NU-1000 is a stable, zirconium-based metal–organic framework (MOF) that has been used extensively as a scaffold for the installation of catalytic species, among other applications. The synthesis of NU-1000 follows a two-step modulated procedure, whereby the MOF grows as modulator molecules bound to the node are replaced with organic linker molecules. Manipulating the competition between the modulator and linker molecules for the binding sites on the node leads to control of reaction rate and the resulting NU-1000 particle size. By modifying the linker, modulator, and base concentrations and zirconium precursor, we can synthesize high-purity and monodisperse NU-1000 from 300 nm to almost 10 μm in length. Despite a wide range of particle sizes and synthetic conditions, the uptake of a dicobalt complex remained consistent per node. Further control over particle size can lead to more facile high-resolution characterization using methods like electron microscopy and spectroscopy as well as open a wider range of potential applications, including nanoscale applications like biological imaging.

Sulfate-rich wastewater poses ecological hazards to freshwater ecosystems, and sulfate is highly regulated in many Minnesota lakes. Biological sulfate reduction results in the reduction of sulfate to sulfide, and this process is used to remediate acid mine drainage. Theoretically, the aqueous sulfide can be immobilized into a solid-phase material and removed from the aqueous system. This study focuses on sulfide immobilization using iron-bearing waste minerals. Specifically, the extent of reaction of siderite (FeCO 3 ), an abundant ferrous mineral in some mining wastes, with sulfide was studied. Mildly acidic batch reactors containing powdered siderite were consecutively injected with a sodium sulfide solution. Solid reaction products were identified and characterized using powder X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive Xray spectroscopy. Mackinawite (FeS) appeared to be the most abundant product, with greigite (Fe 3 S 4 ) also detected. Results reveal that the immobilization capacity of sulfide by siderite is limited by the concentration of the Fe 2+ (aq) presented in the system immediately before the initial sulfide exposure as the Fe 2+ (aq) levels are not replenished after sulfidation. These results improve our understanding of the sulfidation of siderite and provide insight to improve the viability of using siderite-containing mining waste rock in a sulfate remediation technology.

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