Photocatalytic Activity of Magnetically Responsive Green Synthesised Co<sub>3</sub>O<sub>4 </sub>Nanoparticles

Utilising an uncomplicated, environmentally friendly strategy to synthesise nanoparticles presents a prospective substitute for dangerous chemical and expensive physical techniques. Therefore, this study was initiated with the objectives of synthesising Co 3 O 4 nanoparticles using a facile green route and evaluating their magnetic properties and photocatalytic activities. Spherical Co 3 O 4 nanoparticles with dimensions ranging from 8 to 32 nm were successfully produced using garlic extract. Magnetic analysis revealed weak ferromagnetism at low temperatures, with a coercive field of 14×10 -4 T. This low-temperature weak ferromagnetism may be attributed to uncompensated surface spins that form a short-range ordered cluster of spins. However, inside the sample, an antiferromagnetic exchange interaction occurs between non-magnetic tetrahedral Co 2+ ions and magnetic octahedral Co 3+ ions. Consequently, an exchange bias field of approximately 8.76 ×10 -4 T was observed. Above the Néel temperature, the thermal energy overcomes the antiferromagnetic ordering, resulting in paramagnetic behaviour at room temperature. Furthermore, the photocatalytic activity of the green synthesised Co 3 O 4 nanoparticles demonstrated 55% degradation of methyl orange (MO) dye within 90 minutes. However, more efficient degradation (63% degradation within 90 minutes) of MO was achieved in the presence of a small amount of NaBH 4 , which typically functions as a source of electrons to enhance the degradation rate. The photocatalytic (dye degradation) activity of these green synthesised room temperature paramagnetic Co 3 O 4 nanoparticles could be applicable for water purification processes.