Spatial Decoupling of Redox Chemistry for Efficient and Highly Selective Amine Photoconversion to Imines.

Light-driven primary amine oxidation to imines integrated with H2 production presents a promising means to simultaneous production of high-value-added fine chemicals and clean fuels. Yet, the effectiveness of this strategy is generally limited by the poor charge separation of photocatalysts and uncontrolled hydrogenation of imines to secondary amines. Herein, a spatial decoupling strategy is proposed to isolate redox chemistry at distinct sites of photocatalysts, and CoP core-ZnIn2S4 shell (CoP@ZnIn2S4) coaxial nanorods are assembled as the proof-of-concept photocatalyst. Directional and ultrafast carrier separation occurs between the CoP core and the ZnIn2S4 shell, as confirmed by in situ X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and transient absorption spectroscopy analyses. Toward the photoconversion of model substrate benzylamine to N-benzylbenzaldimine, CoP@ZnIn2S4 exhibits a 48-time higher production rate and >99% selectivity when compared to ZnIn2S4 (ca. 20% selectivity), and the detailed reaction mechanism has been verified by in situ diffuse reflectance infrared Fourier transform spectroscopy.

Narrowing the band gap and suppressing electron-hole recombination in ß-Fe2O3 by chlorine doping.

The effects of halogen (F, Cl, Br, I, and At) doping in the direct-band-gap ß-Fe2O3 semiconductor on its band structures and electron-hole recombination have been investigated by density functional theory. Doping Br, I, and At in ß-Fe2O3 leads to transformation from a direct-band-gap semiconductor to an indirect-band-gap semiconductor because their atomic radii are too large; however, F- and Cl-doped ß-Fe2O3 remain as direct-band-gap semiconductors. Due to the deep impurity states of the F dopant, this study focuses on the effects of the Cl dopant on the band structures of ß-Fe2O3. Two impurity levels are introduced when Cl is doped into ß-Fe2O3, which narrows the band gap by approximately 0.3 eV. After doping Cl, the light-absorption edge of ß-Fe2O3 redshifts from 650 to 776 nm, indicating that its theoretical solar to hydrogen efficiency for solar water splitting increases from 20.6% to 31.4%. In addition, the effective mass of the holes in halogen-doped ß-Fe2O3 becomes significantly larger than that in undoped ß-Fe2O3, which may suppress electron-hole recombination.

Continuous strain tuning of oxygen evolution catalysts with anisotropic thermal expansion.

Compressive strain, downshifting the d-band center of transition metal oxides, is an effective way to accelerate the sluggish kinetics of oxygen evolution reaction (OER) for water electrolysis. Here, we find that anisotropic thermal expansion can produce compressive strains of the IrO6 octahedron in Sr2IrO4 catalyst, thus downshifting its d-band center. Different from the previous strategies to create constant strains in the crystals, the thermal-triggered compressive strains can be real-timely tuned by varying temperature. As a result of the thermal strain accelerating OER kinetics, the Sr2IrO4 exhibits the nonlinear lnjo - T-1 (jo, exchange current density; T, absolute temperature) Arrhenius relationship, resulting from the thermally induced low-barrier electron transfer in the presence of thermal compressive strains. Our results verify that the thermal field can be utilized to manipulate the electronic states of Sr2IrO4 via thermal compressive strains downshifting the d-band center, significantly accelerating the OER kinetics, beyond the traditional thermal diffusion effects.

Cu NPs-embedded cross-linked microporous 3D reduced graphene hydrogels as photocatalyst for hydrogen evolution.

Three-dimensionally (3D) structured Cu nanoparticles (NPs)-embedded graphene hydrogels were synthesized from inexpensive graphite and low-cost copper acetate by a novel self-assembly and in-situ slow-release photoreduction method. The cross-linked microporous 3D reduced graphene oxide framework ensures full contact of the photocatalyst with water and promotes electron transfer. The EDA-reduced Cu-rGH hydrogel with an 11.3% Cu NPs mass ratio exhibits the best hydrogen evolution rate (16.92 mmol·g-1·h-1). This rate is almost 17 times faster than pure Cu NPs. EDA played an important role in both forming a hydrogel as the reducing agent and slowly releasing Cu NPs as a ligand in the process of in-situ photoreduction, allowing small sized and uniformly distributed Cu NPs. Therefore, the number of reaction sites in the composite increases and the recombination of photoinduced electron-hole pairs in Cu NPs decreases. Under irradiation, the SPR-excited (surface plasmon resonance) hot electrons from Cu NPs quickly transfer through the rGH channel. 3D rGH was found to be a promising substrate for boosting hydrogen production by Cu NPs.