Search Results (240)

A novel ternary nanocomposite, comprising reduced graphene oxide/polyaniline/gadolinium oxide (RGO-PANI-Gd₂O₃), was successfully synthesized using the Hummers method, followed by in situ emulsion polymerization of polyaniline. The final composite was produced by hydrothermally adding gadolinium nitrate. The composite was subjected to a systematic analysis that included optical, microstructural, physical, and Raman spectroscopic analysis, as well as current-voltage (J-V) measurements. The morphology of this composite material was investigated using scanning electron microscopy (SEM). The addition of Gd₂O₃ nanoparticles decreases the band gap energy from 3.5 eV (PANI) to 2.7 eV (RGO-PANI-Gd₂O₃). The UV–Vis spectra revealed a redshift in the π-π* transition peak from 318 nm (PANI) to 346 nm, indicating increased conjugation length and synergistic effects. This eco-friendly material has excellent catalytic activity for triiodide reduction. The manufactured counter-electrode (CE) demonstrated remarkable transparency and conversion efficiency comparable to platinum, with a current density of 11.7 mA·cm⁻² versus 8.2 mA·cm⁻² for platinum. Under simulated solar light (AM 1.5 G, 100 mW·cm⁻²), the RGO-PANI-Gd₂O₃ based nanocomposite CE achieved an excellent 4.3% photo conversion efficiency. These findings indicate that RGO-PANI-Gd₂O₃ nanocomposites have potential as efficient, platinum-free counter electrodes in dye-sensitized solar cells (DSSCs). Full article

A series of catalytic oxides (Fe₂O₃, CuO, ZnO, and Cu₂O) were investigated as prospective additives shaping the thermal features of a model solid rocket propellant (SRP) formulation utilising ammonium nitrate as the oxidising agent. An extensive investigation of the thermal behaviour (DSC and ignition/explosion temperature studies) of the model and catalyst-bearing SRP formulations was conducted, providing insights into both the thermodynamics and mechanism of combustion of these systems. XRD analysis of post-combustion residues was used to validate the mechanistic claims, as well as to provide information about the behaviour of copper oxides in the SRP system. In addition, the linear combustion velocity was experimentally determined, and the power output was estimated from density, linear combustion velocity and DSC data, in order to assess the potential motor performance of the tested formulations. The obtained results show that the utilisation of metal oxides significantly improves the combustion performance of ammonium nitrate-based SRP formulations relative to the unmodified ammonium nitrate-based propellants. Full article

Nitrate pollution in groundwater poses severe threats to ecosystems and human health, making the electrochemical nitrate reduction reaction (NO₃RR) a promising remediation technology. Conductive metal–organic frameworks (cMOFs) with π-d conjugation, dispersed active sites, and tunable structures are ideal candidates for electrocatalysis. Herein, we synthesized a series of cMOFs (M₃(HHTP)₂, M = Fe, Zn, Cu, Co, Ni) via conjugated coordination between hexahydroxytriphenylene (HHTP) ligands and metal ions and systematically investigated their NO₃RR performance. Electrochemical tests revealed that Fe₃(HHTP)₂ exhibits superior catalytic performance for nitrate reduction, achieving a high NH₃ selectivity of 99.5% and a yield rate of 676.4 mg·g_cat⁻¹·h⁻¹ at −1.0 V vs. RHE (reversible hydrogen electrode), along with excellent cyclic and structural stability. In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy identified key intermediates (*NO₂, *NH₂OH) and proposed the reaction pathway: NO₃⁻ → *NO₃ → *NO₂ → *NO → *NOH → *NH₂OH → *NH₂ → *NH₃. DFT calculations revealed that Fe center exhibited a lower energy barrier for NO₃RR compared to other metal ions (Zn, Cu, Co, Ni). This study demonstrates the significant potential of Fe₃(HHTP)₂ for efficient NO₃RR and provides new insights into the structure-function relationship of cMOF-based electrocatalysts. Full article

Al-rich NH₄-ZSM-5 with highly oriented crystals was directly synthesized through a one-pot hydrothermal technique, using ammonium nitrate as a metal-free mineralizer. The samples were characterized by XRD, N₂ adsorption–desorption, SEM, FTIR, Py-FTIR, ²⁷Al MAS NMR, ²⁹Si MAS NMR, ¹H MAS NMR, and TGA techniques. The impact of aluminum source, ammonium source, and H₂O/SiO₂ molar ratio was studied. XRD results showed that the ZSM-5 catalyst with a low Si/Al ratio (13) was successfully synthesized without any amorphous phase, including a microporous/mesoporous structure. A low H₂O/SiO₂ molar ratio (75) resulted in coffin-shape surface morphology, large b-axis-oriented particles (ca. 19 µm), and high specific surface area (>300 m² g⁻¹), providing a large portion of straight channels (90.5%). The catalytic activity of the catalysts was evaluated in the CO₂ hydrogenation reaction in tandem configuration with a Na/Fe₂O₃ catalyst. The results confirmed that highly b-oriented crystals improved the product shape selectivity to p-xylene by affecting the diffusion resistance. Therefore, the developed catalyst provided high CO₂ conversion (45%) and high aromatic selectivity (77%), with p-xylene accounting for 82% of the produced xylene compounds, over a long-term time on stream (17 h). These results demonstrate the effectiveness of the direct synthesis strategy in producing Al-rich ZSM-5 catalysts with tailored textural and acidic properties for tandem and shape-selective catalysis. Full article

Copper-based electrocatalytic materials with high surface area are essential for various processes, such as water splitting and the electroreduction of carbon dioxide and nitrates. Three-dimensional nanostructured electrodes offer distinct advantages in these applications due to their expansive surface area, which enhances charge transfer and mass transport. For bimetallic systems, however, the phase state, whether a solid solution or a mechanical mixture of metals, is critically important for catalytic performance. This study explores the formation of Cu-Ni solid solutions via electrodeposition using the dynamic hydrogen bubble template method. Two types of electrolyte were employed: sulfate-based and citrate-based. Through characterization by X-ray diffraction, scanning electron microscopy, elemental mapping, and X-ray fluorescence spectroscopy, we demonstrate that metallic foams deposited from sulfate solutions are heterogeneous, with poor control over nickel content. In contrast, the use of citrate-based solutions allows the nickel content in the deposits to be effectively controlled by varying the solution composition, thereby enabling the formation of a solid solution. Full article

Activated carbon has shown good catalytic performance in water treatment, but its wide application is limited by its high price. Activated coke exhibits functional groups and is low-cost. However, there is limited research on activated coke as a catalyst. In our previous study, powdered activated coke (PAC) exhibited good catalytic performance in NH₃-N treatment with ozonation. Increasing nitrogen selectivity is the key to harmless degradation of NH₃-N, which has received little attention. In this paper, manganese-loaded powdered coke (Mn–PAC) was prepared, aiming to further improve the nitrogen selectivity. Under the same conditions, the PAC/O₃ system achieved 92.16% NH₃-N removal and 49.46% nitrogen selectivity, while the Mn–PAC/O₃ system achieved almost 100% NH₃-N removal and 79.31% N₂ selectivity. When Mn–PAC was reused for the sixth time, the system achieved about 70% and 46% NH₃-N removal and N₂ selectivity, both of which were about 10% higher than those of PAC. Complex redox and synergistic interactions existed in the Mn–PAC/O₃ system. The Mn–PAC surface contains reactive sites such as C=C, C=O, π–π bonds, ArOH, and various MnO_x. These components collectively facilitate ozone decomposition into ·OH, ·O₂⁻, and ¹O₂. The ¹O₂ may play a significant role in converting NH₃-N to N₂. Full article

To avoid dependence on conventional raw materials, global emphasis has been placed on obtaining alternative plant celluloses and the chemical synthesis of cellulose. The use of synthetically derived cellulose as a precursor for cellulose nitrates (NCs) is currently absent in global practice, which underscores the undoubted relevance of this research. Cellulose nitrate (NC) was synthesized in a 138% actual yield by nitration of synthetic cellulose (SC)—a new type of cellulose—prepared by electropolymerization from an aqueous glucose solution in the presence of catalytic tungsten–vanadium heteropolyacid of the 1–12 series with the chemical formula H₆[PW₁₀V₂O₄₀]: a nitrogen content of 11.83%, a viscosity of 198 mPa·s, a high solubility of 91% in an alcohol–ether solvent, and an ash content of 0.05%. SEM provided a general concept of the morphological structure of SC and SC-derived NC. The initial SC consisted of flat, curly fibers with a smooth surface approximately 10–20 μm wide, with no aggregation observed. The fibers of SC-derived NC had a cylindrical shape with a diameter of up to 25 μm and a rough surface. FT-IR spectroscopy revealed that SC and SC-derived NC have the main functional groups characteristic of classical cellulose (3346, 2901, 1644, 1429, 1162, and 1112 cm⁻¹) and nitrate esters of cellulose (1650, 1278, 832, 747, and 689 cm⁻¹), respectively. For the first time, a full-profile analysis discovered that SC is made up of the monoclinic phase of cellulose Iβ with an antiparallel chain arrangement. SC with a crystallinity index (CrI) of 81–86% was shown to undergo amorphization upon nitration, with the CrI declining to 17% and the crystallite sizes decreasing from 44 × 62 × 59 × 94 Å to 29 × 62 × 26 × 38 Å. Coupled TGA/DTA revealed that SC exhibits a high-temperature endothermic peak of decomposition of 374 °C, with a weight loss of 84%. The thermostable SC-derived NC exhibits a high onset temperature of intense decomposition of 200 °C and an exothermic peak of 208 °C, with a weight loss of 88%, and is characterized by a high specific heat of decomposition of 7.74 kJ/g. This study provides new insights into the functionalization of SC with a high degree of polymerization, expanding the classical concepts of cellulose nitration. Full article

Nitrate (NO₃⁻), as a stable nitrogen-containing compound, has caused serious harm to the ecological environment and human health. To reduce nitrate pollution, the catalytic reduction of nitrate (NO₃RR) to ammonia (NH₃) is a very promising solution. Recently, single-atom catalysts (SACs) have received extensive attention due to their excellent activity and stability. Here, we study the nitrate catalytic reduction properties of hexagonal-boron-nitride-(h-BN)-supported single-atom Cu systematically and theoretically and compare it with monolayer h-BN. We find that (1) due to the stronger electronegativity of the N atom, Cu atom is preferentially doped at the N top site, resulting in the significant electron rearrangement; (2) the doped Cu atom at the N top site for monolayer h-BN can provide extra 3d-orbital electrons at the Fermi level, which can significantly enhance the conductivity, reduce the bandgap width, and increase the reducibility; (3) the NO₃⁻ ion preferentially adsorbs at the hollow site of monolayer h-BN, while the NO₃⁻ ion is adsorbed more strongly at the Cu top site of h-BN-supported single-atom Cu due to the abundant d-electron supply from the Cu atom; (4) single-atom Cu can significantly reduce the energy barrier of the rate-determining step (RDS) and increase the probability of nitrate reduction. In conclusion, h-BN-supported single-atom Cu exhibits excellent catalytic performance of NO₃RR. Full article

Nitrate contamination of water resources poses significant ecological and public health risks. This study developed a cobalt-immobilized microplastic catalyst (Co–MP) capable of activating peroxymonosulfate (PMS) and facilitating formic-acid-assisted catalytic denitrification of nitrate. Characterization via Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray diffractometry (XRD) confirmed successful Co deposition, with the surface cobalt content reaching 5.2%. The system’s performance was optimized using Response Surface Methodology (RSM), identifying catalyst dosage and Co(II) concentration as the most significant factors. Under the optimized conditions (pH 5.5, reaction time 120 min, catalyst dosage 1.5 g L⁻¹, and Co(II) concentration 60 mg L⁻¹), the system achieved a nitrate removal efficiency of 90.6%, in excellent agreement with the model prediction (90.93%), along with an 86.7% reduction in total nitrogen, confirming stepwise denitrification to gaseous nitrogen species (N₂). The Co(II)/Co(III) redox cycle, sustained by PMS-assisted regeneration and driven by formic acid as the electron donor, ensured stable performance with minimal cobalt leaching (0.05 mg L⁻¹). This coupled oxidative–reductive system offers a sustainable dual-remediation strategy that simultaneously achieves selective nitrate conversion and valorizes microplastic waste for catalytic environmental applications. Full article

Dry reforming of methane (DRM) is a method whereby two greenhouse gases (methane and carbon dioxide) are synthesized into a high-value gas. Suitable catalysts with optimal compositions are still in development, as problems concerning coking and metal sintering remain unresolved. Since the late 20th century, catalysts prepared via solution combustion synthesis (SCS) have been applied for catalytic reactions, as these materials (catalyst or supports) demonstrate high catalytic performance; for example, SCS catalysts have been tested in DRM. This review describes the history of solution combustion synthesis, compares it with traditional methods of preparing catalysts for DRM, and charts recent developments in SCS catalytic systems based on Ni and Co. SCS catalysts are prepared by burning nitrates (oxidizing agents) and fuels (reducing agents) at mild pre-ignition temperatures. In this review, the effects of fuel type and mixed-fuel systems on the catalyst composition, as well as its activity in DRM, are described. These catalysts have shown high metal dispersion, good coke resistance, and stable catalytic performance in long-term tests. This review demonstrates the main reasons for catalyst deactivation, such as coke deposition on the catalyst surface, and suggests ways to reduce them. Full article

Ammonia serves as a critical industrial feedstock and a potential carbon-free energy carrier. However, its conventional synthesis method (the Haber–Bosch process) suffers from high energy consumption and substantial carbon emissions. The electrochemical nitrate reduction reaction (eNO₃RR) has emerged as a promising alternative pathway, capable of converting nitrate pollutants in water into high-value ammonia under mild conditions, enabling green synthesis while offering dual benefits of environmental remediation and energy conversion. Single-atom catalysts (SACs), with their maximal atom utilization efficiency, well-defined active sites, and highly tunable electronic structures, have demonstrated exceptional catalytic performance and selectivity in eNO₃RR. This review systematically summarizes recent advances of SACs in eNO₃RR, with a focus on reaction mechanisms, advanced in situ characterization techniques, theoretical calculation, and the catalytic behavior and structure–activity relationships of various non-noble metal centers (e.g., Cu, Fe, Co). Key strategies for enhancing SACs performance are elaborated, alongside an analysis of microenvironmental influences such as electrolyte composition, pH, and potential. Finally, we outlines current challenges in material design, dynamic active site identification, and the industrial application of SACs, and propose future research directions aimed at facilitating the practical implementation of eNO₃RR technology and contributing to the establishment of a sustainable ammonia economy. Full article

The fabrication of highly loaded and uniformly dispersed metal oxide nanoparticles (NPs) is much desired but still remains a great challenge. Herein, the NiO NPs exclusively confined in mesoporous silica SBA-15 were obtained by using nickel nitrate hydrate as a precursor through a facile solvent-free preparation method, which comprised manual grinding of Ni(NO₃)₂·6H₂O with SBA-15 and subsequent air calcination. Characterization results from X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed that aggregation-free NiO nanoparticles with sizes of 3–5 nm were obtained at loading as high as 20 wt.% (weight%). Further increasing the NiO loading to 30 wt.% led to partial agglomeration of discrete nanoparticles to rod-like particles, while no external particles were observed. By comparing the sample derived from nickel acetate with exclusively external NiO particles, it was established that the pore confinement provided NiO nanoparticles with high thermal stability. Lastly, the catalytic performance of the prepared sample was evaluated in the model reaction of ammonia decomposition to CO_x-free H₂, and the stable NH₃ conversion of 93.7% was achieved at the weight hourly space velocity (WHSV) value of 30,000 mL·g⁻¹·h⁻¹ and at high temperature of 650 °C for 60 h, demonstrating the great potential of the solvent-free method in preparing thermally stable and robust supported catalysts. Full article

Developing bifunctional electrocatalysts that simultaneously enable green hydrogen production and water purification is essential for advancing sustainable energy and environmental technologies. In this study, we present Cu@Pd core–shell nanostructures fabricated through template-assisted electrodeposition of Cu, followed by galvanic Pd modification on pyrolytic graphite electrodes (PGEs). The optimised catalyst exhibited superior hydrogen evolution reaction (HER) activity, with an onset potential of 70 mV, a low Tafel slope of 33 mV dec⁻¹ and excellent stability during prolonged HER operation. In addition to hydrogen evolution, Cu@Pd/PGE shows significantly enhanced nitrate reduction reaction (NRR) activity compared to Cu/PGE in both alkaline and neutral conditions. Under ideal conditions, the catalyst achieved 60% nitrate removal with high selectivity towards ammonia and minimal nitrite formation, emphasising its superior performance. This enhanced bifunctionality arises from the synergistic Cu–Pd interface, facilitating efficient nitrate adsorption and selective hydrogenation. Despite their high catalytic activity for both HER and NRR, the Cu@Pd nanostructures could often emerge as a versatile platform for integration into sustainable hydrogen production and an effective denitrification process. Full article

Introduction: 5-HMF is a molecule found in carbohydrate-rich foods that is associated not only with cancer and anaphylactic reactions, but also with anti-oxidant properties. Questions arose as to whether 5-HMF exhibited a catalytic effect in relation to lipid peroxidation and lipoprotein oxidation in presence of metals and/or radicals. Methods: Peroxynitrite (ONOO⁻)-induced chemiluminescence and ONOO⁻ nitration of tyrosine residues on BSA using anti-nitro-tyrosine-antibodies were used to measure the protection of 5-HMF against peroxides or nitration compared to vitamin C (VitC). The reductive potential of 5-HMF or VitC on Cu²⁺ or Fe³ was estimated using the bicinchoninic acid (BCA) or Fenton-complex method. Human plasma was used to measure the generation of malondialdehyde (MDA), 4-hydroxynonenal (HNE), and total thiols after Fe²⁺/H₂O₂ oxidation in the presence of different concentrations of 5-HMF or VitC. Finally, Cu²⁺ oxidation of LDL after 4 h was carried out with 5-HMF or VitC, measuring the concentration of MDA in LDL with the thiobarbituric assay (TBARS). Results: VitC was 4-fold more effective than 5-HMF in scavenging ONOO⁻ to nearly 91.5% at 4 mM, with the exception of 0.16 mM, where the reduction of ONOO⁻ by VitC was 3.3-fold weaker compared to 0.16 mM 5-HMF. VitC or 5-HMF at a concentration of 6 mM inhibited the nitration of tyrosine residues on BSA to nearly 90% with a similar course. While 5-HMF reduced free Fe³⁺ in presence of phenanthroline, forming Fe²⁺ (phenantroleine)₃ [Fe²⁺(phe)₃] or complexed Cu²⁺(BCA)₄ to Cu⁺(BCA)₄ weakly, VitC was 7- to 19-fold effective in doing so over all the used concentrations (0–25 mM). A Fe²⁺—H₂O₂ solution mixed with human plasma showed a 6–10 times higher optical density (OD) of MDA or HNE in the presence of 5-HMF compared to VitC. The level of thiols was significantly decreased in the presence of higher VitC levels (1 mM: 198.4 ± 7.7 µM; 2 mM: 160.0 ± 13.4 µM) compared to equal 5-HMF amounts (2562 ± 7.8 µM or 242.4 ± 2.5 µM), whereas the usage of lower levels at 0.25 µM 5-HMF resulted in a significant decrease in thiols (272.4 ± 4.0 µM) compared to VitC (312.3 ± 19.7 µM). Both VitC and 5-HMF accelerated copper-mediated oxidation of LDL equally: while the TBARS levels from 4 h oxidized LDL reached 137.7 ± 12.3 nmol/mg, it was 1.7-fold higher using 6 mM VitC (259.9 ± 10.4 nmol/mg) or 6 mM 5-HMF (239.3 ± 10.2 nmol/mg). Conclusions: 5-HMF appeared to have more pro-oxidative potential compared to VitC by causing lipid peroxidation as well as protein oxidation. Full article

In this work, bare copper oxide-based catalysts were synthesized and evaluated for their dual (photo)catalytic activity in two model reactions: hydrogen generation via formic acid decomposition (FAD) and the photocatalytic hydroxylation of benzene to phenol. Catalysts were prepared from copper nitrate and copper acetate precursors and calcined for either 10 min or 2 h. Their structural and surface properties were characterized by wide-angle X-ray diffraction (WAXD), Raman spectroscopy, and BET surface area analysis. FAD was conducted under mild thermal conditions and monitored via ¹H NMR spectroscopy. At the same time, benzene hydroxylation was performed under UV irradiation and analyzed by gas chromatography (GC) and high-performance liquid chromatography (HPLC). All synthesized catalysts outperformed commercial CuO in the selective oxidation of benzene. The nitrate-derived sample calcined for 10 min (NCuO 10 min) achieved the best performance, with a phenol yield of ~10% and a selectivity of up to 19%, attributed to improved surface properties and the presence of Cu(I) domains, as indicated by Raman spectroscopy. For FAD, complete conversion of formic acid was achieved at low temperatures, with selective H₂ and CO₂ evolution and complete suppression of CO, even under short reaction times and low catalyst loadings. These results demonstrate the potential of nitrate-derived CuO catalysts as versatile, dual-function materials for sustainable applications in selective aromatic oxidation and low-temperature hydrogen generation, without the need for noble metals or harsh conditions. Full article