Peumus boldus extract as corrosion inhibitor for carbon steel in 0.5 M sulfuric acid

Figures & data

Figure 1. Microstructure of the as-received 1018 carbon steel.

Table 1. Effect of P. boldus concentration on the weight loss, inhibitor efficiency and Θ at 25°C, 40°C and 60°C.

Cinh (g/L)	25°C			40°C			60°C
	ΔW (mg/cm^2)	I.E. (%)	Θ	ΔW (mg/cm^2)	I.E. (%)	Θ	ΔW (mg/cm^2)	I.E. (%)	Θ
0	11.6	–	–	14.1	–	–	37.9	–	–
0.1	9.3	20	0.20	12.6	10	0.10	36.1	5	0.5
0.3	8.1	31	0.31	11.2	21	0.21	32.2	15	0.15
0.5	6.3	45	0.45	9.1	35	0.35	26.4	30	0.30
0.7	5.3	54	0.54	7.7	45	0.45	22.7	40	0.40
1.0	3.05	73	0.73	4.5	67	0.67	12.5	59	0.59

Figure 2. (a) Tempkin and (b) Langmuir type of adsorption isotherms for 1018 carbon steel in 0.5 M H₂SO₄ in presence of P. boldus extract.

Figure 3. Arrhenius plot for log (ΔW) versus 1000/T for 1018 carbon steel in 0.5 M H₂SO₄ with 0 and 1.0 g/L of P. boldus.

Figure 4. Effect of P. boldus concentration in the polarization curves for 1018 carbon steel in 0.5 M H₂SO₄ at 25°C.

Table 2. Electrochemical parameters obtained from PC for 1018 carbon steel in 0.5 M H₂SO₄ at different concentrations of P. boldus at 25°C.

Cinh (g/L)	Ecorr (mVSCE)	Icorr (mA/cm^2)	βa (mV/dec)	−βc (mV/dec)	I.E. (%)
0	−455 ± 3.2	0.48 ± 2 × 10^−3	66 ± 3.7	137 ± 6.5	–
0.1	−436 ± 2.4	0.29 ± 1.4 × 10^−3	46 ± 1.5	132 ± 6.3	39
0.3	−419 ± 2.6	0.22 ± 1.1 × 10^−3	33 ± 1.4	118 ± 5.5	49
0.5	−415 ± 3.3	0.12 ± 3 × 10^−4	31 ± 1.2	128 ± 6.2	74
0.7	−429 ± 2.6	0.07 ± 3.5 × 10^−5	33 ± 1.4	139 ± 6.4	87
1.0	−428 ± 2.4	0.03 ± 1.5 × 10^−5	25 ± 1.2	140 ± 7-1	94

Figure 5. Effect of temperature in the polarization curves for 1018 carbon steel in 0.5 M H₂SO₄ containing 1.0 g/L of P. boldus.

Figure 6. Effect of P. boldus concentration in the (a) Nyquist and (b) Bode curves for 1018 carbon steel in 0.5 M H₂SO₄ at 25°C. Symbols are experimental data, lines are the fitted results.

Figure 7. Electric circuits used to simulate obtained EIS data at 25°C.

Figure 8. Temkin type of adsorption isotherm for 1018 carbon steel in 0.5 M H₂SO₄ in presence of P. boldus extract by using data from the PC and EIS measurements.

Table 3. Electrochemical parameters used to fit EIS data shown in Figure 6.

Cinh (g/L)	Rs (ohm cm^2)	Rct (ohm cm^2)	CPEdl (μF cm^−2)	ndl	Rf (ohm cm^2)	CPEf (μF cm^−2)	nf	I.E. (%)
0	2.6 ± 0.13	103 ± 5.1	143 ± 7	0.78	–	–	–	–
0.1	4.4 ± 0.22	110 ± 5.5	52 ± 2.6	0.82	60 ± 3	44 ± 2.2	0.78	6
0.3	5.3 ± 0.25	123 ± 6.1	90 ± 4.5	0.88	75 ± 3.7	32 ± 1.6	0.84	27
0.5	4.3 ± 0.21	154 ± 7.5	13 ± 0.6	0.92	144 ± 7.2	22 ± 1.1	0.90	52
0.7	5.7 ± 0.27	358 ± 17.4	20 ± 1	0.87	100 ± 5	13 ± 0.6	0.85	69
1.0	5.6 ± 0.25	558 ± 27.5	49 ± 2.4	0.79	220 ± 11	7 ± 0.3	0.74	85

Figure 9. Effect of P. boldus concentration in charge transfer resistance, R_ct and double-layer capacitance, C_dl, values for 1018 carbon steel in 0.5 M H₂SO₄ at 25°C.

Figure 10. Effect of temperature in the Nyquist diagrams for 1018 carbon steel in 0.5 M H₂SO₄ containing (a) 0 and (b) 1.0 g/L of P. boldus.

Table 4. Variation of R_ct values for 1018 carbon steel in 0.5 M H₂SO₄ with 0 and 1.0 g/L of P. boldus together with the inhibitor efficiency as a function of testing temperature.

	Testing temperature (°C)
	25	40	60
Rct at 0 g/L (ohm cm^2)	103	50	25
Rct at 1.0 g/L (ohm cm^2)	778	175	50
I.E. (%)	86	72	50

Figure 11. SEM micrographs of 1018 carbon steel immersed in 0.5 M H₂SO₄ containing 0 g/L (a, c and e) and 1.0 g/L (b, d and f) of P. boldus at 25°C (a and b), 40°C (c and d) and 60°C (e and f).

Figure 12. Chemical structure of the main components found in the methanol P. boldus extract showing (a) p-cymene, (b) limonene, (c) eucalyptol, (d) tabanone, (e) α-tocopherol (vitamin E), (f) chrysin and (g) indolo[1-1, 2]isoquinoline, 5,6,12,12a-tetrahydro-2,3,9,10-tetramethoxy (7).

Table 5. Identified compounds according to the chromatogram of P. boldus extract.

Compound name	tr (min)	Relative abundance (%)	[M]+	Fragmentation ions (m/z)
p-Cymene (1)	6.93	1.51	134	119, 103, 91,77
Limonene (2)	6.99	1.48	136	121, 107, 93, 79, 68
Eucalyptol (3)	7.05	2.48	154	139,125, 108, 93, 81, 71
CNI	10.23	7.90	–	–
Tabanone (4)	15.26	1.59	190	175, 148, 133, 119, 105, 92, 77, 69
CNI	25.13	33.96	–	–
Chrysin (5)	27.99	40.53	254	226, 197, 165, 152, 124, 113, 96, 69
Vitamin E (6)	32.43	9.08	430	205, 165
Indolo[2,1-1]isoquinoline, 5,6,12,12a-tetrahydro-2,3,9,10-tetramethoxy (7)	32.79	6.84	341	326, 298, 280, 252, 222, 169, 147, 77

Note: t_r: Retention time; [M+]: molecular ion.

Table 6. Comparison of results obtained with different green inhibitors for steel in different acid environments.

Green corrosion inhibitor	Inhibitor type	Environment	Metal	Efficiency (%)	Adsorption mechanism	Ref.
Spirogyra algae	Mixed	0.5 M HCl	Mild Steel	93	Physical adsorption	(41)
Brassica oleracea	Mixed	0.5 M H2SO4	C-Mn Steel	95	chemisorption	(42)
Pimienta dioica	Mixed	0.5 M HCl	Mild Steel	91	Physisorption and chemisorption	(47)
Retama monosperma	Mixed	1 M HCl	Carbon Steel	94	Physisorption	(48)
Aloe vera	Mixed	1 M HCl	Mild Steel	90	Physisorption and chemisorption	(49)
Psidium guajava	Mixed	1 M H3PO4	Mild Steel	92	Chemisorprtion	(50)
Peumus boldus	Mixed	0.5 M H2SO4	Carbon steel	94	Physisorption	this work

Özcan, M.; Dehri, I.; Erbil, M. Appl. Surf. Sci. 2004, 236, 155–164. doi: 10.1016/j.apsusc.2004.04.017

 Web of Science ®Google Scholar

Solmaz, R.; Kardas, G.; Culha, M.; Yazıcı, B.; Erbil, M. Electrochim. Acta, 2008, 53 (12), 5941–5952. doi: 10.1016/j.electacta.2008.03.055

 Web of Science ®Google Scholar

Verma, D.K.; Khan, F. Green Chem. Lett. Rev. 2016, 9 (1), 52–60. doi: 10.1080/17518253.2015.1137976

 Web of Science ®Google Scholar

Ngobiri, N.C.; Oguzie, E.E.; Li, Y.; Liu, L. Int. J. Corr. 2015, 2015, 9.

 Google Scholar

Poornima, T.; Nayak, J.; Shetty, A.N. J. App. Electrochem. 2011, 41 (2), 223–233. doi: 10.1007/s10800-010-0227-2

 Web of Science ®Google Scholar

Bontiss, F.; Lagrence, M.; Traisne, M. Corrosion, 2000, 56 (6), 733–742. doi: 10.5006/1.3280577

 Google Scholar