A novel flake-ball-like magnetic Fe3O4/gamma-MnO2 meso-porous nano-composite: Adsorption of fluorinion and effect of water chemistry

A novel flake-ball-like magnetic Fe3O4/gamma-MnO2 meso-porous nano-composite was synthesized and characterized for defluoridation. Adsorption process, characters, and effects of solution chemistry on the adsorption of flourinion in Fe3O4/gamma-MnO2 were evaluated. The results show that the adsorption of fluorinion in the Fe3O4/gamma-MnO2 nano-composite is fitted with the Pseudo-first model and the Langmuir model, indicating that the adsorption process of fluorinion in the Fe3O4/gamma-MnO2 nano-composite was a physical process and not only controlled by the film diffusion but also controlled by the intra-particle diffusion and surface adsorption. It shows that the adsorption of fluorinion sharply decrease with the increase of pH due to the negative changed surface of Fe3O4/gamma-MnO2 in water and the competition of OH- for the active points. The competition from decreases the adsorption of fluoride in the order of Cl- < NO3- < SO42-, which relied on the ratio of charge towards radius (z/r) of the anions, and the negatively charged humic acid competed with fluorinion for the adsorption sites. Based on the adsorption results and the XPS analysis, the O-Mn bond in the raw adsorbent supported the active site (O-Mn-OH) for fluoride adsorption by forming an O-Mn-F bond on the surface of Fe3O4/gamma-MnO2. (C) 2018 Elsevier Ltd. All rights reserved.