8-羟基喹啉缓蚀剂在镁表面吸附的理论研究

Theoretical Study on Adsorption of 8-hydroxyquinoline Inhibitor on Magnesium Surface

8-羟基喹啉(8HQ)是常见的用于镁合金表面腐蚀防护的缓蚀剂,为了从理论上探讨其缓蚀机理,采用密度泛函理论进行量子化学计算。运用Materials Studio中的DMol3程序分析了8HQ分子的结构和性质(键长、键角、电荷、红外光谱、热力学性质、反应活性及稳定性)及其在Mg(001)表面的吸附能力。结果表明,通过键长和键角的计算,得到C—N键键长较短,推测喹啉环中C—N键更难断裂。缓蚀剂的前线轨道密度分布主要在N原子及与喹啉环相连的羟基上,还有喹啉环上的C上,可以预测缓蚀剂分子在金属表面的吸附反应位点主要在此部位。通过红外光谱和不同温度下的热力学性质,分析了缓蚀剂分子的振动光谱,热力学结果显示该分子的气态热容、熵、焓等热力学性质与温度之间存在函数关系。通过对8HQ分子在Mg(001)表面的吸附能,证实了吸附位点主要是N和O原子且吸附自发进行。

8-hydroxyquinoline(8HQ)is a common corrosion inhibitor used for surface corrosion protection of magnesium alloys.In order to theoretically explore its mechanism,quantum chemical calculations were performed using Density Functional Theory(DFT).The structure and properties(bond lengths,bond angles,charges,infrared spectra,thermodynamic properties,reaction activity,and stability)of the 8HQ molecule and its adsorption on the Mg(001)surface were analyzed using the Dmol3 program.The results show that through the calculation of bond length and bond angle,the C—N bond length is shorter,suggesting that the C—N bond in the quinoline ring is more difficult to break.The distribution of frontier orbital density of the corrosion inhibitor molecule is mainly on the N atom and the hydroxyl group connected to the quinoline ring,as well as on the C atom,which can predict that the main adsorption reaction site of the corrosion inhibitor molecule on the metal surface is at this location.Through the analysis of the vibrational spectrum of 8HQ by infrared spectroscopy and thermodynamic properties at different temperatures,it was found that there is functional relationship between the thermodynamic properties such as gas heat capacity,entropy,and enthalpy of the molecule and temperature.The adsorption energy of the 8HQ on the Mg(001)surface confirmed that the adsorption sites are mainly N,O atoms and the adsorption proceeds spontaneously.