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ZnO-NiFe 2 O 4 magnetic nanocomposite photocatalysts were successfully synthesized by simple solvothermal method using nitric salts as starting materials and ethanol as solvent. The synthesized samples were characterized by XRD, FESEM-EDX, TEM, DRS-UV-vis, VSM, and FTIR instruments. Photocatalytic activity of the samples was evaluated by dye degradation under solar light irradiation. The results show that the diffraction peaks of nanocomposites correspond to the hexagonal wurzite of ZnO and spinal cubic structure of NiFe 2 O 4 . The microstructure studies revealed that nanocomposites were dominated by granular-like of ZnO nanoparticles were synthesized at 180°C and rod-like at 200°C. The estimated band gap value of ZnO-NiFe 2 O 4 (1:0.01) nanocomposites is 2.78 eV which is lower than ZnO. The magnetic saturation (Ms) result showed a superparamagnetic behavior for nanocomposites. It was found that the photocatalytic activity of synthesized nanocomposites were higher than ZnO and NiFe 2 O 4 .

In this work, the semiconductor of ZnO-CoFe2O4 composites were prepared by green synthesis approach using rambutan peel extract (Nephelium lappaceum L.) as a capping agent. X-ray diffraction patterns of composites showed the main peaks of ZnO at 2θ = 31.8°, 34.5°, and 36.2° corresponding to hexagonal wurtzite structure and weak peak at 2θ = 35.4° for cubic structure of CoFe2O4. The formation of rice-like and small granular morphology were confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM), whereas the superparamagnetic behavior of the samples were determined by vibrating sample magnetometer (VSM). The spectrum of Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopy (XPS) showed absorption bands related to a number of interactions and binding energy in the samples respectively. The photocatalytic performance of composites under solar light was evaluated for the degradation of Direct Red 81 and the dye from washing water of batik garments. The composites showed good photocatalytic activity with the degradation percentage reaching 99.6% for Direct Red 81 dye after 2 hours.

Magnetically separable ZnO-MnFe 2 O 4 nanocomposites were synthesized in organic-free media. The samples were characterized by several techniques. The photocatalytic activities of the nanocomposites were tested by degradation of Rhodamine B and wastewater of batik dye under natural sunlight irradiation. X-ray diffraction (XRD) pattern of composites is well in agreement with the standard of the hexagonal wurtzite phase of ZnO and spinel cubic phase of MnFe 2 O 4 . Scanning Electron Microscope (SEM) image illustrates the morphology of the nanocomposites are square plate-like and porous. The magnetic properties of composites were characterized by Vibrating Sample Magnetometer (VSM) show the superparamagnetic properties of all nanocomposites. Optical properties study indicated that addition of MnFe 2 O 4 to ZnO decreases the band gap. The removal of Rhodamine B (10 mg L −1 ) and wastewater of batik dye solution by ZnO-MnFe 2 O 4 (1:0.1) composite after 3 h reached 96.7% and 95.1 %.

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The effect of thermal and chemical modification on the catalytic performance of illite-kaolinite clay (obtained from Bukittinggi, West Sumatra) in the transesterification of palm oil was investigated. Characterization with XRD, XRF and FTIR indicated a slight change in the composition of the crystal phase and the Si/Al molar ratio after such clay was calcined at 450 °C. XRF measurements also confirm that after treatment with two nickel salts, the natural clay absorbs more nickel sulfate than nitrate, while temperature played an important role in increasing the performance of the clay in loading nickel about 2 times bigger at a higher temperature. All clay-based materials prepared in this study were tested for their catalytic activity and selectivity in the transesterification of palm oil to produce Fatty Acid Methyl Ester (FAME) using the previously reported procedure. Chemical modification of clay samples with nickel sulfate and nickel nitrate was found to increase the catalytic performance of the clay in producing FAME from 38 to about 60 % while thermally treated at 450 °C yielded slightly higher to about 67 %. In terms of selectivity, all clay-based catalysts in this study gave almost the same amount of saturated and unsaturated FAME