Selective Cu4Pd alloy nanoparticles anchoring on amine functionalized graphite nanosheets and their use as reusable catalysts for a C–C coupling reaction with the sacrificial role of Cu for Pd-regeneration

Abstract

A facile method for the synthesis of phase selective alloy nanoparticles (NPs), Cu₄Pd and their in situ anchoring on the surface of amine functionalized graphite nanosheets (AFGNS) by solvothermal process has been demonstrated. It has been seen that upon adding CuCl₂·H₂O and PdCl₂ into the reaction medium containing AFGNS, the –NH₂ group initially helps to immobilize Cu²⁺ ions from CuCl₂·H₂O. During the solvothermal reaction in presence of N,N-dimethylformamide (DMF; solvent cum reducing agent) Pd²⁺ gets reduced first due to its higher reduction potential. These Pd NPs in turn help in the reduction of Cu²⁺ to Cu in an epitaxial manner. Finally at high temperature and long reaction time Cu and Pd combine to form the Cu₄Pd alloy NPs along with a small fraction of Cu NPs. The conditions to obtain Cu₄Pd NPs have been optimized through controlled reactions. The as prepared Cu₄Pd@AFGNS composite has been successfully used for Suzuki–Miyuara C–C coupling reaction with sufficiently high yield and reusability of up to five cycles. The progress of the reaction was monitored using a fluorimeter. Interestingly, it has been observed that the small fraction of the Cu NPs present in the system played a sacrificial role in regenerating metallic Pd NPs in the first and second reaction cycles, followed by Cu from the Cu₄Pd alloy itself from the third cycle onwards which played the sacrificial role to regenerate Pd(0). A probable reaction mechanism of the catalytic reaction with Cu₄Pd@AFGNS has been suggested.