H2020 PSust-MOF Project: Metal-organic frameworks as multifunctional materials towards P-sustainability

Absorbing Phosphate Fertilizers from Agricultural Wastewater A team of EU researchers created zirconium-based metal-organic frameworks to absorb pollutants from agricultural wastewater and reuse them in new fertilizers. Although chemical fertilizers are an essential part of modern agriculture, they are far from perfect. “Conventional fertilizers are not only very inefficient, but many leach phosphorus into the soil, negatively impacting the environment and human health,” says Jorge Rodríguez Navarro, a professor at the University of Granada. With support from the EU-funded PSust-MOF (Metal-Organic Frameworks as multifunctional materials towards P-sustainability) project, Rodríguez Navarro, along with his colleague and researcher Francisco Carmona, led an effort to create a circular economy for phosphorus. “The main objective of the project was to develop an innovative adsorbent capable of detoxifying agricultural wastewater by recovering and reusing phosphate fertilizers,” explains Carmona.

Sustainable Metal-Organic Frameworks To achieve this goal, the project, which received support from the Marie Skłodowska-Curie Actions program, focused on an emerging class of porous materials called zirconium-based metal-organic frameworks, or Zr-MOFs, which have a high affinity for phosphate groups. But the researchers didn't simply want to create Zr-MOFs; they wanted to do it sustainably. "The exceptional properties of metal-organic frameworks make them promising materials for a wide variety of applications," says Rodríguez Navarro. "Unfortunately, they are usually prepared with toxic solvents and under harsh conditions." Instead, the researchers demonstrated the feasibility of synthesizing Zr-MOFs through a microwave-assisted approach.

The innovative process uses water as a solvent and can easily and finely modulate the particle size of the resulting materials. "By making their industrial production easier, less expensive, and more sustainable, this process will facilitate the actual use of these materials," adds Carmona. Ability to Absorb Phosphate Ions Beyond developing a sustainable process for manufacturing Zr-MOF materials, the project also demonstrated the ability of these materials to efficiently absorb phosphate ions at relevant concentrations. Once the phosphate ions are captured, they can be reused in the manufacture of new phosphate-absorbing fertilizers.

"We have shown that Zr-MOFs can not only reversibly adsorb phosphate ions, but are also capable of simultaneously degrading toxic organophosphate pesticides into harmless compounds," says Rodríguez Navarro. "This capability opens the door to being able to detoxify wastewater derived from agricultural activities." Addressing the Challenges of Scarcity and Inefficiency Phosphorus scarcity and fertilizer inefficiency are two fundamental obstacles to achieving a sustainably productive agricultural sector. The PSust-MOF project has helped overcome both. "By recovering phosphorus from agricultural wastewater and then reusing that phosphorus in the creation of new effective fertilizers, our work demonstrates the potential of metal-organic frameworks to simultaneously address the challenges of scarcity and inefficiency by creating a circular phosphate economy," Carmona notes.

"This project has raised awareness about the sustainability of phosphorus and has demonstrated how research is key to finding strategies and solutions to overcome these significant challenges," adds Rodríguez Navarro. Researchers are currently working to advance the processability of metal-organic materials using composites or mixed membrane matrices, a breakthrough that would allow them to be produced at scale.