Graduation Year

2017

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Mechanical Engineering

Major Professor

Manoj K. Ram, Ph.D.

Co-Major Professor

Ashok Kumar, Ph.D.

Committee Member

Rajiv Dubey, Ph.D.

Committee Member

Andrew Hoff, Ph.D.

Committee Member

Sylvia Thomas, Ph.D.

Committee Member

Sagar Pandit, Ph.D.

Keywords

nanoparticle vs nanowire, doping, surfactant, binder, photoelectrochemical catalysis

Abstract

The techniques mostly used to decontaminate air as well as water pollutants have drawbacks in terms of higher costs, require secondary treatment, and some methods are very slow. So, emphasis has been given to water though the use of photocatalysts, which break organic pollutants to water and carbon dioxide and leave no trace of by-products at the end. Photocatalytic remediation aligns with the waste and wastewater industries’ zero waste schemes with lower cost, eco-friendly and sustainable treatment technology. The commonly used photocatalysts such as titanium oxide (TiO2), zinc oxide (ZnO), tungsten oxide (WO3) have band gap of nearly 3.2 eV. The lower energy band-gap of a semiconductor makes it a better photocatalyst. The major drawbacks of photocatalysts are its inefficiency to work under visible light and high photocorrosion which limits its uses. These limitations can be mitigated through dopants and the formation of varying morphologies like nanowires, nanoparticles, nanotubes etc. Several organic pollutants are insoluble in water, which inhibits the pollutant (insoluble) to come in contact with photocatalytic material thus hindering remediation characteristic of a photocatalyst. Binder material used to immobilize the photocatalytic material tends to decompose due to oxidative and reduction reactions around the photocatalyst which causes the loss of photocatalytic material.

This investigation displays the advantage of organic remediation in visible radiation using graphene (G) doped TiO2 nanoparticles and nanowires. The nanostructured G-TiO2 nanoparticles and G-TiO2 nanowires were synthesized using sol-gel and hydrothermal methods. The nanostructured materials were characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and particle analyser procedures. The remediation of organic compounds (methyl orange) in water was achieved under visible radiation using graphene doped nanostructured photocatalytic materials. The sol-gel synthesized G-TiO2 nanoparticles has shown complete remediation of methyl orange (MO) in less than four hours, thus displaying enhanced photocatalytic activity achieved through graphene doping on TiO2 nanostructures

The dopant and structure introduced in zinc oxide (ZnO) nanomaterials bring foundation for enhanced photocatalytic activity due to lowering of the band gap, and decreasing of photocorrosion through delaying of electron-hole recombination. The challenge to synthesize both nanowire and nanoparticle structures of ZnO doped with graphene (G) are carried out by simple and cost effective hydrothermal as well as super saturation precipitation techniques, respectively. Various nanostructures of ZnO have been synthesized using precipitation and hydrothermal methods are ZnO nanoparticles, G doped ZnO nanoparticles, ZnO nanowires, G doped ZnO nanowires, TiO2 seeded ZnO nanowires and G doped TiO2 seeded ZnO nanowires The synthesized ZnO based nanostructures were characterized using SEM, TEM, XRD, UV-vis, FTIR and particle analyser methods respectively. The standard organic pollutant methyl orange (MO) dye was employed in the water to understand the effective remediation using ZnO nanostructured materials under visible light radiation. The G-ZnO NW structure has shown effective remediation of MO in water in three hours compared to other synthesized nanostructured ZnO materials.

The petroleum compounds were photocatalytically remediated from water using G- TiO2 nanoparticles material in visible light radiation. The G-TiO2 nanoparticle was synthesized using sol-gel technique and used on various petroleum-based chemicals (toluene, naphthalene and diesel) were remediated, and samples were analysed using optical and gas chromatography (GC) techniques. The importance of pollutant to come in contact with photocatalyst have been demonstrated by employing surfactant along with G-TiO2 nanoparticles to remediate naphthalene.

Earlier studies in this investigation have shown that graphene (G) doping in both titanium oxide (TiO2) and zinc oxide (ZnO), has brought about a reduction in photocorrosion, and an increase in the photocatalytic efficiency for remediation of organics under visible light (λ > 400nm). However, the graphene doped photocatalysts have proven to be hard to coat on a surface, due to the strong hydrophobic nature of graphene. So, attempts have been made to use polyaniline (PANI), a conducting polymer, as a binder material by insitu polymerization of aniline over G-TiO2 nanoparticles (G-TiO2 NP) and G-ZnO nanowires (G-ZnO NW) & characterized using SEM, XRD, UV-vis and FTIR techniques. The photocatalytic, as well as photoelectrochemical catalytic performance of PANI:G-TiO2 NP and PANI:G-ZnO NW, were investigated. The standard MO in water was used for both PANI:G-TiO2 NP and PANI:G-ZnO NW electrodes on conducting substrates. 1:1 PANI:G-TiO2 NP shows an increase of 31% in the remediation of MO in water at potential of +1000 mV, and with the ease in coating PANI:G-TiO2 NP and PANI:G-ZnO NW on various substrates, on top of the visible light remediation allows for the use of these materials and process to be used for practical applications of remediation of organics from water.

Available for download on Wednesday, June 20, 2018

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