Characterization and Electrocatalytic activity analysis

1. The morphology of TNTs array and SnO2-Sb electrodes were analyzed by SEM(S4700, Hitachi Ltd), including Figure 1 and Figure 3.2. The wettability of TNTs substrates were examined by a contact angle test with absolute ethyl alcohol, as shown in Figure 2.3. The crystalline patterns of TNTs array and SnO2-Sb electrodes were analyzed by XRD (D/max-rB, Rigaku) with Cu Kα radiation, as shown in Figure 4. Effect of preparation conditions for TNTs arrays on the average crystal size of SnO2-Sb calculated by Scherrer Formula, as shown in Table 1. Scherrer Formula: D=Kλ/(βcosθ), where D is the crystallite size, K is the Scherrer constant (0.89), λ is the wavelength of incident ray, β is the full width at half maximum of the peak, and θ is the position of plane peak.4. Electrochemical analysis was carried out in a system consisted of a SnO2-Sb working electrode, a platinum sheet counter electrode, and a saturated Ag/AgCl reference electrode. Oxygen evolution potential was tested by LSV measurement in H2SO4 solution (0.5 mol/L), as shown in Figure 5. The double electrode layer structure was analyzed by EIS measurement inNa2SO4 solution ( 0.25 mol/L) with frequency range from 105 to10-1 Hz under an impedance amplitude signal of 5 mV. The aforementioned experiment was conducted in a three-electrode system using an electrochemical workstation (Auto Lab PGSTAT128N, Metrohm), as shown in Figure 6, and the EIS fitting results of TNTs/SnO2-Sb electrodes with different substrate preparation voltages was shown in Table 2. 5. The electrocatalytic degradation of phenol was operated in a cylindrical reactor containing 0.25 mol/L Na2SO4 with the addition of 100 mgL-1 artificial phenol wastewater. As-prepared samples measuring 20mm×20mm were utilized as the working anode, while stainless steel plates of the same size served as the cathode, with a distance of 10 mm between them. All degradation experiments operated under a certain stirring speed and 10 mA/cm2 current density. The concentration variations of phenol were determined by UV-Vis spectrophotometry (TU-1810PC, PERSEE) as a function of electrolysis time. The logarithmic relationship between phenol concentration and electrolysis time was analyzed using a pseudo-first-order kinetics model. The kinetic rate constant (k) of the electrode for phenol degradation was determined using the equation : ln(C0/Ct)=kt, where C0 represents the initial concentration of phenol and Ct is its concentration at a given time t.Electrochemical degradation of phenol on TNTs/SnO2-Sb electrodes with TNTs substrates under different preparation conditions (a) Variations of concentration of phenol with electrolysis time (b) The first-order kinetics curves of phenol degradation was shown in Figure 7.6. The wettability of TNTs substrates were examined by a contact angle test with absolute ethyl alcohol. SnO2-Sb loading on different substrates was weighed by the balance. The effect of preparation voltage of TNTs arrays on the contact angle of substrate surface and loading amount of SnO2-Sb was shown in Table 3. 7. The surface chemical environment element was analyzed by XPS (PHI5700 ESCA) with Al Kα radiation (hυ=1486.6eV), as shown in Figure 8 and Figure 9, and the XPS analysis of TNTs/SnO2-Sb electrodes with different substrate preparation voltages was shown in Table 4.8. The oxygen vacancy concentration were detected by EPR (Bruker ER200D-SRC) measurement, as shown in Figure 10.9. The presence of hydroxyl radicals (‧OH) generation in a Na2SO4 solution (0.25 mol/L) with terephthalic acid (0.5 mmol/L) as the trapping agent was determined using fluorescence spectroscopy technology (FP-6500, JASCO). The hydroxyl radicals generation ability on the SnO2-Sb electrode with different substrate preparation voltages was shown in Figure 11.10. The reactive radicals generated during electrochemical degradation of organics were detected by using a free radical quenching experiment, with a quencher of p-benzoquinone for ‧OH, and isopropyl alcohol for superoxide radical (‧O2-). The quenching experiment of the active radicals on the SnO2-Sb electrodes with different substrate preparation voltages was shown in Figure 12, and the computed result from the quenching experiment was shown in Table 5.