Solar-driven hydrogen evolution in alkaline seawater over earth-abundant g-C3N4/CuFeO2 heterojunction photocatalyst using microplastic as a feedstock

Production of sustainable H2 fuel by photoreforming plastic waste is an emerging novel approach to tackling environmental pollution and energy shortage. We developed a n-p heterojunction g-C3N4/CuFeO2 photocatalyst made of only earth-abundant elements using a simple and scalable process. The heterostructure effectively suppresses the charge recombination, which is evident from a significant reduction in the emission of photoluminescence in g-C3N4/CuFeO2 compared to that of g-C3N4. g-C3N4/CuFeO2 exhibits promising performance in photoreforming various kinds of polyester plastics. Notably, g-C3N4/CuFeO2 outperforms g-C3N4 and CuFeO2, showing more than 60-fold and 100-fold enhanced activity for H2 evolution by photoreforming hydrolyzed polyester microfiber, respectively. On the other hand, the nuclear magnetic resonance study suggests formate is the main oxidizing organic product. Interestingly, g-C3N4/CuFeO2 can also perform photoreforming using nonpretreated plastics in alkaline solutions. g-C3N4/CuFeO2 maintains 84 % of activity toward H2 evolution by replacing pretreated poly(butylene succinate) solution with non-pretreated poly(butylene succinate) as the feedstock. Given the freshwater resource shortage, seawater, the most abundant on Earth, also served as the water resource under investigation. g-C3N4/CuFeO2 photocatalyst preserves its almost intact photocatalytic activity by replacing pure water with 25 % content seawater, although a decrease in activity is observed in higher seawater content. Activities for H2 evolution of 241 +/- 6.2 mu mol h-1 gcat- 1 and 150 +/- 8.2 mu mol h- 1gcat achieved by photoreforming hydrolyzed polyester microfiber over g-C3N4/CuFeO2 in 25 % and 100 % seawater content, respectively. This study demonstrates that non-toxic and noble-metal-free g-C3N4/CuFeO2 serves as an efficient and well environmentally adaptive photocatalyst for plastic reforming.

Automated summary

Production of sustainable H2 fuel by photoreforming plastic waste is an emerging approach to address environmental pollution and energy shortage. The use of a n-p heterojunction g-C3N4/CuFeO2 photocatalyst made of earth-abundant elements effectively suppresses charge recombination and shows promising performance in photoreforming various types of polyester plastics.