# Catalytic Advanced Oxidation Processes for Sulfamethoxazole Degradation
## 2 Materials and Methods
### Preparation and Characterization of Catalysts  
For the evaluation of SMX degradation, by the tested catalytic processes, four catalysts were selected. CNTs (Nanocyl 3100, Nanocyl SA., Sambreville, Belgium) were used as received. TiO\({}_{2}\) was prepared by the sol-gel method [34; 35]. Briefly, the precursor titanium (IV) isopropoxide (C\({}_{12}\)H\({}_{28}\)O\({}_{4}\)Ti) was dropwise added to 125 mL of ethanol at room temperature under magnetic stirring, and the solution was maintained under stirring for 30 min. Then, 1 mL of nitric acid was added, and the solution was stirred until gel formation. After evaporation of the solvent at room temperature, the sample was ground, and the powder obtained was thermally treated at 400 \({}^{\circ}\)C under nitrogen flow for 2 h. The iron catalyst supported on carbon nanotubes (Fe/CNT) was prepared by the incipient wetness impregnation method using CNT as the support of the metal phase (Fe). For this, a solution of 324.8 mg Fe(NO\({}_{3}\))\({}_{3}\cdot\)9H\({}_{2}\)O was added dropwise through a peristaltic pump (Ismate\({}^{\circledR}\), Wertheim, Germany) to 2.2 g of CNT in order to obtain a content of 2% of iron (% wt). The addition was performed under ultrasonic mixing. After impregnation, the sample was dried at 100 \({}^{\circ}\)C during 24 h. Finally, the material was thermally treated under nitrogen flow (purity of 99.999% purchased from Linde Portugal, Lda., Lisboa, Portugal) of 100 cm\({}^{3}\) min\({}^{-1}\) at 400 \({}^{\circ}\)C for 1 h, followed by a reduction under hydrogen (purity of 99.999% purchased from Linde Portugal, Lda.) with 100 cm\({}^{3}\) min\({}^{-1}\) flow rate during 3 h at 400 \({}^{\circ}\)C. The iron reduction temperature was determined by the temperature programmed reduction (TPR) technique. The composite TiO\({}_{2}\)/CNT was prepared in a ball milling, according to optimal conditions previously determined, during 30 min at 10 vibrations s\({}^{-1}\) in a Retsch MM 200 equipment using 90% TiO\({}_{2}\) and 10% of CNT [36].  
To evaluate the chemical and textural properties, the prepared catalysts were characterized by several techniques. Thermogravimetric analyses were performed in an STA 409 PC/4/H Luxx equipment of Netzsch until 900 \({}^{\circ}\)C using helium as insert carrier gas and air as burning gas. Textural properties were evaluated by nitrogen adsorption isotherms at \(-\)196 \({}^{\circ}\)C, held in a Quantachrome NOVA 4200e apparatus. Approximately 0.1 g of each sample was previously submitted to a degassing program for 3 h at 150 \({}^{\circ}\)C. Additionally, the catalyst Fe/CNT was analyzed by temperature programmed reduction (TPR) in an AMI-200 (Altamira Instruments, Pittsburgh, PA, USA). Fe/CNT was reduced under a gas stream of 5% (_v/v_) of H\({}_{2}\) diluted in Ar until 700 \({}^{\circ}\)C. The H\({}_{2}\) consumption was measured by a thermal conductivity detector (TCD). The morphology of this sample was also analyzed by transmission electron microscopy (TEM) in a LEO microscope model 906E with an acceleration voltage of 120 kV. The sample was previously dispersed in ethanol in an ultrasonic bath. One drop of this suspension was deposited on a copper grid with a formvar film.  
TiO\({}_{2}\)-based catalysts were also analyzed by X-ray diffraction, performed by a PANalytical X'Pert PRO diffractometer with a Cu Ka radiation source (\(\lambda\) = 1.54 nm). The voltage and current used were 50 kV and 40 mA, respectively. The results were collected in the range of 20 between 10\({}^{\circ}\) and 90\({}^{\circ}\) with a speed of 0.017\({}^{\circ}\) s\({}^{-1}\). The Rietveld refinement was used to analyze the results.