Ionic Liquid Modification Research Articles

Enhanced photovoltaic performance of SnO2 based flexible perovskite solar cells via introducing interfacial dipolar layer and defect passivation

Low processing temperature of tin dioxide (SnO 2 ) is essential for flexible perovskite solar cells (f-PSCs). However, the low processing temperature of SnO 2 results in an inferior photovoltaic performance due to compromised carrier transport capacity in devices. The deteriorated carrier transport mainly results from the suppressed interfacial charge transfer. To overcome these issues, we used ionic liquid to modify the interface between perovskite films and SnO 2 in f-PSCs. Density Function Theory calculations were implemented to demonstrate the ionic liquid modification induced the formation of interfacial dipolar layer (IDL) and defect passivation in perovskites. The IDL and defect passivation improves the interfacial charge transfer and intra-perovskite charge transport, respectively. As a result, the f-PSCs based on ionic liquid modified SnO 2 yield the champion power conversion efficiency (PCE) of 19.0%. This work provides a method to effectively improve the performance of f-PSCs using low-temperature processed SnO 2 ESLs using affordable materials and a facile approach. • Ionic liquid is used to form an interfacial dipole layer (IDL). • Ionic liquid can also passivate defects in perovskite. • IDL and defects passivation contribute to the performance improvement of f-PSCs. • All fabrication processes of f-PSCs are conducted at the low temperature (≤100 °C). • Power conversion efficiency of f-PSCs is improved from 13.5% to 18.1%.

Thermal stability enhancement mechanism of engine oil using hybrid MoS2/h-BN nano-additives with ionic liquid modification

One of the primary causes of lubricating oil failure in automobile engines is thermal degradation caused by high temperatures, which prejudices the lube oil capacity between friction pairs. This research aims to comprehensively investigate the effect of the h-BN/MoS2 hybrid nanoparticles and ionic liquid (IL) on the thermal performance of engine oil (5 W-40). The rheological results showed that nanolubricants (NL) behave like non-Newtonian fluids and IL promoted the viscosity value of lubricant due to the extension of alkyl chains. The thermal peculiarities of lube oil were analyzed by thermogravimetric (TGA/DTG/DSC) analysis to explore the thermal stability of h-BN/MoS2 hybrid nano-lubricants modified by IL and further revealed how IL improved the thermal characteristics. The results strongly showed the synergistic effect between the IL and h-BN/MoS2 hybrid nanoparticles produces a complicated interaction at high temperatures, forming a layer of film which can delay the erosion of high temperature on the surface of the nanoparticles. Ultimately, this study revealed a delay of burnout temperature in thermal degradation by approximately 8.1% under the use of hybrid nano-lube oils in a wide temperature range.

Enhancement of CO2 adsorption on natural zeolite, modified clinoptilolite with cations, amines and ionic liquids

The modification of clinoptilolite as a natural zeolite via a simple route was carried out for CO2 adsorption. Cation exchange with Li+, Mg2+, and Ca2+, amine modification using monoethanolamine (MEA), triethanolamine (TEA) and hexyl amine, and ionic liquid modification using [bmim]X (X = PF6⁻, NO3⁻, Br⁻, Cl⁻, and bmim = 1-Butyl-3-methylimidazolium) were performed in a different amount of the modifiers. The samples were characterized by several methods (XRD, FT-IR, BET, and SEM), and adsorbed CO2 was evaluated utilizing adsorption isotherm at a wide range of pressure. The results showed enhancement in CO2 adsorption capacity for all the samples and 4.18, 3.58, and 4.35 times increase in CO2 adsorption were obtained where clinoptilolite/Li+, clinoptilolite/2% MEA and clinoptilolite/5% [bmim]PF6 were used as adsorbent at 4 bar pressure of CO2, respectively.

The Activity Enhancement Effect of Ionic Liquids on Oxygen Reduction Reaction Catalysts: From Rotating Disk Electrode to Membrane Electrode Assembly

Ionic liquids (ILs) have been explored as a surface modification strategy to promote the oxygen reduction reaction (ORR) on Pt/C and their chemical structures were identified to have strong influence on the ORR activities. To better understand the roles of anion and cation of ILs on the catalytic reaction, two cations ([MTBD]+ and [bmim]+) were paired with three anions ([TFSI]−, [beti]−, and [C4F9SO3]−) to form various IL structures. By systematically varying the IL combinations and studying their effects on the electrochemical behaviors, such as electrochemical surface area and specific ORR activities, it was found that cation structure had a higher influence than anion, and the impact of the [MTBD]+ series was stronger than the [bmim]+ series. In addition to the investigation in the half-cell, studies were also extended to the membrane electrode assembly (MEA). Considerable performance enhancements were demonstrated in both the kinetic region and high current density region with the aid of IL. This work suggests that IL modification can provide a complementary approach to improve the performance of proton exchange membrane fuel cells.

Synergistic Catalysis of Ionic Liquid-Decorated Covalent Organic Frameworks with Polyoxometalates for CO2 Cycloaddition Reaction under Mild Conditions

The cycloaddition of carbon dioxide (CO2) with epoxides to yield highly value-added cyclic carbonates is an effective way to chemically utilize and convert CO2. Here, a heterogeneous catalyst of imidazole ionic liquid-decorated covalent organic framework with polyoxometalates (POM@ImTD-COF) was constructed by the covalent modification of ionic liquids to COFs and the electrostatic interaction between POMs and ionic liquids. The obtained POM@ImTD-COF shows high catalytic activity for CO2 cycloaddition reaction under mild conditions (1 atm and 80 °C) in the presence of a co-catalyst, and the catalytic activity of POM@ImTD-COF has no obvious decrease during reusing five times. The excellent catalytic performance is mainly attributed to the synergistic effect of ionic liquids, POMs, and COFs. In the cycloaddition process, ionic liquids and the co-catalyst weaken the C-O bond of epoxides and promote the ring opening of epoxides. POMs as the Lewis acids facilitate the insertion of CO2 to form reaction intermediates. The multiple activation effect of ionic liquids and POMs together with the CO2 adsorption effect and well-dispersed active sites in COFs contribute to the remarkable catalytic performance.

Enhanced oxygen reduction performance of nitrogen and sulfur Co-doped graphene oxide by immobilized ionic liquid

The development of robust metal-free catalysts for electrochemical oxygen reduction reaction (ORR) is a great challenge due to the large energy barriers for the intermediate *OO− formation. In this work, an ionic liquid (IL) modified N/S co-doped graphene oxide (IL-SNG) was synthesized and explored as a metal-free ORR catalyst in alkaline conditions. Compared to the electrode without IL modification (SNG), the onset and half-wave potentials of IL-SNG were positively shifted by 130 and 110 mV, respectively. The IL and co-doping effects enable IL-SNG a comparable activity to that of Pt/C catalyst in alkaline solution. In addition to impressive activity, IL-SNG exhibits a superior tolerance to methanol and excellent long-term stability over Pt/C under the identical conditions, enabling it a potential candidate for ORR in alkaline conditions. DFT calculation shows that IL enhances O2 adsorption and stabilizes the high-energy *OO− intermediate by forming ion pairs and therefore boosts the catalytic activity.

Effective hydrogenation of CO2 to formate catalyzed by ionic liquid modified acetate-Cu

The catalytic ability of acetate-Cu was greatly enhanced by ionic liquid modification in the hydrogenation of CO2.

Ionic liquid modification of metal-organic framework endows high selectivity for phosphoproteins adsorption

Zr-based metal-organic framework, UiO-66-NH2, provides favorable adsorption capacity to phosphoproteins, however, it exhibits obvious nonspecific adsorption to other proteins. In the present work, we report a facile strategy to reduce the nonspecific adsorption of nonphosphoproteins by modifying UiO-66-NH2 with imidazolium ionic liquids (ILs). With respect to bare UiO-66-NH2, the modified counterpart, UiO@IL, exhibits much improved selectivity to phosphoproteins while maintains comparable adsorption performance. The surface of UiO@IL presents a strong hydrophilicity due to the modification of ILs. Hydrophobic and electrostatic interaction between the absorbent and nonphosphoprotein is significantly reduced. In addition, the interaction between imidazole group of ILs moiety and phosphate group in phosphoprotein ensures the favorable adsorption capacity of UiO@IL for phosphoproteins. Anionic moieties of ILs, i.e., Cl−, Br−, BF4−, CF3SO3−, play negligible effect in the adsorption process. As a representative, phosphoprotein β-casein (β-ca) is selectively enriched at a mass ratio of BSA:β-ca = 100:1. UiO@IL was further applied for the selective enrichment of phosphoprotein in milk.

Lipase nanogel catalyzed synthesis of vitamin E succinate in non-aqueous phase.

In order to improve the stability of vitamin E and broaden its scope of application, an effective solution is to convert vitamin E into its derivatives. This work developed a new Candida rugosa lipase (CRL) nanogel based on modification of ionic liquid with vinyl functional groups. This novel CRL nanogel was used in the preparation process of vitamin E succinate based on the principle of non-aqueous enzymology. At the same time, various factors including enzyme concentration, substrate molar ratio, reaction temperature and reaction time, that affect the yield of vitamin E succinate were optimized and analyzed. Different solvents with various hydrophobicity parameters (LogP values) from -1.3 to 3.5 were studied, it was found that dimethyl sulfoxide (DMSO) had the lowest LogP value among organic solvents but vitamin E succinate had the highest yield in DMSO. Furthermore, the effect of different operating conditions, such as molar ratios of substrate, enzyme concentration, reaction temperature and reaction time was studied. Under the optimal process conditions (enzyme concentration 6 mg mL-1 , substrate molar ratio 4:1, reaction temperature 55 °C and reaction time 15 h), the product yield was 62.58 ± 1.16%. CRL and CRL nanogel were characterized using Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). It was shown that CRL nanogel influenced the catalytic behavior of lipase significantly by changing the structure and surface properties of CRL. Novel lipase nanogel was an excellent biocatalyst for enzymatic synthesis of vitamin E succinate. © 2020 Society of Chemical Industry.

Effect of alkyl chain length on the extraction properties of U and Th using novel CnmimNTf2/isophthalamide systems

An attempt was made to investigate the structural modification of CnmimNTf2 ionic liquid in combination with a novel ligand, 5-bromo-N1,N3-bis(1-methyl-1H-pyrazol-3-yl)isophthalamide on the extraction properties of tetra and hexavalent actinides. In C4mimNTf2, C6mimNTf2, the extraction processes predominantly followed the ‘cation exchange’ mechanism involving the species: [UO2(NO3)L]+ and [Th(NO3)2L]2+, whereas, in C8mimNTf2, the ‘solvation’ mechanism was found to be predominant involving neutral species UO2(NO3)2L2 and Th(NO3)4L3. The speciation was further confirmed by investigating the participation of imidazolium cation in extraction. In ionic liquid, the extraction processes were slower compared to that in the molecular diluent. The time required to attain the equilibrium D values followed the trend: C4mimNTf2 < C6mimNTf2 < C8mimNTf2. This was attributed to the viscosity induced slow mass transfer. At 1 M HNO3, the D values for uranyl and thorium follow the trend C4mimNTf2 > C6mimNTf2 > C8mimNTf2, which was ascribed to the enhancement in organophilicity of the cation on increasing the length of the side chain and hence the effect on their dissolution in water. Three cycles of 1 mM aqueous sodium carbonate solution and four cycles of 1 mM oxalic acid solution were sufficient for almost quantitative back extraction of U and Th, respectively.C8mimNTf2 based systems were better radio-resistant compared to the lower homologue.

Enhanced enantioselectivity of tartaric acid in capillary electrophoresis: From tartaric acid to tartaric acid-based ionic liquid

This work presents, for the first time, a systematic and step-by-step methodology on how to improve the enantioseparation performance of tartaric acid (TT) in capillary electrophoresis (CE) using ionic liquid (IL) technology. A series of chiral and achiral ILs were applied in different separation modes to evaluate their influence on TT's enantioselectivity. Unlike previous ILs-related chiral CE studies, which typically report positive synergistic effect, in this work, negative synergistic effect was observed between TT and most chiral ILs (including several amino acids ILs and a saccharide-based IL). Instead, achiral ILs (the precursors of chiral ILs, mainly tetraalkylammonium hydroxides) exhibited significantly better performance in system modifications when used in combination with TT. The influence of the configuration of TT and chiral ILs on enantioseparation was investigated to explore the synergistic mechanism. The result showed that the existence of the chiral part of the ILs may cause interference rather than facilitation in the selector-selectand interactions. On the basis of the above results, we further designed a novel TT-based IL-type chiral selector, di-tetramethylammonium-D-tartrate ((TMA)2-D-TT). It is able to achieve excellent enantioseparation of all model analytes without adding any other chiral or achiral additives. This study demonstrates that TTs, which have almost been abandoned in chiral CE, are still able to provide satisfactory enantioselectivities with the help of ILs. In some application modes, e.g., under the achiral ILs modification or using TT-based ILs, their chiral separation performance is comparable or even superior to the well-established and widely used TT ester-type chiral selectors

Ionic liquid-modified poly(propylene carbonate)-based electrolyte for all-solid-state lithium battery

Due to their high safety and excellent thermal stability, all-solid-state lithium batteries have been explored widely in the recent years, which are highly in demand for future energy storage. Herein, we propose a novel type of all-solid-state electrolyte, which is prepared by the modification of ionic liquid with poly(propylene carbonate) (PPC)-based polymer electrolyte. The selected ionic liquid, 1-vinylimidazole bis(trifluoromethanesulfonyl)imide (VIm-TFSI), acts as a plasticizer to be integrated into the PPC matrix. Such a VIm-TFSI-modified PPC-based electrolyte (PPC-25IL) has an ionic conductivity of 8.2 × 10−5 S cm−1 at room temperature. Moreover, it enables a highly reversible Li plating/stripping for Li anode, resulting in a dramatically improved rate and cyclic performance of LiFePO4-Li all-solid-state batteries. The VIm-TFSI plasticizer not only increases the ionic conductivity of PPC-based electrolyte but also improves the interfacial comparability of PPC-based electrolyte with the electrode. This work proposes a new strategy to develop all-solid-state lithium battery for real applications.

Enhancing bio-catalytic activity and stability of lipase nanogel by functional ionic liquids modification

A novel integrated lipase nanogel based on functional ionic liquid modification and polymerization immobilization with improved stability was designed. Characterization before and after modification and polymerization was conducted using infrared spectroscopy, Circular dichroism spectroscopy, fluorescence spectroscopy, and scanning electron microscopy. It was shown that the modification of the ionic liquid influenced the catalytic behavior of lipase significantly due to the changed structure and surface properties of lipase. The enzymatic properties, including acid-base stability, thermal stability, organic solvents stability, and storage stability of CRL nanogel, were investigated in the p-nitrophenyl palmitate hydrolysis reaction (CRL, Lipase from Candida Rugosa). The results indicated that CRL nanogel has a better pH, heat, and organic solvent tolerance after immobilization. After seven weeks of storage, the natural CRL gradually lost its enzymatic activity, and only 17.5±1.7 % of the catalytic activity remained, the residual activity of CRL nanogel was 97.3±1.8 %. It was indicated that the novel CRL nanogel was an excellent biocatalyst.

(Invited) Boosting Non-Precious Metal Catalysts Toward the Oxygen Reduction Reaction through Ionic Liquid Modification

Finding cost effective catalysts for the oxygen reduction reaction (ORR) is one of the most overriding challenges in the field of electrochemistry [1]. Carbon-based materials emerge as one of the promising candidates due to their remarkable advantages of low cost, abundant structural variety, tailorable surface chemistry, and good conductivity. Tremendous efforts have been made to improve the performance of carbon-based materials for the ORR, mainly through modifying the inherent structures of carbon by doping heteroatoms (e.g., B, N, P) or combining with metal/metal oxides. We have demonstrated recently that modifying Pt-based catalysts by a minor amount of ionic liquid (IL, e.g., [BMIM][NTf2], [MTBD][NTf2]) could significantly boost their ORR activity [2-5]. This innovative strategy has also been successfully transferred to some non-precious metal Fe-N-C catalysts, on which an ionic liquid ([BMMIM][NTf2]) modification is found to boost both their activity and stability [6]. In the current contribution, we will present our latest progress toward boosting the emerging zeolitic imidazolate framework (ZIF)-derived carbons (ZDC) for the ORR using IL modification strategy. First we verified again the boosting effect of IL toward the ORR on the as-synthesized ZDC materials. The half wave potential of ORR on these ZDCs is positively shifted by up to 18 mV and their intrinsic kinetic current (@ 0.85 V) is increased by a factor of 2 after being modified with [BMMIM][NTf2]. At the same time, it is observed that the boosting effect from IL modification is highly sensitive to the exact loading amount of the IL. Exceeding a specific loading amount, however, leads to a mass transport related activity drop. Moreover, it is also unraveled that the IL takes effect by increasing electrochemically accessible surface area, as reflected by the significantly enhanced double layer capacitance of ZDCs after IL modification. These results again demonstrate the great promise of the IL modification strategy as a generic method to improve ORR catalysts, and at the same time are anticipated to form the basis for an unprecedented perspective in developing high-performing non-precious metal catalysts for low temperature fuel cell applications.

Post-synthetic modification of ionic liquids using ligand-exchange and redox coordination chemistry

Ionic liquids (ILs) derive their useful properties from molecularly tunable compositions, but methods to diversify anion identities and probe ion speciation remain limited.

Ionic-liquid-stabilized fluorescent probe based on S-doped carbon dot-embedded covalent-organic frameworks for determination of histamine.

An ionic-liquid-stabilized fluorescent probe for histamine is described. Sulfur-doped carbon dots (S-CDs) were incorporated into a covalent organic framework (COF) that was prepared from 1,3,5-triformylphloroglucinol and 2,5-dimethyl-p-phenylenediamine by one-pot hydrothermal polymerization in the dark. The blue fluorescence of the S-CDs (with excitation/emission maxima at 350/440nm) is enhanced (compared to undoped CDs) due to element doping by ionic-liquid modification. The COF is resistant to acids, bases, and boiling water. The fluorescence of the probe is statically quenched by histamine, and quenching follows the Stern-Volmer equation. The normalized fluorescence of the probe drops in the 10 to 1000μgkg-1 histamine concentration range, and the limit of detection is 5.3μgkg-1. The probe was successfully applied to the analysis of wine and fermented meat products. The recoveries from spiked samples range between 84.6 and 115.3%. The method is selective, sensitive, stable and repeatable. The mechanisms of the fluorometric response and molecular recognition were explored. Graphical abstractSchematic presentation of ionic-liquid-stabilized fluorescent probe based on S-doped carbon dot-embedded covalent organic framework for determination of histamine. The ionic liquid [VBIm][BF4] reacts with MPTS-modified carbon dots to enhance the fluorescence signal for analyte recognition.

Ionic liquid combined with NiCo2O4/rGO enhances electrochemical oxygen sensing

Ionic liquids are promising electrolytes for electrochemical gas sensors that have unique physicochemical properties such as negligible vapor pressure and high thermal stability. The modification of ionic liquid (IL) by combining metal oxide with reduced graphene oxide (rGO) is an effective method to improve its gas-sensing properties. In this study, the mesoporous structure of NiCo2O4/rGO is synthesized by simple one-step method, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) is mixed with it to form the composite material NiCo2O4/rGO/[BMIM][PF6]. Electrochemical test results indicate that the three electrolytes exhibit response current and long-term stability in the oxygen environment. The oxygen sensor based on NiCo2O4/rGO/[BMIM][PF6] significantly improves the response current and working stability of pure ionic liquid. The sensitivity of the sensor is 0.1087 μA/[%O2], and the linear regression coefficient of the reduction peak current calibration curve is 0.9995. After continuous cyclic voltammetry, the reduction peak current remains at 90% of the initial current value. The interaction of IL and NiCo2O4/rGO significantly enhances electrochemical oxygen sensing performance.

Effect of Ionic Liquid Modification on the ORR Performance and Degradation Mechanism of Trimetallic PtNiMo/C Catalysts.

Ionic liquids (ILs) modification, following the concept of “solid catalyst with ionic liquid layer (SCILL)”, has been demonstrated to be an effective approach to improving both activity and stability of Pt-based catalysts for the oxygen reduction reaction. In this work, the SCILL concept has been applied to a trimetallic PtNiMo/C system, which has been documented recently to be significantly advantageous over the benchmark PtNi-based catalysts for oxygen reduction. To achieve this, two hydrophobic ILs ([BMIM][NTF2] and [MTBD][BETI]) were used to modify PtNiMo/C with four IL-loading amounts between 7 and 38 wt %. We found that the Pt mass activity (@0.9 V) could be improved by up to 50% with [BMIM][NTF2] and even 70% when [MTBD][BETI] is used. Exceeding a specific IL loading amount, however, leads to a mass transport related activity drop. Moreover, it is also disclosed that both ILs can effectively suppress the formation of nonreactive oxygenated species, while at the same time imposing little effect on the electrochemical active surface area. For a deeper understanding of the degradation mechanism of pristine and IL modified PtNiMo/C, we applied identical location transmission electron microscopy and in situ scanning flow cell coupled to inductively coupled plasma mass spectrometry techniques. It is disclosed that the presence of ILs has selectively accelerated the dissolution of Mo and eventually results in a more severe degradation of PtNiMo/C. This shows that future research needs to identify ILs that prevent the Mo dissolution to leverage the potential of the IL modification of PtNiMo catalysts.

Ionic Liquid-Modified Microporous ZnCoNC-Based Electrocatalysts for Polymer Electrolyte Fuel Cells

Non-platinum group metal (non-PGM) oxygen reduction reaction (ORR) catalysts have been widely reported, but their application in proton exchange membrane fuel cells (PEMFCs) is challenging because of their poor performance in acidic environments. Here, [BMIM][NTf₂] ionic liquid (IL) modification of microporous ZnCoNC catalysts (derived from ZIF-ZnCo) is investigated to study their behavior in PEMFCs and to elucidate the catalytic mechanisms in practical operation. The high O₂ solubility of ILs enhances the utilization of active sites with porous ZnCoNC, and their hydrophobic nature facilitates the water transport during fuel cell operation. The half-cell measurement in aqueous HClO₄ shows that with the 20 wt % IL modification, the electron-transfer number increases from 2.58 to 3.88, approaching the desired 4-electron-transfer ORR. The power density obtained shows 140% improvement in single-cell PEMFC tests. The catalyst also yields an interesting performance in alkaline anion-exchange membrane fuel cells.

Green alternative treatment for cellulosic fibers: ionic liquid modification of Abelmoschus esculentus fibers with methyl-tri-n-butyl ammonium methyl sulphate

In this research, Okra (Abelmoschus esculentus) fibers were treated with an ionic liquid, methyl-tri-n-butyl ammonium methyl sulphate, to modify surface of the fibers. The fibers were exposed to aqueous ionic liquid solutions at different concentrations such as; 2, 5, 10 and 20 w/v% at ambient temperature. Ionic liquid treatment led to enhanced surface hydrophobicity of the okra fibers by means of increase in surface carbon/oxygen ratio. The proportion of C–C and C–H bands in the okra fibers were increased as a result of the treatment. The untreated and treated okra fibers gave similar crystalline index (CI) values. The CI results varied between 61.12 and 65.92%. Thermal stability of the fiber deteriorated after the treatment. However, char yield values increased indicating possibly enhanced flame retardancy after the treatments. Scanning electron microscopy observation confirmed the existence of ionic liquid both in intercellular gaps and on the surface of the okra fibers.