BiVO4-Based Heterojunction Photocathode for High-Performance Photoelectrochemical Hydrogen Peroxide Production.

Photoelectrochemical (PEC) cells provide a promising solution for the synthesis of hydrogen peroxide (H2O2). Herein, an integrated photocathode of p-type BiVO4 (p-BVO) array with tetragonal zircon structure coupled with different metal oxide (MOx, M = Sn, Ti, Ni, and Zn) heterostructure and NiNC cocatalyst (p-BVO/MOx/NiNC) was synthesized for the PEC oxygen reduction reaction (ORR) in production of H2O2. The p-BVO/SnO2/NiNC array achieves the production rate 65.46 µmol L-1 h-1 of H2O2 with a Faraday efficiency (FE) of 76.12%. Combined with the H2O2 generation of water oxidation from the n-type Mo-doped BiVO4 (n-Mo:BVO) photoanode, the unbiased photoelectrochemical cell composed of a p-BVO/SnO2/NiNC photocathode and n-Mo:BVO photoanode achieves a total FE of 97.67% for H2O2 generation. The large area BiVO4-based tandem cell of 3 × 3 cm2 can reach a total H2O2 production yield of 338.84 µmol L-1. This work paves the way for the rational design and fabrication of artificial photosynthetic cells for the production of liquid solar fuel.

Molecular Engineering of Hydrogen-Bonded Organic Framework for Enhanced Nitrate Electroreduction to Ammonia.

Electrocatalytic nitrate reduction is an efficient way to produce ammonia sustainably. Herein, we rationally designed a copper metalloporphyrin-based hydrogen-bonded organic framework (HOF-Cu) through molecular engineering strategies for electrochemical nitrate reduction. As a result, the state-of-the-art HOF-Cu catalyst exhibits high NH3 Faradaic efficiency of 93.8%, and the NH3 production rate achieves a superior activity of 0.65 mmol h-1 cm-2. The in situ electrochemical spectroscopic combined with density functional theory calculations reveals that the dispersed Cu promotes the adsorption of NO3- and the mechanism is followed by deoxidation of NO3- to *NO and accompanied by deep hydrogenation. The generated *H participates in the deep hydrogenation of intermediate with fast kinetics as revealed by operando electrochemical impedance spectroscopy, and the competing hydrogen evolution reaction is suppressed. This research provides a promising approach to the conversion of nitrate to ammonia, maintaining the nitrogen balance in the atmosphere.

Fundamentals and Recent Progress in Magnetic Field Assisted CO2 Capture and Conversion.

CO2 capture and conversion technology are highly promising technologies that definitely play a part in the journey towards carbon neutrality. Releasing CO2 by mild stimulation and the development of high efficiency catalytic processes are urgently needed. The magnetic field, as a thermodynamic parameter independent of temperature and pressure, is vital in the enhancement of CO2 capture and conversion process. In this review, the recent progress of magnetic field-enhanced CO2 capture and conversion is comprehensively summarized. The theoretical fundamentals of magnetic field on CO2 adsorption, release and catalytic reduction process are discussed, including the magnetothermal, magnetohydrodynamic, spin selection, Lorentz forces, magnetoresistance and spin relaxation effects. Additionally, a thorough review of the current progress of the enhancement strategies of magnetic field coupled with a variety of fields (including thermal, electricity, and light) is summarized in the aspect of CO2 related process. Finally, the challenges and prospects associated with the utilization of magnetic field-assisted techniques in the construction of CO2 capture and conversion systems are proposed. This review offers a reference value for the future design of catalysts, mechanistic investigations, and practical implementation for magnetic field enhanced CO2 capture and conversion.

Preparation of SnS2/MoS2with p-n heterojunction for NO2sensing.

Conventional metal sulfide (SnS2) gas-sensitive sensing materials still have insufficient surface area and slow response/recovery times. To increase its gas-sensing performance, MoS2nanoflower was produced hydrothermally and mechanically combined with SnS2nanoplate. Extensive characterization results show that MoS2was effectively integrated into SnS2. Four different concentrations of SnS2-MoS2composites were evaluated for their NO2gas sensitization capabilities. Among them, SnS2-15% MoS2at 170 °C demonstrated the greatest response values to NO2, 7.3 for 1 ppm NO2, which is about three times greater than the SnS2sensor at 170 °C (2.58). The creation of pn junctions following compositing with SnS2was determined to be the primary reason for the composite's faster recovery time, while the heterojunction allowed for the rapid separation of hole-electron pairs. Because the MoS2surface has multiple vacancy defects, the adsorption energy of these vacancies is significantly higher than that of other places, resulting in increased NO2adsorption. Furthermore, MoS2can serve as active adsorption sites for SnS2micrometer sheets during gas sensing. This study may help to build new NO2gas sensors.

Effect of fluorine doping on the NO2-sensing properties of MoS2nanoflowers.

The somewhat slow recovery kinetics of NO2sensing at low temperatures are still challenging to overcome. To enhance the gas sensing property, fluorine is doped to MoS2nanoflowers by facile hydrothermal method. Extensive characterization data demonstrate that F was effectively incorporated into the MoS2nanoflowers, and that the microstructure of the MoS2nanoflowers did not change upon F doping. The two MoS2doped with varying concentrations of fluorine were tested for their sensing property to NO2gas. Both of them show good repeatability and stability. A smaller recovery time was seen in the F-MoS2-1 sample with a little amount of F loading, which was three times quicker than that of pure MoS2. The key reason for the quicker recovery time of this material was found to be the fluorine ions that had been adsorbed on the surface of F-MoS2-1 would take up some of the NO2adsorption site. Additionally, the sample F-MoS2-2 with a higher F doping level demonstrated increased sensitivity. The F-MoS2-2 sensor's high sensitivity was mostly due to the lattice fluorine filled to the sulfur vacancy, which generated impurity levels and reduced the energy required for its electronic transition. This study might contribute to the development of new molybdenum sulfide based gas sensor.

Photothermal CO-PROX reaction over ternary CuCoMnOx spinel oxide catalysts: the effect of the copper dopant and thermal treatment.

The purification of carbon monoxide in H2-rich streams is an urgent problem for the practical application of fuel cells, and requires the development of efficient and economical catalysts for the preferential oxidation of CO (CO-PROX). In the present work, a facile solid phase synthesis method followed by an impregnation method were adopted to prepare a ternary CuCoMnOx spinel oxide, which shows superior catalytic performance with CO conversion of 90% for photothermal CO-PROX at 250 mW cm-2. The dopant of copper species leads to the incorporation of Cu ions into the CoMnOx spinel lattice forming a ternary CuCoMnOx spinel oxide. The appropriate calcination temperature (300 °C) contributes to the generation of abundant oxygen vacancies and strong synergetic Cu-Co-Mn interactions, which are conducive to the mobility of oxygen species to participate in CO oxidation reactions. On the other hand, the highest photocurrent response of CuCoMnOx-300 also promotes the photo-oxidation activity of CO due to the high carrier concentration and efficient carrier separation. In addition, the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed that doping copper species could enhance the CO adsorption capacity of the catalyst due to the generation of Cu+ species, which significantly increased the CO oxidation activity of the CuCoMnOx spinel oxide. The present work provides a promising and eco-friendly solution to remove the trace CO in H2-rich gas over CuCoMnOx ternary spinel oxide with solar light as the only energy source.

Engineering MoOx /MXene Hole Transfer Layers for Unexpected Boosting of Photoelectrochemical Water Oxidation.

The development of semiconductor photoanodes is of great practical interest for the realization of photoelectrochemical (PEC) water splitting. Herein, MXene quantum dots (MQD) were grafted on a BiVO4 substrate, then a MoOx layer by combining an ultrathin oxyhydroxide oxygen evolution cocatalyst (OEC) was constructed as an integrated photoanode. The OEC/MoOx /MQD/BiVO4 array not only achieves a current density of 5.85 mA cm-2 at 1.23 V versus a reversible hydrogen electrode (vs. RHE), but also enhances photostability. From electrochemical analysis and density functional theory calculations, high PEC performance is ascribed to the incorporation of MoOx /MQD as hole transfer layers, retarding charge recombination, promoting hole transfer and accelerating water splitting kinetics. This proof-of-principle work not only demonstrates the potential utilization of hole transfer layers, but also sheds light on rational design and fabrication of integrated photoanodes for feasible solar energy conversion.

Highly improved ethanol gas-sensing performance of mesoporous nickel oxides nanowires with the stannum donor doping.

Mesoporous nickel oxides (NiO) and stannum(Sn)-doped NiO nanowires (NWs) were synthesized by using SBA-15 templates with the nanocasting method. X-ray diffraction, transmission electron microscope, energy dispersive spectrometry, nitrogen adsorption/desorption isotherm and UV-vis spectrum were used to characterize the phase structure, components and microstructure of the as-prepared samples. The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs. With the increasing Sn content, the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni0.962Sn0.038O1.038, and then decreased to 12.24 for Ni0.946Sn0.054O1.054 to 100 ppm ethanol gas at 340 °C. The high surface area from the Sn-doping improved the adsorption of oxygen on the surface of NiO NWs, resulting in the smaller surface resistance in air. Furthermore, owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping, the total resistance in ethanol gas enhanced greatly. It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be greatly improved by the higher surface area and high-valence donor substitution from Sn-doping.

Wide bandgap mesoporous hematite nanowire bundles as a sensitive and rapid response ethanol sensor.

In this study, α-Fe2O3 nanowires were synthesized using mesoporous SBA-15 silica as the hard templates with the nanocasting method, and then mesoporous α-Fe2O3 nanowire bundles (NWBs) were separated from the well-dispersed α-Fe2O3 nanowires (NWs) by the centrifugation technique. Both samples were characterized by x-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption isotherm and UV-vis spectra. All results indicated that the α-Fe2O3 NWBs with mesoporous structure presented a higher BET surface area (95 m(2) g(-1)) and wider bandgap (2.08 eV) than those of α-Fe2O3 NWs (32 m(2) g(-1) and 1.91 eV). The bandgap of α-Fe2O3 NWBs was in accordance with the bulk α-Fe2O3, while the BET surface area was much higher. The results from the gas-sensing measurement revealed that the α-Fe2O3 NWBs based gas sensor exhibited a high sensitivity of 21.7, fast response-recovery of 7.5 s and 1 s, and good selectivity to ethanol at 340 °C. The sensitivity (21.7) for ethanol of α-Fe2O3 NWBs was much better than that of the α-Fe2O3 NWs (12.2), which should be attributed to the higher BET surface area and wider bandgap of α-Fe2O3 NWBs.

Au- or Ag-Decorated ZnO-Rod/rGO Nanocomposite with Enhanced Room-Temperature NO2-Sensing Performance.

To improve the gas sensitivity of reduced oxide graphene (rGO)-based NO2 room-temperature sensors, different contents (0-3 wt%) of rGO, ZnO rods, and noble metal nanoparticles (Au or Ag NPs) were synthesized to construct ternary hybrids that combine the advantages of each component. The prepared ZnO rods had a diameter of around 200 nm and a length of about 2 µm. Au or Ag NPs with diameters of 20-30 nm were loaded on the ZnO-rod/rGO hybrid. It was found that rGO simply connects the monodispersed ZnO rods and does not change the morphology of ZnO rods. In addition, the rod-like ZnO prevents rGO stacking and makes nanocomposite-based ZnO/rGO achieve a porous structure, which facilitates the diffusion of gas molecules. The sensors' gas-sensing properties for NO2 were evaluated. The results reveal that Ag@ZnO rods-2% rGO and Au@ZnO rods-2% rGO perform better in low concentrations of NO2 gas, with greater response and shorter recovery time at the ambient temperature. The response and recovery times with 15 ppm NO2 were 132 s, 139 s and 108 s, 120 s, and the sensitivity values were 2.26 and 2.87, respectively. The synergistic impact of ZnO and Au (Ag) doping was proposed to explain the improved gas sensing. The p-n junction formed on the ZnO and rGO interface and the catalytic effects of Au (Ag) NPs are the main reasons for the enhanced sensitivity of Au (Ag)@ZnO rods-2% rGO.

Engineering of ZnO/rGO towards NO2 Gas Detection: Ratio Modulated Sensing Type and Heterojunction Determined Response.

Nanoscale heterostructured zinc oxide/reduced graphene oxide (ZnO/rGO) materials with p-n heterojunctions exhibit excellent low temperature NO2 gas sensing performance, but their doping ratio modulated sensing properties remain poorly understood. Herein, ZnO nanoparticles were loaded with 0.1~4% rGO by a facile hydrothermal method and evaluated as NO2 gas chemiresistor. We have the following key findings. First, ZnO/rGO manifests doping ratio-dependent sensing type switching. Increasing the rGO concentration changes the type of ZnO/rGO conductivity from n-type (<0.6% rGO) to mixed n/p -type (0.6~1.4% rGO) and finally to p-type (>1.4% rGO). Second, interestingly, different sensing regions exhibit different sensing characteristics. In the n-type NO2 gas sensing region, all the sensors exhibit the maximum gas response at the optimum working temperature. Among them, the sensor that shows the maximum gas response exhibits a minimum optimum working temperature. In the mixed n/p-type region, the material displays abnormal reversal from n- to p-type sensing transitions as a function of the doping ratio, NO2 concentration and working temperature. In the p-type gas sensing region, the response decreases with increasing rGO ratio and working temperature. Third, we derive a conduction path model that shows how the sensing type switches in ZnO/rGO. We also find that p-n heterojunction ratio (np-n/nrGO) plays a key role in the optimal response condition. The model is supported by UV-vis experimental data. The approach presented in this work can be extended to other p-n heterostructures and the insights will benefit the design of more efficient chemiresistive gas sensors.

Two-Dimensional Defective Boron-Doped Niobic Acid Nanosheets for Robust Nitrogen Photofixation.

Direct nitrogen photofixation is a feasible solution toward sustainable production of ammonia under mild conditions. However, the generation of active sites for solar-dirven nitrogen fixation not only limits the fundamental understanding of the relationship among light absorption, charge transfer, and catalytic efficiency but also influences the photocatalytic activity. Herein, we report two-dimensional boron-doped niobic acid nanosheets with oxygen vacancies (B-Vo-HNbO3 NSs) for efficient N2 photofixation in the absence of any scavengers and cocatalysts. Impressively, B-Vo-HNbO3 NS as a model catalyst achieves the enhanced ammonia evolution rate of 170 µmol gcat-1 h-1 in pure water under visible-light irradiation. The doublet coupling representing 15NH4+ in an isotopic labeling experiment and in situ infrared spectra confirm the reliable ammonia generation. The experimental analysis and density functional theory (DFT) calculations indicate that the strong synergy of boron dopant and oxygen vacancy regulates band structure of niobic acid, facilitates photogenerated charge transfer, reduces free energy barriers, accelerates reaction kinetics, and promotes the high rates of ammonia evolution. This work provides a general strategy to design active photocatalysts toward solar N2 conversion.

Bis(2,6-dihy-droxy-benzoato-κO,O)(nitrato-κO,O')bis-(1,10-phenanthroline-κN,N')samarium(III).

The title mononuclear complex, [Sm(C(7)H(5)O(3))(2)(NO(3))(C(12)H(8)N(2))(2)], is isostructural with that of other lanthanides. The Sm atom is in a pseudo-bicapped square-anti-prismatic geometry, formed by four N atoms from two chelating 1,10-phenanthroline (phen) ligands and by six O atoms, four from two 2,6-dihy-droxy-benzoate (DHB) ligands and the other two from a nitrate anion. π-π stacking inter-actions between phen and DHB ligands [centroid-centroid distance = 3.528 (4) and 3.812 (3) Å], and phen and phen ligands [face-to-face separation = 3.420 (10) Å] of adjacent complexes stabilize the crystal structure. Intra-molecular O-H⋯O hydrogen bonds are observed in the DHB ligands.

Color tuning of Bi3+-doped double-perovskite Ba2(Gd1-x ,Lu x )NbO6 (0 ≤ x ≤ 0.6) solid solution compounds via crystal field modulation for white LEDs.

Nowadays, rare-earth-free color-tunable solid solutions are receiving great attention. Here, we synthesize a type of double-perovskite Ba2(Gd1-x ,Lu x )NbO6:Bi3+ (0 ≤ x ≤ 0.6) solid solution compound using high temperature solid state reaction. The structural phase purity and photoluminescence (PL) properties of the samples are characterized by powder X-ray diffraction (XRD), density functional theory (DFT) calculations, UV-visible diffuse reflectance spectroscopy and PL spectroscopy. Structural analysis shows that all the samples are crystallized in the double-perovskite structure with a cubic space group of Fm3̄m. Moreover, with the increase of Lu3+ content, the XRD positions are gradually shifted toward higher diffraction angles, indicating the shrinkage of the crystal lattice. Our PL results show that the Ba2(Gd1-x ,Lu x )NbO6:Bi3+ solid solutions can show Bi3+ tunable emissions from 462 nm to 493 nm and excitation peaks from 363 nm to 390 nm with the increase of Lu3+ content from 0 to 0.6, owing to the crystal field modulation around the Bi3+ ion. In addition, the blue-shift of the host excitation peaks is also observed, which is ascribed to the increase of bandgap energies (i.e., from 3.01 eV to 4.14 eV based on the DFT calculations). Besides, due to the closer structural rigidity induced by the replacement of larger Gd3+ ions with smaller Lu3+ ions, the Ba2(Gd1-x ,Lu x )NbO6:Bi3+ solid solutions show an increase of Bi3+ emission intensity and QE values followed by a subsequent decrease. As a result, the highest QE value, which corresponds to Ba2Gd0.8Lu0.2NbO6:Bi3+, is 49%. Finally, by coating this optimal blue phosphor and the red CsPb(Br0.4I0.6)3 phosphor on a commercial UV LED chip, a white LED device with a color temperature (CT) of 3633 K, CIE value at (0.381, 0.379), color rendering index (CRI) of 78.4, and luminous efficiency of 48 lm W-1 is achieved.

Preparation and Characterization of Graphene/Fe3O4 Composites by Solvothermal Method.

In the present study, graphene/Fe3O4 nanocomposites were prepared by solvothermal method using graphite oxide (GO) and FeCl3 x 6H2O as starting materials and the products were characterized by X-ray Diffraction (XRD), Scanning Electronic Microscope (SEM) and Vibrating Sample Magnetometer (VSM). Effects of Fe ion concentration, temperature and time of solvothermal reaction on the magnetic properties, microstructures and morphologies of graphene/Fe3O4 nanocomposites were investigated. The results showed that with the raising of Fe ion, particle size of the products became bigger, and saturation magnetization of the products got higher. The saturation magnetization and particle size of the products can be enhanced by increasing the reaction time and temperature, but the change of saturation magnetization and particle size were not obvious after the time got 8 h and temperature was at 200 degrees C, which demonstrated that the products became stable under this condition. The morphologies, microstructures and properties of products can be controlled by adjusting synthesis conditions.