Construction of recyclable and photo-regenerative composite catalyst Fe3O4@IPTS-Azo@βCD-AuNPs for green and sustainable detoxication of aquatic 4-nitrophenol

Gold nanoparticles (AuNPs) exhibit excellent catalytic activity in reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using sodium borohydride (NaBH4). However, due to their high surface energy, AuNPs tend to aggregate, leading to reduced catalytic efficiency and stability. To overcome this limitation, in this study, azobenzene (Azo) modified Fe3O4 was utilized as a magnetic carrier to load beta-cyclodextrin (beta-CD) modified AuNPs. The reversible multivalent host-guest interaction between Azo and beta-CD was employed to develop a recyclable and photo-regeneratable catalyst, Fe3O4@IPTS-Azo@beta CD-AuNPs (IPTS refers to (3-isocyanoisopropyl) triethoxysilane). Through photo-induced isomerization of Azo between its trans and cis forms, the AuNPs could be selectively removed from or reloaded onto the carrier. This process is controlled by UV irradiation (causing transto-cis isomerization) or visible light irradiation (inducing cis-to-trans isomerization), thereby switching the hostguest behavior of the photo-responsive linker Azo@beta-CD. The results showed that the average size of the synthesized beta CD-AuNPs was 8.56 nm, and the crystal structure of the AuNPs was validated by HR-TEM and XRD. The clearance rate of 4-NP reaches 99 % in 5 min with the rate constant (k) of 0.3001 min-1 at 25 degrees C. AuNPs, in both 20th recycled and 12th photo-regenerated composite catalysts, exhibited high efficiency in reducing nitroaromatic pollutant 4-NP. This work presents a pathway to achieve a green and sustainable technology for efficiently intoxicating aqueous nitroaromatic pollutants.