This paper examines the formation of cobalt (II) ferrite on the surface of an organic support in stages: mixing metal salts, interaction with ammonia and citric acid solutions, and the subsequent thermolysis of the intermediate products. The resulting materials were characterized by X-ray diffraction, electron microscopy, and elemental analysis. A comparative analysis of the materials’ morphological properties suggests the formation of a cobalt (II) ferrite film on the surface of the organic support. This film forms as small cubic crystals measuring 50–100 nm in size, with a simultaneous significant (2–5 times) increase in the specific surface area of the synthesized composite materials compared to the support surface. The typical pore diameter of the composites is 20–40 nm. The synthesized material of CoFe₂O₄/sunflower husk biochar exhibits high catalytic activity; dye is removed from the solution within 60 min. The material of CoFe₂O₄/sunflower husk ash is less active in this process: dye removal is observed 140 min after the start of the reaction. These data may be useful for developing catalytically active materials for wastewater and soil solution treatments to remove persistent pollutants.

In this work, we introduce the novel possibility of producing blue fluorescent ultraviolet pigments from phosphogypsum. The obtained materials are characterized by X-ray diffraction (XRD), transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). The formation of the CaS phase in the sample during the reduction of calcium sulfate was established. Thermal treatment of phosphogypsum in the presence of a reducing agent (potato starch) under environmental isolation conditions is found to yield high-quality products with high added value. The highest luminosity is established in samples containing 0.6 mol. %, which were heat-treated under a temperature of 1100 °C for 60 min. The synthesized CaS:Cu materials are shown to emit light in the blue region of the spectrum, with an emission maximum at a wavelength of 480–490 nm. The developed technological methods open the possibility to recycle chemical industry waste, which contributes to the achievement of sustainable development goals, in particular, the goal of ensuring rational consumption and production patterns.

This paper studies the formation process of a composite material based on an organic substance, biochar from sunflower husks, and an inorganic substance, nickel (II)-copper (II) ferrites of the composition Cu_xNi_1−xFe₂O₄ (x = 0.0; 0.5; 1.0). The obtained materials were characterized by X-ray phase analysis, scanning electron microscopy, and FTIR spectroscopy. It is shown that when replacing copper (II) cations with nickel (II) cations, the average parameters and volume of the unit cell gradually decrease, and the cation–anion distances in both the tetrahedral and octahedral spinel grids also decrease with regularity. The oxide materials were found to form a film on the surface of biochar, repeating its porous structure. The obtained materials exhibit high catalytic activity in the methyl orange decomposition reaction under the action of hydrogen peroxide in an acidic medium; the degradation of methyl orange in an aqueous solution occurs 30 min after the start of the reaction. This result may be associated with the formation of the Fenton system during the oxidation–reduction process. A significant increase in the reaction rate in the system containing mixed nickel–copper ferrite as a catalyst may be associated with the formation of a more defective structure due to the Jahn–Teller effect manifestation, which creates additional active centers on the catalyst surface.