules, respectively. The binary-heterojunction Mg/Al-LDH@g-C3N4 showed its outstanding photocatalytic activities under UV irradiation, including avoiding PY molecules from degradation and macromolecular polymerization, which was attributed to the new channel for electron-hole recombination and built-up photocatalytic routes between Mg/Al-LDH and g-C3N4. This work provided a perspective for tailoring promising protective agents for bitumen anti-UV aging through building reasonable photocatalytic routes for heterogeneous structures.