Molecular Adsorption Mechanism of Elemental Carbon Particles on Leaf Surface

Plant leaves can effectively capture and retain particulate matter (PM), improving air quality and human health. However, little is known about the adsorption mechanism of PM on leaf surface. Black carbon (BC) has great adverse impact on climate and environment. Four types of elemental carbon (EC) particles, carbon black as a simple model for BC, graphite, reduced graphene oxide, and graphene oxide, and C36H74/C44H88O2 as model compounds for epicuticular wax were chosen to study their interaction and its impact at the molecular level using powder X-ray diffraction and vibrational spectroscopy (infrared and Raman). The results indicate that EC particles and wax can form C-H center dot center dot center dot pi type hydrogen bonding with charge transfer from carbon to wax; therefore, strong attraction is expected between them due to the cooperativity of hydrogen bonding and London dispersion from instantaneous dipoles. In reality, once settled on the leaf surface, especially without wax ultrastructures, BC with extremely large surface-to-volume ratio will likely stick and stay. On the other hand, BC particles can lead to phase transition of epicuticular wax from crystalline to amorphous structures by creating packing disorder and end-gauche defects of wax molecular chain, potentially causing water loss and thereby damage of plants.