Molybdenum (Mo) is a naturally occurring trace element that is present in drinking water mostly in the molybdate (MoO42-) form in well water. Recently, the EPA deemed Mo as a potential contaminant because exposure can lead to health effects such as gout, hyperuricemia, and lung cancer. In this work, we have assessed the sorptive removal of Mo using Douglas fir biochar (DFBC) and its chemically-coprecipitated iron oxide analogue (DFMBC). Adsorption was studied varying the batch sorption conditions; pH, equilibrium time (5 min-24 h), initial Mo concentrations (2.5-1000 mg/L), temperatures (5, 25, and 40 °C) and equilibrium method. Langmuir capacities for DFBC and DFMBC (at pH 3, 2 h equilibrium) were in 359.3-487.9 mg/g and 288.3-571.9 mg/g range, respectively. Adsorbents and Mo-laden adsorbents were characterized by elemental analysis, BET, PZC, SEM, TEM, EDS, XRD, and XPS. These data suggest that DFBC and DFMBC can be potential candidates for Mo sorption.

The aim of this thesis is to advance the field of solid lubrication science by developing coatings that provide reliable performance in ambient conditions, work on rough surfaces, and are amenable to industrial size and design complexities. Two different coating systems, Ti3C2Tx-MoS2 and Ti3C2Tx-Graphene Oxide blends, were studied in this work. The Ti3C2Tx-MoS2 nanocomposites were spray-coated onto rough 52100-grade steel surfaces, and their tribological performance was evaluated in a ball-on-disk configuration in a unidirectional sliding mode. The test results indicate that Ti3C2Tx-MoS2 coatings achieved superlubricity, which has not been previously reported for either pristine material under macroscale sliding conditions. The observed synergistic mechanism enabled the superlative performance, which was explained by the in-situ formation of a robust tribolayer responsible for sustained lubricity even at high contact pressures (>1.1 GPa) and sliding speeds (0.1 m/s). Processing, structure, and property correlation studies were conducted to understand the underlying phenomena. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to reveal the formation of the tribolayer. The Ti3C2Tx-Graphene Oxide blends were also spray-coated onto rough-bearing steel surfaces, and their tribological assessment was carried out in ambient environmental conditions and high contact pressures in a ball-on-disc experimental setup. The coatings led to substantial friction reduction compared to uncoated and single-component-coated surfaces, with a friction coefficient as low as 0.065 at 1 GPa contact pressure and 100 mm/s sliding speed, surpassing the state-of-the-art. The coatings also provided excellent protection against wear loss of the substrate and counter-face. The results were explained based on the observations from Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and nanoindentation measurements. The in-operando formation of a dense, hard, and stiff tribolayer was observed, which was responsible for the sustained lubricity even at high test loads and sliding speeds. This thesis presents a holistic exploration and correlation of structure-property-processing for the advancement of solid lubrication science. It provides insights into the development of solid lubricant materials and their tribological performance, which can be useful for various industrial applications.

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