Exploitation of ZnO/Fe3O4 and TiO2/Fe3O4 nanocomposites on the degradation of organic compounds

Water is the main sources for all living beings. However, with the vast development and advancement of technology, water resources have been seriously contaminated by industries effluent, especially organic dyes. Various methods have been implemented to achieve certain level of acceptable cleanliness. Current most efficient and cost effective process is the photocatalytic process using highly photoreactive ZnO and TiO2 semiconductors. However, separation of the semiconductor powder arises at the end of the decomposition process. Therefore, there have been many researches trying to dope magnetic material into the semiconductor to make it easily separable and cost effective by just applying a magnetic field. However, most of the preparations require various recalcitrant and toxicant precursor chemicals as well as high sintering temperature. In light of these, this study has tried to use simple method of preparation and followed by a significantly moderate sintering temperature. The ZnO/Fe3O4 and TiO2/Fe3O4 nanocomposite materials have been successfully prepared by simple mechanical mixing and sintered at significantly moderate temperature of 300 and 350 oC, respectively. Besides, the prepared nanocomposite exhibit remarkable photocatalytic decomposition on few chosen dyes. The XRD results indicated a good crystallinity with the standard for both nanocomposites. The SEM and TEM results showed ZnO/Fe3O4 nanocomposite was square-like and elongated in shape, whiles it was mostly spherical for TiO2/Fe3O4 nanocomposite. VSM measurements showed that both nanocomposites exhibit ferromagnetism, while ZnO and TiO2 are diamagnetism in nature. Both nanocomposites able to completely decomposed the MB dye. All the photocatalytic measurements show that the photodegradation processes are following the pseudo-first-order kinetics. Both nanocomposites were successfully magnetically separated from the decomposed solution by using a 0.60 T permanent magnet. A 9.0wt% loading of ZnO/Fe3O4 nanocomposite with 10wt% doped Fe3O4 and sintered at 300 oC was able to completely decomposed MB in 30 minutes (99.9%) with kinetic constant of 0.242 min–1. On the other hand, TiO2/Fe3O4 nanocomposite with 1wt% doped Fe3O4 sintered at 350 oC and at optimum loading of 3wt% was able to decompose 98.7% of MB in 60 minutes with kinetic constant of 0.0729 min–1. The repeatability experiments were conducted and the results indicated that there was a minor deactivation (~1.08%) after the second and third run. This shows that both nanocomposites were photocatalytically stable and reusable for wider application on organic dyes decomposition. The effect of the intrinsic properties for the chosen organic dyes, such as their azo groups, benzene groups, molecular weight and absorbance, in relation to their rate of decomposition were evaluated in the last part of this study. The results show that the degradation rate is linearly proportional to the number of azo groups, the number of benzene groups, the molecular weight and inversely proportional to the absorbance of the dye’s solution