Degradation Pathway of Volatile OrganicCompounds of Bitumen in the Presence ofSulfur-Doped Phenol-Rich Bio-oils

We have developed an efficacious methodology for degradation of volatile organic compounds (VOCs)from the matrix of bitumen under visible-light conditions which time dependent density functional theory (TD-DFT)analysis supports the degradation of VOCs by sulfur-doped phenol-rich bio-oil (S_۴^∙-WPn (n = ۱–۳)) prepared byC−S coupling reaction. This method involves two sequential reactions where the degradation of the VOCs is followedby sulfur-doped phenol-rich bio-oil (S_۴^∙-WPn (n = ۱–۳)) with C−S coupling reaction.This study examines how sulfur-doped phenol-rich bio-oil (S_۴^∙-WPn (n = ۱–۳)) reduces the emission of the VOCsfrom the bitumen matrix. To do so, we have evaluated the degradation pathway of two bitumen VOCs (Benzoic acidand Benzofuran) by S_۴^∙-WPn . TD–DFT results indicate that the S_۴^∙-WPn have the potential to retain theseVOCs in the bitumen matrix. Our calculations also predict that the reaction of tetrameric radical sulfur (S_۴^∙) withbio-oil (WPn) and subsequent VOCs could accelerate the degradation of VOCs while diminishing bitumen aging.To gain insight into the C–S cross-coupling mechanism, we have performed UV–Vis spectroscopic measurements forVOCs and VOCs-S_۴-WPn compounds. TD–DFT calculations also predicted a significant red shift in UV-Visspectroscopic absorption spectrum at ۴۰۰ nm albeit with a weaker absorption when S_۴^∙-WPn and VOCs reactedand these peaks resulted from the degradation of VOCs. The study outcomes show the efficacy of sulfur-dopedphenol-rich bio-oils in the degradation of selected VOCs.An interesting phenomenon was found that UV-Vis spectroscopic absorption red shift (~۲۰۰ nm) occurs after the C−Scoupling reaction between S_۴^∙-WPn and VOCs. The absorption spectral of (VOCs-S_۴-WPn) has been red-shiftedto nearly ۴۰۰ nm. The red shift enhanced the ability of these VOCs compounds to absorb light at a wavelength higherthan ۲۰۰ nm, thereby favoring the direct photodegradation of VOCs compounds.

Keywords:

Volatile Organic Compounds , Bitumen , Degradation , Phenol , Sulfur , Ultraviolet Aging