Synthesis of corn straw-based graphene quantum dots (GQDs) and their application in PO43- detection

Phosphate (PO43-) can cause eutrophication of water bodies due to soil erosion and agricultural fertilization, increasing toxic substances in water, therefore detecting PO43- is vital in water eutrophication. Graphene quantum dots (GQDs), zero-dimensional nanometer-sized graphene pieces, are made of a few graphene lattices and exhibit outstanding optical properties. The traditional synthesis precursors are limited by large carbon domains or toxic polycyclic aromatic molecules. Consequently, synthesis of GQDs from renewable biomass has attracted broad interests. Herein corn straw was used to directly prepare GQDs via a one-pot hydrothermal strategy. The as-prepared GQDs, with an average size of 2.67 nm, presented high quantum yield (15.67%), high crystallinity and dispersibility. The as-prepared non-doped GQDs had a special selectivity to Ce4+/Fe3+, causing the fluorescence (FL) quenching of GQDs and the formation of GQDs-Ce4+/GQDs-Fe3+ aggregation. In the presence of PO43-, a strong affinity between PO43- and Ce4+/Fe3+ can destroy GQDs-Ce4+/GQDs-Fe3+ aggregation, resulting in the FL recovery of GQDs. The GQDs-Ce4+ probe system can selectively detect PO43- with a detection limit of 0.06 μM in a linear range from 0.1 to 20.0 μM. Based on this, GQDs-Ce4+ paper-based sensors were also prepared for the visual detection of PO43-, which showed good responses to PO43-. This development is expected to be a promising strategy for convenient and rapid phosphate detection.