pH‐Dependent Galvanic Replacement of Supported and Colloidal Cu₂O Nanocrystals with Gold and Palladium

Abstract

Galvanic replacement reactions (GRRs) on nanoparticles (NPs) are typically performed between two metals, i.e., a solid metal NP and a replacing salt solution of a more noble metal. The solution pH in GRRs is commonly considered an irrelevant parameter. Yet, the solution pH plays a major role in GRRs involving metal oxide NPs. Here, Cu(2)O nanocrystals (NCs) are studied as galvanic replacement (GR) precursors, undergoing replacement by gold and palladium, with the resulting nanostructures showing a strong dependence on the pH of the replacing metal salt solution. GRRs are reported for the first time on supported (chemically deposited) oxide NCs and the results are compared with those obtained with corresponding colloidal systems. Control of the pH enables production of different nanostructures, from metal-decorated Cu(2)O NCs to uniformly coated Cu(2)O-in-metal (Cu(2)O@Me) core-shell nanoarchitectures. Improved metal nucleation efficiencies at low pHs are attributed to changes in the Cu(2)O surface charge resulting from protonation of the oxide surface. GR followed by etching of the Cu(2)O cores provides metal nanocages that collapse upon drying; the latter is prevented using a sol-gel silica overlayer stabilizing the metal nanocages. Metal-replaced Cu(2)O NCs and their corresponding stabilized nanostructures may be useful as photocatalysts, electrocatalysts, and nanosensors.

Wheat ‐Gluten‐Directed Facile Synthesis of AgAuQC: Probing Inner Filter Effects and Electron Transfer for Bilirubin Detection

“…The effect of temperature on the formation of the alloy was studied by varying the temperature of the mixture from room temperature to 80 °C.It was observed that the AgAuQC synthesized at 55 °C exhibited the highest emission intensity (Figure E).Hence, the synthesis conditions like the concentration of HAuCl 4 , the reaction temperature and the pH of the medium were optimized as 1 mM, 55 °C and 5–6 pH, respectively. The influence of the solution pH on the mechanism and products in GERs has not been addressed in most of the published works as the acid and base have no influence on the redox potential of metal ions . Thus, GER is considered to be a pH‐independent reaction.…”

Galvanic Replacement of Electrochemically Restructured Copper Electrodes with Gold and Its Electrocatalytic Activity for Nitrate Ion Reduction

“…Therefore, to promote Au formation on Cu 2 O, the solution should be acidic to force reaction 2 to the right. This is ensured when 5 mM of HAuCl 4 is used for the galvanic replacement process [ 48 ]. Figure 4 shows SEM images of the restructured copper electrode after galvanic replacement with gold using 5 mM HAuCl 4 for 1, 3 and 5 min.…”

“…This approach has been used to create many copper based bimetallic electrodes with interesting properties [ 41 , 42 , 43 , 44 ]. However, this work has also been extended to the galvanic replacement of metal oxide surfaces, such as Cu 2 O to create Cu 2 O/M (M = Pt, Pd, Au) materials that have potentially excellent applications [ 45 , 46 , 47 , 48 , 49 , 50 ].…”

Mechanistic control of a galvanic replacement reaction on cuprous oxide

“…As disproportionation is characteristic of the interfacial chemistry between the acidic media and the Cu 2 O surface, it potentially mediates the GR reaction observed for other noble metal salts, such as Ag + , PtCl 6 2À or PdCl 4 2À , which also have appropriate reduction potentials for driving GR reactions on Cu and Cu 2 O. [31][32][33][34]…”