posted on 2022-02-02, 16:08authored byHaamid Haroon, Malik Wahid, Kowsar Majid
The
C–C coupling is an efficient route toward the synthesis
of symmetric biphenyls from aryl halides. Herein, a cost-effective
visible nanophotocatalyst system (Cu3P/hBN), consisting
of heterogeneous, nanoporous, and nanosized Cu3P (derived
from HKUST MOF) and hexagonal boron nitride (hBN), is employed for
the photocatalytic coupling of aryl halides. The catalyst efficiently
executes the aryl halide coupling to biphenyls under visible light
and in the presence of air at room temperature. The electron/hole
pairs can be readily generated upon visible light excitation of the
Cu3P nanophotocatalyst, but the low band gap of Cu3P promotes the fast recombination of generated electrons/holes,
thereby rendering Cu3P inefficient for photocatalysis.
However, the association of a small amount of hBN, which is a structural
analogue of graphene and carbon nitride, with Cu3P to form
the Cu3P/hBN composite promotes the separation of electrons
as hBN can provide its surface to the excited electrons of Cu3P, making them active to act on surface-adsorbed active reactant
molecules, whereas the holes remain confined to the valence band of
Cu3P. Cu3P is a P-type semiconductor that provides Cu (+1) active sites that change to Cu (+2) during
the photocatalytic cycle. The oxidized active sites consisting of
Cu (+2) promote further enhancement of electrostatic interactions
between the catalyst and the attached aromatic halide molecules. The
excited electrons generated in the catalyst upon light exposure act
on oxygen molecules to further lead to superoxide radical anion (O2–•) radical formation. The formed O2–• radicals then act
on activated halide molecules and convert them to biphenyls.