Application of magnetic nanoparticles for water purification

Abstract Water is one of the main sources of human pathogenic microorganisms in developing countries. Therefore, new low-cost water treatment technologies are required to prevent public health problems. The main goal of this work was to develop a water purification technology using magnetic nanoparticles, to be applied in a water outlet point where the contact time between the two phases is minimal. For that, six different nanomaterials were synthesised based on iron oxide (FeO): FeO, mixed oxides of Fe with Mn, Co or Cu, a composite of FeO with activated carbon, and FeO subsequently coated with carbon by chemical vapour deposition (CVD). Different techniques were used to characterise these nanomaterials and their ability to remove E. coli (a Gram-negative bacteria) and also S. aureus (a Gram-positive bacteria) cells from a suspension was assessed. CuFeO, FeO, MnFeO and FeO/AC composite MNPs showed high removal efficiencies of Escherichia coli (Gram-negative). For the nanoparticles with higher removal efficiencies in the first tests (FeO and CuFeO), 50 mg mL−1 was the optimal concentration of particles and 1 min of contact time it was enough to obtain high removal efficiencies. The removal efficiency of S. aureus was higher than that of E. coli when FeO particles were used. In contrast, the removal efficiency of E. coli was higher than that of S. aureus for CuFeO particles. For both particles, the removal efficiency of microorganisms for the well water sample was lower when compared with the bacteria suspensions, being 64.1 % for FeO and 91.8 % for CuFeO. The reuse tests showed that these particles could be re-used several times without losing efficiency in bacteria removal. The MNPs used are simple and low-cost and show promising results for the elimination of both types of bacteria (gram-positive and gram-negative) demonstrating that this technology is a promising alternative to the conventionally used processes showing an easy, efficient, and inexpensive method for treating water for human consumption.