Influence of biomacromolecule DNA corrosion inhibitor on carbon steel

Accepted Manuscript Title: Influence of biomacromolecule DNA corrosion inhibitor on carbon steel Authors: Ke Hu, Jia Zhuang, Jiating Ding, Zhu Ma, Fang Wang, Xianguang Zeng PII: DOI: Reference:

S0010-938X(17)30287-1 http://dx.doi.org/doi:10.1016/j.corsci.2017.06.004 CS 7108

To appear in: Received date: Revised date: Accepted date:

18-2-2017 31-5-2017 5-6-2017

Please cite this article as: Ke Hu, Jia Zhuang, Jiating Ding, Zhu Ma, Fang Wang, Xianguang Zeng, Influence of biomacromolecule DNA corrosion inhibitor on carbon steel, Corrosion Sciencehttp://dx.doi.org/10.1016/j.corsci.2017.06.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Influence of biomacromolecule DNA corrosion inhibitor on carbon steel Ke Hu1, Jia Zhuang *1, Jiating Ding2 , Zhu Ma1, Fang Wang1, Xianguang Zeng3 1. School of Materials Science and Engineering, Southwest petroleum university, Chengdu610500, China; 2. College of Physics and technology Engineering, Guangxi University, Nanning530004, China; 3. Material Corrosion and Protection Key Laboratory of Sichuan province, Zigong643000, China. *Corresponding

author: E-mail: [email protected]. Tel:86-028-8303-7409

Highlights 

Biomacromolecule DNA was used as a mixed-type corrosion inhibitor.



The corrosion inhibition efficiency of DNA on reached 91.9% in 1 M HCl.



Analysis of adsorption mechanism with Langmuir isotherm, FT-IR and XPS.



Structural-property relationship of inhibitors revealed by quantum chemical calculation.

Abstract: The biological macromolecule DNA was used as green corrosion inhibitor to protect X80 carbon steel against 1M HCl solution, and the corrosion behavior was systematically investigated by weight loss, electrochemical measurements, FTIR, and quantum chemistry calculation et al. The results showed that the maximum inhibition efficiency of compound DNA reached 91.9%. It was found that the chemisorption of DNA inhibitor on carbon steel surface resulted from single-molecular-layer self-assembly. The theoretical calculation verified the relationship between

1

the DNA molecular structure and the corrosion inhibition efficiency. The results further demonstrated that the DNA was a promising environment-friend inhibitor with effective inhibition efficiency.

Keywords: DNA; Corrosion inhibitor; Chemisorption; Quantum chemical calculations;

1. Introduction Corrosion prevention is an important issue for industrial application of materials. Among numerous corrosion prevention measures, corrosion inhibition possesses advantages of economy, high-efficiency, and facile-feasibility, and has been widely applied in various fields [1-4]. The corrosion inhibitor is a chemical compound which adheres to material surface or forms an uniform protective film against the corrosive agents in the environment. Inorganic inhibitors are widely used in industries to control corrosion. However, some inorganic inhibitors, such as chromate and nitrite, have been found toxic to human and easily result in environment pollution [5]. Therefore, the exploration of effective inhibitor with environment-friend property becomes a critical issue, which has attracted tremendous attention [4, 6]. Organic inhibitors are promising alternative strategy, which normally contain heteroatoms (N, O, S, and P), heterocyclic rings, polar functional groups or conjugated double bonds. The organic inhibitor can easily adsorbs on the metal surface by electrostatic interaction between inhibitor and metal (physical adsorption) or by coordinate covalent bonds (chemical adsorption) [6-10]. Recently, pollution-free organic inhibitors, such as natural organic materials, have been highlighted as a candidate to conventional organic inhibitors due to their high corrosion inhibition efficiency, environmental-friend and low cost. Zhuang and Deng et al. synthesized several amino acid derivatives and investigated their corrosion inhibition efficiency. The corresponding corrosion experimental results showed that these derivatives exhibited good corrosion inhibition performance [11, 12]. Fares et al. used natural pectin molecules as inhibitor, and they also built adsorption model to explain the mechanism of corrosion inhibition [13]. Biswas et al. studied the xanthan gum and its graft copolymer as corrosion inhibitor for carbon steel in acidic medium by using the frontier orbital theory. The results of theoretical calculation indicated that this novel 2

bio-inhibitor was able to donate electrons to the metal surface. The HOMO and LUMO of inhibitor were mainly distributed around the polar groups which contain oxygen atoms [14]. Although the natural pollution-free organic inhibitor exhibited effective corrosion inhibition on metal, performance of these inhibitors was still limited by the quantity of polar groups with N, O, and S atoms in molecule. As known, the biological macromolecule is not only environmental-friend materials, but also has more polar groups with coordination atoms, compared to above-mentioned organic inhibitors. Sufficient coordination atoms of bio-macromolecules may lead to stronger adsorption on carbon steel surface. The metal surface can be covered with compact bio-macromolecules film and the amount of corrosion inhibitor can be significantly reduced. Moreover, the inhibition mechanism of green biological macromolecules is rarely developed. Here, for the first time, a novel bio-macromolecule inhibitor, deoxyribonucleic acid (DNA), was used to protect API 5L X80 steel corrosion in 1 M HCl solution by fabricating compact inhibitor film. As expected, the DNA inhibitor exhibited good corrosion inhibition efficiency (91.6%) with the optimized inhibitor concentration. Further characterization, such as weight loss measurement, electrochemical methods, fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and theoretical calculations, were carried out to systematically reveal the inhibition ability and the working mechanism of DNA inhibitor.

2. Experimental part 2.1. Materials The test reagents with analytical grade (AR) and salmon sperm DNA (high purity grade) were bought from Chengdu Kelong Chemical Co., LTD, and Shanghai Aladdin Bio-Chem Technology Co., LTD. The concentration range of DNA employed was 5 mg·L-1-20 mg·L-1. The chemical compositions of X80 steel sample (wt.%) are C(0.065%), P(0.011%), S(0.0028%), Si (0.24%), Mn(1.58%), Nb(0.057%), V(0.005%), Ti(0.024%), Cr(0.022%), Cu(0.01%), B(0.0006%) and Fe(remainder). The X80 steel specimens (length=3.0 cm, width=2.0 cm, thickness=0.2 cm) were pre-treated prior to the experiments by grinding with emery paper SiC (400#, 600#, 800# and 1000#), subsequently rinsed by acetone and ethanol, and stored in a desiccator for drying. 1 M 3

HCl solutions of corrosive media were prepared by diluting AR grade 37% HCl into distilled water. 2.2. Weight loss measurements The gravimetric measurements were performed according to the standard methods [15]. Firstly, the specimens were weighted using an analytical balance (precision ± 0.1 mg). After weighing accurately, the specimens were immersed in 250 mL beakers which containing 200 mL 1 M HCl within and without a series of concentrations inhibitors at definite time interval of 72 h at 303K. And then the steel specimens were taken out, carefully rinsed with bidistilled water, ultrasonic cleaned in acetone, dried at room temperature and then weighted. The average weight loss of steel specimens with same treatments were used to calculate the corrosion rate (Vcorr), and the corrosion inhibition efficiency (η1%) was calculated by using the following equations [16, 17]:

Vc o r  r

1 (%) 

W0  Wt S t

(1)

* Vcorr  Vcorr 100 Vcorr

(2)

where W0 and Wt are the weight loss values in absence and presence of inhibitor, respectively. S is the surface area (cm2) of the specimen, t is the immersion time (h), Vcorr and V*corr are the values of corrosion rate (mg·cm-2·h-1) in uninhibited and inhibited solutions, respectively. 2.3. Electrochemical measurements The electrochemical experiments were carried out using a conventional three electrode system. The X80 steel sheets with 1 cm2 exposed surface area were used as working electrode. The platinum electrode and saturated calomel electrode (SCE) were used as auxiliary electrode and the reference electrode, respectively. An Ag/AgCl (3 M KCl) electrode was used as the reference electrode. All potential values in this paper were referred to the SCE. Electrochemical measurements were carried out on the CHI660D electrochemical work-station (Shanghai Chenhua Instrument Co., LTD.). During the experiments, the test solutions were exposed in atomsphere and the temperature was thermostatically controlled at 303 K. Before performing the electrochemical measurements, the working electrode were immersed in 1 M HCl solution with and without various concentrations of DNA for 1 h to establish a steady state open circuit potential (OCP). The potentiodynamic polarization curves were obtained from -800mV to -200 mV (vs. SCE) with a 4

scan rate of 1 mV·s-1. In addition, the electrochemical impedance spectroscopy (EIS) experiments were carried out in between highest frequency limit of 100 kHz and lowest frequency limit of 0.01 Hz at open circuit potential with amplitude of 10 mV using AC signal. All the experiments were performed in triplicate and average values were obtained. 2.4. Scanning electron microscopy studies The X80 steel discs were immersed in unstirred 1 M HCl solutions without and with addition of 20 mg·L-1 DNA for 72 h at 303 K. And then, the specimens were washed with distilled water, dried in cold air. The surface morphology of specimens was observed using a Scanning Electron Microscope (SEM) (EVO MA15, Carl Zeiss AG, Germany). 2.5. X-ray photoelectron spectroscopy (XPS) XPS measurements were performed based on a XPS KRATOS, AXIS Ultra DLD spectrometer with a monochromated Al-Kα X-ray source（hv = 1486.6 eV, 200 W）and an X-ray beam of around 1 mm in ultrahigh vacuum conditions (base pressure P~2×10-7 Pa). Pass energies of 20 eV and 50 eV were used for detection and high resolution measurements. The spectrometer was calibrated against C 1s at 284.8 ± 0.1 eV. Quantification and simulation of the photo peaks was analyzed using the Casa XPS software in a computer system. Sample for measurement was prepared as follow: The X80 steel sheet was immersed in 1 M HCl solution containing 20 mg·L-1 DNA for 72 h, rinsed with ultra-purity water and dried using cold air. The organic powder was scraped off from steel surface and collected using double sided adhesive tape which base on an aluminum substrate. 2.6. Quantum chemical calculations Quantum chemical calculations were performed with DMol3 module which based on density function theory (DFT) in Materials Studio7.0 software from Accelrys Inc [18]. The generalized gradient approximation (GGA)/Becke exchange plus Lee-Yang-Parr (BLYP) method was used to optimize the structure of DNA single chain unit with double numerical plus d-functions (DND) basis set. Fine convergence criteria and global orbital cutoffs were employed on basis set definitions.

3. Results and discussion 5

3.1. Weight loss measurements In order to investigate the inhibition performance of biological macromolecule DNA, the weight loss method was used in the absence of DNA and presence of different concentrations of DNA in 1 M HCl after 72 h of immersion at 303 K. The detailed corrosion parameters are summarized in Table 1. It can be seen that the corrosion rate is 0.478 mg·cm-2·h-1 without inhibitor, and dramatic reduces after adding inhibitor. With the increasing of DNA concentration in HCl solution, the corrosion rates decrease from 0.136 mg·cm-2·h-1 to 0.040 mg·cm-2·h-1, and the maximum inhibition efficiency reaches 91.6% at 20 mg·L-1. The results show that DNA inhibitor exhibits good inhibitive performance, which may derive from the stronger chemical adsorption and better coverage of DNA.

3.2. Electrochemical studies As known, it is important to provide steady state conditions before performing the potentiodynamic polarization and impedance measurements [3]. The open circuit potential (EOCP) of the working electrode with immersion time (t) in 1 M HCl solution in absence and presence of DNA at 303 K is depicted in Fig. 1. For all cases, the EOCP gradually becomes stable after about 1 hour immersion in 1 M HCl solution without and with 20 mg·L-1 DNA inhibitor, and the OCP values are -499 mV and -452 mV (versus SCE), respectively. It is obviously seen that the OCP values shift towards more positive potentials in the presence of DNA inhibitor, which can be explained by the adsorption of DNA inhibitor on metal surface. And then, the potentiodynamic polarization and impedance measurements are performed after the attainment of the steady state OCP. Tafel polarization curves for X80 steel in 1 M HCl for different concentrations of DNA are depicted in Fig. 2. The detailed electrochemical parameters such as corrosion potential (Ecorr), corrosion current density (Icorr), Tafel anodic slope (ba) and Tafel cathodic slope (bc) are summarized in Table 2. The inhibition efficiency (η2%) of DNA inhibitor obtained via Eq. (3) [19]:

2 (%) 

 I corr  I corr 100 I corr

(3)

where Icorr and I*corr are uninhibited and inhibited current density (mA·cm-2), respectively. 6

As shown in Fig. 2 and Table 2, the corrosion potential values of X80 steel exhibited slightly change. The displacement in Ecorr (ΔEcorr) between in the absence and presence of the DNA are less than 85 mV (17 mV), which indicates that DNA is a mixed-type inhibitor [20-22]. In addition, the corrosion current density, anodic and cathodic Tafel slopes change, which indicates that the inhibitor controls both anodic, as well as cathodic reactions and act as a mixed inhibitor. The above changes might derive from the adsorption of bio-macromolecules DNA on carbon steel surface, anodic iron dissolution and cathodic hydrogen evolution. Table 2 shows that the Icorr decreases in the presence of DNA and continuously decreases with increasing the inhibitor concentration. Correspondingly, the inhibition efficiency (η2%) increases with increasing the inhibitor concentration and reaches 91.9% at 20 mg·L-1, which is consistent with the result obtained by the method of weight loss. The corrosion inhibition property of DNA on carbon steel is examined by electrochemical impedance spectroscopy (EIS). The effect of inhibitor concentrations on the impedance behavior of X80 steel in 1 M HCl solution at 303 K is presented in Fig. 3. The impedance data are fitted with low error by the equivalent circuit (Fig. 4) containing polarization resistance (Rp), constant phase element (CPE) and solution resistance (Rs). CPE includes the double-layer capacitance Cdl. The impedance of CPE is expressed as the following [23, 24]:

ZCPE  Y01  jw

n

(4)

Cdl  n Y0  RP 

1 n

(5)

where Y0 is a proportionality coefficient, w is the angular frequency and j2 = -1 is the imaginary number. The value of n represents the deviation from the ideal behavior and it lies between 0 and 1. When corrosion inhibitor is presented in the solution, RP=Rct+RF+RA+RD, where Rct, RF, RD and RA are charge transfer resistance, inhibitor film resistance, diffuse layer resistance and all other accumulated species resistance, respectively [21]. The impedance parameters are shown in Table 3. and the inhibition efficiency (η3%) are calculated using the following equation [25]:

3 (%) 

RP  RP 100 RP

(6)

where RP and R*P are the polarization resistances (Ω·cm2) without and with DNA, respectively. Combined with Fig. 3(a) and Table 3, it can be seen that the diameter of Nyquist plot shows 7

the impedance differences with low and high frequency. The minimum polarization resistance (Rp) is observed in the absence of DNA as 40 Ω·cm2. After increasing the concentration of DNA, the R*p increases with increasing DNA concentration. The maximum R*p is 358 Ω·cm2, which is much higher than the steel sample without DNA, and η3 reaches 89.0% at 20 mg·L-1 DNA. The results show that the charge transfer between the carbon steel and the solution is dramatically hindered by the addition of DNA. The Bode and phase angle plots for X80 steel electrode in 1 M HCl solution with different DNA concentrations are depicted in Fig. 3(b) and Fig. 3(c), respectively. It can be seen that the absolute impedance at low frequencies in Bode plots gradually increases, which is attributed to the better protection of X80 steel and improved adsorption of DNA molecules with the increasing of DNA concentration [26, 27]. As shown in Fig. 3(c), the aperture of phase angles increase with the increasing of DNA concentration, suggesting that the adsorption property due to better surface coverage of DNA molecule on X80 steel surface [28]. As shown in Table 3, the value of Cdl decreases with the increasing of inhibitor concentration, which could demonstrate that the thickness of electric double layer increases or the dielectric constant reduces. Moreover, the results also verify that the interaction between inhibitor and metal surface could form a protective layer, which can be interpreted by the Helmholtz model [29]:

Cdl 

 0 A d

(7)

where ε0 is the vacuum dielectric constant, ε is the dielectric constant, A is the surface area of the electrode and d is the thickness of the double layer. The results illustrate that DNA molecules adsorb on the metal surface by dispelling water molecules on the metal surface and forming a protective film [30], which impedes the electron transfer and inhibits the corrosion process.

3.3. Adsorption isotherm In order to investigate the behavior about the interaction between DNA molecules and carbon steel, the analysis of isotherm of Langmuir adsorption is carried out. This isotherm can be represented as [9, 31]:

Cinh





1  Cinh K ads

(8)

where Cinh and θ are the concentration of inhibitor and the surface coverage, respectively. And Kads 8

represents the adsorption equilibrium constant. The plot of Cinh/θ versus Cinh is a straight line as shown in Fig. 5. The linear regression coefficient (R2) reaches 0.9998. This indicates that the adsorption of DNA molecules on the X80 steel surface is monolayer adsorption, which follows the Langmuir’s adsorption isotherm in 1 M HCl solution.

3.4. UV and FTIR Spectra Characterization Normally, the interaction mechanism between DNA molecule and metal can be analyzed UV-Vis diffuse reflectance spectrophotometer (PerkinEImerLambda850，Elmer Perkin Limited by Share Ltd). Here, 1 M HCl solution with 20 mg·L-1 FeCl3, 1 M HCl solution with 20 mg·L-1 DNA, 1 M HCl solution with 20 mg·L-1 FeCl3 and 20 mg·L-1 DNA after soaking for 72 h at 303 K are prepared for UV-Vis absorption spectra measurement. As depicted in Fig.6 (a) and (b), two wave peaks can be seen in the ultraviolet zone for DNA solution. The absorption wavelengths of wave peaks are 204.5 nm and 269.2 nm, respectively. In Fig.6(c), when adding Fe3+ into DNA solution, the peaks and trough position of DNA absorption curve are shifted. The first absorption peak shows 2.5 nm red shift (207.0 nm), and the second absorption peak exhibits 5.5 nm blue shift (263.7 nm). The result may attribute to the formation of coordination compound DNA-Fe3+. It can be predicted that the chemical adsorption of DNA on X80 steel surface derives from the formation of coordination bonds between DNA and iron atoms. The adsorption of DNA molecules on the surface of X80 steel was further investigated by infrared spectrometer (WQF520，Beijing Rayleigh Analytical Instrument Co., Ltd.). The infrared spectra of two X80 steel sheets are shown in Fig.7. Fig.7a is the infrared spectrum of carbon steel surface after soaking with 1 M HCl containing DNA. Fig.7b is the infrared spectrum of pure DNA. It can be seen that, two peaks at 1690.61 cm-1 (C=O double bond stretching vibration) and 1400.21 cm-1 (N-O bond stretching vibration) in the pure DNA samples are disappeared after the corrosion experiments, which indicates that the DNA structure changes. A new peak at 1598.25 cm-1 appears, which is the vibration peak of C=O double bond and shows the band of antisymmetric stretching vibration of ionized carboxyl group. The peak at 2019.17 cm-1 is the absorption peak of C≡C, this peak is probably caused by the recombination of carbon atoms in the structure of DNA molecules. Therefore, the two peaks indicates that the DNA inhibitor form a conjugated structure on the metal surface. 9

3.5. X-ray photoelectron spectroscopy(XPS) Analysis The X-ray photoelectron spectroscopy analyses were carried out to investigate the chemical composition of inhibited interface. As shown in Fig.8, the XPS spectra with five elements (C 1s, O 1s, N 1s, P 2p and Fe 2p) are detected, which are the basic elements of DNA molecule. From the C1s spectra, it can be seen that the peak profile located at 284.9 eV, 286.4 eV and 288.2 eV, which is similar with the standard map of pure DNA C1s manual data (284.6 eV, 286.5 eV and 287.9 eV). The peaks derive from C-C or C=O, C-OH, and N-C=O, respectively, which are parts of DNA structure [32, 33]. In Fig.9b, two binding energy peaks of N1s (399.4 eV and 400.6 eV) are detected, which may belong to N-Fe and C-N [2]. From O 1s line deconvolution presented in Fig.9c, oxygen appears in two chemical states, which derive from the formation of hydroxide FeOOH (531.4 eV) and the adsorption of H2O (532.8 eV) [34, 35]. From the spectra of P 2p (Fig.9d), the binding energy peak is 133.9 eV, attributing to the pure DNA[32]. The Fe 2p spectra (Fig.9e) locate at 710.8 eV (Fe 2p3/2) and 724.3 eV (Fe 2p1/2) together with an associated ghost structure on the high energy side showing the subsequent oxidation of the steel surface. The peak at 710.8 eV assigns to FeOOH [36], which coincides with the O 1s spectrum of iron hydroxide layer. Comparing the atoms binding energies of organic powder sample with pure DNA [32], the binding energies of C 1s, O 1s and N 1s are changed. The phenomena indicated that the N, C, and O atoms of DNA interact with the carbon steel surface. Moreover, it was found that before and after chemical adsorption between the different atoms could result in a 0.5 eV or higher binding energy in previous work [37]. In this work, the peak of N1s shifts from 398.8 eV (pure DNA) to 399.4 eV, generates a 0.6 eV binding energy, which demonstrates the chemical action between N and Fe. The above results show that DNA contains a polar group with nitrogen atoms can adsorb onto the metal surface, creating a resistance to corrosion medium for steel protection.

3.6. Quantum chemical calculations Quantum chemical calculations using the Density Functional Theory (DFT) were employed to investigate the inhibition behavior of DNA inhibitors [38]. The highest occupied molecular orbital (HOMO) is often associated with the electrons-donate capacity of a molecule, and the lowest unoccupied molecular orbital (LUMO) represents the ability of electrons-accept [39]. The 10

HOMO and LUMO of DNA single chain unit and the constituents of DNA single chain unit (Adenine nucleotide, Cytosine nucleotide, Guanine nucleotide, Thymine nucleotide ), are shown in Fig.10 and Fig.11, respectively. It is seen that the active regions of the molecules are mainly distributed around the polar groups containing N and O atoms. This illustrates that the DNA molecule interacts with the Fe atom by those polar groups, and provides electrons for Fe atoms with unoccupied d-orbitals [40]. The result is coincided with the XPS analysis and proves the prediction of weight loss method. According to the frontier molecular orbital theory, the corrosion inhibition performance of DNA related to the highest occupied molecular orbital energy (EHOMO) and the lowest unoccupied molecular orbital energy (ELUMO), and ΔE (ΔE=ELUMO-EHOMO). The higher EHOMO value indicates that the inhibitor molecules could easily donate electrons to the empty d-orbital of metal [41]. In contrast, the lower values of ELUMO imply a higher electron accepting ability from the superficial metal [42]. On the other hand, the value of ΔE represents the stability of transition complex which determines the interaction between the adsorbed inhibitor and the metallic substrate. Smaller ΔE indicates the higher reaction activity and inhibition efficiency of the compound [43]. The value of ΔN represents the number of transferred electrons from the inhibitor to metallic surface. When ΔN is smaller than 3.6, the inhibition efficiency of organic inhibitor increases with increasing electron donating ability at the metal surface[44]. Generally, ΔN is calculated depending on the quantum chemical method [45, 46]:

N 

 Fe   inh 2  Fe  inh 

(9)

where χinh is absolute electronegativity of the inhibitor molecule, ηinh is global hardness of the inhibitor molecule, they are approximated as follows:



ELUMO  EHOMO 2



(10)

 EHOMO  ELUMO 2

(11)

For iron, the theoretical values of χFe and ηFe are 0 and 7 eV·mol-1, respectively [47-49]. 11

The detailed data of theoretical computations are summarized in Table 4. It can be seen that the ΔE of DNA single unit structure is the minimum and the ΔN is the maximum, which indicates that the reaction activity of DNA single chain unit is the highest and the number of electrons from DNA to transition metal atoms is the most. Therefore, the DNA single chain unit exhibits the best corrosion inhibition performance, which directly demonstrates the effective inhibition ability of DNA macromolecule.

3.7. SEM analysis and adsorption model In order to directly reveal the corrosion inhibition ability of DNA, the scanning electron microscopy is performed to detect the surface morphology of the X80 steel sheets in 1 M HCl solution in the absence and presence of 20 mg·L-1 DNA at 303K for 72h. As shown in Fig. 12, the steel without DNA inhibitor exhibits rough and non-uniform morphology (Fig.12a). In contrast, in the presence of DNA inhibitor, the surface improves markedly and corrosion state is not obvious (Fig.12b). This improvement in surface morphology mainly derives from the effective corrosion inhibition of DNA. To further describe the corrosion inhibition mechanism of DNA macromolecules, an adsorption model was presented, as shown in Fig.13. It can be seen that, the carbon steel surface is covered by water molecules, hydrogen ions and chloride ions, without adding DNA inhibitor in corrosive medium. In the presence of DNA, the DNA molecules adsorb on the metal surface and dispel water molecules, hydrogen ions and chloride ions on the surface. The inhibitor film derives from the donor-acceptor interaction by lone pair of heteroatoms (N, O) and the d-orbitals of the surface iron atoms (donation). In addition, because of the particular advantages of DNA, such as large molecular weight, large number of polar groups and long molecular chain, the DNA could adsorb firmly and cover uniform on the carbon steel surface, which effectively isolates the steel from corrosive medium.

4. Conclusions Bio-macromolecule DNA worked as a novel environment-friend and effective corrosion inhibitor on X80 steel in 1 M HCl. The inhibition performance was evaluated by using electrochemical techniques, XPS and quantum chemical calculations et al. It was shown that he DNA inhibitor exhibited 91.9% maximum inhibition efficiency for carbon steel in 1 M HCl at 12

308K. The results indicated that DNA molecule is a mixed type corrosion inhibitor, which suppresses both anodic metal dissolution and cathodic hydrogen evolution reactions. The results of UV and FTIR spectrum manifested that the molecular structure of DNA changed when DNA reacted with metal to form coordination complex. XPS analysis proved the evidence of the chemisorption of DNA on the carbon steel surface 1 M HCl. SEM measurements showed that the formation of DNA inhibitor film on the steel surface was effectively inhibited the corrosion process. The theoretical calculations revealed that DNA molecules were able to provide a large number of electrons to the d-orbital of transition metal atoms. The results further demonstrated that the DNA is an effective corrosion and bio-macromolecule is promising candidate for green inhibitor.

Acknowledgments The authors are greatly thankful to the Doctoral Scientific Fund Project of the Ministry of Education of China (Project No. 20135121110008) for financial support.

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References [1] A.K. Singh, S. Mohapatra, B. Pani, Corrosion inhibition effect of Aloe Vera gel: Gravimetric and electrochemical study, Journal of Industrial and Engineering Chemistry, 33 (2016) 288-297. [2] A. Zarrouk, B. Hammouti, T. Lakhlifi, M. Traisnel, H. Vezin, F. Bentiss, New 1H-pyrrole-2,5-dione derivatives as efficient organic inhibitors of carbon steel corrosion in hydrochloric acid medium: Electrochemical, XPS and DFT studies, Corrosion Science, 90 (2015) 572-584. [3] R. Yıldız, An electrochemical and theoretical evaluation of 4,6-diamino-2-pyrimidinethiol as a corrosion inhibitor for mild steel in HCl solutions, Corrosion Science, 90 (2015) 544-553. [4] M. Finšgar, J. Jackson, Application of corrosion inhibitors for steels in acidic media for the oil and gas industry: A review, Corrosion Science, 86 (2014) 17-41. [5] M.N. El-Haddad, Chitosan as a green inhibitor for copper corrosion in acidic medium, International journal of biological macromolecules, 55 (2013) 142-149. [6] S. Kaya, B. Tüzün, C. Kaya, I.B. Obot, Determination of corrosion inhibition effects of amino acids: Quantum chemical and molecular dynamic simulation study, Journal of the Taiwan Institute of Chemical Engineers, 58 (2016) 528-535. [7] H. Tian, W. Li, B. Hou, D. Wang, Insights into corrosion inhibition behavior of multi-active compounds for X65 pipeline steel in acidic oilfield formation water, Corrosion Science, 117 (2017) 43-58. [8] M. Farsak, H. Keleş, M. Keleş, A new corrosion inhibitor for protection of low carbon steel in HCl solution, Corrosion Science, 98 (2015) 223-232. [9] N. Kıcır, G. Tansuğ, M. Erbil, T. Tüken, Investigation of ammonium (2,4-dimethylphenyl)-dithiocarbamate as a new, effective corrosion inhibitor for mild steel, Corrosion Science, 105 (2016) 88-99. [10] R. Yıldız, T. Doğan, İ. Dehri, Evaluation of corrosion inhibition of mild steel in 0.1M HCl by 4-amino-3-hydroxynaphthalene-1-sulphonic acid, Corrosion Science, 85 (2014) 215-221. [11] K. Hu, J. Zhuang, C. Zheng, Z. Ma, L. Yan, H. Gu, X. Zeng, J. Ding, Effect of novel cytosine-l-alanine derivative based corrosion inhibitor on steel surface in acidic solution, Journal of Molecular Liquids, 222 (2016) 109-117. [12] Q. Deng, H.-W. Shi, N.-N. Ding, B.-Q. Chen, X.-P. He, G. Liu, Y. Tang, Y.-T. Long, G.-R. Chen, Novel triazolyl bis-amino acid derivatives readily synthesized via click chemistry as potential corrosion inhibitors for mild steel in HCl, Corrosion Science, 57 (2012) 220-227. [13] M.M. Fares, A.K. Maayta, M.M. Al-Qudah, Pectin as promising green corrosion inhibitor of aluminum in hydrochloric acid solution, Corrosion Science, 60 (2012) 112-117. [14] A. Biswas, S. Pal, G. Udayabhanu, Experimental and theoretical studies of xanthan gum and its graft co-polymer as corrosion inhibitor for mild steel in 15% HCl, Applied Surface Science, 353 (2015) 173-183. [15] ASTM, G 31-72, American Society for Testing and Materials, Philadelphia,PA, 199031-199072. [16] S. Xia, M. Qiu, L. Yu, F. Liu, H. Zhao, Molecular dynamics and density functional theory study on relationship between structure of imidazoline derivatives and inhibition performance, Corrosion Science, 50 (2008) 2021-2029. 14

[17] A.K. Singh, M.A. Quraishi, Effect of Cefazolin on the corrosion of mild steel in HCl solution, Corrosion Science, 52 (2010) 152-160. [18] Materials Studio, Revision 6.0, Accelrys Inc., San Diego, USA, 2013. [19] J. Hu, D. Huang, G.-L. Song, X. Guo, The synergistic inhibition effect of organic silicate and inorganic Zn salt on corrosion of Mg-10Gd-3Y magnesium alloy, Corrosion Science, 53 (2011) 4093-4101. [20] E. Kowsari, S.Y. Arman, M.H. Shahini, H. Zandi, A. Ehsani, R. Naderi, A. PourghasemiHanza, M. Mehdipour, In situ synthesis, electrochemical and quantum chemical analysis of an amino acid-derived ionic liquid inhibitor for corrosion protection of mild steel in 1M HCl solution, Corrosion Science, 112 (2016) 73-85. [21] A. Ongun Yüce, B. Doğru Mert, G. Kardaş, B. Yazıcı, Electrochemical and quantum chemical studies of 2-amino-4-methyl-thiazole as corrosion inhibitor for mild steel in HCl solution, Corrosion Science, 83 (2014) 310-316. [22] C.B. Verma, M.A. Quraishi, A. Singh, 2-Aminobenzene-1,3-dicarbonitriles as green corrosion inhibitor for mild steel in 1 M HCl: Electrochemical, thermodynamic, surface and quantum chemical investigation, Journal of the Taiwan Institute of Chemical Engineers, 49 (2015) 229-239. [23] Y. Liu, Z. Wang, W. Ke, Study on influence of native oxide and corrosion products on atmospheric corrosion of pure Al, Corrosion Science, 80 (2014) 169-176. [24] B.D. Mert, A.O. Yüce, G. Kardaş, B. Yazıcı, Inhibition effect of 2-amino-4-methylpyridine on mild steel corrosion: Experimental and theoretical investigation, Corrosion Science, 85 (2014) 287-295. [25] M. Bobina, A. Kellenberger, J.-P. Millet, C. Muntean, N. Vaszilcsin, Corrosion resistance of carbon steel in weak acid solutions in the presence of l-histidine as corrosion inhibitor, Corrosion Science, 69 (2013) 389-395. [26] B. Xu, W. Yang, Y. Liu, X. Yin, W. Gong, Y. Chen, Experimental and theoretical evaluation of two pyridinecarboxaldehyde thiosemicarbazone compounds as corrosion inhibitors for mild steel in hydrochloric acid solution, Corrosion Science, 78 (2014) 260-268. [27] H. Hamani, T. Douadi, M. Al-Noaimi, S. Issaadi, D. Daoud, S. Chafaa, Electrochemical and quantum chemical studies of some azomethine compounds as corrosion inhibitors for mild steel in 1M hydrochloric acid, Corrosion Science, 88 (2014) 234-245. [28] N.D. Nam, Q.V. Bui, M. Mathesh, M.Y.J. Tan, M. Forsyth, A study of 4-carboxyphenylboronic acid as a corrosion inhibitor for steel in carbon dioxide containing environments, Corrosion Science, 76 (2013) 257-266. [29] A. Kosari, M.H. Moayed, A. Davoodi, R. Parvizi, M. Momeni, H. Eshghi, H. Moradi, Electrochemical and quantum chemical assessment of two organic compounds from pyridine derivatives as corrosion inhibitors for mild steel in HCl solution under stagnant condition and hydrodynamic flow, Corrosion Science, 78 (2014) 138-150. [30] L. Zeng, G.A. Zhang, X.P. Guo, C.W. Chai, Inhibition effect of thioureidoimidazoline inhibitor for the flow accelerated corrosion of an elbow, Corrosion Science, 90 (2015) 202-215. [31] A. Pourghasemi Hanza, R. Naderi, E. Kowsari, M. Sayebani, Corrosion behavior of mild steel in H2SO4 solution with 1,4-di [1′-methylene-3′-methyl imidazolium bromide]-benzene as an ionic liquid, Corrosion Science, 107 (2016) 96-106. [32] P.G. Chi-Ying Lee, Gregory M. Harbers, David W. Grainger, David G. Castner, Lara J. 15

Gamble, Surface Coverage and Structure of Mixed DNA/Alkylthiol Monolayers on Gold: Characterization by XPS, NEXAFS, and Fluorescence Intensity Measurements, Anal.Chem, 78 (2006) 3316-3325. [33] L. Tian, J. Liu, C. Gong, L. Ye, L. Zan, Fabrication of reduced graphene oxide–BiOCl hybrid material via a novel benzyl alcohol route and its enhanced photocatalytic activity, Journal of Nanoparticle Research, 15 (2013). [34] A. Welle, J.D. Liao, K. Kaiser, M. Grunze, U. Mäder, N. Blank, Interactions of N,N′-dimethylaminoethanol with steel surfaces in alkaline and chlorine containing solutions, Applied Surface Science, 119 (1997) 185-198. [35] P. Bommersbach, C. Alemany-Dumont, J.P. Millet, B. Normand, Formation and behaviour study of an environment-friendly corrosion inhibitor by electrochemical methods, Electrochimica Acta, 51 (2005) 1076-1084. [36] W. Temesghen, P.M. Sherwood, Analytical utility of valence band X-ray photoelectron spectroscopy of iron and its oxides, with spectral interpretation by cluster and band structure calculations, Analytical and bioanalytical chemistry, 373 (2002) 601-608. [37] Y. Zhou, X. Zhang, Q. Zhang, F. Dong, F. Wang, Z. Xiong, Role of graphene on the band structure and interfacial interaction of Bi2WO6/graphene composites with enhanced photocatalytic oxidation of NO, J. Mater. Chem. A, 2 (2014) 16623-16631. [38] X. Ma, X. Jiang, S. Xia, M. Shan, X. Li, L. Yu, Q. Tang, New corrosion inhibitor acrylamide methyl ether for mild steel in 1M HCl, Applied Surface Science, 371 (2016) 248-257. [39] K.F. Khaled, Corrosion control of copper in nitric acid solutions using some amino acids – A combined experimental and theoretical study, Corrosion Science, 52 (2010) 3225-3234. [40] M.A. Amin, K.F. Khaled, Q. Mohsen, H.A. Arida, A study of the inhibition of iron corrosion in HCl solutions by some amino acids, Corrosion Science, 52 (2010) 1684-1695. [41] K. Zhang, B. Xu, W. Yang, X. Yin, Y. Liu, Y. Chen, Halogen-substituted imidazoline derivatives as corrosion inhibitors for mild steel in hydrochloric acid solution, Corrosion Science, 90 (2015) 284-295. [42] Z. Hu, Y. Meng, X. Ma, H. Zhu, J. Li, C. Li, D. Cao, Experimental and theoretical studies of benzothiazole derivatives as corrosion inhibitors for carbon steel in 1M HCl, Corrosion Science, 112 (2016) 563-575. [43] C. Verma, M.A. Quraishi, A. Singh, A thermodynamical, electrochemical, theoretical and surface investigation of diheteroaryl thioethers as effective corrosion inhibitors for mild steel in 1 M HCl, Journal of the Taiwan Institute of Chemical Engineers, 58 (2016) 127-140. [44] T. Ghailane, R.A. Balkhmima, R. Ghailane, A. Souizi, R. Touir, M. Ebn Touhami, K. Marakchi, N. Komiha, Experimental and theoretical studies for mild steel corrosion inhibition in 1M HCl by two new benzothiazine derivatives, Corrosion Science, 76 (2013) 317-324. [45] N. Yilmaz, A. Fitoz, Ü. Ergun, K.C. Emregül, A combined electrochemical and theoretical study into the effect of 2-((thiazole-2-ylimino)methyl)phenol as a corrosion inhibitor for mild steel in a highly acidic environment, Corrosion Science, 111 (2016) 110-120. [46] I.B. Obot, D.D. Macdonald, Z.M. Gasem, Density functional theory (DFT) as a powerful tool for designing new organic corrosion inhibitors. Part 1: An overview, Corrosion Science, 99 (2015) 1-30. [47] Z. El Adnani, M. McHarfi, M. Sfaira, M. Benzakour, A.T. Benjelloun, M. Ebn Touhami, DFT theoretical study of 7-R-3methylquinoxalin-2(1H)-thiones (RH; CH3; Cl) as corrosion inhibitors 16

in hydrochloric acid, Corrosion Science, 68 (2013) 223-230. [48] H. Zhao, X. Zhang, L. Ji, H. Hu, Q. Li, Quantitative structure–activity relationship model for amino acids as corrosion inhibitors based on the support vector machine and molecular design, Corrosion Science, 83 (2014) 261-271. [49] A. Khadiri, R. Saddik, K. Bekkouche, A. Aouniti, B. Hammouti, N. Benchat, M. Bouachrine, R. Solmaz, Gravimetric, electrochemical and quantum chemical studies of some pyridazine derivatives as corrosion inhibitors for mild steel in 1 M HCl solution, Journal of the Taiwan Institute of Chemical Engineers, 58 (2016) 552-564.

17

 Figures

-0.44 -0.45

E (V vs.SCE)

-0.46 -0.47 Blank 5 mgL-1 10 mgL-1 15 mgL-1 20 mgL-1

-0.48 -0.49 -0.50 -0.51 0

500

1000

1500

2000

2500

3000

3500

4000

t (s)

Fig.1 The change of open circuit potential (EOCP) of the working electrode with immersion time (t) in 1 M HCl solution in absence and presence of DNA at 303K.

0.5 0.0 -0.5 -1.0

log i (Acm-2)

-1.5 -2.0 -2.5 -3.0 -3.5 -4.0 -4.5

Blank 5 mgL-1 10 mgL-1 15 mgL-1 20 mgL-1

-5.0 -0.80 -0.75 -0.70 -0.65 -0.60 -0.55 -0.50 -0.45 -0.40 -0.35 -0.30 -0.25 -0.20

E (V/SCE )

Fig.2 Potentiodynamic polarization curves of X80 steel in 1 M HCl solution without and with different concentrations of DNA at 303K.

18

220

(a)

200

Blank 5 mgL-1

180

10 mgL-1

160

5.62 Hz

15 mgL-1

Z'' (cm2)

140

20 mgL-1

4.64 Hz

120 100 8.25 Hz

80

12.10 Hz

60 40 17.78 Hz

20

0.18 Hz 0.32 Hz

0.32 Hz

0.18 Hz

0.22 Hz

0 0

50

100

150

200

250

300

350

400

2

Z' (cm )

3.0

(b)

Blank 5 mgL-1 10 mgL-1 15 mgL-1 20 mgL-1

2.5

log |Z| (cm2)

2.0

1.5

1.0

0.5

0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

log  (Hz)

19

3.5

4.0

4.5

5.0

80 70

Blank 5 mgL-1 10 mgL-1 15 mgL-1 20 mgL-1

(c)

- Phase Angle (degree)

60 50 40 30 20 10 0 -1.0 -0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

log  (Hz)

Fig.3 Nyquist (a), Bode (b) and phase angle (c) plots for X80 steel 1 M HCl solution without and with different concentrations of DNA at 303K

Fig.4 Equivalent circuit used to fit the obtained Nyquist impedance spectra: Rs-the solution resistance, Rp-the polarization resistance, CPE-the constant phase element.

20

24 22 20

Cinh / (mgL-1)

18

R2=0.9998 16 14 12 10 8 6 4

6

8

10

12

14

16

18

20

22

-1

Cinh (mgL )

Fig.5 Langmuir adsorption plot of X80 steel in 1 M HCl solution containing different concentrations of DNA at 303K

Fig.6 UV Vis spectra for 1 M HCl and containing: (a) 20 mg·L-1 FeCl3; (b) 20 mg·L-1 DNA; (c) 20 mg·L-1 FeCl3 and 20 mg·L-1 DNA solutions at 303 K for 72 h.

21

100

The surface products of the steel sheet after soaking DNA solution

(a)

80 60

2109.17

1329.69

T (%)

40

2724.89

1502.18 1598.25 1159.38

20

3170.30

3545.85

100 pure DNA

(b) 80

60

1225.98 1056.33

40 500

1000

3414.10

1400.21 1690.61

1500

3128.82

2000

2500

3000

3500

4000

W (cm-1)

Fig.7 Fourier infrared spectra: (a) The surface products of the steel sheet after soaking DNA solution; (b) Pure DNA

90000 80000

inhibitor

O1s

70000 O(KLL)

intensity (a.u.)

60000 50000

N1s

40000

Fe2p

30000 20000

C1s

10000

P2p

0 -10000 0

200

400

600

800

1000

1200

Binding energy (eV)

Fig. 8 Wide-scan spectrum of the pressed sample which is a aluminum foil with sticking the scraped organic powder.

22

25000

a

C 1s

intensity (a.u.)

20000

284.9 eV

15000 286.4 eV 10000

288.2 eV

5000

0 278

280

282

284

286

288

290

292

Binding energy (eV)

12000 11000

b

N 1s 400.6 eV

intensity (a.u.)

10000 9000 399.4 eV 8000 7000 6000 5000 394

396

398

400

402

Binding energy (eV)

23

404

406

40000

c

O 1s

35000

532.8 eV

intensity (a.u.)

30000 531.4 eV

25000 20000 15000 10000 5000 526

528

530

532

534

536

538

Binding energy (eV)

2500

P 2p

d

133.9 eV

intensity (a.u.)

2000

1500

1000

500 128

130

132

134

136

Binding energy (eV)

24

138

140

11000

e

Fe 2p 10500 724.3 eV 710.8 eV

intensity (a.u.)

10000

9500

9000

8500

8000 700

705

710

715

720

725

730

735

Binding energy (eV)

Fig. 9 High-resolution X-ray photoelectron deconvoluted profiles of C 1s, N 1s, O 1s, P 2p, and Fe 2p for the scraped organic powder on the aluminum foil.

Fig.10 Frontier molecule orbital density distributions of DNA single chain unit structure.

25

Fig.11 Frontier molecule orbital density distributions of Adenine nucleotide (A), Cytosine nucleotide (C), Guanine nucleotide (G), Thymine nucleotide (T).

26

Fig.12 SEM images of X80 steel specimens after 72 h of immersion in 1 M HCl solution at 303K: (a) without DNA, (b) with 20 mg·L-1 DNA.

Fig.13 Schematic representation of the inhibition mechanism for DNA inhibitor.

27

Table 1 Corrosion information from weight loss tests for X80 steel immersed in1 M HCl with and without various concentrations of DNA for 72h at 303K. η1 (%)

Inhibitor

Cinh (mg·L-1)

Vcorr (mg·cm-2·h-1)

Blank

0

0.478

DNA

5

0.136

71.5

10

0.075

84.3

15

0.051

89.3

20

0.040

91.6

Table 2 Potentiodynamic polarization parameters for X80 steel in 1 M HCl presence and absence different concentrations of DNA at 303K. Inhibitor

Cinh

Ecorr -1

(mg·L )

Icorr

(mV vs. SCE)

bc -2

(mA·cm )

η2

ba -1

(mV·dec )

-1

(mV·dec )

(%)

Blank

0

-469

49.8

-139

95

DNA

5

-462

22.7

-137

88

54.4

10

-475

8.8

-135

76

82.3

15

-464

7.2

-134

66

85.5

20

-479

4.0

-133

60

91.9

Table 3 EIS parameters of steel specimen in the presence and absence of different concentrations of DNA in 1 M HCl at 303 K. Inhibitor

Cinh (mg·L )

Rp (Ω·cm2)

Cdl (µF·cm-2)

n

Blank

0

40

356

0.86

DNA

5

147

178

10

255

15

297

20

358

-1

η3 (%)

θ

0.82

72.8

0.73

170

0.86

84.3

0.84

145

0.84

86.5

0.87

130

0.85

89.0

0.89

Table 4 Calculated quantum chemical indices of Adenine nucleotide (A), Cytosine nucleotide (C), Guanine nucleotide (G), Thymine nucleotide (T) and DNA single chain unit structure. Inhibitors

EHOMO (eV)

ELUMO (eV)

ΔE (eV)

χ (eV)

η (eV)

ΔN

Adenine nucleotide (A)

-5.353

-1.546

3.807

3.45

1.903

0.933

Cytosine nucleotide (C)

-5.09

-0.742

4.348

2.92

2.174

0.938

Guanine nucleotide (G)

-5.138

-1.305

3.833

3.222

1.917

0.984

Thymine nucleotide (T)

-5.748

-2.03

3.718

3.889

1.859

0.837

DNA single chain unit

-5.317

-2.232

3.085

3.775

1.543

1.045

structure

28