Investigations Of Phenothiazine Drugs As Corrosion Inhibitors On Copper In Dilute Sulfuric Acid Solution

Copper is a non-ferrous metal closely related to human beings.It is not only rich in natural resources,but also has remarkable thermal conductivity,machinability,ductility,wear resistance and other excellent properties.Compared with other metals,copper has low resistivity,which is applied to electrical,electronic industry,construction industry,defense industry and machinery manufacturing far and wide.Therefore,copper performs an exceedingly momentous role in our production and life.However,under extremely harsh conditions,copper is prone to severe corrosion,which will not only cause major economic losses(stop production loss,product loss,efficiency loss,product pollution,over-design),but also cause major accidents and waste of resources.Therefore,the corrosion and protection of metals has become a research focus in recent years.Corrosion inhibitor technology has the characteristics of high efficiency,quickness,easy operation,simple equipment,etc.It has made great achievements in protecting metal resources,reducing production accidents and product losses,and curbing environmental pollution.It has become a mature technology applied in the field of metal corrosion and protection.Due to the relatively high toxicity of traditional corrosion inhibitors,with the advancementof green chemistry and the strengthening of environmental awareness,the development and exploration of green and efficient corrosion inhibitors has become an important topic at present.In recent years,some clinically used drugs are considered as corrosion inhibitors,confirming that they have excellent corrosion resistance in acidic solutions.In this paper,four phenothiazine drugs are choosed as suitable corrosion inhibitors,because they are drugs that can be directly taken orally,with low toxicity,low price,and good solubility.The four drugs are perphenazine(PPZ),chlorpromazine(CPZ),dioxypromazine(DPZ),and promethazine(PZ).Through electrochemical experiment tests(AC impedance,potentiodynamic polarization curve),combined with morphological characterization(SEM),the anti-corrosion performance of the four drugs of copper in 0.5 M sulfuric acid solution was explored;Simultaneously,the adsorption isotherm equation is used to explain their adsorption behavior from the perspective of thermodynamics,and the surface analysis technology(FTIR,XPS)is used to further explore the adsorption mechanism.In the end,quantum chemical parameters are acquired via theoretical calculations,the relationship between molecular structure and corrosion inhibition effect can be theoretically analyzed,thereby comparimg the corrosion inhibition efficiency of the four substances,the following conclusions can be obtained:(1)It can be seen from the test results of electrochemical impedance and potentiodynamic polarization curve that all four phenothiazine drugs can slow down the corrosion of copper,and their corrosion inhibition effects all enhance with the increase of concentration,and they are all cathodic corrosion inhibitors.When the maximum concentration is 400mg/L,the corrosion inhibition efficiency reaches the maximum,respectively: PPZ is 94.9%,CPZ is 97.2%,DPZ is 94.4%,and PZ is 97.0%.In the two systems,the order of corrosion inhibition efficiency is: CPZ>PPZ,PZ>DPZ.The order of the corrosion inhibition efficiency of the four substances is:CPZ>PZ>PPZ>DPZ?(2)It can be seen from the analysis results of the scanning electron microscope that after adding the four corrosion inhibitors,the surface of the copper becomes smooth.This is due to the fact that the corrosion inhibitor adsorb on the surface to effectively inhibit the corrosion process of copper.And from the surface topography,it can be confirmed that the corrosion inhibition effect of CPZ is stronger than that of PPZ,and the corrosion inhibition effect of PZ is stronger than that of DPZ.(3)The impedance data is fitted by the adsorption isotherm equation.It is found that the four drugs are in line with the Langmuir adsorption model,and according to the calculated standard adsorption free energy,it shows that the adsorption type of the four drugs on copper is a combination of physical adsorption and chemical adsorption.(4)The research results of infrared analysis and X-ray photoelectron spectroscopy analysis can also confirm that the four phenothiazine drugs effectively adsorb on the copper surface and form strong coordination bonds with copper to protect the copper substrate from corrosion.(5)Theoretical calculations show that the corrosion inhibition effect of the corrosion inhibitor is closely related to its structure.Two drugs with different steric hindrance(PPZ,CPZ),compared with CPZ,PPZ has greater steric hindrance,and the repulsive force between molecules affects its adsorption,so CPZ is easier to adsorb and has a better corrosion inhibition effect.Two drugs(DPZ,PZ)with different active adsorption sites have N and S heteroatoms,but the S atom of DPZ has been occupied by two O atoms,thereby cannot form a bond with copper,but PZ protects copper through the joint action of N-Cu and S-Cu,therefore,the corrosion inhibition effect of PZ is better.According to the molecular dynamics simulation,the adsorption binding energy of the corrosion inhibitor molecules on the Cu(111)crystal plane in a parallel manner shows that the binding energies of the four substances are: PPZ is 155.84 KJ/mol,CPZ is 157.93 KJ/mol,DPZ is 130.96 KJ/mol,and PZ is 143.31 KJ/mol.Theoretically,it can also explain the corrosion inhibition efficiency: CPZ>PPZ,PZ>DPZ.(6)Based on the above experimental investigation,the comparison of the corrosion inhibition efficiency of the four substances shows that under the same matrix,the size of the steric hindrance,the number of heteroatom adsorption sites,and the substituents may all affect the corrosion inhibition performance.The large steric hindrance of organic molecules makes it more difficult to adsorb.Halogen-substituted substances have better corrosion inhibition performance than their bulk.Corrosion inhibitors with multiple active adsorption sites of N and S heteroatoms involved in bonding have better corrosion resistance.