Enhanced photocatalytic nitrogen fixation performance via in situ constructing BiO_(2-x)/NaNbO_(3) heterojunction

The fabrication of heterojunction catalysts is an effective strategy to enhance charge separation efficiency,thereby boosting the performance of photocatalysts.In this study,BiO_(2-x)nanosheets were synthesized through a hydrothermal process and loaded onto NaNbO_(3) microcube to construct a series of BiO_(2-x)/NaNbO_(3) heterojunctions for photocatalytic N_(2) fixation.Results indicated that 2.5%BiO_(2-x)/NaNbO_(3) had the highest photocatalytic performance.The NH_(3) production rate under simulated solar light reached 406.4μmol·L^(-1)·g^(-1)·h^(-1),which reaches 2.6 and 3.8 times that of NaNbO_(3) and BiO_(2-x),respectively.BiO_(2-x)nanosheets primarily act as electron trappers to enhance the separation efficiency of charge carriers.The strong interaction between BiO_(2-x)and NaNbO_(3) facilitates the electron migration between them.Meanwhile,the abundant oxygen vacancies in BiO_(2-x)nanosheets may facilitate the adsorption and activation of N_(2),which may be another possible reason of the high photocatalytic activity of the BiO_(2-x)/NaNbO_(3).This study may offer new insights for the development of semiconductor materials in photocatalytic nitrogen fixation.

Facile preparation of Ag_(2)S/KTa_(0.5)Nb_(0.5)O_(3) heterojunction for enhanced performance in catalytic nitrogen fixation via photocatalysis and piezo-photocatalysis

In this work, a novel heterojunction composite Ag_(2)S/KTa_(x)Nb_(1-x)O_(3)was designed and synthesized through a combination of hydrothermal and precipitation procedures. The Ta/Nb ratio of the KTa_(x)Nb_(1-x)O_(3)and the Ag_(2)S content were optimized. The best 0.5% Ag_(2)S/KTa_(0.5)Nb_(0.5)O_(3)(KTN) sample presents an enhanced photocatalytic performance in ammonia synthesis than KTN and Ag_(2)S. Under simulated sunlight, the NH_(3)generation rate of 0.5% Ag_(2)S/KTN reaches 2.0 times that of pure KTN. Under visible light, the reaction rate ratio of the two catalysts is 6.0.XRD, XPS, and TEM analysis revealed that Ag2S was intimately decorated on the KTN nanocubes surface, which promoted the electron transfer between the two semiconductors. The band structure investigation indicated that the Ag_(2)S/KTN heterojunction established a type-Ⅱ band alignment with intimate contact, thus realizing the effective transfer and separation of photogenerated carriers. The change in charge separation was considered as the main reason for the enhanced photocatalytic performance. Interestingly, the Ag_(2)S/KTN composite exhibited higher NH3generation performance under the combined action of ultrasonic vibration and simulated sunlight. The enhanced piezo-photocatalytic performance can be ascribed that the piezoelectric effect of KTN improved the bulk separation of charge carriers in KTN. This study not only provides a potential catalyst for photocatalytic nitrogen fixation but also shows new ideas for the design of highly efficient catalysts via semiconductor modification and external field coupling.

High piezo/photocatalytic efficiency of Ag/Bi_(5)O_(7)I nanocomposite using mechanical and solar energy for N2 fixation and methyl orange degradation

In this work,Ag/Bi_(5)O_(7)I nanocomposite was prepared and firstly applied in piezo/photocatalytic reduction of N2 to NH3 and methyl orange(MO)degradation.Bi_(5)O_(7)I was synthesized via a hydrothermal-calcination method and shows nanorods morphology.Ag nanoparticles(NPs)were photo deposited on the Bi_(5)O_(7)I nanorods as electron trappers to improve the spatial separation of charge carriers,which was confirmed via XPS,TEM,and electronic chemical analyses.The catalytic test indicates that Bi_(5)O_(7)I presents the piezoelectric-like behavior,while the loading of Ag NPs can strengthen the character.Under ultrasonic vibration,the optimal Ag/Bi_(5)O_(7)I presents high efficiency in MO degradation.The degradation rate is determined to be 0.033 min
1,which is 4.7 folds faster than that of Bi_(5)O_(7)I.The Ag/Bi_(5)O_(7)I also presents a high performance in piezocatalytic N2 fixation.The piezocatalytic NH3 generation rate reaches 65.4 μmol L^(-1)g^(-1)h^(-1)with water as a hole scavenger.The addition of methanol can hasten the piezoelectric catalytic reaction.Interestingly,when ultrasonic vibration and light irradiation simultaneously act on the Ag/Bi_(5)O_(7)I catalyst,higher performance in NH3 generation and MO degradation is observed.However,due to the weak adhesion of Ag NPs,some Ag NPs would fall off from the Bi_(5)O_(7)I surface under long-term ultrasonic vibration,which would greatly reduce the piezoelectric catalytic performance.This result indicates that a strong binding force is required when preparing the piezoelectric composite catalyst.The current work provides new insights for the development of highly efficient catalysts that can use multiple energies.

Enhanced photocatalytic N_(2) fixation using KNbO3/Bi_(4)O_(5)Br_(2) type Ⅱ heterojunction

The fabrication of heterojunction catalysts is an effective strategy to enhance charge separation efficiency,thus boosting the performance of photocatalysts.This work presents the synthesis and investigation of a novel KNbO_(3)/Bi_(4)O_(5)Br_(2) heterostructure catalyst for photocatalytic N_(2)-to-NH_(3) conversion under light illumination.While morphology analysis revealed KNbO_(3) microcubes embedded within Bi_(4)O_(5)Br_(2) nanosheets,the composite exhibited no significant improvement in specific surface area or optical property compared to Bi_(4)O_(5)Br_(2) due to the relatively wide band gap and low surface area of KNbO_(3).The main contribution lies in the enhanced separation efficiency of photogenerated electrons and holes.Besides,the band structure analysis suggests that KNbO_(3) and Bi_(4)O_(5)Br_(2) exhibit suitable band potentials to form a type II heterojunction.Benefiting from the higher Fermi level of KNbO_(3) than Bi_(4)O_(5)Br_(2),the electron drift at the contact region thus occurs and leads to the formation of a built-in electric field with the direction from KNbO_(3) to Bi_(4)O_(5)Br_(2),accelerating electron migration and improving the operational efficiency of the photocatalysts.Consequently,the KNbO_(3)/Bi_(4)O_(5)Br_(2) catalyst shows an increased photoactivity,achieving an NH_(3) generation rate 1.78 and 1.58 times those of KNbO_(3) and Bi_(4)O_(5)Br_(2),respectively.This work may offer valuable insights for the design and synthesis of heterojunction composite photocatalysts.

Three-dimensional electrical structure model of the Yangbajain geothermal field in Tibet:Evidence obtained from magnetotelluric data

The Yangbajain Geothermal Field in Tibet is located in the fault subsidence basin of the central Yadong-Gulu Rift Valley.The spatial distribution of the field is controlled by mountain-front fault zones on the northwestern and southeastern sides of the basin.Geothermal power has been generated in Yangbajain for more than 40 years.However,owing to the lack of threedimensional(3D) geophysical exploration data,key geological issues related to the partial melt body of the Yangbajain Geothermal Field,such as its location,burial depth,and geometric form,as well as the ascending channel of the geothermal fluid,have for a long time been controversial.In this study,3D inversion was performed using measured geo-electromagnetic total impedance tensor data from 47 survey points.The extracted horizontal sections at different depths and profiles,and at different lines,reflect the 3D electrical structure model of the geothermal field in the study area.Subsequently,three findings were obtained.First,the partial melt body,located below the China-Nepal Highway extending along the northeast direction,is the heat source of the Yangbajain Geothermal Field.The burial depth range of the molten body was determined to range between approximately 6.2 and 14 km.Moreover,the geothermal fluid ascended a horn-shaped circulation channel with an up-facing opening,located in the northern section of the sulfur ditch area.The study results revealed that deep rock fissures(>2 km) were not well developed and had poor permeability.In addition,no layered heat reservoirs with high water richness were observed in the northern part of the study area.However,the application of enhanced geothermal system(EGS) technology in the northern region would be essential to improving the power generation capacity of the Yangbajain Geothermal Field.In addition,the study found no deep high-temperature heat storage areas in the southern region of the study area.

ENERGY CONSERVATION FOR SOLUTIONS OF INCOMPRESSIBLE VISCOELASTIC FLUIDS

Some sufficient conditions of the energy conservation for weak solutions of incompressible viscoelastic flows are given in this paper.First,for a periodic domain in R^(3),and the coefficient of viscosity μ=0,energy conservation is proved for u and F in certain Besovs paces.Furthermore,in the whole space R^(3),it is shown that the conditions on the velocity u and the deformation tensor F can be relaxed,that is,u∈B_(3,c(N))^(1/3),and F∈B_(3,∞)^(1/3).Finally,when μ>0,in a periodic domain in R^(d) again,a result independent of the spacial dimension is established.More precisely,it is shown that the energy is conserved for u∈L^(T)(0,T;L^(n)(Ω))for any 1/r+1/s≤1/2,with s≥4,and F∈L^(m)(0,T;L^(n)(Ω))for any 1/m+1/n≤1/2,with n≥4.

Decoration of CdMoO_(4) micron polyhedron with Pt nanoparticle and their enhanced photocatalytic performance in N_(2) fixation and water purification

This study aimed to prepare and apply a novel Pt/CdMoO_(4) composite photocatalyst for photocatalytic N2 fixation and tetracycline degradation. The Pt/CdMoO_(4) composite was subjected to comprehensive investigation on the morphology, structure, optical properties, and photoelectric chemical properties. The results demonstrate the dispersion of Pt nanoparticles on the CdMoO_(4) surface. Close contact between CdMoO_(4) and Pt was observed, resulting in the formation of a heterojunction structure at their contact region. Density functional theory calculation and Mott-Schottky analysis revealed that Pt possesses a higher work function value than CdMoO_(4), resulting in electron drift from CdMoO_(4) to Pt and the formation of a Schottky barrier. The presence of this barrier increases the separation efficiency of electron-hole pairs, thereby improving the performance of the Pt/CdMoO_(4) composite in photocatalysis. When exposed to simulated sunlight, the optimal Pt/CdMoO_(4) catalyst displayed a photocatalytic nitrogen fixation rate of 443.7 μmol·L‒^(1)·g‒^(1)·h‒^(1), which is 3.2 times higher than that of pure CdMoO_(4). In addition, the composite also exhibited excellent performance in tetracycline degradation, with hole and superoxide species identified as the primary reactive species. These findings offer practical insights into designing and synthesizing efficient photocatalysts for photocatalytic nitrogen fixation and antibiotics removal.

Review of the progress in preparing nano TiO_2: An important environmental engineering material

TiO2 nanomaterial is promising with its high potential and outstanding performance in photocatalytic environmental applications, such as CO2 conversion, water treatment, and air quality control. For many of these applications, the particle size, crystal structure and phase, porosity, and surface area influence the activity of TiO2 dramatically. TiO2 nanomaterials with special structures and morphologies, such as nanospheres, nanowires, nanotubes, nanorods, and nanoflowers are thus synthesized due to their desired characteristics. With an emphasis on the different morphologies of TiO2 and the influence factors in the synthesis, this review summarizes fourteen TiO2 preparation methods, such as the sol-gel method, solvothermal method, and reverse micelle method. The TiO2 formation mechanisms, the advantages and disadvantages of the preparation methods, and the photocatalytic environmental application examples are proposed as well.

Cu-doped Bi/Bi_(2)WO_(6) catalysts for efficient N_(2) fixation by photocatalysis

In this paper,Cu-doped Bi_(2)WO_(6)was synthesized via a solvothermal method and applied it in photocatalytic N_(2)immobilization.Characterization results showed the presence of a small amount of metallic Bi in the photocatalyst,indicating that the synthesized photocatalyst is actually Bi/Cu-Bi_(2)WO_(6)composite.The doped Cu had a valence state of+2 and most likely substituted the position of Bi^(3+).The introduced Cu did not affect the metallic Bi content,but mainly influenced the energy band structure of Bi_(2)WO_(6).The band gap was slightly narrowed,the conduction band was elevated,and the work function was reduced.The reduced work function improved the transfer and separation of charge carriers,which mainly caused the increased photoactivity.The optimized NH_(3)generation rates of Bi/Cu-Bi_(2)WO_(6)reached 624 and 243μmol·L^(-1)·g^(-1)·h^(-1)under simulated solar and visible light,and these values were approximately 2.8 and 5.9 times higher those of Bi/Bi_(2)WO_(6),respectively.This research provides a method for improving the photocatalytic N_(2)fixation and may provide more information on the design and preparation of heteroatom-doped semiconductor photocatalysts for N_(2)-to-NH_(3)conversion.

One-step preparation of MoO_(x)/ZnS/ZnO composite and its excellent performance in piezocatalytic degradation of Rhodamine B under ultrasonic vibration

This paper synthesized a new type of ternary piezoelectric catalyst MoO_(x)/ZnS/ZnO (MZZ)by a one-step method.The catalytic degradation of Rhodamine B (RhB) solution (10μg/g,pH=7.0) shows that the composite catalyst has excellent piezoelectric catalytic activity under ultrasonic vibration (40 k Hz).The piezoelectric degradation rate of the optimal sample reached 0.054 min^(-1),which was about 2.5 times that of pure ZnO.X-ray diffraction(XRD),X-ray photoelectron spectroscopy (XPS),Raman,transmission electron microscopy(TEM),scanning electron microscopy (SEM),and electrochemical impedance spectroscopy(EIS) technologies were used to analyze the structure,morphology,and interface charge transfer properties of the MZZ piezocatalysts.The results showed that the composite catalyst may have a core-shell structure.ZnS is coated on the surface of ZnO,while MoO_(x)adheres to the surface of ZnS.This structure endowed MZZ larger specific surface area than ZnO,which benefits the RhB adsorption.More importantly,the formed heterojunction structure between ZnS and ZnO promotes the separation of positive and negative charges induced by the piezoelectric effect.MoO_(x)species may act as a charge trap to further promote more carriers to participate in the reaction.In addition,MoO_(x)may also be beneficial in adsorbing dyes.Active species capture experiments show that superoxide radicals and holes are the main active species in piezoelectric catalytic reactions on MZZ catalysts.

In situ preparation of g-C3N4/Bi4O5I2 complex and its elevated photoactivity in Methyl Orange degradation under visible light

A graphite carbon nitride(g-C3N4)modified Bi4O5I2 composite was successfully prepared insitu via the thermal treatment of a g-C3N4/Bi OI precursor at 400°C for 3 hr.The as-prepared g-C3N4/Bi4O5I2 showed high photocatalytic performance in Methyl Orange(MO)degradation under visible light.The best sample presented a degradation rate of 0.164 min^-1,which is 3.2 and 82 times as high as that of Bi4O5I2 and g-C3N4,respectively.The g-C3N4/Bi4O5I2 was characterized by X-ray powder diffractometer(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman,X-ray photoelectron spectroscopy(XPS),ultraviolet-visible diffuse reflectance spectra(DRS),electrochemical impedance spectroscopy(EIS)and transient photocurrent response in order to explain the enhanced photoactivity.Results indicated that the decoration with a small amount of g-C3N4 influenced the specific surface area only slightly.Nevertheless,the capability for absorbing visible light was improved measurably,which was beneficial to the MO degradation.On top of that,a strong interaction between g-C3N4 and Bi4O5I2 was detected.This interplay promoted the formation of a favorable heterojunction structure and thereby enhanced the charge separation.Thus,the g-C3N4/Bi4O5I2 composite presented greater charge separation efficiency and much better photocatalytic performance than Bi4O5I2.Additionally,g-C3N4/Bi4O5I2 also presented high stability.·O2^- and holes were verified to be the main reactive species.

Application of Ag/AgBr/GdVO_4 composite photocatalyst in wastewater treatment

Ag/AgBr/GdVO_4 composite photocatalysts were designed and synthesized in this paper.The physical and chemical structures, as well as optical properties of the synthesized composite were investigated via XRD, XPS, TEM, and UV–vis. It is found that the composite showed a ternary heterojunction structure of Ag, Ag Br and GdVO_4. Meanwhile, it has a high intensity of light current, indicating its high separation efficiency of electron and hole.Photocatalytic oxidation of rhodamine B（RhB） under visible light irradiation was performed to investigate the activity of the Ag/Ag Br/GdVO_4 composite. Result indicates that it shows excellent photocatalytic activity. Under visible light irradiation for 12 min, about 80% of Rh B（30 μmol/L） was degraded. The degradation rate is estimated to be 0.253 min1, which is three times higher than that of pure AgBr. The high photoactivity can be ascribed to the synergetic effect of Ag Br, GdVO_4, and Ag nanoparticle in separation of electron–hole pairs.

InP-based directly modulated monolithic integrated few-mode transmitter

A monolithic integrated few-mode transmitter comprising of two directly modulated distributed feedback lasers and a multimode-interference-coupler-based mode converter-multiplexer with 66% mode conversion efficiency was designed and demonstrated. A fundamental TE0 mode and a first-order TE1 mode were successfully generated from the transmitter, with the output power of 4 and 5.5 mW at a pump current of around 150 mA, respectively,at the common output port. The small signal modulation bandwidth of the TE0 and TE1 channels reached 17.4 and 14.7 GHz, respectively. Error-free 2 × 10-Gbit∕s direct modulation of the two-mode transmitter was demonstrated, with a power penalty of 4.3 dB between the TE0 mode and the TE1 mode at the bit error rate of 1 × 10^(-9).

InP-based monolithically integrated few-mode devices

Mode-division multiplexing（MDM） has become an increasingly important technology to further increase the transmission capacity of both optical-fiber-based communication networks, data centers and waveguidebased on-chip optical interconnects. Mode manipulation devices are indispensable in MDM system and have been widely studied in fiber, planar lightwave circuits, and silicon and InP based platforms. InP-based integration technology provides the easiest accessibility to bring together the functions of laser sources, modulators, and mode manipulation devices into a single chip, making it a promising solution for fully integrated few-mode transmitters in the MDM system. This paper reviews the recent progress in InP-based mode manipulation devices, including the few-mode converters, multiplexers, demultiplexers, and transmitters. The working principle, structures, and performance of InP-based few-mode devices are discussed.

De Novo Assembly Methods for Next Generation Sequencing Data

The recent breakthroughs in next-generation sequencing technologies, such as those of Roche 454,Illumina/Solexa, and ABI SOLID, have dramatically reduced the cost of producing short reads of the genome of new species. The huge volume of reads, along with short read length, high coverage, and sequencing errors, poses a great challenge to de novo genome assembly. However, the paired-end information provides a new solution to these problems. In this paper, we review and compare some current assembly tools, including Newbler, CAP3, Velvet,SOAPdenovo, AllPaths, Abyss, IDBA, PE-Assembly, and Telescoper. In general, we compare the seed extension and graph-based methods that use the overlap/lapout/consensus approach and the de Bruijn graph approach for assembly. At the end of the paper, we summarize these methods and discuss the future directions of genome assembly.