A research team at the University of Birmingham has optimized a manufacturing process for novel materials for water purification. According to the scientists, the production costs for so-called Metal Organic Frameworks (MOFs) can be significantly reduced through an adapted process management. The results were published in the journal "Green Chemistry."
MOFs are advanced materials composed of metal nodes and organic compound molecules. They form a cage-like molecular structure with extensive internal pore networks. This large internal surface acts like a sponge and can selectively absorb dissolved heavy metals from water. The main application area is the treatment of chemically complex wastewater from mining, electronics, or chemical production.
Previous hurdles in MOF production
So far, two factors have hindered the widespread use of MOFs in water treatment. Many manufacturing and post-processing methods are solvent- or energy-intensive. Additionally, the metals used in MOFs can dissolve in the treated water during application, causing secondary contamination. Most MOF applications in water treatment are therefore still in the pilot or demonstration stage.
The team led by Swaroop Chakraborty, NERC Independent Research Fellow at the School of Geography, Earth and Environmental Sciences at the University of Birmingham, had previously developed a process to produce a green-synthesized MOF in a scalable, water-based process. The material was designed for the recovery of rare earths and heavy metals from industrial waste streams. It is available in pellet form rather than as a fine powder, which according to the researchers, facilitates handling in practice. The university has filed a patent application for the method and material through University of Birmingham Enterprise.
Freeze-drying reduces costs and energy requirements
In the current publication, the team describes a freeze-drying technique to further improve production. According to the researchers, this increases the isolated yield to more than three times. The estimated energy requirement per gram is reduced by about 74 percent. The estimated production costs on a laboratory scale are reduced from about 19 US dollars per gram to just over 5 US dollars per gram compared to conventional processing.
The freeze-dried MOF showed a high capacity for rapid lead removal from solutions in tests. Within the first hour, the material removed more than 90 percent of the lead. This removal rate was maintained over four consecutive treatment cycles. After seven days of exposure to air, freshwater-like conditions, and artificial seawater, the material retained its essential structural properties. In tests with real water samples, it removed lead from chemically complex solutions with low copper leaching.
Seeking industry partners
"For water treatment materials, removing the pollutant is only half the story," says Chakraborty. "We also need to understand how materials like Metal Organic Frameworks are manufactured and how they change during use in the environment. By redesigning a single processing step, we were able to recover significantly more material and reduce the estimated production costs while maintaining strong lead uptake performance under environmentally relevant conditions."
The researchers are now seeking industry partners from the fields of mining, electronic waste recycling, or water treatment. These partners are to license the technology for specific applications or jointly develop a pilot trial in an industrial environment.
