Graphene Oxide (GO) Composites - New Slow Release Fertilisers?.

Phosphatic fertilizers are becoming increasingly expensive and are under mounting scrutiny for pollution of water resources through eutrophication. There is therefore a growing interest in slow- or controlled-release P fertilizers which minimise losses in runoff or leaching immediately after application. Graphene, an emerging 21^st century material, offers opportunities to engineer a range of fertilizer formulations with release rates of P much slower than fully water soluble products. We used a simple chemical procedure for obtaining graphene oxide (GO) from graphene modified with Fe³⁺ ions into a new composite material (GO-Fe) as a potential carrier for phosphate (PO₄^3-) ions. The GO-Fe composite loaded with PO₄^3- (GO-Fe-P) was examined as a new slow-release fertiliser and compared with monoammonium phosphate (MAP). A column release study showed that the GO-Fe-P released 4% of the total P after 10h, rising to 9% released within 48h compared to 85 and 89 % for the same times, respectively, for MAP. Release of P continued slowly over several days from the new material. By monitoring P diffusion through three type of soils with different physicochemical properties, we confirmed slow release of P from the GO-Fe-P composite. The radius of P diffusion after 72h was 4.1-7.6 mm (depending on soil) for GO-Fe-P compared to 12.4-27.5mm for MAP. Acquisition of P from the GO-Fe-P material by plants is currently under investigation.