Molten salt-shielded solid-state synthesis (MS5) reaction-driven >99% pure Ti3AlC2 MAX phase: effect of MAX phase purity on the interlayer separation of MXenes and Na-ion storage.

Ti3C2-X MXenes have attracted tremendous research interest because their 2D laminar morphology provides numerous functional applications. The application options rely on the purity and interlayer spacing of MXenes, which eventually depend on the purity of the MAX phase. This motivated us to synthesize pure MAX phases to produce MXenes at large scale using simpler and less expensive techniques. However, producing prerequisite pure MAX phases at atmospheric pressure and relatively lower temperatures is still a challenging task. This study reports the synthesis of thermally stable pure MAX phases (and MXenes) by systematically varying the molar ratio of the precursors, reaction temperature, and reaction time using a novel MS5 process under atmospheric pressure conditions. The purity of MAX phases under different synthesis conditions shows a direct interrelationship with the 2D laminar morphology of MXenes. The highest purity of >99% for the MAX phase was achieved by reacting Ti : Al : C precursors in a 3 : 1.5 : 1.9 molar ratio at 1350 °C for 90 min and delivered highly distinctive 2D nanostructured laminar MXenes with larger interlayer spacing and specific surface area (i.e., 8.8 ± 0.1 m2 g-1), which are superior to those in previously reported works. These results reveal that the precursor molar ratios and reaction conditions tailor the MAX phase purity, thereupon, they are crucial for achieving good quality 2D laminar MXenes with large specific surface areas, further enhancing the performance of MXene-related devices. The developed MS5-MXenes, when probed as electrodes for Na ion applications, show excellent initial and reversible capacity values of 142 mA h g-1 and 103 mA h g-1 (at 50 mA g-1), respectively.

Low-Intensity Light Detection with a High Detectivity Using 2D-Sb2Se3 Nanoflakes on 1D-ZnO Nanorods as Heterojunction Photodetectors.

Multifunctional photodetectors (PDs) with broadband responsivity (R) and specific detectivity (D*) at low light intensities are gaining significant attention. Thus, we report a bilayer PD creatively fabricated by layering two-dimensional (2D) Sb2Se3 nanoflakes (NFs) on one-dimensional (1D) ZnO nanorods (NRs) using simple thermal transfer and hydrothermal processes. The unique coupling of these two layers of materials in a nanostructured form, such as 2D-Sb2Se3 NFs/1D-ZnO NRs, provides an effective large surface area, robust charge transport paths, and light-trapping effects that enhance light harvesting. Furthermore, the combination of both layers can effectively facilitate photoactivity owing to proper band alignment. The as-fabricated device demonstrated superior overall performance in terms of a suitable bandwidth, good R, and high D* under low-intensity light, unlike the single-layered 1D-ZnO NRs and 2D-Sb2Se3 NF structures alone, which had poor detectivity or response in the measured spectral range. The PD demonstrated a spectral photoresponse ranging from ultraviolet (UV) to visible (220-628 nm) light at intensities as low as 0.15 mW·cm-2. The PD yielded a D* value of 3.15 × 1013 Jones (220 nm), which reached up to 5.95 × 1013 Jones in the visible light region (628 nm) at a 3 V bias. This study demonstrated that the 2D-Sb2Se3 NFs/1D-ZnO NRs PD has excellent potential for low-intensity light detection with a broad bandwidth, which is useful for signal communications and optoelectronic systems.

Investigation of the Structural and Optical Properties of Zinc Ferrite Nanoparticles Synthesized via a Green Route.

We report herein the synthesis of ZnFe2O4 (ZF) nanoparticles via a simple and eco-friendly green route using lemon juice as a reducing agent and fuel. The effect of different calcination temperatures on the particle size and bandgap of grown ZF nanoparticles was investigated. The structural, morphological and optical properties of the synthesized nanoparticles were evaluated using synchrotron x-ray diffraction (S-XRD), field emission scanning electron microscopy (FE-SEM) and UV-visible diffuse reflectance spectroscopy (UV-Vis-DRS), respectively. S-XRD confirmed a spinel F-d3m phase in all four samples calcined at 350°C, 550°C, 750°C and 1000°C. The crystallite size calculated from the Debye-Scherrer equation showed an increase from 14 nm to 20 nm with the increase in calcination temperature. Williamson-Hall (W-H) analysis revealed an increase in the particle size from 16 nm to 21 nm and a decrease in the lattice microstrain from 0.913 × 10-3 to 0.154 × 10-4 with the increase in calcination temperature. The optical bandgap of the ZF nanoparticles obtained from UV-Vis-DRS decreased from 2.265 eV to 2.225 eV with the increase in calcination temperature. The ZF nanoparticles with tunable particle size, lattice microstrain and optical bandgap have potential application in ferrofluid, electromagnetic shielding, photocatalysis, hyperthermia, dye degradation and other areas. Supplementary Information: The online version contains supplementary material available at 10.1007/s11664-022-09813-2.

Dithiophosphonate Anchored Heterometallic (Ag(I)/Fe(II)) Molecular Catalysts for Electrochemical Hydrogen Evolution Reaction.

The dichalcogenide ligated molecules in catalysis to produce molecular hydrogen through electroreduction of water are rarely explored. Here, a series of heterometallic [Ag4(S2PFc(OR)4] [where Fc = Fe(η5-C5H4)(η5-C5H5), R = Me, 1; Et, 2; nPr, 3; isoAmyl, 4] clusters were synthesized and characterized by IR, absorption spectroscopy, NMR (1H, 31P), and electrospray ionization mass spectrometry. The molecular structures of 1, 2, and 3 clusters were established by single-crystal X-ray crystallographic analysis. The structural elucidation shows that each triangular face of a tetrahedral silver(I) core is capped by a ferrocenyl dithiophosphonate ligand in a trimetallic triconnective (η3; µ2, µ1) pattern. A comparative electrocatalytic hydrogen evolution reaction of 1-5 (R = iPr, 5) was studied in order to demonstrate the potential of these clusters in water splitting activity. The experimental results reveal that catalytic performance decreases with increases in the length of the carbon chain and branching within the alkoxy (-OR) group of these clusters. Catalytic durability was found effective even after 8 h of a chronoamperometric stability test along with 1500 cycles of linear sweep voltammetry performance, and only 15 mV overpotential was increased at 5 mA/cm2 current density for cluster 1. A catalytic mechanism was proposed by applying density functional theory (DFT) on clusters 1 and 2 as a representative. Here, a µ1 coordinated S-site between Ag4 core and ligand was found a reaction center. The experimental results are also in good accordance with the DFT analysis.