STUDY ON SYNTHESIS OF POLYPYRROLE MEMBRANES AND THEIR CORROSION PROTECTION ABILITY FOR SOME ACTIVE METALS (Fe, Zn, Al)

New contributions of the thesis The synthesis of PPy films on low carbon steel with the simultaneous use of dopinganions such as salicylate and molybdate has improved the metal protecti

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF EDUCATION

-LE VAN KHOE

STUDY ON SYNTHESIS OF POLYPYRROLE MEMBRANES AND THEIR CORROSION PROTECTION ABILITY FOR

SOME ACTIVE METALS (Fe, Zn, Al)

Specialized : Organic Chemistry

SUMMARY OF DOCTORAL THESIS IN CHEMISTRY

The work was completed at:

Department of Organic Chemistry - Faculty of Chemistry - Hanoi National

University of Education

Scientific supervisor: 1 Associate Professor, Dr Vu Quoc Trung

2 Associate Professor, Dr Ngo Xuan Luong

Reviewer 1: Prof Dr Pham Quoc Long, Institute of Chemistry of NaturalCompounds, Vietnam Academy of Science and Technology

Reviewer 2: Assoc Prof Dr Tran Manh Tri, University of Natural Sciences,Vietnam National University, Hanoi

Reviewer 3: Assoc Prof Dr Duong Quoc Hoan, Hanoi National University ofEducation

The thesis will be defended before the School-level Thesis Evaluation Council

meeting at Hanoi National University of Education

at … hour …day …month…year…

Thesis can be found at the library:

National Library, Hanoi

Or Hanoi National University of Education Library

Metals and alloys have many valuable mechanical, chemical and physical properties,especially metals and alloys of aluminum, iron, zinc, etc Therefore, they are used for manyapplications and play a leading role in most fields, such as in industry and in our daily lives.Metals are present in all products from complex equipment such as airplanes, cars, etc tosimple things such as toys, cooking utensils, etc All metal products during use are exposed

to humid air or other strong corrosive environments such as seawater, acids, etc Therefore,the process of corrosion on the metal surface always occurs Therefore, the control andlimitation of metal corrosion is of great significance and importance worldwide, especially

in areas with long coastal areas such as Vietnam In fact, there are many ways to protect andprevent corrosion such as: cathode protection, anode protection, using corrosion inhibitors,forming insoluble substances on the metal surface and forming a passive layer, paintingorganic coatings on the metal surface The effective method used is mainly to create anti-corrosion coatings, forming a barrier layer to prevent contact between the metal to beprotected and the corrosive environment In fact, chromium coatings have a very goodcorrosion inhibitory effect However, most chromium compounds in the coating, whenwashed away, cause damage and seriously affect the environment, which has encouragedscientists to constantly research to find more environmentally friendly anti-corrosioncompounds In recent years, many new materials have been researched and used toovercome the above situation, in which conjugated conductive polymers have been widelystudied and researched due to their non-toxic, environmentally friendly, highly stable andeasy-to-synthesize properties, being the most promising coating to protect and minimize thecorrosion process of industrial metals There are many works published in the years 2018 -

2023 that have proven this Especially with PPy coatings, the research direction is to makeanti-corrosion coatings, replacing chromium-containing coatings, which are highly topical,there are still many issues that need to be further clarified From the above analysis thetopic: “Study on the synthesis of PPy films and their anti-corrosion ability for some activemetals (Fe, Zn, Al)” was chosen as the research topic of the thesis

Objectives of the thesis

Successfully synthesize PPy films on low carbon steel (PPy/Fe), Zn (PPy/Zn), Al(PPy/Al) with suitable anion corrosion inhibitor systems Determine the characteristics andstructure of anion-doped PPy films on active metals using SEM imaging, infraredspectroscopy, and Raman spectroscopy Evaluate the anti-corrosion protection ability ofPPy films after being doped on Fe, Al, Zn metal substrates Propose a suitable mechanismfor the anti-corrosion protection effect of anion-doped PPy films

Contents of the thesis

 Introduction: General introduction and objectives of the thesis

 Overview of the thesis: Overview of issues on the history of the birth and basic

properties of conductive polymers, preparation methods and their applications in activemetal corrosion protection Mainly works using PPy synthesized in aqueous and non-aqueous environments

 Experimental conditions: Methods to determine the structural morphology,

composition, and thermal stability of PPy films such as: scanning electronmicroscopy (SEM), thermal analysis (TGA), combined scattering (Raman), infraredspectroscopy (FTIR), energy-dependent X-ray scattering (EDX) Electrochemicalmethods to synthesize and study the corrosion process such as: Constant current,constant potential, CV spectroscopy, open circuit potential over time (OCP), Tafelpolarization curve (IE), Impedance spectroscopy (EIS) Salt spray method

 Results and discussion: From the experimental results, using the research method

mentioned above, we analyzed and evaluated the structural morphology of PPyfilms, the ability to protect and self-protect against corrosion of PPy films

 Conclusion: State the main results achieved

 Scientific and practical significance of the thesis

Most metal products are corroded during use due to exposure to humid air or other strongcorrosive environments such as seawater, acid, etc Therefore, scientists are making greatefforts to control and limit metal corrosion Chromium coating has a very good corrosioninhibitory effect However, most chromium-containing compounds in the coating, whenwashed away, cause damage and seriously affect the environment Conjugated conductivepolymer coatings have been widely studied and researched due to their non-toxic,environmentally friendly, high stability and easy synthesis properties, and are the mostpromising coatings to protect and minimize the corrosion process of industrial metals Inwhich, PPy coatings have emerged with many advantages over other conductive polymercoatings Therefore, the successful synthesis of PPy films on low carbon steel (PPy/Fe), Zn(PPy/Zn), Al (PPy/Al) with a suitable corrosion inhibitor anion system has high scientificand practical significance

New contributions of the thesis

The synthesis of PPy films on low carbon steel with the simultaneous use of dopinganions such as salicylate and molybdate has improved the metal protection performancecompared to films when not using or using only one doping anion such as salicylate,

The successful synthesis of PPy film on aluminum metal substrate, especially on zincmetal substrate with 3-Nisa doped anion, has not been mentioned much in previous works,especially with 3-Nisa doped anion, which has increased the anti-corrosion protection effectfor these two metals The OCP measurement results showed a protection time of up to morethan 300 hours, much larger than the use of other doped anions previously published.

CHAPTER I: OVERVIEW

1.1 Introduction to conductive polymers

1.1.1 History of conductive polymers

1.1.2 Electronic structure and conductivity of conductive polymers

1.1.3 Characteristics of conductive polymers

1.1.4 Methods of synthesizing conductive polymers

1.2 Polypyrrole (PPy)

1.2.1 Properties of PPy

1.2.2 Methods of synthesizing PPy

1.3 Corrosion protection ability of PPy

1.3.1 General introduction to corrosion

1.3.2 Mechanism of anti-corrosion protection of metals by conductive polymers

1.3.3 Role of impurity anions

1.3.4 Overview of polymer nanocomposites

1.3.5 Current studies on synthesis and anti-corrosion protection of PPy

Comment: It can be seen that the research on PPy membranes for the purpose of

preventing metal corrosion is of great interest in the world as well as in Vietnam The groups all follow the direction of creating membranes with the support of doped anions such as oxalate, salicylate, dodecylsulfonate which have improved the anti-corrosion protection ability of PPy membranes However, the number of published works by the research groups is not much; the protection time of PPy membranes is not long and mainly focuses on iron metal substrates, there are not many research works for other active metal substrates such as zinc and aluminum There are not many published works on finding new doped anions to improve the anti-corrosion protection ability of PPy membranes Therefore, in this thesis, we will research and develop PPy coatings doped with suitable anions to improve the protection ability for iron metal substrates and especially for aluminum and zinc metal substrates.

CHAPTER II: EXPERIMENT 2.1 Chemicals, research samples, experimental equipment

2.2 Equipment used in the thesis

2.3 Equipment for synthesizing and studying the electrochemical properties of PPy membranes 2.4 Synthesis of PPy membranes.

2.4.1 Synthesis of PPy membranes on low carbon steel substrate

2.4.1.1 Synthesis of PPy/salicylate membranes on low carbon steel substrate

Through studying documents and from practical experiments, it is found that PPymembranes doped with sodium salicylate obtained when using 0.1M pyrrole, current density of1mA/cm2 give the best results The specific composition is presented in Table 2.2

Table 2.2: Composition of polymerized solution doped with salicylate on carbon steel

substrate ORDER Electrolyte

sample

Sodium salicylate (M)

Pyrrole (M)

Current density (mA/cm 2 )

2.4.1.2 Synthesis of PPy/salicylate/molybdate films on low carbon steel substrate

PPy films synthesized from 0.1M pyrrole with different doping ions are shown in Table 2.3

Table 2.3: Composition of polymerization solution doped with salicylate and

molybdate on carbon steel substrate Order Electrolyte

sample

Sodium salicylate (M)

Sodium molybdate (M)

Pyrrole (M)

Current density (mA/cm 2 )

2.4.1.3 Synthesis of PPy/Go nanocomposite membranes doped with salicylate and molybdate

Table 2.4: Solution composition used in the electrolysis of nanocomposite membranes

on carbon steel substrate Orde

r

Electroly

te sample

Pyrrole (M)

Salicylate (M)

GO(mg/L) Molybdate

(M)

Current density (mA/cm 2 )

2.4.2 Synthesis of PPy membrane on aluminum substrate

Table 2.5: Solution composition used in the electrolysis process on aluminum substrate Order Electrolyte sample 3-Nisa (M) Pyrrole (M) Current density (mA/cm 2 )

2.4.3 Synthesis of PPy/SiO2 nanocomposite in anti-corrosion paint for aluminum

2.4.3.1 Synthesis of PPy/SiO2 nanocomposite

Disperse 3 grams of SiO2 in 250 ml of solvent (isopropyl alcohol/water = 3/7) Add 3.5

ml of pyrrole to the mixture, stir with a magnetic stirrer for 25 minutes Dissolve 18 grams ofammonium persulfate in 50 ml of solvent (isopropyl alcohol/water = 3/7) and continue to addvery slowly to the mixture for about 10 minutes Let the reaction take place for about 3 hours,then filter and wash the product and vacuum dry for 24 hours at 500C to a constant mass Using

a mill, we get the PPy/SiO2 nanocomposite product in the form of a fine black powder

2.4.3.2 Synthesis of 3-Nisa-doped PPy/SiO2 nanocomposite

Disperse 3 grams of SiO2 in 250 ml of solution (isopropyl alcohol/3-Nisa = 3/7) Add 3.5 ml

of pyrrole to the above mixture, stir with a magnetic stirrer for 30 minutes Dissolve 18 grams ofammonium persulfate in 50 ml of solution (isopropyl alcohol/3-Nisa = 3/7) and continue to addvery slowly to the reaction mixture for about 10 minutes Carry out the reaction for about 3 hours,then filter and wash the product and vacuum dry for 24 hours at 500C to a constant mass to obtainthe 3-Nisa-doped PPy/SiO2 nanocomposite product (0.01 M; 0.005 M; 0.0025 M)

2.4.3.3 Creating a paint film on an aluminum substrate

Weigh 1 gram of nanocomposite particles (about 2%) evenly dispersed in 7.5 grams ofxylene solvent (about 15%) and conduct ultrasonic vibration for about 2 hours Add 24.9grams of X75 epoxy resin (about 48.8%) and continue ultrasonic vibration for about 2hours, stirring for 1.5 hours Add 16.6 grams of polyamine-polyamide curing agent (about33.2%), the mixture is mixed well and then brushed onto the aluminum substrate

2.4.4 Synthesis of PPy film on zinc substrate

Table 2.6: Electrolyte/PPy coating sample on Zn substrate Order Electrolyte

sample Pyrrole (M) 3-Nisa (M) Current density (mA/cm 2 )

2.6 Investigation of anti-corrosion protection ability

CHAPTER III: RESULTS AND DISCUSSION 3.1 Study on the structure and corrosion resistance of PPy films on carbon steel substrate

3.1.1 PPy/ salicylate films on carbon steel substrate

3.1.1.1 Electrochemical synthesis of PPy films

PPy films synthesized by electrochemical method of samples N1, N2, N3 are presented in

Table 2.2 and in Figure 3.1

Figure 3.1: Variation of potential over time during the synthesis of PPy on carbon steel

substrate of samples N1, N2, N3.

3.1.1.2 SEM image of PPy/salicylate film

Figure 3.2: SEM image of PPy/ salicylate film on carbon steel substrate.

3.1.1.3 Study on FTIR spectrum of PPy/ salicylate membrane

Figure 3.3: FTIR spectra of samples N1, N2, N3.

FTIR spectra analysis of samples N1 - N3 shows that in addition to the characteristicpeaks of PPy, there are also characteristic peaks of sodium salicylate This proves that thedoping process of salicylate ions has occurred

3.1.1.4 TGA characteristics of PPy/ salicylate films

Table 3.2: Thermal analysis spectra of samples N1, N2, N3.

Temperature ≤ 200 o C 200 – 500 o C 500 – 700 o C Remaining mass

3.1.1.5 Corrosion protection test

a OCP measurement results of PPy/ salicylate film

Figure 3.4: OCP of samples N1, N2, N3.

Table 3.3: OCP potential and protection time of the sample Sample Starting potential energy (V) Ending potential (V) Protection time (hours)

b Tafel curves of steel and samples N1, N2, N3

Figure 3.6: Polarization curves in 3% sodium chloride solution of carbon steel and

Conclusion: PPy membrane was successfully synthesized by electrochemical method

in sodium salicylate solution on carbon steel substrate The sample was examined by SEM, TGA, FTIR At the same time, the anti-corrosion role of PPy membrane was studied All electrochemical results such as OCP polarization, EIS and Tafel were reliable to confirm the role of salicylate reducing agent in corrosion protection With sodium salicylate doping anion with a concentration of 0.1M, the best results were obtained.

3.1.2 PPy/ salicylate/ molybdate membrane on carbon steel substrate

3.1.2.1 Synthesis of PPy/ salicylate/ molybdate membrane on carbon steel substrate

Figure 3.8 records the time-course response of PPy synthesis in solutions S1 and S2 at afixed current density of 1mA/cm2

Figure 3.8: Variation of potential over time during the PPy synthesis process in

samples S1, S2

3.1.2.2 SEM image of PPy/ salicylate/ molybdate film on carbon steel

On the SEM image of the doped PPy film in Figure 3.10, it can be observed that the PPy film formed on carbon steel is quite thin, smooth, black and uniform

Figure 3.10: SEM images of PPy films obtained in different solutions a) S1; b) S2

The successful incorporation of molybdate anion was also confirmed by EDX analysis.Elements such as carbon, oxygen, iron and molybdenum were detected in the PPy film as shown

3.1.2.3 FTIR spectra of PPy/Sa and PPy/Sa/Mo films

FTIR spectra of PPy/Sa and PPy/Sa/Mo films are observed in Figure 3.13

Figure 3.13: FTIR spectra of Ppy/Sa and Ppy/Sa/Mo films

3.1.2.4 Thermogravimetric analysis (TGA) of PPy/salicylate/molybdate films on carbon steel substrates

Figure 3.14: TGA curves of PPy/Sa (a) and PPy/Sa/Mo (b) films

3.1.2.5 Corrosion study of PPy/salicylate/molybdate films on carbon steel substrate

a OCP measurement results of PPy/salicylate/molybdate films on carbon steel substrate

The protective effect of doped PPy films on carbon steel was evaluated using OCP curves

Figure 3.15: OCP of PPy/Sa membrane (a); PPy/Sa/Mo membrane sample (b); Carbon

steel sample (c) in 3% sodium chloride solution with aeration.

b Salt spray results

Figure 3.16: Photographs of PPy/Sa films (a, b, c, d) and PPy/Sa/Mo films (e, f, g, h) on carbon steel after salt spray exposure for 0h (a, e); 3h (b, f); 9h (c, g); 21h (d, h)

c Tafel curves of PPy/ salicylate/molybdate films on carbon steel

The corrosion currents and potentials of samples S1, S2 in 3% sodium chloride solution areobserved in Figure 3.17

Figure 3.17: Tafel curves of carbon steel samples; PPy/Sa; PPy/Sa/Mo films in

3% sodium chloride solution Table 3.6: Potential and corrosion current of samples S1, S2 Sample Value E corr (V) Value I corr (A/cm 2 )

Conclusion: PPy films doped with molybdate and salicylate were successfully electroplated in

an electrolyte containing both dopants by a one-step process The obtained PPy/Sa/Mo films were smoother and thicker, and the adhesion was also better than that of PPy/Sa The results showed that other properties of PPy films were also improved by molybdate doping, such as morphology and thermal stability In particular, PPy/Sa/Mo coatings could protect low carbon steel from corrosion with both passive films on the metal surface Corrosion test results indicated that PPy/Sa/Mo coatings provided good protection to carbon steel from corrosion.