吸电子基团对5-羟色胺衍生物缓蚀性能的增效机理

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

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1 mol/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1 mol/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。298 K下添加1 mmol/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。

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 1 mol/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 1 mol/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.