Protoporphyrin Extracted from Biomass Waste as Sustainable Corrosion Inhibitors of T22 Carbon Steel in Acidic Environments

High-Efficiency Corrosion Inhibitor of Biomass-Derived High-Yield Carbon Quantum Dots for Q235 Carbon Steel in 1 M HCl Solution

Eco-friendly self-doped carbon quantum dots (ZCQDs) with excellent corrosion inhibition ability were prepared via solid-phase pyrolysis only using Zanthoxylum bungeanum leaves as the raw material. Compared with the relevant research, a simpler and higher yield (25%) preparation process for carbon quantum dots was proposed. ZCQDs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy, and the average size of ZCQDs with multitudes of O- and N-containing functional groups was about 2.53 nm. The prepared ZCQDs were used to inhibit the corrosion of Q235 steel in HCl solution, and the inhibition behavior was investigated through weight loss, electrochemical test, surface analysis, and adsorption thermodynamic analyses. The results showed that the ZCQDs, acted as a mixed corrosion inhibitor, have an effective corrosion inhibition for Q235, the corrosion inhibition efficiency reached 95.98% at 200 mg/L, and at this concentration, effective protection of at least 132h (IE > 90%) is provided. Moreover, the adsorption mechanism of ZCQDs was consistent with that of Redlich-Peterson adsorption, including chemisorption and physisorption. A new corrosion inhibition mechanism of ZCQDs has been thoroughly studied and proposed; ZCQDs have functional groups containing O and N, which can form a protective barrier through physical adsorption and chemisorption, but the coverage of the protective film is low at low concentrations. With the increase of concentration, the protective film formed by ZCQDs on the metal surface will first increase the coverage and then adsorb more ZCQDs on the protective film to form a thicker and denser protective film to protect the metal. The carbon quantum dots prepared in this paper have advantages including a green, renewable precursor, a fast method, high yield, and excellent corrosion inhibition. Therefore, this work can inspire and facilitate, to a certain extent, the future application of doped carbon quantum dots as efficient corrosion inhibitors in HCl solutions.

Investigation of Dracocephalum extract based on bulk and nanometer size as green corrosion inhibitor for mild steel in different corrosive media

In recent years, green corrosion inhibitors derived from natural plant resources have garnered much interest. In the present work, at first, we investigated the corrosion behavior of mild steel (st-37) in the presence, and absence of Dracocephalum extract based on bulk size as a corrosion inhibitor in two widely used acidic environments (0.5 M H₂SO₄, and 1.0 M HCl), at room temperature. Then, we used Dracocephalum extract based on nanometer size to reduce the optimal concentration of inhibitor, increase the corrosion resistant, and efficiency. Dracocephalum extract does not contain heavy metals or other toxic compounds, and also good characteristics such as low cost, eco-friendly, and widespread availability, make it suitable nature candidate as an environmentally safe green inhibitor. The anticorrosive behavior was assessed using electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PP). In all of the studies, the inhibitory efficiency (IE%) increased as the extract dose was increased. But by using nano extract, in addition to maintaining high efficiency, the amount of inhibitor was reduced significantly. The highest IE% is 94% at the best dose of nano extract (75 ppm), but the highest IE% is 89% at the best dose of the bulk extract (200 ppm) in H₂SO₄ solution. Also, for the HCl solution, the highest IE% is 88% at the best dose of nano extract (100 ppm), but the highest IE% is 90% at the best dose of the bulk extract (400 ppm), by polarization method. The PP results suggest that this compound has an effect on both anodic, and cathodic processes, and that it adsorbs on mild steel surface according to the Langmuir adsorption isotherm. Optical microscopy, scanning electron microscopy (SEM) analysis, and a solid UV-Visible reflection spectrum were used to investigate the alloys' surface morphology.

Synthesis of tolyl guanidine as copper corrosion inhibitor with a complementary study on electrochemical and in silico evaluation

A rapid and new synthetic route for N,N'-di-o-tolyl guanidine (DTG) synthesis from cheap materials is reported. The performance of DTG as an excellent inhibitor for delaying copper (Cu) corrosion with an efficiency higher than 98% at 20 × 10^-6 M in an acidic solution was investigated via electrochemical measurements. These measurements included PDP, EFM, and EIS spectroscopy. The experimental data indicated that DTG has an efficient inhibiting effect on the corrosion of Cu in acidic media.The DTG was adsorbed on to the Cu surface via chemical adsorption and followed the Langmuir route. The PDP measurements revealed that DTG acted as a mixed inhibitor. Furthermore, EIS data showed that the DTG adsorbed through the metal/electrolyte interface. This resulted in forming a DTG protective layer on the Cu surface, thereby impeding the dissolution of Cu in the acidic solution. The corrosive solution containing the DTG inhibitor after immersion of the Cu specimen for 48 h, which promoted the formation of a complex between the Cu cation and DTG, was investigated via ultraviolet/visible spectroscopy. In addition, the formation of a DTG protective layer on the Cu surface was confirmed via scanning electron microscopy and atomic force microscopy analysis of the Cu surface morphology. Moreover, the active centers for interaction with the Cu surface in an acidic solution were investigated via in silico evaluation of DTG.

One A3B Porphyrin Structure—Three Successful Applications

Porphyrins are versatile structures capable of acting in multiple ways. A mixed substituted A₃B porphyrin, 5-(3-hydroxy-phenyl)-10,15,20-tris-(3-methoxy-phenyl)-porphyrin and its Pt(II) complex, were synthesised and fully characterised by ¹H- and ¹³C-NMR, TLC, UV-Vis, FT-IR, fluorescence, AFM, TEM and SEM with EDX microscopy, both in organic solvents and in acidic mediums. The pure compounds were used, firstly, as sensitive materials for sensitive and selective optical and fluorescence detection of hydroquinone with the best results in the range 0.039–6.71 µM and a detection limit of 0.013 µM and, secondly, as corrosion inhibitors for carbon–steel (OL) in an acid medium giving a best performance of 88% in the case of coverings with Pt-porphyrin. Finally, the electrocatalytic activity for the hydrogen and oxygen evolution reactions (HER and OER) of the free-base and Pt-metalated A₃B porphyrins was evaluated in strong alkaline and acidic electrolyte solutions. The best results were obtained for the electrode modified with the metalated porphyrin, drop-casted on a graphite substrate from an N,N-dimethylformamide solution. In the strong acidic medium, the electrode displayed an HER overpotential of 108 mV, at i = −10 mA/cm² and a Tafel slope value of 205 mV/dec.