The modern ammonia synthesis industry founded by Haber-Bosch in 1913 has successfully altered the history of food production, fed explosive population growth, and laid the foundation of heterogeneous ...catalysis and chemical engineering as well. However, its reliance on fossil fuels for reactant H
2
production consumes 1-3% of the world's electric energy and 2-5% of the world's natural gas, accompanied by more than 400 million tons of CO
2
emission annually. Making use of water as the proton source and electric energy to drive the ammonia synthesis reaction will reduce the fossil fuel consumption and CO
2
emission and is thus regarded as a green and sustainable alternative to the conventional Haber-Bosch process. To date, some excellent reviews on electrochemical ammonia synthesis have been published, but most of them were organized according to the type of catalyst. A systematic summary of the performance-improving strategies of the electrocatalyst for ammonia synthesis is rarely reported and therefore highly desirable. In this review, the nitrogen reduction reaction mechanisms and recent theoretical advances are briefly outlined first. Then, strategies for both reactivity and selectivity enhancement of catalysts and catalytic systems are methodically discussed. Last, criteria for the electrochemical nitrogen reduction reaction, ammonia quantification methods, and an outlook for further research are also concluded. This review aims to provide systematic and concise guidance for the design of highly efficient and selective electrochemical ammonia synthesis systems.
A systematic summary of strategies to improve the performance of electrochemical NRR catalysts and NRR catalytic systems.
The main contributions of this article are twofold. Firstly, a guidance law based on a nested saturation function combined with the I&I methodology is proposed for controlling VTOL vehicles subject ...to mass uncertainty and thrust saturation simultaneously. To simplify the calculations, the virtual attitude extracted from the guidance law is propagated through a command filter, the output of which is tracked by the attitude subsystem. The other contribution is that the influence of the command filter’s frequency on the closed-loop system is rigorously analyzed. The main difficulty in proving the stability is that the command filter’s tracking performance could not be guaranteed when the thrust force encounters the singularity problem. The study avoids this problem by utilizing the properties of nested saturation functions and establishes the semi-global ultimate boundness of the overall closed-loop system. Finally, simulations are presented to show the effectiveness of the proposed control scheme.
Biochars are anthropogenic carbonaceous sorbent and their influences on the sorption of environmental contaminants need to be characterized. Here we evaluated the effect of
Pinus radiata derived ...biochars on soil sorption and desorption of phenanthrene. Two biochars separately produced at 350 °C and 700 °C and three soils were tested. Biochar amendment generally enhanced the soil sorption of phenanthrene. The biochar produced at 700 °C generally showed a greater ability at enhancing a soil’s sorption ability than that prepared at 350 °C. The single-step desorption measurement showed an apparent hysteresis in biochar-amended soils. After 28 d equilibration, the sorptive capacity of biochar-amended soil (with an organic carbon content of 0.16%) significantly decreased. This study clearly suggested that biochar application enhanced soil sorption of hydrophobic organic compounds, but the magnitude of enhancement depended on the preparation of biochars, the indigenous soil organic carbon levels, and the contact time between soil and biochar.
Pinus radiata derived biochars influence soil sorption and desorption of phenanthrene.
The addition of ZrMZ into sediments reduced the potential of phosphate–P release from sediments as well as increased the phosphate–P adsorption capacity of sediments.
•A new adsorbent material, i.e., ...zirconium-modified zeolite (ZrMZ) was synthesized.•The ZrMZ was applied to control phosphate–P (PO43−–P) release from sediments.•ZrMZ addition into sediments reduced the potential of PO43−–P release from sediments.•ZrMZ addition into sediments increased the PO43−–P adsorption capacity of sediments.•Most of PO43−–P bound by ZrMZ was unlikely to be released under reducing conditions.
Zirconium-modified zeolite (ZrMZ) may be a lake remediation tool designed to control the internal phosphorus (P) loading from sediments. Batch experiments were conducted to investigate the effect of adsorbent dosage on the adsorption of phosphate on ZrMZ, as well as the adsorption characteristics of phosphate on the raw and ZrMZ-amended sediments. The sequential extraction methods were used to investigate the forms of P in the phosphate-adsorbed ZrMZ. The ZrMZ was effective for the removal of phosphate from water. The sequential extraction of P from the phosphate-adsorbed ZrMZ under laboratory conditions suggested that about 6% of P bound by ZrMZ was release-sensitive, while about 94% of bound P was unlikely to be released under reducing and common pH (5–9) conditions. The equilibrium adsorption data of phosphate on the raw and ZrMZ-amended sediments at initial P concentrations of 1–12mg/L could be described by the Langmuir and Freundlich isotherm models. The adsorption kinetics of phosphate on the raw and ZrMZ-amended sediments followed a pseudo-second-order model, and the adsorption process was spontaneous and endothermic in nature. The presence of Cl− or SO42− showed no competing effect on the adsorption of phosphate on the raw and ZrMZ-amended sediments, while the presence of HCO3− or SiO32− inhibited the adsorption of phosphate. The zero-equilibrium P concentration (EPC0) for the ZrMZ-amended sediment was much lower than that for the raw sediment. The phosphate adsorption capacity for the ZrMZ-amended sediment was much higher than that for the raw sediment. Results of this work indicate that the addition of ZrMZ into the lake sediment can reduce the potential of phosphate–P release from the sediment as well as can increase the phosphate–P adsorption capacity of the sediment.
An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal ...template induced precursor solution dipping strategy, different periodic arrays of semi‐hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb‐shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template‐induced chemical deposition. Additionally, a honeycomb‐shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb‐shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10−11 M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.
Via a colloidal template‐induced precursor solution dipping strategy, a semi‐hollow sphere array is formed, and its morphology changed to a novel ordered honeycomb‐shaped micro/nanostructured array after magnetron sputtering deposition. After coating a gold thin layer, the periodic array is used as SERS active substrate and demonstrates very stable SERS performance.
Sodium-sulfur (Na-S) batteries hold great promise for cutting-edge fields due to their high specific capacity, high energy density and high efficiency of charge and discharge. However, Na-S batteries ...operating at different temperatures possess a particular reaction mechanism; scrutinizing the optimized working conditions toward enhanced intrinsic activity is highly desirable while facing daunting challenges. This review will conduct a dialectical comparative analysis of Na-S batteries. Due to its performance, there are challenges in the aspects of expenditure, potential safety hazards, environmental issues, service life and shuttle effect; thus, we seek solutions in the electrolyte system, catalysts, anode and cathode materials at intermediate and low temperatures (T < 300 °C) as well as high temperatures (300 °C < T < 350 °C). Nevertheless, we also analyze the latest research progress of these two situations in connection with the concept of sustainable development. Finally, the development prospects of this field are summarized and discussed to look forward to the future of Na-S batteries.
Bisphenol A (BPA), a controversial endocrine disruptor, is ubiquitous in the aquatic environment. In this study, the oxidative degradation of BPA and its mechanism using zero valent aluminum ...(ZVAl)–acid system under air-equilibrated conditions was investigated. Under pH <3.5 acidic conditions, ZVAl demonstrated an excellent capacity to remove BPA. More than 75% of BPA was eliminated within 12 h in pH 1.5 reaction solutions initially containing 4.0 g/L aluminum and 2.0 mg/L BPA at 25 ± 1 °C. The removal of BPA was further accelerated with increasing aluminum loadings. Higher temperature and lower initial pH also facilitated BPA removal. The addition of Fe
2+ into the ZVAl–acid system significantly accelerated the reaction likely due to the enhancing transformation of H
2O
2 to HO
via Fenton reaction. Furthermore, the primary products or intermediates including monohydroxylated BPA, hydroquinone, 2-(4-hydroxyphenyl)propane and 4-isopropenylphenol, were identified and a possible reaction scheme was proposed. The remarkable capacity of the ZVAl–acid system in removing BPA displays its potential application in the treatment of organic compound–contaminated water.
► The zero valent aluminum–acid system possesses a relatively high oxidative capacity in removing aqueous BPA. ► Acidic conditions (pH < 3.0) facilitate the reaction. ► Ferrous ion (Fe
2+) accelerates the reaction. ► Humic acid suppresses the reaction.
Soil organic carbon (SOC) is a sensitive indicator of climate change, and small changes in the soil carbon pool will affect the carbon balance. Accurate and robust SOC quantitative prediction is of ...great significance to studying the carbon budget of swamp wetlands and its response to climate change. In this study, a new framework was proposed and assessed for predicting the SOC content based on Sentinel-2 (S2), Sentinel-1 (S1), and the digital elevation model (DEM) together with the extreme gradient boosting with random forest (XGBRF) model. The determination coefficient (R 2 ), root mean square error (RMSE), mean absolute error (MAE), and Lin's concordance correlation coefficient (LCCC) were applied to assess the performances of the models. The results revealed that the prediction performance of the XGBRF regression model was much better than that of extreme gradient boosting and random forest regression models. Compared with single sensor data, using multisensor data to predict the SOC content yielded more accurate results. The XGBRF model based on S1, S2, and DEM fusion yielded the highest prediction accuracy (R 2 _testing = 0.6639, RMSE = 1.3236 g/kg, MAE = 1.2546 g/kg, LCCC = 0.7621). Regarding the importance of the variables, the S1 and S2 features were major contributors to the SOC content prediction (41% and 52%, respectively), followed by the topographic variables extracted from the DEM (7%). The proposed framework can be used for SOC prediction based on a small sample dataset, and it provides a method for long-term and rapid monitoring of the SOC contents in wetlands.
A tropical storm (TS) Roanu occurred in northern Sri Lanka in 2016, which transported northwards along the west coast of the Bay of Bengal (BoB). During the development of the TS, ocean eddies on its ...track had an important effect on the intensity of Roanu. The dynamic mechanism was investigated with multisource reanalysis and Argo float data in this study. The results show that ocean eddies were the main reason why Roanu first enhanced, weakened, and then enhanced again. Warm eddy W1 supports the initial development of the TS, cold eddy C1 weakens Roanu, and warm eddy W2 continues to support Roanu. On May 19, 2016, the maximum average latent heat flux over W1 was 260.85 w/m2, while that of C1 was only 200.71 w/m2. After the passage of Roanu, the tropical cyclone heat potential (TCHP) of eddies significantly decreased. The TCHP of W1, W2, C1 and C2 decreased by 20.95 kJ/cm2, 11.07 kJ/cm2, 29.82 kJ/cm2, 9.31 kJ/cm2, respectively. The mixed layer of warm eddies deepened much more than that of cold eddies, supporting Roanu development. In addition, changes in potential vorticity (PV) values caused by the disturbance of eddies may also reflect changes in the TS intensity. This study offers new insights on the influence of ocean eddies in regulating the development of tropical cyclone (TC) in the BoB.
To achieve the goal of collecting lunar samples and return to the Earth for the Chang’E-5 spacecraft, the lander and ascender module (LAM) of the Chang’E-5 spacecraft successfully landed on the lunar ...surface on 1 Dec., 2020. The guidance, navigation, and control (GNC) system is one of the critical systems to perform this task. The GNC system of previous missions, Chang’E-3 and Chang’E-4, provides the baseline design for the Chang’E-5 LAM, and the new characteristics of the LAM, like larger mass and liquid sloshing, also bring new challenges for the GNC design. The GNC design for the descent and landing is presented in this paper. The guidance methods implemented in the powered descent are presented in detail for each phase. Propellant consumption and hazard avoidance should be particularly considered in the design. A reconfigurable attitude control is adopted which consists of the quaternion partition control, phase and gain stabilization filter, and dual observer. This controller could provide fast attitude maneuver and better system robustness. For the navigation, an intelligent heterogeneous sensor data fusion method is presented, and it is applied for the inertial measurement unit and velocimeter data. Finally, the flight results of the LAM are shown. Navigation sensors were able to provide valid measurement data during descent, and the thrusters and the main engine operated well as expected. Therefore, a successful soft lunar landing was achieved by the LAM.
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