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Biochar co-doped with nitrogen and boron switching the free radical based peroxydisulfate activation into the electron-transfer dominated nonradical process
No full textIn this study, N/B co-doped biochars were employed as metal-free activators of peroxydisulfate (PDS) for tetracycline degradation, more importantly, the roles of dopants and the relative contribution of radical vs nonradical oxidations were comprehensively investigated. Integrating with electron paramagnetic resonance and kinetics calculations, we showed that co-doping N and B into biochars not only boosted the catalytic activity but also switched the radical PDS-activated process into the electron transfer-dominated nonradical process. Compared with pristine biochar/PDS systems (22%), the nonradical contribution of N/B co-doped biochar/PDS systems increased to 59%, exhibiting outstanding stability and selectivity. Galvanic oxidation tests and theoretical simulations unveiled that doped biochars as conductive tunnels accelerate the potential difference-driven electron transfer from the highest occupied molecular orbital of pollutants to the lowest unoccupied molecular orbital of PDS due to the lower energy gap. This study provided new insights into the critical role of heteroatom-doped carbocatalysts in PDS nonradical activation
Laser beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy
No full textTo determine the potential of an AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) as a structural material, its laser beam welding (LBW) performance was evaluated, and the microstructure and mechanical properties of weld joint were studied. A fully penetrated, defect-free joint was obtained, in which the fusion zone (FZ) exhibited a eutectic lamellar microstructure containing FCC(L1(2))/BCC(B2) solid solution phases. The FZ contained refined columnar grains, which grown with the preferential 111 orientation induced by the rapid cooling during LBW. The tensile strength of the FZ was superior than that of the base metal (BM), which was attributed to grain refinement and higher dislocation density. LBW is a suitable process for joining AlCoCrFeNi2.1 EHEAs
Tribological properties of alkylated reduced graphene oxide as lubricant additive
No full textAs lubricant additive, graphene and/or graphene oxide (GO) has received considerable interest due to its excellent tribological performance. Here, grafting octadecylamine(ODA) onto GO via facile amidation was carried out and hydrazine monohydrate was used as reducing agent to attain ODA-RGO as lubricant additive. The physical, chemical properties and morphologies of ODA-RGO and GO were characterized.Tribological properties were evaluated using a ball-on-plate configuration on a UMT-3 tribometer and then worn surfaces were examined by Scanning electron microscope (SEM), Raman spectra and optical microscope. It was found that ODA-RGO was helpful for lubrication and friction-reduction under the applied load of 10 N. The excellent tribological behavior was contributed to the formation of ODA-RGO protective film which could avoid direct contact between tribological mates. The restacked shape of sheet-like ODA-RGO also plays an important role in friction process
The thermal and elastic properties of U3Si5 and their variations induced by incorporated aluminum
No full textUranium silicide compounds have attracted intensive attention as candidate alternative fuels in commercial light water reactors (LWRs). In this work, the electronic, thermal, mechanical and elastic properties of U3Si5 are comprehensively investigated based on first-principles density functional calculations and semi-classical Boltzmann transport theory. U3Si5 is determined to be a brittle and magnetic metal, and thermal conductivity is dominated by its electronic contribution at high temperature. The ratio between the bulk and shear moduli is 1.205. In addition, the elastic ideal strength is strongly anisotropic, with the minimum value only 6.831 GPa at a uniaxial tensile strain of 0.07. This low strength is mainly caused by an emerged structural transition forming silicon-silicon bonds to absorb strain energy. Moreover, the influences of aluminum incorporation on the structural and elastic properties, and thermal conductivities of U3Si5 are further studied. The aluminum atom prefers to replace the silicon atom at the vertex shared by the silicon triangles and pentagons. The incorporated atom impedes the structural transition, and enhances the toughness of U3Si5. The results from this work may provide useful clue for the improvement in the application of U3Si5. (C) 2021 Elsevier B.V. All rights reserved
One stone two birds: Vanadium doping as dual roles in self-reduced Pt clusters and accelerated water splitting
No full textIntegrating active Pt clusters into transition-metal oxides with water-dissociation ability is effective to prepare a bifunctional electrocatalyst for water splitting in alkaline. However, the additional utilization of a reductant and/or the operation at the elevating temperature causes the over-growth and agglomer-ation of Pt clusters, thus losing the high catalytic performance. Herein, we report that V dopant not only favors self-reducing Pt clusters on NiFe layered double hydroxide (LDH) (Pt/NiFeV) at room temperature, but also regulates interfacial charge redistribution to enhance the water-splitting performance. Experimental and theoretical studies reveal that V dopant into NiFe LDH triggers more electrons to trans-fer to adjacent Fe atoms, thus leading to a higher reducing ability compared to that without V-doping. When used as water-splitting electrocatalyst, V doping promotes electron loss of Pt clusters in Pt/ NiFeV, optimizing the free energy of hydrogen adsorption and proton recombination kinetics at the cath-ode. Meanwhile, it also moves the d-band center of Ni away from the Fermi level to optimize the adsorp-tion of *OH intermediates and facilitate the desorption of oxygen molecules at the anode. Thereby, Pt/ NiFeV exhibits much higher bifunctional performance than V-free Pt/NiFe LDH toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This work can spark inspiration of design-ing other bifunctional electrocatalysts for energy conversion and storage. (c) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved
One-step fabrication of transparent Barite colloid with dual superhydrophilicity for anti-crude oil fouling and anti-fogging
No full textHypothesis: Transparent superhydrophilic coatings are very promising in various scenarios. Appropriate fabrication of colloid coatings with superhydrophilicity both in air and under oil would enlarge their application potential in anti-oil fouling and facilitate anti-fogging of transparent surfaces. Experiments: The Barite colloid was obtained from a one-step precipitation method and was transferred onto glasses to prepare transparent coatings with different thicknesses simply by dip-coating. Then, the impact of thickness on wettability and property was studied through the investigation of wettability in various phase, anti-crude oil fouling performance and anti-fogging ability. Findings: Similar surface morphology and roughness of these coatings were achieved and all the coated surfaces showed ultra-hydrophilicity both in air and under oil. Moreover, the hydrophilicity in air and under oil was found to deteriorate with the decrease of coatings' thickness and dual superhydrophilicity could be achieved on thick coatings. More importantly, excellent anti-crude oil fouling property and durable anti-fogging ability were realized on these transparent coatings with dual superhydrophilicity. (c) 2021 Elsevier Inc. All rights reserved
Ultrathin polyamide nanofiltration membranes with tunable chargeability for multivalent cation removal
No full textPositively charged nanofiltration membranes are promising in water softening and heavy metal ion removal. However, facile modulation on their chargeability remains a great challenge. Here, we proposed a charged monomer-engineered interfacial polymerization toward positively charged polyamide membranes. In particular, branched amino macromolecules (BAMs) with different charged group numbers and molecular sizes were selected as aqueous monomers, allowing for wide-range-tunable membrane chargeability. We found that larger BAMs tend to form intramolecularly crosslinked networks with more amino residues, conferring membrane chargeability up to +5.53 mC m(-2). Besides, the slower diffusion of larger BAMs also led to ultrathin membranes down to 9.0 nm in thickness. The optimal composite nanofiltration membrane displayed a high rejection to multivalent cations (e.g., MgCl2 rejection of 98.7%) with ultrahigh pure water permeance of 31.5 L m(-2) h(-1) bar(-1), which was around 2-10 times higher than that of the reported positively charged nanofiltration membranes. Our monomer design strategy for interfacial polymerization may evolve into a facile approach to constructing advanced charged membranes
Electrochemical extraction kinetics of Nd on reactive electrodes
No full textPyroprocessing technology with molten salt electrolysis as the core is a promising technology for the reprocessing of spent fuel. In this work, the electrochemical reduction mechanism and kinetic properties of Nd3+ on various electrodes (inert W and reactive Al, Ga, Bi, Cd, Zn, Pb, and Sn electrodes) were systematically investigated and compared in LiCl-KCl eutectic melts using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel techniques. The electrochemical reduction of Nd3+ was a two-step process on the W electrode including Nd3+-> Nd2+ and Nd2+-> Nd, while it became a one-step process involving three electrons on the reactive electrodes with obvious depolarization effects. Furthermore, the connections between the reduction potentials of Nd3+ on these reactive cathodes and the formation energies of the electrode-rich alloy phases (Al11Nd3, Cd11Nd, Pb3Nd, Zn17Nd2, Ga6Nd, Sn3Nd, BiNd2) were established. After evaluating the physico-chemical, depolarization and kinetic properties of these reactive electrodes, liquid Cd was considered as the most favorable material for the electrochemical extraction of Nd. In addition, Al, Cd, and Bi are also promising candidates for An / Ln separation
Experimental research on the utilization of gold mine tailings in magnesium potassium phosphate cement
No full textGold mine tailings (GT) are fine-grained ore processing wastes with a high variety of minerals and metals. Storing large amounts of GT in impoundments results in a waste of resources and in several cases environmental pollution. Magnesium potassium phosphate cement (MKPC) is green-sustainable cement made by magnesia (MgO, M) and KH2PO4, which can be used to effectively immobilize radioactive and hazardous wastes elements through mineralization and microencapsulation. This paper aimed at the utilization of GT in MKPC.GT was incorporated into MKPC through two different pathways, either partially replacing M or the binder (both M and KH2PO4). The influences of GT on MKPC were evaluated through workability, compressive strength, and microstructure. It was found that the partial replacement of M by GT can result in better workability, denser microstructure and higher late-stage compressive strength. The incorporation of GT generates new types of hydrates in the structure. The compressive strength was improved by a factor of 114.94% when an additional 10% M was replaced by GT; when the displacement of GT was 30%, it yielded a compressive strength approaching the basic group. Therefore, the partial replacement of M with GT was suitable to incorporate GT into MKPC in order to achieve the utilization of GT, reduce the cost and improve the mechanical properties of MKPC
Reduced Graphene Oxide Modified Few-Layer Exfoliated Graphite to Enhance the Stability of the Negative Electrode of a Graphite-Based Potassium Ion Battery
No full textThe intercalation of potassium in graphite provides high energy density owing to the low potential of 0.24 V vs. K/K+, thereby making it a promising anode material for potassium ion batteries. However, the high volume expansion (60%) of graphite after potassium intercalation induces significant stress and electrode pulverization. Additionally, the sluggish kinetics of potassium insertion undermine the rate capability of electrodes. Using few-layer exfoliated graphite (EG) as a negative electrode material effectively relieves expansion-induced stress. Unfortunately, the close stacking of ultra-thin two-dimensional EG impedes ion transport. Furthermore, EG with smooth surfaces lacks sites to adsorb K+, which is unfavorable for intercalation reactions. To address these problems, in this study, we designed an rGO/EG/rGO sandwich that coats EG with reduced graphene oxide (rGO). This complex material has two main advantages: (1) its 3D network can effectively prevent EG from stacking and buffer the volumetric variation of EG to improve the cyclic stability of the electrode, and (2) the loose structure and rich functional groups of rGO can also enhance the kinetic of potassium intercalation. Through hydrothermal reduction, GO was coated onto the EG surface and cross-linked to form a 3D network, by which EG stacking could be effectively mitigated. The rGO : EG ratio was precisely controlled by modulating the amount of reactant GO and EG. Transmission electron microscopy and scanning electron microscopy images showed that the rGO was uniformly coated on the EG surface to form a sandwich structure. X-ray diffraction patterns and Raman spectra demonstrated that rGO was physically adsorbed on the EG surface without notable chemical interactions. The EG structure was retained to ensure that its characteristic electrochemical properties were unaffected. Cyclic voltammetry and galvanostatic cycling tests were performed on the complex material with various rGO : EG ratios, exhibiting that rGO : EG = 1 : 1 (w/w) was optimal with a specific capacity of 443 mAh.g(-1) at 50 mAg(-1). Even when operated at a high current density of 800 mA.g(-1), a specific capacity of 190 mAh.g(-1) was achieved, retaining 42.9% of the low-rate capacity, far exceeding those of pristine EG (14.2%) and rGO (27.2%). These results demonstrate that the rGO coating indeed enhanced the kinetics of potassium intercalation and efficiently improved the capacity and rate capability compared to pristine EG. We hope this work sheds light on novel approaches to improving potassium intercalation mechanisms in graphite