# Heterogeneous Electro-Fenton-like Designs for the Disposal of 2-Phenylphenol from Water
## 2 Materials and Methods
### Sample Preparation and Analytical Methods
#### 2.5.2 Hydrogen Peroxide Concentration  
It was determined according to the Titanium oxalate method developed by [PERSON] [40]. In this method, 2 mL of filtrated sample were mixed with 0.25 mL of sulphuric acid solution (1:17), 0.2 mL of potassium titanium oxide oxalate dihydrate (50 g/L) and 0.05 mL of distilled water for a final volume of 2.5 mL. After 5 min of reaction, the generation of yellow-orange titanium (IV) peroxide complex was spectrophotometrically measured at the maximum absorbance at 400 nm in a GENESYS 150 UV-Vis Spectrophotometer (Thermo Fisher Scientific, Madrid, Spain). Reagents were provided by Sigma-Aldrich (Barcelona, Spain). Current efficiency for hydrogen peroxide production (CE, %) and electric energy consumption (EEC, kWh/kg) was determined following Equations (6) and (7) [41]:  
\[\text{CE (\%)}=\frac{\text{n}\cdot\text{F}\cdot\text{C}_{\text{H}_{2}\text{O }}\cdot\text{V}}{\int_{0}^{\text{t}}\text{I}\,\text{dt}}\cdot 100 \tag{6}\]  
\[\text{EEC = 1000\cdot\text{U}\cdot\text{I}\cdot\text{t}/\text{C}_{\text{H}_{2} \text{O}2}\cdot\text{V}} \tag{7}\]  
where n (=2) is the number of electrons transferred for oxygen reduction to hydrogen peroxide, F: Faraday constant, I: current intensity (A), t: time (s), C\({}_{\text{H}_{2}\text{O}2}\): hydrogen peroxide concentration (mg/L) and V: volume of the solution and U: voltage (V). \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **A** & **B** & **C** \\ \hline  & Carbon Black (g) & Nickel nanofibers (g) & PTFE (g) \\ \hline Level 1 & 0.1 & 0.4 & 2.5 \\ Level 2 & 0.3 & 0.6 & 4.2 \\ \hline \end{tabular}
\end{table} 
Table 1: Screening experiment parameters and level. 2.5.3. Metal Leaching Concentration  
The metal concentration was monitored by Atomic Absorption Spectroscopy (Agilent 240 PS) (C.A.C.T.I., University of Vigo). 2.5.4. TOC Concentration  
Mineralization degree was determined via combustion by multi N/C 3100 Autoanalyzer (Analytik Jena) coupled with a nondispersive infrared (NDIR) detector (C.A.C.T.I. University of Vigo). 2.5.5. Material Characterization  
For the characterization of the different synthesised materials, scanning electron microscopy (SEM) images were used to know the morphological characterization of catalyst and electrocataly. SEM images and Energy Dispersive Microanalysis (EDS) were performed on a JEOL JSM-6700F equipped with an EDS Oxford Inca Energy 300 SEM using an accelerating voltage of 20 kV (Electron Microscopy Service, C.A.C.T.I., University of Vigo, Spain). The hydrophilicity/hydrophobicity of the prepared electrodes was determined based on the contact angle. For this purpose, a Mobile Drop Analyzer (Kruss) was used and the contact angle between a water drop (volume 0.005 mL) and the electrode material was measured. 3.1. Screening of Transition Metals in Homogeneous Electro-Fenton-like Process  
Initially, nickel and zinc ions were evaluated in the electro-Fenton-like process as catalysts for generation of hydroxyl radicals from hydrogen peroxide, which is produced in an electrochemical cell by two-electron reduction of oxygen on a carbonous cathode surface using electrical energy to overcome the unfavourable reactions [42]. In this study, a carbon felt cathode and BDD anode were used, and the hydrogen peroxide production was evaluated at different current intensities. This parameter affects the efficiency of the electro-Fenton process due to the oxygen reduction and generation of hydrogen peroxide on the cathode are directly related to the applied current. The continuous production of hydrogen peroxide at two current intensities (100-300 mA) showed that the efficiencies for the production were increased with the reduction of the current intensity. In both cases, the generation reached an apparent steady-state level after 60 min, which could be explained by the in situ decomposition of hydrogen peroxide [43]. In addition, the energy consumption of 100 mA (161 kWh/kg) was lower than that of 300 mA (998.79 kWh/kg) after 60 min.