3-D self-assembly of flower-like particles via microwave irradiation for water treatment

Three-dimensional (3-D) flower-like shape (FLS) Fe3O4 and Fe particles were successfully synthesized using FLS precursor particles that are prepared through a facile microwave-assisted reaction. The mechanism underlying the self-assembly process and shape evolution of FLS particles was systematically investigated by changing reaction parameters such as reaction temperature, reaction time and reaction pressure. During the reaction, iron alkoxide, alpha-Fe2O3 and FeOOH nanoparticles are formed first and are subsequently transformed to 3-D hierarchical FLS particles by the self-assembly of the primary nanoparticles. Reaction temperature and pressure play critical roles in the formation of the hierarchical flower-like superstructure. There is an optimum window of the reaction temperature (similar to 180 degrees C) for the formation of 3-D FLS particles, which is attributed to the competition between the self-assembly process and growth process of the nanoparticles. Also, since FeCl3, ethylene glycol, and urea are used together as raw materials, the appearance of FLS particles is strongly dependent on the reaction pressure. As the reaction pressure becomes larger than 1 MPa, the flake type particles become more thermodynamically favorable than the FLS particles, due to the limited decomposition of urea. Brunauer-Emmett-Teller (BET) analysis shows that FLS particles have a large surface area (>40 m(2) g(-1)). Because of their high specific surface area and intrinsic reactivity, FLS particles efficiently remove sulfur ions in aqueous solution. This suggests that these flower-like particles can be promising materials to treat toxic gas such as H2S in an environment-friendly way.