Periodic Reporting for period 1 - PSust-MOF (Metal-Organic Frameworks as multifunctional materials toward P-sustainability)
Reporting period: 2020-09-01 to 2022-08-31
Due to the continuous global population growth, the use of chemical fertilizers in agriculture is essential to ensure food security. Specifically, P-fertilizers are mainly produced by mining phosphate rock (PR): a non-renewable source. In addition, only one-fifth of P-mined reaches the global food consumed due to losses at all stages of the anthropogenic one-way P-flow, especially from agricultural lands. This not only entails an inefficient exploitation of a precious resource, but also causes dramatic damages in the environment, such as eutrophication, which is a major societal and economic problem. In addition, the conventional process of P-fertilizers production generates huge amounts of phosphogypsum as waste by-product (PG), which also contains hazardous metals such as Cadmium or Nickel. The 85 % of PG is usually disposed in large stockpiles without any treatment, resulting in serious water and soil pollution.
Zirconium-based Metal-Organic Frameworks (Zr-MOFs) are an emerging class of crystalline porous materials with a high chemical water-stability and exceptionally elevated porosity. In this sense, PSust-MOF project studies the potentiality of Zr-MOFs as multifunctional materials toward Phosphorous sustainability. Specifically, the main goals of PSust-MOF project are: i) design of green synthetic routes to produces Zr-MOFs with controlled particle features pointing two specific applications: ii) Capture and recovery of phosphate ions to be reused as P-fertilizers (P-circular economy) and iii) grreener production of P-fertilizers from PR.
Zirconium-based Metal-Organic Frameworks (Zr-MOFs) are an emerging class of crystalline porous materials with a high chemical water-stability and exceptionally elevated porosity. In this sense, PSust-MOF project studies the potentiality of Zr-MOFs as multifunctional materials toward Phosphorous sustainability. Specifically, the main goals of PSust-MOF project are: i) design of green synthetic routes to produces Zr-MOFs with controlled particle features pointing two specific applications: ii) Capture and recovery of phosphate ions to be reused as P-fertilizers (P-circular economy) and iii) grreener production of P-fertilizers from PR.
We firstly selected the Zr-MOF (Zr6O4(OH)4(OH)4(H2O)4(1,3,6,8-tetrakis(p-benzoate)pyrene)2), known as NU-1000, because it shows a mesoporous matrix with a high density of accessible Zr-OH sites to capture P-compounds. As agriculture wastewater contains phosphate ions and other hazardous agrochemicals (like organophosphorus pesticide, OP), we decided to evaluate the ability of NU-1000 to capture phosphate ions and a commercial P-pesticide (fenamiphos) as OP-model. Interestingly, we demonstrated that NU-1000 not only shows a high adsorption capacity of both P-pollutants separately, but also it is able to capture both compounds simultaneously without detriment to the individual adsorption performances (0.77 mmol P-pollutant per gram of material). In addition, NU-1000 proved to show an elevated selectivity toward both P-pollutants in presence of potential interferences typically found in wastewater. Only highly concentrated hydrogen carbonate solutions competed with phosphate ions for binding the sorption sites. Furthermore, a strategy was designed to recover selectively the captured P-pollutants, both in batch and under dynamic conditions. Thus, the phosphate ions could be selectively recovered toward their reuse as P-fertilizers while the adsorbent could be regenerated, showing an excellent recyclability during at least 3 cycles.
Encouraged by these promising results, we decided to take a step-forward by preparing a Zr-MOF through a green synthetic route toward the simultaneous capture/recovery of phosphate ions and degradation of an organophosphorus pesticide. To do it, we selected the Zr-MOF (Zr6O4(OH)4(trimesate)2(formate)6), known as MOF-808. A microwave-assisted synthetic route, using water as solvent, was designed to prepare MOF-808 materials with controlled particle size. In addition, the performance of several MOF-808 systems with different particle size toward decontamination of water containing phosphate ions and an OP-pesticide (methyl-paraoxon) was evaluated. Interestingly, all materials were able to efficiently capture phosphate ions and degrades fully the OP-pesticide into innocuous compounds, with the materials with bigger crystals showing the worse performance. In this regard, a spectroscopic analysis with several techniques (i.e. 1H- and 31P-NMR and UV-Vis spectroscopy) proved that while the phosphate ions were captured inside the cavities, the catalytic degradation of the toxic OP took place onto the particle surface. Furthermore, it was demonstrated the feasibility of recovering the captured phosphate ions toward their reuse as well as the recyclability of the adsorbent during several adsorption/degradation-regeneration cycles.
Overall, the results derived from PSust-MOF project have demonstrated the potentiality of Zr-MOFs in P-sustainability, because they not only enable the reversible capture of phosphate ions (favoring P-circular economy), but also degrade toxic OP-pesticide presented in agriculture waste water, reducing toxicity risks. Up to date, the results derived from PSust-MOF projects have been published in prestigious international scientific journals, including Materials Today Chemistry and Journal of Materials Chemistry A, and they have been presented in International and National Conferences, highlighting the oral presentations at XXVIII Reunion Bienal de la Real Sociedad Española de Química, 44th International Conference on Coordination Chemistry and the 8th International Conference on Metal-Organic Framework and Open Framework Compounds.
Encouraged by these promising results, we decided to take a step-forward by preparing a Zr-MOF through a green synthetic route toward the simultaneous capture/recovery of phosphate ions and degradation of an organophosphorus pesticide. To do it, we selected the Zr-MOF (Zr6O4(OH)4(trimesate)2(formate)6), known as MOF-808. A microwave-assisted synthetic route, using water as solvent, was designed to prepare MOF-808 materials with controlled particle size. In addition, the performance of several MOF-808 systems with different particle size toward decontamination of water containing phosphate ions and an OP-pesticide (methyl-paraoxon) was evaluated. Interestingly, all materials were able to efficiently capture phosphate ions and degrades fully the OP-pesticide into innocuous compounds, with the materials with bigger crystals showing the worse performance. In this regard, a spectroscopic analysis with several techniques (i.e. 1H- and 31P-NMR and UV-Vis spectroscopy) proved that while the phosphate ions were captured inside the cavities, the catalytic degradation of the toxic OP took place onto the particle surface. Furthermore, it was demonstrated the feasibility of recovering the captured phosphate ions toward their reuse as well as the recyclability of the adsorbent during several adsorption/degradation-regeneration cycles.
Overall, the results derived from PSust-MOF project have demonstrated the potentiality of Zr-MOFs in P-sustainability, because they not only enable the reversible capture of phosphate ions (favoring P-circular economy), but also degrade toxic OP-pesticide presented in agriculture waste water, reducing toxicity risks. Up to date, the results derived from PSust-MOF projects have been published in prestigious international scientific journals, including Materials Today Chemistry and Journal of Materials Chemistry A, and they have been presented in International and National Conferences, highlighting the oral presentations at XXVIII Reunion Bienal de la Real Sociedad Española de Química, 44th International Conference on Coordination Chemistry and the 8th International Conference on Metal-Organic Framework and Open Framework Compounds.
PSust-MOF address one important challenge: P-sustainability. As it was indicated above, P-fertilizers are mined from a non-renewable source (phosphoric rock). In addition, a great part of P-fertilizers applied to crops are lost generating severe problems like eutrophication, which is a significant environmental, economic and health problems. Among the different approaches developed to address this challenge, adsorption is considered as the most simple and cost-effective method for P-removal. Traditional porous systems, like activated carbons or zeolites, have been proposed as P-adsorbents due to their high surface areas, but they lacks of specificity for phosphate. By contrast, very recent few articles have showed that Zr-based MOFs show a high adsorption capacity of phosphate. However, these examples are limited to the removal of one single pollutant (far from real applications), phosphate recovery is not addressed/evaluated and the Zr-MOFs employed are prepared by long solvothermal synthesis using toxic organic solvents, typically DMF which is considered a substance of very high concern by EU Chemicals Agency.
To overcome these shortcomings, the results derived from PSust-MOF have demonstrated the feasibility of using Zr-MOFs for decontaminating water containing several pollutants derived from agriculture (phosphate ions, organophosphorus pesticide and ions typically found in wastewater) both in batch and under dynamic conditions. In addition, the materials not only show a good reusability during several cycles, but also they enables the selective recovery of the phosphate ions captured, favouring the establishment of a P-circular economy. All these evidences demonstrate the utility of Zr-MOFs as P-adsorbent for the remediation of wastewater derived from agriculture, favouring the development of these materials on this field.
On the other hand, the exceptional properties of Zr-MOFs have prompted both academia and industry to explore their potential in a myriad of fields. Therefore, the green MW-assisted synthetic route of Zr-MOFs, avoiding the use of toxic and expensive organic solvent, will have a positive impact toward the industrial development of these materials.
To overcome these shortcomings, the results derived from PSust-MOF have demonstrated the feasibility of using Zr-MOFs for decontaminating water containing several pollutants derived from agriculture (phosphate ions, organophosphorus pesticide and ions typically found in wastewater) both in batch and under dynamic conditions. In addition, the materials not only show a good reusability during several cycles, but also they enables the selective recovery of the phosphate ions captured, favouring the establishment of a P-circular economy. All these evidences demonstrate the utility of Zr-MOFs as P-adsorbent for the remediation of wastewater derived from agriculture, favouring the development of these materials on this field.
On the other hand, the exceptional properties of Zr-MOFs have prompted both academia and industry to explore their potential in a myriad of fields. Therefore, the green MW-assisted synthetic route of Zr-MOFs, avoiding the use of toxic and expensive organic solvent, will have a positive impact toward the industrial development of these materials.