In this work, monoclinic Bi₂O₃ was applied for the first time, to the best of our knowledge, as a catalyst in the process of dye degradation by a non-thermal atmospheric-pressure positive pulsating corona discharge. The research focused on the interaction of the plasma-generated species and the catalyst, as well as the role of the catalyst in the degradation process. Plasma decomposition of the anthraquinone reactive dye Reactive Blue 19 (RB 19) was performed in a self-made reactor system. Bi₂O₃ was prepared by electrodeposition followed by thermal treatment, and characterized by x-ray diffraction, scanning electron microscopy and energy-dispersive x-ray techniques. It was observed that the catalyst promoted decomposition of plasma-generated H₂O₂ into •OH radicals, the principal dye-degrading reagent, which further attacked the dye molecules. The catalyst improved the decolorization rate by 2.5 times, the energy yield by 93.4% and total organic carbon removal by 7.1%. Excitation of the catalyst mostly occurred through strikes by plasma-generated reactive ions and radical species from the air, accelerated by the electric field, as well as by fast electrons with an energy of up to 15 eV generated by the streamers reaching the liquid surface. These strikes transferred the energy to the catalyst and created the electrons and holes, which further reacted with H₂O₂ and water, producing •OH radicals. This was indentified as the primary role of the catalyst in this process. Decolorization reactions followed pseudo first-order kinetics. Production of H₂O₂ and the dye degradation rate increased with increase in the input voltage. The optimal catalyst dose was 500 mg∙dm⁻³. The decolorization rate was a little lower in river water compared with that in deionized water due to the side reactions of •OH radicals with organic matter and inorganic ions dissolved in the river water.

Bismuth basic nitrates (BBNs) were synthesized via an electrochemical method, i.e., by electrodeposition from an acidic solution of bismuth nitrate, followed by thermal treatment in an air environment. For the first time, the influence of various electrochemical parameters on the morphology, crystal structure, and chemical structure of BBNs was examined. The following synthesis parameters were investigated: electrodeposition current density, thermal treatment temperature of the obtained deposit, and working electrode material (cathode). The obtained materials were characterized by SEM-EDX, XRD, FTIR, TG, and N₂ adsorption/desorption methods and were applied for the sorption of the textile dye RB19. The results showed that the electrodeposition current density and thermal treatment temperature affect the surface morphology, chemical composition, and crystal structure of the obtained materials, as well as the RB19 sorption efficiency. On the other hand, the working electrode material does not affect the properties of the synthesized materials mentioned. Kinetic, isotherm, and thermodynamic analysis of the sorption process were also examined.

A new woodchips-ZrO₂ biosorbent (W-ZrO₂) was synthesized using wood residue material generated from the oak tree (Quercus robur) during furniture manufacturing. Biosorbent was tested for the simultaneous removal of both chromium (Cr) ions: Cr(III) and Cr(VI), in the binary component solution. Biosorbent characterization was performed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD). To define optimal process parameters for simultaneous removal of both Cr species, effects of pH, temperature, sorbent dosage and Cr ions concentration on the sorption process were investigated. Sorption of Cr ions onto W-ZrO₂ was highly pH-dependent. Optimal pH for simultaneous removal of both Cr(III) and Cr(VI) ions is 4.0 with removal efficiency over 99.5 % in both cases. Equilibrium experimental results are the best fitted by the Langmuir sorption isotherm model. The maximal sorption capacities of the biosorbent for simultaneous removal of Cr(III) and Cr(VI) ions in binary-component system are 16.18 and 83.52 mg g⁻¹, respectively. The present study shows that using wood residue material to produce a low-cost sorbent can effectively decrease the water pollution simultaneously removing both chromium species from water and also reduce wood waste and increase reuse/recycling options.