The photocatalytic activity of phosphonated Re complexes, Re(2,2′‐bipyridine‐4,4′‐bisphosphonic acid) (CO)3(L) (ReP; L=3‐picoline or bromide) immobilised on TiO2 nanoparticles is reported. The ...heterogenised Re catalyst on the semiconductor, ReP–TiO2 hybrid, displays an improvement in CO2 reduction photocatalysis. A high turnover number (TON) of 48 molCO molRe−1 is observed in DMF with the electron donor triethanolamine at λ>420 nm. ReP–TiO2 compares favourably to previously reported homogeneous systems and is the highest TON reported to date for a CO2‐reducing Re photocatalyst under visible light irradiation. Photocatalytic CO2 reduction is even observed with ReP–TiO2 at wavelengths of λ>495 nm. Infrared and X‐ray photoelectron spectroscopies confirm that an intact ReP catalyst is present on the TiO2 surface before and during catalysis. Transient absorption spectroscopy suggests that the high activity upon heterogenisation is due to an increase in the lifetime of the immobilised anionic Re intermediate (t50 %>1 s for ReP–TiO2 compared with t50 %=60 ms for ReP in solution) and immobilisation might also reduce the formation of inactive Re dimers. This study demonstrates that the activity of a homogeneous photocatalyst can be improved through immobilisation on a metal oxide surface by favourably modifying its photochemical kinetics.
Better on TiO2: A molecular Re complex (see scheme; TON=turnover number) is a more efficient CO2 reduction photocatalyst when immobilised on TiO2 than in solution. Transient absorption measurements suggest that this is due to an increased lifetime of the reduced catalytic intermediate when on the surface.
The quick‐EXAFS (QEXAFS) method adds time resolution to X‐ray absorption spectroscopy (XAS) and allows dynamic structural changes to be followed. A completely new QEXAFS setup consisting of ...monochromator, detectors and data acquisition system is presented, as installed at the SuperXAS bending‐magnet beamline at the Swiss Light Source (Paul Scherrer Institute, Switzerland). The monochromator uses Si(111) and Si(311) channel‐cut crystals mounted on one crystal stage, and remote exchange allows an energy range from 4.0 keV to 32 keV to be covered. The spectral scan range can be electronically adjusted up to several keV to cover multiple absorption edges in one scan. The determination of the Bragg angle close to the position of the crystals allows high‐accuracy measurements. Absorption spectra can be acquired with fast gridded ionization chambers at oscillation frequencies of up to 50 Hz resulting in a time resolution of 10 ms, using both scan directions of each oscillation period. The carefully developed low‐noise detector system yields high‐quality absorption data. The unique setup allows both state‐of‐the‐art QEXAFS and stable step‐scan operation without the need to exchange whole monochromators. The long‐term stability of the Bragg angle was investigated and absorption spectra of reference materials as well as of a fast chemical reaction demonstrate the overall capabilities of the new setup.
Exfoliation of graphite was achieved using a zinc phthalocyanine oligomer that is also an electron donor. The resulting functionalized graphene material was investigated by Raman and electron ...spectroscopy and was trialed in a photoelectrochemical cell.
The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully ...active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy.
Porous organic polymers were used as photosystems to deliver a constant production rate for the CO2 to formate reduction for several days. Their photoactivation pathway is presented, including an ultrafast electronic energy transfer from the photosensitizer to the catalyst as evidenced by time‐resolved spectroscopy and quantum mechanical calculations.
High‐energy radiation detectors such as X‐ray detectors with low light photoresponse characteristics are used for several applications including, space, medical, and military devices. Here, an ...indirect bandgap inorganic perovskite‐based X‐ray detector is reported. The indirect bandgap nature of perovskite materials is revealed through optical characterizations, time‐resolved photoluminescence (TRPL), and theoretical simulations, demonstrating that the differences in temperature‐dependent carrier lifetime related to CsPbX3 (X = Br, I) perovskite composition are due to the changes in the bandgap structure. TRPL, theoretical analyses, and X‐ray radiation measurements reveal that the high response of the UV/visible‐blind yellow‐phase CsPbI3 under high‐energy X‐ray exposure is attributed to the nature of the indirect bandgap structure of CsPbX3. The yellow‐phase CsPbI3‐based X‐ray detector achieves a relatively high sensitivity of 83.6 μCGyair−1 cm−2 (under 1.7 mGyair s−1 at an electron field of 0.17 V μm−1 used for medical diagnostics) although the active layer is based solely on an ultrathin (≈6.6 μm) CsPbI3 nanocrystal film, exceeding the values obtained for commercial X‐ray detectors, and further confirming good material quality. This CsPbX3 X‐ray detector is sufficient for cost‐effective device miniaturization based on a simple design.
High‐energy radiation detectors, such as X‐ray detectors with low light photoresponse characteristics are crucial for several applications in medical diagnostics, astronomy, military, and industrial monitoring. The carrier dynamics of an indirect‐bandgap perovskite is revealed, which can be used for UV/visible‐blind X‐ray detectors with high and stable photoelectric response under high‐energy X‐ray exposure.
Carbon Nanodots
Carbon nanodots solvothermally synthesized from citric acid and formamide result in electron‐rich properties upon in situ addition of NaOH, whereas otherwise electron‐poor ...nanomaterial is obtained with reduced or oxidized citrazinic acid dimers, respectively. These properties are found to impact the anodic photocurrent performance due to the fundamentally different charge‐transfer mechanisms, caused by the different molecular photoactive compounds. More details can be found in article number 2207238 by Bikash Jana, Alejandro Cadranel, Dirk M. Guldi, and co‐workers.
Water interfaces provide the platform for many important biological, chemical, and physical processes. The water–air interface is the most common and simple aqueous interface and serves as a model ...system for water at a hydrophobic surface. Unveiling the microscopic (<1 nm) structure and dynamics of interfacial water at the water–vapor interface is essential for understanding the processes occurring on the water surface. At the water interface the network of very strong intermolecular interactions, hydrogen‐bonds, is interrupted and the density of water is reduced. A central question regarding water at interfaces is the extent to which the structure and dynamics of water molecules are influenced by the interruption of the hydrogen‐bonded network and thus differ from those of bulk water. Herein, we discuss recent advances in the study of interfacial water at the water–air interface using laser‐based surface‐specific vibrational spectroscopy.
Lightly scratching the surface: A central question regarding the water–air interface is to what extent the structure and dynamics of water molecules is influenced by the breaking of hydrogen bonds, and thus how they differ from those in the bulk water? One method to study the water–air interface is the laser‐based surface‐specific vibrational spectroscopy. The advances made by these investigations are presented and discussed.
Owing to their increased absorption of light in the visible region, 70fullerene derivatives provide a high photocurrent when incorporated as the electron acceptor in thin‐film polymer photovoltaic ...cells. An incident‐photon‐to‐current efficiency of 66 % is obtained when 70PCBM (see picture) is used in combination with a poly(p‐phenylene vinylene). These high currents originate from an ultrafast charge transfer that occurs upon photoexcitation of either the fullerene or the polymer.
Go with the flow: A novel spectroelectrochemical flow cell with well‐defined mass transport allows time‐resolved electrochemical and in situ FTIR spectroscopy measurements under continuous ...electrolyte flow (e.g. during electrolyte exchange). Its potential for mechanistic and kinetic studies was demonstrated in studies on the electrooxidation of formic acid.
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