Xiaojing Guo

Non-corrosive green lubricants: strengthened lignin–[choline][amino acid] ionic liquids interaction via reciprocal hydrogen bonding

A series of novel green lubricants with dissolved lignin in [choline][amino acid] ([CH][AA]) ionic liquids (ILs) have been synthesized in this work. The effect of lignin on the thermal and tribological properties of the lignin/[CH][AA] lubricants was systematically investigated by means of thermogravimetric analysis, differential scanning calorimetry, and a friction and wear tester. The lignin in [CH][AA] has been demonstrated to be an effective additive to improve thermal stability, reduce the wear rates and stabilize the friction coefficients of lignin/[CH][AA] lubricants. Density function theory calculations on the electronic structure of [CH][AA] ILs reveal the atomic natural charge of ILs and their hydrogen bonding capability with lignin. Moreover, these green lubricants show excellent anti-corrosive properties against commercial aluminum and iron boards. The strong physical adsorption of [CH][AA] ILs onto the steel surface and the reciprocal hydrogen bonding between [CH][AA] ILs and lignin synergistically contribute to the enhanced lubrication film strength and thus the tribological properties of these new lubricants. This work provides a new perspective on utilizing complete bio-products in advanced tribological lubrication systems. In addition, this will open a new application venue for lignin to improve product value in lignocellulosic biomass utilization.

Compression of ionic liquid when confined in porous silica nanoparticles

[Emim]Br ionic liquid was confined in porous SiO2 nanoparticles. It is shown that the confinement in the nanopores leads to a compression of molecular size and an increase in the melting point. The pore size of SiO2 is a key factor in tuning the anion-cation distance and the melting point of the confined ionic liquids.

Preparation and characterization of superhydrophobic organic-inorganic hybrid cotton fabrics via γ-radiation-induced graft polymerization

A new kind of non-fluorine-based organic-inorganic hybrid superhydrophobic cotton fabric was successfully prepared by simultaneous radiation-induced graft polymerization of γ-methacryloxypropyl trimethoxy silane (MAPS) and subsequent end-capping modification with hexamethyldisilazane (HMDS). The chemical structure and surface topography of the pristine and modified cotton fabrics were investigated in detail by ATR-FTIR, XPS, (29)Si NMR, SEM and TGA to confirm that the graft reaction and end-capping modification had taken place. The above results demonstrated that the grafting polymerization and following end-capping reaction were completed, and a grafting layer was immobilized onto the surface of the cotton fabric. Surface wettability measurement and oil-water separation showed that the modified cotton surface not only exhibited the superhydrophobicity with a water contact angle of 165°, but also afforded a high efficiency of oil-water separation (96%). In particular, this modified cotton fabric retains superhydrophobicity even after 30 laundering cycles or 400 cycles of abrasion.

Optimum complexation of uranyl with amidoxime in aqueous solution under different pH levels: density functional theory calculations

This study aims to understand the complexation of uranyl with amidoxime in aqueous solution under different pH levels using density functional theory calculations. The geometries, relative stabilities of complexes, and changes in Gibbs free energies for different complexing reactions were investigated. Amidoximate ions were gradually added to the equatorial plane of uranyl to understand the complexation process. We modelled the effect of pH by varying the number of OH− and H2O ligands accompanying amidoximate ions in the equatorial plane of uranyl. The ŋ2 binding motif was the most favourable form, regardless of the uranyl/amidoximate ratio and the pH level. Compared with low and high pH, neutral pH condition was more beneficial to the complexation of uranyl with amidoxime.

The Influence of Silica Nanoparticles on Ionic Liquid Behavior: A Clear Difference between Adsorption and Confinement

The phase behaviors of ionic liquids (ILs) confined in nanospace and adsorbed on outer surface of nanoparticles are expected to be different from those of the bulk. Anomalous phase behaviors of room temperature ionic liquid tributylhexadecylphosphonium bromide (P44416Br) confined in ordered mesoporous silica nanoparticles with average pore size 3.7 nm and adsorbed on outer surface of the same silica nanoparticles were reported. It was revealed that the melting points (Tm) of confined and adsorbed ILs depressed significantly in comparison with the bulk one. The Tm depressions for confined and adsorbed ILs are 8 °C and 14 °C, respectively. For comparison with the phase behavior of confined P44416Br, 1-butyl-3-methylimidazolium bromide (BmimBr) was entrapped within silica nanopores, we observed an enhancement of 50 °C in Tm under otherwise similar conditions. The XRD analysis indicates the formation of crystalline-like phase under confinement, in contrast to the amorphous phase in adsorbed IL. It was confirmed that the behavior of IL has clear difference. Moreover, the complex π-π stacking and H-bonding do not exist in the newly proposed phosphonium-based IL in comparison with the widely studied imidazolium-based IL. The opposite change in melting point of P44416Br@SiO2 and BmimBr@SiO2 indicates that the cationic species plays an important role in the variation of melting point.

Grafting heteroelement-rich groups on graphene oxide: Tuning polarity and molecular interaction with bio-ionic liquid for enhanced lubrication

Two different heteroelement-rich molecules have been successfully grafted on graphene oxide (GO) sheets which were then used as lubricant additives in bio-ionic liquid. The grafting was processed with reactions between GO sheets and synthesized heteroelement-rich molecules (Imidazol-1-yl phosphonic dichloride and 1H-1,2,4-triazol-1-yl phosphonic dichloride, respectively). The modified GO (m-GO) was added into [Choline][Proline] ([CH][P]) bio-ionic liquid, and has been demonstrated effective additive in promoting lubrication. Different characterization techniques have been utilized to study the reaction between GO and the two modifiers. The effect of molecular structure of the modifiers on the rheological and tribological properties of m-GO/[CH][P] lubricants was systematically investigated. Both theoretical calculation and experimental results demonstrated that the introduced heteroelement-rich groups are beneficial to increase the robustness of lubrication film by intensified hydrogen bonding and enhance the lubricant/friction surface adhesion by increased polarity of the m-GO. As a result, the interfacial lubrication could be significantly improved by these newly developed m-GO/[CH][P] lubricants.

Synergistic nanofibrous adsorbent for uranium extraction from seawater

Huge reserves of uranium (U) in seawater have been of interest to scientists and energy companies since the 1950s. However, extracting trace concentrations (3.3 ppb) of U from seawater is economically unfeasible without new, high-performance adsorbents. Here, a mat-like nanofibrous composite adsorbent containing binary coordination groups (amidoxime (AO) and carboxyl (AC−)) in a highly porous network of nanofibers is constructed via a parallel-blend electrospinning method. Its U uptake in artificial seawater is more than double those of adsorbents containing AO or AC− groups alone. Density functional theory (DFT) calculations reveal that this synergistic effect is because the AC− group promotes both the U 5f/6d orbital contribution to U–AO bonding and the dissociation of uranyl tricarbonate ions in seawater. In a continuous flow-through experiment with simulated seawater, the nanofibrous adsorbent achieves an adsorption capacity up to 2.86 mg U gads−1 in 30 d but without saturation, indicating a high efficiency for U extraction.

Structural analysis of [Bmim] 2 CuCl 4 ionic liquids in the presence of water and ethanol by XAFS technique

The structure of [Bmim]2CuCl4 ionic liquids (Bmim: 1-butyl-3-methylimidazolium) with different ratios of H2O and C2H5OH was investigated using X-ray absorption fine structure (XAFS) technique. In this study, XAFS was employed to directly probe the conformational variations of copper ions in [Bmim]2CuCl4 with the addition of either water or ethanol. XAFS analysis confirmed that the structure of ionic liquids gradually transformed from tetrahedral to octahedral configuration with the increase in ratio of H2O. Our results also showed that water molecules coordinated with the copper ions of [Bmim]2CuCl4, leading to the conformational change in ionic liquids. However, the XAFS spectra of [Bmim]2CuCl4/C2H5OH indicated no coordination of anhydrous ethanol with the copper ions of [Bmim]2CuCl4. The structure of [Bmim]2CuCl4 ionic liquids is maintained as the tetrahedral configuration in presence of ethanol. Therefore, anhydrous ethanol causes little variation in the structure of ionic liquids and it is a good solvent for the dilution of ionic liquids.

Highly Durable and Robust Superhydrophobic/Superoleophilic Cotton Fabric with Well-designed Roughness for Oil/Water Separation

Herein we report a simple and reproducible method for fabricating highly durable and robust superhydrophobic and superoleophilic cotton fabrics via simultaneous radiation-induced graft polymerization of glycidyl methacrylate and subsequent chemical modifications with aminopropyltriethoxysilane and hexamethyldisilazane. The chemical structure and the surface topography of the pristine and the modified cotton fabrics were investigated in detail by ATR-FTIR, XPS, and 29Si NMR, and a grafting layer was successfully immobilized onto the surface of the cotton fabric by forming covalent bonds. Multi-dimensional surface roughness was created by combining micro-sized fibers of the cotton fabric, nanoscaled protuberances of the grafting chain, and molecular level spherical projection points of silicon methyl. The superhydrophobic cotton fabric exhibited long-term stability, ultra-high durability and robustness, and maintained its properties even after 25 wash cycles. The fabric also showed excellent water repellency with a water contact angle of 153 ° and a high efficiency of oil/water separation (98 %). The superhydrophobic/superoleophilic cotton fabric developed in the present work exhibits important potential applications in superhydrophobic textiles and oil/water separation.

Crystallization and temperature-dependent structure deflection of C6mimBr ionic liquid intercalated in LAPONITE®

The physicochemical properties of large molecules confined in nanopores are expected to be different from those of the bulk. This study investigates the cation–anion relative position and the molecular orientation of the 1-hexyl-3-methylimidazolium bromide (C6mimBr) ionic liquid intercalated in LAPONITE® by a temperature-dependent X-ray absorption fine structure (XAFS) and some traditional methods (TEM, DSC, XRD, and IR). DSC and TEM analyses revealed the formation of C6mimBr crystals intercalated in LAPONITE®. The XAFS and XRD analyses at ambient temperature revealed that an ordered monolayer structure, with C6mim+ cations intercalated in the interlayer nanospace and Br located on the edge of the LAPONITE®, was formed when ILs were intercalated in LAPONITE®. The results also demonstrated that the enhanced interactions, the formed hydrogen bonds, as well as the ordered monolayer arrangement induced the formation of C6mimBr crystals when intercalated in LAPONITE®. In situ XAFS analysis with a combination of XRD patterns at varied temperatures revealed that the structure orientation of the intercalated C6mim+ cations tends to deflect and maintain the ordered monolayer arrangement with the elevation of temperature. The ordered crystal structure still exists at 120 °C and disappears at a higher temperature.