Abstract For this study, the electrochemical oxidation of lignin was investigated at the surfaces of electrochemically (EC) reduced TiO2 nanotube arrays. The effects of nanotube lengths on the lignin oxidation were explored by growing the nanotubes with different lengths through anodization. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and electron paramagnetic resonance (EPR) techniques were employed to characterize the fabricated TiO2 nanotubes. The electrochemical behaviors of the nanotubes before and after the EC treatment were assessed by various electrochemical methods, including cyclic voltammetry (CV), chronopotentiometry (CP), and impedance spectroscopy. The TiO2 nanotubes were treated by applying a cathodic current (5 mA cm−2) for 10 min, which significantly increased its electrocatalytic activity. It was also determined that the nanotube length was linearly increased with the increase of the anodization time, and that the longer the nanotubes and the larger the double layer capacitance. The length of the nanotubes had a significant effect on the level of lignin oxidation, and an optimal TiO2 nanotube length that enabled the most efficient oxidation of lignin was determined. The efficiency of the TiO2 electrodes towards the oxidation of lignin was also compared to a Pt electrode. The TiO2 nanotubes that were grown for 16 h by anodization with ~13.5 μm length exhibited the lowest impedance and the highest lignin oxidation efficacy. The total organic carbon (TOC) of the lignin solution under different oxidation times was also measured to further evaluate the efficiency of the electrochemical degradation of lignin, and 70% TOC removal was achieved in 3 h. The TiO2 electrodes were shown to outperform the Pt electrode in all the lignin oxidation studies. Moreover, the activation energy required for the electrochemical oxidation of lignin was investigated by performing the oxidation under various temperatures and found to be 21.0 kJ mol−1. The EC reduced TiO2 nanotube electrode showed high activity and stability, promising for environmental applications.

中文翻译：

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木质素在电化学还原的 TiO2 纳米管上的电化学氧化

摘要 在本研究中，研究了电化学 (EC) 还原的 TiO2 纳米管阵列表面木质素的电化学氧化。通过阳极氧化生长不同长度的纳米管，探讨了纳米管长度对木质素氧化的影响。采用扫描电子显微镜 (SEM)、X 射线光电子能谱 (XPS)、能量色散 X 射线光谱 (EDS) 和电子顺磁共振 (EPR) 技术来表征制备的 TiO2 纳米管。通过各种电化学方法评估 EC 处理前后纳米管的电化学行为，包括循环伏安法 (CV)、计时电位法 (CP) 和阻抗谱。通过施加阴极电流 (5 mA cm−2) 10 分钟来处理 TiO2 纳米管，显着提高了其电催化活性。还确定纳米管长度随着阳极氧化时间的增加而线性增加，并且纳米管越长，双电层电容越大。纳米管的长度对木质素氧化水平有显着影响，并且确定了能够最有效地氧化木质素的最佳 TiO2 纳米管长度。TiO2 电极对木质素氧化的效率也与 Pt 电极进行了比较。通过阳极氧化生长 16 小时且长度约为 13.5 μm 的 TiO2 纳米管表现出最低的阻抗和最高的木质素氧化效率。还测量了不同氧化时间下木质素溶液的总有机碳 (TOC)，以进一步评估木质素电化学降解的效率，3 小时内 TOC 去除率达到 70%。在所有木质素氧化研究中，TiO2 电极的性能均优于 Pt 电极。此外，通过在不同温度下进行氧化研究木质素电化学氧化所需的活化能，发现为 21.0 kJ mol-1。EC 还原的 TiO2 纳米管电极显示出高活性和稳定性，有望用于环境应用。通过在不同温度下进行氧化研究木质素电化学氧化所需的活化能，发现为 21.0 kJ mol-1。EC 还原的 TiO2 纳米管电极显示出高活性和稳定性，有望用于环境应用。通过在不同温度下进行氧化研究木质素电化学氧化所需的活化能，发现为 21.0 kJ mol-1。EC 还原的 TiO2 纳米管电极显示出高活性和稳定性，有望用于环境应用。