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        Latest Research
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        Article  |  2021-08-31

        Atomic Force Microscopy Measurement in the Lignosulfonate/Inorganic Silica System: From Dispersion Mechanism Study to Product Design

        Designing and preparing high-performance lignin-based dispersants are crucial steps in realizing the value-added utilization of lignin on an industrial scale. Such process depends heavily on an understanding of the dispersion mechanism of lignin-based dispersants. Here, atomic force microscopy (AFM) is employed to quantitatively investigate the dispersion mechanism of a lignosulfonate/silica (LS/SiO2) system under different pH conditions. The results show that the repulsive force between SiO2 particles in LS solution is stronger than it is in water, resulting in better dispersion stability. The Derjaguin–Landau–Verwey–Overbeek (DLVO) formula as well as the DLVO formula combined with steric repulsion is utilized for the fitting of the AFM force/distance (F/D) curves between the SiO2 probe and substrate in water and in LS solution. Based on these fitting results, electrostatic and steric repulsive forces are respectively calculated, yielding further evidence that LS provides strong steric repulsion between SiO2 particles. Further studies indicate that the adsorbance of LS on SiO2 (Q), the normalized interaction constant (A), and the characteristic length (L) are the three critical factors affecting steric repulsion in the LS/SiO2 system. Based on the above conclusions, a novel quaternized grafted-sulfonation lignin (QAGSL) dispersant is designed and prepared. The QAGSL dispersant exhibits good dispersing performance for SiO2 and real cement particles. This work provides a fundamental and quantitative understanding of the dispersion mechanism in the LS/inorganic particle system and provides important guidance for the development of high-performance lignin-based dispersants.

        Jingyu Wang ,   Yong Qian   et al.

        Article  |  2021-08-31

        Selective Laser Melting under Variable Ambient Pressure: A Mesoscopic Model and Transport Phenomena

        Recent reports on the selective laser melting (SLM) process under a vacuum or low ambient pressure have shown fewer defects and better surface quality of the as-printed products. Although the physical process of SLM in a vacuum has been investigated by high-speed imaging, the underlying mechanisms governing the heat transfer and molten flow are still not well understood. Herein, we first developed a mesoscopic model of SLM under variable ambient pressure based on our recent laser-welding studies. We simulated the transport phenomena of SLM 316L stainless steel powders under atmospheric and 100 Pa ambient pressure. For typical process parameters (laser power: 200 W; scanning speed: 2 m?s-1; powder diameter: 27 μm), the average surface temperature of the cavity approached 2800 K under atmospheric pressure, while it came close to 2300 K under 100 Pa pressure. More vigorous fluid flow (average speed: 4 m?s-1) was observed under 100 Pa ambient pressure, because the pressure difference between the evaporation-induced surface pressure and the ambient pressure was relatively larger and drives the flow under lower pressure. It was also shown that there are periodical ripple flows (period: 14 μs) affecting the surface roughness of the as-printed track. Moreover, the molten flow was shown to be laminar because the Reynolds number is less than 400 and is far below the critical value of turbulence; thus, the viscous dissipation is significant. It was demonstrated that under a vacuum or lower ambient pressure, the ripple flow can be dissipated more easily by the viscous effect because the trajectory length of the ripple is longer; thus, the surface quality of the tracks is improved. To summarize, our model elucidates the physical mechanisms of the interesting transport phenomena that have been observed in independent experimental studies of the SLM process under variable ambient pressure, which could be a powerful tool for optimizing the SLM process in the future.

        Renzhi Hu ,   Manlelan Luo   et al.

        Article  |  2021-08-26

        Techno-economic characteristics of wastewater treatment plants retrofitted from the conventional activated sludge process to the membrane bioreactor process

        While a growing number of wastewater treatment plants (WWTPs) are being retrofitted from the conventional activated sludge (CAS) process to the membrane bioreactor (MBR) process, the debate on the techno-economy of MBR vs. CAS has continued and calls for a thorough assessment based on techno-economic valuation.

         

        Article  |  2021-08-25

        PICRUSt2 functionally predicts organic compounds degradation and sulfate reduction pathways in an acidogenic bioreactor

        For comprehensive insights into the influences of sulfate on performance, microbial community and metabolic pathways in the acidification phase of a two-phase anaerobic system, a laboratory-scale acidogenic bioreactor was continuously operated to treat wastewater with elevated sulfate concentrations from 2000 to 14000 mg/L.

         

        Article  |  2021-08-23

        Engineering zirconium-based metal-organic framework-801 films on carbon cloth as shuttle-inhibiting interlayers for lithium-sulfur batteries

        Lithium-sulfur batteries have been regarded as the next-generation rechargeable batteries due to their high theoretical energy density and specific capacity. Nevertheless, the shuttle effect of lithium polysulfides has hindered the development of lithium-sulfur batteries. Herein, a novel zirconium-based metal-organic framework-801 film on carbon cloth was developed as a versatile interlayer for lithium-sulfur batteries. This interlayer has a hierarchical porous structure, suitable for the immobilization of lithium polysulfides and accommodating volume expansion on cycling. Moreover, the MOF-801 material is capable of strongly adsorbing lithium polysulfides and promoting their catalytic conversion, which can be enhanced by the abundant active sites provided by the continuous structure of the MOF-801 films. Based on the above advantages, the lithium-sulfur battery, with the proposed interlayer, delivers an initial discharge capacity of 927 mAh·g–1 at 1 C with an extremely low decay rate of 0.04% over 500 cycles. Additionally, a high area capacity of 4.3 mAh·cm–2 can be achieved under increased S loading.

         

        Article  |  2021-08-23

        Moving policy and regulation forward for single-use plastic alternatives

        Single-use plastics are often used once or cannot be reused for extended periods. They are widely consumed with the rapid development of social economy. The waste generated by single-use plastics threatens ecosystem health by entering the environment and ultimately restricts sustainable human development. The innovation of sustainable and environmentally friendly single-use plastic alternative materials and the joint participation of governments, enterprises and the public are promising technologies and management approaches that can solve the problem of single-use plastics wastes. The development of single-use plastic alternative products can be promoted fundamentally only by improving relevant legislation and standards, providing differentiated industrial policies, encouraging scientific and technological innovation and expanding public participation.

         

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