Visible Light–Driven Cascade Carbon–Carbon Bond Scission for Organic Transformations and Plastics Recycling

Abstract

Significant efforts are devoted to developing artificial photosynthetic systems to produce fuels and chemicals in order to cope with the exacerbating energy and environmental crises in the world now. Nonetheless, the large-scale reactions that are the focus of the artificial photosynthesis community, such as water splitting, are thus far not economically viable, owing to the existing, cheaper alternatives to the gaseous hydrogen and oxygen products. As a potential substitute for water oxidation, here, a unique, visible light-driven oxygenation of carboncarbon bonds for the selective transformation of 32 unactivated alcohols, mediated by a vanadium photocatalyst under ambient, atmospheric conditions is presented. Furthermore, since the initial alcohol products remain as substrates, an unprecedented photodriven cascade carboncarbon bond cleavage of macromolecules can be performed. Accordingly, hydroxyl-terminated polymers such as polyethylene glycol, its block co-polymer with polycaprolactone, and even the non-biodegradable polyethylene can be repurposed into fuels and chemical feedstocks, such as formic acid and methyl formate. Thus, a distinctive approach is presented to integrate the benefits of photoredox catalysis into environmental remediation and artificial photosynthesis.

Conversion of Waste Plastics into Value‐Added Carbonaceous Fuels under Mild Conditions

“…As is well-known, photocatalysis is considered as one of the most promising strategy for energy conversion, [14] which includes water splitting, [15] carbon dioxide (CO 2 ) reduction, [16] nitrogen fixation, [17] and even organic transformations. [18] Inspired by these application fields, solar energy can also be used to degrade the plastics under mild conditions. For example, Tadayoshi et al demonstrated that PVC could be photoconverted to CO 2 and hydrogen (H 2 ) over the Pt/TiO 2 photocatalysts at room temperature, [19] while Joydeep et al manifested that the degradation of low-density polyethylene (LDPE) microplastics could be triggered by the ZnO nanorods under visible light irradiation.…”

Recent Progress in the Chemical Upcycling of Plastic Wastes

“…[49] In a typical photochemical reaction, a semiconductor material is employed as a photocatalyst, which generates in-situ photoexcited electron-hole pairs as the active sites to stimulate the redox reactions. [50]…”

Current Developments in the Chemical Upcycling of Waste Plastics Using Alternative Energy Sources

“…[28] To address this, our group developed a novel, visible-lightdriven photocatalytic route using vanadium(V) photocatalysts to selectively cleave the CÀ C bonds of polyethylene, leading to full conversion of polyethylene into formic acid, alkyl formates, and CO 2 . [20] Notably, formic acid is a form of liquid organic hydrogen carrier and a hydrocarbon fuel that reversibly releases CO 2 and can be directly fed into fuel cells, [29] whereas alkyl formates are widely used as refrigerants, solvents, and platform chemicals. [30] Remarkably, this photocatalytic plastics conversion was achieved using a low-power 48 W white light emitting diode (LED), in contrast to the high-power Xenon lamp that is conventionally used for photocatalytic reactions in the literature.…”