Because of the synergistic effect of the individual nanomaterials, nanocomposites are becoming an important class of materials, allowing the creation of end-products with different properties and greater performance than when used individually. This study aims to create magnetite nanoparticles (MNPs) from iron ore and nanocellulose fibre (CNF) from sugar bagasse to make magnetite–cellulose nanocomposites. X-ray diffraction and Fourier-transform infrared spectroscopy were used to confirm the prepared nanomaterials, and scanning electron microscopy was used to investigate the morphology of the nanomaterials. The nanocomposites were created using two methods: (1) adding CNF before the MNPs precipitated and (2) adding CNF after the MNPs precipitated. There was a difference in crystallite size, with the smallest being 23 nm for the one prepared before precipitation and 31 nm for pure MNPs. The magnetic properties of the as prepared nanomaterials were also investigated using the vibrating sample magnetometer technique. MNPs and MNPs–CNF nanocomposites have superparamagnetic properties, with nearly zero coercivity for all samples and saturation magnetizations of 42.8, 30.7, and 23.2 emu g$^{–1}$ for pure MNPs, MNPs–CNF (before precipitation) and MNPs–CNF (after precipitation), respectively. Thermogravimetric analysis was used to investigate the thermal behaviour of the nanocomposite. The incorporation of cellulose nanofibre prevented aggregation while having a negligible effect onthermal stability.

Iron-doped copper chromate with (Fe$_x$Cu$_{1–x}$Cr$_2$O$_4$) as a black ceramic decoration pigment is successfully synthesized using a solid-state synthesis method with a pure oxide precursor. The powdered pigment was analysed using X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared analysis, ultra violet–visible and colour-measuring instruments. The calcination temperature was determined from literature at 1350°C for 3 h. The result of the PXRD indicated that the sample contains a spinel structure; moreover, the doping of iron caused the diffractogram peak to shift towards the lower angle due to the small ionic radius of iron compared to the replaced copper. The micrograph of the SEM indicated that the powder particles are well dispersed, and the energy dispersive spectroscopy result confirmed that all samples appear in their purest form. In addition, as the doped iron increases the colour axis of the pigment, $L^*$ tends to be more blackish, while the $b^*$ value turns more towards blue. However, the intensity of the red colour $a^*$ increases till half of the total copper is replaced by the doped iron and the optimal result was achieved which is comparable with commercial black pigment at Fe$_{0.5}$Cu$_{0.5}$Cr$_2$O$_4$, having $L^*$ = 32.96.