We herein report the controllable synthesis of spherical cobalt ferrite nanoparticles with average crystallite size in the range of 3.6–12.9 nm using a facile, eco-friendly, hydrothermal method. The hydrothermal treatment was carried out by utilizing cobalt nitrate, ferric nitrate, and ammonium hydroxide in the presence and absence of Arabic gum as a surfactant agent. The purity and crystallinity of the products were tuned by varying reaction conditions such as reaction time (0.5–8 h), reaction temperature (120–180 °C), percentage of ethylene glycol (0–100% (v/v)), pH (8–9.6), and amount of Arabic gum (0–2 g). We characterized the prepared products using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy analysis (EDS), selected area electron diffraction (SAED) patterns, and UV-visible diffuse reflectance spectra (DRS). The optimal hydrothermal treatment was performed at 180 °C and pH 9.6 for 4 h in aqueous media. The results also revealed that the as-prepared spinel cobalt ferrite nanoparticles have an estimated optical band gap energy in the range of ca. 1.6–1.9 eV, indicating the semiconducting characteristics of the products.

We have reported herein the preparation of a pure cobalt ferrite (CoFe ₂ O ₄ ) nanostructure, as an efficient nano-adsorbent, via a template-free hydrothermal and post thermal conversion route.

The current study aimed to investigate the effect of counterions on hydrothermally synthesized hydrozincite (zinc hydroxide carbonate), which was thermally converted to generate ZnO nanostructures, which are an efficient nanoadsorbent for the removal of Reactive Black 5 (RB5) dye from wastewater. Hydrozincite nanospheres and flower-like structures were hydrothermally prepared using various zinc salts (sulfate, acetate, and nitrate) and ammonium carbonate in a molar ratio of 1 : 3, respectively, at 120 °C for 3 h. The morphology and crystallite size of the hydrozincite precursor were effectively controlled via the parameters of the hydrothermal reaction. Interestingly, sulfate was the optimum counterion, as zinc sulfate salt produced pure hydrozincite nanospheres with the smallest crystallite size (∼13.57 nm), which were consequently thermally decomposed at 400 °C for 1 h to produce pure nanosized ZnO (∼10 nm). The compositions of the as-synthesized products were determined by means of FT-IR, FE-SEM, HR-TEM, XRD, zeta potential, BET, and thermal analyses. An adsorption study showed a much higher adsorption capacity (80.9 mg g⁻¹) of the as-prepared ZnO nanoparticles toward RB5 dye. The adsorption of RB5 dye followed pseudo-second-order kinetics. In addition, the equilibrium adsorption of RB5 dye was best described by a Langmuir isotherm model and the calculated thermodynamic parameters, ΔG⁰ (from −4.027 to −7.533 kJ mol⁻¹), ΔH⁰ (30.798 kJ mol⁻¹), and E_a (29.105 kJ mol⁻¹), indicate the spontaneous, endothermic, and physisorptive nature of the adsorption process.

Iron carbonate nanospheres were synthesized via hydrothermal treatment of aqueous solutions of iron sulfate, ascorbic acid and ammonium carbonate with a molar ratio of 1 : 1 : 3, respectively, at 140 °C for 1.5 h. Pure α-Fe₂O₃ nanoparticles with an average crystallite size of 10.5–32 nm were produced by thermal decomposition of FeCO₃ at 400–600 °C for 2 h. The compositions of the products were identified by means of XRD, FE-SEM, HR-TEM, FT-IR, BET, zeta potential and thermal analysis. The adsorption properties of α-Fe₂O₃ were evaluated using reactive red 195 (RR195) dye. Various parameters influencing the adsorption process were investigated, using a batch technique. The results show that α-Fe₂O₃ nanoparticles show good adsorption capacity and the dye removal percentage reaches about 98.77% in 10 min. Plus, increasing the surface area of the α-Fe₂O₃ nanoparticles from 107.7 to 165.6 m² g⁻¹ increases the adsorption capacity from 4.7 to 20.5 mg g⁻¹. Moreover, the adsorption data fit the Langmuir isotherm model well and the thermodynamic parameters exhibited an endothermic and spontaneous nature for the adsorption of RR195 dye on the hematite adsorbent.