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

Abstract

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 non-pretreated 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 μmol h−1 gcat−1 and 150 ± 8.2 μmol h−1gcat−1 were 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.