Metal-nitrogen-co-doped graphene has great potential for use as a high-efficiency catalyst in energy applications. In this paper, density functional theory (DFT) with the projector-augmented wave and ...generalized gradient approximation (PAW-GGA) method was used to explore the catalytic activity of M@Gra (M = Ni, Pd, Pt, and Ru) on different types of graphene for oxygen reduction reaction (ORR) applications. Both the direct hydrogenation and dissociative mechanism of O2 are used to evaluate the ORR performance, and the binding energy of the intermediates, rate-determining step, overpotential, and activation energy of metal-nitrogen-co-doped graphene are considered. The catalytic properties of 4Ru@Gra and 1Pt@Gra make them the best candidates for ORRs, as 4Ru@Gra and 1Pt@Gra exhibit a stronger interaction (ΔG *OH) with the nanosheets and excellent ORR catalytic performance compared to other compounds. Precious metals have a significant influence on reducing O2 and decreasing the reaction energy, and the strong interaction of *O may lead to a high overpotential for the ORR process. This demonstrates that these compounds can moderately bind with the ORR intermediates by tuning the relative free energy, resulting in the ORR intermediates binding neither too strongly nor too weakly, and this may lead to slow or fast kinetics. The 1Ni@Gra support has a higher activation energy for O2 dissociation of 0.74 eV as well as a small activation energy of 0.13 eV, and the rate-determining step is controlled by the binding of *OH. The ORR reduction pathway occurs via direct hydrogenation with four-electron reduction, and it was determined that the energy barrier was 0.35 eV for the *OOH form, which is lower than the energy barrier (0.74 eV) of the 2O* species produced from the O2 dissociation in 1Ni@Gra. This indicates that the direct hydrogenation pathway is preferred as the most favorable of the ORR mechanisms.
This paper proposes a new method in construction fuzzy neural network to forecast travel speed for multi-step ahead based on 2-min travel speed data collected from three remote traffic microwave ...sensors located on a southbound segment of a fourth ring road in Beijing City. The first-order Takagi-Sugeno system is used to complete the fuzzy inference. To train the evolving fuzzy neural network (EFNN), two learning processes are proposed. First, a K-means method is employed to partition input samples into different clusters and a Gaussian fuzzy membership function is designed for each cluster to measure the membership degree of samples to the cluster centers. As the number of input samples increases, the cluster centers are modified and membership functions are also updated. Second, a weighted recursive least squares estimator is used to optimize the parameters of the linear functions in the Takagi-Sugeno type fuzzy rules. Furthermore, a trigonometric regression function is introduced to capture the periodic component in the raw speed data. Specifically, the predicted performance between the proposed model and six traditional models are compared, which are artificial neural network, support vector machine, autoregressive integrated moving average model, and vector autoregressive model. The results suggest that the prediction performances of EFNN are better than those of traditional models due to their strong learning ability. As the prediction time step increases, the EFNN model can consider the periodic pattern and demonstrate advantages over other models with smaller predicted errors and slow raising rate of errors.
Various methods have been proposed to analyse safety and risk of maritime transportation, through modelling techniques and empirical studies, focusing on ship–ship collision. However, an efficient ...method for screening traffic data for the near miss collisions is lacking. Therefore the contribution of this paper is two-fold. First, it proposes a novel method detecting possible near miss ship–ship collisions from AIS data. Second, it discusses how such near miss data can be used to gain further insight in safety of maritime transportation. The developed Vessel Conflict Ranking Operator (VCRO) considers the following factors affecting the complexity of an encounter between two ships: the distance between the two ships, the relative speed of the ships, and the difference between the headings of the ships. The model content and structure are based on expert judgment, whereas the parameterisation is based on AIS data points of a reference encounter situation dataset. The developed model has been applied to the traffic data from the Northern Baltic Sea. The obtained results and the model validity tests suggest the model being adequate for ranking encounters, and for prioritising the encounters to subject to further expert scrutiny.
•We propose a method detecting possible near miss ship–ship collisions from AIS data.•The model we propose can be used to gain further insight in safety of maritime transportation.•The method considers factors: distance, relative speed, and phase defined by course.•The model behaves as expected as maritime traffic over the Northern Baltic Sea.•The risk model can be used to rank ship–ship encounters of various risk levels.
•A Budyko model considering ΔS was used to identify seasonal streamflow changes.•In most cases, human activity had the largest impact on streamflow reduction.•ΔS effects became more important at ...smaller scales, with contributions up to 48%•Water use was the main human factor for the LM-HYK and TDG-HYK sections (60–90%)•Revegetation acted a more vital role in the TDG-LM while the LM-HYK was the check-dam.
Recent climate change and more intensive human activities have induced significant changes in streamflow along the middle reaches of the Yellow River basin (MRYRB), which has attracted considerable attention from the scientific community. However, most previous studies have focused on changes in annual streamflow by examining data from a small number of hydrological stations and the role of the various human activities remains unclear. Here we used an extended Budyko-based framework that considered changes in soil water storage (ΔS) to determine the contributions of changes in streamflow, both at the annual and seasonal scale. These analysis were conducted on 40 catchments and three sections (Toudaoguai–Longmen, TDG–LM; Longmen-Huayuankou, LM–HYK; and Toudaoguai–Huayuankou, TDG–HYK) in the MRYRB from 1971 to 2015. Results showed that streamflow at most catchments and sections declined dramatically after years of abrupt change detected by the Pettitt test, with decreases occurring at a faster rate during flood seasons (42.9%) than during non-flood seasons (31.8%). Although human behaviors were often the main cause of streamflow reductions at the annual and seasonal scales, the effects of ΔS became more important at increasingly finer scales. Indeed, they were of equal or greater importance than human impacts in some catchments, with corresponding relative contributions up to 48%. The effects of human activities may possibly have been overestimated or underestimated by 1–16% in three sections when the impact of ΔS was not considered. Further analysis indicated that human water use – particularly the rapid increase in water withdrawals for domestic purposes, electricity generation, and manufacturing – was the primary factor among human activities that affected streamflow reduction in the LM–HYK and TDG–HYK sections at different timescales, comprising 60–90% of all impacts. By contrast, the effects of water use and other human factors were almost equal in the TDG–LM section. Among the other human factors, vegetation restoration played a more critical role in the TDG–LM section, whereas the construction of check-dams was more important in the LM–HYK section. These findings of our study can enhance the understanding of hydrological changes in response to environmental factors.
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•The band structure, density of states, and differential charge density of samples were studied using density functional theory.•The experimental and calculated results show that the ...La3+ doping can increase the bandgap value of Bi2WO6, inhibit the recombination of e- and h+ pairs, and effectively improve the photocatalytic performance.•The degradation efficiency of 2% La-Bi2WO6 was the highest, and 99% of RhB can be removed within 90 min.
The La3+-doped Bi2WO6 nanoplate-like photocatalyst was successfully synthesized by the hydrothermal method. The results indicate that the degradation rate constant of RhB by La3+-doped Bi2WO6 is obviously higher than that of pure Bi2WO6. In addition, the ultraviolet–visible spectrum shows that La3+ doping can increase the band gap of Bi2WO6. The band structure, density of states (DOS), and differential charge density were studied using density functional theory (DFT). The possible photocatalytic mechanism of La3+-doped Bi2WO6 was studied by DFT and experiment combined investigations. The results show that La3+-doped Bi2WO6 is conducive to the separation of e- and h+ pairs, and the separated h+ and e- are activated by redox reactions in the valence band (VB) and conduction band (CB) respectively, which significantly improve the photocatalytic degradation process and separation efficiency. This result not only promotes the potential application of Bi2WO6 in semiconductor photocatalysts, but also provides new insights into the doping properties of Bi2WO6.
Abstract
With the development of industry and the rapid growth of population, the current water treatment technologies face many challenges. Hydrodynamic cavitation as a green and efficient means of ...water treatment has attracted much attention. During the hydrodynamic cavitation, enormous energy could be released into the surrounding liquid which causes thermal effects (local hotspots with 4600 K), mechanical effects (pressures of 1500 bar) and chemical effects (hydroxyl radicals). These conditions can degrade bacteria and organic substance in sewage. Moreover, the combination of hydrodynamic cavitation and other water treatment methods can produce a coupling effect. In this review, we summarize the methods of hydrodynamic cavitation and the performance of water treatment for different types of sewage. The application of hydrodynamic cavitation reactors with different structures in water treatment are also evaluated and discussed. The design and optimization of high-performance hydrodynamic cavitation reactor are the most crucial issues for the application of hydrodynamic cavitation in water treatment. Finally, recommendations are provided for the future progress of hydrodynamic cavitation for water treatment.
Two types of single metal atoms embedded in graphene were investigated as a potential electrocatalyst for oxygen reduction reaction (ORR) for the application in a fuel cell. ORR was considered in the ...four elementary reaction steps of oxygen hydrogenation, perhydroxyl production, atomic oxygen hydrogenation, and final water form. All calculations of catalytic activity were performed with the Vienna Ab Initio Simulation Package (VASP) on an M@Gra (M = Mn, Fe, Co, and Ir)–embedded structure, indicating that high-efficiency catalytic activity in the oxidation reaction takes place on the top of metal atom sites. Our calculations revealed that ORR is profiled via four-electron transfer pathway. Activity of these catalysts is closely related to the same scaling linear relations between the adsorption energies of the ORR intermediates on different catalytic surfaces; this can improve their catalytic activity for O
2
reduction through a high-efficiency 4e reaction path. Mn- and Ir-doped of cell A graphene exhibited excellent ORR catalytic performance in case of their small overpotential (less than 0.23 V) and low-energy barrier (less than 0.64 eV) of the Ir-doped graphene rate-determining step. Mn@Gra and Fe@Gra of cell B monolayers showed poor ORR catalytic performance due to the strong interaction between various ORR-involved species. Based on the free energy change and activation energy of each intermediate reaction in ORR, Fe@Gra and Ir@Gra are promising catalysts for ORR processes in fuel cells. This provides useful guidance for different types of catalysts in applications to fuel cells.
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•CIP sorbed in interlayer space could be degraded under simulated solar irradiation.•Photodegradation of CIP in interlayer space was more rapid than that in water.•Degradation ...mechanisms, products, and pathways were different from those in water.
Although photolysis of antibiotics in aqueous solution was widely studied for a better understanding of their photolytic behavior in aqueous phase, the knowledge about photodegradation of antibiotics adsorbed on solid surfaces is still very limited. In this study, photodegradation of ciprofloxacin (CIP), a fluoroquinolone antibiotic, adsorbed in the intracrystalline space of montmorillonite (MMT) was examined using a xenon light source (300 W, λ > 320 nm). The gradual decrease of basal spacing of MMT from 1.66 to 1.46 nm with irradiation confirmed CIP decomposition in the intracrystalline space under simulated solar irradiation. Nearly 70 percent of adsorbed CIP was degraded after 5 h irradiation, and the reaction followed the first-order kinetics with a rate constant roughly 3 times than that in aqueous solution, indicating more efficient photodegradation of CIP after being adsorbed in the intracrystalline space of MMT. Spectroscopic analysis revealed that direct photolysis was the main photolytic mechanism. The hydroxyl radical induced by irradiated MMT might play an important role. The major photoproducts were identified with liquid chromatography-tandem mass spectrometry, and the main degradation pathways were proposed. The results demonstrated that the photoproduct distribution and degradation pathways of CIP adsorbed in the intracrystalline space differed from those in aqueous solution.
•A novel rotor-radial groove (RRG) hydrodynamic cavitation reactor was proposed with good cavitation intensity and energy utilization.•The cavitation performance of rectangular-shaped CGU was better ...than the cylindrical-shaped CGU.•The cavitation performance could be improved more effectively by increasing the rotor speed and decreasing the interaction distance.
Hydrodynamic cavitation was widely used in sterilization, emulsion preparation and other industrial fields. Cavitation intensity is the key performance index of hydrodynamic cavitation reactor. In this study, a novel rotor-radial groove (RRG) hydrodynamic cavitation reactor was proposed with good cavitation intensity and energy utilization. The cavitation performances of RRG hydrodynamic cavitation reactor was analyzed by utilizing computational fluid dynamics method. The cavitation intensity and the cavitation energy efficiency were used as evaluation indicators for RRG hydrodynamic cavitation reactor with different internal structures. The amount of generated cavitation for various shapes of the CGU, interaction distances and rotor speed were analyzed. The evolution cycle of cavitation morphology is periodicity (0.46 ms) in the CGU of RRG hydrodynamic cavitation reactor. The main cavitation regions of CGU were the outflow and inflow separation zones. The cavitation performance of rectangular-shaped CGU was better than the cylindrical-shaped CGU. In addition, the cavitation performance could be improved more effectively by increasing the rotor speed and decreasing the interaction distance. The research results could provide theoretical support for the research of cavitation mechanism of cavitation equipment.
Evapotranspiration (ET) is a key ecological process connecting the soil-vegetation-atmosphere system, and its changes seriously affects the regional distribution of available water resources, ...especially in the arid and semiarid regions. With the Grain-for-Green project implemented in the Loess Plateau (LP) since 1999, water and heat distribution across the region have experienced great changes. Here, we investigate the changes and associated driving forces of ET in the LP from 2000 to 2012 using a remote sensing-based evapotranspiration model. Results show that annual ET significantly increased by 3.4 mm per year (p = 0.05) with large interannual fluctuations during the study period. This trend is higher than coincident increases in precipitation (2.0 mm yr
), implying a possible pressure of water availability. The correlation analysis showed that vegetation change is the major controlling factor on interannual variability of annual ET with ~52.8% of pixels scattered in the strip region from the northeastern to southwestern parts of the LP. Further factorial analysis suggested that vegetation greening is the primary driver of the rises of ET over the study period relative to climate change. Our study can provide an improved understanding of the effects of vegetation and climate change on terrestrial ecosystem ET in the LP.
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