Modulation Of Charge Transfer Research Articles

Enhanced optical absorption and photocatalytic water splitting of g-C3N4/TiO2 heterostructure through C&B codoping: A hybrid DFT study

Our theoretical research indicate that the electric field are generated in the direction of (C doped) TiO2 (101) surface to (B-doped) g-C3N4 monolayer for the pristine, C and B doped g-C3N4/TiO2, and higher band-edge potential on the (C doped) TiO2 (101) surface are observed compared to (B-doped) g-C3N4 monolayer. Thus, the pristine (2.591 eV), C-doped (2.663 eV) and B-doped (2.339 eV) g-C3N4/TiO2 are Z-scheme heterostructures, which promotes charge separation and retains a prominent redox ability. After C doping, the C 2p energy level is introduced which facilitate the separation of photoexcited carriers. The B-doped g-C3N4/TiO2 has a reduced bandgap and the mixing of B 2p and N 2p energy levels, promoting the red-shift of the optical absorption edge. The C&B codoped g-C3N4/TiO2 follows type-II charge transfer mode because of their synergistic effect in C and B atoms, which changes the direction of the built-in electric field. It also has a narrow bandgap (1.309 eV) and effectively separate electron-hole pairs leading to strong optical absorption ability in the range of 360 nm–460 nm. The band-edges matching of the semiconductor photocatalyst and the direction of the built-in electric field jointly determine whether the charges are selected to be Z-scheme or II-type transfer mode. Based on g-C3N4/TiO2 for C or/and B (co)doping, their different charge transfer modes have been established and they are expected to show promising photocatalytic water splitting performance.

Metal organic frameworks constructed heterojunction with α-NiS-β-NiS/CdS: The effect of organic-ligand in UiO-66 for charge transfer of photocatalytic hydrogen evolution

Developing favorable charge transfer mode for photocatalytic hydrogen evolution in a photocatalyst is a promising way to enhance photocatalytic activity. In this study, MOF, decorated with different functional groups, was initially used as charge transfer mode convertor coupled with CdS/α-NiS-β-NiS. The NH2-UiO-66/CdS/α-NiS-β-NiS lead to twice and triple higher H2 evolution compared to (OH)2-UiO-66/CdS/α-NiS-β-NiS and UiO-66/CdS/α-NiS-β-NiS respectively under simulated sunlight. The NH2-UiO-66 provides suitable energy band structure to formed Z-scheme with CdS/α-NiS-β-NiS, which plays a synergistic role in the photocatalytic process. The loading of α-NiS-β-NiS significantly improves the visible light absorption ability and provides abundant active sites. As a result, the α-NiS-β-NiS/CdS/NH2-UiO-66 show considerable photocatalytic hydrogen production rate of 17.88 mmol h−1 g−1, which is 7.9 times and 2.5 times as high as-those of pure CdS and 7-α-NiS-β-NiS/CdS, and it also shows a prominent apparent quantum efficiency (AQE) of 14.7% at 420 nm. This work provides a new insight design a metal organic frameworks based heterojunction with highly-efficient photo-induced charge separation and excellent visible-light absorption ability.

High-Speed Video Observation, Currents, and EM-Fields From Four Negative Upward Lightning to the Peissenberg Tower, Germany

In this article, we analyzed the optical images from high-speed video recordings and the time-correlated waveforms of the current, the electric field, and the magnetic field from four negative upward lightning which struck the Peissenberg Tower, Germany. Two of them were self-initiated ones and two of them were other-triggered ones. From the illumination in the video images, leader activity could clearly be detected during the occurrence of the first of the other-triggered lightning. In contrast, no illumination by leader activity could be found during the occurrence of the second other-triggered lightning and the time period of 2.5 s before. In addition, the current pulses superimposing the initial continuous current/continuing current were examined differing between those which developed in luminous or nonluminous branches. From the total of 26 current pulses which developed in nonluminous branches, 25 (96%) of them had a 10–90%-rise time less than 4 μs, and 23 (88%) of them had a 10–90%-rise time even less than 2 μs. Because the current waveforms resemble those of weak return stroke, we assume that the current pulses indeed represent the leader/return stroke mode of charge transfer to ground. The return strokes were extremely weak, with an arithmetic mean of 2.59 kA (GM: 2.08 kA) for the current peak. On the other hand, from the total of 74 current pulses which developed in already luminous branches, none of them had a 10–90%-rise time less than 4.4 μs. The arithmetic mean is 29.8 μs and the geometric mean is 20.5 μs. Due to the relatively long rise time, we assume that these current pulses represent the M-component mode of charge transfer to ground.

Self-defective ZnS mediated charge transfer for bran-new inter-step mode with boosted photoactivity and enhanced photostability

The appropriate interfacial contact and charges transfer mode of heterojunction photocatalysts were critical for high-efficiency hydrogen production. Inter-step mode heterojunction composite had advantages of enhanced visible-light response, improved charge space separation rate, increased electron utilization, which could also protect catalyst anode from photocorrosion. Zinc-vacancy-rich ZnS decorated CdS heterojunction photocatalyst with inter-step mode was constructed in order to fundamentally enhance photocatalytic performance and overcome photocorrosion of CdS. The charge transfer mode was modulated from pervasive type-II to bran-new inter-step mode by defect engineering. Zinc vacancies functioned as acceptor level for charge separation and up-shifted conduction and valance band energy of ZnS. The defective engineered CdS/ZnS heterojunction displayed a reduced over-potential and enhanced photocatalytic activity. The optimal photocatalytic hydrogen production rate for CdS/ZnS reached 42.1 mmol•g−1 under visible light without any co-catalyst. An apparent quantum yield (AQY) of 38.75% at 450 nm was achieved, which was 269.3 and 71.9 times higher than pristine zinc-vacancy-rich ZnS and CdS, respectively. Meanwhile, holes aggregated on the surface of CdS were blocked and the oxidation corrosion process was suppressed. The charge transfer mechanism and kinetics of charge transfer and separation in inter-step mode heterojunction photocatalysts were investigated and discussed. This work will accelerate practical applications of photocatalysis with inter-step mode and give deep insights into understanding how inherent acceptor levels play a role in designing defect-engineered semiconductor with enhanced photocatalytic performance.

Laboratory generated symmetrical-waveshape lightning current versus arc channel luminosity

Identifying a relation between current and channel luminosity is beneficial for producing an approximation to channel current via channel optical signal. In this paper, damped sinusoidal oscillation currents with more or less symmetrical waveshapes are injected into a tungsten copper hemispherical air gap and into a graphite rod air gap. Repeatability and reliability in channel luminosity measurement are compared between two air gap channels. Parametric correlation analyses, involving 12 sequences of lightning currents with a current peak from 13.0 kA to 34.4 kA, a current 10–90% risetime from 9.7 μs to 20.2 μs, and a current half-peak width from 21.6 μs to 46.4 μs, show the luminosity signatures also exhibit more or less symmetrical pulses, although they lag behind the corresponding current pulses. In initial primary pulses of these damped sinusoidal oscillations, the current peak is approximately direct proportional to the luminosity peak. Direct proportional relations are also observed between current 10–90% risetime and luminosity 10–90% risetime, between current half-peak width and luminosity half-peak width, as well as between current charge transfer and luminosity-time integration. These features are similar to those found in classical M-component current pulses associating with the M-component mode of charge transfer. Applicability of the results is further discussed to estimate the channel current from the channel luminosity.

Zinc Oxide Nanorod Surface-Enhanced Raman Scattering Substrates without and with Gold Nanoparticles Fabricated through Pulsed-Laser-Induced Photolysis

We fabricated surface-enhanced Raman scattering (SERS) substrates using gold nanoparticle (AuNP)-decorated zinc oxide (ZnO) nanorods (NRs). Prior to decoration with AuNPs, ZnO NRs on the glass substrate fabricated using the sol–gel method could enhance the SERS signal for detecting 10−5 M rhodamine 6G (R6G). Microscopic analysis revealed that the thermal-annealing process for fabricating the seed layers of ZnO facilitated the growth of ZnO NRs with the highly preferred c-axis (002) orientation. A decrease in the diameter of ZnO NRs occurred because of the use of annealed seek layers further increased the surface-to-volume ratio of ZnO NRs, resulting in an increase in the SERS signal for R6G of 10−5 M. To combine the localized surface plasmon resonance (LSPR) mode with the charge transfer (CT) mode, ZnO NRs were decorated with AuNPs through pulsed-laser-induced photolysis (PLIP). However, the preferred vertical (002) orientation of ZnO NRs was prone to the aggregation of AuNPs, which hindered the SERS signal. The experimental results revealed that ZnO NRs with the crystalline structure of horizontal (100) and (101) orientations facilitated the growth of homogeneous, independent and isolated AuNPs which serves as “hot spots” for SERS signal of detecting R6G at a low concentration of 10−9 M. Comparing to previous fabrication of SERS substrate, our method has advantage to fabricate AuNP-decorated ZnO NR in a short time. Moreover, the optimization of the SERS behaviors for different fabrication conditions of AuNPs using the PLIP method was investigated in detail.

Tussilago Farfara Extract (TFE) as Green Corrosion Inhibitor for Aluminum in Hydrochloric Acid Solution

The dissolution of aluminum in 2 M HCl medium in the absence and presence of Tussilago Farfara Extract (TFE) was examined utilizing Tafel polarization (TP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), gasometry and mass reduction techniques. The outcomes of these procedures illustrated that the inhibiting effect of this inhibitor depends on its concentration and chemical composition. The inhibitive impact of TFE illustrated the blocking of the Al surface by adsorption of its components through the reacted atoms contained in its molecules. The adsorption model was obeyed to Langmuir isotherm. The influence of temperature on the dissolution rate in the non-existence and existence of TFE was observed. Tafel polarization indicated that TFE acts as a mixed kind inhibitor. Impedance outcomes illustrated that the dissolution of Al is monitored by charge transfer mode at all concentrations of the extract. Varied surface examinations like XPS, FTIR, and AFM were checked to affirm the presence of the defensive film on the Al surface. All outcomes measured from all procedures are in perfect conformity.

Transport and Spectroscopy in Conjugated Molecules: Two Properties and a Single Rationale.

In the context of electron dynamics simulations, when the charge density of a molecule is subject to a perturbation in the form of a short electric field pulse, density fluctuations develop in time. In the absence of dissipation, these oscillations continue indefinitely, reflecting the resonances of the electronic system; as a matter of fact, from the Fourier transform of the time dependent dipole arising from them, the absorption spectrum of the molecule can be calculated. Since these oscillations are the result of the electrons moving through the molecular structrure, it seems plausible that they carry information on the transport properties of the system. This is the idea explored in the present article for the case of conjugated polymers. Specifically, we depart from a nonequilibrium state with the charge concentrated on the ends of the molecule, and estimate the currents flowing back and forth during the evolution of electron dynamics simulations. These show that the charge oscillates between the sides of the polymer with the predominance of a frequency that is coincident with one of the main bands in the absorption spectrum, which can be ascribed to a charge transfer transition. Thus, from the charge transfer band frequency appearing in the absorption spectrum, the molecular conductance of a conjugated molecule can be calculated. Also interestingly, we find that, while a perturbation excites all resonances of an electronic system, the form in which this perturbation is applied can be manipulated to determine the relative manifestation of the response. The electric field pulse excites all resonances according to the transition dipole moment and is then appropriate to produce the absorption spectrum. A charge separated initial state, however, specifically stimulates the charge transfer mode and is then suitable to calculate transport properties. This allows us to propose a simple approach to obtain molecular conductances and tunneling decay constants in agreement with results from much more demanding electronic structure techniques.

Characteristics of different charge transfer modes in upward flashes inferred from simultaneously measured currents and fields

The authors present an analysis of different charge transfer modes during upward negative flashes. The analysis includes a total number of 94 pulses that occurred during two upward negative flashes recorded at the Santis Tower. The pulses included 59 mixed-mode (MM) initial continuous current (ICC) pulses, 17 M-component-type ICC (M-ICC) pulses, 8 return-stroke pulses, and 10 classical M-component (MC) pulses. It is found that the initial stage of the flash is responsible for the largest share of the total charge transferred to the ground. Simulation results for the electric fields associated with the considered charge transfer modes are presented and discussed. Return stroke (RS) and MM pulses were simulated adopting the MTLE model, while MCs and M-ICC pulses were simulated using the guided wave model of Rakov et al. The simulated results are shown to be in good agreement with simultaneous records of electric fields measured at a distance of 15 km from the Santis Tower. The inferred velocities for MCs and M-ICC pulses range from 2.0 × 10 7 to 9.0 × 10 7 m/s, and the corresponding junction point heights range from 1.0 to 2.0 km. The inferred pulse velocities for RSs and MM pulses range from 1.3 × 10 8 to 1.65 × 10 8 m/s. The inferred current attenuation constants of the MTLE model obtained in this study range from 0.3 to 0.8 km, lower than the value of 2 km previously suggested for RSs in downward flashes. The obtained results support the assumption that the mode of charge transfer to the ground giving rise to MM pulses is similar to that of RSs. The results are also in support of the generally assumed similarity between M-ICC pulses and classical MCs.

A facile synthesis of a ZIF-derived ZnS/ZnIn2S4 heterojunction and enhanced photocatalytic hydrogen evolution.

A facile synthetic route, by using rhombic dodecahedral zeolitic imidazolate framework-8 (ZIF-8) as the structure template, is devoted to fabricating the ZnS/ZnIn2S4 hybrid heterojunction; the compact heterostructure was produced by combining the sulfurization of ZIF-8 and the in situ precipitation of ZnIn2S4 in one pot. The resulting ZnS nanoparticles of about 100 nm were uniformly dispersed in the folds of flower-like ZnIn2S4, whose structure is beneficial for charge transfer at the heterointerface. The additional quantities of ZIF-8 are varied to find an optimum ratio of the two components to obtain the best photocatalytic activity. In the photocatalytic hydrogen generation irradiated by simulated solar light, all the ZnS/ZnIn2S4 hybrid photocatalysts displayed improved hydrogen production rates compared to single ZnS or ZnIn2S4, and the best hydrogen production rate of 453.4 μmol h-1 g-1 is obtained by ZnS/ZIS-20, whose value is approximately 4 times higher than that of single ZnIn2S4. The electrochemical properties of the ZnS/ZnIn2S4 hybrid photocatalysts were measured to explore the charge transfer mode at the interface, and the band structure and enhanced photocatalytic hydrogen generation mechanism have been proposed. The excellent recycling properties of hydrogen production indicated the prospective applications of this kind of ZIF-derived metal sulfide in photocatalytic reactions.

A New Engineering Model of Lightning M Component That Reproduces Its Electric Field Waveforms at Both Close and Far Distances

AbstractWe present a new engineering model for the M component mode of charge transfer to ground that can predict the observed electric field signatures associated with this process at various distances, including (a) the microsecond‐scale pulse thought to be due to the junction of in‐cloud leaders and the grounded, current‐carrying channel and (b) the ensuing slow, millisecond‐scale pulse due to the M component proper occurring below the junction point. We examine the features of 13 microsecond‐scale, fast electric field pulses associated with M component processes in upward negative lightning initiated from the Säntis Tower and recorded 14.7 km from it. Eleven out of the 13 pulses were found to be unipolar with pulse widths in the range of 9.8 to 35 μs, and the other two were bipolar. To model the process that gives rise to microsecond‐scale pulses, we hypothesize that the current pulses propagating away from the junction point along the main lightning channel (below the junction point) and along the feeding in‐cloud leader channel (branch) carry the same amount of charge. We further assume that the pulse traversing the branch is similar to a subsequent return‐stroke (RS) pulse. In the model, the RS‐like process is represented by the MTLE model. The millisecond‐scale field signature that follows the initial fast pulse in M components at close distances is simulated in our model using the guided‐wave M component model. The proposed model successfully reproduces the vertical electric field waveforms associated with M‐component processes in upward lightning flashes initiated from the Säntis Tower at 14.7‐km distance from the lightning channel, in which both the fast, microsecond‐scale and the following slower, millisecond‐scale pulses were observed. The model also reasonably reproduces the known features of electric field signatures at close distances (up to 5 km), where the amplitude of the millisecond‐scale hook‐like pulse is much larger than that of the microsecond‐scale pulse, and at far distances (of the order of 100 km), where the microsecond‐scale pulses are dominant.

Nanoscopic and Macro-Porous Carbon Nano-foam Electrodes with Improved Mass Transport for Vanadium Redox Flow Batteries

Although free-standing sheets of multiwalled carbon nanotubes (MWCNT) can provide interesting electrochemical and physical properties as electrodes for redox flow batteries, the full potential of this class of materials has not been accessible as of yet. The conventional fabrication methods produce sheets with micro-porous and meso-porous structures, which significantly resist mass transport of the electrolyte during high-current flow-cell operation. Herein, we developed a method to fabricate high performance macro-porous carbon nano-foam free standing sheets (Puffy Fibers, PF), by implementing a freeze-drying step into our low cost and scalable surface-engineered tape-casting (SETC) fabrication method, and we show the improvement in the performance attained as compared with a MWCNT sheet lacking any macro pores (Tape-cast, TC). We attribute the higher performance attained by our in-lab fabricated PF papers to the presence of macro pores which provided channels that acted as pathways for electrolytic transport within the bulk of the electrode. Moreover, we propose an electrolytic transport mechanism to relate ion diffusivity to different pore sizes to explain the different modes of charge transfer in the negative and the positive electrolytes. Overall, the PF papers had a high wettability, high porosity, and a large surface area, resulting in improved electrochemical and flow-cell performances.

Z-scheme system of WO3@MoS2/CdS for photocatalytic evolution H2: MoS2 as the charge transfer mode switcher, electron-hole mediator and cocatalyst

A novel ternary Z-scheme system of WO3@MoS2/CdS is successfully constructed using a three-step wet-chemical route, where MoS2 locates between the rod-shaped WO3 and CdS nanoparticles and simultaneously plays multiple roles of the charge transfer mode switcher, electron-hole mediator and cocatalyst. As a charge transfer mode switcher, MoS2 can transform the conventional type-Ⅱ charge transfer mode to Z-scheme. In such a Z-scheme system, as an electron-hole mediator, MoS2 is applied to quench the energy of the electrons from WO3 and the holes from CdS in shorten length, and thus the more left electrons from CdS can transfer to MoS2, which can be further applied to photocatalytic evolution H2 owing to the cocatalyst role of MoS2. Benefitting from the multifunctional roles of MoS2, such a Z-scheme system of WO3@MoS2/CdS shows an enhanced photocatalytic performance.

Visible-light-driven, hierarchically heterostructured, and flexible silver/bismuth oxyiodide/titania nanofibrous membranes for highly efficient water disinfection

Constructing a flexible inorganic membrane photocatalyst for efficient visible-light-driven water disinfection is highly desired but remains a great challenge. Herein, we fabricated a flexible and heterostructured silver/bismuth oxyiodide/titania (Ag/BiOI/TiO2) nanofibrous membrane by combining the electrospinning technique with simple successive ionic layer adsorption and reaction (SILAR) and photodeposition process. In this ternary nanocomposite, ultrathin BiOI nanoplates were firmly anchored onto TiO2 nanofibers, while Ag nanoparticles were uniformly decorated on the surface of both BiOI and TiO2. Benefiting from the large surface area, improved visible-light absorption, and the effective interfacial charge transfer induced by multi-heterojunctions, the resultant Ag/BiOI/TiO2 membrane exhibited superior photocatalytic disinfection activity (7.5 log inactivation of E. coli within 1 h) under visible light illumination. Moreover, the plasmonic Z-scheme charge transfer mode was also proposed for Ag/BiOI/TiO2 system according to the band structure and reactive species analysis. More significantly, the Ag/BiOI/TiO2 membrane-based photoreactor could be facilely constructed for high-efficiency disinfection of high volume contaminated water, and the membrane still maintained good structural integrity and mechanical flexibility after utilization. This work may open up new avenues for designing and constructing flexible high-performance photocatalytic membranes for environmental applications.

Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer

AbstractIn upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M‐component or leader/return‐stroke‐like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC‐carrying channel at relatively short distance from the tower top, resulting in the so‐called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M‐component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with the M‐component charge transfer mode (including classical M‐component pulses and M‐component‐type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2‐Dimentional Finite‐Difference Time Domain method, in which the M‐component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, https://doi.org/10.1029/95JD01924 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M‐component and M‐component‐type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of the M‐component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M‐component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M‐component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch‐to‐channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E‐field and 1.9 for the H‐field. For a junction height greater than 6 km, the E‐field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, https://doi.org/10.1109/TEMC.2015.2483018) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed‐mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return‐stroke‐like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 μs or so) for which the tendency reverses. Finally, model‐predicted fields associated with different charge transfer modes, namely, return stroke, mixed‐mode, classical M‐component, and M‐component‐type ICC pulse are compared with experimental observations at the Säntis Tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed‐mode models (1.0 km for the return stroke and 0.8 km for the mixed‐mode pulse) are lower than the value of 2.0 km typically used in the literature.

Enhanced Photocatalytic Activities of RhB Degradation and H2 Evolution from in Situ Formation of the Electrostatic Heterostructure MoS2/NiFe LDH Nanocomposite through the Z-Scheme Mechanism via p-n Heterojunctions.

Designing of an efficient heterostructure photocatalyst for photocatalytic organic pollutant removal and H2 production has been a subject of rigorous research intended to solve the related environmental aggravation and enormous energy crises. Z-scheme-based charge-transfer dynamics in a p-n heterostructure could significantly replicate the inherent power of natural photosynthesis, which is the key point to affect the transportation of photoinduced exciton pairs. In this finding, a series of p-type MoS2 loaded with n-type NiFe-layered double hydroxide (LDH) forming a heterostructure MoS2/NiFe LDH were designed by electrostatic self-assembled chemistry and an in situ hydrothermal strategy for photocatalytic rhodamine B (RhB) dye degradation and H2 production. The creation of p-n heterojunctions of type-II and Z-scheme mode of charge transfer modified the optical and electronic property of the as-synthesized MSLDH3, thereafter promoting the generation, separation, and migration of photoinduced electron-hole pairs. The as-synthesized MSLDH3 showed superior photocatalytic activities in degradation of RhB with H2 evolution, which was enhanced by 3- and 4.5-fold and 10.9 and 19.2 times higher than that of NiFe LDH and MoS2, respectively. Last but not the least, heterostructure MSLDH3 possesses practical stability for its resultant enhanced photocatalytic activity with recyclability for everyday life.

Design and construction of Z-scheme Bi2S3/nitrogen-doped graphene quantum dots: Boosted photoelectric conversion efficiency for high-performance photoelectrochemical aptasensing of sulfadimethoxine

Rational design and fabrication of Z-scheme visible-light-driven photoactive materials have drawn much attention owing to their great potential in handling environment and energy crisis. In this work, Z-scheme Bi2S3/nitrogen-doped graphene quantum dots (NGQDs) with superior photoelectric conversion efficiency were designed and fabricated, which demonstrated enhanced photoactivity compared with Bi2S3 owing to the improved separation efficiency of photogenerated electron and hole pairs. The emphasis was put on designing Z-scheme Bi2S3/NGQDs, and then the mechanism of Z-scheme charge transfer mode was verified by the electron spin resonance (ESR) technique. On this basis, the proposed sensor exhibited a wide linear range of 0.1–120 nM and a detection limit of 0.03 nM (S/N = 3) for SDM, with high sensitivity (0.075 μA nM –1), good selectivity and stability. Moreover, the proposed PEC aptasensor using Bi2S3/NGQDs as the photoelectrode achieved sensitive and selective determination of sulfadimethoxine in milk samples. This work could provide some ideas for designing other Z-scheme photoactive species and insights into the charge transfer mechanism of Z-scheme. Furthermore, the promising applicability of PEC aptasensor using photoactive species could be extended to other accurate monitoring for contaminants.

Controllable synthesis of Cu2O decorated WO3 nanosheets with dominant (0 0 1) facets for photocatalytic CO2 reduction under visible-light irradiation

Systematical design and controllable assembly of nanostructured photocatalysts have received much attention in the field of CO2 reduction. The Cu2O decroted hexagonal WO3 nanosheets with and without dominant (0 0 1) facets (Cu2O/WO3-001 and Cu2O/WO3) were synthesized vertically on the surface of fluorine-doped stannic oxide (FTO) substrate and their photocatalytic performance for CO2 reduction were evaluated in the presence of H2O vapour under visible light irradiation (λ > 400 nm). The Cu2O/WO3-001 catalyst exhibited higher photocatalytic activity than those of Cu2O, WO3-001 and Cu2O/WO3. The maximal product yields of CO, O2 and H2 for Cu2O/WO3-001 after 24 h illumination reached 11.7, 5.7 and 0.7 μmol, respectively, and good cycling ability was discovered after 4 cycles. The (0 0 1) facet of hexagonal phase WO3 nanosheet was in favor of the H2O oxidation in the CO2 reduction process. Additionally, the Z-scheme charge transfer mode of Cu2O/WO3 heterojunction could promote photoinduced charge separation and enhance redox ability of the separated electrons and holes, leading to excellent photocatalytic CO2 reduction performance. The study may provide some insights into the coherent design of specific nanosheet photocatalysts with Z-scheme charge transfer for CO2 reduction.

Enhanced photocatalytic CO2 reduction activity of Z-scheme CdS/BiVO4 nanocomposite with thinner BiVO4 nanosheets

Construction of Z-scheme photocatalysts has drawn much attention in the field of CO2 reduction. However, research on photoreduction CO2 for monoclinic bismuth vanadate (m-BiVO4) is restricted due to its low conduction band potential and short electron diffusion lengths. To address the issues, we herein constructed a series of CdS/BiVO4 nanocomposites by depositing CdS on the surface of BiVO4 coupling with controlling the thickness of BiVO4 nanosheets. The morphological, crystalline, band alignment and optical properties of the samples are investigated intensively. Photocatalytic performance is evaluated by measuring the ability of the photocatalysts to convert CO2 into CO and hydrocarbon fuels, primarily CH4. The composites exhibit more efficient photocatalytic activity than CdS and BiVO4, and the yields of CH4 and CO vary depending on the thickness of BiVO4 substrate. The maximum yields of CH4 and CO for CdS/BiVO4 with 55–75 nm BiVO4 are 2.98 and 1.31 μmol g−1 after 5 h irradiation, while those for its counterpart with 15–30 nm BiVO4 attain 8.73 and 1.95 μmol g−1, respectively. The enhanced photoactivity of the composites is attributed to the band structure and Z-scheme charge transfer mode. Besides, thinner BiVO4 nanosheets are confirmed to be favorable for improving the photoreduction CO2 efficiency due to shorter electron diffusion lengths.

Elucidating mechanisms of Li plating on Li anodes of lithium-based batteries

Lithium metal is known as a very promising anode material for lithium-based batteries possessing a quite high theoretical capacity. But it has been kept away from practical applications due to its extreme reactivity and potential safety hazards led by serious dendrite growth. The origins of dendrite formation may be associated with the mechanisms of Li plating and with the mode of charge transfer during Li reduction or oxidation at the anode-electrolyte interface. Here, density functional theory (DFT) calculations are conducted to analyze the electron transfer between Li (100) and Li cations located in the proximity of the surface in several simulation models. The study includes two common used solvents: ethylene carbonate and dimethoxyethane (EC and DME), and a LiPF6 salt, that surround the Li cation over perfect, defect-containing, and Li2CO3-passivated Li (100) surfaces. Our calculations demonstrate that the Li cation is easily reduced when bonding to DME rather than EC and its preferred deposition site is the hollow site on both perfect and defective Li (100). Additionally, a compact Li2CO3 layer inhibits the charge transfer from Li metal to Li cations, thus modifying Li plating. It is concluded that the extreme reactivity of the Li metal surface induces a strongly inhomogeneous electron distribution upon deposition of a cation on the surface. This strong charge inhomogeneity may promote uneven Li nucleation and growth, eventually resulting in dendritic behavior.