Plant extracts as green corrosion inhibitors for different kinds of steel: A review

Corrosion significantly threatens the structural integrity of steel-based constructions like buildings and industrial units. Traditional corrosion inhibitors, such as chromates, are associated with environmental and health risks. This has led to a growing interest in environmentally sustainable alternatives, with plant extracts emerging as promising candidates. These extracts are widely available, sustainable, and eco-friendly. This review aims to explore the potential of plant extracts as corrosion inhibitors for various types of steel. After examining current scientific literature, over 40 plant extracts have been identified that exhibit corrosion inhibition properties. These extracts have been thoroughly analyzed to understand their effectiveness in preventing corrosion. The review elucidates the mechanisms by which these extracts interact with metal surfaces to form protective layers, effectively hindering the corrosion process. In this review, we focus on the challenges associated with utilizing plant extracts as inhibitors, including optimal extract concentration and temperature considerations.

Insight into Cu (II) adsorption on pyrochar and hydrochar resultant from Acacia Senegal waste for wastewater decontamination

Acacia Senegal waste (ASW) is remaining biomass following gum Arabic harvesting and has no use mentioned in the literature as of yet. This study aims to convert ASW into valuable biochar via two comparative thermal and hydrothermal techniques, which include pyrochar ASW at 300 °C (PC ASW300) and hydrochar ASW at 180 °C (HC ASW180), respectively, for Cu (II) adsorption from aqueous solutions. SEM-EDS, FTIR, XRD, and XPS were used to characterize the biochar. Adsorption performance was studied as a function of pH, contact time, and adsorbent concentration. Adsorption kinetics were best fit for a pseudo-second-order model. And thermodynamics studies revealed that Cu (II) on biochar was endothermic, spontaneous, and best fitted to the Langmuir isotherm model. Pyrochar adsorption capacity (31.93 mg g-1) was seven times that of hydrochar (5.45 mg g-1). ASW treated with phosphorus (PC H3PO4 and HC H3PO4) prior to the carbonization altered the pore structure and surface functional groups as well (O-P-O, P-CH3, and P-OH) of biochar. It was found that treating with phosphorous acid increased adsorption capacity to 141.7 mg g-1 and 22.24 mg g-1 for PC H3PO4 and HC H3PO4, respectively. The surface functional groups of biochar resulted from lignin, alkaloids, and polysaccharides combined with Cu (II) during the adsorption process via surface complexation accompanied by π-electron interaction and Cu (II) reduction. These findings shed light on the ASW biochar potential as a new green cost-effective adsorbent and drew an insightful understanding of Cu (II) adsorption performance and mechanism. It is concluded that ASW-derived biochar is highly effective and a promising alternative for Cu (II) decontamination from wastewater.

Alkaloid Extract of Ageratina adenophora Stem as Green Inhibitor for Mild Steel Corrosion in One Molar Sulfuric Acid Solution

Green corrosion inhibitors are of great interest due to their exciting and environmentally friendly behavior in mild steel corrosion control during and after the acid cleaning process. Herein, alkaloids were extracted from the stem of Ageratina adenophora and were ensured by qualitative chemical tests as well as spectroscopic test methods. The corrosion inhibition efficacy of the alkaloids against mild steel corrosion was evaluated by gravimetric, electrochemical and EIS measurement methods. In addition, the adsorption isotherm, free energy of adsorption and thermodynamic parameters of the process were evaluated. The investigations indicated the most promising inhibition efficacy of the alkaloids for mild steel corrosion. The adsorption isotherm study revealed that the adsorption of inhibitor molecules on the MS interface was manifested by dominant physisorption followed by chemisorption. Free energy and thermodynamic parameters are well suited to endothermic processes.

Alkaloids of Solanum xanthocarpum Stem as Green Inhibitor for Mild Steel Corrosion in One Molar Sulphuric Acid Solution

The residual ions of the acid cleaning processes induce the further corrosion of the metals, and this could be minimized using green inhibitors. Alkaloids extracted from plant parts could be cost effective and efficient inhibitors. In this work, alkaloids from Solanum xanthocarpum stem were successfully extracted, and they were characterized by qualitative chemical tests and spectroscopic measurements. As-extracted alkaloids were employed as green corrosion inhibitors for mild steel. The effectiveness of the inhibitor was determined by the weight loss and electrochemical measurement methods. From the weight loss measurement, the maximum inhibition efficiency of 93.14% was achieved. The temperature effect study revealed that the inhibitor can work up to a temperature of 58 °C. This could be one of the highest working temperatures among the reported green inhibitors. The electrochemical measurement reveals that the alkaloids could inhibit effectively up to 98.14% of the corrosion and serve as a mixed-type green inhibitor. A study on the kinetic parameters reflects that the inhibitor forms a potential barrier for the protection of a mild steel surface against corrosion. The values obtained from the thermodynamic parameters study reflect that the process is a spontaneous endothermic process. Based on the findings, it is revealed that the alkaloids extracted from S. xanthocarpum can serve as an excellent, eco-friendly and a promising green inhibitor against mild steel corrosion.

Coriaria nepalensis Stem Alkaloid as a Green Inhibitor for Mild Steel Corrosion in 1 M H2SO4 Solution

Using natural plant extracts on metallic substances is the most frequently studied green corrosion inhibition approach in corrosion science. In this work, Coriaria nepalensis Stem Alkaloid (CNSA) has been successfully extracted and characterized by qualitative chemical (Mayer’s and Dragendroff’s) test and spectroscopic (UV and FTIR) measurement. CNSA has been employed as a green inhibitor for Mild Steel (MS) corrosion subjected to 1 M H2SO4 solution. The corrosion inhibition efficacy has been assessed by weight loss and polarization measurement methods. The effect of inhibitor concentration, immersion period, and temperature on the inhibition efficiency for the MS immersed in both acid and inhibitor solutions of different concentrations have been investigated. The maximum inhibition effect observed for CNSA is 96.4% for MS immersed in 1000 ppm inhibitor solution for 6 h at 18 °C by the weight loss measurement method. Similarly, the polarization measurement method observed a 97.03% inhibition efficiency for MS immersed for 3 h. The adsorption of inhibitor molecules on the MS surface aligns with the Langmuir model. The free energy of adsorption obtained is −28.75 kJ/mol indicating physical adsorption dominance over chemical adsorption. These findings suggested that CNSA has greater potential as an efficient green inhibitor.