In this work, different methods for fly ash modification were applied to obtain an adsorbent for the efficient removal of selected pharmaceuticals from a multiclass aqueous solution. Morphological and surface properties of the modified fly ash samples were analyzed by scanning electron microscopy, X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy, and point of zero charge, and the influence of the applied modifications was determined by comparison with the results obtained for unmodified fly ash. Experimental parameters of the adsorption of the pharmaceutical onto the modified fly ash were optimized, and special attention was paid to the influence of different parameters on the adsorption capacities. Multivariate methods of analysis, such as artificial neural networks, applied to the obtained results showed that the contact time, the initial concentration of the pharmaceutical solution, and the pH value had the strongest influence on the adsorption process. Fly ash modified with chitosan and magnetic iron oxide showed the best adsorption properties (removal efficiency above 80% for the majority of the selected pharmaceuticals), and artificial neural networks confirmed its susceptibility to the modeling process.

Due to industrial growth and its impact on the environment, the increasing amount of industrial waste requires a comprehensive approach aligned with the principles of sustainable development. The main goals are not only to preserve natural resources but also to encourage innovation in the reuse of waste materials. In an attempt to reduce the problems regarding waste disposal and wastewater treatment in the textile industry, fibrous textile waste was used as a starting material to obtain carbon adsorbents for the removal of pollutants from wastewater. Waste cotton and mixed yarns, mainly consisting of polysaccharide cellulose, were hydrothermally carbonized and activated with KOH to convert them into efficient carbon adsorbents for heavy metal removal from water. Characterization of carbonized material showed that after activation, an increase in specific surface area (up to 872 m²/g) and content of surface oxygen groups (6.04 mmol/g) leads to a higher affinity towards heavy metal ions, especially lead ions, and high adsorption capacity of 19.98 mg/g obtained for activated cotton yarns. The results of this research represent a contribution to the reduction of waste materials by modifying them into adsorbents, while the regeneration of adsorbents is an example of the practical application of polysaccharide-based materials in the purification of wastewater containing various heavy metal ions.

Waste hemp and flax fibers, and cotton and cotton/polyester yarns, available in large quantities from the textile industry, were used as cheap and effective sorbents for the removal of methylene blue from wastewater. Waste fibers and yarns were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, iodine sorption, water retention, and point of zero charge, as well as through the determination of crystallinity index and degree of surface crystallinity. The adsorption of methylene blue was optimized by examining the influence of contact time, initial concentration, temperature, and pH value. It was found that the more ordered structure of cotton and cotton/polyester yarns leads to lower adsorption capacities and better agreement with pseudo-second order kinetic and Langmuir isotherm model, while the more heterogeneous structure of flax and hemp fibers shows higher capacities for methylene blue adsorption, better described by the pseudo-first order kinetic and Freundlich isotherm model. Based on the obtained results, waste lignocellulosic fibers and yarns can be used for the discoloration of wastewater, thereby solving the problem of waste generated in the textile industry.

In an attempt to reuse fibrous textile waste and, at the same time, to address dye pollution in textile wastewater, waste cotton-based yarn was utilized as a cheap and sustainable adsorbent, as well as a row material for carbon adsorbent production. Unmodified yarn and cotton-based carbon adsorbents were used as adsorbents for dye removal from water. Cotton and cotton/polyester yarn samples underwent thermal modification through carbonization followed by chemical activation with KOH. Various techniques, including scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, and surface charge determination, were employed to analyze the morphological and surface characteristics of the cotton-based adsorbents. Adsorption properties were evaluated by testing the removal of selected cationic and anionic dyes from water. The impact of temperature, initial pH and concentration of the dye solution, and contact time on adsorption were investigated, and experimentally obtained data were analyzed using theoretical models. While carbonization alone did not significantly enhance adsorption properties, activated samples exhibited high efficacy in removing both cationic and anionic dyes from water. Despite the negative influence of the polyester component in the carbon precursor on the efficiency of activated samples in removing methyl orange, the results indicated that activated cotton and cotton/polyester yarn could be used to prepare highly efficient adsorbents for the rapid removal of methylene blue from real wastewater samples.

As new technologies are developed, the demand for rare earth elements (REEs) has increased, despite limited awareness of their significant impact on people and the environment. In this study, waste fly ash was used as a precursor to synthesize inorganic aluminosilicate polymers by adding an activator to the alumina and silica compounds of the ash. Due to their structure and adsorption potential, their application for the removal of selected REEs (Gd³⁺, Y³⁺, and Sc³⁺) from water has been investigated. A decrease in the intensity of the quartz peak at 2θ of 26.6° in the XRD spectrum and the disappearance of the albite and mullite peaks due to dissolution during alkaline activation in both modified samples were observed. The appearance of a peaks at 2θ of 29.3° and 39.3° corresponding to calcite in the modified sample indicates the presence of wood ash. A shifting of the band in the DRIFT spectrum to 1030 cm⁻¹ on the spectra of modified samples corresponds to the vibrations of Al-O and Si-O bonds and the formation of a polymeric network structure (Si-O-Si or Si-O-Al). According to pH_PZC values, thermodynamic and kinetic parameters, and chemical composition, the presumed mechanism of REE adsorption is chemisorption and ion exchange. The highest adsorption efficiencies (up to 95%) for all examined REEs in both single and mixed REE solutions were obtained from an alkali-activated mixture of fly ash and wood ash. The results of this research are significant for expanding knowledge about the removal of REEs from the environment, the reduction of waste ash by their modification, and their potential subsequent use in construction as additives.

In this study, the influence of boron doping on structural and surface properties of carbon material synthesized by a hydrothermal method was investigated, and the obtained results were compared with the previously published influence that boron has on characteristics of carbonized boron-doped hydrothermal carbons (CHTCB). Hydrothermal carbons doped with boron (HTCB) were obtained by the hydrothermal synthesis of glucose solutions with different nominal concentrations of boric acid. It was found that glucose based hydrothermal carbon does not have developed porosity, and the presence of boron in their structure has insignificant influence on it. On the contrary, additional carbonization increases the specific surface area of the undoped sample, while an increase in boron content drastically decreases the specific surface area. Boron doping leads to a decrease in the amount of surface oxygen groups, for both, hydrothermally synthesized and additionally carbonized materials. Raman analysis showed that the boron content does not affect a structural arrangement of the HTCB samples, and Raman structural parameters show a higher degree of disorder, compared to the CHTCB samples. Comparison of structural and surface characteristics of hydrothermal carbons and carbonized materials contributes to the study of the so far, insufficiently clarified influence that boron incorporation has on the material characteristics.