The photodegradation and degradation of two azo group containing dyes namely; methyl orange (MO) as mono azo model and congo red (CR) as di azo model moieties, have been investigated, throughout this thesis, in aqueous medium. Three different nitrogen content (2.5%, 5% and 7%) laboratory synthesized doped anatase TiO2 nano particles (N-TiO2) have been employed as a photocatayst utilizing visible light illumination. The N-TiO2 photocatalysts have been characterized employing several spectroscopic and electronic tools encompassing. Scanning Electron Microscope (SEM) which presented smooth and ordered surfaces, Enegry Dispersive X-ray spectrometer (EDXS) and Time of Flight Mass Spectrometer (TOF-MS) which focused on the composition of various nitrogen doped TiO2 photocatalys, X-ray Diffractometer (XRD) which presented via the pattern a neat anatase allotrope without rutile diffraction peaks with particle sizes in the nano range 52.4 nm, Diffused integrated sphere UV-VIS spectrophotometer (DU-UV-VIS) which determined the band gap energies at visible region of the electromagnetic spectrum where Eg of 2.5 % N-TiO2 was 3.02 eV (410nm) compared with 3.26 eV (380nm) of anatase TiO2, Photoluminescence (PLS) spectrometry for the recording of recombination spectra which corroborated that 2.5% N-TiO2 photocatalyst contained the least recombination rate and finally Brunauer–Emmett–Teller (BET) measurements which confirmed the mesoporosity of all the prepared N-TiO2 nano catalysts with surface area of 48.412 m2/g of 2.5% N-TiO2.The effects of some experimental variables for the photodegradation of the two azo dyes have been investigated including, initial solution pH, initial dye concentration, N-TiO2 loading amount, visible light intensity and role of some oxidants.At optimum operational conditions for MO including pH = 2.5, 50 mg/l N-TiO2 loading, and 3.05 x 10-5mol/l (10 mg/l) methyl orange, the value of the apparent rate constant, kapp , obtained has been 0.085 min-1 ( 0.00141 sec-1) and the half life of the process, accordingly is equal to 0.133 hours. Whereas, for CR dye implying pH = 2.5, 40 mg/l N-TiO2 loading, and 2.15 x 10-5 mol/l ( 15 mg/l) , the value of the apparent rate constant, kapp , obtained has been 0.034 min-1 (0.000305 sec-1) and the half life of the process, accordingly is equal to 0.34 hours. The kinetic studies for the photobleaching of MO and CR have revealed that the process follows the pseudo first order pattern regardless of reaction conditions. Moreover, the computed apparent quantum yields for the photodecolorization process have been 0.077 and 0.0135 for MO and CR, respectively. The rate and yield results of the Photo oxidation process show that both dyes are influenced massively by the addition of hydrogen peroxide and other oxidants like persulfate, chlorate, bromate and iodate. The main process activation thermodynamic parameters namely, Gibbs energy, enthalpy and entropy were also deduced following the computation of photolysis activation energy employing the well known Arrhenius relation. The mechanistic study employing GC-MS, NMR, FTIR and HPLC techniques has revealed the probable pathways for the formation of various degradation intermediates and mineralization products.
