Molecular Compartments Created in Metal-Organic Frameworks for Efficient Visible-Light-Driven CO2 Overall Conversion

We report the construction of molecular compartments by the growth of narrow-band semiconductor nanoparticles, tungsten oxide and its hydrate, in the mesopores of a metal-organic framework (MOF), MIL-100-Fe. The location of these nanoparticles in pores and their spatial arrangement across the MOF crystal are unveiled by powder X-ray diffraction and small-angle neutron scattering, respectively. Such a composition with pore-level precision leads to efficient overall conversion of gas-phase CO₂ and H₂O to CO, CH₄, and H₂O₂ under visible light. When WO₃·H₂O nanoparticles are positioned in 2.5 nm mesopores with 24 wt %, the resulting composite, namely, 24%-WO₃·H₂O-in-MIL-100-Fe, exhibits a CO₂ reduction rate of 0.49 mmol·g^-1·h^-1 beyond 420 nm and an apparent quantum efficiency of 1.5% at 420 nm. These performances stand as new benchmarks for visible-light-driven CO₂ overall conversion. In addition to the size and location of semiconductor nanoparticles, the coordinated water species in the crystal are found critical for high catalytic activity, an aspect usually overlooked.

Computation and Investigation of Two-Dimensional WO3·H2O Nanoflowers for Electrochemical Studies of Energy Conversion and Storage Applications

The aim of this study is to prepare a two-dimensional (2D) WO₃·H₂O nanostructure assembly into a flower shape with good chemical stability for electrochemical studies of catalyst and energy storage applications. The 2D-WO₃·H₂O nanoflowers structure is created by a fast and simple process at room condition. This cost-effective and scalable technique to obtain 2D-WO₃·H₂O nanoflowers illustrates two attractive applications of electrochemical capacitor with an excellent energy density value of 25.33 W h kg^-1 for high power density value of 1600 W kg^-1 and good hydrogen evolution reaction results (low overpotential of 290 mV at a current density of 10 mA cm^-2 with a low Tafel slope of 131 mV dec^-1). A hydrogen evolution reaction (HER) study of WO₃ in acidic media of 0.5 M H₂SO₄ and electrochemical capacitor (supercapacitors) in 1 M Na₂SO₄ aqueous electrolyte (three electrode system measurements) demonstrates highly desirable characteristics for practical applications. Our design for highly uniform 2D-WO₃·H₂O as catalyst material for HER and active material for electrochemical capacitor studies offers an excellent foundation for design and improvement of electrochemical catalyst based on 2D-transition metal oxide materials.

A Novel Route for the Easy Production of Thermochromic VO2 Nanoparticles

In this work, a simple, fast and dry method for the fabrication of a thermochromic product with a high load of VO₂(M1) consisting of the controlled heat treatment of pure vanadium nanoparticles in air is presented. After a complete design of experiments, it is concluded that the most direct way to attain the maximum transformation of V into VO₂(M1) consists of one cycle with a fast heating ramp of 42 °C s⁻¹, followed by keeping 700 °C for 530–600 seconds, and a subsequent cooling at 0.05 °C s⁻¹. Careful examination of these results lead to a second optimum, even more suitable for industrial production (quicker and less energy‐intensive because of its lower temperatures and shorter times), consisting of subjecting V to two consecutive cycles of temperatures and times (625 °C for 5 minutes) with similar preheating (42 °C s⁻¹) but a much faster postcooling (∼ 8 °C s⁻¹). These green reactions only use the power for heating a tube open to atmosphere and a vanadium precursor; without assistance of reactive gases or catalysts, and no special vacuum or pressure requirements. The best products present similar thermochromic properties but higher thermal stability than commercial VO₂ particles. These methods can be combined with VO₂ doping.

Formation mechanism of porous rose-like WO3 and its photoresponse and stability study

Fabrication of rose-like WO₃ by chemical bath method.