Unravelling the Correlation of Electronic Structure and Carrier Dynamics in CuInS\u3csub\u3e2\u3c/sub\u3e Nanoparticles

In this work, we report the direct correlation of photoinduced carrier dynamics and electronic structure of CuInS2 (CIS) nanoparticles (NPs) using the combination of multiple spectroscopic techniques including steady-state X-ray absorption spectroscopy (XAS), optical transient absorption (OTA), and X-ray transient (XTA) absorption spectroscopy. XAS results show that CIS NPs contain a large amount of surface Cu atoms with ≪four-coordination, which is more severe in CIS NPs with shorter nucleation times, indicating the presence of more Cu defect states in CIS NPs with smaller size particles. Using the combination of OTA and XTA spectroscopy, we show that electrons are trapped at states with mainly In or S nature while holes are trapped in sites characteristic of Cu. While there is no direct correlation of ultrafast trapping dynamics with NP nucleation time, charge recombination is significantly inhibited in CIS NPs with larger particles. These results suggest the key roles that Cu defect sites play in carrier dynamics and imply the possibility to control the carrier dynamics by controlling the surface structure at the Cu site in CIS NPs

Unravelling the Correlation of Electronic Structure and Carrier Dynamics in CuInS2 Nanoparticles

In this work, we report the direct correlation of photoinduced carrier dynamics and electronic structure of CuInS2 (CIS) nanoparticles (NPs) using the combination of multiple spectroscopic techniques including steady-state X-ray absorption spectroscopy (XAS), optical transient absorption (OTA), and X-ray transient (XTA) absorption spectroscopy. XAS results show that CIS NPs contain a large amount of surface Cu atoms with ≪four-coordination, which is more severe in CIS NPs with shorter nucleation times, indicating the presence of more Cu defect states in CIS NPs with smaller size particles. Using the combination of OTA and XTA spectroscopy, we show that electrons are trapped at states with mainly In or S nature while holes are trapped in sites characteristic of Cu. While there is no direct correlation of ultrafast trapping dynamics with NP nucleation time, charge recombination is significantly inhibited in CIS NPs with larger particles. These results suggest the key roles that Cu defect sites play in carrier dynamics and imply the possibility to control the carrier dynamics by controlling the surface structure at the Cu site in CIS NPs

Direct Observation of Node-to-Node Communication in Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks (ZIFs) with open-shell transition metal nodes represent a promising class of highly ordered light harvesting antennas for photoenergy applications. However, their charge transport properties within the framework, the key criterion to achieve efficient photoenergy conversion, are not yet explored. Herein, we report the first direct evidence of a charge transport pathway through node-to-node communication in both ground state and excited state ZIFs using the combination of paramagnetic susceptibility measurements and time-resolved optical and X-ray absorption spectroscopy. These findings provide unprecedented new insights into the photoactivity and charge transport nature of ZIF frameworks, paving the way for their novel application as light harvesting arrays in diverse photoenergy conversion devices

Elucidating Charge Separation Dynamics in a Hybrid Metal–Organic Framework Photocatalyst for Light-Driven H\u3csub\u3e2\u3c/sub\u3e Evolution

Metal–organic frameworks (MOFs) have emerged as novel scaffolds for artificial photosynthesis due to their unique capability in incorporating homogeneous photosensitizer and catalyst to their robust heterogeneous matrix. In this work, we report the charge separation dynamics between molecular Ru-photosensitizer and Pt-catalyst, both of which were successfully incorporated into a Zr-MOF that demonstrates excellent activity and stability for light-driven H2 generation from water. Using optical transient absorption (OTA) spectroscopy, we show that charge separation in this hybrid MOF occurs via electron transfer (ET) from Ru-photosensitizer to Pt-catalyst. Using Pt L3-edge X-ray transient absorption (XTA) spectroscopy, we observed the intermediate reduced Pt site, directly confirming the formation of charge separated state due to ET from Ru-photosensitizer and unraveling their key roles in photocatalysis

Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy

The kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(I) bis(phenanthroline)/ruthenium(II) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(I)–Ru(II) analogs of the homodinuclear Cu(I)–Cu(I) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These results suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations

2D Covalent Organic Frameworks as Intrinsic Photocatalysts for Visible Light-Driven COMsub\u3e2\u3c/sub\u3e Reduction

Covalent organic framework (COF) represents an emerging class of porous materials that have exhibited great potential in various applications, particularly in catalysis. In this work, we report a newly designed 2D COF with incorporated Re complex, which exhibits intrinsic light absorption and charge separation (CS) properties. We show that this hybrid catalyst can efficiently reduce CO2 to form CO under visible light illumination with high electivity (98%) and better activity than its homogeneous Re counterpart. More importantly, using advanced transient optical and X-ray absorption spectroscopy and in situ diffuse reflectance spectroscopy, we unraveled three key intermediates that are responsible for CS, the induction period, and rate limiting step in catalysis. This work not only demonstrates the potential of COFs as next generation photocatalysts for solar fuel conversion but also provide unprecedented insight into the mechanistic origins for light-driven CO2 reduction

Engineering electrode wettability to enhance mass transfer in hydrogen evolution reaction

In hydrogen evolution reaction, inefficient mass transfer caused by bubble adhesion on electrode, bubble dispersion in electrolyte and slow H2 diffusion, has greatly impeded the reaction process. Existing techniques can only resolve bubble adhesion or bubble dispersion problems. Strategy that simultaneously solve bubble adhesion, bubble dispersion and poor hydrogen diffusion problems is rarely reported. Recently, an article reported a new electrode with special wettability design, which can efficiently promote bubble transfer and dissolved H2 diffusion. This design can simultaneously solve above mentioned three mass transfer issues and improve electrode efficiency. We summarize the remaining challenges of this work and outlook potential approaches to promote mass transfer in gas-evolution reactions

Asynchronous Photoexcited Electronic and Structural Relaxation in Lead-Free Perovskites

Vacancy-ordered lead-free perovskites with more-stable crystalline structures have been intensively explored as the alternatives for resolving the toxic and long-term stability issues of lead halide perovskites (LHPs). The dispersive energy bands produced by the closely packed halide octahedral sublattice in these perovskites are meanwhile anticipated to facility the mobility of charge carriers. However, these perovskites suffer from unexpectedly poor charge carrier transport. To tackle this issue, we have employed the ultrafast, elemental-specific X-ray transient absorption (XTA) spectroscopy to directly probe the photoexcited electronic and structural dynamics of a prototypical vacancy-ordered lead-free perovskite (Cs3Bi2Br9). We have discovered that the photogenerated holes quickly self-trapped at Br centers, simultaneously distorting the local lattice structure, likely forming small polarons in the configuration of Vk center (Br2– dimer). More significantly, we have found a surprisingly long-lived, structural distorted state with a lifetime of ∼59 μs, which is ∼3 orders of magnitude slower than that of the charge carrier recombination. Such long-lived structural distortion may produce a transient “background” under continuous light illumination, influencing the charge carrier transport along the lattice framework

IGF binding protein 3 exerts its ligand-independent action by antagonizing BMP in zebrafish embryos

IGFBP3 is a multi-functional protein that has IGF-dependent and IGF-independent actions in cultured cells. Here we show that the IGF binding domain (IBD), nuclear localization signal (NLS) and transactivation domain (TA) are conserved and functional in zebrafish Igfbp3. The in vivo roles of these domains were investigated by expression of Igfbp3 and its mutants in zebrafish embryos. Igfbp3, and its NLS and TA mutants had equally strong dorsalizing effects. Human IGFBP3 had similar dorsalizing effects in zebrafish embryos. The activities of IBD and IBD+NLS mutants were lower, but they still caused dorsalization. Thus, the IGF-independent action of Igfbp3 is not related to NLS or TA in this in vivo model. We next tested the hypothesis that Igfbp3 exerts its IGF-independent action by affecting Bmp signaling. Co-expression of Igfbp3 with Bmp2b abolished Bmp2b-induced gene expression and inhibited its ventralizing activity. Biochemical assays and in vitro experiments revealed that IGFBP3 bound BMP2 and inhibited BMP2-induced Smad signaling in cultured human cells. In vivo expression of Igfbp3 increase

Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy

The kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(I) bis(phenanthroline)/ruthenium(II) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(I)–Ru(II) analogs of the homodinuclear Cu(I)–Cu(I) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These results suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations