Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Mechanical Engineering

Major Professor

Ashok Kumar, Ph.D.

Co-Major Professor

Manoj K. Ram, Ph.D.

Committee Member

Daniel Hess, Ph.D.

Committee Member

Sylvia Thomas, Ph.D.

Committee Member

Sagar Pandit, Ph.D.

Keywords

Battery, Decontamination, Photocatalyst, Adsorbent, Methylene Blue

Abstract

Nanostructured molybdenum trioxide (MoO3) was synthesized and used as a precursor in a comparative study, along with commercial MoO3, to synthesize molybdenum dioxide (MoO2) nanoparticles. Scanning electron microscope (SEM) images revealed the particles to be approximately 30-50 nm in diameter. X-ray diffraction (XRD) confirmed MoO3 was fully reduced to MoO2 in all cases. Time dependent experiments showed that within two hours no traces of MoO3 are present. All of the experiments showed the materials were excellent absorbent materials, as well as photocatalysts. Both MoO2 materials performed almost exactly the same, with both samples being able to remove 100% of the methylene blue (MB) in one minute with light, and in two minutes without light.

The morphology of MoO2 was controlled in a comparative study by varying the concentration of cetyltrimethylammonium bromide (CTAB) present during the hydrothermal reaction. As the concentration of CTAB increased, the morphology of the material changed from nanoparticles, to nanospheres, to microspheres, to hollow microspheres, and finally a highly agglomerated version of microspheres and particles combined, as confirmed by SEM images. A formation mechanism for the formation of the various sized spheres was proposed with a combination of aggregation and Ostwald ripening. XRD confirmed that all of the MoO3 was reduced to MoO2, along with no residual peaks from the CTAB that was present during the reaction. Upon trying to mix some of the materials into the MB solutions, it became obvious that some of the materials were hydrophobic. The decontamination results once again showed that the synthesized MoO2 materials were not only photocatalysts, but adsorbents as well. Samples synthesized with 0.1-5 mM CTAB were able to remove 100% of the MB in 10 minutes or less. Samples synthesized with 10 mM CTAB were able to remove 54.4% and 35% of the MB in 10 minutes, with and without light, respectively. Samples synthesized with 15 mM CTAB were able to remove 29.4% and 26.3% of the MB in 10 minutes, with and without light, respectively. The apparent decrease in decontamination performance was proposed to be caused by surface morphology induced hydrophobicity. A mechanism to describe why the hydrophobic particles were still able to decontaminate the water was proposed to be caused by coming into direct contact with the magnetic stirrer as the water level dropped due to sample collection.

MoO2 nanoparticles were successfully synthesized onto a copper substrate, in a single step, via a hydrothermal synthesis technique. It is believed to be the first report of such a synthesis method. XRD confirmed all of the MoO3 had been reduced to MoO2, and also confirmed that no other compounds had formed between the molybdenum and copper. SEM images of the MoO2 coated copper substrate showed uniform nanoparticles ranging from 30-50 nm. The MoO2 coated copper substrate was able to decontaminate 57.5% of the MB from water in 10 minutes without exposure to light, while it was able to decontaminate 71.7% of the MB from water in 10 minutes with exposure to light.

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