Synthesis and antibacterial properties of a novel magnetic nanocomposite prepared from spent pickling liquors and polyguanidine

Magnetic nanoparticles have received much interest for their application in wastewater treatment because of their easy retrieval and reuse. However, the methods used to synthesise high saturation magnetization magnetic nanoparticles require expensive and pure precursors. In the current study, we explore the potential for using spent pickling liquor, a wastewater solution from steel factories, as the iron precursor for preparing iron oxide nanoparticles. Here, magnetic Fe(3)O(4) nanoparticles were synthesized via the oxidation–precipitation of spent pickling liquors using a saturated solution of calcium hydroxide at room temperature. The Fe(3)O(4) nanoparticles were then modified with antibacterial polyguanidine to form a nanocomposite. It was found that monodisperse magnetic Fe(3)O(4) nanoparticles with a size in the range 20–30 nm and a high saturation magnetization value of 73.9 emu g(−1) were synthesised. The Fe(3)O(4) nanoparticles were successfully encapsulated with polyguanidine to form an Fe(3)O(4)/polyguanidine nanocomposite. FT-IR and TGA analysis results indicated the presence of the polymer on the Fe(3)O(4) surface and the polymer content in the nanocomposite was about 15% (w/w). The Fe(3)O(4)/polyguanidine nanocomposite exhibited strong antibacterial activity against Escherichia coli (E. coli), demonstrating its potential for use in disinfecting wastewater.