Kseniya A. Litvintseva

Developing regenerable solid sorbents that combine high CO2 uptake, accessible porosity, and mild regeneration remains a key challenge for practical carbon capture. Single-walled carbon nanotubes have been considered an unattractive candidate among carbon substrates due to the high price, despite the benefits of chemical stability, fully accessible surface area, and macroporous structure. Nevertheless, the recent advances in scaling SWCNT production shifted the paradigm, especially in the case of highly reusable sorbents. Here, we introduce a polyethyleneimine (PEI)/SWCNT hybrid sorbent that combines the highly accessible surface area of SWCNTs with localized CO2-affinitive regions provided by PEI. The hybrid was prepared by a simple and scalable method of incipient wet impregnation, with 2 wt.% PEI identified as the optimum loading while preserving the accessible nanotube framework. The resulting material exhibited a dynamic CO2 adsorption capacity of 7.4 mmol/g at 30 °C under 50% CO2/50% N2 and retained a capacity of 1.2 mmol/g under 15% CO2/85% N2. In the presence of 4% moisture, the capacity decreased to 3.5 mmol/g, indicating competitive water adsorption. The PEI–SWCNT hybrid maintained an average regeneration efficiency of around 95% over ten consecutive adsorption–desorption cycles, with effective regeneration at temperatures ≤100 °C. An apparent heat of adsorption of −20.2 ± 3.5 kJ/mol, together with temperature-programmed desorption and density functional theory results, indicates predominantly physisorption accompanied by localized amine-assisted CO2 stabilization. Overall, the results show that the PEI–SWCNT combination provides a regenerable hybrid adsorbent for dynamic CO2 capture.

Anthropogenic contamination of water resources poses a critical global challenge for designing efficient adsorption-based water treatment processes. This work provides a systematic adsorption study of six graphene-based sorbents with different C/O ratios and surface chemistries for the removal of four representative cationic and anionic dyes and two broad-spectrum antibiotics (amoxicillin and norfloxacin) from aqueous solutions, including their mixtures in model wastewater. Overoxidized graphene oxide demonstrates high removal efficiencies for cationic dyes, with maximum sorption capacities of 155 mg/g for methylene blue and 175.5 mg/g for brilliant green. In contrast, under-oxidized graphene oxide shows even higher capacities for several dyes, reaching 369, 444 and 488 mg/g for methylene blue, brilliant green and Congo red, respectively. Thermally reduced graphene oxide combines partial reduction of carbon framework with residual oxygen functionalities and achieves sorption capacities of 153 mg/g for methylene blue and 209 mg/g for methyl orange. All graphene-based sorbents also effectively remove antibiotics, with maximum sorption capacities in the range of 322–487 mg/g. Adsorption kinetics and equilibrium are described using pseudo-second-order and nonlinear Langmuir and Sips models, enabling quantitative comparison of sorbent performance. The effectiveness of the graphene-based sorbents is further validated under near-real conditions in river water purification experiments, where dyes were present at extremely low concentrations (1 ppm). These results demonstrate that controlled oxidation and reduction of graphene oxide provide an effective route for tailoring sorbent selectivity and adsorption performance in wastewater treatment applications.

Designing solid sorbents that combine high CO2 capacity, fast kinetics, and low regeneration energy is a key challenge for large-scale carbon capture. In this work, we develop polyethyleneimine (PEI)-functionalized single-walled carbon nanotubes (SWCNTs) using a scalable incipient wet impregnation method that enables precise control of low PEI loadings while preserving the intrinsic porosity of the nanotube framework. Purification of commercial SWCNTs increases the BET surface area from 416 to 711 m2/g, and subsequent functionalization with ~2 wt.% PEI boosts the dynamic CO2 working capacity from 2.3 mmol/g (pristine) to 7.4 mmol/g under a 50% CO2/50% N2 flow at 30 °C. The optimized sorbent exhibits stable, reversible performance with regeneration efficiencies ≥93% over repeated adsorption–desorption cycles at ≤100 °C, highlighting its suitability for cyclic operation in pre- and post-combustion capture schemes. Comprehensive characterization (BET, TGA, Raman, FTIR, TEM, EDX) confirms effective PEI association without significant structural damage or severe pore blockage. Thermodynamic analysis yields an apparent heat of adsorption of -20.2 ± 3.5 kJ/mol, consistent with physisorption-dominated uptake complemented by weak, non-stoichiometric stabilization near amine sites that facilitates low-temperature CO2 release. Density functional theory calculations qualitatively corroborate this mechanism by revealing enhanced yet non-covalent interactions for CO2 in the vicinity of PEI chains on the SWCNT surface. These results demonstrate that low-loading PEI–SWCNT sorbents can reconcile high dynamic capacity, regeneration efficiency, and moderate energy demand, offering a promising route toward energy-efficient CO2 capture technologies.

The rising concentration of atmospheric CO2 necessitates efficient and scalable capture technologies, particularly for pre- and post-combustion flue gases. In this study, polyethyleneimine (PEI)-functionalized single-walled carbon nanotubes (SWCNTs) were prepared using a simple incipient wet-impregnation approach. The resulting composite sorbent exhibits a dynamic working CO2 uptake of 7.4 mmol/g under flow conditions at an optimal PEI loading of 2 wt.%. The enhanced uptake arises from modification of the surface adsorption environment by PEI, rather than from surface area increase alone. Comprehensive characterization using BET, TGA, Raman spectroscopy, FTIR, EDX, and TEM confirms effective purification and surface functionalization while preserving nanotube structural integrity. Isosteric heat analysis yields an adsorption enthalpy of -20.2 ± 3.5 kJ/mol, indicating physisorption-dominated CO2 adsorption with additional weak stabilization associated with amine functionalities. Density functional theory calculations support this interpretation by identifying weak donor-acceptor interactions between CO2 molecules and amine groups, while excluding the formation of covalent carbamate species under dry conditions. Cyclic adsorption-desorption experiments demonstrate stable and reversible performance, with regeneration efficiencies of ≥93% under repeated cycling. Overall, PEI-functionalized SWCNTs provide a balanced combination of adsorption capacity, reversibility, and moderate regeneration energy demand, highlighting their potential for energy-efficient CO2 capture under dry pre- and post-combustion conditions.

This study demonstrates a robust approach for producing Ni and Au nanowires (NWs) encapsulated by single‐walled carbon nanotubes (SWCNTs), achieving lengths up to 1.2 µm. The process involves nitrogen plasma treatment to create defects in the SWCNTs, followed by the nanotubes filling with the metal precursor and its subsequent reduction. Simulations of carbon nanotube irradiation are performed to investigate the relationship between nitrogen kinetic energy and defect formation under the irradiation, revealing conditions that promote efficient nickel encapsulation. Structural analysis confirmed defect sizes ranging from 3.6 to 9.2 Å, suitable for metal precursor entry. Ni NWs exhibited excellent electrocatalytic activity in urea oxidation reactions (UOR), achieving a specific activity of 1150 A g ⁻¹ at 1.7 V v s . reversible hydrogen electrode (RHE) in 2 M urea and stable performance over 1000 cycles. Comparative simulations of urea adsorption energies showed that nickel‐filled SWCNTs enhance adsorption (−0.35 eV) when compared to pure graphene surface (−0.2 eV), demonstrating a synergistic effect of nickel and carbon structures. The role of defects in enhancing urea adsorption has also been analyzed. This work highlights the potential of SWCNTs as nano‐reactors for producing high‐performance catalytic materials. The findings emphasize the importance of controlled defect engineering and thermal treatment in optimizing nanowire synthesis for advanced catalytic and functional applications.

Structure–performance relationships in functional catalysts allow for controlling their performance in a wide range of reaction conditions. Here, the structural and compositional peculiarities in CTAB-templated CeO₂-ZrO₂-MnO_x catalysts prepared by co-precipitation of precursors and their catalytic behavior in CO oxidation and soot combustion are discussed. A complex of physical–chemical methods (low-temperature N₂ sorption, XRD, TPR-H₂, Raman, HR TEM, XPS) is used to elucidate the features of the formation of interphase boundaries, joint phases, and defects in multicomponent oxide systems. The addition of Mn and/or Zr dopant to ceria is shown to improve its performance in both reactions. Binary Ce-Mn catalysts demonstrate enhanced performance closely followed by the ternary oxide catalysts, which is due the formation of several types of active sites, namely, highly dispersed MnO_x species, oxide–oxide interfaces, and oxygen vacancies that can act individually and/or synergistically.