Berberine as a natural source inhibitor for mild steel in 1 M H2SO4
Introduction
Acid solutions are commonly used for removal of undesirable scale and rust in metal finishing industries, cleaning of boilers and heat exchangers. In these situations sulfuric acid is one of the most widely used agents. To prevent unexpected metal dissolution and excess acid consumption in the process of acid cleaning, therefore, inhibitors will be inevitable to be put into use [1]. The most effective and efficient inhibitors are organic compounds that have π bonds [2] and inorganic compounds such as chromate, dichromate, nitrite, etc. [3]. At the same time, the biology toxicity of these products, especially chromate and organic phosphate, are documented about their environmental harmful characteristics [4], [5]. So, the development of novel corrosion inhibitors of natural source and non-toxic type, which do not contain heavy metals and nutrition salts, has been considered more important and desirable [6].
As an alkaloid, berberine could be readily abstracted from natural coptis [7], and the hydrochloric berberine has also been commonly used as a non-toxic antibiotic for years in China [8]. The ortho alkaloid of berberine is presented in Fig. 1, showing a planar isoquinoline structure and possessing π bonds and O atoms, that are regarded as important factors for a good inhibitor. But so far, little is known about the inhibition behavior of berberine for metallic materials in acidic media.
Mild steel was used widely in engineering for its low cost and good mechanical property and availability; therefore, its corrosion inhibition in sulfuric acid was also studied more frequently [9], [10], [11], [12]. In this article, the authors investigated the inhibition behavior of berberine for mild steel in 1 M H2SO4 through weight loss and electrochemical measurements. The test coupons’ surfaces are analyzed using scanning electronic microscope (SEM) and energy disperse spectrometer (EDS). Quantum chemical method was also employed to discuss the correlation of inhibition effect and molecule structure of berberine.
Section snippets
Abstraction and purification of berberine
The berberine was abstracted from coptis chinensis according to the literature [7], [13]. Then the purity was measured by Flouometric thin-layer chromatography as mentioned in reference [14], and the content of berberine was found to be higher than 97%. Berberine obtained was kept in desiccator for later use.
Specimen preparation
Chemical composition of mild steel samples is shown in Table 1.
Specimens used in the weight loss experiment were mechanically cut into 3.0 cm × 1.2 cm × 1.2 cm dimension, then polished with SiC
Weight loss experiment
The weight loss data are listed in Table 2. It can be found that with the rise in berberine concentration, the weight loss of mild steel decreased, while the inhibition efficiency of berberine increased. At the highest concentration of 5.0 × 10−3 M, berberine has a highest inhibition efficiency of about 98%. This result indicated that berberine could act as an excellent sulfuric acid inhibitor.
Open circuit potential
Fig. 2 shows the variation of steady state OCP values of mild steel specimens with the berberine
Conclusions
Berberine abstracted from Coptis chinensis can act as an effective natural source and green corrosion inhibitor for mild steel in 1 M sulfuric acids. The inhibition efficiency measured through weight loss test can reach about 98% for the berberine concentration higher than 5.0 × 10−3 M. The potentiodynamic measurement result indicated both anodic and cathodic processes are suppressed for berberine concentration higher than 1.0 × 10−4 M and mainly cathodic reaction is hindered for lower concentration.
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2021, Arabian Journal of ChemistryCitation Excerpt :Then, vacant d-orbital of iron may interact with the highest occupied molecular orbital (HOMO) of the berberine molecule to form a coordinate bond (donor–acceptor) (Qiang et al., 2018; Sadeghi Erami et al., 2019). In the berberine molecule, the bonding π-orbital of cycles 1 and 2 (shown in Fig. 10) having a more significant electron density can act as HOMO (Li et al., 2005). The donor–acceptor bonding makes the MS surface accumulates extra negative charge; therefore, iron may give back electrons to the lowest unoccupied molecular (LUMO).