Corrosion Inhibition of Azo Compounds Derived from Schiff Bases on Mild Steel (XC70) in (HCl, 1 M DMSO) Medium: An Experimental and Theoretical Study

The inhibitory activity of three prepared azo compounds derived from Schiff bases, namely, bis[5-(phenylazo)-2-hydroxybenzaldehyde]-4,4'-diaminophenylmethane (C1), bis[5-(4-methylphenylazo)-2-hydroxybenzaldehyde]-4,4'-diaminophenylmethane (C2), and bis[5-(4-bromophenylazo)-2-hydroxybenzaldehyde]-4,4'-diaminophenylmethane (C3), against corrosion of steel type XC70 in (HCl, 1 M DMSO) medium was investigated experimentally by electrochemical measurements and theoretically using density functional theory (DFT). The correlation between corrosion inhibition and concentration is direct. The maximum inhibition efficiency at 6 × 10^-5 M for the three azo compounds derived from Schiff bases was 64.37, 87.27, and 55.47% for C1, C2, and C3, respectively. The Tafel curves indicate that the inhibitors follow a mixed but predominantly anodic inhibitor system and have a Langmuir isothermal adsorption process. The observed inhibitory behavior of compounds was supported by DFT calculation. It was also found that there was a strong correspondence between the theoretical and experimental results.

Modeling and Optimizing the Crystal Violet Dye Adsorption on Kaolinite Mixed with Cellulose Waste Red Bean Peels: Insights into the Kinetic, Isothermal, Thermodynamic, and Mechanistic Study

In this study, a new eco-friendly kaolinite-cellulose (Kaol/Cel) composite was prepared from waste red bean peels (Phaseolus vulgaris) as a source of cellulose to serve as a promising and effective adsorbent for the removal of crystal violet (CV) dye from aqueous solutions. Its characteristics were investigated through the use of X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and zero-point of charge (pH_pzc). The Box-Behnken design was used to improve CV adsorption on the composite by testing its primary affecting factors: loading Cel into the composite matrix of Kaol (A: 0-50%), adsorbent dosage (B: 0.02-0.05 g), pH (C: 4-10), temperature (D: 30-60 °C), and duration (E: 5-60 min). The significant interactions with the greatest CV elimination efficiency (99.86%) are as follows: BC (adsorbent dose vs. pH) and BD (adsorbent dose vs. temperature) at optimum parameters (A: 25%, B: 0.05 g, C: 10, D: 45 °C, and E: 17.5 min) for which the CV's best adsorption capacity (294.12 mg/g) was recorded. The Freundlich and pseudo-second-order kinetic models were the best isotherm and kinetic models fitting our results. Furthermore, the study investigated the mechanisms responsible for eliminating CV by utilizing Kaol/Cel-25. It detected multiple types of associations, including electrostatic, n-π, dipole-dipole, hydrogen bonding interactions, and Yoshida hydrogen bonding. These findings suggest that Kaol/Cel could be a promising starting material for developing a highly efficient adsorbent that can remove cationic dyes from aqueous environments.