Scalable Synthesis of a Plasmonic Copper–Silver Bimetallic Catalyst by Spray-Drying for Nitrophenol and Dye Degradation

The development of efficient, scalable methods for synthesizing bimetallic nanocatalysts is critical for their applications in the fields of environment and energy. Herein, a one-step microdroplet synthesis of copper-silver (CuAg) bimetallic catalysts is reported by leveraging faster reaction kinetics in aqueous microdroplets and utilizing ascorbic acid as a green reductant. Spray-drying served as a scalable method for automated microdroplet generation, enabling a rapid reduction. Immiscibility between copper and silver produced nanometric monometallic grains with abundant Cu-Ag heterojunctions, as confirmed by high-resolution transmission electron microscopy (HR-TEM), selected-area electron diffraction (SAED), and X-ray diffraction (XRD). Evaporation-induced assembly resulted in the aggregation of nanocrystals, whose morphology and size distribution were characterized by using scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS). The CuAg catalysts showed enhanced catalytic activity in 4-nitrophenol reduction and Rhodamine B degradation, surpassing monometallic counterparts. In situ Raman spectroscopy revealed efficient plasmon-driven conversion of nitrothiophenol to dimercaptoazobenzene on the CuAg catalyst at a longer wavelength of 633 nm. The superior catalytic performance is attributed to synergistic electronic interactions between copper and silver. This work establishes spray-drying as a viable, scalable route to produce highly active CuAg catalysts, providing a strategy for the gram-scale synthesis of multimetallic catalysts.