Enhanced electro-catalytic activity of TNTs/SnO2-Sb electrode through the effect mechanism of TNTs architecture
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摘要: 采用溶剂热法制备了TNTs/SnO2-Sb电极，通过调整氧化电压和氧化时间构建出不同结构的二氧化钛纳米管（TNTs）阵列，以探究其对电极结构和电化学性能的影响。SEM和接触角测试表明，相较于阳极氧化时间，阳极氧化电压是影响TNTs阵列形貌和表面亲水性的主要因素。SEM、XRD、LSV和EIS结果表明，TNTs阵列孔径的大小影响了催化涂层的形貌、晶粒尺寸以及电极的析氧电位。XPS、EPR和羟基自由基（·OH）生成测试表明，涂层表面致密且粒径较小有利于电极表面获得更多的氧空位，且氧空位浓度越高，吸附氧物种越多，从而增强了活性自由基的形成以及对有机物的降解。以长度950 nm，孔径100 nm 的TNTs 阵列层为基底时，所制备的电极TNTs (25 V) / SnO2-Sb展现出了最佳的苯酚处理效果（92%±4.6%，2 h）。
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关键词:
- TNTs 结构 /
- SnO2-Sb 电极 /
- 溶剂热 /
- 氧空位 /
- 电催化氧化
Abstract: The TiO2 nanotubes arrays/SnO2-Sb (TNTs/SnO2-Sb) electrode is successfully fabricated using the solvothermal synthesis technique. Various architectures of TNTs are constructed by varying the anodization voltage and time, aiming to investigate their impact on the structural and electrochemical properties of the SnO2-Sb electrode. The anodization voltage is identified as the primary influencing factor on the morphology and surface hydrophilia of TNTs arrays, which is evidenced by scanning electron microscopy (SEM) and contact angle testing. In contrast, the effect of anodization time is relatively small. SEM, X-ray diffraction (XRD), linear sweep voltammograms (LSV), and electrochemical impedance spectroscopy (EIS) results indicate that the morphology and crystal size of the catalytic coating, as well as the oxygen evolution potential of the electrode, are influenced by the pore size of TNTs arrays. The influencing mechanism of enhanced electrochemical activity by adjusting the architecture of TNTs arrays is investigated using X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and hydroxyl radicals (·OH) generation test. The results reveal a higher concentration of oxygen vacancies on the sample with a compact and smaller particle coating, indicating the presence of more adsorbed oxygen species. Consequently, this enhances the generation capacity of active radicals for organic matter degradation. The electrode featuring TNTs arrays with a length of 950 nm and a pore diameter of 100 nm exhibits the most effective remediation of phenol-containing wastewater, achieving approximately 92% ± 4.6% removal after a duration of 2 h. -
Figure 1 TNTs substrate architectures under different preparation conditions ((a) 15V-1h, (b) 15V-2h, (c) 15V-3h, (d) 20V-1h, (e) 20V-2h, (f) 20V-3h, (g) 25V-1h, (h) 25V-2h, (i) 25V-3h, (j) 30V-1h, (k) 30V-2h, (l) 30V-3h)
Figure 2 Contact angle of (a) Ti, (b) TNTs (15 V-2 h), (c) TNTs (20 V-2 h), (d) TNTs (25 V-2 h), (e) TNTs (30 V-2 h), (f) TNTs (25 V-1 h) and (g) TNTs (25 V-3 h)
Figure 3 SEM images of (a) Ti/SnO2-Sb, (b) TNTs (15 V)/SnO2-Sb, (c) TNTs (20 V)/SnO2-Sb, (d) TNTs (25 V)/SnO2-Sb electrode, (e) TNTs (30 V)/SnO2-Sb electrode
Figure 4 XRD patterns of (a) TNTs (25 V) substrate and (b) TNTs/SnO2-Sb electrodes with different substrate preparation voltages
Figure 6 EIS spectrums of TNTs/SnO2-Sb electrodes with different substrate preparation voltages
Figure 7 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)
Figure 9 XPS patterns of the fitted curves of O 1s and Sb 3d of electrodes prepared by different voltages
Figure 10 EPR spectra of TNTs/SnO2-Sb electrodes with different substrate preparation voltages
Figure 11 The hydroxyl radicals generation ability on the SnO2-Sb electrode with different substrate preparation voltages
Figure 12 The quenching experiment of the active radicals on the SnO2-Sb electrodes with different substrate preparation voltages
Table 1 Effect of preparation conditions for TNTs arrays on the average crystal size of SnO2-Sb calculated by Scherrer formula
Sample Crystallite size/nm Ti/SnO2-Sb 23±0.3 TNTs (15 V)/SnO2-Sb 20±0.3 TNTs (20 V)/SnO2-Sb 17±0.4 TNTs (25 V)/SnO2-Sb 15±0.3 TNTs (30 V)/SnO2-Sb 13±0.4 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[30]. 
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Table 2 EIS fitting results of TNTs/SnO2-Sb electrodes with different substrate preparation voltages
Sample Rs/Ω Ch/F Rh/Ω Ct/F Rt/Ω Ti/SnO2-Sb 4.72 5.33×10−8 49.3 2.02×10−5 49 TNTs (15 V)/SnO2-Sb 4.71 5.62×10−8 47.6 2.06×10−5 48 TNTs (20 V)/SnO2-Sb 4.69 5.84×10−8 46.9 2.11×10−5 47 TNTs (25 V)/SnO2-Sb 4.67 6.33×10−8 44.3 2.20×10−5 45 TNTs (30 V)/SnO2-Sb 4.74 6.12×10−8 45.4 2.16×10−5 46
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Table 3 Effect of preparation voltage of TNTs arrays on the contact angle of substrate surface and loading amount of SnO2-Sb
Sample Contact angle/(°) Loading amount/(mg·cm−2) Ti 52 2.05±0.05 TNTs (15 V-2 h) 43 2.15±0.04 TNTs (20 V-2 h) 34 2.24±0.04 TNTs (25 V-2 h) 13 2.36±0.03 TNTs (30 V-2 h) 10 2.42±0.02
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Table 4 XPS analysis of TNTs/SnO2-Sb electrodes with different substrate preparation voltages
Sample Binding energy/eV Oads
(at% = $\dfrac{\rm{O}_{\mathrm{a}\mathrm{d}\mathrm{s} }}{\mathrm{S}\mathrm{n} + \mathrm{S}\mathrm{b} + \mathrm{O}_{\mathrm{a}\mathrm{d}\mathrm{s}} + \mathrm{O}_{\mathrm{l}\mathrm{a}\mathrm{t} }}$ × 100% )Atom ratio of Olat/(Sn + Sb) Sn 3d5/2 Sb 3d5/2 Oads Olat Control 486.91 530.89 532.03 530.73 14.6 2.65 15 V 486.84 530.90 531.98 530.69 17.9 2.41 20 V 486.46 531.19 531.96 530.64 19.8 2.18 25 V 486.21 531.12 531.89 530.55 25.6 1.88 30 V 486.35 530.94 531.91 530.59 23.2 1.97
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Table 5 The computed result from the quenching experiment
Sample The contribution to phenol degradation/% ·O2 − ·OH Control 42.1 74 15 V 45.7 76.3 20 V 47 79 25 V 50.5 84 30 V 48.6 81
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