Modified Brookite-Rutile TiO2: Photoactivity under Visible Light Irradiation in Water Treatment Applications

  • Oluwadamilola I. Pikuda

Student thesis: Master's Thesis

Abstract

Among the advanced oxidation technologies developed to curb the menace of water pollution, titanium dioxide photocatalysis is a very promising one as it makes use of light under mild temperature and pressure conditions to totally degrade organic substances. This work focuses on contributing tangibly to the photocatalytic activity of titanium dioxide under UV-free visible light through synthesis of modified brookite-rutile TiO2 samples both in powder and as thin films, and to their application in water treatment. Modified brookite-rutile catalysts were prepared employing the sol-gel technique through doping (with nitrogen and copper) and metal photodeposition on titania surface (by using copper and platinum). The photocatalytic oxidation power of the prepared samples was tested using 4- nitrophenol as a model pollutant and characterization of selected materials was carried out. Nitrogen doping gave the best photoactivity among the various modifications attempted and ammonium nitrate was the best doping agent with a nominal N-content of 0.8% (w/w), yielding a 5-fold increase of the pseudo-first order kinetic constant of 4-nitrophenol disappearance and a 3-fold increase in the pseudo-first order constant of TOC disappearance, with respect to pure TiO2, when irradiated with LED visible light (> 425 nm). XRD identified brookite and rutile crystal phases in the prepared samples and showed that the most active catalyst has the highest brookite content among the doped ones, along with the largest rutile crystallites. HRTEM and Raman Spectroscopy confirmed the crystal phases obtained from XRD. Raman highlighted as N-doping did not produce oxygen vacancies suggesting interstitial rather than substitutional doping. Surface hydroxylation did not promote oxidation ability, as revealed by TGA-DTA, whereas BET revealed that the samples are partially mesoporous (IV type hysteresis), and the pore size and volume seemed to affect their activity. UVvis DRS analysis showed only slightly narrower band gap for N-doped samples while photoluminescence highlighted that the optimal N-doped catalyst has a normalized emission very close to that of bare TiO2. Under the same irradiation and experimental conditions, commercially available catalysts such as Evonik P25 and mixtures of commercial rutile and brookite failed to work.
Date of AwardDec 2016
Original languageAmerican English
SupervisorGiovanni Palmisano (Supervisor)

Keywords

  • Brookite-Rutile
  • Water Pollution
  • Water Treatment Technologies
  • Photocatalysis
  • Titanium Dioxide
  • Biological Oxidation
  • Membrane Technology
  • Oxidation Technology
  • Ion Exchange Technology
  • Biological Filtration
  • Heterogeneous Photocatalysis

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