Inhibition behaviour of mild steel by three new benzaldehyde thiosemicarbazone derivatives in 0.5 M H2SO4: experimental and computational study

Three new benzaldehyde thiosemicarbazone derivatives namely benzaldehyde thiosemicarbazone (BST), 4-carboxyl benzaldehyde thiosemicarbazone (PBST) and 2-carboxyl benzaldehyde thiosemicarbazone (OCT) were synthesized and their inhibition effects on mild steel corrosion in 0.5 M H2SO4 solution were studied systematically using gravimetric and electrochemical measurements. Weight loss results revealed that PBST exhibited the highest inhibition efficiency of 96.6% among the investigated compounds when the concentration was 300 µM. The analysis of polarization curves indicated that the three benzaldehyde thiosemicarbazone derivatives acted as mixed type inhibitors and PBST and OCT predominantly anodic. The adsorption process of all these benzaldehyde thiosemicarbazone derivatives on Q235 steel surface in 0.5 M H2SO4 solution conformed to Langmuir adsorption isotherm. Scanning electron microscopy was conducted to show the presence of benzaldehyde thiosemicarbazone derivatives on Q235 mild steel surface. The results of theoretical calculations were in good agreement with that of experimental measurements.


Inhibition behaviour of mild steel by three new benzaldehyde thiosemicarbazone derivatives in 0.5 M H 2 SO 4 : experimental and computational study
Have you any concerns about statistical analyses in this paper? No

Recommendation? Accept with minor revision (please list in comments)
Comments to the Author(s) In this paper, the inhibition behavior of three new benzaldehyde thiosemicarbazone derivatives on mild steel in 0.5 M H2SO4 solution was investigated using gravimetric measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy and theoretical calculations. The inhibitor exhibited good inhibition efficiency (96.6%). The work is interesting and I fee that it could be published after making the following corrections/ suggestions. 1. "Acid corrosion" should be added as one of the keyword. 2. In abstract, the sentence "The analysis of polarization curves indicated that the three benzaldehyde thiosemicarbazone derivatives acted were of mixed type and PBST and OCT predominantly anodic." should be rewritten. 3. Throughout the text,"molecule structure" should be replaced by "molecular structure". 4. Page 5, an "η" is missing from equation (5).

Review form: Reviewer 2
Is the manuscript scientifically sound in its present form? Yes

Recommendation?
Major revision is needed (please make suggestions in comments)

Comments to the Author(s)
Title: Inhibition behavior of mild steel by three new benzaldehyde thiosemicarbazone derivatives in 0.5 M H2SO4: Experimental and computational study Journal: Royal Society Open Science Manuscript number Review: RSOS-190192 Reviewer: 1-The English of the manuscript is adequate for its publication but there are some corrections to be made. 2-The introduction is poorly structured. 3-The solubility of inhibitor in the solvent must be explained. The effect of the solvent on the inhibition needs more discussion. 4-In the gravimetric method why did you choose 8 hours as immersion time.
5-It seems that the recommended scan rate for obtaining Tafel slopes is lower than 1 mV s-1 (~0.2 V s-1). Why was the reason to use 1 mV s-1? 6-The figures are not clear? 7-The Ecorr unit must be corrected 6-The OCP vs time should be shown and discussed. 7-The authors used curve fitting or Tafel extrapolation method in obtaining the values of corrosion currents?? 8-Thank you to give a detailed discussion on the Tafl slopes (ba and bc). 9-Nyquist plots should show some define frequencies.
10-11-A representative of example simulation of Nyquist and Bode diagrams with suggested models without and with of inhibitor should be given. It would be necessary to give, in the Table  5, the scattering (error bars) of all fitted parameters to evaluate the accuracy of the used models. 12-The author must justify the choice of use the CPE. 13-In part electrochemical impedance spectroscopy measurements: the authors should give and interpret in detail the variation of n value in the absence and presence of inhibitory molecule. 14-You must add the error for each parameter in the impedance tables. 15-The sentence "The negative value of indicates that the ∆0 adsorption of benzaldehyde thiosemicarbazone derivatives onto Q235 mild steel in 0.5 M H2SO4 solution is spontaneous (due the negative value!!)." is wrong. Please delete this. This parameter is a thermodynamic representation of the equilibrium constant, that is all. 16-Why you did not calculate the other activation parameters? 17-You must add all the equations concerning the theoretical part. 18-The paper includes a rather verbose discussion of DFT calculated molecular electronic properties using HOMO-LUMO type cliche inferences that have been used countless times in the literature. Such an approach is not acceptable in the year 2018, because the DFT methodology to explicitly model the adsorption of molecules on materials surfaces is well established and mature for almost two decades (e.g., see Hammer & Norskov, Advances in Catalysis 45 (2000) 71-129). It has been recently clearly demonstrated that these HOMO-LUMO parameters are not very useful, because for a large data set of corrosion inhibitors the purported correlations between inhibitor's frontier molecular orbital parameters and inhibitor efficiency disappears, see: J. Mater. Chem. A 2 (2014), 16660-16668, Green Chem. 16 (2014), 3349-3357. Please refer to Corros. Sci. 85 (2014) 109-114, stating: "In terms of predictive power, such an approach has at best limited value, and is potentially simply misleading…" 19-It is well known that the benzaldehyde thiosemicarbazone derivatives inhibitors could be protonated in acid solution, so the quantum chemical calculation should be considered the protonated inhibitors. 20-Dynamic molecular simulation needs to be added? Based on my observations, I would recommend this manuscript for publication in "Royal Society Open Science" but after the previous major corrections.

01-Jul-2019
Dear Dr Chen: Title: Inhibition behavior of mild steel by three new benzaldehyde thiosemicarbazone derivatives in 0.5 M H2SO4: Experimental and computational study Manuscript ID: RSOS-190192 Thank you for submitting the above manuscript to Royal Society Open Science. On behalf of the Editors and the Royal Society of Chemistry, I am pleased to inform you that your manuscript will be accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the reviewers' comments at the end of this email.
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2. In abstract, the sentence "The analysis of polarization curves indicated that the three benzaldehyde thiosemicarbazone derivatives acted were of mixed type and PBST and OCT predominantly anodic." should be rewritten. 3. Throughout the text,"molecule structure" should be replaced by "molecular structure". 4. Page 5, an "η" is missing from equation (5).

Reviewer: 2
Comments to the Author(s) Title: Inhibition behavior of mild steel by three new benzaldehyde thiosemicarbazone derivatives in 0.5 M H2SO4: Experimental and computational study Journal: Royal Society Open Science Manuscript number Review: RSOS-190192 Reviewer: 1-The English of the manuscript is adequate for its publication but there are some corrections to be made. 2-The introduction is poorly structured. 3-The solubility of inhibitor in the solvent must be explained. The effect of the solvent on the inhibition needs more discussion. 4-In the gravimetric method why did you choose 8 hours as immersion time. 5-It seems that the recommended scan rate for obtaining Tafel slopes is lower than 1 mV s-1 (~0.2 V s-1). Why was the reason to use 1 mV s-1? 6-The figures are not clear? 7-The Ecorr unit must be corrected 6-The OCP vs time should be shown and discussed. 7-The authors used curve fitting or Tafel extrapolation method in obtaining the values of corrosion currents?? 8-Thank you to give a detailed discussion on the Tafl slopes (ba and bc). 9-Nyquist plots should show some define frequencies. 10-11-A representative of example simulation of Nyquist and Bode diagrams with suggested models without and with of inhibitor should be given. It would be necessary to give, in the Table  5, the scattering (error bars) of all fitted parameters to evaluate the accuracy of the used models. 12-The author must justify the choice of use the CPE. 13-In part electrochemical impedance spectroscopy measurements: the authors should give and interpret in detail the variation of n value in the absence and presence of inhibitory molecule. 14-You must add the error for each parameter in the impedance tables. 15-The sentence "The negative value of indicates that the ∆0 adsorption of benzaldehyde thiosemicarbazone derivatives onto Q235 mild steel in 0.5 M H2SO4 solution is spontaneous (due the negative value!!)." is wrong. Please delete this. This parameter is a thermodynamic representation of the equilibrium constant, that is all. 16-Why you did not calculate the other activation parameters? 17-You must add all the equations concerning the theoretical part. 18-The paper includes a rather verbose discussion of DFT calculated molecular electronic properties using HOMO-LUMO type cliche inferences that have been used countless times in the literature. Such an approach is not acceptable in the year 2018, because the DFT methodology to explicitly model the adsorption of molecules on materials surfaces is well established and mature for almost two decades (e.g., see Hammer & Norskov, Advances in Catalysis 45 (2000) 71-129). It has been recently clearly demonstrated that these HOMO-LUMO parameters are not very useful, because for a large data set of corrosion inhibitors the purported correlations between inhibitor's frontier molecular orbital parameters and inhibitor efficiency disappears, see: J. Mater. Chem. A 2