Nutrient filled graphene

Materials World magazine
1 May 2018

Nutrient-loaded graphene could be the key to effective slow release fertiliser, as Ellis Davies reports.

Graphene’s bag of tricks is being used in low-cost, environmentally friendly fertiliser by researchers at the Fertiliser Technology Research Centre, the University of Adelaide, Australia. The team has displayed the world’s first use of the material in fertiliser by using it to carry essential trace elements, such as zinc and copper. The centre is also looking for other new technologies to use in formulation, investigating metal-organic-frameworks, layered double hydroxides, and polymers. 

Researchers demonstrated that effective slow-release fertilisers could be produced by loading essential trace elements onto graphene oxide sheets. The graphene is used both as a carrier for nutrients and as an additive. ‘It significantly increases the fertiliser’s physical quality,’ said Dr Mike McLaughlin of the University of Adelaide. Slow release for mobile nutrients protects them against leaching into waterways, and can better synchronise the delivery of nutrients with plant demand.

Loading up graphene 

Using a graphene carrier allows for targeted use, which can increase overall fertiliser efficiency and nutrient uptake by plants. An oxidised form of graphene is used as it has a high negative surface charge. Cationic (positively charged) macronutrients and micronutrients are added to this surface. Researchers can also make a composite that binds anions like phosphate, such as an iron-graphene oxide composite. 

The loading process is dependent on the form of graphene being used. In the case of graphene oxide, the cationic nutrients, zinc and copper, are loaded onto the negatively charged surface, whereas if an iron-graphene oxide composite is used, it is loaded using an anionic nutrient, with the phosphate binding to the surface through an iron bridge.

Researchers confirmed the successful loading using X-ray photoelectron spectroscopy, thermogravimetric analysis, and X-ray diffraction. The zinc-graphene oxide and copper-graphene oxide fertilisers showed a biphasic (two-part) dissolution behaviour compared to that of commercial zinc sulfate and copper sulfate fertiliser granules, showing fast and slow micronutrient release.

A pot trial (a trail using potted plants) was carried out using wheat to demonstrate the uptake of the nutrients from the fertilisers. Results showed that it was higher when using the graphene-based fertilisers compared to commercial zinc and copper salts. 

‘The technology for fertilisers has been patented and is under option to a major manufacturer, [but] more evaluation is needed before scale up and commercial use,’ said McLaughlin. The technology is at the early development stage – a proof of concept and investigation of application options – and has not yet progressed to the next level. However, researchers are also looking at coatings and different functionalisation of the surface for different nutrients, as well as exploring fluid/suspension products.

‘It’s early days, but there is no doubt that fertilisers with release rates more tailored to crop demand, and with greater physical strength and robustness, will both improve grower efficiency of fertiliser application and of nutrient uptake,’ said McLaughlin.

The successful commercialisation of the technology will depend on the cost of graphene/graphene oxide and the ability to integrate it into the commercial fertiliser production process.