The Application Of Ferrite-based Microwave-sensitizers In The Degradation Of Triphenylmethane Dye

With cytotoxic and biological genotoxicity, triphenylmethane dyes have been selected as target compounds by a variety of investigators frequently espercially concerning advanced oxidation method, as a type of refractory compounds in biodegradation processes and easy to be observed in aqueous solution. Based on this fact, two typical triphenylmethane dyes were selected as target compounds here, and several typical ferrite-based microwave absorbing nano-materials such as copper ferrite, bismuth ferrite coated carbon nanotubes and barium ferrite are involved into the oxidative removal of triphenylmethane dyes at the household microwave frequency, in addition to investigation concerning the absorption and conversion of microwave energy with ferrite and the element migration process on these materials including the iron loss. The aim of this study is to find one or more types of stable magnetic material with high oxidation ability in microwave-induced oxidation process, to explore the factors that could improve the microwave energy utilization in microwave-induced oxidation, and to understand surface chemical processes on the prepared materials during dye oxidation.Self-synthesized ferrite-based microwave sensitizers like nanoscale y-Fe2O3, spinel-phase nanoscale copper ferrite, perovskite-phase nanoscale bismuth ferrite and magnetoplumbite-phase nanoscale barium ferrite were prepared via citrate assisted sol-gel method and co-precipitation method. The relative characterization of nanoscale copper ferrite suggested that with the increase in calcination temperature, the nanoscale copper ferrite transformed from tetrahedral phase into cube phase gradually, and the grain size increased as well. Bismuth ferrite-carbon nanotube composites were prepared by the first time, and the ferrite coverage were found to be decrease with the gradually increase in the proportion of doped carbon nanotube. The crystal phase of bismuth ferrite was not changed in that proess, and it is surprising that while the doped proportion of carbon nanotubes set as 20%, the nanocrystals with the size of about 5 nm could be found on crystal surface. Barium ferrite nanoparticles obtained in the same manner has good magnetic properties, and in the case of the absence of barium ions, nano-a-Fe2O3 could form instead of nano-y-Fe2O3 below the formation temperature of barium ferrite.The degradation behavior of crystal violet in microwave-induced oxidation reaction with nanoscale copper ferrite was investigated. The variance of surface elements and bulk phase on nanoscale copper ferrite before and after the reaction indicated that trivalent iron were converted to divalent iron gradually, and the poor activity of α-Fe203 and copper oxide mixture proved the effect of nanoscale copper ferrite phase in addition to element value. Some of zero valent copper deposited on the surface and preventd the further reaction of internal ferric. The experiment with hole-trapping agents proved microwave-induced hole should be responsible for oxidation. The higher efficiency in microwave-induced reaction than that in conventional heating reaction confirmed the presence of nonthermal effects in microwave field. The decreace in Cu/Fe ratio also proved that divalent copper ions ran off in the reaction.Nanoscale bismuth ferrite coated carbon nanotubes were prepared for the first time, and applied in the degradation of bright green. It was found that conventional heating and microwave induced degradation efficiency of different materials with different carbon nanotubes doping rate had different sequence. For example, the material with 20% doping rate was the most active material in microwave field, though in conventional heating process this rate was 10%. It proved that carbon nanotubes have a special role in the microwave field. Investigation on the role of carbon nanotubes as molecular radiators proved that carbon nanotubes have a strong microwave absorption and thermal conversion capability. Carbon nanotubes could enhance the solution over-heating and thermoelectric induced cavitation effect in the microwave field; the experiments concerning hole scavenger prove that the presence of carbon nanotubes can enhance thermoelectric induced cavitation in microwave field. There was little loss of iron ions in the microwave field, in addition to the changeless bismuth content, which proves that in this oxidation process bismuth ferrite is a steady material without dissolved-loss. In addition, after the reaction the extraction experiment provided evidences for the removal of the dye which was adsorbed on the surface of carbon nanotube.Hard-magnetic nanoscale barium ferrite was introduction into the microwave field, to expand the range of material selection. y-Fe2O3 and nanoscale barium ferrite could be obtained by different preparation conditions. Comparison among materials with different microwave absorption capacity and microwave oxidative capacity caused by the different preparation conditions implied that oxidative capacity of nanoscale ferrite played a more important role than microwave absorption-thermal conversion ability. For example, y-Fe2O3 was more active than nanoscale barium ferrite. Investigation on the conversion efficiency of microwave energy to heat energy for hard magnetic material barium ferrite proves that magnetic energy could not be converted into heat energy in microwave field. The loss of the element in the microwave induced oxidation process was studied, and confirmed that the loss of metal element in this process was from the dissolution of extra element after preparation instead of the oxidation-reduction reaction. The investigation on degradation products of triphenylmethane dyes Brilliant Green proves its deviation from the ideal pathways and free radicals pathways.In summary, compared to copper ferrite with great main metal element loss or the weak oxidant bismuth ferrite, it was suggestted that barium ferrite, with strong oxidazing capacity and limited metal element loss, was an ideal microwave sensitizer in this paper.