The Study On Preparing Technology And Properties Of Magnetic Nano-TiO₂ Photocatalyst

In the degradation of organic pollutants, Nano-TiO₂ slurries are generally considered as more efficient than immobilized TiO₂ since slurry TiO₂ offers higher specific surface area. However, the TiO₂ nanoparticles are hard to be recovered from slurries after treatment. Magnetic core-shell TiO₂ photocatalyst, which is obtained by depositing a TiO₂ layer onto magnetic materials, keep the high photocatalytic activity of TiO₂ nanoparticls and is easy to be separated under an applied external magnetic field. In this paper, TiO₂ was deposited onto spinel CoFe₂O₄ to produce magnetic core-shell TiO₂/CoFe₂O₄ and TiO₂/SiO₂/CoFe₂O₄ photocatalyst. The prepared composite particles were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), Field Emission Scanning Electron Microscope (FESEM) and Vibration Sample Magnetometer (VSM). The catalytic activity of the synthesized composite particles was tested by photodegradation of TNT, through the degradation conclusions that the catalytic activity of TiO₂/CoFe₂O₄ sample was only a little lower and TiO₂/SiO₂/CoFe₂O₄ was higher than pure anatase were made. The samples also show good features on magnetic properties.Two major methods were utilized in the preparation of magnetic photocatalyst in this paper. The first one followed this way: after CoFe₂O₄ particles were produced in reverse microemulsion water/AOT/isooctane system, Titanium precursors were directly introduced into the system to form core-shell structure. However, the CoFe₂O₄ particles in the microemulsion were amorphous and would react with TiO₂ amorphous shell forming numerous impurities. The result indicates that well-formed TiO₂ core-shell structure only can be obtained when TiO₂ is deposited on well-crystalized magnetic core.The second one followed this way: the core-shell TiO₂/CoFe₂O₄ was formed via hydrolysis and condensation of titanium n-butoxide onto CoFe₂O₄ powders which was produced by coprecipitation. Through XRD patterns, the CoFe₂O₄ powders were found to have higher crystal quality using nitrates as substrate than chlorides. The catalyst, which was produced via titanium n-butoxide hydrolyzing in water adjusted pH value equal to 4～6 with acetic acid, processed in 90 ℃ water bath for 2 hours and heat-treated at 600 ℃, was considered to be the most active TiO₂/CoFe₂O₄ samples in this paper, because it showed the highest efficiency during degradation of TNT.