Uninterrupted galvanic reaction for scalable and rapid synthesis of metallic and bimetallic sponges/dendrites as efficient catalysts for 4-nitrophenol reduction

Abstract

Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu-M, M=Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1-2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4-a widely studied conversion process.

Iridium Oxide Nanoparticles and Iridium/Iridium Oxide Nanocomposites: Photochemical Fabrication and Application in Catalytic Reduction of 4-Nitrophenol

“…It has been reported that the transition metals such as Au, ,, Ag, , Pt–Ni, Pd–Ag, and Ni–Co can catalyze the reduction of 4-nitrophenol by NaBH 4 . It is widely accepted that the following two steps are involved in the transition-metal-catalyzed reduction of 4-nitrophenol by NaBH 4 : , (1) The BH 4 – ions first chemically adsorb on metal surface and then release highly active hydrogen radicals, which are also adsorbed on metal surface. (2) The adsorbed hydrogen radicals react with adsorbed 4-nitrophenol (or 4-nitrophenolate) to produce 4-aminophenol (or 4-aminophenolate), or they react with water to generate H 2 , which can reduce 4-nitrophenol (or 4-nitrophenolate) in solution.…”

Metallic nanosponges for energy storage and conversion applications

“…81 According to the report by Barman and Nanda, metallic (Ag, Cu and Sn) and bimetallic sponges (Cu–M, M = Ag, Au, Pt and Pd) were prepared by etching of a low reduction potential metal with sulfuric acid (H 2 SO 4 ). 82 The application of H 2 SO 4 led to a high yield synthesis without side product formation and prevented the oxide formation. The acid concentration and etching time can control the degree of etching and structural features; for a fixed time, increasing the concentration of HNO 3 for dealloying the Au–Cu alloy led to an increase in Cu leaching to give a bigger pore size and thicker ligaments.…”

“…83 While nitric acid is the most commonly used etchant for chemical dealloying due to strong oxidizing nature, other etchants such as citric acid, ferric nitrate, sulfuric acid, and ammonia have also been reported. 75,[81][82][83] It is important to note that dealloying does not entirely remove the less noble metal and that the residual remaining of less noble metal can signicantly improve the electrocatalytic activity. 80 3.1.2 Electrochemical dealloying.…”