Chitosan-Modified Bentonite as a Controlled-Release Carrier for Tannin: Loading Optimization, Structural Characterization, and Potential Anticorrosion Applications

Bentonite-based carriers can be used to control the release of natural corrosion inhibitors. In this study, sodium-activated bentonite was used to load tannin and was subsequently modified with chitosan to regulate tannin release. The effects of contact time and initial pH on tannin loading were investigated using UV-Vis spectrophotometry. The highest adsorption capacity (56.98 ± 0.72 mg g−1) was obtained at an initial pH of 4.5 and a contact time of 12 h. The prepared materials were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). FTIR results showed changes in the hydroxyl and silicate regions after modification. XRD analysis showed small changes in the basal spacing from 14.42 Å for Bent to 14.88 Å for Bent@Tan and 14.60 Å for Bent@Tan@Chit, indicating that the layered structure was largely preserved. TGA showed an increase in mass loss between 200 and 450 °C from 1.42% for Bent to 2.25% for Bent@Tan and 6.68% for Bent@Tan@Chit, consistent with the presence of additional organic components. Tannin release was investigated in 3.5 wt.% NaCl solution at an initial pH of 5.0 over 48 h. Bent@Tan showed rapid initial release, while Bent@Tan@Chit showed lower early release followed by a gradual increase. Kinetic analysis showed the highest goodness of fit for the first-order model for Bent@Tan (R2 = 0.816) and the zero-order model for Bent@Tan@Chit (R2 = 0.968). These results demonstrate differences in the apparent tannin release profiles of Bent@Tan and Bent@Tan@Chit. The prepared composite may be considered for future studies of anticorrosion coatings; however, its corrosion-inhibiting performance has not yet been experimentally evaluated.