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.