In this paper, we report the preparation of magnetite nanoparticles combined with polyaniline and activated carbon. The results of the X-Ray diffraction data analysis showed that the samples had a magnetite crystal phase without other phases. The existence of polyaniline and activated carbon was confirmed using Fourier transform infrared spectroscopy characterization shown by the presence of S=O, C-N, and C-C. The sample of synthesis results in this work had the band gap of 3.23 eV. Moreover, the results of data analysis using vector network analyzer revealed the maximum reflection loss value of -14 with the absorbance of 50%. Thereby, the synthesis optimization needs to be done to increase the sample absorbance to the radar wave.

This study investigated the effects of annealing temperature on the structure evolution and antifungal performance of TiO2/Fe3O4 nanocomposites. The TiO2/Fe3O4 nanocomposites were fabricated through a combination of sonochemical and coprecipitation routes. The TiO2 structure evolved from an amorphous phase to a crystalline anatase phase starting at an annealing temperature of [Formula: see text]C while Fe3O4 evolved to [Formula: see text]-Fe2O3 and [Formula: see text]-Fe2O3 starting at an annealing temperature of [Formula: see text]C. The increases in the crystallite sizes and lattice parameters were also identified because of the increase in the annealing temperature. The TiO2/Fe3O4 nanocomposites tended to agglomerate due to van der Waals forces. The molecular structural dynamics of TiO2/Fe3O4 nanocomposites were also studied by infrared spectroscopy within the wavenumber range of 400–4000[Formula: see text]cm[Formula: see text]. The antifungal activity of TiO2/Fe3O4 nanocomposites was better than those of individual TiO2 and Fe3O4. These results showed that structure evolution plays an essential role in the antifungal performance of TiO2/Fe3O4 nanocomposites.

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Fe2O3/MWCNT/ZnO nanocomposites were successfully synthesized through the precipitation method. The synthesis was carried out through a variation of ZnO mass, with (Fe2O3/MWCNT):ZnO mass ratio of 1:0, 1:0.5, 1:1, 1:1.5, and 0:1. The XRD analysis results suggested that the nanocomposites were composed of two phases, namely Fe2O3 with centered hexagonal structure and ZnO with hexagonal wurtzite structure. The ZnO diffraction peak tended to increase following the increasing ZnO composition within the nanocomposites. The presence of MWCNT was confirmed by the FTIR results signifying the detection of C=C vibration at wavenumbers of 1631-1640 cm -1 . The crystallite size of Fe2O3 and ZnO was in the range of 30.97-31.12 nm and 30.46-35.64 nm, respectively. The nanocomposites were comprised of the spherical, tube, and sheet particles, representing Fe2O3, MWCNT, and ZnO, respectively, with particle size ranged from 33.97 nm to 55.19 nm. The nanocomposites were observed to present weak ferromagnetic, with a decrease in saturation magnetization value following the increase of ZnO composition. The optical properties of the nanocomposites tended to decrease as the increasing ZnO composition.

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In this work, the Fe3O4 nanoparticles from natural iron sand were combined with active carbon (AC) and polyaniline (PANI) to obtain Fe3O4/AC/PANI nanocomposites with mass variations of the AC of 0.1, 0.2, 0.3, 0.4, and 0.5 g. The crystalline phase of Fe3O4/AC/PANI nanocomposites formed from Fe3O4 with PANI having an amorphous phase. Meanwhile, the crystalline phase of AC was unmatched because of its very small composition. The presence of AC was observed through vibrations from the CC and COOH functional groups. The existence of PANI was indicated by the vibrations of the benzoic ring and quinonoid bonds. Besides, the presence of Fe3O4 was confirmed by the presence of Fe-O functional groups from octahedral and tetrahedral positions. The optical properties of Fe3O4/AC/PANI nanocomposites were shown by increasing the energy gap along with decreasing absorption wavelength. Interestingly, increasing AC composition made the absorption bandwidth of the Fe3O4/AC/PANI nanocomposites wider, so that the radar absorption also increased marking by the greater reflection loss that reached-15.8 dB. The increase in the radar absorption performance of Fe3O4/AC/PANI nanocomposites came from the efficient complementarity between dielectric loss and magnetic loss and interfacial polarization between Fe3O4-AC or between Fe3O4-PANI.

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