Rational chemical design of solar-powered nano photocatalysts for environmental applications

Katubi, Khadijah Mohammedsaleh M.

Abstract

Photo-catalysis, which relies on semiconducting materials as catalysts, has become an important approach in the search for ways to utilise solar energy. Because titanium dioxide has excellent properties, shows oxidative power and has a high efficiency for the photocatalytic degradation of harmful pollutants, it is considered to be the best semiconductor photo-catalyst. However, it absorbs in the ultraviolet region, due to its large band gap. To narrow this band gap accompanied with visible light absorption, N- and S-modifying were used in this project.

First, there are successfully synthesised pure anatase TiO₂ nanoparticles with a crystallite size ranging between 6 nm and 20 nm. The preparation involved only titanium (IV) isopropoxide, a small amount of water and a tube furnace, instead of alcohols, acidic chemicals or an autoclave pressure vessel as in other studies. The Fourier Transform Infrared (FT-IR) data proved the formation of the Ti—O—Ti bonds. The UV-Vis data showed the absorption at a wavelength of 384 nm with a band gap at 3.22 eV, in good agreement with the TiO₂ in the anatase phase. The Selected Area (Electron) Diffraction (SAED) also proved that the defined (hkl) planes formed TiO₂ anatase. Additionally, the Electron Energy Loss Spectroscopy (EELS) clearly showed that the Ti L₂,₃ edge was present for the Ti⁴⁺ compounds, in particular for the formula TiO₂.

Second, the N-modified TiO₂ chapter showed the forming of new potential titanium-oxycarbodiimide in the general formula TiO₂₋ₓ(CN₂)x by reacting the urea with amorphous titanium isopropoxide hydroxide /anatase TiO₂. The FT-IR spectra showed the band at about 2055 cm⁻¹ for the carbodiimide group and a decrease of the band gap less than 3.22 eV. TiO₂₋ₓ(C2N₃)₂ₓ and TiO₂₋ₓ(CN₂H)₂ₓ are two other possible new formulas that were produced by reacting amorphous Ti(OCH(CH₃)₂)4₋ₓ(OH)ₓ with cyanamide at 400 °C. This reaction also showed a new decomposition of cyanamide, which is N-(iminomethylene)-cyanamide.

Third, the S-modified TiO₂ chapter showed a cationic-anionic co-modifying TiO₂ accompanied with the producing an estimation of the possible coordinations: SO4—TiO₂ and CS—TiO₂. This was done by reacting the carbon disulfide gaseous with anatase TiO₂. On the other hand, reacted thiourea with amorphous Ti(OCH(CH₃)₂)4₋ₓ(OH)ₓ at 500 °C for 4 hours produced cationic-cationic-anionic co-modifying accompanied with the producing an estimation of a possible coordinations: Ti—O—S, CS—TiO₂, and Ti—S. Additionally, this product showed one absorption edge in the UV-Vis spectra.

Citation

Katubi, K. M. M. (2015). Rational chemical design of solar-powered nano photocatalysts for environmental applications. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4217184

• Thesis Type: Thesis
• Deposit Date: Oct 8, 2015
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4217184
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Jan 1, 2015