A new type of ternary hybrid, Pd@MCM-Calix
ox
, based
on mesoporous silica, calixarene conjugate, and Pd(0) nanoparticles
(NPs) was synthesized by sacrificial oxidation of allylic calixarene
conjugate eventually functionalized with mesoporous silica without
using any external reducing agent. The role of the calix conjugate
in the formation of Pd@MCM-Calix
ox
has been established.
The hybrid, Pd@MCM-Calix
ox
, was characterized by different
techniques to support the formation of well-dispersed Pd(0) NPs of
12 ± 2 nm size. The catalyst, Pd@MCM-Calix
ox
, has
been proven to be a resourceful one in water in three different types
of reactions, namely, Suzuki C–C cross coupling, reduction
of both hydrophilic and hydrophobic nitroaromatic compounds, and reduction
and degradation of cationic, anionic, and neutral organic dyes. The
catalyst exhibited higher turnover frequencies for all these transformations
even when a very low concentration of Pd-based catalyst was used.
The Pd@MCM-Calix
ox
hybrid catalyst can be recycled several
times without experiencing any significant loss in the activity. Also,
the regenerated catalyst showed retention of well-spread Pd(0) species
even after several catalytic cycles. The tetraallyl calixarene, allylCalix,
conjugate acts as a reducing agent, also controls the size, and yields
the well-dispersed Pd(0) NPs. The calix conjugate further provides
a hydrophobic core in assisting the diffusion of hydrophobic substrates
toward catalytic sites.