Reduced Graphene Oxide-Sodium Manganese Oxide Nanowire Nanocomposite Aerogels for Asymmetric Supercapacitors: Impact of Composite Concentration

Transition metal oxides are considered potential candidates for supercapacitor electrodes but often suffer from lower ionic diffusivity and poor electronic conductivity. Addressing these challenges requires the development of electrode materials with well-engineered architectures and precise designs. This research focused on fabricating nanocomposites by combining one-dimensional (1D) sodium manganese oxide (Na0.4MnO2) nanowires (NMO NWs) with a three-dimensional (3D) reduced graphene oxide aerogel (RGA). The NMO NWs are aligned and interconnected within the graphene layers, forming a 3D NMO/RGA composite (NRGA) matrix with excellent integration. NMO NWs increase the nanocomposite surface area by acting as spacers between graphene layers. The percentage of NMO NWs significantly influences the structural properties of the electrode, thereby affecting its supercapacitor performance. Notably, the RGA composite with a 40% loading of NMO NWs (N4RGA) achieved a specific capacitance of 576 F g-1 at 6 mA cm-1. The fabricated asymmetric supercapacitor (ASC) device demonstrated a potential of 1.8 V and achieved an energy density of 48.58 Wh kg-1 at a power density of 222.2 W kg-1, along with excellent cyclability. This study highlights a pathway for developing aerogel-based nanocomposites by integrating nanomaterials of varying dimensions, offering potential for advanced energy storage applications.

Coralloid W18O49@covalent organic frameworks S-scheme heterojunction for high efficiency photocatalytic aerobic oxidation

Reasonably designing and constructing efficient artificial S-mechanism photocatalysts, expanding their application in the field of photocatalytic organic synthesis, have become a hot and challenging topic in the photocatalysis. Herein, a series of coral-like W18O49@TpPa-H (TpPa-H represents COFs generated by the reaction of 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-H)) composites were successfully prepared by using a simple in-situ encapsulation strategy. Given the internal electric field at the S-scheme interface, W18O49 acts as an oxidative photocatalyst with sufficient positive valence band (VB) position and TpPa-H as a reductive one with enough negative conduction band (CB) position for the efficient amines oxidative coupling to imines. The resulting W18O49@TpPa-H-0.1 hybrid material shows both optimal benzylamine to imine conversion and selectivity exceeding 99 % within 4 h under 10 W 420 nm LED light irradiation, which is 9.9 and 2.8 fold greater than that of W18O49 and TpPa-H, respectively. The photocatalytic activity is even extended to 740 nm. Furthermore, the photocatalytic mechanism research confirmed that a high efficiency S-scheme heterojunction was formed between W18O49 and TpPa-H, and multiple active species, such as ·O2-, 1O2, and h+, synergistically participated in the reaction, imparting its excellent photocatalytic performance. This work may open new avenues for the development of high-efficiency COFs-based S-scheme heterojunction for organic photosynthesis.

Unveiling the mechanism for selective cleavage of C-C bonds in sugar reactions on tungsten trioxide-based catalysts

Conversion of naturally occurring sugars, the most abundant biomass resources on Earth, to fuels and chemicals provides a sustainable and carbon-neutral alternative to the current fossil resource-based processes. Tungsten-based catalysts (e.g., WO3) are efficient for selectively cleaving C-C bonds of sugars to C2,3 oxygenate intermediates (e.g., glycolaldehyde) that can serve as platform molecules with high viability and versatility in the synthesis of various chemicals. Such C-C bond cleavage follows a mechanism distinct from the classical retro-aldol condensation. Kinetic, isotope 13C-labeling, and spectroscopic studies and theoretical calculations, reveal that the reaction proceeds via a surface tridentate complex as the critical intermediate on WO3, formed by chelating both α- and β-hydroxyls of sugars, together with the carbonyl group, with two adjacent tungsten atoms (W-O-W) contributing to the β-C-C bond cleavage. This mechanism provides insights into sugar chemistry and enables the rational design of catalytic sites and reaction pathways toward the efficient utilization of sugar-based feedstocks.

Enhanced d–d transitions in HKUST/Bi2WO6 nanocomposite mediated visible-light driven selective conversion of benzyl alcohol to benzaldehyde

Graphical representation of the involvement of the d–d transition in the photocatalytic conversion of benzyl alcohol to benzaldehyde.

Faceting-Controlled Zeeman Splitting in Plasmonic TiO2 Nanocrystals

Dynamic manipulation of discrete states in nanostructured materials is critical for emerging quantum technologies. However, this process often requires a correlation of mutually competing degrees of freedom. Here we report the control of magnetic-field-induced excitonic splitting in colloidal TiO₂ nanocrystals by control of their faceting. By changing nanocrystal morphology via reaction conditions, we control the concentration and location of oxygen vacancies, which can generate localized surface plasmon resonance and foster the reduction of lattice cations leading to the emergence of individual or exchange-coupled Ti(III) centers with high net-spin states. These species can all couple with the nanocrystal lattice under different conditions resulting in distinctly patterned excitonic Zeeman splitting and selective control of conduction band states in an external magnetic field. This work demonstrates the concept of using nanocrystal morphology to control carrier polarization in individual nanocrystals using both intrinsic and collective electronic properties, representing a unique approach to multifunctionality in reduced dimensions.

Graphene oxide/titania photocatalytic ozonation of primidone in a visible LED photoreactor

A graphene oxide-titania (GO/TiO₂) composite was synthesized via sol-gel method, and studied in aqueous Primidone mineralization with ozone and LED visible light. The photocatalyst was characterized by different techniques (XRD, TEM, SBET, TGA, UV-vis diffuse reflectance spectroscopy). The band gap value decrease from 3.14 eV for bare TiO₂ samples to 2.5 eV in GO/TiO₂ composites clearly shows the interaction of GO with TiO₂ structure. Approximately 20 mg L^-1 of Primidone was removed in less than 20 min if ozone was applied, regardless of the presence or absence of light and catalyst. However, reactivity tests show a synergism effect between photocatalysis and ozonation for mineralization purposes. The combination of ozone and GO improved the activation of TiO₂ under visible light. Process optimization led us to select a catalyst dosage of 0.25 g L^-1, a light radiance of 359 W m^-2 and a GO loading in the catalyst around 0.75%. At these conditions, with photocatalytic ozonation, the presence of GO in the catalyst improved mineralization up to 82% in 2 h compared to 70% reached with bare TiO₂. Catalyst reusability shows no decrease of photocatalytic activity. Scavenger tests point to hydroxyl radicals as the main species responsible for Primidone removal.

Highly selective conversion of guaiacol to tert-butylphenols in supercritical ethanol over a H2WO4 catalyst

The conversion of guaiacol is examined at 300 °C in supercritical ethanol over a H₂WO₄ catalyst. Guaiacol is consumed completely, meanwhile, 16.7% aromatic ethers and 80.0% alkylphenols are obtained. Interestingly, tert-butylphenols are produced mainly with a high selectivity of 71.8%, and the overall selectivity of 2,6-di-tert-butylphenol and 2,6-di-tert-butyl-4-ethylphenol is as high as 63.7%. The experimental results indicate that catechol and 2-ethoxyphenol are the intermediates. Meanwhile, the WO₃ sites play an important role in the conversion of guaiacol and the Brønsted acid sites on H₂WO₄ enhance the conversion and favour a high selectivity of the tert-butylphenols. The recycling tests show that the carbon deposition on the catalyst surface, the dehydration and partial reduction of the catalyst itself are responsible for the decay of the H₂WO₄ catalyst. Finally, the possible reaction pathways proposed involve the transetherification process and the alkylation process during guaiacol conversion.

H₂WO₄ is an effective catalyst for the conversion of guaiacol, and the Brønsted acid sites on H₂WO₄ surface promote a high selectivity of tert-butylphenols.

Synthesis and Characterization of WO₃/Graphene Nanocomposites for Enhanced Photocatalytic Activities by One-Step In-Situ Hydrothermal Reaction

Tungsten trioxide (WO₃) nanorods are synthesized on the surface of graphene (GR) sheets by using a one-step in-situ hydrothermal method employing sodium tungstate (Na₂WO₄·2H₂O) and graphene oxide (GO) as precursors. The resulting WO₃/GR nanocomposites are characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The results confirm that the interface between WO₃ nanorod and graphene contains chemical bonds. The enhanced optical absorption properties are measured by UV-vis diffuse reflectance spectra. The photocatalytic activity of the WO₃/GR nanocomposites under visible light is evaluated by the photodegradation of methylene blue, where the degradation rate of WO₃/GR nanocomposites is shown to be double that of pure WO₃. This is attributed to the synergistic effect of graphene and the WO₃ nanorod, which greatly enhances the photocatalytic performance of the prepared sample, reduces the recombination of the photogenerated electron-hole pairs and increases the visible light absorption efficiency. Finally, the photocatalytic mechanism of the WO₃/GR nanocomposites is presented. The synthesis of the prepared sample is convenient, direct and environmentally friendly. The study reports a highly efficient composite photocatalyst for the degradation of contaminants that can be applied to cleaning up the environment.