Enhancing visible-light-driven photocatalytic degradation of nitric oxide with lignite-derived graphene quantum dots/BiOBr heterojunctions

In this work, lignite was used to prepare value-added graphene quantum dots (L-GQDs) via the chemical oxidation process. The prepared L-GQDs were then hybridized with bismuth oxybromide (BiOBr) to form composite photocatalysts by a semi-solvothermal method. The composites catalytically degraded NO under visible-light irradiation. Multiple characterizations demonstrated that L-GQDs were successfully deposited onto BiOBr without changing the valence states of the elements in BiOBr. The addition of L-GQDs not only boosted the NO removal efficiency from 48.44% to 80.17%, but also significantly improved the environmental friendliness of the catalyst. Experimental investigations and theoretical calculations confirmed the formation of a type II heterojunction between L-GQDs and BiOBr. Such a heterojunction facilitated the separation of photogenerated electrons and holes, thus enhancing the photocatalytic activity. Furthermore, the prepared composite catalyst demonstrated good stability, maintaining 94.40% of its original photocatalytic activity after five cycles. The synthesis and environmentally conscious application of the value-added L-GQDs in this work provides a cleaner alternative for utilizing low-rank coals.