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Morphological and optical properties of a multilayer film (CAZO/CZAO/ZACO) prepared by spin-coating method and deposited on a glass substrate were evaluated. The study was initially carried out for each layer, individually and then as a multilayer subsequently. Structural properties using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), infrared spectra (IR) and X-ray photoelectron Spectroscopy (XPS) showed the presence of three phases of zinc, copper and silver oxides at different levels. The CZAO sample observed with scanning electron microscope (SEM) showed an excellent porous surface with a large deformation in the multilayer configuration. Doping with zinc and copper in the silver crystal lattice improved the crystal structure and reduced the optical energy gap, thus increasing the optical absorbance and refractive index. The dielectric constants and showed an increase in the optical polarization values for lower photonic energies. The maximum degradation rate for photocatalysts of methylene blue was 89 % for a 5-h exposure period with CAZO/CZAO/ZACO while it reached 71 % for the CZAO sample during the same time period. The sensitivity of samples to light proved that the presence of ultraviolet radiation increases the number of holes trapped by oxygen ions and causes more free electrons and contribute to a better production of photocurrent than in darkness.
The aim of this work was to study in detail the physical-chemical aspects of water and wastewater treatment using different so-called “advanced oxidation systems”. Our target was to construct an annular multiphase falling film reactor with a fixed photocatalyst (TiO2) and to compare its performance with that of a planar reactor in different chemical oxidation regimes. The annular design of the falling film reactor was prepared for heterogeneous photocatalytic oxidation systems by combining three different phases (solid fixed photocatalyst, falling liquid wastewater and an ozone/oxygen gaseous mixture). UVA light sources were employed for irradiation of the photocatalyst surface. In the first step, the design, construction and characterisation of the reactor was performed. The next step was the assessment of the performance of the falling film reactor in the decomposition of selected organic chemicals as model compounds. Six different oxidation methods were evaluated for the degradation of model compounds. Photo-oxidation (UVA/O2), photo-ozonation (UVA/O3), ozonation (O3), catalytic ozonation (TiO2/O3), photocatalytic oxidation (TiO2/UVA/O2) and photocatalytic ozonation (TiO2/UVA/O3) processes were investigated in this study. It was shown that due to the synergetic effects between ozone molecules and the irradiated surface of TiO2, photocatalytic ozonation was the most effective oxidation process for the decomposition of model compounds. Oxalic acid, dichloroacetic acid, citric acid, terephthalic acid, p-chlorobenzoic acid, methyl tert-butyl ether, ethyl tert-butyl ether, tert-amyl ethyl ether and tert-butanol were chosen as model compounds. Two different immobilisation techniques were employed and evaluated for fixing TiO2 nanoparticles onto the reactor walls. The immobilisation of photocatalysts was performed on borosilicate glass and polymethylmethacrylate. It was observed that the photoactivity of fixed TiO2 particles on borosilicate glass was higher than that on polymethylmethacrylate. The stability of immobilised photocatalysts on both substrates was good. The influences of different experimental parameters, such as the initial concentration of model compounds, ozone concentration, solution pH, temperature and solution recycling rate on the degradation rate and efficiency of the oxidation systems were studied and discussed. In terms of the characterisation of the falling film reactor, different aspects were studied. The thickness and distribution pattern of falling films, the gas washing effects of falling films, the absorption of ozone in the falling films, the adsorption of organic pollutants on the photocatalyst surface, the effect of UVA irradiation on ozone decomposition, etc. were studied in detail. The concentration of model compounds was determined by ion chromatography (IC), high performance liquid chromatography (HPLC) and headspace techniques. Chemical oxygen demand (COD) was applied to quantify the quality of wastewaters and total organic carbon (TOC) measurements were employed for the determination of model compound mineralisation. At the end of this study, treatment of real wastewater was performed by means of the falling film reactor as a case study. The real wastewater was produced in a pyrolysis process. More than 30 organic and inorganic compounds were included in the composition of this wastewater. The application of ozone-based advanced oxidation processes showed good results in terms of colour and odour removal of pyrolysis wastewater as well as in terms of decreasing its COD.