Competitive removal of Pb2+ and malachite green from water by magnetic phosphate nanocomposites

The competitive removal of Pb2+ and malachite green (MG) from water by three magnetic phosphate nanocomposites (Fe3O4/Ba-3(PO4)(2), Fe3O4/Sr-5(PO4)(3)(OH), and Fe3O4/Sr5xBa3x(PO4)(3)(OH), namely FBP, FSP, and FSBP, respectively) was systematically investigated compared with Fe3O4 (F) nanoparticle. Temperature and adsorbent dosage for competitive removal were optimized to be 20 degrees C and 0.05 g in 50 mL. The kinetic and isothermal adsorption results were fitted well with the pseudo-second-order model and Langmuir model, respectively. In the competitive removal process, FSP showed a high affinity to Pb2+ (202.8 mg/g) while FBP possessed high selectivity for MG (175.4 mg/g), and FSBP was effective at simultaneous removal of Pb2+ and MG, with a capacity of 143.7 and 90.9 mg/g, respectively. The magnetic contents in nanocomposites allow magnetic separation of materials from the water after treatment. We proposed that the simultaneous removal mechanism by FSBP was due to ion exchange between Pb2+ and Sr2+ in the lattice and then the formation of hydrogen bonds between PO43- outside the material's surface and positively charged hydrogen in MG. This study indicates the potential of these phosphate nanocomposites to be used as effective materials for selective or simultaneous removal of Pb2+ and MG from water. (C) 2018 Elsevier Ltd. All rights reserved.