Surface roughness is an important factor that affects dynamic wetting behavior, which can improve the surface hydrophobicity, so it is of great significance to obtain a better understanding of ...roughness effect from both theoretical and practical perspectives. In this paper, we studied the influence of macro-size surface roughness on contact angle hysteresis and spreading work and analyzed the relationship between contact angle hysteresis and spreading work. Results showed that as the surface roughness increased, both the advancing contact angle and the receding contact angle continued to increase until their maximum values were reached, and then started to decrease within the range of surface roughness studied, while the contact angle hysteresis presented the opposite trend. In addition, with the increase of surface roughness the spreading work initially increased to a certain maximum value, then continuously decreased to the minimum value, and then began to increase within the range of the surface roughness studied. These trends could be attributed to the surface wetting state (Wenzel state, Cassie state, and transition state) changing with the change of surface roughness. These findings can provide guidance for the preparation of wetted surfaces with specific functions, especially when it is required to change the wettability without changing the surface chemical properties.
Rational design and bottom-up synthesis based on the structural topology is a promising way to obtain two-dimensional metal–organic frameworks (2D MOFs) in well-defined geometric morphology. Herein, ...a topology-guided bottom-up synthesis of a novel hexagonal 2D MOF nanoplate is realized. The hexagonal channels constructed via the distorted (3,4)-connected Ni2(BDC)2(DABCO) (BDC = 1,4-benzenedicarboxylic acid, DABCO = 1,4-diazabicyclo2.2.2octane) framework serve as the template for the specifically designed morphology. Under the inhibition and modulation of pyridine through a substitution–suppression process, the morphology can be modified from hexagonal nanorods to nanodisks and to nanoplates with controllable thickness tuned by the dosage of pyridine. Subsequent pyrolysis treatment converts the nanoplates into a N-doped Ni@carbon electrocatalyst, which exhibits a small overpotential as low as 307 mV at a current density of 10 mA cm–2 in the oxygen evolution reaction.
•The drag coefficient of a single bubble rising in water was studied experimentally.•An improved drag model for bubble was obtained based S-N drag model.•The proposed model obtained good agreement ...with the experiment (within 0.4%).•The proposed model gives a better prediction of data from existing literature.•The proposed model can capture the fluctuation of drag coefficient.
The drag coefficient has a significant effect on the calculation of bubble motion. This paper experimentally investigated the drag coefficient of a single bubble rising in deionized water with the help of a high-speed video system. First, it is found that the terminal velocity presented periodical fluctuation, indicating that the drag coefficient is not a constant value. Then the measured drag coefficient was compared with correlations available in literatures. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated drag coefficient. Based on massive data analysis, a new correlation combined Reynolds number, Eotvos number and Weber number was proposed to calculate the fluctuation of drag coefficient. The drag coefficient predicted by this new model is in excellent agreement with the experimental results over the range of 550⩽Re⩽1700, and the largest relative error is less than 0.4%. Comparing with data of water from existing literature under the condition of 8<Re<12,000 and 0.01<Eo<600, the proposed model gives better predictions than available drag models.
The purpose of this study was to investigate the effect of particle size on lignite reverse flotation with a focus on reverse flotation kinetics in the presence of sodium chloride. Six flotation ...kinetic models were applied to data from the tests using the 1stOpt statistical analysis software package to estimate the relationship between the flotation rate constant, the maximum ash flotation recovery and the particle size. Within the range studied, the best reverse flotation performance was obtained at a grinding fines (−74-μm size fraction) content of 42.34% with a concentrate ash content of 11.30% at 65.29% combustible recovery after 20min of flotation time. The results show that all kinetic models except the classical first-order flotation kinetic model gave excellent fits to the experimental data under various grinding fines contents and various size fractions. The high flotation rate constant was limited to a narrow particle size range. The maximum flotation rate constant was obtained at a grinding fines content of 42.34% and with the −250+150μm fraction. We concluded that the reverse flotation of lignite in the presence of sodium chloride can be described with the first-order and second-order models. Furthermore, the reverse flotation performance as a function of particle size was further evaluated using the reverse flotation efficiency index. We found that the −425-μm size fraction with a grinding fines content of 42.34% resulted in the greatest index value compared with the investigated narrow size fractions at any given flotation time.
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The spreading behavior of droplets on solid surfaces in air has been widely investigated; however, relatively few studies are conducted on the spreading of oil droplets over solid surfaces in aqueous ...environments, and furthermore, the differences in the oil droplet spreading behavior in the two media environments have not been specifically reported. In this work, the spreading dynamics behavior of a millimeter-sized oleic acid droplet (referred to as oil droplet) on a highly hydrophilic substrate (glass slide) in air and deionized water environments was studied in terms of dynamic contact angle by using a high-speed imaging technology, and their spreading behavior differences were revealed. Results showed that the spreading of an oil droplet on the glass slide in air could be divided into three stages: the early linear rapid spreading stage dominated by inertial force, the intermediate exponential slow spreading stage dominated by viscous forces and the long-term spreading stage tending to the quasi-equilibrium state. In contrast, the spreading process of oil droplets on glass slides in deionized water consisted of two sub-processes: the initial linear slow spreading process and the long-term spreading process tending to the equilibrium state. It is clear that the spreading behavior of oil droplets on glass slides in air and deionized water was different, and their differences were mainly due to the presence of the hydration layer on the glass slide surface and the action of the fluid around the oil droplet in deionized water. These findings can provide guidance for the recovery of crude oil in geological reservoirs and help to understand the spreading mechanism of oil droplets on solid surfaces.
Graphical abstract
Increasing global population and decreasing arable land pose tremendous pressures to agricultural production. The application of conventional chemical fertilizers improves agricultural production, ...but causes serious environmental problems and significant economic burdens. Biochar gains increasing interest as a soil amendment. Recently, more and more attentions have been paid to biochar-based slow-release of fertilizers (SRFs) due to the unique properties of biochar. This review summarizes recent advances in the development, synthesis, application, and tentative mechanism of biochar-based SRFs. The development mainly undergoes three stages: (i) soil amendment using biochar, (ii) interactions between nutrients and biochar, and (iii) biochar-based SRFs. Various methods are proposed to improve the fertilizer efficiency of biochar, majorly including in-situ pyrolysis, co-pyrolysis, impregnation, encapsulation, and granulation. Considering the distinct features of different methods, the integrated methods are promising for fabricating effective biochar-based SRFs. The in-depth understanding of the mechanism of nutrient loading and slow release is discussed based on current knowledge. Additionally, the perspectives and challenges of the potential application of biochar-based SRFs are described. Knowledge surveyed from this review indicates that applying biochar-based SRFs is a viable way of promoting sustainable agriculture.
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•Enhancing nutrient utilization in fertilizers is an urgent demand.•The development of biochar-based slow-release fertilizers is briefly summarized.•Various methods proposed for biochar-based SRFs synthesis are reviewed.•Biochar-based slow-release fertilizers are viable for promoting sustainable agriculture.
The breakage and liberation of minerals are the key to fluidized mining for minerals. In the ball milling process, steel balls function as not only a grinding action implementer but also energy ...carrier to determine the breakage behavior of ores and the production capacity of the mill. When ground products present a much coarse or much fine particle size distribution, the separation process will suffer, resulting in inefficient recovery of useful minerals. Optimal control of the particle size distribution of the products is therefore essential, but the complexity and randomness of ball mill grinding make it difficult to determine the appropriate ball size. To solve the problem in the precise measurement of grinding ball diameters, this paper carried out magnetite grinding experiments with grinding balls of different diameters under the same grinding conditions to study the influence pattern of steel ball diameters on the particle break behavior, the particle size distribution of ground products, and the mineral liberation degree distribution. The research proposed on the matching relation between the ball size and the quality of ground products is essential for improving the ground product quality and reducing energy consumption.
Materialization of coal is one of effective and clean pathways for its utilization. The microstructures of coal-based carbon materials have an important influence on their functional applications. ...Herein, the microstructural evolution of anthracite in the temperature range of 1000–2800 °C was systematically investigated to provide a guidance for the microstructural regulation of coal-based carbon materials. The results indicate that the microstructure of anthracite undergoes an important change during carbonization-graphitization process. As the temperature increases, aromatic layers in anthracite gradually transform into disordered graphite microcrystals and further grow into ordered graphite microcrystals, and then ordered graphite microcrystals are laterally linked to form pseudo-graphite phase and eventually transformed into highly ordered graphite-like sheets. In particular, 2000–2200 °C is a critical temperature region for the qualitative change of ordered graphite crystallites to pseudo-graphite phase, in which the relevant structural parameters including stacking height, crystallite lateral size and graphitization degree show a rapid increase. Moreover, both aromaticity and graphitization degree have a linear positive correlation with carbonization-graphitization temperature in a specific temperature range. Besides, after initial carbonization, some defect structures in anthracite such as aliphatic carbon and oxygen-containing functional groups are released in the form of gaseous low-molecular volatiles along with an increased pore structure, and the intermediates derived from minerals could facilitate the conversion of sp3 amorphous carbon to sp2 graphitic carbon. This work provides a valuable reference for the rational design of microstructure of coal-based carbon materials.
In this work, the assembly behavior and structure of a compound collector with different carboxyl group positions at the low-rank coal (LRC)-water interface were investigated through coarse-grained ...molecular dynamics simulation (CGMD) combined with sum-frequency vibration spectroscopy (SFG). The choice of compound collector was dodecane +decanoic acid (D-DA) and dodecane +2-butyl octanoic acid (D-BA). CGMD results showed that the carboxyl group at the carbon chain's middle can better control the assembly process between carboxylic acid and D molecules. SFG research found that the carboxyl group at the carbon chain's termination had a greater impact on the displacement of the methyl/methylene symmetric stretching vibration peak, while the carboxyl group at the carbon chain's middle had a greater impact on the displacement of the methyl/methylene asymmetric stretching vibration peak. The spatial angle calculation results revealed that the methyl group's orientation angle in the D-BA molecule was smaller and the carboxyl group's orientation angle in the BA molecule was bigger, indicating that D-BA spread more flatly on the LRC surface than D-DA. This meant that the assembled structure had a larger effective adsorption area on the LRC surface. The flotation studies also verified that the assembly behavior and structure of D-BA with the carboxyl group at the carbon chain's middle at the LRC-water interface were more conducive to the improvement of flotation efficiency. The study of interface assembly behavior and structure by CGMD combined with SFG is crucial for the creation of effective compound collectors.
The pollutants degradation rate of iron ore tailings–based heterogeneous catalysts is the main factor limiting its application. Herein, an iron ore tailings–based Fenton-like catalyst ...(I/W(3:1)-900-60) with a relatively fast catalysis rate was constructed by co-pyrolysis (900°C, 60 min holding time) of iron ore tailings and wheat straw with a mass ratio of 3:1. With wheat straw blending, the generated I/W(3:1)-900-60 presented a larger surface area (24.53 m
2
/g), smaller pore size (3.76 nm), reduced iron species (Fe
2+
from magnetic), and a higher catalytic activity (0.0229 min
−1
) than I-900-60 (1.32 m
2
/g, 12.87 nm, 0.012 min
−1
) pyrolyzed using single iron ore tailing under the same pyrolysis conditions. In addition, biochar and iron ore tailings in I/W(3:1)-900-60 were tightly combined through chemical bonding. The optimal catalyst remains active after three cycles, indicating its catalytic stability and recyclability. The good Fenton-like methylene blue degradation efficiency of I/W(3:1)-900-60 was ascribed to the sacrificial role of biochar, as well as the electron transfer between biochar and iron active sites or the redox cycles of ≡Fe
3+
/Fe
2+
. This finding provides a facile construction strategy for highly active iron ore tailings–based Fenton-like catalyst and thereby had a great potential application in wastewater treatment.
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