Catalytic Activity of Ti‐based MXenes for the Hydrogenation of Furfural

Comparative Effects of Hydrazine and Thermal Reduction Methods on Electromagnetic Interference Shielding Characteristics in Foamed Titanium Carbonitride MXene Films

The urgent need for the development of micro-thin shields against electromagnetic interference (EMI) has sparked interest in MXene materials owing to their metallic electrical conductivity and ease of film processing. Meanwhile, postprocessing treatments can potentially exert profound impacts on their shielding effectiveness (SE). This work comprehensively compares two reduction methods, hydrazine versus thermal, to fabricate foamed titanium carbonitride (Ti3CNTx) MXene films for efficient EMI shielding. Upon treatment of ≈ 100 µm-thick MXene films, gaseous transformations of oxygen-containing surface groups induce highly porous structures (up to ≈ 74.0% porosity). The controlled application of hydrazine and heat allows precise regulation of the reduction processes, enabling tailored control over the morphology, thickness, chemistry, and electrical properties of the MXene films. Accordingly, the EMI SE values are theoretically and experimentally determined. The treated MXene films exhibit significantly enhanced SE values compared to the pristine MXene film (≈ 52.2 dB), with ≈ 38% and ≈ 83% maximum improvements for the hydrazine and heat-treated samples, respectively. Particularly, heat treatment is more effective in terms of this enhancement such that an SE of 118.4 dB is achieved at 14.3 GHz, unprecedented for synthetic materials. Overall, the findings of this work hold significant practical implications for advancing high-performance, non-metallic EMI shielding materials.

Synthesis of Three Families of Titanium Carbonitride MXenes

Layered MAX phases and two-dimensional (2D) MXenes derived from them are among the most studied materials due to their attractive properties and numerous potential applications. The tunability of their structure and composition allows for every property to be modulated over a wide range. Particularly, elemental replacement and formation of a solid solution without changing the structure allow fine-tuning of material properties. While solid solutions on the M (metal) site have received attention, the partial replacement of carbon with nitrogen (carbonitrides) has received little attention. By applying this concept, herein we report the synthesis of three families of titanium carbonitride Tin+1Al(C1-yNy)n MAX phases and Tin+1(C1-yNy)nTx MXenes with one, two, and three C/N layers. This greatly expands the variety of known MAX phases and MXenes to encompass 16 titanium carbonitrides with tunable X-site chemistries and different 2D layer thicknesses, including MXenes in the Ti4(C1-yNy)3Tx system, which have not been previously reported. We further investigated the relationship among the composition, structure, stability, and synthesis conditions of the MXenes and their respective Al-based MAX phases. This range of materials will enable fundamental studies of the N/C ratio effect on optoelectronic, electromagnetic, and mechanical properties of MXenes, as well as tuning those properties for specific applications.

Efficient CO2 Capture and Activation on Novel Two-Dimensional Transition Metal Borides

The large-scale production of CO₂ in the atmosphere has triggered global warming, the greenhouse effect, and ocean acidification. The CO₂ conversion to valuable chemical products or its capture and storage are of fundamental importance to mitigate the greenhouse effect on the environment. Therefore, exploring new two-dimensional (2D) materials is indispensable due to their potential intriguing properties. Here, we report a new family of 2D transition metal borides (M₂B₂, M = Sc, Ti, V, Cr, Mn, and Fe; known as MBenes) and demonstrate their static and dynamic stability. These MBenes show a metallic nature and exhibit excellent electrical conductivity. The CO₂ adsorption energy on MBenes ranges from -1.04 to -3.95 eV and exhibits the decreasing order as Sc₂B₂ > Ti₂B₂ > V₂B₂ > Cr₂B₂ > Mn₂B₂ > Fe₂B₂. The spin-polarization calculation shows a reduction in the adsorption energy for magnetic systems. Bader charge transfer indicates the formation of CO₂^δ- moiety on the MBene surface, so-called activated CO₂, which is essential for its reaction with other surface chemicals. Differential charge density plots reveal a significant charge accumulation around the CO₂ molecule. Our theoretical results predict the usage of new MBenes as a cost-effective catalyst for CO₂ capture and activation.

Catalytic Transfer Hydrogenation and Acid Reactions of Furfural and 5-(Hydroxymethyl)furfural over Hf-TUD-1 Type Catalysts

Heterogeneous catalysis, which has served well the petrochemical industry, may valuably contribute towards a bio-based economy by sustainably enabling selective reactions to renewable chemicals. Carbohydrate-containing matter may be obtained from various widespread sources and selectively converted to furanic platform chemicals: furfural (Fur) and 5-(hydroxymethyl)furfural (Hmf). Valuable bioproducts may be obtained from these aldehydes via catalytic transfer hydrogenation (CTH) using alcohols as H-donors under relatively moderate reaction conditions. Hafnium-containing TUD-1 type catalysts were the first of ordered mesoporous silicates explored for the conversion of Fur and Hmf via CTH/alcohol strategies. The materials promoted CTH and acid reactions leading to the furanic ethers. The bioproducts spectrum was broader for the reaction of Fur than of Hmf. A Fur reaction mechanism based on literature data was discussed and supported by kinetic modelling. The influence of the Hf loading and reaction conditions (catalyst load, type of alcohol H-donor, temperature, initial substrate concentration) on the reaction kinetics was studied. The reaction conditions were optimized to maximize the yields of 2-(alkoxymethyl)furan ethers formed from Fur; up to 63% yield was reached at 88% Fur conversion, 4 h/150 °C, using Hf-TUD-1(75), which was a stable catalyst. The Hf-TUD-1(x) catalysts promoted the selective conversion of Hmf to bis(2-alkoxymethyl)furan; e.g., 96% selectivity at 98% Hmf conversion, 3 h/170 °C for Hf-TUD-1(50).

Experimental and Computational Analysis of MnO2@V2C-MXene for Enhanced Energy Storage

Herein, we studied the novel and emerging group of 2D materials namely MXene along with its nanocomposites. This work entails detailed experimental as well as computational study of the electrochemical behavior of vanadium carbide (V2CTx) MXene and MnO2-V2C nanocomposite with varying percentages of MnO2. A specific capacitance of 551.8 F/g was achieved for MnO2-V2C nanocomposite in 1 M KOH electrolyte solution, which is more than two times higher than the gravimetric capacitance of 196.5 F/g obtained for V2C. The cyclic stability achieved for the MnO2-V2C nanocomposite resulted in a retentivity of 96.5% until 5000 cycles. The c-lattice parameter achieved for MXene is 22.6 Å, which was 13.01 Å for MAX phase. The nanocomposite resulted in a c-lattice parameter of 27.2 Å, which showed that the spatial distance between the MXene layers was efficiently obtained. The method of wet etching was used for the preparation of pristine MXene and the liquid phase precipitation method was opted for the synthesis of the MnO2-V2C nanocomposite. Density functional theory calculation was exercised so as to complement the experimental results and to understand the microscopic details, such as structure stability and electronic structure. The current report presents a comprehensive experimental and computational study on 2D MXenes for future energy storage applications.