The paper proposes a simple one-stage synthesis of organic-inorganic composite materials based on oxide compounds of iron (III) and cobalt (II) with a developed surface. The process of cobalt(II) ferrite (CoFe₂O₄) structure formation on the biochar surface was studied. As an organic component, biochar was obtained from agricultural waste, including sunflower husks, rice husks, and pea kernels. Composite materials cobalt ferrite/biochar were obtained for the first time using these wastes. The obtained materials were characterized using X-ray phase analysis, fourier transform infrared spectroscopy (FTIR), transmission electron microscopy, and N₂ adsorption-desorption. A mechanism for forming composite materials is proposed, including the stage of formation of chelate complexes of transition element cations with citric acid on the biochar surface and their subsequent thermal decomposition. High adsorption activity of the synthesized materials in the process of removing chromium (VI) ions from aqueous solutions was established. The sunflower husk biochar composite material based on CoFe₂O₄ has the highest adsorption capacity of 6.98 mg/g. The results suggest that biochar composites based on CoFe₂O₄ have great potential for the practical industrial wastewater treatment.

Currently, one of the most important problems of environmental protection is the deep and complex processing of mineral raw materials. This problem is especially relevant when processing substandard ores and production waste, one of which is phosphogypsum. This study examines the process of CaSO₄/CaS composite material formation during the reduction of phosphogypsum with citric acid. The composite structure formation mechanism is proposed. The resulting materials are characterized using various methods, including X-ray diffraction (XRD), transmission electron microscopy, the Scherrer method, thermogravimetric analysis (TGA), and FT-IR spectroscopy. The reduced sample emits orange radiation in the range of 500–750 nm with a quantum yield of 0.17. Experimental results showed that the sample decomposition process in the solid state consisted of two components with a predominant contribution from the long-lived component (~46 ns). The optimal conditions for producing luminescent materials by reducing phosphogypsum with citric acid were determined: a heat treatment temperature of 1073 K, a holding time of 60 min, and a reducing agent mole fraction of 37%. It was found that an increase in temperature with a simultaneous decrease in heat treatment time, as well as a decrease in temperature with a simultaneous increase in heat treatment time, led to a decrease in the luminescent properties of the synthesized material compared to optimal values. The results can be used to develop technology for recycling large-tonnage waste from the chemical industry into luminescent materials.

The article presents results for the magnetic nanoparticles sol–gel method synthesis of cobalt (II) ferrite and organic–inorganic composite materials based on it. The obtained materials were characterized using X-ray phase analysis, scanning and transmission electron microscopy, Scherrer, Brunauer–Emmett–Teller (BET) methods. A composite materials formation mechanism is proposed, which includes a gelation stage where transition element cation chelate complexes react with citric acid and subsequently decompose under heating. The fundamental possibility of obtaining an organo–inorganic composite material based on cobalt (II) ferrite and an organic carrier using the presented method has been proved. Composite materials formation is established to lead to a significant (5–9 times) increase in the sample surface area. Materials with a developed surface are formed: the surface area measured by the BET method is 83–143 m²/g. The resulting composite materials have sufficient magnetic properties to be mobile in a magnetic field. Consequently, wide possibilities for polyfunctional materials synthesis open up for various applications in medicine.

In this paper, composite materials based on cobalt (II) ferrite, which is a promising object of research as a magnetic material, are obtained. Thus, it is known to be used for producing organo / inorganic and non-organo/inorganic compositions. The introduction of cobalt ferrite makes it possible to give new properties to carrier materials. As a carrier, waste from the production of phosphoric acid – phosphogypsum, ash – and – slag waste from thermal power stations and cullet-foam glass, and activated carbon were used. Finding a way to process waste to produce new composite materials is an urgent task of chemical technology. The obtained samples were studied using X-ray phase analysis and electron microscopy. In the course of the conducted research, the principal possibility of using the specified number of production wastes for the synthesis of catalytically active materials is shown. Photocatalytic reactions are widely used in water treatment processes for wastewater treatment from organic pollutants. A simple method for obtaining composite materials of the composition of foam glass/ cobalt ferrite (II), phosphogypsum/ cobalt ferrite (II), activated carbon/ cobalt ferrite (II) is proposed. The catalytic properties of synthesized materials in the process of oxidative destruction of an organic dye in the presence of hydrogen peroxide are studied. It was found that the highest activity under the specified conditions is observed for the activated carbon/ cobalt (II) ferrite composite: complete removal of the organic dye from the aqueous solution is achieved after 90 min from the beginning of the reaction. The phosphogypsum-based composite shows the least pronounced activity. The results obtained can serve as a guide for choosing a method for producing non-toxic materials that are promising for use in water treatment systems and ensuring environmental safety of industrial enterprises that use organic dyes in the production process.

One of the priority goals of sustainable socio-economic development for the period up to 2030 is providing food for the planet’s population. This entails an increase in the output of mineral fertilizers and, consequently, an increase in the quantities of solid industrial waste. Phosphogypsum, a by-product of phosphate fertilizer production from apatite ore, is one example of such waste. The problem of solid industrial waste recycling is urgent. The present study examines the process of converting calcium sulfate, in the form of a reagent, and phosphogypsum into a composite material of calcium sulfate/sulfide. An environmentally friendly material, sucrose, is used as a reducing agent. Reduced phosphogypsum (as well as calcium sulfate) luminescence is suggested to be associated with the formation of a CaS/CaSO₄ composite material. The synthesized materials are characterized by X-ray phase analysis, X-ray photoelectron spectroscopy, elemental analysis, and calcium sulfide qualitative and quantitative content in the samples. It is shown that in the reduction process at the phase contact point, crystal grids are formed with a significant number of defects, which contributes to the convergence of some of the energy levels of the calcium cation and sulfide anion, facilitating the transitions of electrons from the valence zone to the core zone and the formation of luminescence centers (cross-luminescence). Both samples of reduced phosphogypsum and alkaline earth metal sulfates are found to exhibit luminescence properties under ultraviolet radiation. The data obtained open up broad prospects for the use of solid industrial waste for the synthesis of new materials.