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• Microreaction systems for preparing oxidant and droplet template were constructed. • The effects of reactant conditions on crystal morphology of BaCrO 4 were investigated. • The UV–vis absorption peak of BaCrO 4 varied with decreasing crystal thickness. • A microdroplet-confined coupling polymer self-assembly theory was proposed. • Homogeneous mixed B/BaCrO 4 particulates with high delay precision were prepared. Restricted by the macroscopic spatial scale conditions in traditional preparation methods, the improvement of delay precision of the delay composition gradually arrives at the bottleneck. Therefore, a microdroplet-confined coupling polymer self-assembly theory based on microfluidics was proposed to prepare ultramixed self-assembled composite energetic material particulates in order to make a breakthrough in its delay precision. Taking boron (B)/barium chromate (BaCrO 4) delay composition as the research object, nano-BaCrO 4 particles were prepared and microdroplet templates were generated by using the micromixing and microdispersing reaction systems respectively. With the excellent mixing efficiency of the micromixing reaction system, the effect of reactant concentration and temperature on crystal morphology and particle size of BaCrO 4 was investigated, and the spectral response of BaCrO 4 particles was analyzed on-line by using an on-line UV–vis spectrophotometer. The results indicated that the reactant concentration exerted a great influence on crystal morphology and particle size of BaCrO 4 , and the characteristic absorption peak of BaCrO 4 was red-shifted regularly with the decrease of crystal thickness at low reactant concentration. Microdroplet templates for self-assembly of B/BaCrO 4 nano-composite particles were generated by using a microdispersing reaction system, and the self-assembled B/BaCrO 4 particulates were prepared. The particulates were characterized by thermal analysis and the delay precision was measured. The results exhibited that the composite energetic particulates with ultra-homogeneous mixing, excellent combustion performance and high delay precision were prepared. In summary, in this study, ultramixed self-assembled B/BaCrO 4 particulates with high delay precision were prepared based on microfluidics, which can provide a novel technology and method for the preparation and mixing of other composites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrogenation of conjugated C = O is thermodynamically unfavored. • Highly dispersed Pt nanoparticles are well-embedded within S-1 microchannel. • Confinement effect of S-1 is employed to improve unsaturated alcohol selectivity. • C = O group is preferentially adsorbed on Pt@S-1 via on-top η 1 mode. • The on-top η 1 adsorption mode is more favored to C = O hydrogenation than d i -σ CO η 2. The issue for thermodynamically favored C = C hydrogenation needs to be overcome in the hydrogenation of ɑ, β-unsaturated aldehydes to unsaturated alcohols. Herein, we employ confinement effect in the catalyst-designing engineering to orient the C = O adsorption by the zeolitic microchannel, where highly dispersed Pt nanoparticles are homogeneously well-embedded within the silicalite-1 framework (Pt@S-1). Comprehensive characterizations, such as HAADF-STEM, H 2 -TPR, FT-IR of CO adsorption and XPS are carried out to demonstrate the geometric, confinement and electronic properties of metal species. In the hydrogenation of ɑ, β-unsaturated aldehydes with suitable molecular size, Pt@S-1 displays preferential C = O hydrogenation. For example, Pt@S-1 gives conversion of 99.8% and meanwhile the aiming cinnamal alcohol selectivity of 98.7% in the hydrogenation of cinnamaldehyde, outperforming larger Pt nanoparticles ill-suitedly embedded within silicalite-1 (Pt@S-1- is) and highly dispersed Pt nanoparticles supported on the silicalite-1 surface (Pt/S-1). For the hydrogenation of smaller 3-methyl-2-butenal, though the confinement effect boosts the C = O hydrogenation to some extent, the synergetic electronic effect via introducing Fe species effectively increases the unsaturated alcohol selectivity. Investigations on the adsorption configuration by in-situ FT-IR spectroscopy clearly indicate that the unsaturated aldehyde with suitable molecular size is preferentially adsorbed on Pt sites of Pt@S-1 via the oxygen atom of C = O with on-top η 1 mode, thus favoring high unsaturated alcohol selectivities, while the d i -σ CO η 2 and η 4 adsorption modes on Pt@S-1- is and Pt/S-1 are relatively adverse for prioritized C = O hydrogenation. [ABSTRACT FROM AUTHOR]

• A new microfluidic strategy was used for modification and coating of HNS based PBX. • The PBX has narrow particle size distribution due to the uniform crystallization environment. • The mechanism of coating PBX was analyzed based on the rapid screening function. • The effects of micro-mixing conditions on PBX were studied from micro-scale growth. • The PBX breaks the limitation that HNS cannot resist high overload. Polymer bonded explosives (PBXs) have the characteristics of high energy density, and excellent safety and mechanical performances. In this work, a microfluidic crystallization system (MCS) based on microscale chaotic advection is proposed to control and optimize the crystallization environment of PBXs. Comparison with the macroscale method not only verifies the feasibility of the MSC in the preparation of PBXs, but it also boasts a narrower particle size distribution, regular morphology, and high crystal quality. Furthermore, based on the advantages of the rapid and simple preparation of the MCS, the suitable polymer-coated explosive composite system can be quickly screened out. Four typical binders were selected by the MCS to coat the nano-hexanitrostilbene (nano- HNS), and their properties were analyzed. On this basis, the surface modification and coating mechanism of the binder on HNS crystals and the effect of micro mixing conditions on PBXs crystal growth were studied. Finally, the anti-overload performance of four different PBXs was evaluated through air gun experiments. The results show that all four PBXs can maintain the stability of the charge under strong external dynamic load conditions. This study provides an efficient route to prepare PBXs with narrow particle size distribution, high crystal quality and resistant high overload. This work serves those studying the composite system of crystals and polymers, as well as polymer-coated crystals. [ABSTRACT FROM AUTHOR]

• HNS microspheres with micro/nano hierarchical structure were prepared. • A spheroidization model and microfluidic experiments for explosives was proposed. • A continuous platform was built by coupling microfluidics and spray drying. • HNS microspheres have similar firing sensitivity to nano HNS. The spheroidization of explosives with micro/nano hierarchical structure is a feasible and efficient way to meet the requirements of energy and safety. In order to achieve the expectation, a microfluidic strategy consisting of a spheroidization model and verification experiments was proposed. The model states a possible spheroidization process and three spheroidization types by theoretical analysis. Furthermore, a continuous microfluidic platform was established for the verification experiments, which is consisting of a combinatorial microfluidic module and a spray-drying module. Here we used HNS (2,2′,4,4′,6,6′hexanitrostilbene) to verify the applicability of the strategy. The spheroidization process was verified by deconstructing HNS microspheres and adjusting the internal-outside pressure at the microscale. The spheroidization types were verified by tuning flow rate ratios of the solvent and antisolvent. It was found that the model is quite applicable for the spheroidization of micro/nano hierarchical structure by microfluidics. According to the detonation test, it was found the HNS microspheres have similar firing sensitivity to nano HNS under short-pulse shock wave, which means the better fluidity and higher bulk density can be realized while retaining the firing sensitivity. This study demonstrates an efficient, safe strategy to realize the high-quality spheroidization and continuous preparation of explosives with micro/nano hierarchical structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • LTL-zeolite was used as a novel support for selective phenol hydrogenation. • LTL has one-dimensional large-pore diffusion system and adjustable base-acid sites. • Palladium nanoparticles were in-situ encapsulated within LTL-zeolite. • High Pd dispersions were obtained after encapsulation. • Switching chemical microenvironments around Pd sites changed the kinetic profiles. Cyclohexanone, as a significant raw material in the production of nylon 6 and nylon 66, is preferentially synthesized via selective phenol hydrogenation while the key point is to modulate the acidic/basic properties and metal dispersion of the catalytic system. Here, we report the fabrication of Pd@L core–shell catalysts via the in-situ encapsulation of Pd nanoparticles within the L zeolite with a one-dimensional large-pore diffusion system for the selective hydrogenation of phenol to cyclohexanone. The different Pd amounts and acidic/basic properties of the L zeolite catalyst were modulated to study the effects of the microenvironment around the Pd centers in the Pd@L on the catalytic performances of selective phenol hydrogenation. The results show that the basicity of L zeolite greatly favors high selectivity to cyclohexanone. In contrast, modulating the microenvironment to weak or strong acid states can result in the dehydration product forming on the acid sites or even the suppression of phenol hydrogenation. The conversion of phenol increases from 14.0% to 99.9% and meanwhile the selectivity of cyclohexanone ranges from 67.5% to 93.8%. In the optimum condition, the obtained Pd@KL catalyst can demonstrate excellent catalytic performance with the phenol conversion of 99.9% and the cyclohexanone selectivity of around 93.8%. Our work presents a promising tactic to effectively control the target reaction pathway by means of maneuvering the microenvironment in the proximity of metal nanoparticles. [ABSTRACT FROM AUTHOR]

• A versatile microreaction system for handling high-solid-content fluids was set up. • The stability of fluids with Zr powder was investigated by UV–vis spectroscopy. • The surface reaction mechanism of Zr powder based on HF concentration was proposed. • The contradiction between the activity and sensitivity of Zr powder was reconciled. The regulation of energy release characteristics and safety of highly active metal fuels has attracted significant attention. In response to the limitations of using hydrofluoric acid (HF) to modify zirconium (Zr) powder in batch reactors, a microfluidic method coupling ultrasound and coaxial flow microreactors was proposed to achieve the control of the microstructure on the surface of Zr powder. The fluid flow and mixing characteristics in the microreactor were analyzed using on-line detection devices, leading to the determination of suitable fluid parameters. Through analysis of the reaction process between Zr and HF, a reaction model based on the HF concentration was established and subsequently verified through a microreaction system. The results indicate that the HF concentration greatly influences the morphology and composition of Zr powder, thereby determining the material and structural transformation of the Zr powder surface. The excellent thermal oxidation performance and electrostatic safety of HF-modified Zr powder were confirmed through thermal analysis and electrostatic discharge sensitivity tests. This study provides valuable insights for controlling the microstructure and properties of ultrafine Zr powder. [ABSTRACT FROM AUTHOR]

• Co-reduction method and freeze-drying technology were used to prepare HEAs aerogels. • PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 displays extremely high activity and outstanding durability. • The plausible catalytic mechanism of PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs were proposed. • This work paves the way for fabricating the hybrids of HEAs and aerogels. High-entropy alloy aerogels (HEAAs) have become promising electrochemical catalysts because of the advantageous combination of high-entropy alloys and aerogel structure. However, how to fabricate 3D porous high-entropy alloys accurately is still a great challenge due to their inherent thermodynamic instability and differences in reduction potentials of metal ions. Herein, PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs have been synthesized by combining co-reduction method and freeze-drying technology. The resulting PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs have the structural and morphological benefits of both high-entropy alloys and aerogels. Both XPS and DFT results confirm that the d-band center of PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs shifts to lower binding energy compared to Pt/C, indicating the effective regulation of electronic structure on the surface of PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs. As a demonstration in the methanol oxidation reaction (MOR), a mass activity of 4.19 A mg Pt −1 and long-term stability (>0.33 A mg Pt −1 after 10 cycles of 3600 s stability test) can be obtained on the PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs, outperforming binary Pt-based alloys and commercial Pt/C. The CO adsorption strength of PtBi 1.5 Ni 0.2 Co 0.2 Cu 0.2 HEAAs is more weaker than that of PtBi 1.5 alloys and Pt/C, which proves the enhanced CO tolerance. The results pave the way for fabricating the hybrids of high-entropy alloys and aerogels with superior activity and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The intelligent VO 2 /cellulose nanofiber (VO 2 /CNF) composites were designed and fabricated successfully. • The lattice distortion across the phase transition of VO 2 induced by thermal stimuli changes EM parameters of composites. • The application of composites in control of the wireless transmission was demonstrated. Intelligent electromagnetic interference (EMI) shielding materials, which can generate reversible and real-time EM responses to external stimuli, have an attractive prospect in smart wearable electronics. Herein, we design and fabricate flexible and intelligent vanadium dioxide (VO 2)/cellulose nanofiber (CNF) shielding composites, showing a controllable EM response based on the reversible metal-to-insulator transition characteristic of VO 2 by thermal stimuli. With the phase transition of VO 2 between the insulating M phase and metallic R phase at ∼68 °C, the electrical conductivity of VO 2 /CNF composites is reversibly changed between ∼0.3 and ∼446.5 S/m, leading to a tunable shielding effectiveness (SE) between ∼18.7 and ∼52.8 dB in the frequency of 8.2–12.4 GHz. The lattice strain of VO 2 driven by thermal stimuli radically changes the EM parameters and impedance matching of VO 2 /CNF composites, which dominates the attenuation mechanism of EM waves. Uniquely, we demonstrate the VO 2 /CNF composites with a proof of concept to reversibly control the on and off of the wireless transmission. Moreover, the VO 2 /CNF composites exhibit an outstanding near-field shielding performance, which is potential to be applied in the electronic packaging field. This intelligent EMI shielding material has a broad prospect in the smart EM devices of next generation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Exciplex emission was achieved by a single molecular system with flexible chain. • Ho-exciplex eliminates the phase separation drawback of physical blended exciplex. • Ho-exciplex can enable the fabrication of fully-solution-processed OLEDs. Exciplex has long been recognized as a mixture of donor and acceptor components. Here, for the first time, it was demonstrated that exciplex emission can also be achieved by single pure molecule, we named it as homojunction exciplex (ho-exciplex). By using the flexible alkyl chain to link the donor and acceptor unit, the result compound not only maintain efficient exciplex emission property, but also eliminate the notorious phase separation drawback. Different from the conventional heterojunction exciplex (he-exciplex), such unique molecular concept of homojunction system will provides a bright avenue toward structure-simplified and high-stable OLEDs without sophisticated stoichiometric and physical blending process. By using such a single molecular PhTRZ-CzTPA as both emitter and host, the solution-processed device achieved a comparable electroluminescence performance with its hybrid blending he-exciplex counterpart. Importantly, the unified molecule of PhTRZ-CzTPA makes it superior solvent resistance to isopropanol, which enable the fabrication of fully-solution-processed device with all spin-coated organic layers. Therefore, the homojunction strategy will open a new avenue for exciplex design and application, not only in OLEDs, but also other semiconductor devices or sensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel strategy was proposed to achieve flexible liquid metal/cellulose nanofiber film. • The film exhibits excellent structural stability and EMI shielding effectiveness of ~ 65 dB. • Simulation in the frequency domain was introduced to investigate the shielding mechanism. Liquid metal (LM) is a promising candidate for electromagnetic interference (EMI) shielding due to the superb electrical conductivity and easy processing. However, poor compatibility caused by high surface tension, insulated oxide shells formed during processing, and unmanageable fluidity at elevated temperature of LM severely hinder its application in the field of EMI shielding. Herein, we develop a novel processing strategy integrating ball-milling dispersion, freeze-drying and compression molding to achieve free-standing and flexible LM/cellulose nanofiber composites (LM/CNF) film, in which the oxide shells of LM droplets generated by ball-milling are broken by mechanical compression, and LM droplets are coalesced while confined by CNF to construct a continuously conductive path. As a result, the robust LM/CNF film shows tensile strength of above 30 MPa, and it possesses electrical conductivity of 96,000 S/m, leading to remarkable shielding effectiveness (SE) of above 65 dB with a thickness of only 300 µm in a broad frequency range of 4–18 GHz covering C-band, X-band and Ku-band. Moreover, LM/CNF film exhibits excellent structural stability and EMI shielding performance reliability after high-temperature treatment. Besides, simulation in the frequency domain with ANSYS HFSS 2019 R2 is performed to intuitively understand the shielding mechanism of LM/CNF film. It is found that the attenuation of electromagnetic waves is mainly based on reflection. This study proposes a fresh scenario to achieve high-performance EMI shielding material and paves the way for potential applications of LM in portable and wearable smart electronics. [ABSTRACT FROM AUTHOR]

• Trace Cu(II) activates S(IV) to oxidize As(III) under alkaline condition. • The produced Cu(I) complexes with S(IV) to form CuI(SO 3) n −2n+1 complexes. • The CuI(SO 3) n −2n+1 complexes react with O 2 to form Cu(III)-peroxo species. • Cu(III)-peroxo species and SO 4 •− are important oxidants in As(III) oxidation. Sulfate radical (SO 4 •−) is always thought to be an important oxidizing species in the metal-sulfite [S(IV)] systems, however, the oxidizing species correlated with the metal species have rarely been mentioned. In this study, the oxidizing species that oxidize arsenite [As(III)] in the Cu(II)-S(IV) system were investigated under alkaline conditions. Kinetic results indicate that complexation between Cu(II) and S(IV) is the pre-requisite to initiate various oxidizing species, followed by internal electron transfer from S(IV) to Cu(II) with the formation of SO 3 •− and the CuI(SO 3) n −2n+1 complexes. Quenching experiments rule out contributions of SO 5 •−, peroxymonosulfate (HSO 5 −, PMS), hydroxyl radical (•OH), superoxide radical (O 2 •−) and singlet oxygen (1O 2) to As(III) oxidation in the Cu(II)-S(IV) system and indicate that some kinds of peroxo species contribute. On the other side, apart from the oxidizing species such as SO 5 •−, PMS and SO 4 •− generated via a series of reactions between SO 3 •− and O 2 , the CuI(SO 3) n −2n+1 complexes also react with O 2 to form CuII-O 2 •−-(SO 3 2−) n superoxo species and CuIII-O 2 2−-(SO 3 2−) n peroxo species, as revealed by Raman analysis. UV–vis spectrum further confirms the presence of Cu(III) in the Cu(II)-S(IV) system. We therefore suggest that both SO 4 •− and the Cu(III)-peroxo species play important roles in the oxidation of As(III) in the Cu(II)-S(IV) system. This study enriches our understanding on the diversity of oxidizing species in the metal-S(IV) systems under alkaline conditions. [ABSTRACT FROM AUTHOR]

• A new strategy is developed to achieve chemically stable Ti 3 C 2 T x MXene. • Mechanical properties of IL-MXene film is significantly improved. • The mechanism for improved chemical stability of IL-MXene sheet is proposed. Ti 3 C 2 T x MXene with two-dimensional (2D)-layered structure shows potential application in various fields owing to its superb metallic conductivity and excellent solution processability. However, a fundamental challenge limiting the implementation of Ti 3 C 2 T x in practical applications is its susceptibility to oxidation in either humid or aqueous environments only within a few days, which results in the disassembly of the 2D-layered structure and severely deteriorates the functional properties including electrical conductivity, mechanical strength and EMI shielding performance. Herein, we firstly demonstrate a robust procedure to protect sensitive Ti 3 C 2 T x from degradation by modification with imidazolium-based inion liquid (IL), which remarkably improves the chemical stability of Ti 3 C 2 T x in aqueous and significantly increases the mechanical strength of assembled freestanding Ti 3 C 2 T x film (IL-MXene). The crystalline structure of IL-MXene sheet remains intact up to 30 days and preserves the 2D-layered structure as long as 8 months in aqueous, meanwhile, the tensile strength of freestanding IL-MXene film is as high as 75.9 ± 4.9 MPa and the increment is up to 84% when compared to that of untreated MXene film (41.2 ± 4.5 MPa). A novel mechanism for improved chemical stability of MXene sheet was proposed and elucidated based on the radical-scavenging ability of IL and the surface chemistry of MXene sheet. This study provides a new strategy to achieve chemically stable Ti 3 C 2 T x and improved mechanical strength of assembled MXene film, which is also available for other type of MXenes. [ABSTRACT FROM AUTHOR]