This research investigates the photocatalytic decolourisation of two selected dyes using multiple thin film coatings (three, four and five layers) of a TiO 2 photocatalyst under a low intensity ultraviolet A (UVA) light source. The TiO 2 photocatalyst was prepared using a simplified sol-gel process, and the decolourisation efficiencies of the two experimental dyes, indigo carmine and reactive black 5, were studied. The kinetics of the photocatalytic decolourisation reactions under low intensity UVA were described by a pseudofirst order kinetic model, and the photocatalytic kinetic rate constants were reported. An increase in the number of coating layers contributed to the TiO 2 photocatalyst's smaller grain size, higher surface area and narrower optical band gap. The findings also revealed a positive relationship between the number of TiO 2 coating layers and the efficiencies and kinetics of dye decolourisation in the experimental photocatalytic process. In addition, the TiO 2 thin film photocatalyst induced high photocatalytic activity, even under low intensity UVA light.

Ammonium ( NH 4 + ) is an undesirable by-product of photocatalytic nitrate ( NO 3 − ) reduction since it is harmful to aquatic life once it converts into ammonia (NH3). This research investigated the removal efficiency of NO 3 − and for the first time quantified the relationships of initial nitrate concentrations ([ NO 3 − ]0) and photocatalyst dosages on the remaining ammonium ( NH 4 + ) in synthetic wastewater using photocatalytic reduction process with either nanoparticle titanium dioxide (TiO2) or 1.0%Ag-TiO2 under Ultraviolet A (UVA). The experiments were systematically carried out under various combinations of [ NO 3 − ]0 (10, 25, 50, 80, and 100 mg-N/L) and photocatalyst dosages (0.1, 0.5, 1.0, and 2.0 g). The NO 3 − removal efficiency of both photocatalysts was 98.96-99.98%, and the catalytic selectivity products were nitrogen gas (N2), nitrite ( NO 2 − ), and NH 4 + . Of the two photocatalysts under comparable experimental conditions, 1.0%Ag-TiO2 provided better NO 3 − removal efficiency. For both photocatalysts, the remaining NH 4 + was predominantly determined by [ NO 3 − ]0; higher [ NO 3 − ]0 led to higher NH 4 + . Multiple linear regression analysis confirmed the dominant role of [ NO 3 − ]0 in the remaining NH 4 + . The photocatalyst dosage could play an essential role in limiting NH 4 + in the treated wastewater, with large variation in [ NO 3 − ]0 from different sources.

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In this research, we compared the COD removal efficiencies of titanium dioxide (TiO2) thin films coated on the surfaces of borosilicate glass that prepared by three different numbers of coating layer; i) 3 layers ii) 4 layers and iii) 5 layers by sol-gel method. All of the prepared TiO2 thin films consisted of pure anatase crystalline structure with grain sizes in the range 20-250 nm. The calculated optical band gaps of the TiO2 thin films were 3.24. The total apparent surface area per total weight of TiO2 thin films were 4.74, 3.86 and 2.79 m 2 g -1 for 3, 4 and 5 layers coating, respectively. The kinetics of the photodegradation reactions of COD under UVA light source were described by the Langmuir-Hinshelwood (L-H) kinetic model. The specific rates of the photodegradation of TiO2 thin films at 3 layers coating was 1.40×10-4 min -1 mW -1, while for the 4 layers coating and the 5 layers coating were 1.50×10 -4 and 4.60×10 -4 min -1 mW -1 , respectively. The photocatalytic performance of COD degradation was higher with smaller grain size, higher surface area and narrow optical band gaps. Moreover, the numbers of coating layer on substrate also have great influence for kinetic of COD removal.