Abstract:
The development of easily recoverable and re-usable catalytic nanostructures exhibiting high
performances using simple and cheap procedures for applications in bio-sensing and
wastewater treatment technologies is currently a prominent area of research. Noble-metal
inclusive magnetic nano-catalysts in particular, have of recent gathered interest owing to their
ease of separation from reaction products, environmental benignity and improved activities
through synergistic qualities and photo-thermal effects. Herein, silver-magnetite core-shell
nanocomposites (Fe3O4@AgNPs) displaying enhanced peroxidase-like catalytic properties
were successfully synthesised via a facile one step solvo-thermal procedure. Governed by
Michaelis-Menten kinetics, the nanocomposites’ capacity to oxidize the colourless o phenylenediamine to the yellow coloured 2, 3-diaminophenazine in the presence of hydrogen
peroxide progressively improved relative to Fe3O4 alone with increasing precursor AgNO3 to
an optimum of 50 mM. Following a study and reaction optimisation conditions on the
inhibitory behaviour of cysteine; a biomarker for Alzheimer and other neurological
conditions, towards the peroxidase-like catalytic activity of these nanocomposites, a
considerably cheap, selective and highly sensitive detection method for this amino acid was
developed. With a low limit of detection of 87 nM, the formed cysteine sensor proved to be
superior to some of the existing sensors.
A simple silver mirror reaction was also employed to fabricate nano-silver decorated
magnetite (Ag@ Fe3O4) free of the often activity limiting and environmentally unfriendly
organic reagents. The nano-sized magnetite supports were synthesised using the precipitation
method. Following synthesis optimisation procedures, these composites were found to
effectively catalyse the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride
more than 8 times repeatedly. With a normalised activity parameter k of 1.44 ×10−3 L. s−1
mg−1, the synthesised catalyst performed better than some reported nanostructures.
Furthermore, the catalytic degradation methylene blue and Rhodamine 6G which are some of
the many water pollutant dyes in textile industry effluents was achieved by these
nanocomposites. Also, owing to their SERS property, Ag@ Fe3O4 particles were efficient in
real-time monitoring the catalytic degradation of p-Nitrothiophenol by NaBH4.
Characterisation of all the synthesised nanocomposites in this work was carried out via
transmission electron microscopy, scanning electron microscopy, X-ray diffraction,
Thermogravimetric analysis and surface-enhanced infrared absorption spectroscopy.
