Instrumental Investigations studies of green Inhibition Potential (Case Study: Zea mays cobs extracts on mild steel in Acidic Medium)
Obagboye Fredrick O., Olasehinde Emmanuel F., Oyewumi Mayowa, Tomilawo Busayo A.
Federal University of Technology, Akure
*Corresponding Author E-mail: obagboye.19@gmail.com
ABSTRACT:
Corrosion inhibitors are compounds that are added in small quantities to an environment to prevent corrosion of metal [7]. In the fight against corrosion, different inhibitors have been introduced which are classified into synthetic and natural inhibitors. The synthetic inhibitors are toxic and not environmentally friendly. They contain compound like moly- dates, phosphates Sulphur and oxygen which make them to be unsuitable for the purpose [8]. The natural inhibitors which are also known as green inhibitors characteristics include non-toxic, harmless environmentally friendly, biodegradable and cheap [9]. The action of a corrosion inhibitor is characterized by the reduction in rate of either anodic reaction or cathodic reaction or both. Study has shown that natural inhibitors potency is attributed to their content which include hydroxyl (-OH) group, carboxylic acid (-COOH) group, amide (-CONH2) group etc. [10].
Recent researches on corrosion inhibition had centered on natural inhibitors which are non-toxic, eco-friendly and readily available obtained from plants. Some natural materials that have been reported to have corrosion inhibitory properties include Tithonia diverstifolia, Carica papaya, Murraya umbellate, water hyacinth, Psidium quajava, Sida acuta, Sidaacuta, Hibiscus sabdariffa, Ficustricopoda, Jathro curcas [11,12, 13, 14, 15, 16, 17 and 18]. Plants materials as metallic corrosion inhibitors reported include Rice husk [19], Corn water [20], and Corn hub [21].
According to [21] investigation on the effect of concentration, contact time and temperature on inhibitory potential of green inhibitors using Zea mays cobs extract on mild steel as a case study, the result showed that Zea mays cobs acid extract exhibits corrosion inhibitory properties. This study is aimed instrumental investigation of the effect of Zea mays cobs (corn cob) extract on mild steel in acidic medium at room temperature using FTIR, SEM-EDX and AAS analysis.
MATERIALS AND METHODS:
Materials:
Material used for the study was mild steel sheet of composition (wt. %); Si (0.056), C (0.187), Mn (0.474), S (0.039), Al (0.124), Cu (0.198), Fe (98.7). It was sectioned into uniform dimension of 18 x 16 x 4 mm before carrying out corrosion test on it.
Sample extract preparation:
The Zea mays cobs sample was dried in the sun for 8 weeks, pulverized into fine powders and sieved with 50 m mesh. 10g of powdered material was initially dissolved in 100 mL of 1M H2SO4 solution. The blank was 100 mL of 1M H2SO4 solution. The plant materials were boiled at 90oC for 3 hours in water-bath, cooled, filtered and stored. Inhibitor test solutions were prepared in concentration ranges 0.1-0.5% (v/v) H2SO4 solution from the respective stock solution.
Determination of phytochemicals
The spectrophotometric method of determination was used to investigate the phytochemical content of the extract. Phytochemicals investigated include of CH2O, Tannin, Saponim, Steriod, Anthraquinone, Phenol, Cardiac Glycoside, Phtobatanin and total Flavonoid content.
Fourier Transform Infrared Spectroscopy (FTIR) Analysis:
Finely powdered (iron filing) mild steel specimen was immersed in the solution of H2SO4 containing the plants extracts (0.5% v/v) for 4hours to make the adsorption product of mild steel and the extract. FTIR spectrum was recorded for the extracts and adsorption product. These spectra were recorded in a Buck Scientific 210 Spectrometer using KBr pellets. This was done to investigate the structural organization of the extracts and adsorption product also identify the functional group present using FTIR
Scanning Electron Microscopy (SEM) Analysis:
SEM-EDX was used to analyze the surface morphology of mild steel before immersion, after immersion without the presence of inhibitor (0.5% v/v) and after immersion in the presence of inhibitors were examined with scanning electron microscope (Model: Aspex 3020). This is to investigate if the inhibitor had effect on the surface of the mils steel.
Atomic Absorption Spectrometric (AAS) Analysis: Atomic absorption spectrophotometric analysis was done to determine the concentration of Iron ion in the acidic solution using atomic adsorption spectrometer model: Buck Scientific 210 VGP. This was carried out to determine the change in concentrations of iron (II) ions in 1M H2SO4 after 4hours immersion time in the presence of different concentration of the extracts of Zea mays cob. The calibration curve of iron ions was drawn before analyzing the electrolyte solution. All samples containing iron ions were diluted with distilled water to ensure that the concentrations of metal ions are within the range of the calibration curve.
RESULTS AND DISCUSSION:
Phytochemicals
Table 1.0 show the phytochemical analysis result of the extract. Phytochemical analysis of the extracts carried out showed that the extracts contains phytochemicals such as flavonoid, steroid, terpenoid and saponin, Anthraquinone and CH2O and alkanoid which are similar to phytochemicals in most plants [22]. These phytochemicals all have anti-oxidant activity and show good chelating behavior with Fe2+ ions in solution. According to [22] they may form a film, spread over metal surface causing a barrier between metal surface and corrosion environment since inhibition process was attributed to the formation of a surface film resulting from interaction between metal ions and inhibitor molecules.
Table 1: Phytochemicals in Zea mays cobs extract
|
Saponim CH2O Terpene Anthraquinone Phenol Flavonoid Cardiac Glycoside Tannins Phtobatanin Steroid Alkanoid |
+ + + + - + - + - + - - + |
Keys:
+ + + = highly present
+ + = moderately present
+ = Trace amount
- =Absent
Fourier Transform Infrared Spectroscopy (FTIR)
The Figure 1 and 2 show IR spectrum of acid extract of Zea mays cob and dried solid product of acid extract of Zea mays cobs (AEZMC) on the mild steel respectively. Absorption bands were observed at 3437.26cm‑1, 1641.48cm‑1, 1198.0cm-1, 869.92cm-1, 581.56cm-1 and 434.96cm-1 which correspond to stretch in amino group (-NH2), Amide group (-CONH2), unsaturated group (C=O, C=C, C=H), far-infrared region (C, N, O, F) and finger-print region. In Amine group, there was blue shift to a higher frequency from 3410.26cm-1 to 3437.26cm- in Figures 1 and 2 respectively. These blue shifts imply that there was strong interaction between the inhibitors molecules and mild steel. There were weak absorption bands at 2937.68cm-1, 2608.81cm-1, 2477.65cm‑1, 2344.55cm-1 and 2206.64cm‑1 respectively which were due to lack of strong interaction between the mild steel surface and the functional groups in the inhibitor.
Figure 1: FT-IR spectrum of acid extract of Zea mays cobs (AEZMC)
Figure 2: FT-IR spectrum of dried solid adsorption product of AEZMC on mild steel
Scanning Electron Microscope-Energy Dispersive X-Ray Spectroscopy (SEM-EDX)
SEM micrographs of the mild steel before and after immersion in 1M H2SO4 solution in the absence and presence of inhibitor are presented in Figure 3-5 respectively while the EDX results are shown in Figure 6-8. EDX analysis revealed that the weight of the mild steel before immersion was 93.39% (Figure 6). However, the weight of the mild steel immersed in 1M H2SO4 reduced to 55.45% (Figure 7), but when immersed in presence AEZMC, the weight increased to 74.41% (Figure 8). This confirms that the extract reduced the corrosion rate of mild steel, hence, reduced the dissolution rate of the iron. The Figures 3 - 5 provide more information on the level of attack as well as inhibitive strength of the extract on the surface of the mild steel used for the study. Figure 3 shows a parallel feature of the polished mild steel before exposure to the corrosion medium, this shows that no corrosion product has been formed on the metal surface while Figure 4 shows unpolished surface confirming corrosion effect on the mild steel as areult of the acid and Figure 5 shows another polished surface (after addition of the inhibitor) indicating that the AEZMC corrosion inhibition on the mild steel was potent.
Figure 3: Photomicrograph of clean mild steel strip (not immersed in acid)
Figure 4: photomicrograph of mild steel strip immersed in 1M H2SO4 acid (blank) solution
Figure 5: Photomicrograph of mild steel strip immersed in 1M H2So4 acid containing 0.5 %v/v
Figure 6: The SEM-EDX spectrum of mild steel
Figure 7: The SEM-EDX spectrum of mild steel in acid
Figure 8: The SEM-EDX spectrum of mild steel in acid with Zea mays cob extract
Atomic Absorption Spectroscopy (AAS):
The dissolution of the extracts in 1M H2SO4 acid for 4 hours and weight loss of mild steel in each concentration of the extract were determined. The calibration curve of iron (II) ions was drawn before analyzing the electrolyte solution. All samples containing irons were diluted with ultra-pure water to ensure that the concentration of metal ions is within the range of the calibration curve. Figure 9 shows the weight loss of the Iron (11) in solution with increase in the concentrations of the extract. It was observed that there was reduction in the concentration of Fe2+ in solution as the concentration of extract increased. This is due to the adsorption of the extracts on surface of iron filing in acidic medium, hence, reduction was observed in the concentration solution.
CONCLUSION:
Figure 9: The plot of Fe2+ in (ppm) against the various concentration of extract in (%v/v)
The research has shown that Zea may cob extract contain phytochemicals that are suitable for the corrosion inhibition, furthermore these phytochemicals all have anti-oxidant activity and show good chelating behavior with Fe2+ ions in solution. The FT-IR result proved that the extract contains inhibition compound and gives an insight on the mode of adsorption of the inhibitor on the mild steel showing that there is strong interaction between the inhibitors molecules and mild steel which supports its inhibition process. Furthermore, The SEM-EDX and AAS analysis support the findings that Zea mays acid extract inhibit corrosion of mild steel in acid medium.
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Received on 14.12.2019 Modified on 31.12.2019
Accepted on 18.01.2020 ŠAJRC All right reserved
Asian J. Research Chem. 2020; 13(2):146-150.
DOI: 10.5958/0974-4150.2020.00029.2