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• A steady cone-jet occurs in a greater range of liquid flow rates for a hemispherical capillary. • Varicose and whipping regimes are easily obtained with a hemispherical nozzle. • The transition from varicose and whipping usually depends on interfacial forces on the jet. • A general parameter to determine varicose, transition, and whipping regimes is presented. A cone-jet regime in electrohydrodynamic atomization (EHDA) is widely applied into printing, electro-spinning, spray-coating, and biological mass spectrometry. Regulating different instabilities of jet is crucial for optimizing its operating parameters. In present work, an atypical, hemispherical capillary with inner diameter of 0.40 mm and cap size of 6.20 mm was employed as atomization nozzle, through which a steady cone-jet regime was confirmed versus suitable feeding liquid flow rate and electric potential. A permanent and highly charged jet emits from a Taylor cone apex and further disintegrates into fine highly charged drops in the form of varicose or whipping instabilities. The results indicate that a steady cone-jet is observed in the specific ranges of the feeding liquid flow rate, electric potential and conductivity. The typical breakup instabilities including varicose and whipping are clearly observed with an increase in liquid flow rate for a fixed electric potential for most of liquids, and the transition from varicose to whipping instability easily occurs. For a steady cone-jet, the jet breakup instabilities usually depends on the competition between interfacial forces on the electrified jet. The transition process involving a low-viscosity jet with a large flow rate is observed, and the general parameter G = Γ 2 δ μ 0.52 is calculated to account for surface charge, surface tension, and viscosity effects, where Γ is the electric force to surface tension ratio and δ μ is the inertia to viscous force ratio. Finally, the varicose, transition regime, and whipping are classified with first and second critical threshold values G = 40 and G = 102, respectively. Meanwhile, as the electrified jet transforms from varicose to whipping instabilities, the jet breakup length shows a trend of increasing first and then decreasing. [ABSTRACT FROM AUTHOR]

• The necking time is independent of electric field in a reasonable range of flow rate. • The transition from dripping to jetting is enhanced by electric field for relatively small tube. • A model for the transition from periodic dripping to jetting is established in an electric field. • A critical criterion for the transition is presented and in reasonable agreement with experiments. A liquid is issued from the outlet of the capillary tube vertically, and drop formation may be in the form of periodic dripping, dripping faucet and jetting, which usually depends on flow rate or Weber number. We consider the critical Weber number (W e C = ρV 0 2 D / σ) at which the transition from periodic dripping to jetting occurs in the presence of an electric field, where high-resolution images are recorded. The necking time is mainly related to nozzle diameter and surface tension, and independent of electric potential and flow rate (in a reasonable range).The first threshold limit decreases with an increase in electric potential, where the dripping faucet is clearly affected and the point of drop detachment gradually increases. When the drop formation is in the form of dripping faucet, the transition from dripping faucet to jetting regime is enhanced by electric potential, where a sudden transition could be observed in an extremely limited range of liquid flow rate. The critical criterion (Weber number) is presented to determine the transition from dripping to jetting in the presence of an electric field. The critical Weber number is in a reasonable agreement with the experiment, although the predicted results are quantitatively divergent with experimental data. [ABSTRACT FROM AUTHOR]

A two-stage process has been developed for the pyrolysis of high-density polyethylene to obtain light olefins, where probable mechanisms for each stage pyrolysis were proposed in our previous study. This work aims to establish molecular-level kinetic models for the first-stage pyrolysis at a lower temperature and for the second-stage pyrolysis at a higher temperature, respectively, to predict the overall reaction performances in accordance to the role of detailed mechanisms. A structure-oriented lumping (SOL) method based molecular-level kinetic model can effectively describe the first-stage pyrolysis, while a detailed molecular-level kinetic model is developed for the second-stage pyrolysis to track the evolutions of all alkanes, olefins, and diolefins, with special focus on the formation of light olefins. The established separate models can achieve the automatic generation of complex reaction networks and present good agreement with experimental data obtained from the first- and second-stage. In addition, the first-stage model indicates that the random scission plays an important role in the pyrolysis process at lower temperatures, while the chain-end scission mechanism dominates the second-stage reaction to produce light olefins at higher temperatures. As a whole, the molecular-level modelling scheme behaves excellently at a wide range of temperature, which provides guidance for upgrading the pyrolysis process. • A molecular level kinetic model is established for the two-stage HDPE pyrolysis. • The reaction network is generated automatically and visualized. • This model achieves excellent agreement with experimental data. • The competition of two scissions and important role of temperature are quantified. [ABSTRACT FROM AUTHOR]

• The onset and termination electric potential to form the steady cone-jet electrospray increase as conductivity increasing. • The lower and upper limitation of liquid flowrate to form the steady cone-jet electrospray decrease as conductivity increases. • The varicose instability can transform into whipping instability as the electrical conductivity increasing. • The jet breakup instability transition mechanism is interpreted by theoretical analysis. • The whipping to similar micro-dripping instability can be observed for EG with higher conductivity. In present work, the effect of the electrical conductivity on the steady cone-jet electrospray are experimentally investigated, where the operating diagram and the jet breakup instability are extensively examined. A hemispherical tube is employed as spraying nozzle severed as high electric potential electrode in a needle-plated electrode configuration compared to the common and sheathed tubes. The cone-jet electrospray is visualized by a high-resolution camera and extensively analyzed offline. The aqueous solution in ethanol, Diethyleneglycol (DEG) and Ethylene glycol (EG) are atomized with varied electrical conductivity under different high electric potentials and flowrates. Experimental results indicate that the cone-jet electrospray can operate in the certain ranges of operating parameter for all types of capillaries. The operating diagram for the hemispherical tube is significantly broader than other tubes because of various electric field strength distribution. The onset electric potential to determine a steady cone-jet electrospray gradually increases and the termination value also increases as the electrical conductivity increases. The lower and upper flowrate to form a steady cone-jet electrospray also increase as the electrical conductivity increases. The jet breakup instability can transit from varicose to whipping due to low the reference flow rate as electrical conductivity increases, which is agreement with theoretical analysis. In particular, for EG, the transition from whipping to similar micro-dripping is observed as the electrical conductivity increases, while the transition also occurs as flowrate increases for EG with higher electrical conductivity. The increase in the electrical conductivity and flowrate elongates the cone due to EHD body force, which causes the electric field varying, further resulting in the difference in jet breakup instability. Moreover, the electrical conductivity also plays an important role in jet breakup length. The instability variation of jet with conductivity (DEG), q V =1000 nL/s, ϕ =8.00 kV (Hemispherical nozzle with D o =0.70mm); The variation with liquid flow rate of EG with higher conductivity (K =8.5 × 10−4 s/m, ϕ =10.20 kV, (Hemispherical nozzle with D o =0.70mm) [Display omitted] [ABSTRACT FROM AUTHOR]

Waste plastics have emerged as a global environmental issue. Polyethylene, accounting for about 25% of global plastic production, has been acknowledged as the major cause of "white pollution". In this paper, a generalized molecular-level kinetic model was proposed to understand the pyrolysis of polyethylene applying structure-oriented lumping, Poisson distribution, and genetic algorithm. The number of ordinary differential equations derived from the reaction kinetics were dramatically reduced by this simplified network with 14-rule design. The generalizability was confirmed by case studies without any change in the rule design. Under most conditions, the mean relative error between experimental and model data could be controlled within 5%, while abnormal deviations indicate the obstacle of heat transfer. The simulation curve could provide guidance for the experiments by locating the peak value of products. From 400–470 °C in Case 2, the increase in the reaction proportion of producing light oil explains the experimental results from the perspective of molecular-level reaction network. The comparison between PE and PS pyrolysis elaborates different pyrolysis mechanisms based on the different molecular structures. • Established a generalized molecular-level model for polyethylene pyrolysis. • Offered an efficient tool avoiding repeated work in pyrolysis simulation. • Confirmed the generalizability by case studies without changing the rule design. • Provided guidance for the experiments by locating the peak value of products. [ABSTRACT FROM AUTHOR]

The accumulation of waste plastics has been one of the most urgent and difficult environmental challenges. In this work, the pyrolysis of polyethylene (PE) has been studied by thermogravimetric analysis (TGA), pyrolysis/gas chromatography/mass spectrometry (PyGC-MS), and a two-stage tube reactor. The pyrolysis behavior of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) is compared, and there are almost no differences in the thermogravimetric curves obtained by TGA and the yield of gaseous products obtained in a two-stage process. The evolution of light olefins (C 2 –C 4) during the pyrolysis of PE is investigated in a two-stage process with a constant condition in the first stage (500 °C) and various conditions in the second stage (700–1000 °C, 0.2–0.4 s). The temperature in the second stage has a more significant effect on the yield and selectivity of light olefins than the residence time, and the ethylene, propylene, and butene yields do not increase monotonously as the temperature rises. The highest yield of light olefins of 76.1 wt% is obtained at 800 °C with a selectivity of 91.7%. The maximum yields of ethylene, propylene, and butene are 45.1 wt%, 17.3 wt%, and 24.3 wt%, respectively. The scission mechanisms are proposed to provide insight into the process during which PE molecules transform into light olefins. • There are almost no differences between the pyrolysis characteristics of high-density and low-density polyethylene. • The evolution of light olefins during the polyethylene pyrolysis is investigated by PyGC-MS and a two-stage tube reactor. • A high yield of light olefins of 76.1 wt% with a high selectivity of 91.7% is obtained at 800 °C. • Probable mechanisms for two-stage pyrolysis of PE are proposed to reveal the interplay of reactions. [ABSTRACT FROM AUTHOR]

High-energy lithium-ion batteries (LIBs) have been actively pursued for practical applications in advanced electric vehicles and large-scale energy storage systems. The silicon (Si) material has been considered as a promising anode candidate due to its impressive lithium storage capacity, but is facing the challenge to ameliorate its cycling and rate performance. We here report a structure integration strategy to overcome major issues of poor capacity retention and slow kinetics during the lithium storage of Si anode, through in situ embedding Si nanoparticles into V 2 C MXene nanosheets. The MXene-supported Si@V 2 C nanocomposite anode reveals significantly enhanced cycling stability and improved lithium storage kinetics compared to that of the pristine Si anode. A high capacity exceeding to 430 mAh g−1 can be retained for 150 cycles at 200 mA g−1 current density. In addition, the conductive MXene supporter has been demonstrated to facilitate lithiation/delithiation processes for the Si by enhancing the charge transfer kinetics, as it is demonstrated by in situ electrochemical impedance spectroscopic (EIS) and Galvanostatic Intermittent Titration Technique (GITT) measurements. Findings from this work may inspire feasible structural designs for the practical deployment of MXene composited Si anode materials for next-generation lithium-ion batteries. [Display omitted] • Si@V 2 C composite anode was explored using V 2 C MXene as supporting substrate with enhanced Si stability performance. • A high capacity of 430 mAh g−1 can be retained for 150 cycles at 200 mA g−1 current density. • The V 2 C MXene can provide improved electronic conductivity and structural support of the Si anode during cycling. [ABSTRACT FROM AUTHOR]

Our study developed the one-step catalytic cracking conceptual design using a two-stage riser reactor (OSCO). Molecular-level process models and multi-objective optimization strategies are also carried out. Results show that the OSCO process exhibits superior techno-economic, society, people's livelihood, and environmental performance. [Display omitted] • A novel process is proposed to crack naphtha, kerosene, diesel and heavy oil in the two-stage riser reactor efficiently. • A novel integration model of mixed fraction structure and molecular level is proposed. • The multi-objective optimization strategies using systematic solution algorithm are performed. • The novel process shows superior techno-economic, society, people's livelihood, and environmental performance. With the demand for vehicle fuels (i.e., gasoline and diesel) is expected to decline soon, crude oil to chemical technology exhibits great potential to drive the next industry transition. This megatrend has led to studies on maximizing the production of low-carbon petrochemicals at the cost of fuels, which requires aggressive ways of converting oil into chemicals in a clean and efficient pattern. Herein, we proposed a novel process, termed OSCO, to crack naphtha, kerosene, diesel and heavy oil in a two-stage riser reactor efficiently, which can perform several refining procedures in the two-stage riser reactor vessel. A novel integration model of mixed fraction structure and molecular level is proposed. The multi-objective optimization strategies are also carried out to solve the optimization problem. As a result, the OSCO process can stably convert untreated heavy Daqing crude oil into light olefins with total yields of ethylene and propylene over 33 wt%, which also exhibits superior techno-economic, society, people's livelihood, and environmental performance. These insights may have a positive pushing role in engineering design, process intensification, and the optimization of direct catalytic cracking of crude oil. [ABSTRACT FROM AUTHOR]

[Display omitted] • A rational coating-integrated-into-synthesis design was used to prepare surface Ti-enriched NMC811 material. • The Ti substitute has a unique tri-valence (Ti3+) in a gradient surface distribution. • The surface Ti-enriched NMC811has high cationic ordering both in the bulk and surface. • Theoretical simulations certify enhanced stability of lattice oxygen for the NMC811#Ti material. • The NMC811#Ti cathode shows improved cycling performance and thermal/ storage stabilities. High-Ni cathodes are being intensely pursued worldwide for electric vehicles and other energy-dense applications due to their high capacity and low cost. However, structural instabilities during electrochemical cycling and when subjected to thermal treatment have been the major issues hindering their practical deployment. We here report a rational design of coating-integrated-into-synthesis protocol for fabricating surface Ti-enriched LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811#Ti) material. The coating to intermediates is crucial to obtain high structural ordering, both in the bulk and surface of high-Ni cathodes, and the Ti substitute has a unique tri-valence (Ti3+) in a gradient surface distribution. The simulations of projected density of states in the atomistic understanding further certify significantly enhanced stability of lattice oxygen for the NMC811 through such a Ti3+-based structure reinforcement. Consequently, the NMC811#Ti cathode delivers a high capacity up to 200 mAh g−1 at 0.1 C, along with superior stabilities during air-storage and thermal treatment (up to 297 °C at the fully charged state under differential scanning calorimetric measurements). The corresponding NMC811#Ti||graphite full cell exhibits a desired 83.6 % capacity retention after 1000 cycles at 0.5 C in a voltage range of 2.8–4.3 V. This work demonstrates a delicate surface reinforcement to stabilize high-Ni cathodes for long-life and safe lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The environmental pollution caused by waste plastics and their potential of resource recovery are receiving increasing attention. In this study, a molecular level kinetic model was established to simulate the polypropylene pyrolysis based on the SOL method, Poisson distribution model and genetic algorithm, which was simplified and effective without the introduction of extensive chemical databases and stiff differential equations. The automatic generation of complex reaction network was based on the representation of species and reactions at molecular level and the design of 14 reaction rules consistent with the mechanism. The model prediction achieved good agreement with experimental data affected by the primary and secondary reactions, verifying the generalizability of the models. The model prediction according to the kinetic parameters provided guidance for the pyrolysis experiments. In general, the molecular-level model behaves exquisite in the evaluation, validation, and prediction, and can gain an insight into the pyrolysis of polymers. • A molecular level kinetic model with automatic reaction network generation is established for polypropylene pyrolysis. • The automatic network generation is based on the Poisson distribution model, the SOL method and the design of reaction rules. • This model achieves excellent agreement with experimental data and can predict pyrolysis performance in more details. • The important role of temperature on the pyrolysis and the competition of two scissions are quantified by this model. [ABSTRACT FROM AUTHOR]

[Display omitted] • The I 2 nanotraps were used by introducing adjacent IBSs and LBSs on the skeleton. • The absorbent shows high I 2 uptake capacity (37 wt%) among all COF materials. • IBSs and LBSs synergistically promote iodine adsorption. Covalent organic frameworks have been recognized as promising porous materials for the radioactive iodine capture. However, most COFs often suffer from low adsorption capacity under practical conditions (typically ≥ 150 °C, ≤ 150 ppmv I 2) due to the lack of strong binding sites and low affinity toward iodine, which restricts their application in industrial relevant conditions. Here, we develop a strategy of constructing highly efficient I 2 nanotraps by manipulating two kinds of adsorption sites (ionic binding sites and Lewis binding sites) located at adjacent spatial positions, thereby realizing the synergistic binding toward I 2. The obtained I 2 nanotrap 4F-iCOF-TpBpy-I- delivers a remarkable I 2 uptake capacity of 37 wt% at 150 °C and 150 ppmv of I 2 , which illustrate a record-high value for all COFs reported so far. This work opens a new avenue for the rational design of COF materials toward highly efficient I 2 capture and related application. [ABSTRACT FROM AUTHOR]

α-MgAgSb is considered as a potential near-room-temperature thermoelectric material in virtue of its excellent electrical properties, ultralow lattice thermal conductivity and abundant constituent elements. However, it is hard to obtain high-quality phase pure α-MgAgSb due to its complex phase transition and high reactivity of element Mg, which cloaks material's intrinsic thermoelectric performance. Herein, through adopting a tantalum-sealing melting technique, we achieved highly-quality pure α-MgAgSb with large grain size and less oxygen content, as compared with our ball milled samples. The as-synthesized tantalum-sealing melted α-MgAgSb, without element doping or alloying, exhibited intrinsically low thermal conductivity, large weighted mobility, and high carrier concentration closes to the optimum range. Eventually, we attained a maximum thermoelectric figure of merit zT value of 1.3 at around 500 K in the tantalum-sealing melted α-MgAgSb. The average power factors and average zT values are also as high as 25 μW cm−1 K−2 and 1.1 respectively in the low-temperature range of (300 - 550) K, both of which rank as top values among the known materials. This study not only sheds new light on the understanding of intrinsic properties of α-MgAgSb but also demonstrates its great promise for harvesting low-grade waste heat. Record-high average power factor of 25 μW cm−1 K−2 and average zT of 1.1 were achieved in the melted α-MgAgSb sythesized by the tantalum-sealing melting technique. [Display omitted] [ABSTRACT FROM AUTHOR]