Silver Nanocatalysts Supported by Multiple Melanin Carriers with a Photothermal Effect for Reduction of Methylene Blue and 4-Nitrophenol

Although the photothermal effect can effectively enhance catalytic wastewater treatment reactions, the development of high-efficiency, low-cost, and stable catalysts with a photothermal effect still presents a challenging endeavor. Through the utilization of an in situ reduction strategy, an economical and convenient modification of small-sized silver (Ag) nanoparticles (NPs) on sepia eumelanin (SE) and artificial allomelanin (AMNP) supports was achieved, leading to the formation of Ag/SE and Ag/AMNP nanocomposite materials. Simultaneously, Ag/AMNPs lacking nitrogen elements were employed as a control, and the contribution of nitrogen-containing groups in Ag/SE to the loading of Ag NPs was investigated. Unique SE nanospheres with high surface area exhibited excellent light absorptivity and photogenerated carrier separation efficiency as well as superior light-driven thermogenesis, which can further increase the temperature of the reaction system to accelerate the catalytic reduction of MB (5 min, 80 × 10–2 min–1) and 4-NP (240 s, 14.12 × 10–3 s–1). A possible mechanism for the synergistic action of photothermal catalysis is proposed. This study demonstrates that SE not only serves as an effective support for immobilized silver NPs but also functions as a photothermal conversion center, thereby enhancing catalytic reactions. This provides a promising avenue for the design of stable catalyst composites with high-performance photothermal synergistic catalysis.