Combustion of hydroxylammonium nitrate (95 wt.% HAN) ‒ water solution in presence of high specific surface area activated carbons is investigated in a constant-pressure bomb within the pressure range of 1‒6 MPa. The linear burning rate increased for the system of HAN admixed with activated carbons compared to those of the HAN alone. Moreover, the thermal decomposition of HAN (95 wt.%) ‒ water solution spiked with activated carbons was assessed by DTA – TG method. In the presence of activated carbons, the ability to trigger the decomposition at a lower temperature (86 °C vs 185 °C) was observed. The volatile products formed in the course of thermal decomposition of HAN, spiked with activated carbons were characterized by electron ionization mass spectrometry analysis. Primary products of HAN decomposition: m/z = 33 (NH2OH) and m/z = 63 (HNO3), which are further responsible for the formation of secondary products such as N2O, NO, HNO2, NO2, O2 etc. Significant reduction of NOx emissions during thermal decomposition of HAN (95 wt.%) ‒ water solution was observed (ca. 30%) in presence of activated carbons.

After undergoing biological treatment, wastewater still contains substances with endotoxic activity, such as lipopolysaccharide. However, due to the increasing practice of treating wastewater to make it suitable for drinking (potable reuse), the removal of these endotoxic active materials is crucial. These substances can be harmful to human health, leading to a condition called endotoxaemia. Furthermore, environmental endotoxins pose risks to pharmaceutical manufacturing processes and the quality of the final pharmaceutical products. Ultimately, the most significant concern lies with the patient, as exposure to such substances can have adverse effects on their health and well-being. Activated carbon has a proven efficiency for endotoxin removal; rice husk (RH), as a type of natural lignocellulosic agricultural waste, is a unique carbon precursor material in terms of its availability, large-scale world production (over 140 million tons annually), and is characterized by the presence of nanoscale silica phytoliths, which serve as a template to create additional meso/macropore space within the nanoscale range. High surface area RH/lignin-derived honeycomb monoliths were prepared in this study via extrusion, followed by carbonization and physical and chemical activation to develop additional pore space. The nanoporosity of the carbon honeycomb monoliths was established by means of low-temperature nitrogen adsorption studies, using calculations based on QSDFT equilibrium and BJH models, as well as mercury intrusion porosimetry (MIP) and SEM investigations. An alternative method for the elimination of the bacterial lipopolysaccharide (LPS)—a conventional marker—using filtration in flowing recirculation systems and the adsorbent activity of the monoliths towards LPS was investigated. Since LPS expresses strong toxic effects even at very low concentrations, e.g., below 10 EU/mL, its removal even in minute amounts is essential. It was found that monoliths are able to eliminate biologically relevant LPS levels, e.g., adsorption removal within 5, 30, 60, 90, and 120 min of circulation reached the values of 49.8, 74.1, 85.4, 91.3%, and 91.6%, respectively.

P-cresol, indole and indole-3-acetic acid (IAA) are catabolites of amino acids, formed by the gut microbiome. Most of these aromatic hydrocarbon derivatives are excreted by the colon before reentering the body to form “exogenous” protein-bound uremic toxins (PBUTs), which aggravate chronic kidney disease (CKD). Removal efficiencies of these PBUT precursors from model phosphate-buffered saline solutions by three different surface-modified nanoporous carbon adsorbents (PCs) were studied. PCs were produced by physicochemical and/or acid base activation of carbonized rice husk waste. Removal rates achieved values of 32–96% within a 3 h contact time. High micro/mesoporosity and surface chemistry of the N- and P-doped biochars were established by N₂ adsorption studies, SEM/EDS analysis, XPS and FT-IR-spectroscopy. The ammoxidized PC-N1 had the highest adsorption capacity (1.97 mmol/g for IAA, 2.43 mmol/g for p-cresol and 2.42 mmol/g for indole), followed by “urea-nitrified” PC-N2, whilst the phosphorylated PC-P demonstrated the lowest adsorption capacity for these solutes. These results do not correlate with the total pore volume values for PC-N2 (0.91 cm³/g) < PC-P (1.56 cm³/g) < PC-N1 (1.84 cm³/g), suggesting that other parameters such as the micropore volume (PC-N1 > PC-N2 > PC-P) and the interaction of surface chemical functional groups with the solutes play key roles in the adsorption mechanism. N-doped PC-N1 and PC-N2 have basic functional groups with higher affinity with acidic IAA and p-cresol. The ion-exchange mechanism of phenolic and indolic compound chemisorption by nanoporous carbon adsorbents, modified with surface N- and P-containing functional groups, has been proposed.

The article describes the synthesis of an activated carbon-carbon/ash composite based on carbonized rice husk (CRH) and Ca-lignosulfonate. The obtained adsorbents were characterized by modern physicochemical research methods: scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS analysis), X-ray photoelectron spectroscopy (XPS), and low-temperature nitrogen adsorption. It was established that despite the presence of residual mineral impurities in an amount of about 15 wt. %, the synthesized CRH-lignosulf@850 composite exhibits a high specific surface area and a well-developed pore volume. These impurities are represented by the phases CaSiO3, MgSiO3, CaSO4 and SiO2, which proved to be resistant to alkaline leaching. The morphology of the obtained composites features a well-developed structure with both micro- and mesoporosity. According to calculations based on the Quenched solid density functional theory (QSDFT), the specific surface area of the obtained СRH-lignosulf@850 sample is 1144 m²/g, and the total pore volume is 0.947 cm³/g. Studies of methylene blue (MB) sorption under static conditions showed that the CRH-lignosulf@850 composite demonstrates high adsorption performance. According to the adsorption isotherms, the Toth model effectively describe the process, with the maximum sorption capacity of the material reaching 283.4 mg/g. The results obtained indicate the potential for using CRH-lignosulf@850 blocks to capture toxic compounds in emissions from enterprises producing organic products.

Rice husk (RH) is a renewable siliceous lignocellulosic waste providing a unique, greener and less toxic alternative to conventional synthetic polymeric precursors in the production of carbon-based materials for biomedical applications. In this work we studied the porous structure of RH-lignin-based activated carbon produced in the form of honeycomb carbon monoliths and assessed their potential as hemoadsorbents for blood purification in the treatment of patients with serious medical conditions, such as kidney failure and sepsis. To determine their clinical suitability for such an application, the hemocompatibility and cytotoxicity of the monoliths were investigated using the standard ISO guidelines. The monoliths did not cause any changes in the cell viability or cell lysis. High micro/mesoporosity and surface chemistry of the initial monolith-C, N- and P-doped nanostructured carbon honeycomb monoliths were established by low-temperature nitrogen adsorption (LTNA) studies, mercury porosimetry data (MIP), SEM/EDS analysis and FT-IR spectroscopy. The micro-mesoporous, activated carbon-based filtration/adsorbent prototype devices, in the form of three-dimensional (3D) carbon matrix, functionalized with ion-exchange amino- and phosphate groups and encased in polyolefin heat shrink cable sleeve, have been developed with the capacity to remove protein-bound uremic toxins (PBUTs), such us PCS and IS, as well as inflammatory cytokines (IL-6 and IL-8) from human plasma in a flowing model system. The ammoxidized monolith-N, derived from the monolith-C, had the highest removal efficiency (40.05% for PCS, and 28.4% for IL-6). By contrast, phosphorylated monolith-P demonstrated the highest removal efficiency (54.62% for IS, and 54.4% for IL-8), whilst the monolith-C has the lowest removal efficiency for these adsorbates. These results do not correlate with the LTNA and MIP study results, suggesting that the interaction of surface chemical functional groups with the solutes play key roles in the adsorption mechanism. The ion-exchange mechanism of PBUTs and inflammatory cytokine chemisorption by the monoliths, modified with surface N- and P-containing functional groups, has been proposed.