Rapid, Selective Heavy Metal Removal from Water by a Metal-Organic Framework/Polydopamine Composite

Drinking water contamination with heavy metals, particularly lead, is a persistent problem worldwide with grave public health consequences. Existing purification methods often cannot address this problem quickly and economically. Here we report a cheap, water stable metal-organic framework/polymer composite, Fe-BTC/PDA, that exhibits rapid, selective removal of large quantities of heavy metals, such as Pb2+ and Hg2+, from real world water samples. In this work, Fe-BTC is treated with dopamine, which undergoes a spontaneous polymerization to polydopamine (PDA) within its pores via the Fe3+ open metal sites. The PDA, pinned on the internal MOF surface, gains extrinsic porosity, resulting in a composite that binds up to 1634 mg of Hg2+ and 394 mg of Pb2+ per gram of composite and removes more than 99.8% of these ions from a 1 ppm solution, yielding drinkable levels in seconds. Further, the composite properties are well-maintained in river and seawater samples spiked with only trace amounts of lead, illustrating unprecedented selectivity. Remarkably, no significant uptake of competing metal ions is observed even when interferents, such as Na+, are present at concentrations up to 14»000 times that of Pb2+. The material is further shown to be resistant to fouling when tested in high concentrations of common organic interferents, like humic acid, and is fully regenerable over many cycles.

Construction of MOF/Polymer Composites for Metal Ion Capture

Daniel Teav Sun

Metal ion capture is of environmental and economic significance. The industrial revolutions have discharged increasing amounts of heavy and precious metals into complex water sources. The key is that these types of metal ions tend to be at trace amounts in water mixtures containing high concentrations of inorganic and organic interferents. It is extremely difficult to extract and concentrate such species from these complex water mixtures. In this thesis, we show that novel inner pore structural modifications inside of metal-organic frameworks or MOFs, achieved via in-situ polymerization can enhance specific metal ion capture performance from aqueous media. One unique property of MOFs is the presence of open metal sites along the pore surface, which can give rise to interesting redox activity. By taking advantage of this phenomenon, in Chapter 2 we show that a MOF named Fe-BTC polymerizes dopamine to polydopamine (PDA) inside its porous network via its Fe3+ open metal sites. The heavy metal scavenging PDA, now pinned on the internal MOF surface results in a material that has high capacities for Pb2+ and Hg2+ and removes over 99.8 % of these contaminants from a 1 ppm solution rapidly, yielding drinkable levels in seconds and maintains its properties in river water, waste water (obtained from Swiss industry) and sea water spiked with only trace amounts of lead and mercury. The material is further shown to be resistant to fouling due to its unique pore architecture and is fully regenerable over many cycles. Further, a number of characterization techniques are defined and employed to help fully understand the interface of these materials. By changing the polymer building blocks, in Chapter 3 we demonstrate that a new material, Fe-BTC/PpPDA, is able to selectively and rapidly extract ultra-trace amounts of gold from several complex water mixtures that include waste water, fresh water, ocean water, and solutions used to leach gold from electronic waste and incinerated sewage sludge. The material has an exceptional removal capacity and completely extracts gold from these complex mixtures in under 2 minutes. Further, due to the high cyclability, we demonstrate that the composite can effectively concentrate gold and yield purities up to 23.9 K. For large-scale implementation, these materials must be scaled up and considered in a dynamic continuous flow through operation. As such, the objectives are to 1) construct a continuous flow through apparatus, 2) scale up the synthesis of the MOF/Polymer composites, 3) optimally structure the fine powder material and 4) optimize and model continuous fix-bed column experiments. In Chapter 4, the progress for these endeavors from the Clean Water Initiative is shown.

EPFL2020

Rapid, Selective Extraction of Trace Amounts of Gold from Complex Water Mixtures with a Metal-Organic Framework (MOF)/Polymer Composite

Natalia Gasilova, Emadeddin Oveisi, Wendy Lee Queen, Daniel Teav Sun, Shuliang Yang

With the ever-increasing production of electronics, there is an ensuing need for gold extraction from sources other than virgin mines. Currently, there are no technologies reported to date that can effectively and selectively concentrate ultratrace amounts of gold from liquid sources. Here, we provide a blueprint for the design of several highly porous composites made up of a metal-organic framework (MOF) template and redox active, polymeric building blocks. One such composite, Fe-BTC/PpPDA, is shown to rapidly extract trace amounts of gold from several complex water mixtures that include wastewater, fresh water, ocean water, and solutions used to leach gold from electronic waste and sewage sludge ash. The material has an exceptional removal capacity, 934 mg gold/g of composite, and extracts gold from these complex mixtures at record breaking rates, in as little as 2 min. Further, due to the high cyclability, we demonstrate that the composite can effectively concentrate gold and yield purities of 23.9 K.

AMER CHEMICAL SOC2018

Preserving Porosity of Mesoporous Metal-Organic Frameworks through the Introduction of Polymer Guests

Mehrdad Asgari, Aron Joel Huckaba, Sudabeh Jawahery, Seyedmohamad Moosavi, Mohammad Khaja Nazeeruddin, Emadeddin Oveisi, Li Peng, Wendy Lee Queen, Berend Smit, Shuliang Yang

High internal surface areas, an asset that is highly sought after in material design, has brought metal-organic frameworks (MOFs) to the forefront of materials research. In fact, a major focus in the field is on creating innovative ways to maximize MOF surface areas. Despite this, large-pore MOFs, particularly those with mesopores, continue to face problems with pore collapse upon activation. Herein, we demonstrate an easy method to inhibit this problem via the introduction of small quantities of polymer. For several mesoporous, isostructural MOFs, known as M-2(NDISA) (where M = Ni2+, Co2+, Mg2+, or Zn2+), the accessible surface areas are increased dramatically, from 5 to 50 times, as the polymer effectively pins the MOFs open. Postpolymerization, the high surface areas and crystallinity are now readily maintained after heating the materials to 150 degrees C under vacuum. These activation conditions, which could not previously be attained due to pore collapse, also provide accessibility to high densities of open metal coordination sites. Molecular simulations are used to provide insight into the origin of instability of the M-2(NDISA) series and to propose a potential mechanism for how the polymers immobilize the linkers, improving framework stability. Last, we demonstrate that the resulting MOF-polymer composites, referred to as M-2(NDISA)-PDA, offer a perfect platform for the appendage/immobilization of small nanocrystals inside rendering high-performance catalysts. After decorating one of the composites with Pd (average size: 2 nm) nanocrystals, the material shows outstanding catalytic activity for Suzuki-Miyaura cross-coupling reactions.

2019

Construction of MOF/Polymer Composites for Metal Ion Capture

Daniel Teav Sun

EPFL2020