Facile Synthesis of FeO@Tannic Acid@Au Nanocomposites as a Catalyst for 4-Nitrophenol and Methylene Blue Removal.

A facile, cost-effective, and eco-friendly method was proposed to synthesize FeO@tannic acid@Au nanocomposites (FeO@TA@Au). First, FeO nanoparticles with diameters of 20 and 200 nm were synthesized by co-precipitation and solvothermal methods, respectively. Gold nanoparticles were deposited on magnetic FeO through tannic acid-metal-polymer intermediate-layer-mediated reductions. The catalytic activities of the as-prepared FeO@TA@Au were investigated by spectroscopically monitoring the reduction of 4-nitrophenol (4-NP) and methylene blue (MB), which could be achieved within several minutes with an excess of NaBH. The impact of the FeO size on the overall catalytic ability of the FeO@TA@Au was systematically studied. The reaction rate constants of the FeO-20 nm@TA@Au for 4-NP and MB reduction were 0.432 and 0.543 min, respectively. For the FeO-200 nm@TA@Au nanocomposite, the optimized reaction rate constants for 4-NP and MB reduction were 3.09 and 0.441 min, respectively. Due to magnetic separation, the FeO@TA@Au could be easily harvested and recycled. After five recycling cycles, the catalytic ability remained over 90%, and the recycling process could be completed in several minutes, highlighting its potential as a catalyst for 4-NP and MB removal.