Synthesis of titanium dioxide meshes by plasma electrolytic oxidation for advanced oxidation processes of drug contaminated wastewater

The aim of this thesis project was the synthesis of a proper titanium dioxide catalyst and the usage of it in Advanced Oxidation Processes finalized to the degradation of organic molecules in contaminated water. Titanium dioxide catalyst was synthesized through Plasma Electrolytic Oxidation (PEO) technique onto two different types of titanium grade II substrates. Small titanium foils (10 x 6.5 x 0.01 cm3) were used study the effect of processing parameters on the photoelectrocatalytic activity. Diluted sulfuric acid solution was used as electrolyte, and operating parameters such as electrolyte concentration, processing temperature, polarization voltage and processing time were changed in order to improve the photoactivity of the synthesized TiO2 layers (see table 0.1). TABLE 0.1: PROCESSING PARAMETERS INVESTIGATED Electrolyte concentration of H2SO4 (M) 0.5 ÷ 3.0 Processing temperature (°C) -3.5 ÷ -10 Polarization voltage (V) 100 ÷ 160 Processing time (min) 5 ÷ 30 Either current or voltage response was measured during the PEO process in order to have an insight on the mechanism of titanium oxide formation and to design the scaling up of the process. Surface morphology was observed by means of SEM analysis, lattice structure and phase composition were determined by XRD analysis, photoelectrochemical activity was assessed by means of linear sweep voltammetry tuning the UV irradiation at 0 and 8 W/m2. The best photoelectrochemical activity was measured on TiO2 samples obtained in 1.5M H2SO4, processing temperature -5°C, polarization voltage 130V (with voltage ramp) and processing time 21minutes. The process was then upscaled to a titanium cylinder having Ø=2.6cm and length ranging from 19cm to 46cm. The following processing parameters were used: TABLE 0.2: OPERATING CONDITIONS FOR THE SYNTHESIS OF TITANIUM OXIDE MESHES Operating polarization voltage: 130V (without voltage ramp); [H2SO4]: 1.5M; Processing T: -5°C; Processing time: 21minutes The synthesized titanium dioxide meshes were delivered to 2 Italian companies working in the field of water treatment (CEA-COOP and GDF SUEZ-srl) but also used in a laboratory scale reactor for treatment of contaminated water. In particular, laboratory experiments were carried out on water containing either Ethylene glycol or Carbamazepine, at starting concentrations of 4500mg/l and 0.1mg/l, respectively. Decontamination through photoelectrochemical catalysis was compared to the effect of UV irradiation, photocatalysis and electrochemical polarization individually considered. Photoelectrocatalytic treatment of ethylene glycol diluted in tap water led to an almost complete removal of the organic compound (less than 3% of the initial concentration) after 7 days.