吸电子基团对5-羟色胺衍生物缓蚀性能的增效机理

目的 减缓碳钢在盐酸(HCl)溶液中的腐蚀，揭示吸电子基团(羧基)增效5-羟色胺缓蚀性能的机理。方法 采用动态质量损失、动电位极化曲线与电化学阻抗谱(EIS)考察1mol/L盐酸(HCl)溶液中5-羟色胺(5-HT)与5-羟色氨酸(5-HTP)对20#钢的缓蚀性能。通过吸附等温拟合，明确两种物质在碳钢表面的吸附行为本质。借助形貌观察，验证5-HT与5-HTP对碳钢的缓蚀性能。基于密度泛函理论(DFT)，计算并比较两种物质的差分电荷密度。结果 5-HT与5-HTP均可有效减缓20#钢在1mol/L HCl溶液中的腐蚀速率，缓蚀率与添加浓度和环境温度密切相关。298K下添加1mmol/L 5-HT与5-HTP时，缓蚀率分别达到92.19%与95.76%。极化曲线结果显示，向腐蚀介质中加入两种物质后，腐蚀电流密度均降低。EIS结果表明，添加5-HT与5-HTP后，界面电荷转移电阻得到提升。两种物质在碳钢表面的吸附符合Langmuir等温吸附模型。对比动力学与阻抗参数发现，HCl溶液中，5-HTP对20#钢的缓蚀性能优于5-HT。DFT计算结果显示，5-HT质子化位点呈缺电子状态，而质子化5-HTP的电子密度均匀分布于整个分子骨架。结论 羧基的吸电子效应可促进5-HTP分子中富电子区域将盈余电荷流入质子化位点，从而使电子密度均匀分布于分子骨架。均匀的电子密度分布有利于5-HTP以平行构型吸附于碳钢表面，最大限度覆盖活性位点，并高效缓蚀。

Enhancing Mechanism of Electron-withdrawing Group for theCorrosion Inhibition of 5-Hydroxytryptamine Derivatives

The work aims to reduce the corrosion of carbon steel in HCL solution and disclose the enhancing mechanism of corrosion inhibition of electron-withdrawing group (carboxyl) for 5-hydroxytryptamine (5-HT). Dynamic weight loss, potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) measurements were performed to explore the corrosion inhibition effect of 5-HT or 5-hydroxytryptophane (5-HTP) for 20# carbon steel in 1mol/L HCl solution. By adsorption isotherm fitting, the nature of adsorption behavior of the two substances on carbon steel surface was clarified. Surface morphology was observed to verify the corrosion inhibition effect of 5-HT and 5-HTP for carbon steel. Based on density functional theory (DFT), the difference in deformation charge density between 5-HT and 5-HTP was calculated and compared. The corrosion rate of 20# carbon steel in 1mol/L HCl solution could be reduced effectively by 5-HT and 5-HTP and closely related to concentration and environment temperature. When 1 mmol/L 5-HT and 5-HTP were added at 298 K, the inhibition efficiency reached 92.19% and 95.76%, respectively. Potentiodynamic polarization revealed that after 5-HT and 5-HTP were added in corrosion medium, the corrosion current density reduced. In addition, as explained by EIS data, the interfacial charge transfer resistance was significantly enhanced in the presence of 5-HT and 5-HTP. The adsorption of 5-HT and 5-HTP on steel surface followed Langmuir isotherm model. Through comparison of dynamics and impedance parameters, 5-HTP had better corrosion inhibition effect than 5-HT for carbon steel in HCl solution. The outcomes of DFT calculations indicated that the protonation sites of 5-HT were electron deficient, while the electron density of protonated 5-HTP was uniformly distributed throughout the molecular skeleton. The electron-withdrawing effect of carboxyl group can promote the surplus charge to flow into protonation sites in the electron-rich region of 5-HTP molecule, so that the electron density is uniformly distributed in the molecular skeleton. Uniform electron density distribution is beneficial to the adsorption of 5-HTP on the surface of carbon steel in parallel configuration, covering the active sites to the maximum extent, and inhibiting corrosion efficiently.