Rani At Jeeja, Thomas Asha, Kuruvilla Mathew, Arshad Muhammed, Joseph Abraham
Department of Chemistry, University of Calicut Kerala-673 635 India
St. Thomas College, Ranni Pathanamthitta Kerala India.
RSC Adv. 2022 May 12;12(23):14328-14341. doi: 10.1039/d2ra02109a.
This study evaluates the corrosion inhibition property of the aqueous and alcoholic leaf extracts of the medicinal plant . The major components in the extracts are thymohydroquinone dimethyl ether (THQ) and coumarin. It is clear from the weight-loss studies that the water extract of the leaves (AYW) is superior to the alcoholic extract (AYA) in terms of offering corrosion inhibition. The 96% efficiency of 4% (v/v) AYW in 0.5 N HCl at room temperature changes to 84.62% at 323 K. The mixed-type inhibition behaviour of AYW shows slight dominance in the anodic direction. Studies suggest the multilayer adsorption of phytochemicals on the metal surface and that the adsorption follows the Temkin model. Theoretical studies using DFT and BIOVIA Materials Studio investigations establish THQ as a good inhibitor with high adsorption characteristics. Even though the concentration of coumarin in the extract is low, its presence in the extract facilitates the adsorption of THQ on the metal surface, which is evident from the MD simulation study. The changes in the surface topography and elemental composition of the metal specimen in the inhibited and uninhibited solution are monitored by SEM and EDX spectral studies. XPS data support the presence of both THQ and coumarin on the metal surface and the existence of co-ordinate bonding between the metal's d orbital and the O atoms of THQ. Theoretical and experimental studies support the mixed mode of adsorption of THQ as physisorption followed by chemisorption.
本研究评估了该药用植物水提取物和醇提取物的缓蚀性能。提取物中的主要成分是百里氢醌二甲醚（THQ）和香豆素。从失重研究中可以明显看出，就提供缓蚀作用而言，叶的水提取物（AYW）优于醇提取物（AYA）。4%（v/v）的AYW在室温下于0.5 N HCl中的缓蚀效率为96%，在323 K时变为84.62%。AYW的混合型缓蚀行为在阳极方向上表现出轻微优势。研究表明植物化学物质在金属表面存在多层吸附，且吸附遵循Temkin模型。使用密度泛函理论（DFT）的理论研究以及BIOVIA Materials Studio研究确定THQ是具有高吸附特性的良好缓蚀剂。尽管提取物中香豆素的浓度较低，但从分子动力学（MD）模拟研究可以明显看出，其在提取物中的存在促进了THQ在金属表面的吸附。通过扫描电子显微镜（SEM）和能谱仪（EDX）光谱研究监测了金属试样在有缓蚀剂和无缓蚀剂溶液中表面形貌和元素组成的变化。X射线光电子能谱（XPS）数据支持金属表面存在THQ和香豆素，以及金属的d轨道与THQ的O原子之间存在配位键。理论和实验研究支持THQ的混合吸附模式，即先为物理吸附，后为化学吸附。
