B(C6F5)3-catalyzed hydrogermylation of enones: a facile route to germacycles.

Organogermacycles are important skeletons for medicinal chemistry and materials. Herein, we reported a B(C6F5)3 mediated domino hydrogermylation reaction of enones with dihydrogermanes, affording 21 variants of organogermacycle compounds. These germacyclic compounds were obtained in good to excellent yields (up to 99% yield) under mild reaction conditions.

A label-free photoelectrochemical sensor of S, N co-doped graphene quantum dot (S, N-GQD)-modified electrode for ultrasensitive detection of bisphenol A.

S, N co-doped graphene quantum dot (S, N-GQD) materials have been composited via a one-pot pattern and used as photosensitive materials to construct a label-free photoelectrochemical (PEC) sensor. The PEC experiments show an enhanced photocurrent response toward Bisphenol A (BPA) sensing due to the increased charge transfer rate and the enhanced absorption of visible light. Compared with dark conditions, the photocurrent signal (- 0.2 V vs. SCE) is greatly increased because of the effective oxidation of BPA by photogenerated holes and the rapid electron transfer of S, N-GQDs on the PEC sensing platform. Under optimal conditions linear current response to BPA is in two ranges of 0.12-5 µM and 5-40 µM. The limit of detection is 0.04 µM (S/N = 3). The designed sensor has enduring stability and admirable interference immunity. It  provides an alternative approach for BPA determination in real samples with recoveries of 99.3-103% and  RSD of 2.0-4.1%.

Dynamic Core Polarization in High Harmonic Generation from Solids: The Example of MgO Crystals.

Previously, the strong field processes in solids have always been explained by the single-active-electron (SAE) model with a frozen core excluding the fluctuation of background electrons. In this work, we demonstrate the strong field induced dynamic core polarization effect and propose a model for revealing its role in high harmonic generation (HHG) from solids. We show that the polarized core induces an additional polarization current beyond the SAE model based on the frozen cores. It gives a new mechanism for HHG and leads to new anisotropic structures, which are experimentally observed with MgO. Our experiments indicate that the influences of dynamic core polarization on HHG are obvious for both linearly and elliptically polarized laser fields. Our work establishes the bridge between the HHG and the dynamic changes of the effective many-electron interaction in solids, which paves the way to probe the ultrafast electron dynamics.

Generation of isolated circularly polarized attosecond pulses by three-color laser field mixing.

We propose and theoretically demonstrate a method to generate the circularly polarized supercontinuum with three-color electric fields. The three-color field is synthesized from an orthogonally polarized two-color (OTC) laser field and an infrared gating field. All driving pulse durations are extended to 40 fs. We demonstrate that the three-color field imposes curved trajectories for ionized electrons and extends the time interval between each harmonic emitting. Through adjusting intensity ratios among three components of the driving field, a nearly circular isolated attosecond pulse can be generated.

Photo-electrochemical detection of dopamine in human urine and calf serum based on MIL-101 (Cr)/carbon black.

A new photo-electrochemical sensor based on MIL-101(Cr) MOF/carbon black (CB) is fabricated and characterized. By using differential pulse voltammetry, dopamine (DA) can be effectively detected using a photo-electrochemical MIL-101(Cr)/CB sensor under visible light. The CB acts as the electron bridge to combine with the large specific surface area and photo-catalytic feature of MOF, which contribute to the improvements of sensitivity of DA detection. The concentration of the catalyst, pH value, accumulation potential, and accumulation time were also optimized. Furthermore, the electrochemical performances of MIL-101(Cr)/CB sensor was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scan rate, electrochemically active surface area (ECSA), and amperometric responses. A detection limit of 0.38 nM (LOD = 3 sb/S, sb = 0.028) and a working range of 1 nM to 2.22 µM has been achieved. The MIL-101(Cr)/CB sensor exhibits excellent reproducibility, stability, and selectivity and also has satisfactory recovery rate for the analysis of real samples including calf serum and human urine. Graphical abstract.

Single-shot molecular orbital tomography with orthogonal two-color fields.

Molecular orbital tomography (MOT) based on high-order-harmonic generation opens a way to track the molecular electron dynamics or even follow a chemical reaction. However, the real-time imaging of the evolution of electron orbitals is hampered by the multi-shot measurement of high-order harmonics. Here, we report a single-shot MOT scheme with orthogonal two-color (OTC) fields. This scheme enables the tomographic imaging of molecular orbital with single-shot measurement in experiment, owing to the two-dimensional manipulation of the electron motion in OTC fields. Our work paves the way towards tracking the molecular electron dynamics with combined attosecond temporal and sub-Ångström spatial resolutions.

Attosecond Probing of Nuclear Dynamics with Trajectory-Resolved High-Harmonic Spectroscopy.

We report attosecond-scale probing of the laser-induced dynamics in molecules. We apply the method of high-harmonic spectroscopy, where laser-driven recolliding electrons on various trajectories record the motion of their parent ion. Based on the transient phase-matching mechanism of high-order harmonic generation, short and long trajectories contributing to the same harmonic order are distinguishable in both the spatial and frequency domains, giving rise to a one-to-one map between time and photon energy for each trajectory. The short and long trajectories in H_{2} and D_{2} are used simultaneously to retrieve the nuclear dynamics on the attosecond and ångström scale. Compared to using only short trajectories, this extends the temporal range of the measurement to one optical cycle. The experiment is also applied to methane and ammonia molecules.

A facile fabrication of copper particle-decorated novel graphene flower composites for enhanced detecting of nitrite.

We describe a simple electrochemical preparation method of a novel three dimensional (3D) graphene material, porous flower-like reduced graphene oxide (f-RGO) nanosheets, which was explored as the support for Cu particles on a glassy carbon electrode (Cu/f-RGO/GCE) for detecting nitrite. In morphology studies, scanning electron microscopy (SEM) demonstrates the 3D porous structure of f-RGO enlarges the surface area of the electrode and promotes more Cu particles depositing on the surface of f-RGO with homogeneous dispersion. In cyclic voltammetry (CV), a well-defined voltammetric peak along with the remarkable reduction current indicates excellent electrocatalytic activity of the Cu/f-RGO/GCE for NaNO2 reduction compared with other corresponding electrodes. The effects of pH value and detection potential on the current responses of Cu/f-RGO/GCE towards nitrite were optimized to obtain the maximal sensitivity. In the optimal experimental conditions, Cu/f-RGO/GCE displays the wide detection range from 0.15 µM to 10,500 µM and the low limit of detection of 0.06 µM (S/N = 3) with fast response time 2 s for detecting NaNO2 through an amperometric method. Furthermore, the presence of K(+), Na(+), Cl(-), NH4(+), NO3(-), SO4(2-) and ascorbic acid show a negligible effect on the current response of nitrite determination suggesting Cu/f-RGO/GCE have the high selectivity for detecting nitrite even in the presence of high concentration of interferents. Moreover, the real sample determination experiment indicated practical feasibility of the obtained sensor. The prepared sensor for determination of NaNO2 exhibited wide liner range, low detection limit, good reproducibility, nice stability and remarkable anti-interference ability. In this paper, not only did the Cu/f-RGO/GCE show high performance for determination of nitrite, but also it was simple to prepare, user-friendly and cost-effective.

Reduced graphene oxide modified highly ordered TiO2 nanotube arrays photoelectrode with enhanced photoelectrocatalytic performance under visible-light irradiation.

In this paper, reduced graphene oxide modified highly ordered TiO2 nanotube arrays (RGO-TNTs) have been fabricated and used for photoelectrocatalytic (PEC) degradation of organic pollutants under visible light irradiation. Firstly, the RGO-TNT electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, FT-IR, X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. The responsive photocurrent and electrochemical impedance spectroscopy (EIS) results indicated that our present RGO-TNTs displayed superior photoresponsive and electron transfer performances compared with bare TNTs. Moreover, by comparison with bare TNT electrode, the RGO-TNT arrays showed stable and evidently improved PEC activity for degradation of methyl orange (MO) under visible light illumination. This might be attributed to the introduction of RGO, which extended the absorption edge and promoted electron-hole separation in the PEC process. Furthermore, owing to the synergetic effect of photocatalysis and electrocatalysis in the PEC process, the efficiency of PEC process (3.0 × 10(-3) min(-1)) is ca. 7.9 and 2.5 times faster than that of the electrochemical process (3.8 × 10(-4) min(-1)) and photocatalytic process (1.2 × 10(-3) min(-1)), respectively. Our investigation likely provides new opportunities for developing stable and efficient one-dimensional graphene modified TNT-based catalysts for PEC degradation of organic pollutants under visible light illumination.

Honeycomb-like CuO@C for electroreduction of carbon dioxide to ethylene.

The electrochemical CO2 reduction (ECR) of high-value multicarbon products is an urgent challenge for catalysis and energy resources. Herein, we reported a simple polymer thermal treatment strategy for preparing honeycomb-like CuO@C catalysts for ECR with remarkable C2H4 activity and selectivity. The honeycomb-like structure favored the enrichment of more CO2 molecules to improve the CO2-to-C2H4 conversion. Further experimental results indicate that the CuO loaded on amorphous carbon with a calcination temperature of 600 °C (CuO@C-600) has a Faradaic efficiency (FE) as high as 60.2% towards C2H4 formation, significantly outperforming pure CuO-600 (18.3%), CuO@C-500 (45.1%) and CuO@C-700 (41.4%), respectively. The interaction between the CuO nanoparticles and amorphous carbon improves the electron transfer and accelerates the ECR process. Furthermore, in situ Raman spectra demonstrated that CuO@C-600 can adsorb more adsorbed *CO intermediates, which enriches the CC coupling kinetics and promotes C2H4 production. This finding may offer a paradigm to design high-efficiency electrocatalysts, which can be beneficial to achieve the "double carbon goal."

Visible-light driven p-n heterojunction formed between α-Bi2O3 and Bi2O2CO3 for efficient photocatalytic degradation of tetracycline.

To improve the efficiency of photocatalytic oxidative degradation of antibiotic pollutants, it is essential to develop an efficient and stable photocatalyst. In this study, a polymer-assisted facile synthesis strategy is proposed for the polymorph-controlled α-Bi2O3/Bi2O2CO3 heterojunction retained at elevated calcination temperatures. The p-n heterojunction can effectively separate and migrate electron-hole pairs, which improves visible-light-driven photocatalytic degradation from tetracycline (TC). The BO-400@PAN-140 photocatalyst achieves the highest pollutant removal efficiency of 98.21% for photocatalytic tetracycline degradation in 1 h (λ > 420 nm), and the degradation efficiency was maintained above 95% after 5 cycles. The morphology, crystal structure, and chemical state of the composites were analysed by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Ultraviolet-visible diffuse reflection, transient photocurrent response, and electrochemical impedance spectroscopy were adopted to identify the charge transfer and separation efficiency of photogenerated electron-hole pairs. The EPR results verified h+ and ˙OH radicals as the primary active species in the photocatalytic oxidation reactions. This observation was also consistent with the results of radical trapping experiments. In addition, the key intermediate products of the photocatalytic degradation of TC over BO-400@PAN-140 were identified via high-performance liquid chromatography-mass spectrometry, which is compatible with two possible photocatalytic reaction pathways. This work provides instructive guidelines for designing heterojunction photocatalysts via a polymer-assisted semiconductor crystallographic transition pathway for TC degradation into cleaner production.

Self-Assembly of Bi2Sn2O7/ß-Bi2O3 S-Scheme Heterostructures for Efficient Visible-Light-Driven Photocatalytic Degradation of Tetracycline.

Fabrication of S-scheme heterojunctions with enhanced redox capability offers an effective approach to address environmental remediation. In this study, high-performance Bi2Sn2O7/ß-Bi2O3 S-scheme heterojunction photocatalysts were fabricated via the in situ growth of Bi2Sn2O7 on ß-Bi2O3 microspheres. The optimized Bi2Sn2O7/ß-Bi2O3 (BSO/BO-0.4) degradation efficiency for tetracycline hydrochloride was 95.5%, which was 2.68-fold higher than that of ß-Bi2O3. This improvement originated from higher photoelectron-hole pair separation efficiency, more exposed active sites, excellent redox capacity, and efficient generation of ·O2 - and ·OH. Additionally, Bi2Sn2O7/ß-Bi2O3 exhibited good stability against photocatalytic degradation, and the degradation efficiency remained >89.7% after five cycles. The photocatalytic mechanism of Bi2Sn2O7/ß-Bi2O3 S-scheme heterojunctions was elucidated. In this study, we design and fabricate high-performance heterojunction photocatalysts for environmental remediation using S-scheme photocatalysts.

Self-standing three-dimensional PdAu nanoflowers for plasma-enhanced photo-electrocatalytic methanol oxidation with a CO-free dominant mechanism.

Precise design of high efficacious catalysts and the insight into the mechanism for photo-electrocoupling catalytic methanol oxidation reaction (MOR) are two major issues for the development and practical application of direct methanol fuel cells (DMFCs). Herein, a novel self-standing three-dimensional nanosheet assembly PdAu nanoflower with local surface plasmon resonance effect is fabricated to acquire excellent catalytic performance and explore the photo-electrocatalytic mechanism for MOR. Interestingly, the Pd1Au1 nanoflower electrocatalyst exhibits superior mass activity than pure Pd and Pd/C catalysts thanks to the abundant active sites and efficacious charge transfer. Further on, with the assistance of LSPR effect, the catalytic activity for MOR of Pd1Au1 catalyst (4179.04 mA mg-1Pd) under visible light illumination achieved 2.41-fold than dark conditions (1731.42 mA mg-1Pd). Moreover, the long-term durability of Pd1Au1 catalysts with visible light is also improved compare to dark condition and other mentioned Pd catalyst. More significantly, a photo-electrocoupling CO-free dominant mechanism is proposed to in-depth understand the promotion of catalytic activity and durability for MOR. This contribution provides the rational design of plasma-enhanced high-effective photo-electrocatalyst and reveals a CO-free dominant MOR mechanism for the progress of future liquid direct fuel cells.

Pt nanoclusters embedded Fe-based metal-organic framework as a dual-functional electrocatalyst for hydrogen evolution and alcohols oxidation.

Design and construction of high-efficiency and durable dual-functional electrocatalyst for clean energy electrocatalytic reaction is urgently desirable for mitigating the energy shortage and environmental deterioration issues. Herein, we prepared Pt nanoclusters with exposed (111) face plane embedded Fe-based metal-organic frameworks (Fe-MOF, MIL-100(Fe)) catalyst for electrocatalytic hydrogen evolution reaction (HER) and ethylene glycol oxidation reaction (EGOR). It is noted that the available oxygen sites on the surface of MIL-100(Fe) would form Pt-O interaction with Pt nanoclusters to acquire strong interfacial interaction, which endows Pt/MIL-100(Fe) electrocatalyst effective electron transfer, increasing catalytic active sites, accelerating proton-electron coupling, and improving conductivity. Benefitting from the desirable metal-supports interaction and derive merits for catalysis, the high electrocatalytic activity and durability for HER and EGOR were achieved as expected. Impressively, superior HER performance with higher current density, lower overpotential (46/29 mV in acidic/alkaline electrolyte) and smaller Tafel slope (19.7/37.8 mV dec-1 in acidic/alkaline electrolyte) were acquired compared to commercial Pt/C. Moreover, Pt/MIL-100(Fe) electrode exhibits a rather high mass activity of 11826 mA mg-1Pt and long-term stability for EGOR. The present investigation demonstrates the promise of active metal/MOF combination for the interfacial strategy and rational design of dual-functional electrocatalyst, which has potential applications for future electrocatalysis field.

A Stable Rechargeable Aqueous Zn-Air Battery Enabled by Heterogeneous MoS2 Cathode Catalysts.

Aqueous rechargeable zinc (Zn)−air batteries have recently attracted extensive research interest due to their low cost, environmental benignity, safety, and high energy density. However, the sluggish kinetics of oxygen (O2) evolution reaction (OER) and the oxygen reduction reaction (ORR) of cathode catalysts in the batteries result in the high over-potential that impedes the practical application of Zn−air batteries. Here, we report a stable rechargeable aqueous Zn−air battery by use of a heterogeneous two-dimensional molybdenum sulfide (2D MoS2) cathode catalyst that consists of a heterogeneous interface and defects-embedded active edge sites. Compared to commercial Pt/C-RuO2, the low cost MoS2 cathode catalyst shows decent oxygen evolution and acceptable oxygen reduction catalytic activity. The assembled aqueous Zn−air battery using hybrid MoS2 catalysts demonstrates a specific capacity of 330 mAh g−1 and a durability of 500 cycles (~180 h) at 0.5 mA cm−2. In particular, the hybrid MoS2 catalysts outperform commercial Pt/C in the practically meaningful high-current region (>5 mA cm−2). This work paves the way for research on improving the performance of aqueous Zn−air batteries by constructing their own heterogeneous surfaces or interfaces instead of constructing bifunctional catalysts by compounding other materials.

Facile Synthesis of Fe@C Loaded on g-C3N4 for CO2 Electrochemical Reduction to CO with Low Overpotential.

Electrochemical CO2 reduction has been acknowledged as a hopeful tactic to alleviate environmental and global energy crises. Herein, we designed an Fe@C/g-C3N4 heterogeneous nanocomposite material by a simple one-pot method, which we applied to the electrocatalytic CO2 reduction reaction (ECR). Our optimized 20 mg-Fe@C/g-C3N4-1100 catalyst displays excellent performance for the ECR and a maximum Faradaic efficiency (FE) of 88% with a low overpotential of -0.38 V vs. RHE. The Tafel slope reveals that the first electron transfer, which involves a surface-adsorbed *COOH intermediate, is the rate-determining step for 20 mg-Fe@C/C3N4-1100 during the ECR. More precisely, the coordinating capability of the g-C3N4 framework and Fe@C species as a highly active site promote the intermediate product transmission. These results indicate that the combination of temperature adjustment and precursor optimization is key to facilitating the ECR of an iron-based catalyst.

Protonation-induced DNA conformational-change dominated electrochemical platform for glucose oxidase and urease analysis.

Cytosine and protonated cytosine base pairs (C·CH+)-supported i-motif conformation has been widely employed in some interdisciplinary fields such as biology, medicine and chemistry. In this work, we report a new electrochemical biosensing method for the detection of glucose oxidase (GOx) and urease based on pH-induced DNA conformational-change. The constructed platform mainly includes TdT-mediated catalytic synthesis, GOx- or urease-catalyzed biological reaction and pH-induced DNA conformational-change. In the beginning, a kind of C-rich DNA is produced by TdT catalysis, and multiple C·CH+-supported i-motif structures appear under acidic condition. Then, the oxidation of glucose catalyzed by GOx or the hydrolyzation of urea aroused by urease can result in a generation of acidic or alkaline environment owing to the generated gluconic acid or ammonia. Herein, protonation and deprotonation interaction in TdT-yielded C-rich DNA can lead to different electrochemical impedance spectroscopy (EIS) toward Fe(CN)63-/4-. Based on it, the EIS response changes proportionally toward GOx concentrations from 0.01 to 20 U/L or urease concentrations from 0.01 to 50 U/L, and the detection limit of GOx or urease is 0.0061 U/L or 0.0028 U/L (S/N = 3), respectively. Beyond this, we also construct a series of molecular logic gates (YES, AND, NOT, and NAND) with good performance by altering inputs under long C-rich DNA substrate. These excellent properties indicate that the unique sensing platform is potential to monitor GOx or urease in practical biosystems and clinical medical examinations.

Synthesis of Pt nanoparticles supported on a novel 2D bismuth tungstate/lanthanum titanate heterojunction for photoelectrocatalytic oxidation of methanol.

The combination of different semiconductors to form a heterojunction plays an important role for exploring new visible-light-driven electrocatalysts. Herein, a two-dimensional (2D) Bi2WO6/La2Ti2O7 (LTO) heterojunction has been synthesized and to be as carrier of Pt nanoparticles. Subsequently, electrocatalytic activity and stability of the as-obtained Pt-Bi2WO6/LTO has been evaluated in methanol oxidation reaction (MOR) under the action of visible light and electricity. Results indicate that Pt-Bi2WO6/LTO sample displays excellent catalytic performance and stability with assistance from visible light. Under identical conditions, the current intensity of MOR on the Pt-Bi2WO6/LTO modified electrode is found to reach 1409 mA mg-1Pt, which is 3.92 times higher than the measured Pt-Bi2WO6 modified electrode (359.8 mA mg-1Pt). In addition, the current density of MOR on Pt-Bi2WO6/LTO electrode decreases by 2.85% after scanning for 300 cycles. Furthermore, Pt-Bi2WO6/LTO is 6.99 times more resistant to poisoning than the Pt-Bi2WO6 electrode determines by chronopotentiometry under visible light illumination. The presented results indicate that a Pt-Bi2WO6/LTO nanocomposite is a viable alternative photo-electric catalyst, providing a potential new basis for the future development of catalysts in fuel cell reactions.

Monitoring Transport Behavior of Charge Carriers in a Single CdS@CuS Nanowire via In Situ Single-Particle Photoluminescence Spectroscopy.

Examination of the spectral and kinetic characteristics of charge carrier recombination on nanostructured semiconductors by photoluminescence (PL) plays a significant role in understanding the photocatalytic process. Here, with an in situ single-particle PL technique, we studied the transport behavior of charge carriers in individual one-dimensional (1D) core-shell structures of CdS@CuS nanowires. Through the PL intensity changes in the single-particle PL spectroscopy, effective interfacial electron transport along the interface of CdS and CuS was observed, which contributes to the significant improvement (i.e., 13.5-fold increase) of photocatalytic H2 production compared to that for pure CdS nanowires. The present study provides visual experimental evidence for understanding restraining of charge carrier recombination in the semiconductor.

Highly efficient ethylene glycol electrocatalytic oxidation based on bimetallic PtNi on 2D molybdenum disulfide/reduced graphene oxide nanosheets.

In this paper, a two-dimensional (2D) hybrid material of molybdenum disulfide (MoS2)/reduced graphene oxide (RGO) is facilely synthesized and used as an ideal support for the deposition of Pt nanoparticles. The as-prepared Pt/MoS2/RGO composites are further worked as electrocatalysts towards ethylene glycol oxidation reaction (EGOR). In addition, when alloying with Ni, the composite shows obvious enhancement in electrocatalytic performance for EGOR. Specifically, the optimized molar ratio of Pt to Ni is 3:1, namely Pt3Ni/MoS2/RGO performs the strongest current density of 2062 mA mg-1Pt, which is 11.1, 5.80 and 2.40 times higher than those of Pt, Pt3Ni and Pt/MoS2/RGO electrodes, respectively. The systematically electrochemical measurements indicate that the largely promoted electrocatalytic performances of Pt3Ni/MoS2/RGO are mainly attributed to the synergistic effect of Ni and Pt, and 2D sheets of MoS2/RGO. This excellent performance indicates that the reported electrocatalytic material could be an efficient catalyst for the application in direct ethylene glycol fuel cell and beyond.