SEMIKONDUKTOR KOMPOSIT MAGNETIK ZnO-MFe2O4: SINTESIS, KARAKTERISASI DAN UJI AKTIVITAS FOTOKATALITIK TERHADAP DEGRADASI ZAT WARNA DALAM AIR DI BAWAH SINAR MATAHARI

Rahmayeni, Rahmayeni (2017) SEMIKONDUKTOR KOMPOSIT MAGNETIK ZnO-MFe2O4: SINTESIS, KARAKTERISASI DAN UJI AKTIVITAS FOTOKATALITIK TERHADAP DEGRADASI ZAT WARNA DALAM AIR DI BAWAH SINAR MATAHARI. Doctoral thesis, Universitas Andalas.

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Abstract

Zinc oxide (ZnO) is an n-type semiconductor that attracts the attention of researchers because it is chemically stable, non-toxic, readily available, cheaper, morphology can be controlled, biodegradable and environmentally friendly. Because of its unique character, ZnO has been widely used for various applications such as semiconductors, gas sensors, spintronics, antibacterial/biotic, photodetectors and photocatalysts. As a catalyst in the photocatalytic process ZnO better than TiO2 due to it has high activity. But it looks like TiO2, ZnO also has a large band gap is about 3.37 eV so that this material more active absorbs in the region of UV light with the wavelength of 387 nm. For photocatalytic applications in the area of visible light and sunlight, it is less favorable. Efforts to increase the activity of this material in the area of visible light have been carried such as by doping ZnO with a metal atom, non-metal or metal oxides but the resulting material difficult to recycle and reuse. Spinel ferrite of MFe2O4 n-type semiconductor with a narrow band gap (<2 eV) is a magnetic material that absorbs invisible light. This ferrite can be used as a dopant to increase the activity of ZnO in the visible light region. The combination of ZnO and MFe2O4 producing ZnO-MFe2O4 composites that are not only absorbed in the visible light region but also be a magnet, so it can be easily separated from the liquid by using the influence of the external magnetic field. Many studies have been conducted to the manufacture of composite materials by using a variety of methods and materials. From the literature search that has been done, no one has reported the synthesis of these composites using two sets of methods of sol-gel-hydrothermal and hydrothermal-hydrothermal then applied as a catalyst for the degradation of organic substances in the water under solar light. Therefore, in this study conducted the synthesis of ZnO-MFe2O4 via sol-gel-hydrothermal and hydrothermal-hydrothermal methods. In synthesis performed variations of the M (Mn, Co, Zn, and Ni) to see the influence of these metals on the formation and properties of ZnO-MFe2O4 composites. Nanocomposites obtained were characterized by various types of equipment such as SEM-EDX, TEM-SAED, XRD, VSM, DRS UV-Vs, BET, FTIR and TGA to analyze the morphology, elemental composition, phase, optical and magnetic properties, porosity, group functions and stability thermal. Composite photocatalytic activity was determined on photodegradation of dyes (Rhodamine B, methylene blue, Congo red), under solar light irradiation. Some of the parameters associated with the testing of catalytic activity were also examined. From the research that has been conducted found that the nanocomposite ZnO-MFe2O4 successfully synthesized by the methods of sol-gel-hydrothermal and hydrothermal-hydrothermal. Color and morphology of the composites were influenced by metal (M) used in MFe2O4 and methods of synthesis. The composition of the elements contained in the composite approach the theoretically calculated results. The specific peaks appearing in the composite XRD pattern is suitable for cube crystals of spinel ferrite MFe2O4 and a hexagonal crystal wurtzite of ZnO in which this pattern by the standards of the ICDD. The magnetic properties of the material were measured by VSM showed that ZnFe2O4 is paramagnetic, CoFe2O4 is ferromagnetic, MnFe2O4 is superparamagnetic, and NiFe2O4 is ferrimagnetic. The magnetic properties of the materials depend on the value of magnetic saturation (MS), remanent magnetic (MR) and coercivity (Hc). The magnetization of composites tends to follow the ferrite pattern that is given and the value of magnetism lower than their ferrite. With the magnetic properties of the composites will facilitate the process of separating the composites from the liquid after use so that it can be used for the subsequent catalytic processes. Thus the use of this composite catalyst will be more efficient. From the measurement results shown that the optical properties of the resulting composite absorb the visible light (> 400 nm) with a smaller band gap than ZnO and greater than ferrite. This proves that the incorporation of the ZnO form a composite ferrite ZnO-MFe2O4 has been successfully carried out. Further, analysis by FTIR showed an absorption band for vibration Fe-O around 437 cm-1, M-O around 562 cm-1 and M-O-Fe in the 1355-1361 cm-1 as building units forming tetrahedral and octahedral spinel structure. As for the composite looks the same uptake for the ferrite and ZnO but a shift in the uptake of M-O caused by the combination of ZnO with ferrite. The results of the BET analysis show that the adsorption-desorption isotherm pattern N2 for the composites were synthesized following the pattern of type IV with a narrow hysteresis curve. Based on the type of curve, the composite is categorized as belonging to the mesoporous. Composite thermal stability, as measured by TGA equipment showed that the composites have a high enough stability as evidenced by a reduction in the weight of the temperature rise are very small (<10%). The photocatalytic activity of composites was determined by degradation of dyes showed that the composites exhibit better activity than ZnO and MFe2O4. Composites with a more homogeneous morphology and particle size smaller to have a higher activity. The ability of the composite to degrade dye and organic substances are influenced by MFe2O4 contained in the composite. Higher activity obtained for composites NCo1HD and NNi1HD with the degradation percentage of dye reached on average above 95% for 3 hours contact time. Additionally, the composites photocatalytic activity also depends on the type of dye and organic substances are degraded. The easier the structure and the bond it will be more easily degradable substances. The ability of the composite to withstand repeated usage (reusability) were tested using a composite return that has been reused used for photocatalytic process next. These results show not all composites showed good resilience. This is evident from the decline in value of the percentage of degradation after a few times (4x) of use. UV-vis absorption spectrum of the substance showed that no other absorption peaks appear in addition to the peak of the dye it self. It gives information that the dye degraded into simple compounds are H2O and CO2. This data is amplified by absorbance measurement of the retention times using HPLC equipment wherein the spectrum no other peaks that arise in addition to the peak of the dye. It can be concluded that the synthesized composite can be used as a photocatalyst in the photocatalytic process to degrade dye or organic substances in water. From the research data obtained is concluded that the ZnO-MFe2O4 composites can be recommended as a potential catalyst in the photocatalytic process to degrade the dye in the water under sunlight and various other applications in the aquatic environment. Thus the environmental problems caused by the waste of dyes and other substances can be overcome.

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