• Biorecovery of Platinum Nanoparticles by Anaerobic Sludge

      Sierra, Reyes; Simon Pascual, Alvaro; Field, James A.; Li, Guangbin (The University of Arizona., 2018)
      The future supply of platinum (Pt) and the platinum group metals (PGM) is at risk because of their scarcity and their high demand. Therefore, recovery of Pt and PGM is an alternative worth of study to help solving possible future supply problems. This research explored a new alternative for the microbial recovery of Pt. The ability of an anaerobic granular sludge to reduce Pt(IV) and Pt(II) ions to elemental Pt(0) nanoparticles under different physiological conditions was studied. Results demonstrated the ability of a methanogenic consortium (anaerobic granular sludge) to reduce Pt(IV) and Pt(II) ions to elemental Pt(0) nanoparticles under different physiological conditions. X-Ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of nanoparticles that were deposited on the cell surface as well as in the periplasmic space. Ethanol supported the biologically catalyzed Pt(IV) reduction in both cases, Pt(IV) and Pt(II), meanwhile hydrogen (H2) and formate promoted the chemical reduction of Pt(IV) and Pt(II) with some additional biological stimulation in the case of H2. A hypothesis is proposed in which H2 formed from the acetogenesis of ethanol is implicated in subsequent abiotic reduction of Pt(IV) indicating an integrated bio-chemical process. Endogenous controls lacking exogenous electron donor also resulted in slow Pt(IV) removal from aqueous solution. However, the rate of Pt(II) reduction was much faster compared to that of Pt(IV) indicating that Pt(II) should not be expected to accumulate as an intermediate in the reduction of Pt(IV). Finally, both Pt(IV) and Pt(II) were found to cause severe inhibitory effects in the methanogenic activity of anaerobic granular sludge, both having a similar IC50 (concentration causing a 50% of inhibition) at about 3 mg L-1. This Master’s thesis presents a new green and environmental-friendly method for the recovery of Pt from wastewater that could contribute to fight future problems in Pt and PGM supply.
    • Development of Spectrally Tuned, Erbium Doped NaYF4: Yb, Tm, Er Upconverting Nanoparticles and Their Applications

      Romanowski, Marek; Nguyen, Vina; Utzinger, Urs; Kim, Minkyu; Lynch, Ronald (The University of Arizona., 2020)
      Development and characterization of biomaterials capable of upconversion may enable new biomedical applications such as near-infrared (NIR) initiated photochemistry. Most photochemistry requires the 280 nm - 300 nm range of wavelength, regions of UV that often associated with the cause of melanoma, a deadly type of skin cancer, DNA damage, and oxidative stress [1]. Hence the low implementation of photochemical systems in biological environments. The primary characteristic of upconverting systems is the ability of the system to upconvert from energetically low NIR to the energetically high ultra-violet (UV) range. This UV energy can then be sequestered to a substrate to initiate photochemistry. Furthermore, characteristics of these upconverting systems can be modified in a manner that allows for the tuning of their spectral outputs to desired, energetically advantageous, profiles. In this thesis, we seek methods to modify the spectral output in upconversion to demonstrate the possibility of providing spectral output to an external substrate. The principal method to achieve this is to implement an ion Q that would intentionally interfere with the upconversion pathway in these nanoparticles. This quencher ion is tasked with providing a safe down conversion pathway from UV to the low energy region of the spectrum. The spectral output of these nanoparticles is characterized to determine the effects of the manipulation as different combinations of ions are explored. Finally, studies are conducted to demonstrate energy transfer to an external substrate from the nanoparticle to provide an experimental framework for future study of NIR initiated photochemistry.