We
demonstrate an
approach based on substituting a magnetic cation
with a carefully chosen isovalent non-magnetic cation to derive catalytic
activity from otherwise catalytically inactive magnetic materials.
Using the model system considered, the results illustratively present
that the catalytically inactive but highly magnetic strontium hexaferrite
(SrFe
12
O
19
; SFO) system can be transformed into
a catalytically active system by simply replacing some of the magnetic
cation Fe
3+
by a non-magnetic cation Al
3+
in
the octahedral coordination environment in the SFO nanocrystals. The
intrinsic SFO and Al-doped SrFe
12
O
19
(SrFe
11.5
Al
0.5
O
19
; Al–SFO) nanomaterials
were synthesized using a simple, eco-friendly tartrate-gel technique,
followed by thermal annealing at 850 °C for 2 h. The SFO and
Al–SFO were thoroughly characterized for their structure, phase,
morphology, chemical bonding, and magnetic characteristics using X-ray
diffraction, Fourier-transform infrared spectroscopy, and vibrating
sample magnetometry techniques. Catalytic performance evaluated toward
4-nitrophenol, which is the toxic contaminant at pharmaceutical industries,
reduction reaction using NaBH
4
(mild reducing agent), the
Al-doped SFO samples exhibit a reasonably good performance compared
to intrinsic SFO. The results indicate that the catalytic activity
of Al–SFO is due to Al-ions occupying the octahedral sites
of the hexaferrite lattice; as these sites are on the surface of the
catalyst, they facilitate electron transfer. Furthermore, surface/interface
characteristics of nanocrystalline Al–SFO coupled with magnetic properties facilitate the catalyst
recovery by simple, inexpensive methods while readily allowing the
reusability. Moreover, the activity remains the same even after five
successive cycles of experiments. Deriving the catalytic activity
from otherwise inactive compounds as demonstrated in the optimized,
engineered nanoarchitecture of Al-doped-Sr-hexaferrite may be useful
in adopting the approach in exploring further options and designing
inexpensive and recyclable catalytic materials for future energy and
environmental technologies.