Electrochemical C-N coupling of CO2 and nitrogenous small molecules for the electrosynthesis of organonitrogen compounds.

Electrochemical C-N coupling reactions based on abundant small molecules (such as CO2 and N2) have attracted increasing attention as a new "green synthetic strategy" for the synthesis of organonitrogen compounds, which have been widely used in organic synthesis, materials chemistry, and biochemistry. The traditional technology employed for the synthesis of organonitrogen compounds containing C-N bonds often requires the addition of metal reagents or oxidants under harsh conditions with high energy consumption and environmental concerns. By contrast, electrosynthesis avoids the use of other reducing agents or oxidants by utilizing "electrons", which are the cleanest "reagent" and can reduce the generation of by-products, consistent with the atomic economy and green chemistry. In this study, we present a comprehensive review on the electrosynthesis of high value-added organonitrogens from the abundant CO2 and nitrogenous small molecules (N2, NO, NO2-, NO3-, NH3, etc.) via the C-N coupling reaction. The associated fundamental concepts, theoretical models, emerging electrocatalysts, and value-added target products, together with the current challenges and future opportunities are discussed. This critical review will greatly increase the understanding of electrochemical C-N coupling reactions, and thus attract research interest in the fixation of carbon and nitrogen.

Wafer-Scale Single Crystal Hexagonal Boron Nitride Layers Grown by Submicron-Spacing Vapor Deposition.

The direct growth of wafer-scale single crystal two-dimensional (2D) hexagonal boron nitride (h-BN) layer with a controllable thickness is highly desirable for 2D-material-based device applications. Here, for the first time, a facile submicron-spacing vapor deposition (SSVD) method is reported to achieve 2-inch single crystal h-BN layers with controllable thickness from monolayer to tens of nanometers on the dielectric sapphire substrates using a boron film as the solid source. In the SSVD growth, the boron film is fully covered by the same-sized sapphire substrate with a submicron spacing, leading to an efficient vapor diffusion transport. The epitaxial h-BN layer exhibits extremely high crystalline quality, as demonstrated by both a sharp Raman E2g vibration mode (12 cm-1 ) and a narrow X-ray rocking curve (0.10°). Furthermore, a deep ultraviolet photodetector and a ZrS2 /h-BN heterostructure fabricated from the h-BN layer demonstrate its fascinating properties and potential applications. This facile method to synthesize wafer-scale single crystal h-BN layers with controllable thickness paves the way to future 2D semiconductor-based electronics and optoelectronics.

Novel Two-Dimensional AgInS2/SnS2/RGO Dual Heterojunctions: High Spatial Charge and Toxicity Evaluation.

A single semiconductor employed into photo(electro)catalysis is not sufficient for charge carrier separation. Designing a multiple heterojunction system is a practical method for photo(electro)catalysis. Herein, novel two-dimensional AgInS2/SnS2/RGO (AISR) photocatalysts with multiple junctions were prepared by a simple hydrothermal method. The synthesized AISR heterojunctions showed superior photoelectrochemical performance and photocatalytic degradation of norfloxacin, with a high degradation rate reaching 95%. More importantly, the toxicity of photocatalytic products decreased within the reaction process. High spatial separation efficiency of photogenerated electron-hole pairs was evidenced by optical and photoelectrochemical characterizations. Furthermore, a laser flash photolysis technique was carried on investigating the lifetime of the charge carrier of the fabricated dual heterostructures. In addition, sulfur and oxygen vacancies existed in AISR heterojunctions could largely constrain the recombination of electron-hole pairs. Density functional theory calculations were carried out to analyze the mechanism of photoinduced interfacial redox reactions, showing that reduced graphene oxide and AgInS2 act as electron and hole trappers in the photocatalytic reaction, respectively. Due to the interfacial electric field formed from AISR dual heterojunctions, the effective spatial charge separation and transfer contributed to the boosting photo(electro)catalytic performance.

A 5.86 Million Quality Factor Cylindrical Resonator with Improved Structural Design Based on Thermoelastic Dissipation Analysis.

The cylindrical resonator is the core component of cylindrical resonator gyroscopes (CRGs). The quality factor (Q factor) of the resonator is one crucial parameter that determines the performance of the gyroscope. In this paper, the finite element method is used to theoretically investigate the influence of the thermoelastic dissipation (TED) of the cylindrical resonator. The improved structure of a fused silica cylindrical resonator is then demonstrated. Compared with the traditional structure, the thermoelastic Q (QTED) of the resonator is increased by 122%. In addition, the Q factor of the improved cylindrical resonator is measured, and results illustrate that, after annealing and chemical etching, the Q factor of the resonator is significantly higher than that of the cylindrical resonators reported previously. The Q factor of the cylindrical resonator in this paper reaches 5.86 million, which is the highest value for a cylindrical resonator to date.

Single-Photon Emission from Point Defects in Hexagonal Boron Nitride Induced by Plasma Treatment.

Solid-state quantum emitters are gaining significant attention for many quantum information applications. Hexagonal boron nitride (h-BN) is an emerging host material for generating bright, stable, and tunable single-photon emission with narrow line widths at room temperature. In this work, we present a facile and efficient approach to generate high-density single-photon emitters (SPEs) in mechanically exfoliated h-BN through H- or Ar-plasma treatment followed by high-temperature annealing in air. It is notable that the postannealing is essential to suppress the fluorescence background in photoluminescence spectra and enhance emitter stability. These quantum emitters exhibit excellent optical properties, including high purity, brightness, stability, polarization degree, monochromaticity, and saturation intensity. The effects of process parameters on the quality of quantum emitters were systematic investigated. We find that there exists an optimal plasma power and h-BN thickness to achieve a high SPE density. This work offers a practical avenue for generating SPEs in h-BN and holds promise for future research and applications in quantum photonics.

Experimental and computational studies of photoelectrochemical degradation of atrazine by modified nanoporous titanium dioxide.

The presence of herbicides like Atrazine (ATZ) in groundwater from non-target runoff of the agriculture industry becomes a big concern due to its potential negative impacts on the environment and human health. The use of advanced oxidative processes (AOP) to remove harmful contaminants has been shown to be effective for wastewater treatment. Herein, we report on an advanced photoelectrochemical (PEC) approach based on electrochemically modified nanoporous TiO2 electrode for efficient degradation of ATZ. The electrochemical treated TiO2 electrodes were shown to have a six-fold increase in the photo-current density over the untreated ones. This increase in PEC activity was attributed to the increase in Ti3+ sites after the electrochemical modification, which was corroborated by low-temperature electron paramagnetic resonance (EPR) studies. The removal of ATZ by the PEC process resulted in a rate constant of 1.91 × 10-3 s-1, compared to 3.12 × 10-4 s-1 obtained by a strictly photocatalytic process. Liquid-Chromatography Mass-Spectrometric measurements showed the modified TiO2 electrodes highly effective at removing ATZ, with 96.1% removed after 10 h. Monitoring of the common degradation products desethyl atrazine (DEA), desisopropyl atrazine (DIA) and desethyl desisopropyl atrazine (DDA) revealed very low concentrations throughout the degradation process, indicating that further degradation was achieved. Quantum mechanical-based test for overall free radical scavenging activity (QM-ORSA) computational studies were performed and a mechanism for the N-dealkylation processes of ATZ has been proposed.

Progress in Mo/W-based electrocatalysts for nitrogen reduction to ammonia under ambient conditions.

Ammonia (NH3), possessing high hydrogen content and energy density, has been widely employed for fertilizers and value-added chemicals in green energy carriers and fuels. However, the current NH3 synthesis largely depends on the traditional Haber-Bosch process, which needs tremendous energy consumption and generates greenhouse gas, resulting in severe energy and environmental issues. The electrochemical strategy of converting N2 to NH3 under mild conditions is a potentially promising route to realize an environmentally friendly concept. Among various catalysts, molybdenum/tungsten-based electrocatalysts have been widely used in electrochemical catalytic and energy conversion. This review describes the latest progress of molybdenum/tungsten-based electrocatalysts for the electrochemical nitrogen reduction reaction. The fundamental roles of morphology, doping, defects, heterojunction, and coupling regulation in improving electrocatalytic performance are mainly discussed. Besides, some tailoring strategies for enhancing the conversion efficiency of N2 to NH3 over Mo/W-based electrocatalysts are also summarized. Finally, the existing challenges and limitations of N2 fixation are proposed, as well as possible future perspectives, which will provide a platform for further development of advanced Mo/W-based N2 reduction systems.

Experimental Study on Variation of Surface Roughness and Q Factors of Fused Silica Cylindrical Resonators with Different Grinding Speeds.

For the axisymmetric shell resonator gyroscopes, the quality factor (Q factor) of the resonator is one of the core parameters limiting their performances. Surface loss is one of the dominating losses, which is related to the subsurface damage (SSD) that is influenced by the grinding parameters. This paper experimentally studies the surface roughness and Q factor variation of six resonators ground by three different grinding speeds. The results suggest that the removal of the SSD cannot improve the Q factor continuously, and the variation of surface roughness is not the dominant reason to affect the Q factor. The measurement results indicate that an appropriate increase in the grinding speed can significantly improve the surface quality and Q factor. This study also demonstrates that a 20 million Q factor for fused silica cylindrical resonators is achievable using appropriate manufacturing processes combined with post-processing etching, which offers possibilities for developing high-precision and low-cost cylindrical resonator gyroscopes.

Highly boosted gas diffusion for enhanced electrocatalytic reduction of N2 to NH3 on 3D hollow Co-MoS2 nanostructures.

Transition metal chalcogenide MoS2 catalysts are highly selective for the electrochemical reduction of dinitrogen (N2) to ammonia (NH3) in aqueous electrolytes. However, due to the low solubility of N2 in water, limited N2 diffusion and mass transport have heavily restricted the yield and the faradaic efficiency (FE). Here, we have demonstrated a highly efficacious assembled gas diffusion cathode with hollow Co-MoS2/N@C nanostructures to significantly improve the electrochemical reduction of N2 to NH3. Our results revealed that the synthesized Co-MoS2 heterojunctions with abundant graphitic N groups exhibited a superb NH3 yield of 129.93 µg h-1 mgcat-1 and a high faradaic efficiency of 11.21% at -0.4 V vs. the reversible hydrogen electrode (RHE), as well as excellent selectivity and stability. The strategy described in this study offers new inspiration to design high-performance electrocatalyst assemblies for the sustainable environmental and energy applications.

Boosting interfacial charge transfer and electricity generation for levofloxacin elimination in a self-driven bio-driven photoelectrocatalytic system.

Recently, molybdenum disulfide (MoS2) has stimulated significant research interest as a promising electrode candidate in solar cells and energy conservation fields. Unfortunately, the short lower electron/hole migration lifetimes and easy agglomeration hamper its wide practical applications to some extent. Herein, interface engineering coupled with a bio-assisted photoelectrochemical (PEC) strategy is presented to construct a 0D MoS2 quantum dot (QD)/1D TiO2 nanotube electrode for pollutant elimination. Aimed at accelerating charge transfer over the 0D/1D composite interface, three types of coupling PEC models were developed to optimize the catalytic performance. The single chamber microbial fuel cell (SCMFC)-PEC integrated system was found to be the best alternative for levofloxacin (LEV) elimination (0.029 min-1), and the sequential SCMFC-PEC further realized the whole system self-running independently. In addition, the interfacial electron migration and LEV degradation pathways were thoroughly investigated by LC/TOF/MS coupled with density functional theory (DFT) calculations to clearly elucidate the electron transfer paths, LEV-attacked sites and mineralization pathways in a joint sequential SCMFC-PEC system. As such, the constructed self-recycling system provides a new platform for bio-photo-electrochemical utilization, which could exhibit promising potential in environmental purification.

Sulfur vacancy-rich N-doped MoS2 nanoflowers for highly boosting electrocatalytic N2 fixation to NH3 under ambient conditions.

In this communication, optimized sulfur vacancy-rich nitrogen-doped MoS2 nanoflowers were developed, which served as excellent N2 reduction reaction (NRR) electrocatalysts for the conversion of N2 to NH3 under ambient conditions. Electrochemical results demonstrated that the as-prepared N-doped MoS2 electrode afforded a superior NH3 yield and high faradaic efficiency, which exceeded those of the recently reported MoS2 catalysts. The possible NRR catalytic mechanism and electron transfer pathway were further elucidated via density functional theory calculations.

The bioelectrochemical synthesis of high-quality carbon dots with strengthened electricity output and excellent catalytic performance.

The emergence of microbial fuel cell (MFC) technology that can effectively recycle renewable energy from organic pollutants has been regarded as a promising and environmentally friendly route that could be widely used in numerous fields. Here, a novel sustainable self-energy conversion system was successfully constructed to renewably synthesize carbon dots (CDs) via in situ coupling with a MFC system. Interestingly, the generation of CDs was found to largely enhance the electricity production performance of the MFC. Low-temperature electron paramagnetic resonance (EPR) spectroscopic measurements and electrochemical characterization analysis results confirmed that the as-prepared CDs exhibited wide-conversion fluorescence properties and exposed carbon-rich active oxygen sites, and demonstrated a suitable band gap as well as excellent electrocatalytic performance. As a result, the prepared CDs possess high photo-bioelectrocatalytic activity for efficient H2 production, reaching 9.58 µmol h-1. Remarkably, CD-derived photocatalytic ink presented excellent contaminant elimination activity at the solid-solid interface. Thus, this work will provide a new platform for catalyst construction via a bio-assisted method towards the next generation of nano-photocatalytic inks for indoor contaminant removal.

Functionalized nitrogen-doped carbon dot-modified yolk-shell ZnFe2O4 nanospheres with highly efficient light harvesting and superior catalytic activity.

Volatile organic compounds (VOCs), as hazardous gaseous pollutants, have attracted much attention due to their potential threat to both human health and the environment. Accordingly, photocatalysis technology is seen as a promising technology to control low concentration VOCs due to its mild operation conditions, low energy consumption, and mineralization ability. However, there are some issues with photocatalysts, such as low light utility and fast photogenerated carrier recombination, which need to be addressed for practical applications. In this work, novel nitrogen-doped carbon dot (NCD)-modified ZnFe2O4 yolk-shell nanostructure photocatalysts were fabricated for the first time. The yolk-shell structure of ZnFe2O4 efficiently shortened the photogenerated carrier migration path and enhanced light scattering in its void, while the decorated NCDs accelerated the charge transfer from the bulk to the surface. A series of characterizations was conducted to investigate the crystal structure, elemental status, optical properties, and photocatalytic performance of the obtained composite photocatalysts. The NCD-modified ZnFe2O4 yolk-shell photocatalysts exhibited both a wide spectral absorbance and low carrier recombination, resulting in high photocatalytic activity and degradation ability towards gaseous o-dichlorobenzene. Density functional theory (DFT) calculations further revealed that the NCDs effectively promoted charge transfer and weakened the recombination of photo-generated electron-hole pairs. Additionally, in situ Fourier transform infrared (FTIR) spectroscopy was performed to investigate the degradation path in the photocatalytic process, and an electron paramagnetic resonance (EPR) radical trapping experiment was conducted to unveil the reactive oxygen species involved in the system. Combining the results obtained, the synergistic effect in the enhancement of photocatalysis between NCDs and yolk-shell ZnFe2O4 was schematically proposed.

Hollow porous zinc cobaltate nanocubes photocatalyst derived from bimetallic zeolitic imidazolate frameworks towards enhanced gaseous toluene degradation.

Aiming at promoting the photocatalytic performance of spinel oxides, an efficient method of constructing hollow porous zinc cobaltate (ZnxCo3-xO4) nanocubes was established in this work. Bimetallic zeolitic imidazolate frameworks (ZIFs) were prepared through a facile self-assembly strategy, then hollow ZnxCo3-xO4 nanocubes were obtained by calcining the bimetallic ZIFs precursor. The structural features and optical properties of the ZnxCo3-xO4 nanocubes were comprehensively investigated by a series of characterization techniques. With higher specific surface area (about 100 m2 g-1), enhanced light absorbance in the whole range of 350-800 nm and lowered recombination of photogenerated electron-hole pairs, these hollow nanocubes demonstrated attractive photocatalytic activity in degrading gaseous toluene, superior to traditional stoichiometric ZnCo2O4 nanoparticles. The photocatalytic process and related mechanism of toluene degradation were further investigated with in situ Fourier transform infrared (FTIR) spectroscopy and electron paramagnetic resonance (EPR) techniques. Photo-induced O2- and holes were assigned as main reactive species in the photocatalytic system with hollow ZnxCo3-xO4 nanocubes.

Relationships Between Crystal, Internal Microstructures, and Physicochemical Properties of Copper-Zinc-Iron Multinary Spinel Hierarchical Nano-microspheres.

Rational design and fabrication of high quality complex multicomponent spinel ferrite with specific microstructures and solar light harvestings toward CO2 reduction and antibiotic degradation to future energetic and catalytic applications are highly desirable. In this study, novel copper-zinc-iron multinary spinel hierarchical nano-microspheres (MSHMs) with different internal structures (solid nano-microspheres, yolk-shell hollow nano-microspheres, and double-shelled hollow nano-microspheres) have been successfully developed by a facile self-templated solvothermal strategy. The morphology and structure, optical, as well as photoinduced redox reactions including interfacial charge carrier behaviors and the intrinsic relationship of structure-property between intrinsic nano-microstructures and physicochemical performance of copper-zinc-iron ferrite MSHMs composites were systematically investigated with the assistance of various on- and/or off- line physical-chemical means and deeply elucidated in terms of the research outcomes. It is demonstrated that the modification of the interior microstructures can be applied to tune the catalytic properties of multinary spinel by tailoring the temperature programming to fine control the two opposite forces of contraction (Fc) and adhesion (Fa). Among various internal microstructures, the obtained double-shelled copper-zinc-iron MSHMs exhibited the superior catalytic performance toward 8.8 and 38 µmol for H2 and CO productions as well as 80.4% removal of sulfamethoxazole antibiotics. As evidenced from primary characterizations, for example, combined steady-state PL, ns-TAS, and Mössbauer and sequential investigations, the remarkable improvements in the catalytic activity can be primarily attributed to several crucial factors, for example, the more effective e--h+ spatial separations and interfacial transfers, multiple internal light scattering, higher photonic energy harvesting and effective reactive oxygen species generation with long radical lifetimes. The current research provides new insights into the molecular design of novel copper-zinc-iron multinary spinels and the intrinsic relationship of structure-property between interior structures (e.g., different crystal texture, morphologies structures) and the physicochemical performance of the aforementioned multinary spinels.

Rational design and synthesis of highly oriented copper-zinc ferrite QDs/titania NAE nano-heterojunction composites with novel photoelectrochemical and photoelectrocatalytic behaviors.

This work reported that novel highly oriented and vertically aligned stoichiometric copper- and zinc-based ferrites, i.e., Cu0.5Zn0.5Fe2O4 quantum dots (QDs) anchored with TiO2 nanotube array electrode (NAE) composites, with n-n nano-heterojunctions and highly effective simulated solar light harvesting could be successfully achieved via electrochemical anodization followed by a vacuum-assisted impregnation strategy. It has been observed that Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAE composites exhibit distinctly enhanced visible light photoelectrocatalytic (PEC) performance toward the degradation of typical pollutants including sulfamethoxazole (SMX) and methylene blue (MB) as compared to that of pristine TiO2 NAEs, which can be attributed to the synergistic effect of heterostructures with strong interfacial interaction and abundant 1D nanotube array structures to facilitate efficient spatial charge separation and interfacial transfers. The cocatalyst-anchoring of ternary oxides with derived spinel crystal structures onto nanotube arrays forming novel nanocomposites have obviously achieved remarkably enhanced photoelectrochemical (PE) conversion efficiencies, up to a dedicated value of 3.75%, under visible light irradiation as compared to that of 0.88% for aligned standalone TiO2 NAEs. Transient absorption spectroscopy quantitatively indicated long-lived photo-holes with lifetimes exceeding 72.23 µs generated among Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAE nanocomposites. Electron spinning resonance (ESR) demonstrated that more ˙O2- species derived from molecular uptake played the predominant role in the PEC oxidations of SMX and MB species. Moreover, the binding energy of the onset edge (Evf) and Fermi level (Ef) of Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAEs indicated that Cu0.5Zn0.5Fe2O4 QDs modification could considerably enhance the visible light harvesting and adsorption properties of TiO2 NTs. Furthermore, Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAEs achieved up to 50% PEC degradation efficiency and 52.4% COD removal with regard to practical textile wastewater when irradiated by simulated sunlight. This work has provided new insights into the molecular tailing and coupling of multiple spinels with TiO2 NTs possessing remarkable visible light harvesting and sensitization characteristics, which would offer a prospective strategy toward designing highly efficient and easily recyclable photocatalytic materials for environmental remediation and solar energy utilizations and conversions both simultaneously and standalone.

FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin.

A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1-1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1-100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT).