Improving Redox Activity of Colloidal Plasmonic-Magnetic Nanocrystals by Chemical State Modulation

Controlling the redox ability is crucial for optimizing catalytic processes in clean energy, environmental protection, and CO₂ reduction, as it directly influences the reaction efficiency and electron transfer rates, driving sustainable and effective outcomes. Here, we report the plasma-electrified synthesis of composition-controlled FeAu bimetallic nanoparticles, specifically engineered to enhance the redox catalytic performance through precise tuning of their chemical states. Utilizing atmospheric-pressure microplasmas, FeAu nanoparticles were synthesized under ambient conditions without the need for reducing agents or organic solvents, thereby providing a green and sustainable approach. The catalytic activity of the FeAu nanoparticles was significantly influenced by the oxidation states of Au (Au⁰, Au^+, and Au³⁺), which were carefully modulated by adjusting the precursor concentration. This precise tuning directly affects the oxidation-reduction potential (ORP) of the nanoparticles, driving their superior degradation performance. The FeAu-1.52 sample exhibited the highest normalized rate constant (k=46.3 s^-1 g^-1), attributed to an optimal Au⁺/Au⁰ ratio that facilitates efficient electron transfer and redox cycling during the catalytic reduction of 4-NP to 4-aminophenol (4-AP). Beyond 4-NP, the FeAu nanoparticles demonstrated robust catalytic degradation of multiple dye pollutants, including Congo Red, Rhodamine B, Methyl Blue, and Methylene Blue, showing their versatility and potential for industrial wastewater treatment. This study elucidates the critical role of chemical state tuning in determining redox performance and presents a promising nanotechnology platform for sustainable environmental remediation.