The Fe3O4/chitosan nanocomposite is one of the attractive functional materials. It can be applied as active material in a sensor system for an instant Surface Plasmon Resonance (SPR) based sensor. This research aimed at investigating the optical properties of Fe3O4/chitosan and its effect on the SPR angle. The synthesis of nanoparticles used the coprecipitation method. Encapsulation was carried out at a temperature of 50 o C for about 60 minutes. The samples were characterized for their structural properties and phase composition by using X-ray diffraction (XRD) techniques. Their optical properties were characterized by using the Specular Reflectance UV-Vis Spectroscopy technique. The optical properties, such as absorbance (A), absorption coefficient (α), refractive index (n), extinction coefficient (k), optical gap energy (Eg), and Urbach energy (Eu) are investigated. The measurement of the SPR angle toward the ATR curve was carried out in a range of 30 o -60 o by using the Kretschmann configuration. The results show that encapsulation affects the optical properties of the nanoparticles. The SPR angle of prism/Au/Fe3O4/Air and prism/Au/Fe3O4-Chitosan/Air system is about 50.04 o and 50.93 o , consecutively. Chitosan affects an increase of the SPR signal toward the reflectivity where the SPR angle exists. These results imply a future prospective application of the Fe3O4/Chitosan as a signal amplifier material for the SPR sensor.

In this work, we reported the nanostructure and optical properties of the Fe3O4 nanoparticles. The Fe3O4 have been synthesized from local iron sand Halmahera Utara by using the coprecipitation method at a temperature of 80°C and NaOH concentration of 3M. The nanoparticles were calcined at 150°C and 250°C for 4 hours consecutively, while the calcination dwelling time was 2 hours and 4 hours at a temperature of 250°C. The results show that a formation of Fe3O4 nanoparticles with a spinel crystal structure. The lattice parameter of nanoparticles decreases with an increase of calcination temperature and dwelling time due to higher thermal energy driving the atom to move closer to each other. Hence, the crystallite size of the nanoparticles increases due to the expansion process to the grain of the nanoparticles. The optical gap energy of the nanoparticles decreases due to the formation of a larger particle. It also confirms that the existence of Fe3+-O and Fe2+-O bonds in the nanoparticles which are characteristic functional group bond of Fe3O4 in the tetrahedral and octahedral sublattice. This result can prove that a higher calcination temperature and longer dwelling time can improve the nanostructure and optical properties of Fe3O4.

In the case of optical sensors such as the Surface Plasmon Resonance (SPR) sensor, the Fe3O4 nanoparticles play a role to boost the signal however they can increase the detection sensitivity of the biosensor. For this application, the optical properties of Fe3O4 nanoparticles need to be studied. The optical properties are described in terms of their optical constants. Therefore, this work was purposed to study the effect of the particle size and lattice strain on the optical constants of Fe3O4 nanoparticles. Samples were synthesized by using the coprecipitation technique. Two calcination temperatures, i.e., 150oC and 250oC for 4 hours were applied to the samples. Samples were characterized for their diffraction pattern and optical properties by using XRD and Specular UV-Vis Spectroscopy technique, consecutively. The particle size and lattice strain were estimated by using the Williamson-Hall (W-H) method. The effect of the particle size and their optical constants on the reflectance curve in the SPR sensor application was also performed toward a simulation by using Winspall 3.02 software. The results show that calcination temperature causes an increase in particle size and a decrease in lattice strain. The optical constants, such as absorbance (A), absorption coefficient (α), extinction coefficient (k), refractive index (n), dielectric constants (ε), optical conductivity (σ), and the Urbach energy (Eu) significantly depended on particles size and lattice strain. However, the particle size and optical constant were significantly influent the SPR angle in the reflectance curve of Fe3O4

Fe3O4 nanoparticles based iron sand from Maluku Utara have been successfully synthesized by co-precipitation methods with varying of the synthesis temperature by 50oC, 60oC and 70oC. The crystal structures and magnetic properties were characterized using X-ray Diffraction (XRD) and Vibrating Sample Magnetometer (VSM). The XRD showed that the Fe3O4 samples have a single phase invers spinel cubic structure. The Crystalization of the temperature 70oC is better than 50oC and 60oC, with the intensity peak index of 311 of 42.688 a.u, whereas at the temperature of 60oC and 50 oC are 25.731 a.u and 22.719 a.u, respectively. There’s no increase in crystallite size with increasing synthesis temperature, with each sizes 23.047 nm, 24.043 nm and 16.041 nm respectively. The VSM showed that the Fe3O4 samplesare soft-ferrimagnetic. The Mr and Mmax are higher at 70oC than 60 oC and 50oC by 3,785 emu/gr 20,288 emu/gr (70oC), 2,432 emu/gr 14,713 emu/gr (60oC), 1.473 emu/gr 12.519 emu/gr (50oC). The coercivity Hc at 70oC and 60oC relatively identical at 0.011 T, whereas at 50oC Hc is 0.012 T. The nanoparticles that are synthesized at 700C are selected for mercury removal due to their stable crystallinity and good magnetic properties. The nanoparticles were able to remove mercury with an adsorption capacity 0,45 mg/g and easy to separate it from the solution.

Gold mining activity at Tiabo river in the North Halmahera causes the water on the river is contaminated by mercury. The contamination mercury on the water can damage food chain and adverse consequences toward health of people, fish, and so on. The purpose of this study is to obtain the concentration of mercury contamination that was caused by gold mining activity. The water and sediment sample was obtained by purposive sampling. The characterization of concentration mercury in the water and sediment using mercury analyzer HG-300 in the wave length 253.72 nm. The result shows that mercury concentration of the water in the six and five sample point in the rainy session and the dry session respectively is <0.66 µg/L, and the mercury concentration in the sediment shows that the lower value in the upstream river was 1.2 mg/kg and the higher concentration in the middle of river was 8.94 mg/kg respectively in the rainy session. The result indicates that the contamination mercury in the moderate danger level according to the IADC/CEDA data standard.