Quercetin-Functionalized β-Cyclodextrin/nZVI Nanocomposites for Nitrophenol Reduction and Corrosion Protection

Quercetin, a naturally occurring polyphenolic flavonoid widely distributed in fruits, vegetables, tea, and wine, exhibits multiple functional moieties capable of stabilizing and functionalizing nanomaterials. Its catecholic group affords strong coordination with metal surfaces, rendering it an effective ligand for magnetic nanoparticles such as nanoscale zerovalent iron (nZVI). Despite the inherent advantages of nZVI including low cost, high catalytic activity, and magnetic recoverability, its rapid oxidation and agglomeration in aqueous media significantly limit practical applications. To overcome these limitations, a magnetic nanocomposite (QCD-nZVI) was synthesized by anchoring nZVI onto quercetin-functionalized β-cyclodextrin (QCD), thereby enhancing its structural stability and reactivity. The QCD-nZVI system demonstrated excellent catalytic efficiency in the aqueous-phase reduction of nitroaromatic compounds, including p-nitrophenol, 2,4-dinitrophenol, and 2,4,6-trinitrophenol, achieving high turnover numbers (TON), turnover frequencies (TOF), and sustained activity over eight catalytic cycles. Moreover, when incorporated into acrylic coatings, QCD-nZVI significantly improved corrosion resistance, as confirmed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) analyses in a 3.5% NaCl solution. A coating containing only 1.5 wt % QCD-nZVI exhibited an exceptionally low corrosion rate of 3.79 × 10–7 mm/year, surpassing both pristine acrylic and QCD-only coatings. These findings underscore the multifunctionality and sustainability of QCD-nZVI, highlighting its potential as a high-performance material platform for integrated applications in catalysis and advanced corrosion protection.