Introduction: Due to concern about global warming, researchers are focusing on green fuels obtained by reducing captured CO₂ (e-fuels) with green hydrogen. An important example among e-fuels is methane. Ni-based catalysts are currently among the most investigated systems used for CO₂ methanation due to their high activity and selectivity at relatively low temperatures and due to their low cost compared to catalysts based on noble metals. Ni is often paired with a supporter/promoter, like CeO₂.

Methods: In this work, nanocomposite catalysts consisting of a NiO or NiO/CeO₂ active phase dispersed onto mesostructured/mesoporous supports are presented. The use of such supports should allow fine dispersion of the active phase, reaching high activity levels with a low amount of Ni and Ce. To obtain NiO- and NiO/CeO₂-based nanocomposites, two different impregnation strategies are used: two-solvent (TS) impregnation and impregnation based on a self-combustion (SC) reaction. Various Ni:Ce ratios and chemically different mesostructured/mesoporous supports (SiO₂, Al₂O_3, and CeO₂) are studied. The catalysts are characterized with different techniques to determine their structural, textural, and morphological properties and tested for CO₂ methanation.

Results and conclusion: Regardless of the support, the SC method allows us to disperse both NiO and CeO₂ in the form of much smaller nanoparticles compared with the TS approach. The catalytic tests show a positive effect of CeO₂ as a promoter of CO₂ conversion; furthermore, the catalysts obtained via the SC impregnation process show a higher CO₂ conversion, presumably due to the higher dispersion of the active phase. The Ni:Ce ratio also has a remarkable effect on the performance. The effect of different types of support on the performance is also investigated. In particular, CeO₂ support is shown to promote the catalytic performance, achieving CO₂ conversions of >85 mol%, competing with the most promising systems reported in the literature.

Carbon Nanodots (CDs) are a family of carbon-based nanoparticles characterized by intense and tunable absorption–emission in the visible range, which makes them very promising for light-emitting devices, optoelectronics, photocatalysis, and more.

Emulsion-templated assembly has emerged as a scalable approach to fabricate the so-called superparticles (SPs), controlled three-dimensional structures with crystalline or amorphous organization. SPs are obtained by the hierarchical assembly of colloidal nanoparticles, which act as the building blocks, constituting artificial materials with new properties stemming from the crosstalk between individual nanoparticles. Unfortunately, the photophysics governing their optical response remains largely unclear. In particular, little information is available on the dynamics of photoexcited superparticles made from the assembly of CDs.

Here, we report the first synthesis of CD-based SPs by a water-in-oil self-assembly procedure. Before the assembly, CDs were purified by column chromatography to isolate a fraction with narrow size distribution. One type of SP was directly obtained by the spontaneous self-assembly of the purified CDs by a water-in-oil (toluene) procedure. Alternatively, we pegylated (P-CDs) the CDs before self-assembly in order to change the interparticle distance inside the superparticles (P-SPs).

Both SPs are characterized by 1-2 mm diameters, and they display luminescence even in a solid state after dropcasting the sample, which is not common for individual CDs. We have been able to collect the emission and the lifetime from a single SP, demonstrating that the emission depends dramatically on the distance between the CDs inside the superstructure. In fact, when decreasing the distance between CDs, we observed a redshift of the emission band and a shortening of the emission lifetime. This work lays the foundations for the synthesis of new luminescent materials which can be useful in several optoelectronic applications.

Nowadays, the use of fossil fuels and the resulting greenhouse gas emissions have increased. Therefore, to facilitate the energy transition, it is essential to develop large-scale devices like fuel cells. However, their applicability is limited by the oxygen reduction reaction (ORR) at the cathode. This reaction must be catalyzed, and the main catalysts are typically based on platinum (Pt) or transition metals, which are either expensive and scarce or suffer from low durability.

To address these challenges, we propose the use of carbon materials such as activated carbon (AC), derived from industrial waste of the agro-food industry, making these precursors highly accessible and cost-effective. In this work, three different methods to synthesize the ACs, i.e., pyrolysis and thermal treatment with FeCl₃ or FeCl₃/ZnCl_2, were used, doping the most promising catalyst with heteroatoms (N/S) and using them as supports for a small amount of metal (Co/Ni).

These catalysts were characterized both physically,chemically, and electrochemically, and their efficiency in ORR was evaluated. Physical–chemical characterization was carried out by SEM, TEM, XRD, Raman, physical adsorption of N₂, ICP, XPS, and so on, confirming the achievement of different textures in the ACs and the success of the doping process.

The ORR performance of the catalysts was evaluated, and the electrochemical active surface area (ECSA), Tafel Slope, EIS, and durability tests were determined for the most promising catalysts. This analysis revealed a relationship between the textural properties, heteroatom content, metal support, and the improvement electrochemical properties, including charge-transfer and mass-transfer phenomena, and selectivity toward the 4-electron ORR mechanism.

The combination of wastewater treatment with advanced waste-to-energy (WTE) technologies, particularly through membrane-based processes for hydrogen production, represents a promising strategy for sustainable resource management. This paper investigates the application of membrane technologies such as membrane electrolysis, reverse osmosis (RO), forward osmosis (FO), and electrochemical systems in the extraction of hydrogen from wastewater. Membrane electrolysis stands out as a highly efficient method for hydrogen generation, where electrochemical reactions drive the splitting of water into hydrogen and oxygen, utilizing wastewater as a feedstock. By leveraging wastewater’s organic contaminants and high water content, membrane electrolysis can offer a decentralized, scalable, and sustainable solution for clean hydrogen production. Additionally, pressure-driven membrane processes like RO and FO can concentrate waste components in wastewater, improving the recovery of valuable products while facilitating more efficient energy conversion for hydrogen production. The combination of these membrane-based systems with renewable energy sources, such as solar or wind power, enhances the potential for energy-neutral or even energy positive wastewater treatment plants. However, challenges such as membrane fouling, limited long-term operational stability, and energy consumption in membrane separation processes must be addressed to optimize system efficiency and economic viability. Moreover, coupling these technologies with other WTE methods, such as microbial electrolysis cells (MECs) or advanced oxidation processes (AOPs), holds promise for improving overall hydrogen yields and operational efficiency. Life cycle assessments (LCAs) and techno-economic evaluations indicate that while membrane-based hydrogen production from wastewater is still in the experimental phase. This paper highlights the key advances in membrane technology, identifies current research gaps, and proposes directions for future development, emphasizing the potential of hydrogen production as a crucial component in circular economy models, where wastewater treatment and energy recovery work synergistically to promote sustainable water and energy management.

Efficient hydrogen evolution reaction (HER) in alkaline media remains a key challenge for sustainable hydrogen production. In this study, we report a composite catalyst comprising exfoliated palladium selenide (PdSe₂) nanosheets integrated with graphene oxide (GO), designed to enhance the hydrogen evolution reaction (HER) performance.

The exfoliation of PdSe₂ flakes (from the bulk crystal) increases the density of accessible active sites, while GO (by modified Hummer method) serves as a conductive scaffold that promotes electron transport and catalyst dispersion. Electrochemical evaluation in alkaline electrolyte reveals (25% KOH) that the PdSe–GO hybrid exhibits a significantly reduced overpotential and improved Tafel slope compared to pristine PdSe, indicating enhanced HER kinetics.

The synergistic interaction between PdSe and GO contributes to improved charge transfer and catalytic efficiency. This work highlights the potential of PdSe-based 2D materials, when combined with conductive carbon supports, as promising electrocatalysts for hydrogen generation in alkaline environments.

Funding: The authors acknowledge the financial support of the Project No. BG16RFPR002-1.014-0009 “Development and Sustainability of the Center of competence HITMOBIL—Technologies and systems for generation, storage and consumption of clean energy”, funded by the Operational Program “Science and Education for Smart Growth” 202114–2020 2027 and co-funded by the EU through the European Regional Development Fund.

Volatile organic compounds (VOCs), with boiling points below 250 °C, are atmospheric pollutants responsible for adverse effects such as climate change, depletion of the ozone layer and respiratory diseases. Traditional methods for their removal, such as absorption, condensation, membrane separation and thermal oxidation, present some limitations, including high cost, low efficiency or the generation of toxic byproducts. Therefore, more sustainable alternatives are needed, among which adsorption and photocatalytic oxidation stand out.

In this study, photocatalytic materials based on titanium dioxide (TiO₂) were synthesized and doped with nitrogen (N), nitrogen and boron (N-B), and nitrogen and sulfur (N-S) using a hydrothermal synthesis method, with the aim of degrading ethylene and toluene as model VOCs. The materials were obtained from a solution of titanium(IV) tert-butoxide and different doping agents, achieving a doping concentration of 2 wt%. After synthesis, the solids were washed, filtered and calcined. In addition, a sample of pure TiO₂ and several composites of the best-performing material with carbon xerogels doped with sulfur or nitrogen were also synthesized to enhance the performance.

The materials were characterized using complementary techniques such as SEM, XRD, XPS, DRUV and N₂ adsorption. The results showed an anatase crystalline structure with mesoporosity and a specific surface area of approximately 90 m²/g. The introduction of the carbon support increased these values and diminished the bandgap of the composite materials to 2.3 eV due to the formation of bonds between Ti and the heteroatoms. In photocatalytic tests under visible light and dynamic conditions, ethylene was easier to remove than toluene, and co-doped materials exhibited better performance, particularly under dry conditions. Notably, the SN-TiO₂ sample showed the highest activity and its combination with S- and N-doped xerogels significantly improved catalytic efficiency even under humid conditions due to an increase in hydrophobicity, achieving notable gains in terms of turnover frequency (TOF).

Introduction: Significant interest has been given to the development of multifunctional electrocatalysts based on metal nanoparticles and graphitic carbon composite [1,2]. Previously, we reported on the synthesis of heteroatom-doped graphitic carbon nanofibers using the chemical vapor deposition technique for applications in catalytic reactions, including oxygen reduction, evolution, and hydrogen generation [2-4].

Methods: In this work, a cobalt oxide (CoO) and graphene oxide (GO) composite material is synthesized using a solution-based technique. Furthermore, a MoO_x/MoS_x and GO composite material is synthesized by a hydrothermal process, and its electrochemical catalytic reaction performance is explored. The synthesized materials are characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical studies of the materials are performed by Metrohm Autolab potentiostat/galvanostat.

Results: It is noted that the synthesized CoO/GO composite can be utilized for catalytic reactions involving oxygen reduction, oxygen evolution, and hydrogen generation. On the other hand, the synthesized MoO_x/MoS_x and GO composite material exhibits excellent catalytic properties for hydrogen generation, with good stability of the working electrode at high current densities.

Conclusions: This study demonstrates that the GO-based material serves as an excellent host material for CoO and MoO_x/MoSx-based composite materials, enabling the design of effective electrocatalysts for oxygen reduction, evolution, and hydrogen generation. Thus, this research revealed the synthesis of effective composite electrocatalysts for green energy generation and storage device applications.

Acknowledgement: I would like to thank all my colleagues involved in this research work.

References:

1. Adv. Energy Mater., vol. 5, pp. 1500658 (2015).
2. 2. ChemistrySelect, 7, issue 26, pp. e202201386, (2022).
3. J. Phys. Chem. C, vol. 125, issue 45, pp. 25197-25206, (2021).
4. ChemistrySelect, vol. 6, pp. 4867-4873, (2021).

Ceramic cutting tools play a pivotal role in high-speed machining of difficult-to-cut materials owing to their exceptional hardness and unique thermomechanical properties. Al₂O₃-based ceramics, in particular, are widely adopted due to their excellent chemical inertness and cost-effectiveness. In recent years, high-entropy carbides such as (HfNbTaTiZr)C, characterized by superior hardness, have been incorporated into the Al₂O₃ matrix as hardening phases to further enhance tool performance. However, the inherent brittleness of Al₂O₃-(HfNbTaTiZr)C ceramic often leads to premature tool failure, severely limiting service life. Therefore, identifying an optimal toughening strategy to address this issue is of paramount importance. Graphene, a two-dimensional (2D) nanoscale reinforcement phase, offers a novel approach for toughening ceramic cutting tools due to its ultrahigh strength, large specific surface area, and exceptional crack-bridging capabilities.

Despite the emerging potential of graphene as a toughening phase for ceramics, existing studies lack systematic optimization of its microstructural parameters (layer number, flake size, and orientation) and interfacial bonding strength with the ceramic matrix. In this study, we developed a three-dimensional (3D) finite element model to comprehensively investigate the effects of graphene’s microstructural architecture (layer number and flake dimensions) and interfacial bonding strength (ceramic grain boundary-to-grain interior strength ratio and graphene–ceramic interface strength ratio) on the mechanical properties of graphene-toughened Al₂O₃-(HfNbTaTiZr)C ceramic tools, thereby identifying multiscale-optimized parameters. Building on this foundation, the influence of graphene orientation on tool lifespan during high-speed machining of 20CrMnTi steel was further evaluated, revealing the optimal orientations for maximizing tool longevity and minimizing cutting temperature.

The precise description of charge localization is paramount to defining the proper charge transport mechanism, the reactivity and long-term stability of novel materials to be employed in third-generation photovoltaics and photocatalysis. In this context, first-principles atomistic simulations represent a powerful tool for unravelling charge localization in semiconductors and the underlying correlation with the opto-electronic properties and device efficiencies.

We here present the results obtained by employing a plethora of computational techniques to study polaron formation, energetics and migration in the novel vacancy-ordered layered Cs₃Bi₂Br₉ (CBB) material, a novel water-stable metal halide perovskite that has been recently found to be particularly promising as a photocatode for the photocatalytic water splitting reaction.

Our calculations reveal that small electron polarons form in CBB upon photo-excitations, with electron localization induced by sizable distortions of both Bi-Br bonds and displacement of the A-site cations, with a wide spread of the polaron energy levels, due to the soft nature of the CBB lattice. By combining molecular dynamics simulations at the hybrid functional level with the thermodynamic integration technique, we are able to evaluate the polaron energy level in striking agreement with the experiment and we observe its favourable alignment with respect to water redox levels, which is consistent with measurements. However, our analysis of polaron hopping rates based on Marcus–Emin–Holstein–Austin–Mott theory reveals a strong anisotropy, with intra-layer charge mobility being up to four orders of magnitude lower than intra-layer mobility. The consequences of this finding of the use of CBB in heterojunctions for photocatalytic water splitting are discussed in view of the experimental results.

Organic solar cells, as a new type of solar cell, possess outstanding advantages such as light weight, low cost, and easy large-scale fabrication. They have attracted significant attention in both the academic and industrial fields. In recent years, the energy conversion efficiency of polymer solar cells has increased rapidly, and the efficiency value of single-junction devices has exceeded 19%. In material design, developing high-performance mid-bandgap acceptor materials has become an important strategy for improving the efficiency and stability of organic photovoltaic devices. Therefore, by introducing electron-donating units at the side chains and termini of the Y series acceptor molecules, we weakened the charge transfer effect within the acceptor molecules and developed a series of high-performance mid-bandgap acceptor materials. These materials were applied to the construction of efficient organic photovoltaic systems. Among them, the photovoltaic device based on the PM6: PYFO-V system achieved the highest indoor photoelectric conversion efficiency of 27.1% under LED illumination, which is one of the highest values reported for binary indoor full-poly systems to date; moreover, a ternary organic photovoltaic system using BTP-2FClO and BTP-eC9 as non-fullerene acceptors achieved a high efficiency of 19.34% under sunlight. This series of work has opened up new ideas about how to modify the molecular design of mid-bandgap acceptor materials in the future and provided material support for the development of high-efficiency solar cells.