Strong Lewis Acid Base Research Articles

Polysulfide Regulation by Hypervalent Iodine Compounds for Durable and Sustainable Lithium-Sulfur Battery.

Herein, a type of hypervalent iodine compound-iodosobenzene (PhIO)-is proposed to regulate the LiPSs electrochemistry and enhance the performance of Li-S battery. PhIO owns the practical advantages of low-cost, commercial availability, environmental friendliness and chemical stability. The lone pair electrons of oxygen atoms in PhIO play a critical role in forming a strong Lewis acid-base interaction with terminal Li in LiPSs. Moreover, the commercial PhIO can be easily converted to nanoparticles (≈20nm) and uniformly loaded on a carbon nanotube (CNT) scaffold, ensuring sufficient chemisorption for LiPSs. The integrated functional PhIO@CNT interlayer affords a LiPSs-concentrated shield that not only strongly obstructs the LiPSs penetration but also significantly enhances the electrolyte wettability and Li+ conduction. The PhIO@CNT interlayer also serves as a "vice current collector" to accommodate various LiPSs and render smooth LiPSs transformation, which suppresses insulating Li2 S2 /Li2 S layer formation and facilitates Li+ diffusion. The Li-S battery based on PhIO@CNT interlayer (6 wt% PhIO) exhibits stable cycling over 1000 cycles (0.033% capacity decay per cycle) and excellent rate performance (686.6 mAh g-1 at 3 C). This work demonstrates the great potential of PhIO in regulating LiPSs and provides a new avenue towards the low-cost and sustainable application of Li-S batteries.

Vanadium Monoxide-Based Free-Standing Nanofiber Hosts for High-Loading Lithium-Sulfur Batteries

We report the fabrication of free-standing vanadium monoxide-based carbon nanofiber/sulfur (VO-CNFs/S) cathodes via electrospinning and in situ carbothermal reduction reaction followed by sulfur impregnation using an ultrarapid (<90 s) hybrid solution/melt deposition technique. The assembled Li-S batteries using VO-CNFs/S cathodes delivered a stable capacity of 950 mAh·g–1 with 97% retention after 200 cycles at a 0.5 C rate with a moderate electrolyte/sulfur ratio of 20 mL·g–1 of sulfur. Additionally, we develop cathodes with a high sulfur loading of 8.32 mg·cm–2 that exhibits a stable capacity of 900 mAh·g–1 after a few cycles with near 100% retention over 100 cycles. These cells correspond to a stable aerial capacity of 7.5 mAh·cm–2. We integrate our fabrication and electrochemical performance study with fundamental investigations of Li+ diffusion kinetics, in situ visual monitoring of polysulfides, and ex situ post-mortem X-ray photoelectron spectroscopy study to elucidate polysulfide shuttling and polysulfide–host interactions. The unique integration of oxide and nitride groups in this work results in a synergistic effect of strong Lewis acid–base interactions originating from the vacant d-orbitals of the vanadium monoxide phase and improved conductivity originating from the nitrogen doping in CNFs from a polymeric precursor, thus offering active sites for strong polysulfide binding as well as faster reaction kinetics.

Easily modified barium phosphate composites for effective removal of methyl blue from solution

In this work, barium phosphate composites were easily modified by changing the reactants and surfactants to be barium sodium phosphate (NaBaPO4), barium phosphate (Ba3(PO4)2), barium hydroxyl phosphate (Ba5(PO4)3OH), and barium hydrogen phosphate (BaHPO4) (denoted NBP, BP, BPO, and BHP, respectively) using a one-step hydrothermal method. Positively charged cetyl trimethyl ammonium bromide (CTAB) on phosphate composites can slightly increase their removal capacities for methyl blue (MB) though it had no obvious effects on the composition and crystal type of materials. Dye removal experiments were carried out in a batch system to optimize operation variables such as solution pH, temperature, adsorbent dosage, contact time, and initial dye concentration. The kinetic behavior of all the materials agreed well with the pseudo-second-order model. The isothermal data of NBP and BPO fitted to the Langmuir model while Freundlich model was better to describe the isothermal data of BP and BHP. The removal capability for MB solution followed an order of NBP (249.6 ± 6.0 mg/g) > BP (226.0 ± 6.0 mg/g) > BPO (162.5 ± 5.0 mg/g) > BHP (85.84 ± 4.0 mg/g). NBP is most suitable for MB removal because of its high alkalinity: (1) The obvious increase of pH from 6.03 ± 0.10 to 12.26 ± 0.20 after adding NBP in solution can lead to improved decolorization of MB solution. (2) Strong Lewis acid base interaction between cations (Ba2+/Na+) in NBP and –SO3- in MB as well as the hydrogen bonding between PO43- in NBP and N–H or C–H in MB contributed to the high removal capacity of NBP.

Strong Lewis Acid-Base and Weak Hydrogen Bond Synergistically Enhancing Ionic Conductivity of Poly(ethylene oxide)@SiO2 Electrolytes for a High Rate Capability Li-Metal Battery.

Solid-state composite polymer electrolytes (CPEs) usually suffer from intrinsic low ionic conductivity and a solid-solid interface, badly inhibiting their widespread commercial application in all-solid-state Li-metal battery (ASSLMB) energy storage. Herein, a synergetic strategy using strong Lewis acid-base and weak hydrogen bonds was employed for self-assembly in situ construction of three-dimensional (3D) network-structured poly(ethylene oxide) (PEO) and SiO2 CPEs (PEO@SiO2). Ascribed to this synergistically rigid-flexible coupling dynamic strategy, a harmonious incorporation of monodispersed SiO2 nanoparticles into PEO could remarkably reduce crystallinity of PEO, significantly enhancing the ionic conductivity (∼1.1 × 10-4 S cm-1 at 30 °C) and dramatically facilitating solid electrolyte interface stabilization (electrochemical stability window > 4.8 V at 90 °C). Moreover, the PEO@SiO2-based ASSLMBs possess excellent rate capability over a wide temperature range (∼105 mA h g-1 under 2 C at 90 °C), high temperature cycling capacity (retaining 90 mA h g-1 after 100 cycles at 90 °C), and high specific capacity (146 mA h g-1 under 0.3 C at 90 °C). Unambiguously, these high ionic conductivity CPEs along with excellent flexibility and safety can be one of the most promising candidates for high-performance ASSLMBs, evidently revealing that this synergistically rigid-flexible coupling dynamic strategy will open up a way to exploit the novel high ionic conductivity solid-state electrolytes.

Investigating the Effect of Lewis Acid Base Interaction in Non-Stoichiometric Vanadium Oxide Based CNFs in Lithium – Sulfur Battery

Despite the potential of lithium-sulfur batteries to reach practical energy densities of 500–600 Wh/kg, there are still many problems plaguing their development. The sulfur cathode suffers from low electrochemical utilization and poor cycle life owing to the insulating nature of S and the Li2S discharge product, and the shuttling of lithium polysulfide species especially at high areal mass loadings. Enormous progress has been achieved in terms of capacity and static life during the past few years to overcome these issues, by employing various carbon and inorganic materials (metal oxides, metal-organic frameworks). Recently, non-stoichiometric metal oxides have been employed as sulfur host materials due to their high conductivity and ability to bind polysulfides chemically through unsaturated metal ion sites. However, the formation of metal-suboxides involves a high-temperature calcination process, which usually results in dense host materials with lower accessible surface area, and a reduced host/polysulfide interaction. Moreover, these studies are often reported with low sulfur loadings (1–2 mg/cm2) resulting in lower areal capacity. Herein, we report the use of electrospun vanadium monoxide/carbon nanofibers (VCNFs) as cathode host in Li-S batteries, which provide high electrical conductivity for better sulfur utilization and strong Lewis acid-base interaction with polysulfides to suppress shuttle. The developed cathode possesses hierarchical micro-mesoporous architecture with inter-fiber spacing and a high surface area of 181 m2/g. The unique architecture overcomes the challenges associated with dense, low active surface area based powered oxide materials. The developed VCNFs-S cathodes with a high sulfur loading of 3 mg/cm2 exhibit initial discharge capacities of ∼1350, ∼1247, and ∼1113 mAh g–1 at 0.1, 0.2, and 0.5 C rates, respectively, with long-term cycling (Fig 1a) over 200 cycles at 0.5 C rate. Moreover, at ~7mg/cm2, Li-S cells exhibit high areal capacity of 8 mAh/cm2 at a current density of C/10 up to 50 cycles (Fig 1b). The high surface area results in active reaction sites spread throughout the VCNFs, improving the accessible reaction area for better binding of polysulfides, enabling the smooth operation at high-loading in Li-S system. Using postmortem X-ray photoelectron spectroscopy analysis, this study reveals the presence of strong Lewis acid–base interaction between VO (3d3) and Sx 2– through the coordinate covalent V–S bond formation. Additionally, freestanding nature of the cathodes eradicate the need of additional inactive elements, viz., binders, additional current collectors (Al-foil), and additives. Our results highlight the importance of developing high surface area metal-suboxides/monoxide-based conducting polar host materials for next-generation Li–S batteries. Figure 1

Different adsorption-degradation behavior of methylene blue and Congo red in nanoceria/H2O2 system under alkaline conditions

The Fenton-like activity of nanoceria has attracted intensive attention for wastewater treatment in recent years. During the Fenton-like reaction, the adsorption of organic pollutants on catalyst surface plays a key role in their degradation. In this work, the adsorption-degradation of methylene blue (MB) and Congo red (CR) in nanoceria/H2O2 system was investigated under alkaline conditions. The MB exhibited weak adsorption on nanoceria surface via electrostatic attraction, while strong Lewis acid–base interactions between CR and cerium ions was observed. Moreover, the adsorption of MB was enhanced in the presence of H2O2 by the formation of surface peroxide species, but an adsorption competition existed between H2O2 and CR. With more Ce3+, CeO2 nanorods could degrade CR efficiently as Fenton-like catalyst. But the degradation of MB catalyzed by ceria was much lower than that of CR in the presence of H2O2.

Understanding Alkane Dehydrogenation through Alcohol Dehydration on γ-Al2O3

Nonoxidative dehydrogenation of alkanes is an important chemical reaction, as it can be used for production of olefins, commonly used as building blocks for a range of plastics and chemicals. Several metal oxides, including γ-Al2O3, have exhibited dehydrogenation activity, showing promise as candidates for the upgrade of alkanes. In this work we use computational chemistry methods to investigate the mechanism of ethane, propane, n-butane, and i-butane dehydrogenation pathways on strong Lewis acid–base sites of γ-Al2O3. On the basis of our calculations, it was shown that a concerted dehydrogenation mechanism is energetically preferred with the formation of a carbenium-ion-like transition state. An alkane dehydrogenation model was developed on the basis of methodology previously applied in structure–activity relations (SAR) for alcohol dehydration on metal oxides. The carbenium ion stability (CIS), shown to be a descriptor in alcohol dehydration, was used as a quantitative descriptor in alkane dehydrogenati...

Direct transformation of bulk copper into copper single sites via emitting and trapping of atoms

Single-atom catalysts exhibit intriguing properties and receive widespread interest for their effectiveness in promoting a variety of catalytic reactions, making them highly desired motifs in materials science. However, common approaches to the synthesis of these materials often require tedious procedures and lack appropriate interactions between the metal atoms and supports. Here, we report a simple and practical strategy to access the large-scale synthesis of single-atom catalysts via direct atoms emitting from bulk metals, and the subsequent trapping on nitrogen-rich porous carbon with the assistance of ammonia. First, the ammonia coordinates with the copper atoms to form volatile Cu(NH3)x species based on the strong Lewis acid–base interaction. Then, following transportation under an ammonia atmosphere, the Cu(NH3)x species are trapped by the defects on the nitrogen-rich carbon support, forming the isolated copper sites. This strategy is readily scalable and has been confirmed as feasible for producing functional single-atom catalysts at industrial levels. Single-atom catalysts have proven successful in many catalytic applications. Now, Li, Wu and co-workers show that single-atom catalysts can be prepared directly from bulk metals using an ammonia atmosphere, owing to the formation of volatile metal–ammonia species that are trapped by the nitrogen-rich carbon support.

Abnormal synergistic effects between Lewis acid–base interaction and halogen bond in F3B···NCX···NCM

An abnormal synergistic effect was found between the Lewis acid–base interaction and halogen bond in triads F3B···NCX···NCM (X and M are halogen atoms), where the strong Lewis acid–base interaction between F3B and NCX has a larger enhancement than the weak halogen bond between NCX and NCM. This is in contrast with the traditional cooperative effect. It is interesting that the alkali-metal substituent as well as the heavier halogen atom play a more remarkable role in the enhancement of the interaction F3B···NCX than that of NCX···NCM, particularly, the alkali-metal substituent makes the abnormal synergistic effect be the traditional cooperative one.

Oscillational motion properties of bacteria and polystyrene particles on a positively polarized substrate surface

The oscillational motion of bacteria and non-biological particles on a positively polarized substrate surface were investigated in this study using several bacterial species (Staphylococcus epidermidis ATCC12228 and Pseudomonas aeruginosa PA14) and polystyrene particles (modified with sulfate or carboxylate) that have different cell/particle size, surface potential, surface ionizable functional group, and surface appendage with respect to the mean square displacement (MSD) and motion trajectory. The attractive/repulsive interactions between the bacteria/particle and a positively polarized substrate surface are further discussed with the results of the motion analysis based on the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. As our major findings, all the bacterial species and particles showed oscillational motion, a kind of sub-diffusive motion that is more limited than the Brownian motion of the suspended bacteria/particles, on a positively polarized substrate surface. However, the motion properties among the bacteria/particles were found to differ in motion radius and MSD. As the size and negative surface potential of the bacteria/particle got smaller, the oscillational motion became more active, which may result from a decrease in attractive interactions such as van der Waals interaction and electrostatic attractive interaction. In the case in which some surface functional group (e.g., sulfate group) contributed to the formation of a strong Lewis acid–base interaction, the oscillational motion was significantly reduced regardless of the surface potential of the particle. The bacterial surface appendages were found to have no influence in explaining motion differences between the bacteria and non-biological particle.

Examination of fabrication conditions of acrylate-based hydrogel formulations for doxorubicin release and efficacy test for hepatocellular carcinoma cell

The objective of the present study was to develop 2-hydroxypropyl methacrylate-co-polyethylene methacrylate [p(HPMA-co-PEG–MEMA)] hydrogels that are able to efficiently entrap doxorubicin for the application of loco-regional control of the cancer disease. Systemic chemotherapy provides low clinical benefit while localized chemotherapy might provide a therapeutic advantage. In this study, effects of hydrogel properties such as PEG chains length, cross-linking density, biocompatibility, drug loading efficiency, and drug release kinetics were evaluated in vitro for targeted and controlled drug delivery. In addition, the characterization of the hydrogel formulations was conducted with swelling experiments, permeability tests, Fourier transform infrared, SEM, and contact angle studies. In these drug-hydrogel systems, doxorubicin contains amine group that can be expected a strong Lewis acid–base interaction between drug and polar groups of PEG chains, thus the drug was released in a timely fashion with an electrostatic interaction mechanism. It was observed that doxorubicin release from the hydrogel formulations decreased when the density of cross-linking, and drug/polymer ratio were increased while an increase in the PEG chains length of the macro-monomer (i.e. PEG–MEMA) in the hydrogel system was associated with an increase in water content and doxorubicin release. The biocompatibility of the hydrogel formulations has been investigated using two measures: cytotoxicity test (using lactate dehydrogenase assay) and major serum proteins adsorption studies. Antitumor activity of the released doxorubicin was assessed using a human SNU398 human hepatocellular carcinoma cell line. It was observed that doxorubicin released from all of our hydrogel formulations which remained biologically active and had the capability to kill the tested cancer cells.

Unraveling the High Uptake and Selectivity of CO2 in the Zeolitic Imidazolate Frameworks ZIF-68 and ZIF-69

Understanding the CO2 adsorption mechanism of zeolitic imidazole frameworks (ZIFs) is the key to improving the adsorption ability of new metal–organic framework materials for gas capture applications and designing novel frameworks. In this work, the ONIOM2(B3LYP/6-31G**:UFF) method is used to investigate the interactions between CO2 and CO molecules with ZIF-68 and ZIF-69, respectively. Calculation results indicate that a strong Lewis acid–base interaction exists between the gas molecules and nitro groups of 2-nitroimidazole linkers, which thus prevents the entry of gas molecules into the small pores of ZIFs. The simultaneous interaction of both oxygen atoms of CO2 with the H atoms of the benzimidazole (5-chlorobenzimidazole) rings in the large pores results in the high CO2 selectivity observed for both ZIFs. The presence of electron-withdrawing groups in the phenylimidazole linker of ZIF increases the interaction between the oxygen atoms of CO2 and hydrogen atoms of the phenyl rings in its large pores. T...

Lewis acid–base property of P(VDF‐co‐HFP) measured by inverse gas chromatography

AbstractPoly (vinylidene fluoride‐co‐hexafluoropropylene) P(VDF‐co‐HFP) is an excellent material for polymer electrolytes of lithium ion battery. To enhance the lithium ion transference number, some metal oxides were often embedded into P(VDF‐co‐HFP). The promising mechanism for the increase in lithium ionic conductivity was Lewis acid‐base theory. In this experiment, the Lewis acid–base properties of P(VDF‐co‐HFP) were measured by inverse gas chromatography (IGC). The Lewis acid constant Ka of P(VDF‐co‐HFP) is 0.254, and the base constant Kb is 1.199. Compared with other polymers characterized by IGC, P(VDF‐co‐HFP) is the strongest Lewis basic polymers. Except aluminum ion, lithium ion is the strongest Lewis acidic ion according to their η value of Lewis acids. Therefore, a strong Lewis acid–base interaction will exist between lithium ion and P(VDF‐co‐HFP). This will restrict the transference of lithium ion in P(VDF‐co‐HFP). To enhance the lithium ion transference by blending other metal ions into P(VDF‐co‐HFP), it is suggested that the preferential ions should be Al3+, Mg2+, Na+, and Ca2+ because these metal ions have relative large η values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

An investigation on the cation-exchange and Lewis-base interactions of a n-octadecylphosphonic acid-modified magnesia–zirconia stationary phase

The cation-exchange and Lewis-base interactions of a n-octadecylphosphonic acid-modified magnesia–zirconia (C 18PZM) stationary phase have been studied in greater detail than previous studies, which are characterized by the chromatography of some basic drugs of high p K a and some hard Lewis base analytes, respectively. The effect of mobile phase constituents such as pH, type of buffer and buffer concentration on the surface chemistry properties on C 18PZM are elucidated. The results show that at an intermediate pH, the cation-exchange sites are due to both the chemisorbed phosphonate and the adsorbed buffer anion, i.e. acetate, at the hard Lewis acid sites on the C 18PZM phase; at high pH, the cation-exchange interactions mainly result from the chemisorbed phosphonate rather than the inherent zirconol groups. The chromatography of the hard Lewis base analytes indicates that a strong Lewis acid–base interaction still exists on C 18PZM even in the presence of Lewis base buffer (such as acetate or phosphate) in the mobile phase or a high-pH eluents is used. Moreover, the chemisorbed n-octadecylphosphonic acid (C 18P) is found to slowly bleed out of the C 18PZM column when exposed to a phosphate buffer. As expected, the resulting mobile-phase phosphate modified C 18PZM column (p-C 18PZM) exhibits significantly stronger cation-exchange interactions towards the test basic solutes than the “original” C 18PZM column. And the p-C 18PZM column demonstrates a tremendous improvement on the chromatography of the Lewis base analytes over the “original” C 18PZM column. An approach designed to overcome the Lewis acid sites problem by attaching methylphosphonic acid (MPA) onto the C 18PZM column, however, is not successful in improving the chromatography of the troublesome Lewis base solutes.

Nanocomposite polymer electrolyte based on Poly(ethylene oxide) and solid super acid for lithium polymer battery

This Letter reports a novel PEO-based nanocomposite polymer electrolyte by using solid super acid SO 4 2−/ZrO 2 as filler. XRD, DSC, and FT-IR results prove the strong Lewis acid–base interactions between SO 4 2−/ZrO 2 and PEO chains. The addition of SO 4 2−/ZrO 2 can enhance the ionic conductivity and the lithium ion transference number of the electrolyte. The highest room temperature ionic conductivity of 2.1 × 10 −5 S cm −1 is obtained for the sample PEO 12–LiClO 4–7%SO 4 2−/ZrO 2. The excellent performances such as good compatibility with lithium electrode, and broad electrochemical stability window suggest that PEO–LiClO 4–SO 4 2−/ZrO 2 nanocomposite electrolyte can be used as electrolyte materials for lithium polymer batteries.

Ligand exchange ion–molecule reactions of simple silyl and germyl cations

The gas-phase reaction of Me 3Si + with Si(OMe) 4, studied under FT-ICR conditions, reveals that aside from the expected silyl ion– n-donor base association an exchange mechanism exists that gives rise to Me 2SiOMe +. Further reaction of this ion was observed to result in a second exchange of a methyl group by a methoxy group in the silyl ion. The similar reaction between Me 3Si + and Ge(OMe) 4 yields not only the silyl ions with progressive exchange of methyl by methoxy but the different germyl ions, Me n Ge(OMe) 3− n + ( n=0–3). Ab initio calculations for the simple model system MeSiH 2 ++MeOGeH 3 reveal that these reactions proceed by initial formation of a very strong Lewis acid–base complex where migration of the germyl or silyl group can result in a moiety held together by an alkyl bridge. Methide abstraction in this intermediate can then give rise to silyl and germyl cations. The present results suggest that other Si and Ge systems may display this very same kind of rich chemistry.

Capillary electrophoresis and open tubular capillary electrochromatography using a magnesia–zirconia coated capillary

A novel magnesia–zirconia coating was fabricated inside fused-silica capillaries. The capillaries coated with magnesia–zirconia exhibited switchable electro-osmotic flow (EOF) whose magnitude and direction can be manipulated by changing the pH of running electrolyte. In Tris electrolyte at high pH (>5.2), the direction was from anode toward cathode, whereas at low pH (<5.2), the direction of EOF was reversed. The magnesia–zirconia coated capillary can be modified by SO 4 2− and alkylphosphonate easily based on strong Lewis acid–base interaction. The separations of six basic compounds were compared on magnesia–zirconia coated capillary and SO 4 2− modified magnesia–zirconia coated capillary under different conditions. It was found that the SO 4 2− modified magnesia–zirconia coated capillary with reversed EOF in Tris–methanol (80/20, v/v) at pH 2.5 was suitable for the separation of the six basic compounds. For the alkylphosphonate modified magnesia–zirconia coated capillary, the alkyl moiety on the inner wall enabled it to separate polycyclic aromatic hydrocarbon (PAH). Six PAHs were separated on the alkylphosphonate modified magnesia–zirconia coated capillary with CH 3CN+20 mmol/l Tris (25/75, v/v) as the mobile phase within 13 min. The magnesia–zirconia coated capillary was stable over a wide pH range.

Selective oxidation of aromatic compounds on zeolites using N 2O as a mild oxidant : A new approach to design active sites

Dehydroxylated ZSM-5 type zeolites are used for selective oxidation of aromatic compounds, including benzene, chlorobenzene, styrene, difluorobenzenes, phenol, alkylbenzenes into corresponding phenols and diphenols using nitrous oxide as a mild oxidant. In the case of benzene, the yield of phenol reaches 70–80%. Extremely high selectivity (∼98–100%) in the case of benzene and ∼85% in the case of difluorobenzenes and high regioselectivities are observed on the dehydroxylated HZSM-5 zeolite. The active sites are shown to be the strong Lewis acid–base pair sites formed upon dehydroxylation of the zeolites. The reaction mechanism that is alternative to the proposed iron-mediated mechanism is discussed.

Sorption enhancement of some hydrophilic organic solutes through polymeric ligand exchange

This study identifies and characterizes a new class of polymeric sorbents with unusually high affinity toward oxalates, phthalates, and possibly other anionic organic solutes. These sorbents are specialty chelating polymers with immobilized transition-metal cations, such as copper(II), and prefer anionic ligands over competing sulfate and chloride ions. Anion exchange accompanied by strong Lewis acid-base (or metal-ligand) interaction is the underlying reason for their high sorption affinity toward these organic solutes