Bobo Cao

Highly efficient I2 capture by simple and low-cost deep eutectic solvents

The efficient removal and storage of radioactive nuclear contaminants including an isotope of iodine (131I) has attracted great concern especially after the explosion of the Fukushima nuclear power plant. In this study, deep eutectic solvents (DESs) are proposed for the removal and storage of iodine (I2). These DESs can be obtained by simply mixing two simple components (also cheap and biodegradable), which form liquids with melting points far below that of the individual components. A series of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) are selected for the preparation of DESs. The properties and I2 capture efficiency of the prepared DESs have been investigated. The results indicate that some DESs have higher efficiencies for I2 removal than the previously reported materials. Among them, ChI–methylurea shows the best I2 uptake efficiency of approximately 100% within 5 hours. Moreover, ChI–methylurea exhibits a good capability of I2 storage with only 4.6% of the iodine evaporated after 10 hours of strong N2 sweeping, which is also important since I2 is easy to sublimate. Additional calculations also suggest that the high efficiency for I2 capture by DESs mainly comes from the formation of halogen bonding (XB) between DESs and I2. This work opens a new way for the application of DESs.

Carbon dioxide capture by amino-functionalized ionic liquids: DFT based theoretical analysis substantiated by FT-IR investigation

Carbon dioxide capture by amine-functionalized ionic liquids (IL), 1,2-dimethyl-(3-aminoethyl)imidazolium fluoride ([aEMMIM][F]), [aEMMIM][Cl], [aEMMIM][Br], and [aEMMIM][I] were synthesized and characterized by both DFT simulation and experimental methods. The most stable geometrical parameters of structures in this study were optimized at the B3LYP/6-311++G(d,p) level by employing the Gaussian09 program. The results showed that CO2 can be chemically captured in ILs by forming carbamic acid with a 1 : 1 molar ratio stoichiometry. DFT simulations were performed to investigate the configuration variations of the reactants, intermediates, transition states and products, as well as energy barriers and vibration frequency changes in the gas phase using the conductor-like polarizable continuum model (CPCM) in an aqueous solution. The vibration frequency obtained in DFT simulation was consistent with the experimental result by employing a scaling factor. AIM and NBO analysis were also carried out to investigate the nature and features of the studied structures at the molecular level.

Cellobiose as a model system to reveal cellulose dissolution mechanism in acetate-based ionic liquids: Density functional theory study substantiated by NMR spectra.

Cellulose dissolution mechanism in acetate-based ionic liquids was systematically studied in Nuclear Magnetic Resonance (NMR) spectra and Density Functional Theory (DFT) methods by using cellobiose and 1-butyl-3-methylimidazolium acetate (BmimAc) as a model system. The solubility of cellulose in ionic liquid increased with temperature increase in the range of 90-140°C. NMR spectra suggested OAc(-) preferred to form stronger hydrogen bonds with hydrogen of hydroxyl in cellulose. Electrostatic potential method was employed to predict the most possible reaction sites and locate the most stable configuration. Atoms in molecules (AIM) theory was used to study the features of bonds at bond critical points and the variations of bond types. Simultaneously, noncovalent interactions were characterized and visualized by employing reduced density gradient analysis combined with Visual Molecular Dynamics (VMD) program. Natural bond orbital (NBO) theory was applied to study the noncovalent nature and characterize the orbital interactions between cellobiose and Bmim[OAc].

Experiment and DFT studies on radioiodine removal and storage mechanism by imidazolium-based ionic liquid

In order to remove and store radioactive substances effectively, studies on the mechanisms of radioiodine captured by ionic liquids (ILs) with a fixed cation (1-butyl-3-methyl-imidazolium cation [Bmim]+) were carried out in experimental and theoretical methods. Fourier transform infrared attenuated total reflectance (FT-IR ATR) spectra of 2BP8HQ and ultraviolet-visible (UV/vis) spectroscopy were used to investigate the kinetic process of radioiodine removal by ILs in experiment. Corresponding theoretical investigations on the structures and formation mechanisms of ILs, bare anions and complexes as well as hydrogen bonds was carried using density functional theory. The electrostatic potential was used in configuration design and construction. Charge distribution was used to show the variation of atom charge density, Interaction energy and vibration frequency change were performed to explore possible mechanisms on the halogen bond formation between radioiodine molecule and bare anion or anion in ILs when radioiodine captured by ILs. In order to characterize halogen bonds both natural bond orbital analysis and atoms in molecules analysis were performed. Both experimental and computational results showed that radioiodine could be captured by ILs with a 1:1mol stoichiometry. It was noteworthy that [Bmim][Br], [Bmim][I] and [Bmim][Cl], containing high radioiodine capture efficiency anions, were better candidates in removal and reliable storage of radioiodine for their capture efficiencies of over 80% in 5h.

Heterogeneous Nb-containing catalyst/N,N-dimethylacetamide–salt mixtures: novel and efficient catalytic systems for the dehydration of fructose

The development of efficient catalytic systems for the dehydration of carbohydrates to produce 5-hydroxymethylfurfural (HMF) is a very attractive topic. In this work, we synthesized a novel Nb-containing catalyst by the reaction of niobium chloride and nitrilotris(methylenephosphonic acid) (NTMPA), denoted as Nb–NTMPA. The synthesized Nb–NTMPA was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption, and Fourier transform infrared spectroscopy and used as the heterogeneous catalyst for the dehydration of fructose into HMF using the mixture of N,N-dimethylacetamide (DMA) and salts as the reaction solvent. It was found that Nb–NTMPA was very active for the reaction and a HMF yield of 85.6% could be achieved in a DMA–NaBr mixture under the optimal reaction conditions. Further study indicated that the salts could affect the activity of the reaction systems by the formation of DMA·M+ (M = Li, Na and K) macrocations and weakly ion-paired halide ions. Moreover, Nb–NTMPA/DMA–salt systems could also be used in the production of HMF from inulin and sucrose with satisfactory yields.

Theoretical study on the alkylation of o -xylene with styrene in AlCl 3 -ionic liquid catalytic system

To explore sustainable catalysts with innovative mechanisms, the alkylation mechanism of o-xylene with styrene was studied using DFT method in AlCl3-ionic liquid catalytic system. The reaction pathway was consisted of CC coupling and a hydrogen shift, in which two transition states were found and further discussed. The reactive energy catalyzed by superelectrophilic AlCl2+ (12.6kcal/mol) was distinctly lower than AlCl3 (43.0kcal/mol), which was determined as the rate-determining step. Mulliken charge along IRC gave a comprehensive understanding of charge distribution and electron transfer in dynamic progress. Bond orders and AIM theory were used to study the nature of chemical bonds and the driving forces in different reaction stages.

Reversibility of imido-based ionic liquids: a theoretical and experimental study

Multiple techniques were used to study the reversibility of a series of imido-based ionic liquids (ILs). DFT (density functional theory) modeling originally indicated that methyl transfer favorably took place at the unsaturated CX bond in the N–CX (N, O and S) fragment. A series of imido-based ILs derived from the N–CX (N, O and S) fragment were studied and characterized using theoretical and experimental methods. Seven imido-based ILs were facilely synthesized in the experiment, which is consistent with the lower energy barriers obtained in the potential energy surface (PES) compared to the other ILs. Their structures were measured in nuclear magnetic resonance (NMR) spectra. The thermal stabilities were further studied by thermogravimetric analysis (TGA). The bond order results indicated that non-covalent interactions were the major driving force in the methyl transfer process. Non-covalent interactions in these ILs were investigated and characterized using atoms in molecules (AIM), reduced density gradient (RDG) and natural bond orbital (NBO) methods.

DFT study on the dissolution mechanisms of α-cyclodextrin and chitobiose in ionic liquid

Density functional theory (DFT) was employed to study the dissolution mechanisms of α-cyclodextrin and chitobiose in 1-ethyl-3-methyl-imidazolium acetate ([Emim][OAc]). Geometrical analysis of the studied complexes indicated that both anion and cation in ionic liquid interacting withα-cyclodextrin and chitobiose contributed to the dissolution reaction. Intermolecular interactions in the complexes were identified as non-covalent interactions, such as hydrogen bonds, van der Waals interactions and repulsions, which were considered as the driving force of dissolution. Among them, hydrogen bonding interactions played a dominant role, which was further visualized in the real space by combination of atoms in molecules (AIM) and reduced density gradient (RDG) techniques. The nature of intermolecular orbital interactions was characterized using natural bond orbital (NBO) theory.

Theoretical and experimental investigation on the capture of H2S in a series of ionic liquids

H2S absorptions in ionic liquids (ILs), including tetramethyl guanidinelactate (TMGL), 4-bis(2-hydroxypropyl)-1,1,3,3-tetramethyl guanidinium tetrafluoroborate ([TMGHPO2][BF4]) and 1-butyl-3-methylimidazolium cation ([BMIM](+)) with the anions chloride ([Cl](-)), tetrafluoroborate ([BF4](-)), hexafluorophosphate ([PF6](-)), triflate ([TfO](-)), bis-(trifluoromethyl) sulfonylimide ([Tf2N](-)), were studied in experiment and computational methods. [TMGHPO2][BF4] showed the best H2S absorption capacity among the seven ILs. Density functional theory (DFT) calculations were applied to reveal the absorption mechanisms. Interaction energy results were consistent with absorptivities (molar ratio of H2S in IL) measured in experiment. As the best candidate absorbent, [TMGHPO2][BF4] was chosen as an example to characterize the hydrogen bonds and orbital interactions between H2S and [TMGHPO2][BF4] in atoms in molecules (AIM) and natural bond orbital (NBO) methods, respectively. IR spectrums obtained in both experimental and computational method were used to characterize the features of absorption process. The results indicated that H2S was physically absorbed by ILs, in which hydrogen bond was the driving force.