Incorporation of Natural Lithium-Ion Trappers into Graphene Oxide Nanosheets

© 2020 Wiley-VCH GmbH Lithium consumption is estimated to face a considerable rise in the next decade; thus, finding new reproducible lithium resources such as brine deposits and seawater has become a fast-growing research topic. However, Li+ extraction from these resources is challenging due to its low concentration and presence of other monovalent cations exhibiting identical chemical properties. Here, it is discovered that tannic acid (TA) inside graphene oxide (GO) nanochannel acts as natural ion trapper, which possesses lithiophilic elements. The lithium-rich feed is achieved by using the potential-driven TA-GO membrane by excluding lithium ions from other monovalent cations. The results showed that the ion trapping capability of inexpensive TA-GO membrane is Li+ > Na+ > K+ with Li trapping energy of −593 KJ mol−1, respectively, where its trapping efficiency goes into a top rank among their expensive synthetic counterparts. Evaluating the combined effect of three key parameters, including barrier energy, hydration energy, and binding energy illustrates that required energy to transport Li-ion through the membrane is higher than that for other monovalent. This proof-of-concept work opens up an avenue of research for designing a new class of ion-selective membranes, based on the incorporation of naturally low cost available lithiophilic guest molecules into 2D membranes

A Novel Ecdysone Receptor Mediates Steroid-Regulated Developmental Events during the Mid-Third Instar of Drosophila

The larval salivary gland of Drosophila melanogaster synthesizes and secretes glue glycoproteins that cement developing animals to a solid surface during metamorphosis. The steroid hormone 20-hydroxyecdysone (20E) is an essential signaling molecule that modulates most of the physiological functions of the larval gland. At the end of larval development, it is known that 20E—signaling through a nuclear receptor heterodimer consisting of EcR and USP—induces the early and late puffing cascade of the polytene chromosomes and causes the exocytosis of stored glue granules into the lumen of the gland. It has also been reported that an earlier pulse of hormone induces the temporally and spatially specific transcriptional activation of the glue genes; however, the receptor responsible for triggering this response has not been characterized. Here we show that the coordinated expression of the glue genes midway through the third instar is mediated by 20E acting to induce genes of the Broad Complex (BRC) through a receptor that is not an EcR/USP heterodimer. This result is novel because it demonstrates for the first time that at least some 20E-mediated, mid-larval, developmental responses are controlled by an uncharacterized receptor that does not contain an RXR-like component

Integrally hydrophobic cementitious composites made with waste amorphous carbon powder

© 2019 Amorphous carbon powder (ACP) is a hydrophobic by-product material from refining waste materials of paraffin production factory. ACP effects on permeability and mechanical properties of cementitious composites were investigated. A range of properties of modified cement paste and concrete including hydrophobicity, workability, porosity, compressive strength, transport properties comprising sorptivity, water absorption, water desorption rate and electrical resistivity were studied. Results showed that incorporation of 15% ACP by weight of cement reduces water absorption, sorptivity and electrical conductivity of cement paste by 23%, 86% and 65%, respectively. Sorptivity and electrical conductivity of modified concrete samples by 20% ACP by weight of cement, were reduced by 60% and 30%, respectively. Adding ACP to paste samples resulted in higher compressive strength through lowering porosity. However, in the case of concrete, no significant change was observed. It was demonstrated that ACP could reduce the wettability of cementitious composites by refining the pores and altering the hydrophobicity characteristics of cementitious composites

Insight from perfectly selective and ultrafast proton transport through anhydrous asymmetrical graphene oxide membranes under Grotthuss mechanism

Protons transport profoundly affects diverse fields from proton-exchange membrane fuel cells to storing liquid hydrogen. Recent advances have extended proton-exclusive transport to the two-dimensional channels that use hydrous mechanisms for fast proton transport, where the main challenge is the limited selectivity. However, the physical and chemical properties of 2D nanosheets like GO have the potential to implement full selective and ultrafast proton transport. Here, we uncover the physical potential of anhydrous proton transfer mechanism inside two-dimensional space between graphene nanosheets to exploit the exceptional full proton-selective ability and ultrafast conveyance speed of the Grotthuss mechanism. Reactive molecular dynamics simulations illustrate that the interlayer space between two graphene oxide nanosheets, carpeted with hydroxyl functional groups as additional hopping stages to enable the Grotthuss mechanism, can convey protons without water. Further, we dissect three essential factors that provide a deeper insight into ultrafast proton transport: (i) transitional phase to full anhydrous transport, (ii) outlet size for containing undesired species, and (iii) elastic behavior of the membranes under external strain. Our results show that changes in surface geometry can dramatically increase the diffusion rate in the presence of a small electric field by ~70% compared to hydrous transport. These findings can be used not only to guide the efforts in manufacturing a new generation of sustainable nanochannels but also to advance the pioneering technologies revolving around hydrogen

New molecular understanding of hydrated ion trapping mechanism during thermally-driven desalination by pervaporation using GO membrane

© 2019 Elsevier B.V. The graphene oxide (GO)-based membranes have shown effective salt separation from the brine solution. Although several experimental works have been done to study the salt rejection in the thermal-driven desalination system, the behavior of ions inside the GO nanochannels during the pervaporation process remains mostly unelucidated. Moreover, the previous theoretical studies on the driving force for ion transport within the GO membrane only focused on pressure, voltage, or concentration gradient. Here, we investigated the transport of water molecules and hydrated cations through the GO membrane in a temperature-assisted system by using dispersion-corrected density functional theory (DFT) calculations at PBE/Grimme with the ions under extreme confinement, reactive molecular dynamics (MD) simulations as well as validated by experimental methods. The water permeation increases with temperature, while the transport of cations remains minimal, which was not observed in other non-thermal desalination approaches. We have shown that high temperature eases the binding between the hydrated divalent cations and the oxygen functional groups on the GO nanosheets by reducing the hydration shell. Furthermore, the cross-linked cations inside the GO nanochannel create an accessible corridor for water molecules and block other cations such as Na+. Our simulation results provide a new mechanism of ion transport in the GO membranes by the thermal-driven process, which can be tailored by using other cations with higher charge density and high temperature to speed up the process

Low humid transport of anions in layered double hydroxides membranes using polydopamine coating

Lithium carbonate and lithium hydroxide are two compounds used for producing battery cathodes, however, lithium hydroxide is favoured in producing battery compounds as it possesses very high electrochemical potential and low density. As a result, there is substantial demand for development of anion-selective membranes capable of selecting hydroxide over carbonate. Although single-layer nanosheets of Layered Double Hydroxides (LDHs) have shown anion conductivity, the reassembling of the building blocks in a membrane-like morphology will not result in a conductive membrane. Here we show that an appropriate size of LDH nanosheets with post-treatment with polydopamine (PDA) can form a highly conductive hydroxide-selective membrane. Our experimental results show that the in-plane ion conductance of the membrane for different ions is OH− > Br− > I− > NO3− > Cl− > CO32− with corresponding selectivity ratios of OH− to Br−, I−, NO3−, Cl−, CO32− found to be 2.30, 2.83, 2.99, 3.11 and 4.38 respectively, showing the membrane's excellent hydroxide selectivity. Molecular dynamics (MD) simulations revealed that the small nanochannels of LDH increase its diffusion barrier against ion permeation and cause the partial dehydration of ions. We showed that ions move inside the LDH nanochannels in a semi-dry transport manner so that they attract to the surface more than water molecules inside the nanochannels. Selectivity predictions from MD simulations were in excellent agreement with the experimental data, confirming our hypothesis about ion transport in LDH nanochannels. This work takes advantage of the semi-dry transport mechanism of anions in the narrow nanochannels of LDHs to produce a hydroxide selective membrane applicable in the production of LiOH for the new generation of Li-ion batteries