Theoretical and experimental studies on the corrosion inhibition potentials of 3-nitrobenzoic acid for mild steel in 0.1 M H₂SO₄

Figures & data

Figure 1. Chemical structure of 3-nitrobenzoic acid.

Figure 2. Variation of weight loss with time for the corrosion of mild steel in 0.1 M H₂SO₄ containing various concentrations of 3-nitrobenzoic acid at 303, 313, 323 and 333 K.

Table 1. Corrosion rate of mild steel (in solution of 0.1 M H₂SO₄) and inhibition efficiency of 3-nitrobenzoic acid for mild steel corrosion (in 0.1 M H₂SO₄)

C (M)	Corrosion rate (g/h cm^2)				Inhibition efficiency (%)
	303 K	313 K	323 K	333 K	303 K	313 K	323 K	333 K
Blank	0.000198	0.000212	0.000249	0.000294	–	–	–	–
0.002	0.000151	0.000187	0.000219	0.000252	63.40	58.25	51.72	43.39
0.004	0.000145	0.000172	0.000178	0.000229	69.20	62.81	58.22	49.74
0.006	0.000119	0.000160	0.000170	0.000191	78.83	65.14	63.25	54.50
0.008	0.000063	0.000116	0.000133	0.000167	82.14	74.58	69.61	60.23
0.010	0.000023	0.000076	0.000103	0.000133	87.15	79.84	71.20	63.60

Table 2. Polarization data for the corrosion of mild steel in 0.1 M H₂SO₄ in the absence and presence of 3-nitrobenzoic acid at 303 K

C (M)	LPR		PDP
		%I	βa (mV/dec)	βc (mV/dec)	Ecorr (mV)	Icorr (μA)	I %
Blank	20.40	–	139.4	146.1	−863	210.36	–
0.001	68.05	70.02	121.1	128.3	−944	36.97	82.42
0.010	156.54	86.96	118.3	120.2	−991	25.23	88.00
0.015	445.20	95.42	109.1	111.1	−920	19.95	90.51

Figure 3. Potentiodynamic polarization curves for the mild steel in 0.1 M H₂SO₄ in the absence and presence of different concentrations of 3-nitrobenzoic acid.

Figure 4. Nyquist plots for the mild steel in 0. 1 M H₂SO₄ in the absence and presence of different concentrations of 3-nitrobenzoic acid.

Table 3. EIS parameters for corrosion of mild steel in 0.1 M H₂SO₄ in the absence and presence of different concentrations of 3-nitrobenzoic acid at 303 K

C (M)	Rct (Ω cm^2)	Rs (Ω cm^2)	Cdl (μF cm^−2)	% I
Blank	27.8920	4.522	2320	–
0.001	1429.236	75.021	1840	98.05
0.015	4663.606	97.204	1485	99.40

Figure 5. Arrhenius plot for the corrosion of mild steel in 0.1 M H₂SO₄ containing various concentrations of 3-nitrobenzoic acid.

Table 4. Arrhenius and Transition state parameters for the adsorption of 3-nitrobenzoic acid on mild steel surface

C (M)	Arrhenius parameters			Transition state parameters
	A	Ea (J/mol)	R^2	$\mathrm{\Delta }{S}_{\text{ads}}^0(\text{J/mol})$	$\mathrm{\Delta }{H}_{\text{ads}}^0(\text{J/mol})$	R^2
Blank	0.0164	11.20	0.9703	−174.96	−8.58	0.9489
0.002	0.0413	11.68	0.9902	−167.27	−11.47	0.9860
0.004	0.0149	12.31	0.9258	−167.42	−9.07	0.8815
0.006	0.0167	14.09	0.8990	−166.49	−9.69	0.8485
0.008	0.5928	23.26	0.8991	−167.64	−12.57	0.9702
0.010	1.7402	25.45	0.9975	−145.00	−20.69	0.9970

Figure 6. Transition state plot for the corrosion of mild steel in 0.1 M H₂SO₄ containing various concentrations of 3-nitrobenzoic acid.

Figure 7. Langmuir isotherm for the adsorption of 3-nitrobenzoic acid on mild steel surface.

Table 5. Langmuir and Frumkin parameters for the adsorption of 3-nitrobenzoic acid on the surface of mild steel

Isotherm	T (K)	Slope	log bads	“a”	$\mathrm{\Delta }{G}_{\text{ads}}^0\left(\frac{\text{kJ}}{\text{mol}}\right)$	R^2
Langmuir	303	0.7982	0.3396	–	−12.09	0.9982
	313	0.8097	0.2648	–	−11.65	0.9927
	323	0.7939	0.2654	–	−11.66	0.9999
	333	0.7611	0.2763	–	−11.72	0.9988
Frumkin	303	1.8343	2.4358	0.92	−24.25	0.9858
	313	1.6126	1.7404	0.81	−20.88	0.9708
	323	1.5374	1.4600	0.77	−19.82	0.9961
	333	1.5105	1.2417	0.76	−19.04	0.9967

Figure 8. Frumkin isotherm for the adsorption of 3-nitrobenzoic acid on mild steel surface.

Figure 9. Scanning electron micrographs of the corrosion product of mild steel in the absence and presence of 3-nitrobenzoic acid (as an inhibitor) at various magnifications.

Table 6. Frequencies and peak of IR absorption by the corrosion product of mild steel in the absence and presence of 3-nitrobenzoic acid

Corrosion product before adsorption of 3-nitrobenzoic acid			Corrosion product after adsorption of 3-nitrobenzoic acid
Frequency (cm^−1)	Intensity	Functional group	Frequency (cm^−1)	Intensity	Functional group
			651	39.950	C–H bending
741	27.846	C–H bending	746	20.769	C–H bending
			862	34.894	Nitrate N–H stretching
981	60.066	Carbon ring vibration	979	21.909	Carbon ring vibration
1072	16.272	C–O vibration
1128	13.530	Aromatic C–H stretch
1298	12.835	C–O stretch	1266	19.929	C–O stretch
1372	39.619	NO2 symmetry stretch
1454	26.111	Aromatic C=C stretch	1451	16.530	Aromatic C=C stretch
1589	59.932	Aromatic C–H stretch	1589	25.776	Aromatic C–H stretch
			1698	18.851	C=O stretch
1746	14.322	C=O stretch	1750	18.849	C=O stretch
1955	96.234	N–H stretch	1957	78.849	N–H stretch
			2100	87.125	Aromatic –N≡C stretching
2658	84.001	Carboxylic acid OH stretch	2653	61.375	Carboxylic acid OH stretch
2858	15.270	C–H stretch
2952	14.386	C–H stretch	2943	22.560	C–H stretch
3516	77.050	OH stretch	3498	23.560	OH stretch

Table 7. Calculated semi-empirical parameters of 3-nitrobenzoic acid for various Hamiltonians

Hamiltonian	EHOMO (eV)	ELUMO (eV)	Ebinding (eV)	Eelectronic (eV)	ECCR (eV)	μ (Debye)	ETE (eV)
INDO	−12.44	1.11	−5346.13	−293716.58	210194.70	4.025	−83521.87
PM3	−11.11	−1.68	−1853.21	−238756.53	187115.60	4.146	−51640.92
AMI	−11.146	−1.68	−1833.93	−245551.58	189074.61	4.060	−56476.97
RMI	−10.91	−1.53	−1183.16	−244816.68	188990.41	3.736	−55826.20
MNDO	−10.90	−1.71	−1825.19	−245963.55	189320.54	3.947	−56643.01
CNDO	−13.15	0.79	−5637.45	−297254.40	210194.70	4.261	−87059.69

Table 8. Fukui functions for 3-nitrobenzoic acid calculated using Ab initio and DFT

Atom No.	Abinitio		DFT		Huckel charge
	$f_x^{+}$	$f_x^{-}$	$f_x^{+}$	$f_x^{-}$
1 C	0.0274	−0.0617	−0.1938	−0.1315	0.5671
2 C	−0.0406	−0.0521	0.3326	−0.2759	−0.0075
3 C	−0.0212	−0.0013	0.2080	−0.2017	0.0329
4 C	−0.1335	−0.5221	−0.1062	0.1307	0.0863
5 C	−0.0147	−0.0342	−0.2568	0.0641	0.0286
6 C	−0.0162	−0.0696	0.0168	−0.2186	−0.0300
7 C	−0.0265	−0.0674	−0.1763	−0.0045	0.0301
8 O	0.0842	−0.1082	0.1488	−0.2118	−0.6696
9 O	−0.1038	−0.0330	2.2834	−2.3159	−0.1463
10 N	−0.0464	0.0447	−0.0526	0.2781	1.2699
11 O	−0.3272	−0.0698	1.5145	−1.6966	−0.7331
12 O	−0.1255	−0.0299	0.1807	−0.0120	−0.7333

Figure 10. Homo and LUMO diagrams of 3-nitrobenzoic acid calculated from extended Huckel theory.